0

ASME Conference No-Show Policy and Archival Proceedings

2011;():i. doi:10.1115/MSEC2011-NS1.
FREE TO VIEW

This online compilation of papers from the ASME 2011 International Manufacturing Science and Engineering Conference (MSEC2011) represents the archival version of the Conference Proceedings. According to ASME’s conference no-show policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in the ASME Digital Library and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Processing

2011;():1-6. doi:10.1115/MSEC2011-50130.

Semi-solid powder processing (SPP) is a promising technique in the fabrication of composite materials. Former work has experimentally shown that SPP was able to synthesize composite materials with reduced load and high efficiency. However, limited work was found in the modeling of the SPP. In this work, SPP was modeled with Shima-Oyane’s model and compared with experimental data in a closed die compaction setup. The evolution and distribution of the density and stress were analyzed. The model prediction agreed with the experimentally measured values. As the compaction pressure increased, the density gradient in the axial compaction direction decreased, while the stress gradient increased.

Topics: Compacting , Modeling
Commentary by Dr. Valentin Fuster
2011;():7-16. doi:10.1115/MSEC2011-50173.

The monotonic and cyclic behavior of five different casting processes for AZ91 magnesium alloy is evaluated through microstructure characterization and mechanical testing. A passenger car control arm was cast by squeeze cast, low pressure permanent mold, low pressure permanent mold-electricmagnetic-pump, T-mag, and ablation processes. Samples were cut from twelve locations of the control arm for microstructure characterization. The grain size, porosity fraction, and porosity size were measured via optical microscopy. Different types and sizes of defects were present in each type of casting processes. The mechanical behavior characterization included monotonic tension, and fully-reversed fatigue tests. Sources of fatigue crack initiation were quantified using scanning electron microscopy. For both monotonic and cyclic loading conditions, poor mechanical performance was directly linked to the presence of large pores, oxide films, and/or pore shrinkage clusters.

Commentary by Dr. Valentin Fuster
2011;():17-24. doi:10.1115/MSEC2011-50129.

In MIM, fine metal powders are mixed with a binder and injected into molds, similar to plastic injection molding. After molding, the binder is removed from the part, and the compact is sintered to almost full density. The obstacle to sinter bonding a MIM part to a conventional (solid) substrate lies in the sinter shrinkage of the MIM part, which can be up to 20%, meaning that the MIM part shrinks during sintering, while the conventional substrate maintains its dimensions. This behavior would typically inhibit bonding and/or cause cracking and deformation of the MIM part. A structure of micro features molded onto the surface of the MIM part allows for shrinkage while bonding to the substrate. The micro features tolerate certain plastic deformation to permit the shrinkage without causing cracks after the initial bonds are established. In a first series of tests, bond strengths of up to 80% of that of resistance welds have been achieved. This paper describes how the authors developed their proposed method of sinter bonding and how they accomplished effective sinter bonds between MIM parts and solid substrates.

Commentary by Dr. Valentin Fuster
2011;():25-30. doi:10.1115/MSEC2011-50199.

In this paper the processing steps for producing SOFC (Solid Oxide Fuel Cell) supports by means of PIM (Powder Injection Molding) technique were investigated. Injection molding parameters in this study were divided into pressure-related (injection pressure and packing pressure), temperature-related (nozzle temperature and mold temperature), and time-related (injection rate and holding time) parameters. Keeping the other parameters (pressure-related, temperature-related and time-related parameters) constant at an optimized value, the effects of each of the molding parameters above were investigated. The results show that the short shot, warpage, weld line and void are the most common defects in molded parts. According to the results the short shot could be seen in low values of injection pressure, injection rate, nozzle and mold temperature. Also, warpage could be seen in high values of mold temperature, injection and packing pressure. Poor weld line was another defect that could be seen in low values of injection pressure, injection rate, nozzle and mold temperature. Also the void was one of the most common defects that could be seen in high values of injection rate and nozzle temperatures. Finally, using optimized molding parameters, the molded parts underwent debinding and sintering processes. Based on the results of thermal shock tests and the porosity measurements of the sintered parts, these molded parts possessed relatively desirable characteristics.

Commentary by Dr. Valentin Fuster
2011;():31-38. doi:10.1115/MSEC2011-50249.

Aluminum nitride (AlN) exhibits many functional properties that are relevant to applications in electronics, aerospace, defense and automotive industries. However, the successful translation of these properties into final applications lies in the net-shaping of ceramics into fully dense microstructures. Increasing the packing density of the starting powders is one effective route to achieve high sintered density and dimensional precision. The present paper presents an in-depth study on the effects of nanoparticle addition on the powder injection molding process (PIM) of AlN powder-polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles were found to have significantly increased powder packing characteristics (solids loading) in the powder-polymer mixtures. The influence of nanoparticle addition on the multi-step PIM process was examined. The above results provide new perspectives which could impact a wide range of materials, powder processing techniques and applications.

Commentary by Dr. Valentin Fuster
2011;():39-48. doi:10.1115/MSEC2011-50139.

Ultrasonic imaging is an important medical imaging technique. It uses ultrasound over 20K Hz to detect and visualize muscles, tendons, and many internal organs. Previous studies have shown that an improved acoustic performance can be achieved by conformal ultrasound transducer arrays and horns that can wrap conformably around curved surfaces. To address challenges in fabricating such curved ultrasound transducer arrays and horns, we investigate the possibility of using a newly developed additive manufacturing (AM) process named CNC accumulation. In such an AM process, an accumulation tool can have multi-axis motion, which is beneficial for building conformal ultrasound transducer arrays and horns on a curved surface. To address different resolution requirements, we illustrate the use of multiple accumulation tools that can have different curing sizes and power in the fabrication of a single component. The tool path planning methods for any given cylindrical and spherical surfaces have been discussed. Based on the developed prototype system, various test cases have been performed. The experimental results have illustrated the capability of the process and its potential use in the fabrication of conformal ultrasound transducer arrays and horns. The current limitations and future development have also been discussed.

Commentary by Dr. Valentin Fuster
2011;():49-54. doi:10.1115/MSEC2011-50166.

A new type of hydrogel for solid free-form fabrication (SFF) and rapid prototyping (RP) that obtains the qualities of a photocrosslinkable and thermosensitive hydrogel would benefit the tissue engineering field. For a material to best suit SFF and RP, it must: 1) be a low-viscous solution before being printed, 2) involve easily joined on-substrate mixing to form a homogenous gel, 3) have a short solution to gel transition time, 4) be a mechanically strong gel, and 5) have an irreversible gelation processes. A biodegradable, biocompatable thermosensitive triblock copolymer, poly(ethylene glycol-b-(DLlactic acid-co-glycolic acid)-b-ethylene glycol) (PEG-PLGA-PEG), crosslinked with photocrosslinkable Irgacure 2959 allows for quick irreversible transition from solution to gel with a post-processing step utilizing UV light. A material that gels instantaneously from a non-viscous solution to a 3-dimensional building gel could be used in multiple different types of SFF methods already developed. Since the material is also biocompatible, it can be used to replicate many different types of tissues. In this paper, the mechanism of gelation is proposed and the material relationship to the initial viscosity is investigated.

Commentary by Dr. Valentin Fuster
2011;():55-61. doi:10.1115/MSEC2011-50176.

A new type of Solid freeform fabrication (SFF) machine based on Automatically Programmed Tools (APT) language has been developed to construct hydrogel scaffolds and porous structures. The system comprises three servo motors, three motor drives, three appropriate optical linear encoders, digital/analogue input and output interfaces, an air pressure control system, a UV light device, a hot plate, and a nozzle with dispensing controller. In this study, the system was connected into a PC to act as a high-performance servo controller for monitoring the control of a three axis x-y-z moving arms. The printing procedures were repeated layer-by-layer to form a 3D structure. A biocompatible and thermosensitive material, PEG-PLGA-PEG triblock copolymer, has been printed by this new three-dimensional direct printing machine and the experimental results are discussed with respect to potential applications. Our novel SFF printing system has some advantages over other commercial SFF machines, which includes: 1. Changeable printing nozzles for materials with different viscosities. 2. Re-constructible system setup for different printing purposes. 3. Capability for heterogeneous printing. 4. User-friendly software development 5. Economic system design. The study of the hardware and software and their integration are described and its new heterogeneous printing algorithm is discussed for multiple purpose uses. The integrated software has been developed to link all components of the control system together and it is easy to adapt to different applications.

Topics: Design , Printing
Commentary by Dr. Valentin Fuster
2011;():63-72. doi:10.1115/MSEC2011-50205.

Poly(L-lactic acid) (PLLA) has been shown to have potential medical usage such as in drug delivery because it can degrade into bioabsorbable products in physiological environments, and its degradation is affected by crystallinity. In this paper, the effect of film formation method and annealing on the crystallinity of PLLA are investigated. The films are made through solvent casting and spin coating methods, and subsequent annealing is conducted. The resulting crystalline morphology, structure, conformation, and intermolecular interaction are examined using optical microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. It is observed that solvent casting produces category 1 spherulites while annealed spin coated films leads to spherulites of category 2. Distinct lamellar structures and intermolecular interactions in the two kinds of films have been shown. The results enable better understanding of the crystallinity in PLLA, which is essential for its drug delivery application.

Topics: Annealing
Commentary by Dr. Valentin Fuster
2011;():73-79. doi:10.1115/MSEC2011-50247.

Close physical properties with human bone make sintered hydroxyapatite (HAP) a suitable bioceramic material for hard tissue replacement. When being used as implant devices in the human body, the HAP bioceramic needs to be machined to the closest possible configuration with minimal surface roughness. This study investigates the machinability of a newly developed, fully dense nanocrystalline hydroxyapatite (nHAP) bioceramic in turning operations. Efforts are focused on the effects of various machining conditions on surface integrity. Surface roughness is measured using a surface profilometer and the machined surface is observed using a scanning electron microscope (SEM). Chip morphology and tool wear are examined using an optical microscope. Cutting forces are measured using a three-component dynamometer. Based on the experimental results, it is found that the nHAP bioceramic is not very difficult to machine because the tool wear and cutting forces are small. However, the big challenge is how to obtain a smooth and strong surface without chipping or fracturing the material. Two machining strategies are proposed for improving the surface integrity of the sintered nHAP bioceramic in the future.

Topics: Machinability
Commentary by Dr. Valentin Fuster
2011;():81-84. doi:10.1115/MSEC2011-50259.

Tissue engineering is an interdisciplinary field that focuses on restoring and repairing tissues or organs. Cells, scaffolds, and biomolecules are recognized as three main components of tissue engineering. Solid freeform fabrication (SFF) technology is required to fabricate three-dimensional (3D) porous scaffolds to provide a 3D environment for cellular activity. SFF technology is especially advantageous for achieving a fully interconnected, porous scaffold. Bone morphogenic protein-2 (BMP-2), an important biomolecule, is widely used in bone tissue engineering to enhance bone regeneration activity. However, methods for the direct incorporation of intact BMP-2 within 3D scaffolds are rare. In this work, 3D porous scaffolds with poly(lactic-co-glycolic acid) chemically grafted hyaluronic acid (HA-PLGA), in which intact BMP-2 was directly encapsulated, were successfully fabricated using SFF technology. BMP-2 was previously protected by poly(ethylene glycol) (PEG), and the BMP-2/PEG complex was incorporated in HA-PLGA using an organic solvent. The HAPLGA/PEG/BMP-2 mixture was dissolved in chloroform and deposited via a multi-head deposition system (MHDS), one type of SFF technology, to fabricate a scaffold for tissue engineering. An additional air blower system and suction were installed in the MHDS for the solvent-based fabrication method. An in vitro evaluation of BMP-2 release was conducted, and prolonged release of intact BMP-2, for up to 28 days, was confirmed. After confirmation of advanced proliferation of pre osteoblasts, a superior differentiation effect of the HA-PLGA/PEG/BMP-2 scaffold was validated by measuring high expression levels of bone-specific markers, such as alkaline phosphatase (ALP) and osteocalcin (OC). We show that our solvent-based fabrication is a non-toxic method for restoring cellular activity. Moreover, the HAPLGA/PEG/BMP-2 scaffold was effective for bone regeneration.

Topics: Manufacturing , PLGA
Commentary by Dr. Valentin Fuster
2011;():85-92. doi:10.1115/MSEC2011-50281.

Magnesium-Calcium (MgCa) alloys have become attractive orthopedic biomaterials due to their biodegradability, biocompatibility, and congruent mechanical properties with bone tissues. However, process mechanics of machining biomedical MgCa alloys is poorly understood. Mechanical properties of the biomedical magnesium alloy at high strain rates and large strains are determined by using the split-Hopkinson pressure bar testing method. Internal state variable (ISV) plasticity model is implemented to understand the dynamic material behavior under cutting conditions. A finite element simulation model has been developed to study the chip formation during high speed dry cutting of MgCa0.8 (wt %) alloy. Continuous chip formation predicted by the FE simulation is verified by high speed dry face milling of MgCa0.8 using polycrystalline diamond (PCD) inserts. Chip ignition is known as the most hazardous aspect of machining Mg alloys. The predicted temperature distributions may well explain the reason for machining safety of high-speed dry cutting of MgCa0.8 alloy.

Commentary by Dr. Valentin Fuster
2011;():93-100. doi:10.1115/MSEC2011-50005.

The present research deals with a modified optimization algorithm of harmony search coupled with artificial neural networks (ANNs) to predict the optimal cutting condition. To this end, several experiments were carried out on AISI 1045 steel to attain required data for training of ANNs. Feed forward artificial neural network was utilized to create predictive models of surface roughness and cutting forces exploiting experimental data, and Modified Harmony Search algorithm (MHS) was used to find the constrained optimum of the surface roughness. Furthermore, Simple Harmony Search algorithm (SHS) and Genetic Algorithm (GA) were used for solving the same optimization problem to illustrate the capabilities of MHS algorithm. The obtained results demonstrate that MHS algorithm is more effective and authoritative in approaching the global solution than the SHS algorithm and GA.

Commentary by Dr. Valentin Fuster
2011;():101-110. doi:10.1115/MSEC2011-50014.

Grinding the helical surfaces in end-mill cutters using two-axis CNC machines is well investigated in literature. However, the grinding wheels do not have explicit geometric representations and the produced helical angles differ from the designed values. Moreover, to the best knowledge of the authors, no reliable and robust algorithm exists to grind generic shape cutters with constant normal rake angles. Thus, the first part of this work introduces a five-axis grinding process that keeps the normal rake angle constant along the rake face. The parameters that affect the shape of the tool flutes are also analyzed and studied in this part. These parameters are then optimized in the second part to obtain optimum wheel shapes grinding the tool flutes along optimum paths. Overall, the grinding process proposed grinds the tool flutes with close matching to the designed ones and replaces the complex wheel shapes commonly used by simple prismatic ones.

Commentary by Dr. Valentin Fuster
2011;():111-118. doi:10.1115/MSEC2011-50040.

In this paper the three-dimensional dynamic behavior of macro-scale milling tools is modeled using the spectral-Tchebychev technique while considering the actual fluted cross-sectional geometry and pretwisted shape of the tools. The bending and torsional behavior of three different fluted endmills is compared to finite element predictions and experimental results obtained using impact testing with free-free boundary conditions. The percent difference between experiment and the spectral-Tchebychev method predictions is shown to be 3% or less for all three tools while considering the first six bending modes and first two torsional modes. For the same modes, the spectral-Tchebychev and finite element model predictions agreed to better than 1%.

Commentary by Dr. Valentin Fuster
2011;():119-126. doi:10.1115/MSEC2011-50049.

This paper deals with the utilization of topology optimization in the design process. Topology optimization is considered the most challenging task in the structural design optimization problems because the general layout of the structure is not known; however, implementing it in the conceptual design stage has proven to reduce the cost and development time. In this paper, the design process is briefly discussed emphasizing the use of topology optimization in the conceptual design stage. Also, the mathematical formulation for topology optimization with material density contours is presented. Furthermore, two industrial case studies, related to off-road mining and construction trucks, are discussed where the use of topology optimization has proven to dramatically improve an existing design and significantly decrease the development time of a new design.

Commentary by Dr. Valentin Fuster
2011;():127-136. doi:10.1115/MSEC2011-50055.

A mechanistic model for cutting force in ultrasonic-vibration-assisted grinding (UVAG) (also called rotary ultrasonic machining) of brittle materials is proposed for the first time. Fundamental assumptions include: (1) brittle fracture is the dominant mechanism of material removal, and (2) the removed volume by each diamond grain in one vibration cycle can be related to its indentation volume in the workpiece through a mechanistic parameter. Experiments with UVAG of silicon are conducted to determine the mechanistic parameter for silicon. With the developed model, influences of six input variables on cutting force are predicted. These predicted influences trends are also compared with those determined experimentally for several brittle materials.

Commentary by Dr. Valentin Fuster
2011;():137-144. doi:10.1115/MSEC2011-50102.

The optimization of solid carbide twist drills is a very difficult task because of the large number of conflicting design parameters. Former approaches only consider limited design aspects. This article introduces a new holistic simulation-based method for multi-objective twist drill geometry optimization. By using a complete geometry model, numerical simulation models calculate all major properties of the drill. In detail structural stiffness and strength, torque and thrust force, coolant flow resistance, chip evacuation capability and chip flute manufacturability are calculated. Several multi-objective algorithms and evaluation methods are implemented. Hence an entire geometry optimization considering manufacturability and performance is possible.

Commentary by Dr. Valentin Fuster
2011;():145-152. doi:10.1115/MSEC2011-50114.

A comparative study was conducted to investigate drilling of a titanium (Ti) plate stacked on a carbon fiber reinforced plastic panel. The effects on tool wear and hole quality in drilling using micrograin tungsten carbide (WC) tools were analyzed. The experiments were designed to first drill CFRP alone to create 20 holes. Then CFRP-Ti stacks were drilled for the next 20 holes with the same drill bit. This process was repeated until drill failure. The drilling was done with tungsten carbide (WC) twist drills at two different speeds (high and low). The feed rate was kept the same for each test, but differs for each material drilled. A Scanning Electron Microscope (SEM), and a Confocal Laser Scanning Microscope (CLSM), were used for tool wear analysis. Hole size and profile, surface roughness, and Ti burrs were analyzed using a coordinate measuring system, profilometer, and an optical microscope with a digital measuring device. The experimental results indicate that the Ti drilling accelerated WC flank wear while CFRP drilling deteriorated the cutting edge. Entry delamination, hole diameter errors, and surface roughness of the CFRP plate became more pronounced during drilling of CFRP-Ti stacks, when compared with the results from CFRP only drilling. Damage to CFRP holes during CFRP-Ti stack drilling may be caused by Ti chips, Ti adhesion on the tool outer edge, and increased instability as the drill bits wear.

Commentary by Dr. Valentin Fuster
2011;():153-160. doi:10.1115/MSEC2011-50118.

Engineered features on pyrolytic carbon (PyC) have been demonstrated as an approach to improve the flow hemodynamics of the cardiovascular implants. In addition, it also finds application in thermonuclear components. These micro/meso scale engineered features are required to be machined onto the PyC leaflet. However, being a layered anisotropic material and brittle in nature, its machining characteristics differ from plastically deformable isotropic materials. Consequently, this study is aimed at creating a finite element model to understand the mechanics of material removal in the plane of transverse isotropy (horizontally stacked laminae) of PyC. A layered model approach has been used to capture the interlaminar shearing and brittle fracture during machining. A cohesive element layer has been used between the chip layer and the machined surface layer. The chip layer and workpiece are connected through a cohesive layer. The model predicts cutting forces and the chip length for different cutting conditions. The orthogonal cutting model has been validated against experimental data for different cutting conditions for cutting and thrust forces. Parametric studies have also been performed to understand effect of machining parameters on machining responses. This model also predicts chip lengths which have also been compared with the actual chip morphology obtained from microgrooving experiments. The prediction errors for cutting force and chip length are within 20% and 33%, respectively.

Commentary by Dr. Valentin Fuster
2011;():161-168. doi:10.1115/MSEC2011-50128.

In this paper, the basic concepts and requirements of intelligent metal-forming simulation are presented. A general-purpose metal-forming simulator AFDEX developed to meet the requirements is then discussed, with emphasis on its intelligence. The simulator is based on an adaptive and optimal mesh-generation technique and includes many intelligent, application-oriented special functions, which not only enhance solution accuracy but also minimize user intervention during a metal-forming simulation. Characteristics and typical applications of the simulator are described.

Commentary by Dr. Valentin Fuster
2011;():169-174. doi:10.1115/MSEC2011-50148.

An improved approach to simulating the formation of central bursting defects is presented in this paper. The rigid-plastic finite element method and a modified McClintock damage model are employed. An improved node-splitting technique with degenerate element cleaning is proposed. The technique is applied to several cold forward extrusion processes to reveal the effects of reduction of area, die conical angle, and friction on the formation of central bursting defects. A comparison with experimental results and predictions found in the literature shows that the present analysis provides more realistic predictions of the shape of a central bursting defect (i.e., an obtuse V-shape, which is typical).

Commentary by Dr. Valentin Fuster
2011;():175-184. doi:10.1115/MSEC2011-50149.

Chemical mechanical planarization (CMP) is widely used to planarize semiconductor wafers and smooth the wafer surface. In CMP, a diamond disc conditioner is used to condition (or dress) a polishing pad to restore the pad performance. In this paper, a surface element method is proposed to develop a mathematic model to predict the pad surface shape resulted from diamond disc conditioning. The developed model is then validated by published experimental data. Results show that the model is effective to simulate the diamond disc conditioning process and predict the pad surface shape.

Topics: Disks , Diamonds , Shapes
Commentary by Dr. Valentin Fuster
2011;():185-190. doi:10.1115/MSEC2011-50156.

In this paper, finite element prediction of a cold sheet metal forming process is investigated using solid elements. A three-dimensional rigid-plastic finite element method with conventional linear tetrahedral MINI-elements [1, 2] is employed. This technique has traditionally been used for bulk metal forming simulations. Both single- and double-layer finite element mesh systems are studied, with particular attention to their effect on the deformed shape of the workpiece and thickness variation. The procedure is applied to the well-known problem of the NUMISHEET93 international benchmark. The resulting predictions are compared with experimental observations found in the literature, and good agreement is noted.

Commentary by Dr. Valentin Fuster
2011;():191-196. doi:10.1115/MSEC2011-50158.

This paper develops a three dimensional (3-D) finite element modeling (FEM) to predict the workpiece thermal distortion in minimum quantity lubrication (MQL) deep-hole drilling. Drilling-induced heat fluxes on the drilled hole bottom surface (HBS) and hole wall surface (HWS) are first determined by the inverse heat transfer method. The proposed 3-D heat carrier model consisting of shell elements to carry the HWS heat flux and solid elements to carry the HBS heat flux conducts the heat to the workpiece to mimic drilling process. A coupled thermal-elastic analysis is used to calculate the workpiece thermal distortion at each time step based on the temperature distribution. The heat carrier model is validated by comparing the temperature profiles at selected points with those from an existing 2-D axisymmetric advection model. The capability for modeling distortion in the case of drilling multiple deep-holes is also demonstrated.

Commentary by Dr. Valentin Fuster
2011;():197-204. doi:10.1115/MSEC2011-50175.

Dry turning experiments on Ti-6Al-4V were conducted using two grades (finer and coarser) of carbides and polycrystalline diamond (PCD) inserts to study tool wear. Despite of minor compositional difference between two carbide grades, both grades contain 6% Co. Crater wear and flank wear were measured using Confocal Laser Scanning Microscopy (CLSM). Three dimensional rake surface topographies were reconstructed from the CLSM data and wear profiles were extracted. Finite Element Analysis (FEA) was conducted to study the effects of cutting conditions and thermal properties on rake face temperature. Flank wear on the carbide tools indicated that the inserts with the finer grain size exhibited smaller flank wear than the insert of the coarser grain size. This was attributed to reduced abrasive wear in the finer grained inserts as a result of a higher hardness. The carbide grade with a coarser grain size had an enhanced ability to resist crater wear, likely from lower rake face temperatures and the differences in the compositions. It is known that coarser grain carbides have a higher thermal conductivity resulting from increased grain contiguity. FEA was used to study the temperature difference between the two grain-sizes and the effect of thermal conductivity on temperature gradients. Tool wear of the PCD inserts was also studied. The PCD tools showed significant adhesive wear at the 200sfm cutting speed, transitioning to crater wear at 400sfm. With a high thermal conductivity, it is possible that rake face temperatures were low enough to alter the wear mechanism. FEA supports this hypothesis, as the maximum rake face temperature for the PCD inserts were only around 900°C at 200sfm.

Topics: Wear , Turning , Diamonds , Tungsten
Commentary by Dr. Valentin Fuster
2011;():205-213. doi:10.1115/MSEC2011-50197.

To evaluate the residual stress distribution along cutting direction in hard turning process, an explicit dynamic thermo-mechanical orthogonal Finite Element Model (FEM) is developed to consider the correlation between residual stress distribution and chip morphology and plough effect by cutting edge. The FEM adopts Johnson-Cook (J-C) model to describe work material property, the critical equivalent plastic strain criterion to simulate chip separation behavior, and the revised coulomb’s law to capture the friction pattern between the tool and chip interface. The FEM is validated by comparing the predicted and experimental chip morphology and residual stress distribution. The residual stress distribution in hard machined surface along cutting direction is accurately captured by using sharp and honed cutting edge tools. The residual stresses by sharp tool demonstrate a periodical characteristic, the fluctuation amplitudes are determined in the surface and subsurface along the cutting direction, and the fluctuation frequency corresponds to that of the saw-tooth chip. However, the residual stresses by honed cutting edge tool demonstrate an indistinct periodic characteristic, the fluctuation frequency in surface and subsurface is larger than that of the saw-tooth chip. Saw-tooth chip formation process by sharp tool is identified to analyze the residual stress scatter periodic mechanism, which associates with the fluctuation of cutting force and temperature. The plough process by honed cutting edge tool is identified to explain the equilibrium effect on the amplitude and frequency of residual stress scatter in hard turned surface and subsurface. The periodical fluctuation characteristics of residual stress in hard turned surface and subsurface is revealed and verified by determining its amplitude and frequency corresponding to that of the saw-tooth chip. The analysis will enhance the fatigue life prediction accuracy by incorporating the effect of residual stresses periodical fluctuation on the crack initiation and propagation life in hard turned surface and subsurface.

Topics: Stress
Commentary by Dr. Valentin Fuster
2011;():215-224. doi:10.1115/MSEC2011-50208.

To predict the cutting forces and cutting temperatures accurately in high speed dry cutting Ti-6Al-4V alloy, a Finite Element (FE) model is established based on ABAQUS. The tool-chip-work friction coefficients are calculated analytically using the measured cutting forces and chip morphology parameter obtained by conducting the orthogonal (2-D) machining tests. It reveals that the friction coefficients between tool-work are 3∼7 times larger than that between tool-chip, and the friction coefficients of tool-chip-work vary with feed rates. The analysis provides a better reference for the tool-work-chip friction coefficients than that given by literature empirically regardless of machining conditions. The FE model is capable of effectively simulating the high speed dry cutting process of Ti-6Al-4V alloy based on the modified Johnson-Cook model and tool-work-chip friction coefficients obtained analytically. The FE model is further validated in terms of predicted forces and the chip morphology. The predicted cutting force, thrust force and resultant force by the FE model agree well with the experimentally measured forces. The errors in terms of the predicted average value of chip pitch and the distance between chip valley and chip peak are smaller. The FE model further predicts the cutting temperature and residual stresses during high speed dry cutting of Ti-6Al-4V alloy. The maximum tool temperatures exist along the round tool edge, and the residual stress profiles along the machined surface are hook-shaped regardless of machining conditions.

Commentary by Dr. Valentin Fuster
2011;():225-232. doi:10.1115/MSEC2011-50216.

To better predict the temperature distribution in the tool and chip, a modified theoretical model by considering material thermal properties as temperature dependent is developed to quantitatively describe the temperature elevation due to the shear and friction at the tool-chip interface. Work’s thermal properties of thermal conductivity and specific heat are modified and considered as functions of temperature. The semi-infinite method is utilized in the model, in which the back of the chip and the shear band are assumed as adiabatic. Temperature distribution in the tool and chip is then determined simultaneously by shear and friction. An imaginary heat source is set up to be plane-symmetric with respect to each original heat source in this approach. The effects of original heat source and imaginary heat source are superimposed to calculate the final temperature elevation in the tool and chip. To determine the ratio of total heat transferred into the chip and the tool, it is assumed that the temperatures in the tool and in the chip are in balance along the tool-chip interface in the stable cutting state. The model is experimentally validated with peak temperature data from previous literature. Results indicate that the model-experiment deviation is less than 10% when thermal properties are considered temperature dependent, and it is more accurate than that by considering the thermal properties as constants. The patterns of temperature distribution in the tool and chip are further analyzed by the model.

Commentary by Dr. Valentin Fuster
2011;():233-242. doi:10.1115/MSEC2011-50218.

This paper presents a novel technique to estimate the temperature distribution of a milling tool during machining. In this study, heat generation during the machining process is estimated using cutting forces. We consider the heat to be time-dependent heat flux into the tool. In the proposed model, we discretize each rake face on a mill into several elements; each experiences time-dependent heat flux. Second, we approximate the time-dependent heat flux as several constant heat input starts at different time. Finally, we sum the temperature rise from each heat flux to obtain the overall temperature change. A similar concept is applied on the flank surface, where the flank wear area is modeled as an additional heat generation zone. Experimental results are presented to validate the developed model.

Commentary by Dr. Valentin Fuster
2011;():243-251. doi:10.1115/MSEC2011-50219.

A multi-scale model is developed to investigate the heat/mass transport and dendrite growth in laser spot conduction welding. A macro-scale transient model of heat transport and fluid flow is built to study the evolution of temperature and velocity field of the molten pool. The molten pool geometry and other solidification parameters are calculated, and the predicted pool geometry matches well with experimental result. On the micro-scale level, the dendritic growth of 304 stainless steel is simulated by a novel model that has coupled the Cellular Automata (CA) and Phase Field (PF) methods. The epitaxial growth is accurately identified by defining both the grain density and dendrite arm density at the fusion line. By applying the macro-scale thermal history onto the micro-scale calculation domain, the microstructure evolution of the entire molten pool is simulated. The predicted microstructure achieves a good quantitative agreement with the experimental results.

Commentary by Dr. Valentin Fuster
2011;():253-260. doi:10.1115/MSEC2011-50228.

The objective of this research is to identify optimal sensor locations to estimate temperature distribution in an injection mould using finite element analysis. Potential locations (referred to as target nodes) are grouped based on the similarity of their thermal response using a proposed temperature-ratio clustering method. A sensitivity analysis of the temperature distribution for these groups of target nodes identifies the sensor location for each cluster that exhibits the highest sensitivity to variable inputs. Using identified sensor locations with a neural network model, the accuracy in estimation of temperature response is evaluated.

Commentary by Dr. Valentin Fuster
2011;():261-266. doi:10.1115/MSEC2011-50229.

New experimental data on AISI 1045 steel from the NIST pulse-heated Kolsky Bar Laboratory are presented. The material is shown to exhibit a nonequilibrium phase transformation at high strain rate. An interesting feature of these data is that the material has a stiffer response to compressive loading when it has been preheated to a testing temperature that is below the eutectoid temperature using pulse-heating than it does when it has been preheated using a slower heating method. On the other hand, when the material has been pulse-heated to a temperature that exceeds the eutectoid temperature prior to compressive loading on the Kolsky bar, it is shown to exhibit a significant loss of strength. A consequence of this behavior is that fixed-parameter constitutive models, such as the well-known Johnson-Cook model, cannot be used to describe this constitutive response behavior. An argument is made that the phase transition does not occur during high-speed machining operations, and suggestions are made as to how to modify the Johnson-Cook model of Jaspers and Dauzenberg for this material in order to obtain improved temperature predictions in finite-element simulations of high-speed machining processes.

Commentary by Dr. Valentin Fuster
2011;():267-273. doi:10.1115/MSEC2011-50234.

In machining using a diamond-coated tool, the tool geometry and process parameters have compound effects on the thermal and mechanical states in the tools. For example, decreasing the edge radius tends to increase deposition-induced residual stresses at the tool edge interface. Moreover, changing the uncut chip thickness to a small-value range, comparable or smaller than the edge radius, will involve the so-called size effect. In this study, a developed 2D cutting simulation that incorporates deposition residual stresses was applied to evaluate the size effect, at different cutting speeds, on the tool stresses, tool temperatures, specific cutting energy as well as the interface stresses around a cutting edge. The size effect on the radial normal stress is more noticeable at a low speed. In particular, a large uncut chip thickness has a substantially lower stress. On the other hand, the size effect on the circumferential normal stress is more noticeable at a high speed. At a small uncut chip thickness, the stress is largely compressive.

Topics: Cutting , Diamonds
Commentary by Dr. Valentin Fuster
2011;():275-283. doi:10.1115/MSEC2011-50238.

Die structure behavior and its stability are playing more important roles in stamping of advanced high-strength steel (AHSS) sheet metals since the die structure has to maintain steady forming conditions when larger forming load is generated and applied on the die components. Before the workshop try-out, the virtual testing tool is necessary to assure the stamping die design safety. In this paper, a reliable and efficient method to forecast the die structure performance using an updated load mapping algorithm was proposed to verify the stamping die structure design. Furthermore, an improved method for sheet metal forming modeling with non-rigid tooling definition was also presented to enhance the prediction accuracy. In order to validate the proposed method, a step-shaped-bottom cup drawing die was developed and a data collection system was also adopted to measure the strain/stress evolution at specified locations and to reveal the phenomenon of tooling deflection during the AHSS sheet metal drawing process. The comparison between experimental results and prediction demonstrated very good correlation, and the revised method is more accurate and efficient and is expected to be used to verify the industrial AHSS stamping die designs and support the further research on die structure optimization.

Commentary by Dr. Valentin Fuster
2011;():285-293. doi:10.1115/MSEC2011-50275.

The presented work models the geometry of Single Point Cutting Tools (SPCTs) with generic profile. Presently few standard shapes of SPCTs defined in terms of projective geometry are being employed while there is a need to design free-form tools to efficiently machine free-form surfaces with few passes and chosen range of cutting angles. To be able to produce SPCT face and flanks with generic shapes through grinding, a comprehensive geometric model of the tool in terms of the varying grinding angles and the ground depths is required which helps design the tool with arbitrarily chosen tool angles. The surface modeling begins with the creation of a tool blank model followed by transformation of unbounded planes to get the cutting tool surfaces. The intersection of these surfaces with the blank gives the complete model of the tool. Having created the geometric model in two generations of generalization, the paper presents the methodology to obtain the conventional tool angles from the generic model. An illustration of the model has been provided showing variation of tool angles along the cutting edge with changing grinding parameters. When the geometric model is not to be related to the grinding parameters, the SPCT can be modeled as a composite NURBS surface which has been presented towards the end of the work.

Commentary by Dr. Valentin Fuster
2011;():295-302. doi:10.1115/MSEC2011-50279.

Experimental and FEA study is conducted to get an insight into critical mechanisms of temperature, deformation, stress generation and variations with cutting speed and tool wear in hard milling AISI H13 steel (50±1 HRC). The critical issues like energy consumption during milling and the resulting surface integrity of the machined component depend on the tool and workpiece interaction. An insight into tool and workpiece interaction is needed in order to design a better milling process for required surface integrity. 2D finite element simulation of orthogonal cutting model is performed to investigate the variations of temperatures and residual stresses at different cutting speeds and tool wears. Hard milling experiments are conducted to correlate with the simulation results. The fact that in hard milling, the temperature does not penetrate deep into the workpiece and there is no clear evidence of heat affected zone such as white layer is demonstrated. With the finite element simulations and experiments, the capability of hard milling process to achieve better surface integrity on the machined surface is explored.

Topics: Temperature , Milling
Commentary by Dr. Valentin Fuster
2011;():303-311. doi:10.1115/MSEC2011-50280.

Magnesium-Calcium (MgCa) alloys have received considerable attention recently in medical device manufacturing industry specially in making biodegradable bone implants. Deep rolling (DR) is as a promising manufacturing technique to adjust surface characteristics of implants with the ultimate goal of being able to adjust corrosion rates of MgCa implants. Contact mechanics between rolling ball and the workpiece is essential to understand the DR process. Contact mechanics is further complicated by the normal force reduction due to hydraulic pressure loss at the tip of DR tool, and the penetration depth reduction due to elastic recovery. The measured normal force, in this study, shows maximum 23% reduction compared to theoretical value. The normal force drop is not uniform and increases with increasing applied pressure. A 2D axisymmetric, semi-infinite FEM model is developed and validated to predict the amount of elastic recovery after deep rolling. The dynamic mechanical behavior of the material is simulated using the internal state variable (ISV) plasticity model and implemented in FEM code using a user material subroutine. The simulated dent geometry agrees with the measured ones in terms of profile and depth. Simulation results suggest 8% elastic recovery on average.

Commentary by Dr. Valentin Fuster
2011;():313-322. doi:10.1115/MSEC2011-50052.

SLS (Selective Laser Sintering) has been developing rapidly since its initial invention for non-metal materials by Texas University. Nowadays, Direct Metal Laser Fabrication (DMLF), as a variant of SLS technique, has been investigated intensively which is aimed at rapid manufacturing of end-use metal products with full functions. For describing the stability and properties of DMLF process, Top Surface Quality (TSQ) was put forward in this paper, which could be a unique and crucially important feature compared with traditional manufacturing methods. Through the systematic and detailed analysis of DMLF process using related theories of additive manufacturing technologies, it was revealed that TSQ was the key factor for controlling the stability of DMLF process and thus tailoring final properties of metallic parts. TSQ was defined as the surface morphology in macro and micro scopes in laser scanning area of unit layers during DMLF, and could be characterized by three key elements: flatness, compactness and cleanliness. Only good TSQ could ensure the stability of DMLF process and excellent performance of metal parts in theory. The flatness was the significant factor to assure the shaping during DMLF while the compactness and cleanliness are the decisive factors to assure the final properties of metal part for DMLF. As an example, the typical top surface defects and their contributing factors in DMLF for Cu-based metal powder mixtures were investigated thoroughly according to the proposed definition and requirements. Moreover, the specific controlling methods of TSQ were provided and discussed. Eventually, DMLF of three-dimensional Cu-based metal sample with complicate structure was successfully performed by taking some effective measures for adjusting TSQ parameters.

Commentary by Dr. Valentin Fuster
2011;():323-332. doi:10.1115/MSEC2011-50065.

Surface integrity, mechanical deformation, and thermal deformation are among the crucial error generation factors in tool-based micromachining the influence of which should be minimized. As a micromachining process, micro ultrasonic machining (micro-USM) must satisfy the above considerations. In micro-USM, material is removed by fine and free abrasive particles inside a fluid; hence, there is no direct contact between micro-tool and the workpiece. Furthermore, no thermal damage is induced into the machined surface. Therefore, this process can satisfy the requirements of minimum mechanical and thermal deformation as a tool-based micromachining process. However, usually a rather course surface with subsurface microcracks is generated by USM processes. As such, study on surface characteristics and improvement of surface quality in micro-USM is considered necessary in order to introduce this process as a mature micromachining process. In this paper, the effect of various process parameters on surface quality in micro-USM is studied. The parameters include static load, vibration amplitude, abrasive particle size, and slurry concentration. Machining experiments were conducted using a self-developed micro-USM system with the method of workpiece vibration and using a precision static load measurement system with high sampling rate. An average surface roughness as small as 24 nm was achieved through the investigations on machined surface quality which has not been reported in micro-USM process using the workpiece vibration method. Moreover, the effect of process parameters on dominant removal mechanisms is investigated.

Commentary by Dr. Valentin Fuster
2011;():333-335. doi:10.1115/MSEC2011-50068.

A multi-axis WEDM technology is currently developed with an industrial consortium. To achieve this advanced application technology a CAM software and a machine prototype with an integrated two-axis round table was developed and first tests conducted. The assembly of the additional swing and rotational axis and the simultaneous steering with the machine axes enables the manufacturing of complex parts. But only in combination with the CAM software transforming complex shapes into NC programs for 6- and 7-axis manufacturing, the machining of complex geometries is feasible. At present, the technology is adapted to the manufacturing of medical parts from titanium alloys and CoCr alloys. First results of the machining of an involute gear will be presented.

Commentary by Dr. Valentin Fuster
2011;():337-341. doi:10.1115/MSEC2011-50105.

A bunched electrode for Electrical Discharge Machining (EDM) is formed by bunching numerous cell electrodes as a whole and allows better flushing to facilitate removal of more heat and debris produced during machining. This paper proposes a rapid tooling method for preparing bunched electrodes with desired end-face. A specially designed apparatus, which sits on an XY worktable of a CNC machine tool, is employed to hold the pre-bunched with flat end-face. By using a protrusion pin which is fixed on Z-axis, the heights of each cell electrode are protruded one after another according to a CNC program, which is generated by CAD/CAM software. The end-face of the bunched electrode approximates the ideal end-face of the designed 3D model by adjusting the Z positions of each cell electrode. By using this method the cost and time for electrode preparation are dramatically reduced as compared to that made by traditional cutting method. An investigation on 3D cavity machining of bunched electrode was conducted. The result gives a solid verification of the feasibility of using bunched electrode into roughing process of EDM.

Commentary by Dr. Valentin Fuster
2011;():343-348. doi:10.1115/MSEC2011-50109.

The theory and related technology of porous metallic nickel by using jet electrodeposition (JED) are reviewed, and preparation of different porosities of the porous metallic nickel samples was made by the self-developed device. The surface morphology, microstructure, grain size of the micro-cell structure of deposition were studied and analyzed by SEM, and the mechanical properties of the sample, such as surface micro hardness and compressive property were also studied. The results are as follows: the process of porous nickel preparation by jet electrodeposition mentioned in paper is capable of preparing porous metal with dendritic crystal structure as the subject porous structure. Ejection electrodeposition has great advantages in machining efficiency and cost compared with porous metal preparation process of traditional electrodeposition. The porous nickel metal sample prepared, in respects of pore distribution and porosity, are affected by electrodeposited porous dendritic crystal layers. The formula Bath A, which has a relatively low concentration of nickel ions, can make the preparation of porous dendrite structure more favorable in the way that it has more uniform compactness. Current density is the key indicator in forming ideal branched crystal; more than 60A/dm2 can make the process access to a good working state. With the increase in current density, the dendrite formation of porous structure becomes more compact. The porosity of the prepared sample is 48.7%, using jet scanning electrodeposition with the current density at 80A/dm2 . The surface micro hardness of the sample reaches HV 315. The compressive yield stress of porous Nickel is 11.35 MPa, which has a large number of plastic deformations of the absorption capacity. From original data of sample energy absorption rate and fitting curve, it is known that there comes great plastic deformation, which gives the sample better absorption ability and relatively greater energy absorption rate at a relatively low flow stress.

Commentary by Dr. Valentin Fuster
2011;():349-355. doi:10.1115/MSEC2011-50111.

Corrosion processing is an effective way to solve difficult machining of titanium alloy. It can be applied for reducing weight, machining complex shape and fine structure. In this paper, the effects of the bath constituents and operation conditions on corrosion processing rate and surface quality for Ti-6Al-4V were investigated. Corrosion processing rate depends upon hydrofluoric acid concentration, the volume ratio of nitric acid to hydrofluoric acid, temperature. Nitric acid can promote the surface passivation and reduce surface roughness. The surfactant plays a dual role of surface finish improvement and acid fog suppression. During the period of processing, oxide film on the surface is dissolved initially, and there is the faster processing rate. Surface passivation occurs with the extension of time, decreasing processing rate. Finally corrosion processing rate trends to be stable when the growth of passive film and dissolution of the substrate achieve dynamic balance.

Topics: Corrosion
Commentary by Dr. Valentin Fuster
2011;():357-362. doi:10.1115/MSEC2011-50113.

Accurate and precise micro abrasive tools are essential for the micromachining of highly complex features in a wide variety of engineering materials including metals and ceramics. With existing abrasive coating techniques such as sol-gel method, chemical vapor deposition, physical vapor deposition, and composite electroforming, it is difficult to control the aggregation tendency of abrasive grains. This work evaluates the feasibility of implementing electroplating principles to fabricate a micro abrasive tool by co-deposition of nickel and micro diamond powder over a tungsten substrate. In this work, a tungsten rod of diameter 500 μm was deposited with 2–4 μm diamond abrasive grains using nickel as a binder. Scanning Electron Microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) studies reveal that more uniform coating is obtained with multilayer coating of micro diamond abrasive by electroplating. The coating process mechanism is discussed.

Topics: Electroplating
Commentary by Dr. Valentin Fuster
2011;():363-371. doi:10.1115/MSEC2011-50116.

Rotary ultrasonic machining (RUM) has been used to drill holes in brittle, ductile, and composite materials. However, all these experiments were conducted with help of water or oil based coolant. This paper presents an experimental study on RUM of carbon fiber reinforced plastic (CFRP) composite using cold air as coolant. It reports effects of machining variables (ultrasonic power, spindle speed, and feedrate) on outputs (cutting force, torque, surface roughness, and burning) in RUM of CFRP using vortex-tube (VT) generated cold air as coolant.

Commentary by Dr. Valentin Fuster
2011;():373-380. doi:10.1115/MSEC2011-50131.

Inspired by the idea of vibro-mechanical texturing, which adds a tertiary motion to the tool tip in the conventional turning process, and the elliptical vibration cutting process, which adds vibrations both in the cutting direction and feed direction, this paper proposes a new design for an ultrasonic vibrator for the elliptical vibration texturing process. The elliptical locus lies in the plane that is defined by the cutting and the radial directions. The device could be easily adapted for elliptical cutting applications by changing the orientation of the tool tip. The vibrator works in the resonant mode, with in-phase and anti-phase vibration modes at a nearly identical natural frequency. Simulations and experiments have been carried out to study and verify different vibration modes of the system. Different design parameters have been analyzed to control the elliptical trajectory of the tool tip. A set of preliminary experimental result of elliptical vibration texturing is also provided.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2011;():381-390. doi:10.1115/MSEC2011-50145.

In order to further improve the high-temperature oxidation resistance of TiAl intermetallic alloys, MCrAlY coatings were fabricated by plasma spraying and plasma spraying-laser remelting technologies. The microstructures of the as-sprayed and laser-remelted MCrAlY coatings were studied. In addition, the oxidation behaviors at 850 °C for three samples were investigated. One sample is the matrix of TiA1 intermetallic alloys, the other one is processed by plasma-spraying MCrAlY coatings, and the third one is processed by plasma-spraying and laser-remelting MCrAlY coatings. It was revealed that the oxidation resistance of TiAl intermetallics is weak due to lack of protection of Al2 O3 film formed on the surface. The plasma-sprayed MCrAlY coatings have better oxidation resistance than the TiAl intermetallics although the plasma-sprayed MCrAlY coatings have high density of porosity and a typical layered structure. It is demonstrated that most of the holes can be eliminated by laser remelting, leading to the best oxidation resistance of the third sample with the laser-remelted coatings. The high oxidation resistance of the laser-remelted coatings is mainly attributed to three aspects: firstly, an Al enriched zone on the coating surface is formed during laser remelting, which is transformed into a protective Al2 O3 film during oxidation process. Secondly, laser remelting eliminates most of the defects in plasma-sprayed coatings and enhances its density, thus decreases the channel of oxidation diffusion in high temperature oxidation process. Thirdly, rapid cooling of laser remelting results in a grain refinement and a preferred oxidation of Al at the initial stage, leading to a reduction of oxidation rate.

Commentary by Dr. Valentin Fuster
2011;():391-397. doi:10.1115/MSEC2011-50161.

Dry EDM (Electrical discharge machining in gas) is an innovative electrical discharge machining (EDM) method. The machining performances of dry EDM vary from that of the liquid medium due to the different physical properties of gases and liquids. The generator, a key component in an EDM machine tool, supplies electrical energy to ionize the dielectric, therefore generator mode plays important roles in EDM performance. In this work, experiments were conducted to study the machining performances of dry EDM with two generator modes: the iso-frequencial mode and the iso-pulse mode. Experimental results show that the material removal rate (MRR) and surface roughness (SR) value using the iso-frequencial mode are higher than that of the iso-pulse mode in dry EDM and reasons for the experimental phenomena were analyzed. Under the iso-pulse mode, MRR and SR present an approximately linear increase with an increase in the pulse width increase. The iso-frequencial mode could be used in the rough machining gauge and the iso-pulse mode might be used in finish machining. It is concluded that a high frequency and narrow pulse generator with a high opening voltage might be suitable for dry EDM under a certain conditions.

Commentary by Dr. Valentin Fuster
2011;():399-405. doi:10.1115/MSEC2011-50179.

This paper reports on the machining of a construction material (aerated concrete) with a rapid prototyping device, Shapemaker III, which is based on waterjet technology. Preliminary machining tests were carried out to investigate machining conditions (speed and pressure) of separation cuts. Cutting speeds for the waterjet were investigated for two aerated concrete construction materials; autoclaved aerated concrete (AAC) in two strengths (348 and 580 psi compressive strength) and a non-autoclaved, fiber reinforced aerated concrete (FRAC) with a 450 psi compressive strength. Cutting samples were prepared in four thicknesses (0.5, 1, 2, and 3 inches) and cut at two pressures (40 and 60 ksi). The 0.5 and 1 inch specimens were cut with good surface finish at over 600 in/min at 40 ksi. The 2 and 3 inch specimens could be cut at 320 and 80 in/min at 40 ksi, respectively. The experimental data was used in the fabrication of rapid prototyping houses with a pure waterjet machine. As results, full scale houses were fabricated with FRAC and Styrofoam. Additionally, a sub-mold of an outdoor fireplace was manufactured with Styrofoam for casting of customized aerated concrete blocks.

Commentary by Dr. Valentin Fuster
2011;():407-415. doi:10.1115/MSEC2011-50198.

The demands on parameter technologies in Sinking EDM are very high. In each processing step, a certain surface roughness has to be achieved in very precise manner. At the same time removal rate (productivity) and relative wear (costs) have to achieve advantageous values. The generation of these parameter technologies is time-consuming and expensive, since many influencing factors affect the target figures. The procedural methods in practice are often unsystematic and ineffective. The technological possibilities of machine and process configuration are very often not used. This publication deals with methods designed to effectively optimize the target figures. At the same time, effort and time spent for generating parameter technologies are reduced. Continuous parameter technologies are used for the generation of discrete parameter technologies. Two different types of continuous mappings are compared: Nonlinear regression functions and artificial neural networks (ANN). Model accuracy and the handling properties of these variants are evaluated in this context. A variety of methods for assessing the adequacy of mappings are discussed. A new, problem-oriented experimental design method for EDM-processes is also described, focusing on two aspects: a reduction of the experimental effort and the achievement of a sufficient accuracy of the continuous mappings at the same time. In order to achieve these characteristics, different scale methods and transformation methods are discussed, as well. As a result, a problem-adapted CAP-software solution is presented. Nonlinear regression functions as well as ANNs for the continuous parameter technologies can be generated, visualized and evaluated within this software. In a next step, software functions are implemented, allowing the technologist to derive optimal pulse parameter series for processing. The application of the presented methods is first of all useful for manufacturers of EDM die sinking machines.

Commentary by Dr. Valentin Fuster
2011;():417-425. doi:10.1115/MSEC2011-50226.

Bore holes with a high length-to-diameter (l/D)-ratio and small diameters are needed in various industries. Examples are the downsizing of components for medical and biomedical products or for fuel injection in automotive industry due to the increase of injection pressure. For the production of deep holes with very small diameters an adapted process design is necessary, especially when the conditions at the begin of the deep hole drilling process are unfavorable. In these applications, a hybrid process consisting of a laser pre-drilling and a single-lip deep hole drilling can shorten the process chain in machining components with non-planar surfaces, or can reduce tool wear in machining case-hardened materials. In this research, the combination of laser and single-lip drilling processes for the machining of workpieces with non-planar surfaces was realized and investigated for the very first time.

Commentary by Dr. Valentin Fuster
2011;():427-434. doi:10.1115/MSEC2011-50240.

Micro Electro Discharge Machining is a well known process for machining microstructures with highest precision in hard and brittle or tough materials. The deeper the structures and therefore higher the aspect ratio, the more difficult it is to remove the ablated particles from the discharge zone and keep the process in stable condition. Flushing can be aided by vibration of either tool or workpiece. Thus, applying ultrasonic vibration to micro EDM has proven to enhance the process significantly. The vibration is most efficiently induced via the tool or workpiece directly to the discharge zone. However, to achieve an ultrasonic vibration of the tool or workpiece, a complex vibration system that operates in resonant mode is needed. Any crucial change of the vibrating parts results in a demanding and therefore expensive adjustment of the vibrating system. With this setup, the application of ultrasonic vibration is only profitable for large scale serial production. In this work a different approach of ultrasonic superposition to the EDM is proposed. A highly focused ultrasonic vibration is induced into the dielectric in a way to directly influence the discharge zone. This indirect ultrasonic superposition can be easily applied since it is independent of the tool or workpiece geometry. Experiments are carried out to examine the effects of the indirect ultrasonic superposition on the EDM process. First results show the possibility of enhancing micro-EDM by this approach.

Commentary by Dr. Valentin Fuster
2011;():435-441. doi:10.1115/MSEC2011-50283.

Rapid Prototyping (RP)/Layered Manufacturing (LM) machines typically use a Stereolithography (STL) file as a basis to manufacture parts. However, the conversion of the part CAD file to STL results in the distortion of the part geometry, particularly if the part consists of freeform curved surfaces. Existing algorithms and software tend to reduce this distortion globally, which increases the size and memory requirements of the STL file. This paper presents a new approach for reducing the CAD to STL translation error locally, using chordal error as the criteria. The algorithm presented here compares the STL file to the design surface of the part, expressed as a NURBS surface, and computes the chordal error for multiple points on the STL facets. The point within each STL facet having the largest chordal error is modified to coincide with its corresponding point on the design surface. This replaces the original facet of the STL file with three new facets with significantly lower chordal error than that of the original facet. This Vertex Translation Algorithm (VTA), reduces the chordal error in areas with high curvature and areas having tighter profile tolerance specifications and provides the user the flexibility to selectively modify the STL file according to the tolerance requirements. The algorithm has been validated with the help of a test case.

Commentary by Dr. Valentin Fuster
2011;():443-452. doi:10.1115/MSEC2011-50094.

Wrinkling in the flange region has been observed during redrawing operation by few researchers. In the present work an analysis methodology, based on a combination of upper bound and energy approaches, is proposed for the prediction of number of wrinkles and minimum blankholding pressure necessary to avoid wrinkling in redrawing operation. Thickness variation predicted by the upper bound formulation is used as input for the wrinkling analysis by assuming a suitable waveform based on geometrical and process conditions. The flange is constrained at both the ends, i.e. by the blank holder profile radius and at the die entry point (where the sheet enters into the die cavity). The waveform for present analysis is assumed such that it has zero displacement at both the ends (since it is constrained) and the maximum amplitude of the wave at some point in between those ends. The wrinkling predicted by the present methodology seems to be reasonably accurate considering the geometrical and process constraints of the redraw.

Topics: Pressure
Commentary by Dr. Valentin Fuster
2011;():453-458. doi:10.1115/MSEC2011-50120.

Magnesium alloy profiles have attracted more and more attention in automobile and aerospace industries. The rotary draw bending process is suitable to form profiles. A bending test machine is developed to conduct AZ31 profile bending experiment. A 3D elastic-plastic thermo-mechanical coupled finite element model is established and validated by experiment. The effects of process parameters on the geometric dimension of the profile were analyzed by using experimental and numerical methods. The results indicate that the pretension amount is the main parameter which influences the geometric dimension of the bent profile, then the forming temperature, following the bending angle. The dimensional variation of the middle-rib is relatively little, and the dimensional variations of the inside and the outside of the bent profile are large.

Commentary by Dr. Valentin Fuster
2011;():459-463. doi:10.1115/MSEC2011-50126.

The paper presents a new innovative direct extrusion process, Helical Profile Extrusion (HPE), which increases the flexibility of aluminum profile manufacturing processes. The application fields of such profiles can be seen in screw rotors for compressors and pumps. The investigations concentrate on experimental and numerical analyses by 3D-FEM simulations to analyze the influence of friction on the material flow in the extrusion die in order to find out the optimal parameters with reference to the twisting angle and contour accuracy. By means of FEM, the profile shape could be optimized by modifying the die design. The numerical results were validated by experiments. For these investigations, a common aluminum alloy AA6060 was used. The accuracy of the profile contour could be improved significantly. However, increasing the twist angle is limited due to geometrical aspects.

Topics: Extruding
Commentary by Dr. Valentin Fuster
2011;():465-474. doi:10.1115/MSEC2011-50135.

Micro/meso-scale forming is a promising technology for mass production of miniature metallic parts. However, fabrication of micro/meso-scale features leads to challenges due to the friction increase at the interface and tool wear from highly localized stress. In this study, the use of high-frequency vibration for potential application in the technology of micro/meso-scale forming has been investigated. A versatile experimental setup based on a magnetostrictive (Terfenol-D) actuator was built. Vibration assisted micro/meso-scale upsetting, pin extrusion and cup extrusion were conducted to understand the effects of workpiece size, excitation frequency and the contact condition. Results showed a change in load reduction behavior that was dependent on the excitation frequency and contact condition. The load reduction can be explained by a combination of stress superposition and friction reduction. It was found that a higher excitation frequency and a less complicated die-specimen interface were more likely to result in a friction reduction by high-frequency vibration.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2011;():475-485. doi:10.1115/MSEC2011-50142.

The effects of different pre-strain levels, paths and subsequent annealing on the post-annealing mechanical properties of AA5182-O were investigated. Aluminum sheet specimens were pre-strained in uniaxial, plane strain and equibiaxial tension to several equivalent strain levels, annealed at 350°C for short (10 seconds) and long (20 minutes) durations, and then tested for post-annealing mechanical properties, including tensile properties, anisotropy and forming limits. The tensile properties, R-values at 0°, 45° and 90° relative to the sheet rolling direction, and forming limit diagrams (FLDs) exhibited dependencies of pre-strain and annealing history. The importance of the process variables and their effects were identified via designed experiments and analysis of variance. Three-dimensional digital image correlation, which captured the onset of local necking, was employed in the FLD development. Texture in the as-received and deformed sheets was investigated with electron backscattered diffraction and provided a means for linking prestrain and static recovery or recrystallization with microstructure. This guided the understanding of the mechanical property changes observed after preforming and annealing. Ultimately, the expanded forming limit curve demonstrated the advantage of annealing in extending the formability of strained AA5182-O.

Commentary by Dr. Valentin Fuster
2011;():487-493. doi:10.1115/MSEC2011-50146.

The coefficient of thermal expansion (CTE) of multiphase polymeric composite materials represents an important role in the process of engineered materials design, especially while approaching thermal management issues. Tailoring and designing material combinations in order to develop a composite structure to prove stability over a wide range of temperatures, from cryogenic to high values, to withstand extreme environmental conditions is the dream and the purpose of any engineering team involved in such study/research area. The paper aims to approach and to present the variations of the CTE with extreme environmental conditions (e.g. cryogenic, desert and hygroscopic conditioning) for particular combinations of particle-fibers multiphase polymeric composite materials. Influencing factors will be underlined to accompany the experimental research.

Commentary by Dr. Valentin Fuster
2011;():495-502. doi:10.1115/MSEC2011-50151.

Press hardening is an innovative technology being applied to meet the growing demands for both lightweight and crash performance qualities. To further increase the lightweight potential, closed profiles are being used. As a result, a method has been developed at the Fraunhofer Institute for Machine Tools and Forming Technology IWU which allows the integration of press hardening of tubes and closed profiles into the media-based forming process. Using this press hardening technology, the original material strength of 500 MPa can be increased to between 1200 and 1900 MPa, depending on the chosen material. The engineering of tube press hardening is more complex than other forming processes, specifically the time dependence in combination with heat management makes it difficult. Therefore the use of FEA is indispensible when dealing with aspects such as heat treatment, the forming process itself, the cooling caused by the gaseous forming media and the general heat management of the tooling. To control and improve the process and therefore the part quality and process reliability, all these factors and their dependencies have to be taken into account. In addition to 22MnB5, other manganese-boron alloyed steels and different heating strategies have been tested. Based on these experiments the process capability was successfully proven and technological limits were obtained. Current investigations are focused on realizing tailored properties thus creating areas with varied strength and ductility in a single part.

Commentary by Dr. Valentin Fuster
2011;():503-515. doi:10.1115/MSEC2011-50153.

The pre-form design in hydroforming process plays a key role in improving product quality, such as defect-free property and proper final product. This approach, however, leads not only to the increase of significant tool cost but also to the extended down-time of the production equipment. It is thus necessary to reduce time and man power through an effective method of pre-form design. In this paper, the equi-potential lines designed in the electric field are introduced to find an appropriate pre-form shape. The equi-potential lines generated between two conductors of different voltages show similar trends for minimum work paths between the undeformed shape and the deformed shape. Based on this similarity, the equi-potential lines obtained by arrangement of the initial and final shapes are utilized for the design of the pre-form, and then the finite element simulations are done for finding the forming pressure of each pre-form shape. Finally, the pre-form and its corresponding forming pressure with other parameters are used for training an artificial neural network. This trained neural network can be used for estimating the proper pre-form shape and forming pressure for a SUS304 tube inside an square die or other configurations of die (Geometrical shape) and tube (Diameter and thickness).

Topics: Shapes
Commentary by Dr. Valentin Fuster
2011;():517-526. doi:10.1115/MSEC2011-50165.

Tube Hydroforming (THF) is a metal-forming process that uses a pressurized fluid in place of a hard tool to plastically deform a given tube into a desired shape. In addition to the internal pressure, the tube material is fed axially toward the die cavity. One of the challenges in THF is the nonlinear and varying friction conditions at the tube-tool interface, which make it difficult to establish accurate loading paths (pressure vs feed) for THF. A THF process control model that can compensate for the loading path deviation due to frictional errors in tube hydroforming is proposed. In the proposed model, an algorithm and a software platform have been developed such that the sensed forming load from a THF machine is mapped to a database containing a set of loading paths that correspond to different friction conditions for a specific part. A real-time friction error compensation is then carried out by readjusting the loading path as the THF process progresses. This scheme reduces part failures that would normally occur due to variability in friction conditions. The implementation and experimental verification of the proposed model is discussed.

Commentary by Dr. Valentin Fuster
2011;():527-532. doi:10.1115/MSEC2011-50169.

As everyday equipment becomes smaller and smaller, it is of increasing importance that the manufacturing processes used for metals are capable of producing parts of appropriate sizes. Currently, manufacturing processes assume macromaterial properties can be applied for microscale production, but is this a valid assumption? This paper investigates the accuracy of applying macroscale tensile properties in microscale applications. In order to test the soundness of this supposition, tensile tests were performed on both macroscale and microscale brass specimens, and the resulting calculated material properties, strain hardening exponent (n) and strength coefficient (K), were compared. Specimens were heat treated to various temperatures before tensile tests were performed, and the strength coefficient and strain hardening exponents of micro and macro tensile specimens were compared. Additionally, it is investigated whether average grain size correlates to material properties. The results showed that in general it is not accurate to apply macroscale tensile properties to microscale applications. However, at mesocale grain sizes, (12–20 microns), the strain hardening exponent values were similar for both macro and microscale specimens.

Topics: Brass (Metal)
Commentary by Dr. Valentin Fuster
2011;():533-539. doi:10.1115/MSEC2011-50177.

The formability curves of the AZ31B magnesium alloy were constructed by following a novel approach that best resembles the conditions of actual Superplastic Forming (SPF) operations. Sheet samples were formed at 400 °C and a constant strain rate of 1×10−3 s−1 , by free pneumatic bulging into a set of progressive elliptical die inserts. By doing so, the material in each of the formed domes was forced to undergo biaxial stretching at a distinct strain ratio, which is simply controlled by the geometry (aspect ratio) of the selected die insert. Material deformation was quantified using circle grid analysis (CGA), and the recorded planar strains were used to construct the forming limit diagram (FLD) of the material. The aforementioned was carried out with the sheet oriented either along or across the direction of major strains, in order to establish the relationship between the material’s rolling direction and the corresponding limiting strains. Great deviations between the two sets of formability curves are realised, hence a compound forming limit diagram is constructed as an improved way for characterising the material behaviour. The presented pneumatic stretching approach is shown to produce accurate friction-independent formability diagrams, with clear distinction between the safe and unsafe deformation zones, even though the developed diagrams are confined to the biaxial strain region (right side quadrant of an FLD). Moreover, the approach proves to be a viable means for providing formability maps under conditions where traditional mechanical stretching techniques (Nakajima and Marciniak tests) are limited.

Commentary by Dr. Valentin Fuster
2011;():541-545. doi:10.1115/MSEC2011-50183.

Magnesium alloy is the lightest in practical metals, and it is used for housing small home appliance products and automobile parts. It is also expected to be a new material for stents, because of its possibility of systemic absorption. Fineness, thinness, adequate strength and high-quality surface are required for the medical tube. It is known that cold-plastic working of magnesium alloy is very difficult. In this study, fabrication of a magnesium-alloys medical fine tube by cold fluid-mandrel drawing was attempted. Fineness, thinness, adequate strength and high-quality surface are required for the medical tube. Firstly, plug drawing was carried out, because it was thought to be one of the methods for satisfying the requirements. After all it was found to be impossible to apply this method, because magnesium alloy is too brittle for plug drawing. Secondly, soft-metal mandrel drawing was tried. Drawing was possible, but it was difficult to extract the mandrel, because there is a possibility that the tube might break due to its high drawing stress. So newly-processed fluid-mandrel drawing was carried out. As a result, it was found that the fabrication of medical tubes by fluid-mandrel drawing was possible. It is easy to extract mandrel after drawing, as the mandrel is fluid. And it is possible to prevent tube break during drawing, because drawing stress is lower than that of soft-metal mandrel drawing.

Commentary by Dr. Valentin Fuster
2011;():547-556. doi:10.1115/MSEC2011-50212.

Sheet metal forming of parts with microscale dimensions is gaining importance due to the current trend towards miniaturization, especially in the electronics industry. In microforming, although the process dimensions are scaled down, the polycrystalline material stays the same (e.g., the grain size remains constant). When the specimen feature size approaches the grain size, the properties of individual grains begin to affect the overall deformation behavior. This results in inhomogeneous deformation and increased data scatter of the process parameters. In this research, the influence of the specimen size and the grain size on the distribution of plastic deformation through the thickness during a 3-point microbending process is investigated via digital image correlation. Results showed that with miniaturization, a decrease in the strain gradient existed which matched previous research with respect to micro-hardness measurement.

Commentary by Dr. Valentin Fuster
2011;():557-564. doi:10.1115/MSEC2011-50213.

Strain-based forming limit diagrams (FLDs) are the traditional tool used to characterize the formability of materials for sheet metal forming processes. However, this failure criterion exhibits a significant strain path dependence. Alternatively, stress-based forming limit diagrams (FLDs) have been proposed and shown to be less sensitive to the deformation path. The stress-based failure criterion can be conveniently implemented in numerical simulations. However, for reliable numerical modeling, the sensitivity of the models to the selection of discretization parameters, in particular, the element type must be assessed. In this paper, Marciniak tests have been numerically simulated to investigate failure prediction using three different element types (shell, solid and solid-shell). Seven different specimen geometries were modeled in order to vary the loading paths. The results show that despite differences in stress calculation assumptions, shell, solid and solid-shell elements do not provide differences in failure prediction when a stress-based failure criterion is used.

Topics: Stress , Failure
Commentary by Dr. Valentin Fuster
2011;():565-571. doi:10.1115/MSEC2011-50235.

Incremental sheet forming using water jet (ISF-WJ) is a new sheet metal forming process proposed in recent years. Few reports can be found on this process and some basic questions are unanswered, i.e., the water jet pressure required for plastic forming and the accuracy of this forming process. In this paper, an analytical model was developed to evaluate the size effect in the ISF-WJ process with respect to some key parameters, such as sheet thickness, part dimension, jet size and jet pressure. Three commonly used engineering sheet materials (aluminum, stainless steel and titanium) are studied in the analysis and the formability of water jet on these materials was evaluated. In addition, comparisons are made between the ISF-WJ and conventional ISF process with rigid tool based on finite element simulations. The result suggests that the dimensional accuracy of ISF-WJ may be controlled by a supporting back plate and ISF-WJ shows a better distribution of strain and thickness reduction than ISF process. It also provides a good reference for future ISF-WJ equipment design and development.

Commentary by Dr. Valentin Fuster
2011;():573-582. doi:10.1115/MSEC2011-50250.

Recent development of Electrically-Assisted Manufacturing processes proved the advantages of using the electric current, mainly related with the decrease in the mechanical forming load and improvement in the formability when electrically-assisted forming of metals. The reduction of forming load was formulated previously assuming that a part of the electrical energy input is dissipated into heat, thus producing thermal softening of the material, while the remaining component directly aids the plastic deformation. The fraction of electrical energy applied that assists the deformation process compared to the total amount of electrical energy is given by the electroplastic effect coefficient. The objective of the current research is to investigate the complex effect of the electricity applied during deformation, and to establish a methodology for quantifying the electroplastic effect coefficient. Temperature behavior is observed for varying levels of deformation and previous cold work. Results are used to refine the understanding of the electroplastic effect coefficient, and a new relationship, in the form of a power law, is derived. This model is validated under independent experiments in Grade 2 (commercially pure) and Grade 5 (Ti-6Al-4V) titanium.

Commentary by Dr. Valentin Fuster
2011;():583-587. doi:10.1115/MSEC2011-50254.

This paper aims to present an optimization process for three different types of loading paths studied in the numerical simulation of tube hydroforming of diamond-shaped sheet products. These three different types of loading paths werestudied in a numerical simulation of tube hydroforming of diamond-shaped products. The loading paths by which the best final shapes were obtained in the simulation were adopted in actual processing operation. A series of experiments were conducted within the temperature range of 270±10°C. Constitutive behavior was assumed to be elasto-plastic, and the material parameters used in the simulation were obtained from corresponding literature. The designed loading ratios were incorporated into the model to obtain the corresponding hydroforming results. The simulation results are used in the experimental verification and the products were compared with the simulation results. The experimental results showed a good agreement with the predicted numerical results, indicating that FEM simulation is an effective tool in optimizing processing procedures.

Topics: Diamonds
Commentary by Dr. Valentin Fuster
2011;():589-594. doi:10.1115/MSEC2011-50257.

Research of the micro tube hydroforming (MTHF) process is being investigated for potential medical and fuel cell applications. This is largely due to the fact that at the macro scale the tube hydroforming (THF) process, like most metal forming processes has realized many advantages. Unfortunately, large forces and high pressures are required to form the parts so there is a large potential to create failed or defective parts. Electrically Assisted Manufacturing (EAM) and Electrically Assisted Forming (EAF) are processes that apply an electrical current to metal forming operations. The intent of both EAM and EAF is to use this applied electrical current to lower the metals required deformation energy and increase the metal’s formability. These tests have allowed the metals to be formed further than conventional methods without sacrificing strength or ductility. Currently, various metal forming processes have been investigated at the macro scale. These tests also used a variety of materials and have provided encouraging results. However, to date, there has not been any research conducted that documents the effects of applying Electrically Assisted Manufacturing (EAM) techniques to either the tube hydroforming process (THF) or the micro tube hydroforming process (MTHF). This study shows the effects of applying a continuous direct current to the MTHF process.

Commentary by Dr. Valentin Fuster
2011;():595-601. doi:10.1115/MSEC2011-50258.

The cyclic and compressive mechanical behavior of ultra-thin sheet metals was experimentally investigated. A novel transparent wedge device was designed and fabricated to prevent the buckling of thin sheets under compressive loads, while also allowing full field strain measurements of the specimen using digital imaging methods. Thin brass and stainless steel sheet metal specimens were tested using the micro-wedge device. Experimental results show that the device can be used to delay the onset of early buckling modes of a thin sheet under compression, which is critical in examining the compressive and cyclic mechanical behavior of sheet metals.

Commentary by Dr. Valentin Fuster
2011;():603-611. doi:10.1115/MSEC2011-50262.

Single Point Incremental Forming (SPIF) is plagued by an unavoidable and unintended bending in the region of the sheet between the current tool position and the fixture, which leads to significant geometric inaccuracies. Double Sided Incremental Forming (DSIF) uses two tools, one on each side of the sheet to form the sheet into the desired shape. This work explores the capabilities of DSIF in terms of improving the geometric accuracy as compared to SPIF by using a novel toolpath strategy in which the sheet is locally squeezed between the two tools. Experiments and simulations are performed to show that this strategy can improve the geometric accuracy of the component significantly. An examination of the forming forces indicates that after a certain amount of deformation using this strategy a loss of contact occurs between the bottom tool and the sheet. The effects of this on the geometric accuracy are discussed as well.

Commentary by Dr. Valentin Fuster
2011;():613-619. doi:10.1115/MSEC2011-50273.

Micro surface textures have various applications, such as friction/wear reduction and bacteria sterilization. Deformation-based micro surface texturing has the potential of economically creating micro surface textures over a large surface area. A novel desktop micro surface texturing system is proposed for efficiently and economically fabricating micro channels on the surface of thin sheet material for micro fluid and friction/wear reduction applications. Both experimental and numerical studies were employed to analyze the problems of the flatness of the textured sheet, the uniform of the channel depth and pile-ups built up during the micro surface texturing process. The results demonstrated a clear relationship between relative velocity of the upper and lower rolls and the flatness of the textured sheet and the final profile of the micro channels.

Topics: Deformation
Commentary by Dr. Valentin Fuster
2011;():621-627. doi:10.1115/MSEC2011-50284.

Incremental sheet metal forming (ISMF) has demonstrated its great potential to form complex three-dimensional parts without using a component specific tooling. The die-less nature in incremental forming provides a competitive alternative for economically and effectively fabricating low-volume functional sheet parts. However, ISMF has limitations with respect to maximum formable wall angle, geometrical accuracy and surface finish of the component. In the present work, an experimental study is carried out to study the effect of incremental sheet metal forming process variables on maximum formable angle and surface finish. Box-Behnken method is used to design the experiments for formability study and full factorial method is used for surface finish study. Analysis of experimental results indicates that formability in incremental forming decreases with increase in tool diameter. Formable angle first increases and then decreases with incremental depth and it is also observed that the variation in the formable angle is not significant in the range of incremental depths considered to produce good surface finishes during the present study. A simple analysis model is used to estimate the stress values during incremental sheet metal forming assuming that the deformation occurs predominantly under plane strain condition. A stress based criterion is used along with the above mentioned analysis to predict the formability in ISMF and its predictions are in very good agreement with the experimental results. Surface roughness decreases with increase in tool diameter for all incremental depths. Surface roughness increases first with increase in incremental depth up to certain angle and then decreases. Surface roughness value decreases with increase in wall angle.

Topics: Finishes
Commentary by Dr. Valentin Fuster
2011;():629-637. doi:10.1115/MSEC2011-50287.

A metal forming technique which has more recently come of interest as an alternative to processes that use elevated temperatures at some stage during manufacturing is Electrically-Assisted Forming (EAF). EAF is a processing technique which applies electrical current through the workpiece concurrently while the material is being formed. At present, this method has only been studied on an experimental level in laboratory settings, and the heuristic results show increased fracture strain, reduced flow stress, and reduced springback; the enhanced process capability is beyond the range that would be expected from pure resistive heating alone. Thus far, when applying the electrical current through the workpiece during deformation, the current magnitude flowing through the workpiece has remained constant. Hence, for a compression loading, the current flux or density decreases as a result of an increasing specimen area. This work examines the effect of a non-constant current density (NCCD) and a constant current density (CCD) on the deformation behavior of 304 Stainless Steel and Ti-6Al-4V during uniaxial compression testing. Additionally, the application of a CCD is used to modify existing empirically-based EAF flow stress models for these materials. From this testing, it is shown that a CCD during forming can significantly reduce the flow stress of the material as compared to the NCCD tests. The reductions in the flow stress were increased at higher strains by approximately 30% and 15% for the 304 Stainless Steel and Ti-6Al-4V, respectively. More importantly, these flow stress curves are better representative of how the material responds to an applied electrical current as the specimen shape change is removed from the results. Also, the NCCD tests were approximated using an existing empirically-based EAF flow stress model and the CCD tests concluded that a new flow stress predictor model be introduced.

Commentary by Dr. Valentin Fuster
2011;():639-644. doi:10.1115/MSEC2011-50025.

Biofuels are an alternative to petroleum-based liquid transportation fuels. Cellulosic biomass can be used as feedstocks for befoul manufacturing. Low density of cellulosic feedstocks causes difficulties in handling them during transportation and storage, thus hindering large-scale and cost-effective manufacturing of cellulosic biofuels. Pelleting can increase the density of cellulosic feedstocks by compacting bulky biomass into pellets. Pellet durability, an important quality parameter, measures the ability of pellets to withstand impact and other destructive forces during transportation and handling. ASABE standard S269.4 specifies a procedure to determine pellet durability using 500 grams of pellets. However, it does not provide any justification of choosing this amount of pellets. This paper investigates the feasibility of using a smaller amount of pellets (50 grams) to determine pellet durability. Results show that 50 grams of pellets can generate comparable durability results as 500 grams of pellets.

Topics: Biomass , Durability , Testing
Commentary by Dr. Valentin Fuster
2011;():645-651. doi:10.1115/MSEC2011-50080.

Both U.S. and world economies have long depended on fossil energy (coal, oil, and natural gas). Supplies of fossil energy are expected to decline in the future and become more expensive. Meanwhile, their use contributes to the accumulation of greenhouse gas in the atmosphere. Therefore, an urgent need exists for renewable energy sources. In order to enhance the global competitiveness of the U.S. in renewable energy manufacturing, there is a dramatic need for a skilled workforce that has been trained in this field. A survey on renewable energy courses at more than 100 U.S. universities has been conducted. It is found that manufacturing aspects of all forms of renewable energy are not emphasized, and there are no sophomore-level courses that cover manufacturing of all forms of renewable energy at these universities.

Commentary by Dr. Valentin Fuster
2011;():653-657. doi:10.1115/MSEC2011-50117.

Cellulosic biofuels can reduce greenhouse gas emissions and the nation’s dependence on foreign oil. In order to convert cellulosic biomass into biofuels, size reduction of biomass is a necessary step. Most related studies in the literature claimed that smaller particles produced higher sugar yields. However, some researchers reported that this claim was not always true. The literature does not have satisfactory explanations for the inconsistence. This paper presents an experimental study on size reduction of poplar wood using a metal cutting process (milling). The results provided one explanation for this inconsistence. It was found for the first time that milling orientation had a strong effect on poplar wood sugar yield. Although smaller poplar particles had a higher sugar yield when they were milled from the same orientation, this trend did not exist for particles milled from different orientations.

Commentary by Dr. Valentin Fuster
2011;():659-668. doi:10.1115/MSEC2011-50136.

Cellulosic ethanol is one type of renewable energy, and can be used to replace petroleum based transportation fuels. The technologies of converting cellulosic biomass into ethanol are relatively mature. However, the manufacturing costs of cellulosic ethanol are too high to be competitive. Economic analyses of cellulosic ethanol manufacturing have appeared regularly to estimate manufacturing costs of cellulosic ethanol. But the estimated manufacturing costs of cellulosic ethanol have a wide range due to differences in used assumptions. It is very difficult to judge which one is most reliable among the markedly different cost estimates in the literature. This paper reviews the literature on cost estimates in manufacturing of cellulosic ethanol. Cost estimates of each manufacturing process are summarized. Cost components and their data sources are discussed. This review provides a foundation to develop a comprehensive cost model for cellulosic ethanol manufacturing.

Commentary by Dr. Valentin Fuster
2011;():669-675. doi:10.1115/MSEC2011-50163.

It is widely recognized that industrial production inevitably results in an environmental impact. Energy consumption during production is responsible for a part of this impact, but is often not provided in cradle-to-gate life cycles. Transparent description of the transformation of materials, parts, and chemicals into products is described herein as a means to improve the environmental profile of products and manufacturing machine. This paper focuses on manufacturing energy and chemicals/materials required at the machine level and provides a methodology to quantify the energy consumed and mass loss for simple products in a manufacturing setting. That energy data are then used to validate the new approach proposed by (Overcash et.al, 2009a, and 2009b) for drilling unit processes. The approach uses manufacturing unit processes as the basis for evaluating environmental impacts at the manufacturing phase of a product’s life cycle. Examining manufacturing processes at the machine level creates an important improvement in transparency which aids review and improvement analyses.

Commentary by Dr. Valentin Fuster
2011;():677-684. doi:10.1115/MSEC2011-50215.

Ethanol produced from cellulosic biomass is an alternative to petroleum-based transportation fuels. However, manufacturing costs of cellulosic ethanol are too high to be competitive. Low density of cellulosic feedstocks increases their handling and transportation costs, contributing to high overall costs of cellulosic ethanol manufacturing. Pelleting can increase density of cellulosic feedstocks, reduce transportation and storage costs, and make cellulosic ethanol production more competitive. UV-A (ultrasonic vibration-assisted) pelleting is a new pelleting method (available only in lab scale now). Preliminary research showed that UV-A pelleting could significantly increase pellet density and pellet durability but it has never been compared with other pelleting methods (e.g., using an extruder, a briquetting press or a ring-die pelleting). The objectives of this research are to compare UV-A pelleting with ring-die pelleting in terms of pellet density, pellet durability, energy consumptions of pelleting. The results will be useful to find a better pelleting method for cellulosic ethanol manufacturing.

Commentary by Dr. Valentin Fuster
2011;():685-692. doi:10.1115/MSEC2011-50230.

Microwave torrefaction of corn stover with particle size of 4 mm was investigated and the effects of reaction temperature and time on the yields of volatile, bio-oil and torrefied biomass were determined. The response surface analysis of the central composite design (CCD) showed that the yields of volatile, bio-oil and torrefied biomass were significantly affected by the reaction temperature and time. Three linear models were developed to predict the yields of conversion products as a function of temperature and time. A first order reaction kinetics was also developed to model the corn stover torrefaction. Ph values of torrefaction bio-oils ranged from 2.3 to 2.76 which were similar to those of bio-oils from biomass pyrolysis. GC/MS analysis for torrefaction bio-oils showed that the organic acid was about 2.16% to 12.00%. The torrefaction bio-oils also contain valuable chemical compounds such as phenols, furan derivatives and aliphatic hydrocarbons determined by a GC/MS. There are no aromatic compounds and polycyclic aromatic hydrocarbons (PAHs) detected in the torrefaction bio-oils. The torrefaction biogas was mainly consisted of ch4 , c2 h6 , c3 h8 , which was about 56 wt% of the total bio-gas. The biogas can be used for chemical synthesis or electricity generation. The heating values of torrefied biomass were from 18.64–22.22 MJ/kg depending on the process conditions. The heating values of torrefied biomass were significantly greater than those of raw biomass and similar to those of coals. The energy yields of torrefied biomass from 87.03–97.87% implied that most energy was retained in the torrefied biomass. Economic analysis indicated that the biomass microwave torrefaction plant located in a farm is profitable.

Topics: Microwaves
Commentary by Dr. Valentin Fuster
2011;():693-701. doi:10.1115/MSEC2011-50274.

The manufacture of biodiesel generates 10 wt% of glycerol as a byproduct. Currently, the majority of this waste glycerol is treated in wastewater treatment plants or incinerated. In this study, single chamber, membrane-free microbial electrolysis cells (MECs) was evaluated to produce hydrogen from pure glycerol and waste glycerol. At an applied voltage of 0.6 V, a maximum current density of 7.5 ± 0.4 A/m2 (238.6 ± 12.7 A/m3 ) was observed, the highest reported current density for a microbial electrochemical system operating on glycerol. Maximum current densities on 0.5% waste glycerin were 0.1–0.2 A/m2 , much lower than those on pure glycerol, possibly due to the high salt and soap concentration in the waste glycerol. The maximum hydrogen yield on 50 mM glycerol was 1.8 ± 0.1 mol hydrogen/mol glycerol at a hydrogen production rate of 1.3 ± 0.1 m3 /day/m3 . The presence of methanol in the waste glycerin reduced hydrogen yield by nearly 30%. The energy efficiency on 0.5% of waste glycerol reached 200% at an applied voltage of 0.6 V. Conversion of all of the waste glycerol currently generated annually in global biodiesel manufacture to hydrogen using optimized MEC technology could generate ∼ 180 million kg of H2 , representing a value of nearly $540 million, or the amount of H2 required for the production of 4.8 billion kg of green diesel. This study indicates that the generation of useful products (such as hydrogen) from waste glycerol will greatly increase the viability of the growing biodiesel industry.

Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In