ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V02AT00A001. doi:10.1115/IMECE2015-NS2A.

This online compilation of papers from the ASME 2015 International Mechanical Engineering Congress and Exposition (IMECE2015) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Advanced Manufacturing: 3D Printing and Additive Manufacturing

2015;():V02AT02A001. doi:10.1115/IMECE2015-50937.

In the rapidly growing field of additive manufacturing (AM), the focus in recent years has shifted from prototyping to manufacturing fully functional, end-use parts, particularly using metals. In order for these parts to be designed to function both safely and effectively, it is necessary to have a thorough understanding of the mechanical behavior of materials produced via the AM process.

This research focuses on characterizing Inconel 718 produced via the Direct Metal Laser Sintering (DMLS) process. Specimens from three orthogonal build orientations were tested as both machined and as-fabricated specimens. Surface roughness was evaluated using non-contact profilometry. Tensile testing was performed in order to characterize material yield strength. Finally, high cycle fatigue (HCF) testing was conducted on a rotating beam apparatus.

Results show that the measured elastic modulus of the as-fabricated material was 162.7 GPa for the in-plane build orientation and 72.1 GPa for the vertical build orientation. In addition, the measured fatigue strength of horizontal build orientations was greater than that of specimens built in a vertical orientation. Furthermore, it was found that the fatigue lives of the machined specimens were at least 7 times greater than those of as-fabricated specimens.

Topics: Fatigue , Metals , Lasers
Commentary by Dr. Valentin Fuster
2015;():V02AT02A002. doi:10.1115/IMECE2015-50953.

The purpose of this study is to validate the design of plastic PLA extruded everyday use parts created in open source 3D printers, and to provide examples of design alterations so a 3D printed part will function similar to the OEM component. The methodology begins with selection of a common everyday use component that may fail under a load and need replacement. As a test specimen an aluminum coat hook is purchased, measured, modeled with 3D CAD software, analyzed and physically tested. Using AM a coat hook with identical specifications is created on a Delta style RepRap 3D printer with PLA as a material in the orientation providing the maximum strength. The 3D printed coat hook is analyzed using finite element analysis as well as physically using a loading apparatus test with identical loading and supporting conditions. The software used for the experimentation and data collection are NX9, ANSYS and NI LabVIEW. Material physical properties of open source 3D printed PLA parts obtained from tensile testing indicate that the strength of a 3D printed part will be less than that of an aluminum OEM part. Initial finite element analysis reveals the Coat Hook 3D printed using PLA deflects almost 20 times that of the OEM aluminum component when subjected to an identical load. This indicates that the component cannot be replaced with identical specifications even if there was a large factor of safety applied to the coat hook design. As a result of the study, part reinforcement features are proposed for redesign of a 3D printed part to perform as well as the OEM part under a similar load. Additional part redesigns utilizing these reinforcement features include shelf support brackets and solar photovoltaic mounting bracket systems.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A003. doi:10.1115/IMECE2015-51174.

The material extrusion family of additive manufacturing processes, such as the fused deposition modelling (FDM) process, can be very expensive for component fabrication due to the long production times for large, thick walled, complex components, and the material costs. Introducing light weighting strategies could balance the required strength and material usage. As the material extrusion processes exhibit anisotropic mechanical characteristics, physical experimentation is required to calibrate simulation models. In this research, an easily programmable light-weighting methodology for a variety of internal structures is presented. A variety of advanced CAD tools are explored; however, using Rhinoceros® with the Grasshopper® graphical programming add-on, allows designers to visualize the internal structure geometry dynamically. Tensile and compression samples are quickly generated for a variety of interior configurations. Selected sample models and results, built using ABS material, are presented here. Unexpected failure occurred with the face center cubic void lattice for the compression tests. There are disjoint segments in the tool path, and unexpected voids are interspersed within the test specimen. It is found that the bead deposition path has an influence on the observed mechanical characteristics. Design constraints, and alternative internal structures are proposed, and modelled.

Topics: Extruding
Commentary by Dr. Valentin Fuster
2015;():V02AT02A004. doi:10.1115/IMECE2015-51583.

Fabricating fully dense and functional metallic components is one of the important challenges in Additive Manufacturing (AM). Additive Manufacturing is a technology in which functional components can be fabricated rapidly and efficiently from their CAD models. It is also referred as Layered Manufacturing (LM) as the object is created by slicing the CAD model into layers and realizing each layer at a time. These layers are thin and stacked or glued together to get the physical shape of the CAD model. However, realizing overhanging features is a difficult task due to deficiency of support mechanism for metals. A separate support structure has to be deposited to build overhanging structures. Although, use of a distinct support material is quite common in non-metallic AM processes, such as Fused Deposition Modelling (FDM), and the same for metals is not yet available. The various techniques in AM process for fabricating metal parts can be mainly classified as laser based, electron beam based and arc based processes. While some Additive Manufacturing processes like Selective Laser Sintering (SLS) employ easily-breakable-scaffolds made of same material to realize the overhanging features, the same approach cannot be extended to deposition processes like laser or arc based direct energy deposition processes. Even though it is possible to realize small overhangs by exploiting the inherent overhanging capability of the process or by blinding some small features like holes, the same cannot be extended for more complex geometries. A different approach to solve this problem is feature based slicing. Unlike uniform and adaptive slicing techniques, where the thickness of a given slice is constant, in feature based slicing inclined slicing; the thickness varies even within a given slice, based on its feature. The current work presents a novel approach for realizing complex overhanging features without the need of support structures. This can be possible by using higher axis kinematics or by adding extra degrees of mobility to the work piece or to the deposition system and suitably aligning the overhang with the deposition direction. Some Vital concepts required in realizing and depositing overhangs are feature based non-uniform slicing and non-uniform area-filling and the same are briefly discussed here. This research will summarize the issues and related approaches in the research, development, and integration. This includes understanding of the weld deposition process by establishing proper geometries, and automated process planning. This technique can be used to fabricate or repair fully dense and functional components for various engineering applications. Although this approach has been implemented for weld-deposition based system, the same can be extended to any other direct energy deposition processes also.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A005. doi:10.1115/IMECE2015-51698.

Laser Engineered Net Shaping (LENS®) is a Direct Laser Deposition (DLD) additive manufacturing technology that can be used for directly building complex 3D components from metal powders in a combined deposition/laser-melting process. In this study, the effect of LENS process parameters, such as laser power, powder feed rate and traverse speed, on the resultant microstructure, hardness and tensile strength of Ti-6Al-4V components is experimentally investigated. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) are used to characterize the microstructure in terms of grain size and morphology. Relationships between process parameters and the microstructural/mechanical properties are provided. Results indicate that the scale of columnar grains increases with slower laser traverse speeds while other process parameters are maintained constant. The size of the α and β laths increases with higher laser powers and slower traverse speeds. The ultimate tensile and yield strengths of the LENS specimens were found to be higher than those of cast and wrought materials, and this can be generally attributed to the different cooling rates inherent to LENS — which impacts grain size. The percent elongation to failure, however, was consistently lower than that of the wrought material.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A006. doi:10.1115/IMECE2015-51903.

Polymeric fused filament fabrication technology (FFF), a subfield within additive manufacturing (AM), is becoming a contender for the reintroduction of the small-scale manufacturing of customized consumer products to a mass-production dominated world market. However, before this technology can be widely implemented, there remain significant technological hurdles to overcome. One issue that has been addressed at great length in other traditional polymer manufacturing fields is the inclusion of fillers in the component for physical property enhancement or the introduction of entirely new properties to the matrix material. Experiments conducted in this study examined the inclusion of carbon microfibers (CMFs) into the matrix material prior to the printing process, and the effect of different processing parameters on the final filler structure of the composite parts post printing.

Prior work on microstructural evolution during extrusion in a 3D printer has been conducted computationally to study the effects of extrusion rate, matrix rheology, and nozzle geometry on fiber orientation [1]. It was found that varying the nozzle geometry generated significantly different microstructures, and that the remainder of the parameters could be varied to fine-tune microstructural characteristics. Findings indicated that, by varying the nozzle geometry from a converging to a diverging conical section, microstructures ranging from axially oriented (with respect to the extrusion direction) to radially oriented are theoretically possible. Current work performed on extruders and FFF platforms indicates that during the extrusion process, fibers tend to align very closely to the axis of extrusion in shear flow (i.e. converging or straight dies). However, in some applications, this may not be the most effective filler structure for property enhancement, so there remains interest in exploring methodologies for fiber rotation during extrusion.

For this study, CMFs and acrylonitrile butadiene styrene (ABS) were compounded using a 28mm fully-intermeshing co-rotating twin-screw (CoTSE) extruder. 3D printer feedstock was manufactured in-house. A range of concentrations from 0%wt to 15%wt fabricated and tested. Analysis of the feedstock indicated nearly axial fiber alignment post-manufacture. This feedstock was then used in a Lulzbot TAZ4 printer to manufacture composite tensile testing specimens. Printed composite properties were then identified and compared to neat ABS and bulk composite properties. It was found that using a purely converging die, highly aligned filler structures were produced (with respect to the bead laid by the printer). Using a diverging nozzle, more random filler structures were produced. Improvements in both intra-layer properties were observed using the diverging nozzle geometries to reorient fibers during extrusion. Property improvements were not found to be as high as longitudinal properties for highly aligned filler structures. Using insights gained through these experiments, we are currently working on exploring added functionality for the composites using different types of fillers as well as multi-scale filler combinations.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A007. doi:10.1115/IMECE2015-52165.

Selective Laser Melting (SLM), a laser powder-bed fusion (PBF-L) additive manufacturing method, utilizes a laser to selectively fuse adjacent metal powders. The powders are aligned in a bed that moves vertically to allow for layer-by-layer part construction-Process-related heat transfer and thermal gradients have a strong influence on the microstructural features, and subsequent mechanical properties, of the parts fabricated via SLM. In order to understand and control the heat transfer inherent to SLM, and to ensure high quality parts with targeted microstructures and mechanical properties, comprehensive knowledge of the related energy and mass transport during manufacturing is required. In this study, the transient temperature distribution within and around parts being fabricated via SLM is numerically simulated and the results are provided to aid in quantify the SLM heat transfer. In order to verify simulation output, and to estimate actual thermal gradients and heat transfer, experiments were separately conducted within a SLM machine using a substrate with embedded thermocouples. The experiments focused on characterizing heat fluxes during initial deposition on an initially-cold substrate and during the fabrication of a thin-walled structure built via stainless steel 17-4 powders. Results indicate that it is important to model heat transfer thorough powder bed as well as substrate.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A008. doi:10.1115/IMECE2015-52204.

Currently, there is a major shift in medical device fabrication research towards layer-by-layer additive manufacturing technologies; mainly owing to the relatively quick transition from a solid model (.STL file) to an actual prototype. The current manuscript introduces a Custom Multi-Modality 3D Bioprinter (CMMB) developed in-house, combining the Fused Filament Fabrication (FFF), Photo Polymerization (PP), Viscous Extrusion (VE), and Inkjet (IJ) printing technologies onto a single additive manufacturing platform. Methodologies to address limitation in the ability to customize construct properties layer-by-layer and to incorporate multiple materials in a single construct have been evaluated using open source 3D printing softwares Slic3r and Repetier-Host. Such customization empowers the user to fabricate constructs with tailorable anisotropic properties by combining different print technologies and materials. To this end, procedures which allow the integration of more than one distinct modality of the CMMB during a single print session were developed and evaluated, and are discussed. The current setup of the CMMB provides the capability to fabricate personalized medical devices using patient data from an MRI or a CT scan. Initial experiments and fabricated constructs demonstrate the potential of the CMMB for research in diverse application areas within biomedical engineering.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A009. doi:10.1115/IMECE2015-52209.

Polyether ether ketone (PEEK) is introduced as a material for the additive manufacturing process called fused filament fabrication (FFF), as opposed to selective laser sintering (SLS) manufacturing. FFF manufacturing has several advantages over SLS manufacturing, including lower initial machine purchases costs, ease of use (spool of filament material vs powder material), reduced risk of material contamination and/or degradation, and safety for the users of the equipment. PEEK is an excellent candidate for FFF due to its low moisture absorption as opposed to other common FFF materials, such as Acrylonitrile Butadiene Styrene (ABS).

PEEK has been processed into a filament and samples have been manufactured using several build orientations and extrusion paths. The samples were used to conduct tensile, compression, flexural, and impact testing to determine mechanical strength characteristics such as yield strength, modulus of elasticity, ultimate tensile strength and maximum elongation, etc. All tests were conducted at room temperature. A microscope analysis was also conducted to show features on the failures surfaces. The mechanical property results from this study are compared to other published results using traditional thermo-plastic manufacturing techniques, such injection molding.

Tensile testing was conducted at three raster orientations, 0°, 90° and alternating between 0° and 90°. Average ultimate tensile stresses were determined to be 73 MPa for 0° orientation, and 54 MPa for 90° orientation, with alternating 0°/90° orientations of 66.5 MPa. Compression testing was conducted at two raster orientations, 0° and alternating between 0° and 90°. Average ultimate strength for the single orientation direction was 80.9 MPa with the alternating orientations at 72.8 MPa. Flexural testing was conducted at three raster orientations, 0°, 90° and alternating between 0° and 90°. Ultimate flexural stress was determined to be 111.7 MPa for 0°, 79.7 MPa for 90°, and 95.3 MPa for orientations alternating between 0° and 90°. Finally, impact testing was conducted at three raster orientations, 0°, 90° and alternating between 0° and 90°. Average impact energy absorbed was determined to be 17.5 Nm in the 0° orientation, 1.4 Nm in the 90° orientation, and 0.7 Nm for the alternating 0° and 90° orientations.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A010. doi:10.1115/IMECE2015-52261.

Fused deposition modelling (FDM) creates three-dimensional parts by feeding a rigid thermoplastic filament through a heated barrel to achieve a semi-fluid state and then extruding it layer-by-layer to create a part geometry. The melt flow behavior within FDM must be analyzed in order to correctly understand the temperature gradients within the system to promote part quality, process control, and efficiency. The presented research consists of analyzing the melt flow behavior of polymer poly(lactic) acid (PLA) within FDM. This includes an experimental analysis of the power output of the resistive heat source, a theoretical analysis of external coefficients of heat-transfer, and an experimental validation of liquefier temperatures. A three-dimensional fluid-flow model is created using the accurate geometry of the extruder assembly, calculated conditions from initial experimental results, and referenced material properties. Results of this research include a significant temperature difference between the areas of the liquefier assembly close in proximity to the power source to those further away such as the inlet and outlet, suggesting that external heat transfer mechanisms play a significant role in liquefier dynamics, contrary to the more common assumption of constant wall temperature or constant heat flux used in modeling. The research presented provides new information regarding the melt flow of PLA, a method of modeling external heat transfer, and a way of understanding power consumption that can lead to liquefier design improvements. The process itself will also aid in identifying modeling considerations for further investigations of melt flow involving various extruder designs and material options. Specifically, the use of this type of comprehensive model is of interest to the additive manufacturing community with respect to thermally sensitive component specification and heating and cooling needs within process based on changing system parameters such as extrusion temperature and mass flow rates (i.e. material feed rate and/or change in extrusion diameter).

Commentary by Dr. Valentin Fuster
2015;():V02AT02A011. doi:10.1115/IMECE2015-52270.

The centrifugal casting is a classical manufacturing method and it has been widely studied. However, when it comes to manufacture thin walled lattice materials with complex three-dimensional meso-structures, a multiscale flow-fill analysis may be needed for macro-filling at the sprue system and micro-filling at lattice structures. On the micro-filing analysis for a thin walled lattice structure, the surface tension of molten metal appears to be an important factor. On the other hand, flow inertia may affect the flow-filling process more than the surface tension of molten metal does. Our hypothesis is that there exist a range of ratios of cell wall thickness to length that are primarily affected by surface tension or density. From comparison with two different molten metals — aluminum and copper alloys, we can estimate the characteristic of flow, which will be of benefit when designing lattice structures and selecting materials for the manufacturing process. The objective of this study is to test the hypothesis by constructing an analytical model on flow filling of molten metals (aluminum alloy and copper alloy) associated with manufacturing lattice structures. The Naiver-Stokes equation with surface tension is considered for modeling of the flow of molten metal along the micro-channel of lattice structures and is numerically implemented with MATLAB. Temperature dependent properties of the liquid metals; e.g., density, viscosity, and conductivity, are considered for building the analytical model. Numerical simulations with a commercial code, ANSYS are conducted using a user defined function. Experimental validation is followed to manufacture a cubic truss lattice structure with a varying wall thickness; 0.5–1mm. Two molten metals — aluminum alloy and copper alloy are used for filling the mold at the centrifugal casting system. The mold is prepared by removing sacrificial lattice patterns made by a polyjet 3D printer. The preliminary result shows that the final lattice structures with an aluminum alloy through the 3D printing of sacrificial pattern followed by centrifugal casting have relatively good flow filling property at thin wall thickness (∼0.5mm) due to low surface tension of aluminum alloy. On the other hand, the high surface tension of a copper alloy prevents flow-fill to micro-channel mold cavity, resulting in early solidification. The indirect additive manufacturing based casting shows an excellent surface quality, which can be used for manufacturing cellular structures. A coupled flow and heat transfer of molten metal successfully simulate flow-fill and solidification and is compared with the experiment. Faster filling-time and faster solidification for the temperature-dependent material properties were shown.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A012. doi:10.1115/IMECE2015-52274.

In the advancement of Additive Manufacturing (AM) technologies, 3D desktop printers have become an accessible solution to address the current manufacturing practices for most industries and the general public. This study explores the effect default build parameters have on the tensile properties of additive manufactured parts by comparing the Young’s Modulus and tensile strength of polylactic acid (PLA) in the elastic region before and after the AM process through experiments and numerical simulations. The build parameters are specified via MakerBot Desktop — the file preparation software for the MakerBot Replicator 3D printer used to create the specimens tested herein. This work presents the tensile mechanical properties for specimens built using low infill rate, low layer resolution, and standard build speed and extrusion temperature to recreate the worst possible part quality attainable using MakerBot 3D Desktop printers. Using these build parameters results in a part with a hollow honeycomb interior structure, and due to its heterogeneous cross sectional area, experimental stress-strain curves do not accurately represent its physical response to tensile loading. Therefore in this case, an experimental-numerical study of the 3D printed specimens is performed, using the load-displacement experimental data acquired from tensile tests to calibrate the ANSYS Structural Mechanics simulations. The goal is to optimize the material properties in our simulation such that the equivalent strain magnitude matches the experiments. This is an approach to determine the experimental Young’s modulus of PLA additive manufactured parts where the AM process, heterogeneous structure, and size greatly influence the part strength. This is completed by studying the worst part quality possible first to better understand this effect. Tensile tests are performed using an ADMET 5603 Universal Test Machine (UTM) synched with a Correlated Solutions 3D Digital Image Correlation (DIC) system. A fine heterogeneous speckle pattern is sprayed on the specimens and used by the DIC system to obtain surface contours of deformation. This data is compared to the displacement fields in the finite element analysis (FEA) simulation of the specimen.

When compared to the pre-manufacturing PLA, additive manufactured parts exposed that the post-processed stiffness of the material is increased when tested under this loading condition. The Poisson’s ratio for printed PLA was also noted to decrease when compared to pre-manufactured PLA, due to the larger longitudinal deformation compared to the transverse. Specimens failed by brittle fracture across the hex pattern, showing limited deformation and failing short after. The failure location based on the influence interior geometry has on failure showed that specimens failed by brittle fracture across the hex pattern, initiating fracture in the same region of all specimens.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A013. doi:10.1115/IMECE2015-52343.

The powder-bed electron beam additive manufacturing (EBAM) process is a relatively new AM technology that utilizes a high-energy heat source to fabricate metallic parts in a layer by layer fashion by melting metal powder in selected regions. EBAM can be able to produce full density part and complicated components such as near-net-shape parts for medical implants and internal channels. However, the large variation in mechanical properties of AM build parts is an important issue that impedes the mass production ability of AM technology. It is known that the cooling rate in the melt pool directly related to the build part microstructure, which greatly influences the mechanical properties such as strength and hardness. And the cooling rate is correlated to the basic heat transport process physics in EBAM, which includes a moving heat source and rapid self-cooling process. Therefore, a better understanding of the thermal process of the EBAM process is necessary. In this study, a 3D thermal model, using a finite element method (FEM), was utilized for EBAM heat transport process simulations. The process temperature prediction offers information of the cooling rate during the heating-cooling cycle. The thermal model is applied to evaluate, for the case of Ti-6Al-4V in EBAM, the process parameter effects, such as the beam speed and power, on the temperature profile along the melt scan and the corresponding cooling rate characteristics. The relationship between cooling rates and process parameters is systematically investigated, through multiple simulations, by incorporating different combinations of process parameters into the thermal model. The beam scanning speed vs. beam power curves of constant cooling rates can be obtained from 3D surface plots (cooling rate vs. different process parameters), which may facilitate the process parameters selections and achieve consistent build part quality through controlling the cooling rate.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A014. doi:10.1115/IMECE2015-52362.

The present article focuses on the mechanical properties and microstructural features of Selective Laser Melted (SLM) 17-4 precipitation hardening (PH) stainless steel (SS) as well as their comparison to conventionally built materials. The topics investigated are the effects of different building orientations and post-fabrication heat treatment (solution annealing and aging) on the mechanical and microstructural characteristics of samples fabricated by SLM. Yield and ultimate tensile strengths of SLM-produced 17-4 PH SS were found to be lower than those of wrought materials (H900 condition). In addition, building orientations showed a noticeable effect on tensile properties. Presence of defects, such as pores resulting from entrapped gas, un-melted regions, and powder particles resulting from lack of fusion were the main reasons for lower elongation to failure of SLM-produced 17-4PH SS in this study.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A015. doi:10.1115/IMECE2015-52386.

Accurate evaluation of residual stresses in structures is very important because they play a crucial role in the mechanical performance of the components. As residual stresses can be introduced into mechanical components during various thermal or mechanical processes such as heat treatment, forming, welding and additive manufacturing. As an additive manufacturing method, selective laser melting (SLM) has become a powerful tool for the direct manufacturing of three dimensional nano-composite components with complex configurations directly from powders using 3D CAD data as a digital information source and energy in the form of a high-power laser beam. Therefore, the application of the SLM technology is necessary to manufacture Inconel 718 superalloy, which has been widely employed in industrial applications due to its remarkable properties. Hence, it is critical to measure and reduce the residual stress in the Inconel 718 parts formed by SLM due to rapid cooling and reheating. In this study, the process-induced residual stress in Inconel 718 parts produced by selective laser melting (SLM) has been investigated using the model established by Carlsson et al., which is an instrumented indentation technique based on the experimental correlation between the indentation characteristic and the residual stress. The samples were sectioned from an Inconel 718 block along its build direction, and subsequently prepared with general metallographic methods for Vickers indentation and measurements by optical microscopy. The residual stress on the scanning surface (Z-plane) and side surface (X-plane) at different build heights have been evaluated in micro-scale with the contact area, indentation hardness and the equai-biaxial residual stress and strain fields. The results show that the residual stress is unevenly distributed in the SLMed parts with some areas have an maximum absolute value around 350 MPa, about 30 percent of the yield strength of Inconel 718. The average residual stresses in the Z-plane and X-plane samples are tensile and compressive, respectively. Besides, the residual stress does not change significantly along the building direction of the part. Moreover, the Vickers hardness of the parts built with the SLM process is comparable to the literature, and the X-plane surface has a higher hardness than the Z-plane surface. The microstructures and texture evolution of the SLM processed Inconel 718 alloy are also investigated. The X-plane shows the columnar structure due to the large temperature gradient while the Z-plane presents the equiaxed structures. The random texture is shown in the SLM processed specimens.

Topics: Metals , Lasers , Stress , Melting
Commentary by Dr. Valentin Fuster
2015;():V02AT02A016. doi:10.1115/IMECE2015-52417.

Cellular (or lattice) metals are increasingly gaining attention for their having combinations of mechanical, thermal, and acoustic properties that provide potential opportunities for diverse multifunctional structural implementations. These include ultra-light structures with high specific strength and high specific strain, excellent impact absorption, acoustic insulation, heat dissipation media and compact heat exchangers. The emerging 3D printing technologies including direct and indirect additive manufacturing processes may accelerate the realization of their structural applications of cellular metals. For indirect additive manufacturing processes, sacrificial patterns are 3D printed with castable polymers, followed by metal filling into a mold cavity to make final cellular metals. With a high stiffness of a castable polymer, e.g., VisiJet® Procast, it is possible to build network lattice cellular structures, replacing wax which has been used for traditional investment casting processes. In general, a high thermal stress is expected during burning-out process of the rapid casing. Due to the castable polymer’s new properties, no literature is available on thermal stress between the castable polymer and ceramic shells for indirect additive manufacturing of cellular structures. The objective of this study is to investigate i) thermal stress by thermal expansion mismatch between a sacrificial pattern made of a castable polymer and a coated gypsum shell and ii) an effect of the thickness of the coated gypsum shell on thermal cracking. Starting with thermal analysis, glass transition temperature, melting temperature and thermal expansion coefficient are obtained from experiments. An analytical model for thermal stress analysis is constructed with thermo-mechanical constitutive equations and compatibility equations, followed by a failure analysis at the coated shells where gypsum is used for coating the sacrificial pattern. The thermo-mechanical analysis is conducted as a function of temperature and coated shell thickness followed by a numerical validation with a finite element (FE) based simulation. The castable polymer has the potential to be used as a base material for manufacturing 3D network cellular sacrificial patterns with thin cell walls over conventional wax materials due to its high modulus and low thermal expansion coefficient during the burning out process of the sacrificial pattern.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A017. doi:10.1115/IMECE2015-52615.

The 3D Printing (3DP) “binder jetting” process is an additive manufacturing process that fabricates components and assemblies by layering powered material, and applying a binder where a ‘solid interior’ should be. This process creates brittle components as a powder is set with a weak binder material; however, the component strength characteristics can be significantly modified when infiltrating the component during post processing operations. The different factors that can influence the mechanical properties when engaging in post-processing operations need to be understood. A full factorial design of experiments (DOE) is conducted for tensile, compressive, and flexural specimens for 10 infiltrate and various build conditions. The experiment and resultants are set up to perform an analysis of variance (ANOVA). All of the observed stress-strain curves for the specimens are non-linear, or have limited linear regions. The infiltrate absorption depth affects the mechanical characteristics, and the binder jetting specimens are stronger in compression than tension. The tensile test results are similar to those of biological materials. Certain infiltrates do not improve the mechanical performance characteristics, which are validated using the Tukey method. This research needs to be extended in scope to include additional build orientations as well as torsion, fatigue, and notch tests to be able to predict model sensitivities effectively for components built using the binder jetting process, and to develop optimization strategies, which include time, material, and strength conditions.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A018. doi:10.1115/IMECE2015-52634.

In this study, a preliminary effort was undertaken to represent the mechanical properties of a 3D printed specimen as a function of layer number, thickness and raster orientation by investigating the correlation between the mechanical properties of parts manufactured out of ABS using Fused Filament Fabrication (FFF) with a commercially available 3D printer, Makerbot Replicator 2x, and the printing parameters, such as layer thickness and raster orientation, were considered. Specimen were printed at raster orientation angles of 0°, 45° and 90°. Layer thickness of 0.2 mm was chosen to print specimens from a single layer to 35 layers. Samples were tested using an MTS Universal Testing Machine with extensometer to determine mechanical strength characteristics such as modulus of elasticity, ultimate tensile strength, maximum force and maximum elongation as the number of layers increased. Results showed that 0° raster orientation yields the highest mechanical properties compared to 45° and 90° at each individual layer. A linear relationship was found between the number of layers and the maximum force for all three orientations, in other words, maximum force required to break specimens linearly increased as the number of layers increased. The results also found the elastic modulus and maximum stress to increase as the number of layers increased up to almost 12 layers. For samples with more than 12 layers, the elastic modulus and maximum stress still increased, but at a much slower rate. These results can help software developers, mechanical designers and engineers reduce manufacturing time, material usage and cost by eliminating unnecessary layers that do not increase the ultimate stress of the material by improving material properties due to the addition of layers.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A019. doi:10.1115/IMECE2015-53428.

Developing high-resolution 3D printed metallic microchannels is a challenge especially when there is an essential need for high packing density of the primary metal. While high packing density could be achieved by heating the structure to the sintering temperature, some heat sensitive applications require other strategies to improve the packing density of primary metal. In this study the goal is to develop microchannels with high green (bound) or pack densities on the scale of 100–300 microns which have a robust mechanical structure. Binder-jet 3D printing is an additive manufacturing process in which droplets of binder are deposited via inkjet into a bed of powder. By repeatedly spreading thin layers of powder and depositing binder into the appropriate 2D profiles, complex 3D objects can be created one layer at time. Microchannels with features on the order of 500 microns were fabricated via binder jetting of steel powder and then sintered and/or infiltrated with a secondary material. The droplet volume of the inkjet-deposited binder was varied along with the print orientation. The resolution of the process, the subsequent features sizes of the microchannels, and the overall microchannel quality were studied as a function of droplet volume, orientation, and infiltration level.

Commentary by Dr. Valentin Fuster

Advanced Manufacturing: Advanced Forming

2015;():V02AT02A020. doi:10.1115/IMECE2015-50019.

Producing fuel cells bipolar plates and other devices such as microscale heat exchangers for electronics requires both macroscale and microscale forming processes. At the macroscale, typically, mechanical properties of sheet metal are determined by performing tensile tests. In addition, it has long been recognized that bi-axial tension tests, dome tests, and hydroforming or viscous bulge tests provide the basis for improved understanding of the mechanics of sheet metal forming. At the microscale strain gauges are too large for measuring strains in small regions and membrane theory is only valid at the poles of the bulge. Continuum mechanics models are useful but require tedious thickness measurements for multiple work pieces, requiring extensive sample preparation and analysis.

In this paper experimental results from hydroforming tests for 0.2-mm thick annealed ASTM 304 stainless steel sheet in 11 mm, 5 mm, and 1 mm diameter open dies at various pressures were evaluated. The height of the bulge at the pole and strains based upon measurements of 127 micron strain grids were determined. These dies represent the transition from a small macroscale process to a microscale forming process. Two methods were used to estimate material properties: an analytical model and an iterative method which compared experimental strain results with the strains from a finite element model where the Holloman constitutive properties of the sheet were varied. The problems estimating material properties based upon grid strain measurement, membrane theory, and the iterative finite element approaches were investigated and the results were compared. This study indicates that membrane theory will provide adequate predictions for Holloman constructive properties provided the assumptions for membrane theory are not violated. However, using measured microscale grid deformation strains does not produce very good agreement estimates of the Holloman constitutive model when comparing experimental results with FEA strains. It is believed that while the grid strain measurement method used results in strain measurement errors of less than 1.5% of strain, this error is sufficient to result in enough uncertainty to produce results that are inconsistent with other methods.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A021. doi:10.1115/IMECE2015-50172.

A stamp forming die, whose flexible blank holder was designed using FEA, was built. A closed-loop control system was used to control local punch forces and wrinkling by controlling both blank holder forces and draw bead penetration. The controllers for the draw beads featured an advanced PID controller with a Smith Predictor and Kalman Filter. A Bang-bang controller was also incorporated into the control system in order prevent control saturation. Fuzzy logic was used to transition from once controller to the other. Once closed-loop was implemented, tests were performed to evaluate the strains in the pans for various forming conditions. These results were compared to open-loop tests and it was found that the strains measured from closed-loop control tests resulted in more uniform strains and that the strains were further from the forming limit curves than strains from tests that were performed under open-loop conditions. Furthermore, it was seen that the strains in the regions were local force were controlled resulted in more uniform strain fields. Hence it was concluded that controlling local punch forces resulted in the strain control of critical regions.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A022. doi:10.1115/IMECE2015-50231.

In the recent manufacturing trend and, in particular, in sheet metal forming, the requirement of customized production is still growing. Incremental forming is a special technique requiring no high capacity presses or set of dies, thus meeting the increasing demand for low volume production and rapid prototyping. The complex three dimensional parts of sheet metals are formed by the computer numerical control (CNC) movement of a simple generative hemispherical tool. In this paper, the single point incremental forming process is performed on friction stir processed AA 6063-O alloy. The process parameters for the experiment are taken based on L9 Orthogonal array. In this paper the maximum wall angle or the formability is investigated on a formed pyramid frusta. It is inferred that Friction stir process has improved the ductility of the aluminium alloy thus contributing to enhanced formability.

Topics: Friction , Alloys
Commentary by Dr. Valentin Fuster
2015;():V02AT02A023. doi:10.1115/IMECE2015-50939.

Infeed swaging is a type of rotary swaging process. It is usually used to reduce the cross section from the beginning to the end of the tube. Compared with the infeed swaging with mandrel, the infeed swaging without mandrel has the advantages of less-loading, chipless forming, giving high production rate and low tool costs. It has been widely used in aeronautic and automotive industries. In this paper, using the finite element (FE) simulation code, TRANSVALOR FORGE 2011, three-dimensional (3D) FE model and experiment were developed to investigate the stress state and deformation pattern during the infeed swaging of tube without mandrel. Results show that the stress state varies with the regions. In the sinking zone, the stress state in the middle of the tube is biaxial compressive, while that at the other regions is triaxial. In the forging zone, the material suffers from tensile axial stress, compressive thickness stress and circumferential stress. After unloading, tensile residual stresses occur at the forging zone and the inner surface in the sinking zone. The maximum tensile residual stress is 69.5MPa, which is 77.3% of the yield stress. In the sinking zone, more metal flows radially inside and the deformation type is compressive. In the forging zone, more material tends to flow along the axial direction. The deformation type in the forging zone is tensile. Moreover, experiments were also conducted to validate the FE model. The experimental and simulated results have a good agreement. After the infeed swaging, the microstructure of the tube became smaller and denser. The metal flow lines are continuous, contributing to improve the strength and the fatigue life of tube.

Topics: Deformation , Stress
Commentary by Dr. Valentin Fuster
2015;():V02AT02A024. doi:10.1115/IMECE2015-51093.

The casting-rolling compound forming process is a new process to produce seamless ring shaped components. In the new process, the input blank for the new process is a ring shaped casting blank. Edge crack affects severely the quality of rolled ring parts in ring rolling process based on cast blank. Theoretical analysis, numerical simulation and experiments were combined to study the edge crack and its prevention methods during ring rolling. Conclusions are obtained that: (1) for casting blank, the initial stage of ring rolling is crucial to prevent the initiation and propagation of the edge cracks. (2) in the ring rolling process, the occurrence of cracks were influenced mainly by rolling temperature and feed speed of the core-roller. Cracks could be avoided by controlling above two rolling parameters. (3) in the initial stage of ring rolling, higher rolling temperature and lower feed speed of the core-roller are beneficial to improve the plasticity of the materials and restrain effectively the initiation and propagation of cracks. The work is a part of the research of the new casting-rolling compound forming process. It will promote the development of the new process.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A025. doi:10.1115/IMECE2015-51227.

Incremental Sheet Forming (ISF) is a flexible and innovative rapid prototyping technique for the fabrication of limited sheet metal components. In the present investigation, the dependency of formability and thickness reduction of ISF parts on tool diameter, incremental step depth along with the preheating of sheet material has been determined. After preheating, initial grain size of the sheet material is selected as a parameter under study. Incremental Sheet Forming process has been studied using Taguchi design of experiments along with Response surface methodology (RSM). ANOVA, 3D surface graphs, S/N ratio and main effect plots have been analyzed. Results indicated that the initial grain size is the most significant parameter as far as forming load and thickness reduction is concerned in ISF. Preheating of the sheet material reduces forming load and favors homogenous thickness distribution. Response surface is optimized and a model developed can be used to predict forming load and thickness reduction within the limits of factors being studied.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A026. doi:10.1115/IMECE2015-51253.

Automatic soldering technic called Sleeve soldering has been developed recently. In the technic, a ceramic tube has been used instead of a soldering iron. It is called Sleeve. Fixed amount of solder is loaded into this Sleeve. The melted solder is poured from tip of the Sleeve to glue electronic parts into electronic boards. At present Sleeve soldering has been produced and introduced. However condition of soldering failure and concept of process design are not clear due to a few data of melting behavior and solidification. In this research we intended to express these standards by comparing numerical analysis and experiment. Moreover we explain about the establishment of numerical analysis method in this paper.

Result in the behavior using the solder model has been similar to actual phenomenon in this simulation. Besides, we have confirmed that the fillet and back fillet was arisen on both sides of the electronic board.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A027. doi:10.1115/IMECE2015-51270.

Wire solders usually contain flux and it can remove an oxide film on the metal surface chemically. The influence of the flux is important in soldering. Recently, the new packaging technology was developed, it is called Sleeve soldering. It is a kind of through-hole technology. Sleeve soldering can prevent to spatter flux contained in the wire solder and solder balls. It is not known behaviors of melting wire solder in the sleeve. The purpose of this study is to investigate the behaviors and to obtain proper conditions for Sleeve soldering. The proper condition consists of two factors. One is temperature of the sleeve. The other is amounts of wire solder. The behavior of melting wire solder in the sleeve is observed using a high speed camera. This paper describes observation results using a high-speed camera and influences of the flux in Sleeve soldering.

Topics: Solders , Soldering , Wire , Melting
Commentary by Dr. Valentin Fuster
2015;():V02AT02A028. doi:10.1115/IMECE2015-51368.

Superplastic forming (SPF) takes the advantage of the metallurgical phenomenon of superplasticity (SP) to form complex and highly intricate bulk and sheet metal parts. SP refers to the extraordinary formability of certain metals and alloys, ceramics, composites (both metallic- and ceramic-based), dispersion strengthened materials, nanostructured materials and bulk metallic glasses, which allows them to suffer elongations of several hundred percent under the action of tensile forces. The superplastic forming characteristics of materials like aluminium, titanium and magnesium alloys have been clearly identified in order to produce complicated near-net shapes. These materials are used in the aeronautical manufacturing industry and automotive manufacturing industries due to the significant weight (by ∼ 30%) and cost (by ∼ 50%) saving that is possible. Some research work has proved superplastic forming of friction stir welded (FSW) joints also. The FSW joint efficiencies have been characterized by mechanical and metallurgical examination. Studies are also available on the behavior of FSW joints of similar and dissimilar metals.

Information on the performance of friction stir welded joints during superplastic forming is rather limited, but it is important to achieve excellent properties in the friction stir welded joints also during superplastic forming. FSP (friction stir processing) – SPF (superplastic forming) is presently being promoted as a very viable near-net shape technology for making very large and complicated sheet metal products. To achieve this superplastic material parameters are much required in industry to develop new shapes. One has to understand the flow rule relationship and mechanics involved during sheet metal forming at high temperature to select the material and forming tool with selected process parameters.

This paper deals with the determination of superplastic material properties of non-superplastic aluminum alloy AA6061-T6. The superplastic material properties like strain rate sensitivity index, flow stress and strain rate were determined for both the selected material and friction stir welded sheets at various tool rotation speeds. The superplastic free blow forming experiments were performed for various constant temperatures and pressure for the parent material. Similarly the superplastic free blow forming experiments were performed for the friction stir welded joint for various tool rotation speed at constant temperature. The methods were used to determine the material properties are straight line fit method and polynomial regression method. The superplastic forming height is significantly high in case of the FSW specimens at 2000 rpm, the initial forming rate is faster and the strain rate sensitivity index obtained is also higher when compared to the parent material properties. The strain rate sensitivity index obtained for friction stir welded specimen during superplastic forming was foundto have improved when compared to the parent material.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A029. doi:10.1115/IMECE2015-51877.

Twin-screw polymer extrusion has shown increased utility for creating composite materials. However, in order to achieve the desired product properties, sufficient mixing is essential. Dispersive mixing, or the breaking-up of particle agglomerates, is critical to create filled compounds with the required material properties. In a twin-screw compounding process, the Residence Stress Distribution (RSD) has been used to quantify the dispersive mixing induced by the stresses in the polymer melt. These stresses are quantified by the percent break-up of stress-sensitive polymeric beads. It was found that the amount of material that experiences the critical stress is a function of the operating conditions of screw speed and specific throughput [1]. The quantification of dispersive mixing allows for better control of a compounding process and can be used to design new processes.

During the development of a new compounding process, screw geometries and operating conditions are often refined on a laboratory-scale extruder and then scaled up to a manufacturing level. Scale-up rules are used to translate the operating conditions of a process to different sizes of extruders. In a compounding process, the goal when scaling-up is to maintain the same material properties on both scales by achieving equivalent mixing. The RSD methodology can be used to evaluate the effectiveness of scale-up rules by comparison between two or more scales.

This paper will demonstrate the utility of the RSD in evaluation of two unique scale-up rules. Conventional industry practice is based on the volumetric flow comparison between extruders. The proposed approach demonstrates that in order to maintain equivalent dispersive mixing between different sizes of extruders, the degree of fill, or the percent drag flow (%DF), must be kept equivalent in the primary mixing region. The effectiveness of both rules has been evaluated by experimental application of the RSD methodology. A design of experiment approach was used to generate predictive equations for each scale-up rule that were compared to the behavior of the original small-scale extruder.

Statistical comparison of the two scale-up rules showed that the %DF rule predicted operating conditions on the large-scale extruder that produced percent break-up behavior more similar to the small-scale behavior. From these results, it can be concluded that the %DF scale-up rule can be used to accurately scale operating conditions between different-sized extruders to ensure similar dispersive mixing between two processes. This will allow for greater accuracy when recreating the material properties of a small-scale twin-screw compounding process on a larger, mass production machine.

Topics: Screws
Commentary by Dr. Valentin Fuster
2015;():V02AT02A030. doi:10.1115/IMECE2015-51919.

The addition of nano-scale and micro-scale fillers has been proven to increase tensile and thermal properties in polymer composites. Orientation of high aspect fillers, however, has not been studied before despite being crucial to altering physical properties. When fibers are included during extrusion, they tend to align in the direction of the flow. This phenomena leads to longitudinal improvements in mechanical properties, and thus provides great benefits in some applications; however, it is beneficial to have improved properties in the transverse direction as well. Therefore, it is crucial to study reorientation phenomena in composites.

The purpose of this experiment is to study property enhancement resulting from fiber structure. The material properties are compared for the range of weight percentages of fillers. This is done for the purpose of finding an ideal fill concentration. Two dies are used to study different orientation distributions: straight and divergent. Thermal and tensile properties and optical micrographs are analyzed and compared.

Composites were processed on a Coperion ZDSK-28mm co-rotating, fully-intermeshing, twin-screw extruder. Polybutylene terephthalate (PBT) was used as the polymer matrix. 0 W% to 2 W% multi-walled carbon nanotubes (CNTs) and 0 W% to 30 W% carbon microfibers (CMFs) were used as fillers.

Preliminary results showed a clear trend in increased tensile strength of the composite with the increase of concentration of CMFs and CNTs in the slit die up to 25 W% CMF. After 25 W% CMF, however, there was a depreciation in properties. Similarly, thermal conductivity results have shown a clear peak at 25 W% CMF with 30 W% showing a decrease in thermal properties.

Preliminary results for the divergent die showed that, with addition of carbon microfibers to the polymer matrix, thermal properties of the composite increased up to 15 W%, then dropped and increased again as more CMFs were added. In addition, on average, material extruded through the divergent die showed better results of thermal conductivity than that extruded through the slit die. This indicates that when using a diverging die, fiber become oriented perpendicular in relation to the direction of the flow, thus improving heat flow in the transverse direction.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A031. doi:10.1115/IMECE2015-52215.

Frequently it is desired to calculate the blanking shear force of a cospel using an angled matrix as main characteristics of the cutting die. There are two reasons that support the development of this calculation: the first is that the product may change its shape or material, which makes necessary to modify the operating parameters according to the geometric size and metal composition changes. The second is that the nominal capacity of the working press is established by the manufacturer and cannot be altered to adapt to a new product, this means that any new product parameters must be adapted to the capabilities of the machine. Also, the force equation must contain the main variables of the product and not just “proportions” or “factors”, allowing a better approximation of the cutting operation. In this work, a new expression for the blanking force calculus of a cospel is obtained, based on the geometric characteristics of the cutting die (punch and matrix). A matrix die angled is considered as a main characteristic of the sheet metal cutting die, maintaining the punch geometry without cut angles. Two formulas derived from analytical and graphical proposed methods are used and several blanking tests were conducted with a die designed and fabricated properly to run the laboratory tests. The graphical methods are based on a projected area of the metal cospel, obtained from the three dimensional cospel area to cut, this two dimensional projected area is utilized in the expression for the cutting force calculus. On the other hand, the analytical approach considers an area limited from a mathematical equation obtained from a model based on the geometry regions of the blanking die; this area has also utilized as the shear area in the cutting force calculus of a metal cospel. The experimental procedure consisted in reproduce the blanking operation of several metal cospels using the designed and fabricated die. The cutting force was measured using three different matrix die angles probed during the blanking tests, maintaining the same cut angle of the punch during the tests. The tests results were compared with both analytical and graphical methods showing good agreement. Similarly, the cutting force was calculated with analytical and experimental expressions obtained from the specialized literature in order to determine the degree of accuracy of the calculations.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A032. doi:10.1115/IMECE2015-52390.

Selective laser melting (SLM) is an important additive manufacturing process. It applies focused laser energy to quickly melt and solidify material powders, and a controlled layered operation can result in a free form build that is often out of reach for machining processes. As such, it has attracted much attention in recent years. However, metal components produced by this process often have inferior mechanical properties, as compared with the counterparts by the traditional manufacturing processes. To strengthen the metal components by SLM, adding reinforcement particles and applying post treatment are regarded as the two effective ways. Although adding reinforcement particles to create metal matrix composites has been studied by researchers in literature, much fewer has been done to use post treatment processes to further improve the properties and performance of the metal matrix composites from SLM.

In this study, a nano-TiC reinforced Inconel 718 composite is prepared using SLM technique. The material has 0.5 wt.% nano-TiC addition. Solid solution treatments at three levels of temperature (940, 980, 1020 °C) are carried out to evaluate the effect of the heat treatment methods on the microstructure and resulted mechanical properties of the composite material. The results of samples with and without heat treatment are also compared. SEM observations are carried out to analyze the microstructure of the composite and understand the reinforcing mechanism. Tensile tests are conducted to evaluate the mechanical properties of the formed composites. It is discovered that compared with the pure Inconel 718 by SLM, the Inconel 718-TiC composite exhibits improved ultimate tensile strength. Microscopy observation of as-built samples indicates that the dendritic structures of Inconel 718 is remarkably refined by the TiC particles. Suspected laves phase particles are observed in as-built Inconel-TiC composite, and they partially transform to large amount of needle-like δ phase during the solid solution treatment.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A033. doi:10.1115/IMECE2015-53071.

In the last decade, press hardening has become a fully established technology in both science and industry for the production of ultra-high-strength structural components, especially in the automotive industry. Beside the improvement of car performance such as safety and lightweight design, the production process is also one focus of trends in technology development in the field of press hardening.

This paper presents an overview about alternative approaches for optimized process chains of press hardening, also including pre- and post-processing in addition to the actual forming and quenching process. Investigations on direct contact heating technology show new prospects regarding fast and flexible austenitization of blanks at compact device dimensions. By applying high speed impact cutting (HSIC) for trimming of press hardened parts, an alternative technology is available to substitute the slow and energy-intensive laser trimming in today’s press hardening lines. Combined with stroke-to-stroke control based on measuring of process-relevant parameters, a readjustment of the production line is possible in order to produce each part with individual, optimal process parameters to realize zero defect production of property-graded press hardened components with constant high part quality.

Significant research in the field of press hardening was carried out at Fraunhofer Institute for Machine Tools and Forming Technology IWU, in the hot forming model process chain which enables the running of experiments under conditions similar to industrial scales. All practical tests were prepared by design of experiments and assisted by thermo-mechanical FE simulations.

Topics: Hardening , Chain
Commentary by Dr. Valentin Fuster
2015;():V02AT02A034. doi:10.1115/IMECE2015-53146.

This paper presents the effect of shell element formulations on the response parameters of incremental sheet metal forming process. In this work, computational time, profile prediction and thickness distribution are investigated by both finite element analysis and experimentally. The experimental results show that the thickness distribution is in good agreement with the results obtained with Belytschko-Tsay (BT) and Improved Flanagan-Belytschko (IFB) shell element formulations. These two shell element formulations do trade-off between computational time and accuracy. For more accurate results, the BT shell element formulation is better and for less computational time with good results, the IFB shell element is preferable. Finally, BT shell element formulation has been chosen for FE Analysis of ISF process in HyperWorks, since the results of thickness distribution and profile prediction is in better agreement with the experimental results as well as the computational time is less among the shell elements.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A035. doi:10.1115/IMECE2015-53282.

This work explores the effect of tool geometry on surface finish in incremental sheet forming (ISF) process. In the present work, two different tool geometries i.e. hemispherical shaped tool and ellipsoidal shaped tool are considered. Area at tool-sheet contact and scallop height were calculated for both the tool geometries. To assess the effect of tool geometry on the surface finish of the formed components, both analytical and experimental approaches have been used. A test geometry having the shape of frustum of pyramid was considered for the proposed investigation and four surface roughness parameters i.e. arithmetic mean surface roughness (Ra), root mean square surface roughness (Rq), maximum peak-to-valley height (Rt) and average peak-to-valley height (Rz) have been selected as response parameters. Based on the analytical model and experimental investigations, both qualitative and quantitative comparisons had been made among the effects of hemispherical and ellipsoidal tool geometries on surface finish. The investigation deduces that better surface finish of the formed component can be achieved by using ellipsoidal shaped tool rather than the hemispherical shaped tool.

Topics: Finishes , Shapes
Commentary by Dr. Valentin Fuster
2015;():V02AT02A036. doi:10.1115/IMECE2015-53355.

In recent years, the use of optimization methods in sheet metal forming has been increased remarkably. In the finite element simulation of the sheet metal stamping operations, the model parameters are determined from the several tests like tensile, compression, and biaxial stretching tests (bulge test). In this study, Yld2000-2d anisotropic yield function parameters are determined for DP800 advanced high strength steel using a 60° V-shaped die bending process. The difference between the simulation and experiment is found to be 1 degree using the classical determination method of the anisotropy parameters. The difference is 0.1 degree using the optimization method.

Commentary by Dr. Valentin Fuster

Advanced Manufacturing: Advanced Machining and Finishing

2015;():V02AT02A037. doi:10.1115/IMECE2015-50224.

Stainless steel is the most widely used alloys of steel. The reputed variety of stainless steel having customised material properties as per the design requirements is Duplex Stainless Steel and Austenitic Stainless Steel. The Austenite Stainless Steel alloy has been developed further to be Super Austenitic Stainless Steel (SASS) by increasing the percentage of the alloying elements to form the half or more than the half of the material composition. SASS (Grade-AL-6XN) is an alloy steel containing high percentages of nickel (24%), molybdenum (6%) and chromium (21%). The chemical elements offer high degrees of corrosion resistance, toughness and stability in a large range of hostile environments like petroleum, marine and food processing industries. SASS is often used as a commercially viable substitute to high cost non-ferrous or non-metallic metals. The ability to machine steel effectively and efficiently is of utmost importance in the current competitive market. This paper is an attempt to evaluate the machinability of SASS which has been a classified material so far with very limited research conducted on it. Understanding the machinability of this alloy would assist in the effective forming of this material by metal cutting. The novelty of research associated with this is paper is reasonable taking into consideration the unknowns involved in machining SASS. The experimental design consists of conducting eight milling trials at combination of two different feed rates, 0.1 and 0.15 mm/tooth; cutting speeds, 100 and 150 m/min; Depth of Cut (DoC), 2 and 3 mm and coolant on for all the trials. The cutting tool has two inserts and therefore has two cutting edges. The trial sample is mounted on a dynamometer (type 9257B) to measure the cutting forces during the trials. The cutting force data obtained is later analyzed using DynaWare supplied by Kistler. The machined sample is subjected to surface roughness (Ra) measurement using a 3D optical surface profilometer (Alicona Infinite Focus). A comprehensive metallography process consisting of mounting, polishing and etching was conducted on a before and after machined sample in order to make a comparative analysis of the microstructural changes due to machining. The microstructural images were capture using a digital microscope. The microhardness test were conducted on a Vickers scale (Hv) using a Vickers microhardness tester. Initial bulk hardness testing conducted on the material show that the alloy is having a hardness of 83.4 HRb. This study expects an increase in hardness mostly due to work hardening may be due to phase transformation. The results obtained from the cutting trials are analyzed in order to judge the machinability of the material. Some of the criteria used for machinability evaluation are cutting force analysis, surface texture analysis, metallographic analysis and microhardness analysis. The methodology followed in each aspect of the investigation is similar to and inspired by similar research conducted on other materials. However, the novelty of this research is the investigation of various aspects of machinability and drawing comparisons between each other while attempting to justify each result obtained to the microstructural changes observed which influence the behaviour of the alloy. Due to the limited scope of the paper, machinability criteria such as chip morphology, Metal Removal Rate (MRR) and tool wear are not included in this paper. All aspects are then compared and the optimum machining parameters are justified with a scope for future investigations.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A038. doi:10.1115/IMECE2015-50404.

Intermetallic titanium aluminides are recognized as the possibly alloys for high performance aerospace and automobile application. There is an increasing interest of this material due to their extraordinary material properties. The understanding of the machinability of titanium aluminides during various metal cutting processes is very much essential for its wide acceptance over various fields of application. Drilling, with high aspect ratio is a key machining area to be explored because of its complex nature. In the present work, holes were drilled on a titanium aluminide intermetallic alloy with an aspect ratio of 9.37, focusing on the machinability under dry environment using coated and uncoated twist drill. Machinability investigations were evaluated based on the, thrust force, torque, surface integrity, chip morphology, burr formation and performance of the tool. From the results of thrust force and torque, it is revealed that the coated tool doesn’t show any significant advantages over the uncoated tool. The variation of chip shapes was observed as the depth progresses. Small ring shape, uniform and non-uniform roll back burr were observed as the cutting parameters are varied. The adherence of workpiece material on to the tool and various surface defects were observed under all cutting conditions.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A039. doi:10.1115/IMECE2015-51059.

Basic and advanced metal cutting research has been an ongoing effort since Cocquilhat’s early work directed towards measuring the work required to remove a given volume of material when drilling in the year 1851. Over the 150+ years since his experiments, one of the persistent issues in metal cutting has been how best to determine the flow stress in a metal undergoing cutting. In all the many models proposed since then, the flow stress of metal flowing in front of a cutting tool has not proven to be the same as the flow stress of metal undergoing a tensile pull. This paper examines the flow stress phenomenon using an improved Videographic Quick Stop equipment at Auburn University.

The orthogonal machining plates and tensile specimens were all cut from the same stock. Tensile testing of the stock was performed immediately prior to the machining of the plates in a standard MTS load frame to allow actual metal cutting experiments to be performed and compared to actual load frame data from the same stock.

Machining was conducted in a specially modified Cincinnati Horizontal Milling machine using an improved Videographic Quick Stop Device (VQSD) to capture the geometry of the cutting formation simultaneously with the forces in the X, Y and Z-axes using a standard Kistler force plate dynamometer. Utilizing the VQSD greatly increases the number of replicates available for statistical analysis by the metal cutting researcher. This allows for comprehensive multivariate analysis of the data with high confidence (> 95%) in the meaning of the results obtained, along with for powerful regression.

The results of the data collection and statistical analysis are then used to populate the various historical models predicting the flow stress in metal cutting. The results indicate that one model is superior to all the other models in predicting the flow stress as predicted by the accompanying tensile test data. Further improvements in this model may lead to instantaneous tensile strength measurement when metal cutting with the need for load frames. This in turn would allow optimization of cutting conditions to match material conditions, resulting in a better product and longer-lived tools.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A040. doi:10.1115/IMECE2015-51355.

In this research work, experiments were conducted using Electrical Discharge Machining (EDM) in dry and conventional mode, and the results were compared and analyzed. LM13 Aluminium alloy is used as the workpiece and pure cylindrical copper rod is used as the tool electrode. Since the machining was difficult in dry EDM, some modifications were made in the existing tool design to conduct the experiments in dry EDM. The experiments were designed using Taguchi’s L27 orthogonal array. Discharge current (I), gap voltage (V), pulse on time (TON), pressure (P) and speed (N) were chosen as the various input parameters. Three levels of values were chosen for each input parameter, whereas speed was chosen as the fixed parameter. The variation in the material removal rate (MRR), surface roughness (SR), surface morphology and elemental composition of the machined surface due to variation in the input parameters were analyzed in both dry and conventional mode. Better MRR, and surface roughness were observed in the work piece machined under conventional EDM process. The MRR is observed to be 84% more in the conventional mode when compared with dry EDM. Also, when compared to the dry EDM, about 15.33% better SR values is observed in the conventional EDM process.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A041. doi:10.1115/IMECE2015-51526.

Metal working fluids remain in common use throughout many industries where metal cutting is necessary. Optimizing the use of a metal working fluid must balance environmental needs, production needs and economic needs.

An orthogonal tube turning machining experiment on 6061-T6 aluminum alloy was conducted to study the performance of uncoated carbide tool inserts utilizing cold compressed air and liquid nitrogen environments as the metal working fluid of choice. The tool inserts selected for this study did not have any chip breaker and studied at 3 different rake angles of 0°, 7° and 15°. Aluminum alloy 6061-T6 was used because of its commercially dominant availability and usage. Cold cryogenic cooling was selected because of its growing usage in high performance machining applications. The use of cold compressed air has been much less studied in the machining of metals than in the machining of plastics and composites where it is quite commonly used. The comparisons between these two methods represent the first published values comparing the current extremes of gaseous metal working fluid applications in a commercially dominant aluminum alloy.

This statistically designed experiment produced a large amount of comparative data that focused on the wear of the tools in two different cutting environments allowing for multivariate analysis of variance and regressive curve fitting. The orthogonal tube turning was set up on a conventional two axis HAAS TL-2 CNC tool room lathe. Forces were collected utilizing a standard Kistler force dynamometer to record the force data in X, Y and Z axes. Two levels of uncut chip thickness, 0.002” and 0.004” per revolution were maintained with a constant feed and depth of cut of 0.125”. Tool rake angles and depth of cuts were selected to ensure maximum statistical power / decisiveness of the experiment. The experiment was carried out for duration of 1 minute while the force data was collected for the entire duration of cut. New tool insert was used for each factor level combination.

The traditional force analysis results are provided for an orthogonal tube turning experiment. In addition, all tools were analyzed for 3-dimensional rake face wear using an innovative Keyence white light microscope in conjunction with a Dektak surface profilometer. Although cutting forces were statistically the same, the inexpensive, simple cold compressed air produced less rake wear than the more expensive liquid nitrogen for all cutting factor level combinations. There was no measureable benefit in using the more expensive liquid nitrogen system.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A042. doi:10.1115/IMECE2015-51534.

The growing cost associated with insurance, handling and disposing of conventional metal working fluids (oil and water based) continues to drive a need for alternative metal working fluids.

An orthogonal tube turning machining experiment on AISI 1020 alloy steel was conducted to study the performance of High Speed Steel (HSS) tool inserts and carbide tool inserts utilizing cold compressed air and liquid nitrogen environments as the metal working fluid of choice The use of both high speed steel and carbide inserts allowed for direct comparison of geometrically identical inserts in customized tool holders that were used to present the tools with the geometrically identical tool rake angle alpha. Tool holder stiffness was therefore common to all tool rake angles compared.

AISI 1020 steel was used because of its commercially dominant availability and usage. Cold cryogenic cooling was selected because of its growing usage in high performance machining applications. The use of cold compressed air has been much less studied in the machining of metals than in the machining of plastics and composites where it is quite commonly used. The comparisons between these two methods represent the first published values comparing the current extremes of gaseous metal working fluid applications in a commercial steel.

This statistically designed experiment produced a large amount of comparative data that focused on the wear of the tools in two different cutting environments allowing for multivariate analysis of variance and regressive curve fitting. The orthogonal tube turning was set up on a conventional two axis HAAS TL-2 CNC tool room lathe. Forces were collected utilizing a standard Kistler force dynamometer to record the force data in X, Y and Z axes. Two levels of uncut chip thickness, 0.002 and 0.004” per revolution were maintained with a constant feed and depth of cut of 0.125” at different tool rake angles of 0°, 7° and 15°, with no chip breaker installed in the tool. Tool rake angles and depth of cuts were selected to ensure maximum statistical power/decisiveness of the experiment. The experiment was carried out for duration of 1 minute while the force data was collected for the entire duration of cut. New tool insert was used for each factor level combination. The traditional force analysis results are provided for an orthogonal tube turning experiment. In addition, all tools were analyzed for 3-dimensional rake face wear using an innovative Keyence white light microscope. Surprisingly, the inexpensive, simple cold compressed air produced less wear than the more expensive liquid nitrogen for all cutting factor level combinations.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A043. doi:10.1115/IMECE2015-53169.

Thermal error modeling and prediction of a heavy floor-type milling and boring machine tool was studied in this paper. An FEA model and a thermal network of the machine tool’s ram was established. The influence of boundary conditions on thermal error was studied to find out the boundary conditions that needn’t to be calculated precisely, reducing the time cost of the work. Superposition principle of heat sources was used in the FEA to get the simulation data of thermal error and temperature. A model based on the simulation data was established to predict the thermal error during the work process. An experiment was performed to verify the accuracy of the model. The result shows that the model accuracy is 87%. The method in this paper is expected to be used in engineering application.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A044. doi:10.1115/IMECE2015-53537.

The Micro-Electrical Discharge Machining, popularly known as micro-EDM, is a nonconventional machining process mainly used for producing micro features like micro holes, micro gears, micro moulds etc. that are difficult to be obtained by conventional process. It can machine different types of conductive materials especially the ones which are difficult to cut and machine. Microholes have been drilled using micro-EDM process on various alloys like Ti-6Al-4V, Inconel 718 etc. using electrodes like Copper, Tungsten etc. The parts produced by micro-EDM are widely used in micro-electro-mechanical systems (MEMS), biomedical applications, automotive industry, and defence industry. Selection and use of correct process parameters is of paramount importance for achieving superior surface quality and higher machining rates while performing micro drilling. However, this process has been characterized by low tool wear rate, low machining rate and longer machining time as compared to other non-conventional processes. This paper aims at studying the influence of various process parameters while drilling micro holes on Maraging Steel 300 alloy using a brass electrode. Maraging Steel 300 alloy is widely used in aerospace, tooling and machinery applications. Brass was selected as the electrode material so as to know its influence in the microdrilling process as it is known for achieving high material removal rate along with high wear ratio. Machining parameters considered in this work were pulse on time, pulse off time, tool diameter and current. A total of 27 micro holes of 300 μm, 400 μm and 500 μm were drilled on Maraging Steel 300 alloy as per the orthogonal array design based Taguchi methodology. Experiments were carried out on Toolcraft V04056 micro-EDM machine. Dielectric used was distilled water. The output responses observed were material removal rate, tool wear rate and overcut. Analysis was carried out using signal to noise ratio analysis. Material removal rate, tool wear rate and overcut were found to be influenced mainly by pulse on time and current. In order to know and better understand the surface morphology of the micro-holes, SEM micro-graphs were obtained. Presence of spatters and re-deposited eroded material were observed in few of the drilled micro holes. The results were verified by performing confirmation experiment at the obtained optimum combination. The confirmation results were in close proximity to the predicted results.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A045. doi:10.1115/IMECE2015-53711.

Abrasive flow machining (AFM) process is a fine finishing process employing abrasive laden self modulating putty for the finishing of mainly internal recesses. Though the AFM is suitable for the finishing of internal cavities, but the material removal is very low during this finishing process. Helical abrasive flow machining (HLX-AFM) has been recently developed to improve the machining efficiency of AFM process. This process employs a coaxially fixed helical twist drill-bit during the extrusion of the abrasive laden media through an internal cylindrical recess. The presence of a fixed drill-bit inside a cylindrical cavity of the work-piece results in considerable increase in material removal and improvement in surface finish. In the present investigation, the same HLX-AFM setup has been used and the effects of two more helical profile rods viz. a 3-start helical profile and a spline have been studied along with the helical twist drill-bit for improving the quality characteristics of material removal and percentage improvement in the surface roughness during the fine finishing of internal cylindrical surface of brass work-pieces. The experiments were planned according to L9 orthogonal array of Taguchi method and the optimal process parameters were selected. The employment of a rod with six splines and a 3-start helical profile results in improved finishing in comparison to the drill-bit profile, due to the presence of more number of flutes and grooves on the coaxially held stationary rods. The helical profile type has 3.75% contribution towards the percentage improvement in the surface roughness, but is not significant in affecting material removal. The presence of 3-start helical profile led to 61.40% improvement in surface roughness (from Ra - 1.3 μm to 0.5 μm) at optimal level with no effect on material removal, which means no extra machining is taking place. The parameter of abrasive-to-media concentration ratio (varying from 0.75 to 1.25) is the most contributing factor with 85.90% contribution toward suface finish improvement and 71.71% contribution towards material removal. The finishing performance of 3-start profile is 15% better than the standard helical drill-bit with no increase in the operating pressures. SEM micrographs corroborated the fact that 3-start profile led to more number of light abrasive cutting grooves and thus more surface finish. HLX-AFM with 3-start helical profile rods can be employed for the finishing, form corrections of internal cylindrical cavities of any size. Presence of the profile rod results in increase in the reduction ratio and thus more machining action. The developed process can also generate cross-hatch lay pattern on internal cylindrical surfaces.

Commentary by Dr. Valentin Fuster

Advanced Manufacturing: Advanced Materials Design, Synthesis, Processing, and Application

2015;():V02AT02A046. doi:10.1115/IMECE2015-50103.

In this research work two different composites are manufactured using Aluminum Alloy (AA) 2900 and 2024 as matrix with SiC and Al2O3 as reinforcement material through powder metallurgy technique. The objectives of this research work are to determine the influence of the sintering duration on the properties of composites and to understand the effect of different aging time on the properties of the composites. The weight percentage of reinforcement materials, sintering duration and aging duration were considered as variable parameters in this experimental work. The metal powder and the reinforcement are blended in high energy ball mill and compacted in Universal Testing Machine at a constant load of 500Mpa to fabricate green compacts. The green compacts were subjected to microwave sintering at 500°C for 60 minutes as per the design of experiments. The sintered samples are quenched in water till it reaches the temperature close to room temperature and loaded again into the sintering furnace for artificial aging (for a varying duration of 60 & 120 minutes). This will allow the samples to form CuAl2 and CuMgAl2 precipitates which are confirmed using SEM and X-ray diffraction studies. Hardness studies are carried out using Rockwell and Brinell hardness tester respectively.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A047. doi:10.1115/IMECE2015-50621.

The reliability of experimental data obtained in friction welded titanium alloy and stainless steel with copper interlayer by using various interlayer thicknesses and upset time are investigated using the maximum likelihood method for the estimation of the Weibull parameters of the results. The results indicate that among the various process parameters, interlayer thickness was significant. Further the reliability of the tensile strength was estimated using weibull distribution. Using this technique in conjunction with the experimental data, we can predict the output, in this case tensile strength more accurately and minimize their impact. Titanium alloy when directly bonded to stainless steel, improper bonding happens. Hence an interlayer in the form of copper is added to have successful joints.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A048. doi:10.1115/IMECE2015-51218.

The objective of this paper is to experimentally investigate the machinability of nano-TiC reinforced Nickel based super alloy Inconel 718 fabricated by direct metal selective laser melting (SLM). Four 10×10×3 square test coupons were fabricated with different amount of nano-TiC: (1) pure Inconel 718, (2) Inconel 718+0.25% TiC, (3) Inconel 718 + 0.5% TiC, of 508 microns. The machinability of the four materials were examined in terms of cutting forces, tool wear and chip morphology. Three level of federates (1.0, 1.5 and 2.0 um/flute) and three level of spindle speeds (12,000, 15,000 and 18,000 rpm) were selected and a 32 full factorial experiment was performed on each test coupon. Full immersion slotting was selected with a fixed axial depth of cut at 20 microns. The SEM images of the tools reveal that the dominant wear mechanisms were abrasive wear at the tool tip and flank face. The adhesion and build up edge were also common. The wear rate increases with the addition of nano-TiC. The loss of the AlTiC coating will result in accelerated wear, which was observed for machining of nano-TiC reinforced Inconel 718, but not on pure Inconel 718. The edge chipping and abrasive wear at the tool tip reduced the effective cutting diameter, enlarged the edge radius, and caused the increase of the cutting force. For all the materials tested, the cutting chips had serrated edge on the free surface and much smoother surface on the other side, which suggests that a cyclic chip formation of alternating high shear strain followed by low shear strain. This is in agreement with the chip formation mechanism for the Inconel 718 fabricated with conventional method rather than DMLS. The serration is more severe with the and (4) Inconel 718 + 1% TiC. Tensile tests were performed on all four material and the material strength increases with the increase of the TiC content up to 0.5% then plateaued. The elongation drop significantly with the inclusion of TiC in Inconel substrate. Micro-endmilling experiments were conducted using AlTiN coated WC micro-mill with nominal diameter addition of nano-TiC. The cutting forces were collected with a Kistler 3-axial load cell 9017B. The cutting forces increases with the increase spindle speed (hence surface speed) within the range examined, but the effect of feedrate is not statistically significant. The cutting forces were much higher for TiC reinforced Inconel and the magnitude of the cutting forces increases with the increase of the weight percentage of TiC contents.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A049. doi:10.1115/IMECE2015-51351.

In the present work, ZrB2/Al alloy composites were processed through the salt-melt reaction technique. Aluminum alloy (LM4) was taken as a matrix material. The ZrB2 reinforcement particles were formed in-situ by the reaction of precursor salts K2ZrF6 and KBF4 within the aluminum melt. Relative to the parent alloy, the hardness of the composites reinforced with 2.5, 5 and 7.5 wt.% ZrB2 showed an increase of 8.24%, 17.64% and 33.77%, respectively. The tensile strength also improved initially but decreased when the amount of reinforcement exceeded 5-wt.%. The elongation varied in the same fashion as the tensile strength. The microstructure of the composites showed moderately uniform distribution of particles. However, agglomeration of reinforcement particles became a problem at the highest amount of reinforcement. Wear experiments to determine the influence of load, sliding velocity, sliding distance and the amount of reinforcement on the wear rate of composites were designed in accordance with the Taguchi model. The results revealed that both load and sliding velocity have the highest influence.

Commentary by Dr. Valentin Fuster

Advanced Manufacturing: Advanced Sensing, Measurement, and Process Control in Manufacturing

2015;():V02AT02A050. doi:10.1115/IMECE2015-50445.

Tool status monitoring is a fundamental aspect in the evolution of production techniques. As the quality of the cutting tool is directly related to the quality of the product, the level of tool status should be kept under control during machining operations. An attempt is made here to extract maximum information from image captured from machine vision and Acoustic Emission (AE) signals acquired during turning of Inconel 718 nickel alloy. Nickel-base super alloy Inconel 718 is a high-strength, thermal-resistant. Because of its excellent mechanical properties, it plays an important part in recent years in aerospace, petroleum and nuclear energy industries. Due to the extreme toughness and work hardening characteristic of the alloy, the problem of machining Inconel 718 is one of ever-increasing magnitude. The experiments were conducted for different cutting speed and feed combinations. An image processing method, the blob analysis technique, was used to extract parameters called features representing the state of the cutting tool. Area and perimeter of the machine vision, AE RMS and AE COUNT of the AE signals studied as features and found to be effective in tool condition monitoring. Once all these features are extracted after preliminary processing of image and AE signals, tool Status, whether worn out or not worn out (serviceable), is decided on the basis of extracted features. In this study, theoretical estimation using ANN is carried out for machine vision parameters like Wear area and perimeter Acoustic Emission parameters like AE RMS and AE COUNT. In estimating vision parameter i.e. Wear area: perimeter, machining time, AE RMS, AE COUNT are considered as the independent variables and vice versa in order to have the performance well in multi sensory situations. In order to identify the tool status based on the signal measured, an Artificial Neural Network, using a Feed Forward Back-Propagation algorithm, has been adopted. The input parameters that are being used for estimation in this study were found to be non linearly varying with the desired output. The training and estimation has generated closer outputs as compared to the wear area observed from the machine vision approach and AE RMS from the acoustic emission approach. Artificial neural network estimates have better correlation at higher feed rate. Under these conditions, there will be large scale values, resulting in vision and AE parameters. Due to higher values, correlation may have been better.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A051. doi:10.1115/IMECE2015-50588.

Wire Electrical Discharge Machining (WEDM) is a specialized thermo electrical machining process capable of accurately machining parts with varying hardness or complex shapes. Present study outlines the comparison of machining performances in the wire electric discharge machining using group method data handling technique and artificial neural network. HCHCr material was selected as a work material. This work material was machined using different process parameters based on Taguchi’s L27 standard orthogonal array. Parameters such as pulse-on time, pulse-off time, current and bed speed were varied. The response variables measured for the analysis are surface roughness, volumetric material removal rate and dimensional error. Machining performances were compared using sophisticated mathematical models viz., Group Method of Data Handling (GMDH) technique and Artificial Neural Network (ANN). GMDH is ideal for complex, unstructured systems where the investigator is only interested in obtaining a high-order input-output relationship. Also, the method is heuristic in nature and is not based on a solid foundation as regression analysis.

The GMDH algorithm is designed to learn the process by training the algorithm with the experimental data. The experimental observations are divided into two sets viz., the training set and testing set. The training set is used to make the GMDH learn the process and the testing set will check the performance of GMDH. Different models were obtained by varying the percentage of data in the training set and the best model were selected from these, viz., 50%, 62.5% & 75%. The best model was selected from the said percentages of data. Number of variables selected at each layer is usually taken as a fixed number or a constantly increasing number. It is usually given as fractional increase in number of independent variables present in the previous level. Three different criterion functions, viz., Root Mean Square (Regularity) criterion, Unbiased criterion and Combined criterion were considered for estimation. The choice of the criterion for node selection is another important parameter for proper modeling.

The Artificial Neural Network is used to study and predict the machining responses. Input data are fed into the neural network and corresponding weights and bias are extracted. Then weights and bias are integrated in the program which is used to calculate and predict the machining responses. Estimation of machining performances was obtained by using ANN for various cutting conditions. ANN estimates were obtained for various percentages of total data in the training set viz., 50%, 60% & 70%. The best model was selected from the said percentages of data. Estimation and comparison of machining performances were carried out using GMDH and ANN. Estimates from GMDH and ANN were compared and it was observed that ANN with 70% of data in training set gives better results than GMDH.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A052. doi:10.1115/IMECE2015-50596.

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. Selection of cutting parameters for obtaining higher cutting efficiency or accuracy in WEDM is still not fully solved, even with most up-to-date CNC WEDM machine. It is widely recognised that Acoustic Emission (AE) is gaining ground as a monitoring method for health diagnosis on rotating machinery. The advantage of AE monitoring over vibration monitoring is that the AE monitoring can detect the growth of subsurface cracks whereas the vibration monitoring can detect defects only when they appear on the surface. This study outlines the estimation of AE parameters viz., signal strength, absolute energy, RMS in the WEDM. Stavax (modified AISI 420) steel material was machined using different process parameters based on Taguchi’s L’16 standard orthogonal array. Among different process parameters voltage and flush rate were kept constant. Parameters such as pulse-on time, pulse-off time, current and bed speed was varied. Molybdenum wire having diameter of 0.18 mm was used as an electrode. Simple functional relationships between the parameters were plotted to arrive at possible information on surface roughness and AE signals. But these simpler methods of analysis did not provide any information about the status of the work material. Thus, there is a requirement for more sophisticated methods that are capable of integrating information from the multiple sensors. Hence, methods like Multiple Regression Analysis (MRA) and Group Method of Data Handling (GMDH) have been applied for the estimation of surface roughness, AE signal strength, AE absolute energy and AE RMS. The GMDH algorithm is designed to learn the process by training the algorithm with the experimental data. The experimental observations are divided into two sets: the training set and testing set. The training set is used to make the GMDH learn the process and the testing set will check the performance of GMDH. Different models can be obtained by varying the percentage of data in the training set and the best model can be selected from these, viz., 50%, 62.5% and 75%. The best model is selected from the said percentages of data. Number of variables selected at each layer is usually taken as a fixed number or a constantly increasing number. It is usually given as fractional increase in number of independent variables present in the previous level. Three different criterion functions, viz., Root Mean Square (Regularity) criterion, Unbiased criterion and Combined criterion were considered for the estimation. The choice of criterion for node selection is another important parameter for proper modeling. From the results it was observed that, AE parameters and estimated surface roughness values were correlates well with GMDH when compare to MRA.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A053. doi:10.1115/IMECE2015-51382.

The production of micro-components in high quantities by means of cutting plays a central role in the area of metal forming. Generally, these components are manufactured with mechanical high speed presses with modified drive kinematics which provide stroke rates of up to 4,000 strokes per minute (spm) and punching forces of up to 2,000 kN. Depending on the application, this may result in a significant oversizing both in terms of maximum cutting force and size of the punching machine. This leads to higher production costs due to increased space and energy consumption which could be improved by a better adaptability of the machine to the process. To fulfill both requirements, a prototype of an electromagnetically driven punch machine with highly efficient resonance drive and miniaturization potential is proposed in this paper. Electromagnetic actuators induce oscillations of a mass-spring system at its resonance frequency by storing potential energy in the system’s springs. An advantage of the resonance propulsion is that only magnets with low nominal force are needed, since only small forces are necessary during the swing-up. The resulting oscillation frequency can be adjusted for the given task by using a modular concept with exchangeable springs. After discussing the concept and essentials, the requirements and constraints are pointed out. Subsequently, a model of the system is created and an energy based bang-bang control concept is implemented utilizing model based filter techniques. Based on the simulation results a test rig was built and obtained measurements were compared to the simulation data. The test rig provides stroke rates up to 2,000 spm and cutting forces up to 20 kN. A prototype, which will be able to achieve higher stroke rates and cutting forces will be part of future work.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A054. doi:10.1115/IMECE2015-52101.

The construction and validation of an apparatus for measuring the permeability of ceramic foam filters (CFFs) at varying water flow rates is presented here. Commercially available CFFs are specified by pores per inch, which does not uniquely determine the flow characteristics of CFFs. Permeability, the pressure drop per unit filter thickness as a function of velocity, is desired for modeling and quality control purposes. Permeability is typically described with the Forchheimer equation, which can be broken into linear (Darcy) and quadratic (non-Darcy) components. Linear dependence comes from laminar flow at low flow rates, and is scaled by viscosity, while the square dependence dominates at high flow rates, and is scaled by fluid density.

CFF measurement systems are not commercially available, and while several examples are found in literature, they are expensive and labor intensive to operate, and are usually limited to specific sizes of filter. The methodology, apparatus, and verification work presented here aims to reduce the cost, time, and complexity of measuring the permeability of commercially available CFFs of different sizes and porosities.

Water is used as the working fluid, which is pumped through a CFF held in a modular cartridge. Pressure transducers are mounted close to the filter on either side. For testing different diameters of commercially available CFFs, different inlet and outlet pipe sizes are used to approximately match the diameter of the filter. This approach avoids the need for computational modeling of an effective filter diameter when the pipe and filter diameters do not match. Long, straight rigid pipe runs are used on the inlet to ensure fully developed flow profiles. Flow is measured with a magnetic flow meter. Pressure drop and flow rate are recorded at discrete flow rates after allowing the system to settle to a constant flow rate. A continuously variable methodology was evaluated and rejected. During testing, it was found that the decreased viscosity of water heated by the pump during long testing runs affected the measured permeability. To compensate, water temperature is measured during each run, and the viscosity is calculated for each run. The linear and quadratic permeability coefficients are determined by fitting a quadratic model through pressure drop data as a function of flow rate.

In order to verify the accuracy of the device, a validation disc was created. A 49.6 mm disc of aluminum was drilled with 1,467 evenly spaced holes. An analytical formula from literature was used to calculate the theoretical permeability of the array. The measured permeability was below the calculated value, but surface defects in the disk were shown to have a large impact on measured permeability.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A055. doi:10.1115/IMECE2015-53030.

In order to improve the prediction accuracy of the thermal error models, grey cluster grouping and correlation analysis were proposed to optimize and select the heat-sensitive points to improve the performances of the thermal error model and minimize the independent variables to reduce modeling cost. Subsequently, the neural network with back propagation (BP) algorithm was proposed to construct the strongly nonlinear mapping relationship between spindle thermal errors and typical temperature variables. However, the shortcomings of the BP network restricted the accuracy, robustness and convergence of thermal error models. Then, a genetic algorithm (GA), which regarded the reciprocal of the absolute value sum of the differences between the predicted and desired outputs as the number of nodes in the hidden layer, was proposed to optimize the structure and initial values of the network. And the number of the nodes in the hidden layer can be determined by performing such operations of GAs. Moreover, the reciprocal of the sum square of the difference between the predicted and expected outputs of individuals is regarded as the fitness function and the weights and thresholds of the BP neural network are optimized by setting the control parameters of GAs. Then, the elongation and thermal tilt angle models of high-speed spindles were proposed based on BP and GA-BP networks and the fitting and prediction abilities were compared. The results showed that the grey cluster grouping and correlation analysis could depress the multicollinearity among temperature variables and improve the stability and accuracy of the thermal error models. Moreover, although the traditional BP network had better fitting ability, its convergence and generality were far worse than the GA-BP model and it is more suitable to use the GA-BP neural network as the thermal error modeling method in the compensation system.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A056. doi:10.1115/IMECE2015-53314.

Friction stir processing (FSP), an offshoot from friction stir welding (FSW), is an intricate operation that involves refining the material by a rotating tool. Active control of the resulting size and distribution uniformity of grain structure is desirable. Achieving such a control across the processed area requires real-time control of the process input variables in order to control the pertinent state variables (e.g., temperature, strain, and strain rate) throughout the process. Many active control schemes typically used in friction stir processes (such as position-, speed-, force-, and torque-control schemes) require the utilization of dynamometers to provide feedback to the control loop. Many drawbacks are associated with such utilization including the complexity of the required instrumentation and control systems. Another complexity is the required rigidity of the machine tool needed to perform friction stir processes.

In this work, we advance the notion of eliminating the usage of dynamometers by using the readily available motor current signals from the NC machine tool in the computer numeric control (NC) machines. This approach would drastically reduce the cost of FSP machine retrofitting. Presented in this work are guidelines for the implementation of affordable automation of CNC milling machines to perform friction stir processes. The guidelines are demonstrated by retrofitting a vertical machining center with current transducers to replace the usage of a dynamometer. The current transduces were tapped on the output of the drivers of the spindle and the z-drive motors. A custom LabVIEW software program was developed to control the machining center via direct numeric control mode and to monitor current signals which were in turn, correlated to the generated forces.

To demonstrate the methodology, friction stir processing was performed on magnesium alloy sheets for a wide range of process parameters. The tool rotational speed was varied from 600 RPM to 2000 RPM and the traverse feed from 75 mm/min to 900 mm/min. Current signals were monitored during frictions stir processing and were related to the process forces which were measured using a 4-component dynamometer. Linear relations between thrust force and torques with current signals of the spindle and the z-drive motors were established and the signal to noise ratio for each correlation was investigated.

It was found that the current spindle signals are highly correlated to the process torque where results can be used in a torque control loop without the need for expensive dynamometers. To a lesser extent was the correlation satisfactory between thrust force and z-drive motor signal due to bad signal to noise ratio.

Topics: Friction
Commentary by Dr. Valentin Fuster
2015;():V02AT02A057. doi:10.1115/IMECE2015-53390.

This paper presents experimental study on conditions for built-up-edge (BUE) formation and its effects in micromilling. Surface finish and BUE area density on a micromilled surface are used to quantify the presence of BUE. A model for surface finish is derived based on the topography of milled surface and tool geometry. Assuming no BUE formation, this empirical model shows the dependence of surface finish on chip load, tool concavity angle, and includes the effect of cutting parameters and milling modes (up-milling or down-milling). Micromilling tools of 100–400 μm diameters are used for milling stainless steel at 10–60 m/min cutting speed, 0.05–1 μm/flute chip load, in minimum quality lubrication condition (MQL). A BUE, embedded onto either a milled surface or tool cutting edge or chip, is identified by scanning electron microscopy and energy dispersive spectroscopy techniques; the severity of BUE formation is quantified as area density when observing a machined surface at high magnification with optical microscopy or interferometry.

Condition for BUE formation is presented by mapping the surface finish and BUE area density against cutting speed and chip load. A microtool would fracture catastrophically at high cutting speeds and/or high chip loads due to excessive dynamic stresses on a microtool; such tool would also fail at the other extreme when low cutting speeds and chip loads promote formation and detachment of BUE on the tool surface, therefore, chipping the fragile microcutting edges of a microtool. There is an optimal zone for effective micromilling without tool failure and BUEs. The measured surface finish approaches the theoretical value when BUE is absent, i.e. micromilling in minimum quantity lubrication at cutting speed between 40–60 m/min and chip load higher than 0.15μm/tooth. The BUE area density for up-milling is lower than that for down-milling at low cutting speed; such difference gradually diminishes when selecting milling parameters in the optimal zone where BUE is practically absent.

Topics: Micromilling
Commentary by Dr. Valentin Fuster
2015;():V02AT02A058. doi:10.1115/IMECE2015-53632.

This study presents wetting characteristic of several lubricants for minimum quantity lubrication (MQL) by comparing their respective contact angles on different tool and workpiece materials. The size of an airborne droplet is estimated by measuring the profile of average droplets depositing on a polished and flat glass surface. The droplet velocity field in front of a nozzle is simulated numerically, and compared against measured data using anemometry and laser particle image velocimetry techniques.

A favorable contact angle of ∼5° is obtained for oil-based lubricants on titanium, stainless steel, and tungsten carbide samples. Such low contact angle is preferred over a higher contact angle of ∼30° typically found when using water-based cutting fluids. The micromist used in the study forms a conical flow of ∼ 20° in front of a coaxial nozzle. High air pressure can atomize lubricant into microdroplets with characteristics droplets of 4–11 μm in size, which are comparable with published data for microdroplet diameters. An optimum size of 3–5 μm microdroplets is preferred since airborne microdroplets below 2 μm may cause a health concern to some machine operators. When the input pressure is above 300 kPa, the air speed in front of a nozzle is at least 100 m/s (6,000 m/min) along a working distance of 20–100 mm from the nozzle tip. Since this droplet speed could be 5 times faster than the cutting speed of a diamond tool in ultrahigh speed machining, such microdroplet could penetrate the boundary layer of a fast rotating tool, adhere and wet the tool and workpiece surfaces for effective lubrication and heat removal. The axial microdroplet speed, however, is drastically reduced in the direction perpendicular to the flow due to vortices forming beyond ∼50 mm downstream from the nozzle tip. A single nozzle would be sufficient for a single point cutting tool — as in turning operation — if the working distance is short and the airstream is near the laminar regime, but multiple MQL nozzles should be utilized for a larger milling tool.

Topics: Machining
Commentary by Dr. Valentin Fuster

Advanced Manufacturing: Biomanufacturing and Bioinformatics

2015;():V02AT02A059. doi:10.1115/IMECE2015-51555.

Biomanufacturing research involving solid freeform fabrication techniques has become fairly widespread in recent times. The layer-by-layer building concept provides an opportunity towards the development of a modular 3D printer to broaden the scope of biomanufacturing research. This research discusses the features of a Custom Multi-Modality 3D Bioprinter (CMMB) developed in the MARS lab at the University of Texas at Arlington (http://mars.uta.edu/). The CMMB currently includes a number of printing modules; two Fused Filament Fabrication (FFF), one Photo Polymerization (PP), one Viscous Extrusion (VE) and one Inkjet (IJ). The development of the custom bioprinter and each module are discussed; focusing on the advantages of a modular design, and on the unique features present in each individual module. Select constructs fabricated using individual or a combination of modules are presented and discussed. Design of Experiments (DOE) principles employing statistical software were used to characterize the CMMB; interactions between fabrication process parameters and their effect on deposited strand characteristics were analyzed. These results were employed to improve the quality of subsequently fabricated constructs. Initial experiments and fabricated constructs demonstrate that the custom bioprinter is a novel CAD-CAM biomanufacturing platform for research in methodologies, materials and processes for the fabrication of biomedical devices.

Commentary by Dr. Valentin Fuster
2015;():V02AT02A060. doi:10.1115/IMECE2015-51990.

In this paper, the authors propose a novel method whereby a prescribed simulated skin graft is 3D printed, followed by the realization of a 3D model representation using an open-source software AutoDesk 123D Catch to reconstruct the entire simulated skin area. The methodology is photogrammetry, which measures the 3D model of a real-word object. Specifically, the principal algorithm of the photogrammetry is structure from motion (SfM) which provides a technique to reconstruct a 3D scene from a set of images collected using a digital camera. This is an efficient approach to reconstruct the burn depth compared to other non-intrusive 3D optical imaging modalities (laser scanning, optical coherence tomography). Initially, an artificial human hand with representative dimensions is designed using a CAD design program. Grooves with a step-like depth pattern are then incorporated into the design in order to simulate a skin burn wound depth map. Then, the *.stl format file of the virtually wounded artificial hand is extruded as a thermoplastic material, acrylonitrile butadiene styrene (ABS), using a commercial 3D printer. Next, images of the grooves representing different extents of burned injury are acquired by a digital camera from different directions with respect to the artificial hand. The images stored in a computer are then imported into AutoDesk 123D Catch to process the images, thereby yielding the 3D surface model of the simulated hand with a burn wound depth map. The output of the image processing is a 3D model file that represents the groove on the plastic object and thus the burned tissue area. One dimensional sliced sections of the designed model and reconstructed model are compared to evaluate the accuracy of the reconstruction methodology. Finally, the 3D CAD model is designed with a prescribed internal tissue scaffold structure and sent to the dedicated software of the 3D printing system to print the design of the virtual skin graft with biocompatible material poly-ε-caprolactone (PCL).

Commentary by Dr. Valentin Fuster

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