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Design and Manufacturing

2007;():1-7. doi:10.1115/IMECE2007-41120.

Automating material handling of flexible sheet-metal blanks in stamping process requires attention due to its significant impact on product quality and productivity. This paper investigated the capability of a fully dynamic and nonlinear finite element technique in developing virtual material handling process of compliant sheet-metal blanks subject to time varying movability conditions. The technique used explicit time integration to avoid the formulation of stiffness matrix by a direct integration of the equations of motion. The influence of holding end-effector layout scheme and movability conditions on the final part quality was investigated.

Commentary by Dr. Valentin Fuster
2007;():9-15. doi:10.1115/IMECE2007-41520.

Geometrically complex, high aspect ratio microstructures and limited aspect ratio nanostructures have been successfully fabricated in supercooled Bulk Metallic Glass (BMG) substrates by molding against patterned Silicon and Silicon dioxide substrates. However, demand exists for similar metallic substrates with high aspect ratio, nanoscale features. Van Der Waals based interfacial energies between the supercooled liquid BMG and the Silicon cavity represent a substantial obstacle to the direct scaling of the molding process to the nanoscale. In an effort to investigate these effects, experiments were conducted using molds of various compositions: Silicon, SiO2 and SiO2 coated with Gold. The Gold coating failed to impact molding performance due to the thin layer deposited. However, drastically superior results were obtained by using a Silicon mold because of the variation in interfacial interaction between the BMG and the mold material. In addition, a theoretical model to predict achievable aspect ratio is presented and was found to be in qualitative agreement with experimental results. Finally, a value for the surface tension of Viterloy-1b within it’s supercooled liquid state was deduced from experimental data.

Commentary by Dr. Valentin Fuster
2007;():17-21. doi:10.1115/IMECE2007-41692.

Servo presses providing flexible ram motions are extensively developed nowadays; the merit of such presses is the capability of generating versatile punch motions to fulfill the stamping. This paper studies a cup-shaped drawing process using a servo press. The aim of this research is to study the effect of the forming speed on preventing the cracks and wrinkles in drawing. A finite element method (FEM) software package—ABAQUS®, is utilized to predict the distribution of displacement stress, strain of the work material in drawing. Crack (related to thinning behavior) and wrinkle are two indices of the drawing failure criteria in simulation. An optimal forming speed could be estimated by simulation. The optimal forming speed would cause the maximum limit drawing ratio which is beneficial to prevent drawing failure. The analytical results were verified experimentally. The results show that the predicted drawing speed was consistent with the real experiment and simulation.

Commentary by Dr. Valentin Fuster
2007;():23-32. doi:10.1115/IMECE2007-42150.

This paper presents a 3D transient numerical approach for thermal and strain/stress modeling of the multilayer laser solid freeform fabrication process, by which correlations between the main process parameters and their effects on the final build-up properties can be studied. This model can be used to optimize the process parameters to increase the controllability of the geometrical and metallurgical variations resulted from the thermal and stress fields. Using this modeling approach, the geometry of the material deposited as well as temperature and thermal stress distributions across the process domain can be predicted based on the process parameters such as powder feed rate, process speed and laser power, assuming the interaction between the laser beam and powder stream is decoupled. The main process parameters affected by a multilayer deposition due to the formation of non-planar surfaces such as powder catchment are also incorporated into the modeling approach. To verify the proposed method, fabrication of a four-layer thin wall of stainless steel AISI 304L on a low carbon steel substrate is modeled with the same process parameters throughout the build-up process. The results show that the temperature and stress slightly increase at the end-points of layers 2, 3, and 4 which cause over deposited materials and micro-crack formations at these regions. The results are then used to discuss optimum process parameters which can be used to have a buildup with better geometrical and physical qualities. The reliability and accuracy of the model are experimentally verified.

Commentary by Dr. Valentin Fuster
2007;():33-38. doi:10.1115/IMECE2007-43379.

Recent low emission, lightweight, safety requirements, automotive manufacturers are implementing lighter and stronger materials and new manufacturing processes into body structural components. Typical widely used forming process in automotive body structures is stamping process. Other forming processes currently used in body structural applications are hydroforming, Rollforming and hot stamping processes. Initially, hydroforming process was used for chassis applications. Few applications of chassis are cross members, engine cradle, instrument panel (IP) beams, and bumper beams. Recently, a few automotive manufacturers are already implemented the hydroforming process into front end structures. Hydroform process gives more part consolidation, and perhaps even weight reduction. However, depending on applications some brackets may be needed to attach other components. Some of the issues related to bracket attachments can be avoided in the design phase. Audi A2, and Chrysler Pacifica have implemented roof rails in the body structures arena. Latest developments are even pushing the hydroforming process into High Strength Steels arena. Pontiac Solstice and Saturn Sky implemented Dual Phase 600 material on the chassis rails. In this paper, current trends of hydroforming process with advanced high strength steels (AHSS) will be discussed. Hydroforming process involves, bending, preforming (low pressure), and final forming (high pressure) with mechanical properties of DP780 material at various stages of the hydroforming process will be discussed.

Commentary by Dr. Valentin Fuster
2007;():39-44. doi:10.1115/IMECE2007-43394.

Blow molded parts require a strict control of the wall thickness distributions so as to achieve the required mechanical performance and to minimize the usage of material. In this work, an online wall thickness control strategy for the extrusion blow molded part was presented. A multichannel ultrasonic thickness measuring system was used to obtain the part wall thickness. A feedback control system based on fuzzy iterative learning control (ILC) algorithm was designed and implemented to control the part thickness. Instead of using the pure numerical method, engineer knowledge and experience were combined in the control algorithm using fuzzy rules. The results showed that the online wall thickness control system developed in this work can automatically achieve the die gap profile and the resulting part thickness can satisfy the desire thickness distribution.

Commentary by Dr. Valentin Fuster
2007;():45-52. doi:10.1115/IMECE2007-43847.

Complex deformation processes such as forming and machining involve large strain, high strain rate, high temperatures, strain rate/temperature coupling, and potential loading history effects. The conventional empirical and semi-empirical plasticity models are not adequate for characterizing dynamic mechanical behavior of work materials at the complex loading scenarios. The accuracy of characterizing the dynamic mechanical behavior in deformation processes using any constitutive models is strongly affected by materials testing data in which a constitutive model is fitted. Tension or compression tests have been widely used to approximate material properties in various manufacturing processes. However, it has been a critical question whether tension or compression test should be utilized for capturing the true nature of complex material deformations. In this study, the influences of two material testing modes on mechanical behavior of AISI52100 steel (62 HRc) were investigated using the internal state variable (ISV) plasticity model. Twenty material constants have been found by nonlinear fitting the ISV plasticity model to the base line test data obtained from each deformation mode. It has shown that the material testing modes have profound effects on some materials constants of the ISV model. The stress sensitivity study to ISV model parameters has identified the critical material constants for reflecting the nature of material deformation. The different testing modes have significant influence on the material constants associated with isotropic hardening rather than kinematic hardening.

Commentary by Dr. Valentin Fuster
2007;():53-59. doi:10.1115/IMECE2007-42547.

Polylactic acid (PLA) is a biodegradable semi-crystalline thermoplastic polymer that can be used in many applications such as tissue engineering scaffolds and packaging. The crystallinity of PLA is an important factor that affects its process-ability, mechanical strength, and biodegradability. The solid-state foaming of semi-crystalline PLA has been a subject of recent investigations. In this paper, crystallization through out the solid state foaming process was studied. It was found that the crystallization reaches the equilibrium once the gas sorption reaches the equilibrium. There are two main factors that will affect the PLA crystallization: gas sorption during the saturation stage and the heating and stretching during the foaming stage. Within the range of 2 to 5 MPa saturation pressures and 60 to 100 °C foaming temperatures, a maximum crystallinity of approx. 25% was observed in the foamed PLA. Effects of stretching and foaming temperature on crystallinity of foamed specimens were also investigated.

Topics: Crystallization
Commentary by Dr. Valentin Fuster
2007;():61-66. doi:10.1115/IMECE2007-42666.

Polycaprolacton (PCL) is a synthetic biodegradable polymer that is widely used in tissue engineering related studies. It is a semi-crystalline polymer, and has a glass transition temperature (Tg ) of −60°C and a melting temperature of 60°C. In this paper, we report on the progress in creating porous PCL foams using the solid-state foaming process. The objective of this study is to examine the foam-ability of PCL using room temperature saturation. PCL specimens were made using compression molding. A “quenching” process was introduced to manipulate the crystallinity of PCL samples. CO2 was used for gas saturation. The effects of saturation pressure and foaming temperature were studied. The created microstructures were characterized using scanning electron microscopy (SEM). The preliminary results have shown that microstructures with pores on the scale of hundreds of nanometers were generated.

Commentary by Dr. Valentin Fuster
2007;():67-73. doi:10.1115/IMECE2007-42775.

An L18 Taguchi experiment was used to determine the robust processing control factor settings to maximize dimensional stability and reduce warpage for a 3-dimensional thin-walled injection molded component. The robust control factor settings were determined for seven control factor settings and also included three noise factors. The noise factors were: wall thickness, glass fiber content and production cycle pull point. A scientific molding technique where an on-line rheology study was performed to determine the relative viscosity versus effective shear rates was used to determine the injection speed settings. The proper shot size was also established for each experiment. A laser measuring system was used to analyze the entire component and to determine the shrinkage rates and warpage of the component. A warpage index was created to determine the entire warpage of the component.

Topics: Warping
Commentary by Dr. Valentin Fuster
2007;():75-81. doi:10.1115/IMECE2007-42776.

An anisotropy study was performed on a constrained thin-walled injection molded component using measurements made from a laser measuring system. Wall thickness and material glass fiber concentration were varied to determine their effects on parallel and perpendicular shrinkage rates. Several ranges of the processing control factors were used in the study. The shrinkages were determined and were described as a function of glass fiber concentration and wall thickness. The shrinkage ratio (a ratio representing the parallel shrinkage rate divided by the correlative perpendicular shrinkage rate) was used to investigate the influence of wall thickness and glass fiber (G.F.) concentration on shrinkage.

Topics: Anisotropy
Commentary by Dr. Valentin Fuster
2007;():83-88. doi:10.1115/IMECE2007-43360.

Polypropylene (PP)/organic montmorillonite (OMMT) nanocomposite was compounded in a twin-screw extruder. The objective is to investigate the relationship between rheological properties and microstructure of the nanocompsite. The samples were taken along the screws. Effect of feeding rate on the dynamical rheological property development and microstructure of samples was investigated. The yield stress of nanocomposite was obtained using steady-state shear sweep. The intercalated structure was probed by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Rheological results showed that the complex viscosity of samples increased along the twin-screw extruder. In addition, with the decrease of feeding rate, the yield stress of nanocomposite increased and MMT was dispersed better in PP matrix. Finally, the relationship between dynamical rheological properties and the dispersed state of MMT was analyzed.

Commentary by Dr. Valentin Fuster
2007;():89-97. doi:10.1115/IMECE2007-42795.

The dynamic characteristic and response of the Japanese A51-type slab track subjected to the Japanese S.K.S. high-speed train are under investigation. The high-speed train running on the slab track is modeled as a sequence of individual loads moving on a layered beam on viscoelastic foundation. The dynamic stiffness matrix of a layered beam on viscoelastic foundation is established for the structural analysis. Finally the structural performance of the dynamic stability and vibrational control of the slab track to the high speed train are intensively studied and discussed.

Topics: Slabs , Trains
Commentary by Dr. Valentin Fuster
2007;():99-103. doi:10.1115/IMECE2007-43851.

With a recent growth in the demand of the rubber products globally, the latest technology is adopted to improve the design and manufacturing of those rubber products in term of part quality and production lead time and cost. The cold runner system is one of the technologies which can assist in unfilling part problem and raw material saving. Nevertheless, with the lack of numerical tool with an ability to predict the behavior of rubber during the injection molding process, designers still need to use their experience and trial-and-error method to design the mold and the cold runner system. Therefore, in this research, the use of CAE and a cold runner system is applied to the design and manufacturing of rubber injection molding process with a gasket mold made of SBR as a case study. The empirical and simulated results agree well and the use of raw material in the actual system is decreased by 12% shot weight which can lead to the reduced cost of products. Finally, it can be seen that the use of CAE can assist the mold designers and manufacturers to get better understanding of flow pattern and behavior of rubber during the injection process so the better part quality can be obtained.

Commentary by Dr. Valentin Fuster
2007;():105-112. doi:10.1115/IMECE2007-41027.

This paper introduces a sophisticated methodology that guides the design of the non-standard geometry of cylindrical gearwheels, methodology for the evaluation of operation life depending on flank damage (pitting) in shortened lifetime tests of gearwheels and also number of other research results. The methodology for the design of gearwheels modifications is solved by using FEM system and takes into account real geometry of the whole gearbox and its component. Processed samples designs are tested in experimental testing stand and compared with samples which are designed using DIN 3990 standard Method B. The test results serves for verification of created designs. The back-to-back test-rig allowing smooth control of virtual power up to 785 kW (1053 HP) is also described. The methodology for evaluation of pitting area is solved by using digital documentation and automatic evaluation of damaged tooth flank surface.

Topics: Design , Gears , Testing
Commentary by Dr. Valentin Fuster
2007;():113-122. doi:10.1115/IMECE2007-41513.

This paper presents our exploration in Haptic-guided Dynamics Simulation in a mainstream Computer-aided Design (CAD) System. Haptic interface, by providing force feedback in human-computer interaction, can improve the working efficiency of CAD/CAM (Computer-aided Design and Manufacturing) systems in a unique way. The full potential of the haptic technology is best realized when it is integrated effectively into the product development environment and process. For large manufacturing companies this means integration into a commercial CAD system [Stewart 1997]. Built on our past foundation work on an infrastructure of haptically enhanced CAD system [Zhu 2006], this research continues to explore the algorithms for dynamics simulation guided with haptic interface. This is fundamental to other tasks such as Virtual Assembly and Digital Mock-up. The research follows a modular haptic rendering algorithm for stable and transparent 6-DOF manipulation as presented in [Otaduy 2006], with improvements by leveraging the built-in CAD system functions and third party Dynamics Engines. The native CAD models are converted to triangulated meshes which are used in object-object collision detection and dynamics response computation. The major contribution of this paper is that we have developed a feasible methodology for haptic-guided dynamic interactions among CAD models inside mainstream CAD systems. It lays the foundation for future tasks such as direct CAD model modification and virtual assembly with the aid of haptic interface.

Commentary by Dr. Valentin Fuster
2007;():123-132. doi:10.1115/IMECE2007-41705.

The domain of Electrical Computer-Aided Design and Engineering (ECAD/ECAE) has been subject to major and rapid change over the past couple of years. Electrical Engineering Computer-Aided Design (CAD) tools developed in the early to mid-1990s no longer meet future requirements. Consequently, a new generation of Electrical Engineering CAD systems has been under development for about a decade now. An overview of advances in this field is presented in the introductory part of this paper. This overview also sets the context and provides background information for the main topic, MCAD-ECAD-integration, to be addressed in the remainder of this paper. Many complex engineered systems encompass mechanical as well as electrical engineering components. Unfortunately, contemporary CAE environments do not provide a sufficient degree of integration in order to allow for multi-disciplinary product modeling and bi-directional information flow (i.e. automated design modifications on either side) between mechanical and electrical CAD domains. Overcoming this barrier of systems integration would release a tremendous efficiency potential with regard to the efficient development of multidisciplinary product platforms and configurations. An overview of the state-of-the-art in MCAD-ECAD integration is presented. In addition, associated research questions are postulated and potential future research perspectives discussed.

Commentary by Dr. Valentin Fuster
2007;():133-141. doi:10.1115/IMECE2007-41728.

In this study, a functional and behavioral representation model for collaboration in product development is developed to represent assembly-related product knowledge, including its geometry, spatial relationships, function and behavior, which will be used to create a knowledge representation scheme to capture, store, and retrieve product knowledge. In this model, the function, behavior and artifact information is interrelated based on assembly associations. Functional and behavioral inputs and outputs are defined based on the spatial relationships in the assembly, as well as on the geometry of the product. The functional associations among artifacts define the “Behavior Model” with engineering formulas and physical rules. “Behavior Models” then define the behavior of the artifact. Behavior has four different forms for different phases in life cycle: (1) Intended Behavior in the conceptual design phase, (2) Estimated Behavior in the design phase, (3) Observed Behavior in the operation stage, and (4) Evaluated Behavior in the design and operation phases. When an unintended event (behavior) occurs, an additional function can be added to eliminate that effect. As a result, the functional and behavioral model is updated dynamically.

Topics: Collaboration
Commentary by Dr. Valentin Fuster
2007;():143-148. doi:10.1115/IMECE2007-41778.

User-centred design methods improve the understanding of user work practices and enable construction of customized and user-friendly products. Applying these methods is, however, challenging since the users must to be able to test prototypes which is too time consuming and expensive with real prototypes. This is particularly true in the case of a mobile work machine cabin because the cabin forms an integral part of the machine so that elements need to be prototyped. The main properties of the cabin are the drivers’ visibility, functionality, ergonomics and safety. Virtual environment (VE) offers an effective way to realize prototyping and provides a means to study the drivers’ visual field from the cabin. Today’s design work is already performed using 3D CAD software. Introducing such models in VE is, however, not without its obstacles, since no native CAD format is supported in VE. Employing a general-purpose 3D graphics format usually destroys the model structure and also visualization parameters such as textures and lighting. When the aim is to have users test the functionality of the cabin, the VE model is unsatisfactory because certain physical parts are also required. First the bench is needed to ensure natural posture of the test driver. Second, the steering wheel and pedals are the objects with which the driver most typically interacts. Third, a set of control panels, including gauges and switches, are also often interacted by the driver. This study presents a setup for virtual testing of a mobile work machine cabin as a resource for user-centred design. The study focuses on the importance of physical objects in making the test situation realistic for hands-on professionals. The prototypes are tested by cabin design professionals experienced the use of CAD tools and real prototypes. The aim is to obtain designers’ evaluations and interpretations of different combinations of virtual and physical objects in prototypes. To achieve this a procedure for user-centred design of mobile work machine cabins is presented. More generally, the study discusses the participation of users in the design process employing VE as a design tool.

Topics: Machinery , Design
Commentary by Dr. Valentin Fuster
2007;():149-157. doi:10.1115/IMECE2007-42285.

Commonly used terms such as form, function, and behavior often take on varying definitions in the literature related to product design and development. This is especially true as the point of reference moves through various stages of development from conceptual design, through product disposal. This can become problematic from the standpoint of interpretation and implementation when an information model is being created that is intended to be useful to a product throughout its entire lifecycle. A product changes throughout its useful life, so a lifecycle model of a product must also be dynamic and able to grow and age with it. If this is to be the case, descriptive terms and definitions should be specific and retain their definition throughout the life of the model. In this paper, we attempt to select a set of terminology that can be uniquely descriptive of the classes needed to define a product lifecycle model. Terms such as form, function, affordance and behavior are defined within a hierarchy of a product’s lifecycle development. Terminology as presented in this context becomes less ambiguous. An example of a home-shop built pendulum clock serves to illustrate the utility of this new design lexicon. The terminology outlined here may not be optimal and significant additions and alterations may be justifiably suggested; but it is hoped that this paper will begin a dialogue eventually resulting in the elimination of much ambiguity in product modeling terminology.

Commentary by Dr. Valentin Fuster
2007;():159-168. doi:10.1115/IMECE2007-42379.

A common difficulty in designing mechanical systems is in handling the effects that design changes in one subsystem have on another, or on the system as a whole. This is made more difficult in early engineering design, when frequent changes are required and design information is preliminary. Increased efforts have been made to capitalize on the benefits of numerical optimization methods (search methods) in early engineering design – because of the large impact early decisions have on subsequent development activities. An important step toward executing meaningful optimizations in early design is the development of a design optimization framework that can be used when objectives, constraints, variables, and other conditions are expected to change as the design progresses and new information is gained. This paper presents a design framework that considers such change by subjecting the parametric updating of CAD models to optimization criteria. Under the proposed framework, a part is generically and parametrically modeled in a CAD system; when changes are made to the design of subsystems that interact with the part, the part is then automatically updated subject to design objectives and constraints. In this way, the updated part or subassembly satisfies system and subsystem level optimization criteria. Thus reducing the need for the designer to react to design changes in one subsystem by manually correcting the affected design of another. The proposed framework carries practical implications that are demonstrated in the development of a suspension rocker for a formula SAE car designed and built at Brigham Young University, resulting in a rocker weight savings of 18%.

Commentary by Dr. Valentin Fuster
2007;():169-177. doi:10.1115/IMECE2007-42434.

Under increasingly uncertain environment of long term life-cycle costs arising from such causes such as material price increases and carbon regulation, product development design decision makers need an improved method for evaluating project net present value under significant risks. This paper seeks to expose this need for an interdisciplinary design method capable of proactively managing long-term uncertainties and risks. First, the paper provides an overview of trends and uncertainties in material prices and environmental regulations. Second, we highlight a variety of existing work relevant to this research. The third section describes Customer Value Chain Analysis and Quality Function Deployment exercises towards addressing the nature of the challenge at hand. The study found that the primary customers for this research are engineering managers involved in strategic product development decisions. The most important aspects of a new methodology are to identify and characterize the uncertainties specific to a project, and to facilitate modeling. The final section describes a research path leading towards the development of a new design methodology. The paper concludes that a new framework will draw upon a variety of fields including Design For Reliability, Decision Analysis, Industrial Ecology, and Informatics.

Commentary by Dr. Valentin Fuster
2007;():179-185. doi:10.1115/IMECE2007-42555.

The need to exchange information between organizations or departments of the same corporation is hampered by interoperability problems that mostly originate from the necessity to comply with diverse standards while using dissimilar applications. Each organization generally uses different standards (both local and international) for products which they produce or use. The differences and similarities of these standards, or gaps and overlaps between these standards create problems when exchanging product information through the product life cycle. Defining gaps and overlaps for these standards will help us better understand the interoperability issues. This will aid in the development of strategies for reducing interoperability problems, thus improving efficient information exchange. In this study, we present different approaches for comparing standards and for identifying gaps and overlaps in standards. A Matrix–based evaluation mechanism developed for this purpose is also described.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2007;():187-195. doi:10.1115/IMECE2007-42680.

Material waste in the Printed Circuit Board Assembly consist of parts and components that are purchased above and beyond what is required to complete a project. Controlling such material waste identified in this paper as Quantity Variance is in a direct relationship to minimizing the cost of variance that increases the profitability of each job in a low volume high mix production. This Quantity Variance occurs as defects at key steps of the manufacturing process. Six sigma is used to define, measure, analyze and control occurrences resulting in the need to purchase additional components for the completion of the order.

Commentary by Dr. Valentin Fuster
2007;():197-205. doi:10.1115/IMECE2007-42754.

In this paper, we present a formal approach to modeling continuous system dynamics in SysML using differential algebraic equations (DAE’s). To support model-based design, the Object Management Group has recently developed the Systems Modeling Language (OMG SysML™). The language is well-suited for modeling many different aspects of large-scale, multidisciplinary engineering projects. It allows systems designers to capture information concerning system requirements, tests, structures, functions, and behaviors. However, SysML lacks explicit support for modeling continuous system dynamics using DAE’s. Such models are important for representing system behavior resulting from energy or signal exchange between system components. We introduce support for modeling system dynamics in the form of a language mapping between SysML and Modelica, an equation-based, object-oriented behavioral simulation language. The bidirectional mapping provides support for creating system dynamics models in SysML that can exist alongside other SysML information models, but that can also be transformed into executable simulations by a Modelica solver. To illustrate the approach, we provide an example SysML model of a hydraulic pump.

Commentary by Dr. Valentin Fuster
2007;():207-213. doi:10.1115/IMECE2007-43009.

Integration of factory floor Computer Numerical Control (CNC) information into Enterprise Resource Planning (ERP) subsystems has been difficult, if not impossible, as traditionally, factory floor machines have been “islands of automation.” Boeing/NIST/Okuma jointly collaborated on a pilot project for using a CNC open architecture controller to collect real-time Boeing-specific part accounting data during the production of Boeing 737 Leading Edge (LE) Panels. The goal was to develop a practical and standardized approach in which to capture the real-time part data and then provide this information to an Enterprise Resource Planning (ERP) subsystem. This paper presents the results from our Boeing/Okuma/NIST pilot project that evaluated Ole for Process Control (OPC) as an integration strategy for the LE Production Line part accounting at Boeing. Using OPC, automatic logging of the relevant part production statistics was done for each production line, which in turn was used to more accurately determine the total cost of making each LE production line.

Commentary by Dr. Valentin Fuster
2007;():215-228. doi:10.1115/IMECE2007-43226.

Decisions made during conceptual design can have a major impact on the success of a design project, and designers must take care to select a concept that leads to a desirable design solution. However, the inherently imprecise nature of design concepts complicates decision making. A single concept relates to a large set of specific design implementations, each of which has a different level of desirability based on the tradeoffs designers are willing to make. Thus, designers must consider tradeoffs across the many possible implementations of a design concept in order to decide between concepts rigorously. To accomplish this efficiently, designers require an abstract understanding of the characteristics of a design concept. In this paper, we describe an approach to modeling design concepts that is based on an extension of the notion of a Pareto set, called a parameterized Pareto set. Using this construct, designers can generate a model based on information about prior implementations of a design concept in a way that includes tradeoff information while being independent of implementation details and reusable for different design problems. We demonstrate the approach on the conceptual design of a gearbox. The example involves two different design scenarios that serve to demonstrate the reusability of the model and effectiveness of the overall approach.

Topics: Design
Commentary by Dr. Valentin Fuster
2007;():229-235. doi:10.1115/IMECE2007-43362.

This paper describes an information model and interface by which a general purpose robotic manipulator can publish its kinematic- and dynamic parameters to enable real-time trajectory control. The motivation for the work was the control of various robotic manipulators in USARSim, an urban search and rescue simulation environment, wherein manipulators are dynamically introduced. The objective was to avoid a static description, such as a configuration file, in favor of real-time communication channels. Although the interface originated with simulations, it has been applied to real robotic manipulators, including serial- and parallel kinematics. The interface is being used as the basis for robot competitions in the RoboCup Rescue Simulation league, which provides a plug-and-play software environment for robots and the competing controllers.

Commentary by Dr. Valentin Fuster
2007;():237-246. doi:10.1115/IMECE2007-43448.

The goal of Quality Engineering is to design quality into every product, service and manufacturing process. In particular a methodology is claimed to be very important for Quality design and management: Quality Function Deployment (QFD). QFD is a structured methodology and mathematical tool used to identify and quantify customer requirements and translate them into key critical parameters of systems and processes. The aim of the paper is to show how a quality management approach can support the increase of the process capability in a global vision of every business. QFD represents one of the most successful tools used in industrial management. By using actual and real cases, the paper shows the effectiveness of the QFD in improving both the management of a process and its capability. Four examples are presented. They take into account different environments: pharmaceutical, mechanical, healthcare and transportation markets. The first case study is deployed in a pharmaceutical company to satisfy the new customer requirements for the introduction of a nasal spray product on the Japanese market. The second example is applied to the automotive market for the production of air-cooling devices for deluxe vehicles. Finally, the other two cases show the implementation of the QFD tool in transactional processes, such as Cargo Center activities and healthcare services.

Topics: Manufacturing
Commentary by Dr. Valentin Fuster
2007;():247-255. doi:10.1115/IMECE2007-43453.

The tolerance allocation problem consists of choosing tolerances on dimensions of a complex assembly so that they combine into an ‘optimal state’ while fulfilling certain requirements on an allowed variation. This optimal state often coincides with the minimum manufacturing cost of the product. Sometimes it is balanced with an artificial cost that the deviation from target induces on the quality of the product. This paper suggests a multiobjective formulation of the tolerance allocation problem to automatically decompose requirements for an allowed variation on a set of critical product dimensions. This formulation is demonstrated using a rear lamp on a car with multiple requirements on allowed variation. In this case only the tolerances on locators that locates the lamp on the body are considered. The paper also reviews a selection of work that has been made on solving tolerance allocation problems.

Commentary by Dr. Valentin Fuster
2007;():257-264. doi:10.1115/IMECE2007-43738.

This paper presents the development of a sketch-based interactive digital prototyping method by using the level-set method as the underlying technology. Various deformative operations (e.g., warping, smoothing) are developed by the level-set method to design 2D sketches. Fast and robust numerical techniques are utilized to support the real-time performance of level-set operations. B-spline function-based shape transformation method is developed to construct 3D volumetric data from multiple 2D sketches. Virtual prototypes are then visualized by reconstructing surface models from the volumetric data. Computational cost and memory requirement of the presented method are analyzed to evaluate its real-time performance. Example virtual prototypes are shown to demonstrate the capability of the developed method.

Commentary by Dr. Valentin Fuster
2007;():265-273. doi:10.1115/IMECE2007-44055.

New paradigms and accompanying software systems are necessary to support the integration of system level design and discipline level analysis activities for the implementation of product lifecycle management. In this paper, we present an information driven product development method for the integration in the context of multidisciplinary product realization. The method contains three constituents: product information model which represents the associativities among design requirements, product components, and design parameters; compromise Decision Support Problem which maps the information model directly into design problems; and knowledge based Finite Element Analysis which generates analysis model automatically from the information model. Information driven product development uses product information model as a communication media between design and analysis activities, hence provides an effective way to trace the impact of design changes, facilitates the reuse of analyses models, and supports collaborative decision-making. An electronic chip package design and analysis scenario is presented to illustrate and demonstrate this method.

Commentary by Dr. Valentin Fuster
2007;():275-280. doi:10.1115/IMECE2007-41015.

This paper presents redesign of a car body for material weight reduction for the cost saving by material as well as fuel efficiency improvement. ULSAB (Ultra Light Steel Auto Body Structure) concept is used for weight reduction in redesigning process. Modularization is used for redesigning to reduce parts cost. Four factors: cost of modules, cost of assembly, common design and weight of the car are considered. Comparison for the material cost, weight and assembly time has been done for proposed design and existing design. Redesign car shows efficient fuel consumption car. Automotive sector could reduce their total manufacturing cost per vehicle by using modularization in design. The customers will get cheaper and fuel efficient car.

Topics: Doors , Steel , Automobiles
Commentary by Dr. Valentin Fuster
2007;():281-286. doi:10.1115/IMECE2007-41559.

Titanium nitride (TiN) films were grown on Si (111) and 95W18Cr4V high-speed steel substrates using DC reactive magnetron sputtering technique with different deposition time. The changes in crystal growth orientation of the TiN films were measured by X-ray diffraction (XRD). The surface & cross-sectional morphologies of TiN films were analyzed using field emission scanning electron microscopy (FESEM). The hardness and adhesive property of TiN films were evaluated as well. It is found that the increase of the film thickness favors the formation of the {111} preferred orientation of TiN films. When the {111} preferred orientation is presented, TiN films exhibit a kind of surface morphology of triangular pyramid with right angles. With the increase of the film thickness, the columnar grains continuously grow lengthwise and breadthwise. The size of grains influences the hardness of TiN films more greatly. The adhesive property of the film/substrate interface decreased with increasing film thickness.

Commentary by Dr. Valentin Fuster
2007;():287-294. doi:10.1115/IMECE2007-42199.

Ceramics are suitable for use in high temperature applications as well as corrosive environment. These characteristics were the reason behind selection silicone carbide for a high temperature heat exchanger and chemical decomposer, which is a part of the Sulphur-Iodine (SI) thermo-chemical cycle. The heat exchanger is expected to operate in the range of 950°C. The proposed design is manufactured using fused ceramic layers that allow creation of micro-channels with dimensions below one millimeter. A proper design of the heat exchanges requires considering possibilities of failure due to stresses under both steady state and transient conditions. Temperature gradients within the heat exchanger ceramic components induce thermal stresses that dominate other stresses. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer and stresses in the decomposer. Temperature distribution in the solid is imported to finite element software and used with pressure loads for stress analysis. The stress results are used to calculate probability of failure based on Weibull failure criteria. Earlier analysis showed that stress results at steady state operating conditions are satisfactory. The focus of this paper is to consider stresses that are induced during transient scenarios. In particular, the cases of startup and shutdown of the heat exchanger are considered. The paper presents an evaluation of the stresses in these two cases.

Commentary by Dr. Valentin Fuster
2007;():295-303. doi:10.1115/IMECE2007-43067.

Journal bearings are widely used in many industrial applications. In journal bearings, under boundary lubricated conditions, the surfaces are considered to be technically dry or only slightly lubricated, so that the resistance to relative motion is due to the interaction between the highest asperities covered by the boundary film. A thin film of lubricating oil exists under this condition and there is partial metal to metal contact. The ideal situation where the two sliding surfaces are completely separated by a thin film of a viscous fluid or a gas is referred to as hydrodynamic lubrication. In hydrodynamic bearings, due to frequent starting and stopping, misalignment of the shaft with the bearing, application of heavy loads and unexpected sudden non flow of lubricant and such other service conditions result in boundary lubrication by squeezing out the lubricating film or allow the surface asperities to break through the film so that the shaft and bearing are pressed into contact with one another. The maximum wear occurs in fluid film bearings during boundary lubricated conditions. The use of dry bearings has therefore become more essential as it requires practically no lubricant to function. Moreover it is less expensive, resist contamination better compared to rolling element bearings and easier to design.

Commentary by Dr. Valentin Fuster
2007;():305-311. doi:10.1115/IMECE2007-43109.

Phase transitions and CTE of 10mol%Sc2 O3 -1mol%CeO2 -ZrO2 ceramics sintered from two commercial powders produced by Praxair Surface Technologies, USA and DKKK, Japan are studied. Morphology of powders and grain structure of ceramics were studied by SEM and AFM. Ceramics produced from Praxair powder exist in cubic phase while DKKK-based ceramics exhibit slow phase transformation from cubic to rhombohedral (β) phase at temperatures 350–400°C. c-β Phase transition temperature is 440°C obtained by high temperature x-ray diffractometry (HTXRD) and differential scanning calorimetry. Coefficients of thermal expansion of cubic and β-phases were calculated from temperature dependence of lattice parameters obtained by HTXRD in the temperature range of 25–800°C. These results can be further used for the optimal design of SOFC layered structures as well as for determination of their reliability and durability under operational conditions.

Commentary by Dr. Valentin Fuster
2007;():313-318. doi:10.1115/IMECE2007-43114.

Multilayer and superlattice coatings of TiN/CrN coating are deposited on Si(100) substrate at different modulation wavelength by reactive unbalanced magnetron sputtering and characterized using X-ray diffraction, nanoindentation, AFM. Nano-roughness of films is in good correlation with hardness and modulus and this effect has been used for optimization of deposition parameters. Preliminary results have shown slightly better mechanical properties for multilayered TiN/CrN coatings compared to single layer TiN and CrN coatings. The XRD results have shown a preferred orientation in <100> direction for TiN/CrN multilayer coatings at modulation wavelengths below 80 nm. At 100 nm layer thickness, TiN revealed small amount of crystals with <111> orientation and their content significantly increases with increase in layer thickness while CrN layers only show preferred orientation of <100>. Multilayered coatings exhibit better mechanical properties due to presence of large number of interfaces which act as barrier to dislocations. Fracture toughness and tribological properties of these coatings are also expected to show significant improvement and the investigation in this area is under progress.

Commentary by Dr. Valentin Fuster
2007;():319-328. doi:10.1115/IMECE2007-43242.

In this paper I discuss my invention that solves the problem of designing and manufacturing springs made of elastic materials, particularly steel springs, with prescribed characteristic (dependence of flex on external load) given by a smooth (i.e. differentiable) non-linear function. The method according to the invention consists in forming an elastic body with suitably shaped regions of diversified stiffness and (possibly) diversified initial internal stresses. This suitable shape of the regions lies at the hart of the invention and is briefly discussed in the paper. I also give some formulas for the spring characteristic of the springs according to the invention and describe a method for obtaining these formulas. The paper is a companion to my patent applications “Smooth non-linear springs, particularly smooth progressive rate steel springs, progressive rate vehicle suspensions and method”, US 11/950,935 and PL P380,914.

Topics: Steel , Springs
Commentary by Dr. Valentin Fuster
2007;():329-338. doi:10.1115/IMECE2007-43816.

Thermal barrier coatings (TBCs) are thin ceramic coatings used to insulate gas turbine hot section components. The degradation of interfacial fracture toughness between the coating and the metallic substrate is a key concern for TBC systems. Previous research by the authors has explored the use of conical (Brale) indentation to measure the interfacial fracture toughness of electron beam physical vapor deposition (EB-PVD) TBCs. However, indentation using a standard 120° Brale indenter can fail to yield an ideal debond size for accurate measurement for poorly adhered coatings subjected to long-term thermal exposures, or for as-processed coatings that are well-adhered to the metallic substrate. These limitations of existing conical indentation tests have lead to the study of different shapes of indenters to obtain optimal debond sizes. In this paper, the differences in measuring the interfacial fracture toughness in thermal barrier coating systems due to indentation by rigid cones with various tip angles, namely, 60°, 90°, 120°, and 150° are addressed. Interfacial stress intensity factor distributions, i.e., curves of the interfacial stress intensity factor (K) vs. normalized radial distance (R/a), are obtained through numerical simulations coupled with thin film fracture mechanics relations. Results from experimental studies on an exposed EB-PVD TBC specimen are presented. The goal of this work is to obtain larger debond sizes for high toughness specimens and smaller debond sizes for low toughness specimens, while maintaining an adequate indentation depth.

Commentary by Dr. Valentin Fuster
2007;():339-353. doi:10.1115/IMECE2007-41351.

Jet engine impeller blades are flank-milled with tapered, helical, ball-end mills on five-axis machining centers. The impellers are made from difficult-to-cut titanium or nickel alloys, and the blades must be machined within tight tolerances. As a consequence, deflections of the tool and flexible workpiece can jeopardize the precision of the impellers during milling. This work is the first of a two part paper on cutting force prediction and feed optimization for the five-axis flank milling of an impeller. In Part I, a mathematical model for predicting cutting forces is presented for five-axis machining with tapered, helical, ball-end mills with variable pitch and serrated flutes. The cutter is divided axially into a number of differential elements, each with its own feed coordinate system due to five-axis motion. At each element, the total velocity due to translation and rotation is split into horizontal and vertical feed components, which are used to calculate total chip thickness along the cutting edge. The cutting forces for each element are calculated by transforming friction angle, shear stress and shear angle from an orthogonal cutting database to the oblique cutting plane. The distributed cutting load is digitally summed to obtain the total forces acting on the cutter and blade. The model can be used for general five-axis flank milling processes, and supports a variety of cutting tools. Predicted cutting force measurements are shown to be in reasonable agreement with those collected during a roughing operation on a prototype integrally bladed rotor (IBR).

Commentary by Dr. Valentin Fuster
2007;():355-369. doi:10.1115/IMECE2007-41353.

This paper presents optimization schemes for the five-axis flank milling of jet engine impellers based on the mechanics model explained in Part I. The process is optimized by varying the feed automatically as the tool-workpiece engagements, i.e. the process, varies along the tool path. The feed is adjusted by limiting feed-dependent peak outputs to a set of user-defined constraints. These outputs are tool shank bending stress, tool deflection, maximum chip load (to avoid edge chipping) and the torque limit of the machine. The linear and angular feeds of the machine are optimized by two different methods — a multi-constraint based virtual adaptive control of the process and a non-linear root finding algorithm. The five-axis milling process is simulated in a virtual environment, and the resulting process outputs are stored at each position along the tool path. The process is recursively fitted to a first order process with a time varying gain and a fixed time constant, and a simple Proportional Integral controller is adaptively tuned to operate the machine at threshold levels by manipulating the feedrate. As an alternative to virtual adaptive process control, the feedrate is optimized by a non-linear root-finding algorithm. The optimum feed is solved for iteratively, respecting tool stress, tool deflection, torque and chip load constraints, using a non-linear root finding algorithm. Both methods are shown to produce almost identical optimized feed rate profiles for the roughing tool path discussed in Part I of the paper. The new feed rate profiles are shown to considerably reduce the cycle time of the impeller while avoiding process faults that may damage the part or the machine.

Commentary by Dr. Valentin Fuster
2007;():371-382. doi:10.1115/IMECE2007-41414.

Modeling the milling process requires cutter/workpiece engagement (CWE) geometry in order to predict cutting forces. The calculation of these engagements is challenging due to the complicated and changing intersection geometry that occurs between the cutter and the in-process workpiece. This geometry defines the instantaneous intersection boundary between the cutting tool and the in-process workpiece at each location along a tool path. This paper presents components of a robust and efficient geometric modeling methodology for finding CWEs generated during 3-axis machining of surfaces using a range of different types of cutting tool geometries. A mapping technique has been developed that transforms a polyhedral model of the removal volume from Euclidean space to a parametric space defined by location along the tool path, engagement angle and the depth-of-cut. As a result, intersection operations are reduced to first order plane-plane intersections. This approach reduces the complexity of the cutter/workpiece intersections and also eliminates robustness problems found in standard polyhedral modeling and improves accuracy over the Z-buffer technique. The CWEs extracted from this method are used as input to a force prediction model that determines the cutting forces experienced during the milling operation. The reported method has been implemented and tested using a combination of commercial applications. This paper highlights ongoing collaborative research into developing a Virtual Machining System.

Commentary by Dr. Valentin Fuster
2007;():383-392. doi:10.1115/IMECE2007-41434.

Cutter-workpiece engagement maps, or cutting flute entry/exit locations as a function of height, are a requirement for prediction of cutting-forces on the tool and workpiece in machining operations such as milling. This paper presents a new method of calculating tool-part intersection maps for five-axis flank milling of jet engine impellers with tapered ball-end mills. It is called the parallel slicing method (PSM) and is a semi-discrete solid modeling technique written in C++ using the ACIS B-rep solid modeling environment. Although it is tailored towards five-axis flank milling, it can also be applied to both planar and multi-axis milling processes. The tool swept envelope is generated and intersected with the workpiece to obtain the removal volume. The removal volume is then sliced into a number of parallel planes along a given axis and the intersection curves with the tool and each plane are determined analytically. The swept area between the intersection curves of successive tool moves is calculated by solving for the area enclosed by the tangent lines. This area is removed from the workpiece material, which deletes the material cut between tool moves. Finally, the intersection curves are compared with the planar slices of the updated part, which results in a series of arcs. The end points of these arcs are joined with linear segments to form the engagement polygon which is used to calculate the engagement maps. Using this method, cutter-workpiece engagement maps are generated for a five-axis flank milling toolpath on a prototype integrally bladed rotor (IBR) with a tapered ball-end mill. These maps are compared with those obtained from a benchmark cutter-workpiece engagement calculation method – the Manufacturing Automation Laboratory’s Virtual Machining Interface (MAL-VMI). The MAL-VMI uses an application programming interface (API) in a commercial NC verification software package to obtain cutter-part intersections through a fast, z-buffer technique. Overall, the parallel slicing method appears to obtain more accurate engagement zones than those given by the MAL-VMI, although the calculation time is longer.

Commentary by Dr. Valentin Fuster
2007;():393-397. doi:10.1115/IMECE2007-41733.

A novel means for 3-D microfabrication is proposed. First, a process for generating metal patterns on the outer surface of a CCFL (Cold Cathode Fluorescent Lamp) was developed. The CCFL with the integrated mask was then used as an exposure source for subsequent lithography process to achieve the pattern transfer on the inner surface of a Cu tube. After wet etch, various grooves were successfully fabricated onto the inner surface of the Cu tube with a 2.47mm inner diameter. By the proposed method, the minimum achievable line-width could be less than 20μm. Compared with traditional manufacturing methods, the proposed approach could improve the machining precision and roughness, reduce the manufacturing difficulties, and lower the manufacturing cost substantially.

Commentary by Dr. Valentin Fuster
2007;():399-407. doi:10.1115/IMECE2007-41831.

Many experiments have been conducted to study various types of outputs (such as material removal rate, material removal mechanisms, cutting force, surface roughness, wheel wear, and edge chipping) while rotary ultrasonic machining (RUM) of different workpiece materials. However, literature review has revealed that there is no reported study on wheel wear while RUM of titanium alloys. This paper reports experimental investigations on the wheel wear mechanisms in RUM of a titanium alloy. The types of wheel wear mechanisms observed include: attritious wear, grain pullout, diamond grain cracking and fracture, metal bond cracking and fracture.

Commentary by Dr. Valentin Fuster
2007;():409-413. doi:10.1115/IMECE2007-41961.

Since the discovery of carbon nanotubes (CNTs), there has been great interest in CNT-based composites. Well-developed micromachining processes are necessary to realize micron-size CNT-based composite products. Micro electro discharge machining (micro-EDM) has been applied into many challenge-to-cut materials such as ceramic composites. In this study, micro-EDM is used to machine CNT-reinforced polymer composites in the micro scale. CNT-based polymer composites were fabricated using solution casting, in which CNTs were dispersed in the polymer-solvent solution via high energy sonication, followed by precipitation and hot pressing. The investigation uses design of experiments (DOE) approach to screen of influential input factors for process measures. A 2 level fractional factorial design was used with four input factors; CNT loading on the workpiece, μ-EDM supply voltage, pulse on-time duration, and pulse on-time ratio. With 16 μ-EDM experiments, supply voltage was found to be most influential to the material-removal-rate (MRR). Scanning electron microscope (SEM) was used to investigate characteristics of the machined CNT-based nanocomposite surfaces.

Commentary by Dr. Valentin Fuster
2007;():415-424. doi:10.1115/IMECE2007-41982.

The paper is aimed at finding all relative rigid-body positions of two conical involute gears that mesh together with no backlash. The results are then specialized to determine two key setting parameters for a hobbing machine that has to cut a conical involute gear. A numerical example shows application of the presented results to a case study.

Topics: Kinematics , Gears
Commentary by Dr. Valentin Fuster
2007;():425-430. doi:10.1115/IMECE2007-42129.

Cutting stress coupled with clamping stress and initial stress affects the workpiece deformation. To predicate the workpiece deformation during machining, the multi-stress coupled model was developed. The finite element model of milling process is established and the milling forces were predicted. The predicated milling force, clamping force and initial stress were taken as initial conditions and were inputted into the multi-stress coupled model. Workpiece deformation during machining and reaction forces of locators were predicated. To maintain workpiece in a stable condition during machining, reaction forces of the locators when the cutting tool moving along the clamp side must be monitored.

Topics: Deformation , Stress
Commentary by Dr. Valentin Fuster
2007;():431-440. doi:10.1115/IMECE2007-43017.

Because the contact bearings of spiral bevel and hypoid gears are highly sensitive to tooth flank geometry, it is desirable to reduce the flank deviations caused by machine errors and heat treatment deformation. Several methods already proposed for flank correction are based on the cutter parameters, machine settings, and kinematical flank motion parameters of a cradle-type universal generator, which are modulated according to the measured flank topographic deviations. However, because of the recently developed six-axis Cartesian-type computer numerical control (CNC) hypoid generator, both face-milling and face-hobbing cutting methods can be implemented on the same machine using a corresponding cutter head and NC code. Nevertheless, the machine settings and flank corrections of most commercial Cartesian-type machines are still translated from the virtual cradle-type universal hypoid generator. In contrast, this paper proposes a flank-correction methodology derived directly from the six-axis Cartesian-type CNC hypoid generator in which high-order correction is easily achieved through direct control of the CNC axis motion. The validity of this flank correction method is demonstrated using a numerical example of Oerlikon Spirac face-hobbing hypoid gears made by the proposed Cartesian-type CNC machine.

Commentary by Dr. Valentin Fuster
2007;():441-447. doi:10.1115/IMECE2007-43028.

A time domain approach is used to study the cutting conditions in reaming process that leads the system to regenerative chatter vibrations. The dynamic analysis of the system includes inertia of the tool, centripetal and Coriolis terms, damping and the first mode bending of reamer. A model of cutting forces proportional to chip cross sectional area and process damping proportional to cutting speed is considered. Numerical simulation based on the Euler integration scheme is carried out to obtain time domain solution of the equation. Despite linearization in force modelling, the model is nonlinear due to the change in the tool engagement area. Another nonlinearity included in the model jumping out of is the tool from cutting. The results of this model are presented and compared to the results of a linear model regenerated in time domain from previous works.

Commentary by Dr. Valentin Fuster
2007;():449-456. doi:10.1115/IMECE2007-43029.

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows the effectiveness of approach.

Commentary by Dr. Valentin Fuster
2007;():457-461. doi:10.1115/IMECE2007-43158.

This paper presents a groove reconstruction method based on the local rule of Cellular Automata (CA). A local rule for groove reconstruction is proposed to design and optimize the groove of milling insert. The insert is firstly divided into a large number of cells that typically form a regular grid over the domain. The domain consists of regular square cells with discrete variables and the discrete CA model is built. As the cells in the CA domain only interact with their neighboring cells when performing local computations, the governing equation for the whole domain is not necessary. Then the states of cells are modified according to the local rule applied. The state of the entire system is updated based on the state of the cell and its neighboring cells. Collectively, these cells’ states define the state of the entire domain, and the groove can be reconstructed according to the state of the domain. The reconstructed groove is tested by a FEM simulation. The simulation results show that the reconstructed groove has a satisfied performance on the stress field.

Topics: Milling
Commentary by Dr. Valentin Fuster
2007;():463-470. doi:10.1115/IMECE2007-43298.

This paper presents the results of the experimental work done in applying the Fused Deposition Modelling (FDM) rapid prototyping technique to fabricate and characterise the porous polymeric matrix for controlled drug delivery device (DDD). With FDM technique, both macro and micro level structures of the device matrix can be produced and controlled, which provide several advantages over the conventional techniques of DDD fabrication. The paper investigates effect of various FDM parameters viz. Raster Width, Contour Width, Air-gap and Raster Angle on the controlled drug release profiles, drug infiltration and porosity of fabricated device matrices. The paper concludes that effective DDD matrices with desired release regimes can be fabricated using FDM technology with careful selection of FDM control parameters.

Commentary by Dr. Valentin Fuster
2007;():471-475. doi:10.1115/IMECE2007-43473.

Recent advances in abrasive waterjet (AWJ) technology have resulted in new processes for surface treatment that are capable of introducing compressive residual stresses with simultaneous changes in the surface texture. While the surface residual stress resulting from AWJ peening has been examined, the subsurface residual stress field resulting from this process has not been evaluated. In the present investigation, the subsurface residual stress distribution resulting from AWJ peening of Ti6Al4V and ASTM A228 steel were studied. Treatments were conducted with the targets subjected to an elastic prestress ranging from 0 to 75% of the substrate yield strength. The surface residual stress ranged from 680 to 1487 MPa for Ti6Al4V and 720 to 1554 MPa for ASTM A228 steel; the depth ranged from 265 to 370 μm for Ti6Al4V and 550 to 680 μm for ASTM A228 steel. Results showed that elastic prestress may be used to increase the surface residual stress in AWJ peened components by up to 100%.

Commentary by Dr. Valentin Fuster
2007;():477-483. doi:10.1115/IMECE2007-43480.

Stability analysis is needed to maximize milling performance while avoiding chatter. However, such an analysis is time-consuming, requiring the use of sophisticated instrumentation, and has significant level of uncertainty, which impedes the widespread use by industry. A main source of uncertainty is believed to be the changes in dynamics of the tool-holder-spindle system during the milling operation. This study investigates the variation in the tool point dynamics reflecting the dynamics of the tool-holder-spindle system and associated machining stability. The investigation focuses on the effects of the conditions generated by typical milling operations, such as tool changes and spindle warm up. The results of analyses demonstrate the necessity of continuous updates of the tool point dynamics during milling process by in-situ measurements to minimize uncertainty in evaluation of machining stability.

Commentary by Dr. Valentin Fuster
2007;():485-490. doi:10.1115/IMECE2007-43561.

The fatigue life tests carried out on two groups of ball bearings confirm the positive influence of the compressive residual stresses induced by a previous loading in the elastic-plastic domain. The values of residual stresses are numerically evaluated by employing a three-dimensional strain deformation analysis model. The model is developed in the frame of the incremental theory of plasticity by using the von Mises yield criterion and Prandtl-Reuss equations. To consider the material behaviour the Ramberg-Osgood stress-strain equation is involved and a nonlinear equation is considered to model the influence of the retained austenite. To attain the final load of each loading cycle the two bodies are brought into contact incrementally, so that for each new load increment the new pressure distribution is obtained as the solution of a constrained system of equation. Conjugate gradients method in conjunction with discrete convolution fast Fourier transform is used to solve the huge system of equations. Both the new contact geometry and residual stresses distributions, are further considered as initial values for the next loading cycle, the incremental technique being reiterated. The cyclic evaluation process of both plastic strains and residual stresses is performed until the material shakedowns. Comparisons of the computed residual stresses and deformed profiles with corresponding measured values reveal a good agreement and validate the analysis model. The von Mises equivalent stress, able to include both elastic and residual stresses, is considered in Ioannides-Harris rolling contact fatigue model to obtain theoretical lives of the ball bearings groups. The theoretical analysis reveals also greater fatigue lives for the ball bearings groups with induced residual stresses than the fatigue lives of the group without induced residual stresses.

Commentary by Dr. Valentin Fuster
2007;():491-496. doi:10.1115/IMECE2007-43610.

The use of femtosecond lasers for the micromachining of engineering materials with micro and submicron size features is slowly but steadily increasing. This increase though presents challenges in understanding the interaction mechanism of femtosecond laser pulses with a material and defining process parameters for quality machining. This manuscript will present the setup for a 3DOF femtosecond laser microfabrication (FLM) system and its use in studying the ablation (single and multi shot) characteristics and incubation coefficient of nickel-titanium (NiTi) shape memory alloy. Understanding of these characteristics could allow for the identification of new applications of smart materials in the macro, micro, nano and MEMS domains.

Commentary by Dr. Valentin Fuster
2007;():497-508. doi:10.1115/IMECE2007-43678.

A numerical simulation code is developed and used to derive relationships between the incident laser radiation, the thermal stress field, and the size and shape of the heat affected (HAZ) and melt zones for a pulsed laser transmission welding process. The material used in the investigation is a high density polyethylene thermal plastic. The numerical model uses the Fourier heat conduction thermal model and the welding process involves the lap welding of two thin layers of thermoplastic films with the welding conditions of a transparent material over a semi-transparent or opaque material. The Fourier model is valid due to the high thermal pulse velocity through the material. The results are compared to the published data on thermoplastic welding criteria and the legitimacy of these criteria are discussed.

Commentary by Dr. Valentin Fuster
2007;():509-515. doi:10.1115/IMECE2007-43848.

Compared with lithographic techniques, mechanical micromachining is a potential competitive process for fabricating 3D micro/meso components or macro parts with micro-features from diverse materials at high accuracy, efficiency, and low costs, but the size effect induced by the comparable size of microstructures, cutting edge radius, and depth-of-cut results in a plowing dominated process. A methodology to incorporate model random microstructure in finite element analysis (FEA) of micromachining multiphase materials has been developed to understand the plowing, tribological, and heat transfer mechanisms. An internal state variable plasticity model has been developed to model the dynamic mechanical behavior including the effect of randomly distributed microstructure, materials damage and evolution. The simulated process variables including chip morphology, forces, and temperatures agree well with the observed experimental phenomena. The simulation recovers the shearing-plowing transition and increased specific energy in micromachining.

Commentary by Dr. Valentin Fuster
2007;():517-522. doi:10.1115/IMECE2007-44013.

Silicon wafers are the fundamental building blocks for most integrated circuits. Chemical mechanical polishing is used to manufacture silicon wafers as the final material removal process to meet the ever-increasing demand for flatter wafers and lower prices. The polishing pad is one of the critical factors in planarizing wafer surfaces and its properties play critical roles in polishing. However, pad properties change during the process. This paper reviews the measurement methods for thickness, hardness, and Young’s modulus of polishing pads.

Topics: Polishing
Commentary by Dr. Valentin Fuster
2007;():523-526. doi:10.1115/IMECE2007-41115.

In operating the air cleaner for a long time, people in a quiet enclosed space expect calm sound at low operational levels for a routine cleaning of air; in contrast, a powerful, yet not-annoying, sound is expected at high operational levels for an immediate cleaning of pollutants. In this context, it is important to evaluate and design the air cleaner noise to satisfy such contradictory expectation from the customers. In this study, a model for evaluating the air cleaner sound quality was developed based on the objective and subjective analyses. Sound signals from various air cleaners were recorded and they were edited by increasing or decreasing the loudness at three wide specific-loudness bands: 20–400 Hz (0–3.8 Bark), 400–1250 Hz (3.8–10 Bark), 1.25k–12.5k Hz bands (10–22.8 Bark). Subjective tests using the edited sounds were conducted by the semantic differential method (SDM) and the method of successive intervals (MSI). SDM test for 7 adjective pairs was conducted to find the relation between subjective feeling and frequency bands. Two major feelings, performance and annoyance, were factored out from the principal component analysis. We found that the performance feeling was related to both low and high frequency bands; whereas the annoyance feeling was related to high frequency bands. MSI test using the 7 scales was conducted to derive the sound quality index to express the severity of each perceptive descriptor. Annoyance and performance indices of air cleaners were modeled from the subjective responses of the juries and the measured sound quality metrics: loudness, sharpness, roughness, and fluctuation strength. Multiple regression method was employed to generate sound quality evaluation models. Using the developed indices, sound quality of the measured data were evaluated and compared with the subjective data. The difference between predicted and tested scores was less than 0.5 point.

Topics: Sound quality
Commentary by Dr. Valentin Fuster
2007;():527-533. doi:10.1115/IMECE2007-41142.

A computer aided tool for tire sound quality evaluation was developed. Automotive engineers can evaluate a tire structure by listening to synthesized sound that the tire would radiate when it rolls on a specific type of road surface. Among three kinds of tire sound, this study dealt with only the tire sound that radiates through its structural vibration caused by road surface texture excitation. The tool can be used on personal computers. To make it happen, tire sound radiation process is modeled into two parts. One is excitation. Tire deformation at the contact patch was calculated from road surface texture database by rolling contact analyses using multi-body dynamics simulation software. The model includes rolling tire structure model with contact compliance and simple suspension system for the wheel axle. Observation of the calculation results gives such an insight that excitation waveforms from road surface have prominent peaks that occur only at high peaks isolated from others, and do not have dips. This transformation process from road surface waveform to excitation is more accurate than tire envelope model and also not prohibitive considering today’s low-price computing power. The other process is tire structure vibration response. By limiting the usage of tire structure models just in representing over all vibration modal responses to road surface excitations in relatively low frequency range, a simple structural finite element model (FEM) was created. In this FEM, tire wall composite structures are modeled as assembly of solid elements with uniform material properties. The trick in using this FEM model lies in its boundary condition setting. By measuring vibration transfer functions from many points on a contact patch to tire tread and sidewalls, excitation in the middle of the contact patch was found to be blocked to travel to the sidewalls in higher frequency range due to the contact restriction on the periphery of the patch. This finding is essential in giving suitable boundary conditions to the FEM model and choosing the excitation points. To make the computing time minimum for synthesis, the vibration responses of the tire are represented by infinite impulse response (IIR) digital filter banks. The waveform obtained by applying the measured road texture waveforms to the IIR filter, was transferred to sound waves by the sound command of Matlab. By modifying the IIR filter, automotive engineers can judge the effect of tire structural design changes.

Commentary by Dr. Valentin Fuster
2007;():535-544. doi:10.1115/IMECE2007-42419.

Although numerous firms have been shifting toward automated assembly, most still rely on manual assembly when complex assembly operation is required for large-scaled systems. Furthermore, because firms design variants of a system to satisfy diverse customer needs, they may manufacture these system variants in the same assembly line. This type of operation, called mixed model assembly, may improve the utilization of existing manufacturing facilities; however, it may also increase assembly errors due to interchanging geometrically similar parts between system variants. Design for Assembly (DFA) is a design guideline that assists engineers in designing systems that are easier to assemble. However, because DFA guidelines group geometrically similar parts in the same part category, it may be impossible to distinguish geometrically similar but functionally different parts (modules) used in different systems. This paper proposes experimenting how cognitive effects of non-geometric part features influence the productivity and quality in mixed model assembly operations. Furthermore, because the productivity and quality of manual assembly may be influenced by the motivation of operators, this paper examines how productivity and quality may be influenced by different incentive schemes.

Topics: Manufacturing
Commentary by Dr. Valentin Fuster
2007;():545-552. doi:10.1115/IMECE2007-42423.

In the past several decades, Quality Function Deployment (QFD) has gained its popularity among engineers as a tool to relate (map) customer requirements (inputs) to system requirements or system components (outputs), and to calculate relative worth of these requirements and components. The benefits of QFD in system development include cost reduction, fewer design changes after the start of production, and improved communication among engineers. Despite the observed benefits, the needs for QFD research have been addressed by researchers. These research needs include decision-making process in QFD, rating scales used in QFD matrices, and calculation schemes for calculating the worth of outputs (e.g., system requirements) from the importance of inputs (e.g., customer requirements). The purpose of this paper is to empirically study sensitivity of the relative worth and rank of outputs in QFD matrices to rating scales and worth calculation schemes. We collected QFD matrices from journal articles and textbooks; then calculated the changes of relative worth and the rank of outputs when one type of rating scale and/or worth calculation scheme was changed to the other. The results suggest that the relative worth and rank of outputs are relatively insensitive to rating scales and worth calculation schemes in the QFD matrices studied in this paper.

Commentary by Dr. Valentin Fuster
2007;():553-560. doi:10.1115/IMECE2007-42427.

In the modern system development approach, engineers with diverse discipline form teams and work together in engineering projects. An example is a cross functional team in concurrent engineering. It is important to design incentive systems that maximize team achievements; however, there is a tradeoff between rewarding individual vs. team achievements. Rewarding solely on individual achievements may hinder the overall team achievements, while rewarding solely on team achievements may lead to the phenomenon called social loafing or free riding in which individuals tend to perform worse or contribute less in group. This paper studied the effects of competitive rewards based on individual and team’s achievements by conducting experiments using prisoner’s dilemma game (PDG) in which participants face tradeoff between working more or less in hypothetical individual and team assignments. The unique approach in this paper is to decompose the overall PDG payoff matrix into payoff matrix for individual achievements and that for team achievements to test the effects of individual and team competitive rewards. The experiment results suggested that introduction of team competitive rewards resulted in higher cooperation among team members and overall productivity, compared to when individual competitive rewards were introduced.

Topics: Teams , Collaboration
Commentary by Dr. Valentin Fuster
2007;():561-566. doi:10.1115/IMECE2007-41231.

The tool wear mechanism in machining of metal matrix composites (MMC) and its dependence on the percentage of reinforcements with MMC was investigated. Silicon carbide metal matrix composites of two samples were prepared by using stir casting method. Samples having 10 percentage & 20 percentage of silicon carbide particles (grain size ranging from 55 to 85 micron meter) by weight were fabricated in the form of cylindrical bars. Experiments were conducted in medium duty lathe by using poly crystalline diamond (PCD) insert of 1500 grade as cutting insert and the experiment was performed by using design of experiments (L27 orthogonal array) on two different samples and the parameters obtained were optimized by analyzing the power consumed by main spindle and surface finish of machined component. The results from machining of this fabricated Aluminum Alloy A356, reinforced with SiC particles MMC is highlighted in this paper. All trails were carried out with time duration of one minute. By setting these optimum parameters, tool wear study was carried out till the flank wear reached 0.4mm. The results showed that tool life was minimum while machining 20 percentage of SiC reinforcement MMC as compared with 10 percentage of SiC reinforcement. The tool wear images were captured by Cam scope with a magnification of 100X which supports the results.

Commentary by Dr. Valentin Fuster
2007;():567-572. doi:10.1115/IMECE2007-41593.

The anisotropic nature of laminated composites creates a unique opportunity and also a great challenge for tailoring their behavior during the forming processes according to the design requirements. In this work, design and simulation of a deep drawing process for fiber-reinforced laminated composites were conducted by using finite element analysis. The effects of the fiber orientation and stacking order on the deep drawing process were investigated based on the basic understanding of forming process of the isotropic aluminum alloy (Al-1100) and laminated composite material (Grilon RVZ-15H nylon/glass). A three dimensional finite element model incorporating layered structural laminates with various fiber orientations was developed. The load-stroke relationship, changes in thickness, and stress-strain distribution were investigated and compared for both aluminum alloy and laminated composites of [0]12 , [0/90]6 and [0/90/45/135]3 , which can be employed for detailed design and process optimization.

Commentary by Dr. Valentin Fuster
2007;():573-582. doi:10.1115/IMECE2007-41775.

Non-traditional process like wire electro-discharge machining (WEDM) is found to show a promise for machining metal matrix composites (MMCs). However, the machining information for the difficult-to-machine particle-reinforced material is inadequate. This paper is focused on experimental investigation to examine the effect of electrical as well as nonelectrical machining parameters on performance in wire electro-discharge machining of metal matrix composites (Al/Al2 O3 p). Taguchi orthogonal array was used to study the effect of combination of reinforcement, current, pulse on-time, off-time, servo reference voltage, maximum feed speed, wire speed, flushing pressure and wire tension on kerf width and cutting speed. Reinforcement percentage, current, on-time was found to have significant effect on cutting rate and kerf width. The optimum machining parameter combinations were obtained for cutting speed and kerf width separately.

Commentary by Dr. Valentin Fuster
2007;():583-589. doi:10.1115/IMECE2007-42226.

Resin Transfer Molding (RTM) is an advanced process to manufacture high quality thermoset polymeric composites. The quality of the composite depends on the resin infusion stage and the cure stage during the RTM process. The resin curing is a complex exothermic process which involves resin mechanical property evolution, resin volume shrinkage, thermal expansion, heat transfer, and chemical reaction. Since the fibers and resin have many differences in their physical properties, the composite cure stage inevitably introduces the undesired residual stress to the composite parts. As the residual stress could sometimes generate local matrix failure or degrade the performance of the composite, it is important to model and minimize the residual stress. This paper presents a model to predict the residual stress development during the composite cure process. By slightly disturbing the manufacturing parameters such as the mold heating cycle and the cure kinetics of polymer, the variations of residual stress development during the RTM process can be modeled and compared. A parametric uncertainty study of the residual stress development in the polymeric composite manufactured with RTM will be performed and discussed.

Commentary by Dr. Valentin Fuster
2007;():591-596. doi:10.1115/IMECE2007-42538.

One of the problems in machining of composites is related with the fibers as reinforcement, due to their abrasiveness, causing fast tool wear and deterioration of machined surface. Among all the damages that can occur in the drilling of a composite plate, delamination is the most serious, as it can cause loss of mechanical strength of laminate plates. The main mechanism responsible for delamination is the axial thrust force exerted by the stationary center of the drill – chisel-edge – whose action is more similar to an extrusion that to a drilling. It can be shown that 40% to 50% of the thrust force is because of the chisel edge. Therefore, in this paper a new set of hollow drill bits is introduced and tested on the composite materials with different properties and drilled hole quality mainly, surface roughness, roundness, hole oversize and delamination investigated. With these hollow drill bits we were able to achieve lower thrust forces. Also drill bit geometry changed to be optimized for the best hole quality.

Commentary by Dr. Valentin Fuster
2007;():597-605. doi:10.1115/IMECE2007-42671.

We present a novel method to compute the three dimensional orientation tensors of carbon nanofibers in CNF/polymer composites. Performance properties of nanofiber composites are significantly affected by fiber orientation patterns. So an accurate description of the fiber orientation is necessary to validate models relating processing technique and properties of the final composites. Orientation tensors and probability distribution functions (PDF) are commonly used to describe orientation patterns. But physical dimensions of nanofibers and the imaging technique (Transmission Electron Microscopy, TEM) make all currently available methods of image analysis useless to accurately computing these descriptions in 3-dimensions. In this study TEM sections are cut with specific thickness and angle that result in majority of the fibers being cut at both ends. Fiber projection dimensions measured from this special section provide the complete three dimensional orientation of each fiber. This method is benchmarked by using simulated 3D samples in AutoCAD.

Commentary by Dr. Valentin Fuster
2007;():607-618. doi:10.1115/IMECE2007-43830.

The field of polymer-clay nanocomposites has attracted considerable attention as a method of enhancing polymer properties and extending their utility. In this research, different nanocomposites have been manufactured by modifying the EPON828 resin system through the infusion of 0.5%, 1%, 1.5% and 2% by weight of clay (Nanocor® 1.30E) nanoparticles. Mechanical properties such as flexural, compressive, tensile and high strain rate strengths and moduli of polymer matrix were improved in nano structured materials owing to their unique phase morphology and improved interfacial interactions. A dynamic Mechanical analysis was performed to monitor changes in the thermal properties of the nanocomposite. Nanoclay reinforced epoxy showed consistent improvement in all the mechanical as well as Thermomechanical properties. High strain rate compressive modulus showed a progressive improvement over the neat values for all the strain rates used. SEM micrographs of the fracture surfaces for both tensile and flexural samples showed regular and continuous patterns of cracks for the neat samples. The nanophased samples on the other hand showed multiple irregular cracks which increased in densities with nanoclay loading.

Commentary by Dr. Valentin Fuster
2007;():619-624. doi:10.1115/IMECE2007-44012.

In the present work, effects of two types of natural fibres on mechanical properties of polyester composites were investigated at different volume fractions of fibre. Tensile, compression, and flexural properties of oil palm bunch and oil palm fruit fibres reinforced polyester composites were investigated. Additionally, tensile strength of the selected composites was calculated theoretically. Scanning electron microscope was used to observe the fracture mechanism of the specimens. Single fiber pull-out tests were carried out to determine the interfacial shear strength between polyester resin and both types of oil palm fibre. As results, it was found that both types of oil palm fibre enhanced the mechanical performance of polyester composites. At higher volume fraction (≈41%), tensile strength was improved, when polyester reinforced with oil palm fruit fibres, i.e. 2.5 folds improvement in the tensile strength value. Further, experimental tensile strength values of oil palm bunch/polyester composites was found to be less varied compared to theoretical results. Flexural strength of polyester was worsened with oil palm fibres at all of fibre volume fraction.

Commentary by Dr. Valentin Fuster
2007;():625-630. doi:10.1115/IMECE2007-41154.

This research program evaluates the residual properties of 7136-T76511 aluminum extrusions joined through friction stir welding (FSW). AA 7136 is a new aluminum alloy developed by Universal Alloy Corporation for high strength aerospace applications that also demand good corrosion resistance, such as those on the Boeing 787 or the Airbus A380. Mechanical and corrosion testing were performed on the baseline material and on panels friction stir welded at 175, 225, 250, 300, 350 and 400 RPM (all other welding parameters were held constant). Mechanical test results demonstrate that the highest joint efficiency, 74%, is achieved at 350 RPM, but for each weld condition, the elongation of the welded material is significantly reduced, 50 – 75%, from the baseline value. Fracture of the tensile specimens consistently occurred on the retreating side of the weld along the interface between the heat affected zone (HAZ) and the thermo-mechanically affected zone (TMAZ), independent of the rotational speed. Examination of fracture surfaces through SEM revealed microvoid nucleation and coalescence around secondary phase particles in the microstructure, as well as numerous stepped or laminar facets characteristic to both the baseline and welded conditions. Exfoliation corrosion testing revealed a performance gradient across the weld with the weld nugget rating the poorest at EC and the heat affected zone rating the best at EA. Qualitative assessment of corrosion resistance is supported by mass loss calculations between the baseline and welded conditions.

Commentary by Dr. Valentin Fuster
2007;():631-632. doi:10.1115/IMECE2007-41178.

Composite materials and laminates are being widely used in aerospace and automotive industries due to their less weight to stiffness ratio. Especially the use of composite laminates, made up of Carbon or Graphite Fiber Reinforced Plastics (CFRP/GFRP), in military and commercial aircraft structures has progressed steadily over the past few decades. Drilling holes and making cutouts in these laminates are unavoidable for practical reasons. These holes (or) cutouts introduces stress concentration near the hole (or) cutout edge and reduces the load-bearing capacity of the structure. Cutouts are made at the edges of composite laminates for practical purposes, which is capable of reducing the delamination effect in notched laminates. The stress distribution in notched composite laminates can vary according to the location of the notch in the laminate, which leads to the variation in strength and reliability values of notched laminates. The objective of the present work is to study the effect of notch location on the stress concentration and reliability of notched composite laminates. Composite laminate displays significant variation in material and strength properties and the stress distribution in the laminate becomes stochastic in nature. Thus the notched laminates were analyzed using a stochastic approach and designed based on a reliability-based design approach.

Commentary by Dr. Valentin Fuster
2007;():633-641. doi:10.1115/IMECE2007-41291.

A three-dimensional nonlinear finite element analysis model is presented to study mixed-mode interfacial delamination for a pull-off test consisting of a thin film strip debonded from a glass substrate. Since the strain energy release rates of all three modes (Mode I, Mode II, and Mode III) and the mode mixities vary along the width of the debond front, prediction of the in-situ shape of the debond front remains an interesting and challenging topic. A cohesive zone model is incorporated into the three-dimensional finite element model to predict the interfacial crack propagation profile for the film deformation regime ranging from bending plate to stretching membrane. This three-dimensional finite element model is found to provide additional insights for interfacial delamination for the pull-off test.

Commentary by Dr. Valentin Fuster
2007;():643-647. doi:10.1115/IMECE2007-41376.

Titanium alloys have found increased applications in various industrial sectors. One of the critical issues in quality control is the weld penetration during welding. In the present paper, tungsten inert gas (TIG) welding was used to weld 8.0-mm thick Ti-6Al-4V alloy plates with and without an activating flux. The effect of the activating flux on Ti alloy welding was investigated. A data acquisition system was used to monitor the welding current and voltage signals during welding. These signals were then correlated to the weld penetration information. Results show that by applying the activating flux on the Ti-6Al-4V alloy surface, weld penetration depth increases, while the corresponding weld bead width is reduced. It was also found that various welding conditions, particularly flux thickness, influence the effectiveness of the activating flux. Results from monitoring of the welding current and voltage signals reveal that there is a clear correlation between the signals and the weld penetration. By analyzing the acquired signals, inconsistency in weld penetration can be identified. This demonstrates that process monitoring can provide an effective way to assess the consistency of the weld penetration and thus the quality of the welds.

Commentary by Dr. Valentin Fuster
2007;():649-657. doi:10.1115/IMECE2007-41962.

Minimizing consumed energy in friction stir welding (FSW) is one of the prominent considerations in the process development. Modifications of the FSW tool geometry might be categorized as the initial attempt to achieve a minimum FSW effort. Advanced tool pin and shoulder features as well as a low-conductive backing plate, high-conductive FSW tools equipped with cooling fins, and single or multi-step welding processes are all carried out to achieve a flawless weld with reduced welding effort. The outcomes of these attempts are considerable, primarily when the tool pin traditional designs are replaced with threaded, Trifiute or Trivex geometries. Nevertheless, the problem remains as to how an inclined tool affects the material flow characteristics and the loads applied to the tool. It is experimentally proven that a positive rake angle facilitates the traverse motion of the FSW tool; however, few computational evidences were provided. In this study, numerical material flow and heat transfer analysis are carried out for the presumed tool rake angle ranging from −4° to 4°. Afterwards, the effects of the tool rake angle to the dynamic pressure distribution, strain-rates, and velocity profiles are numerically computed. Furthermore, coefficients of drag, lift, and side force and moment applied to the tool from the visco-plastic material region are computed for each of the tool rake angles. Eventually, this paper confirms that the rake angle dramatically affects the magnitude of the loads applied to the FSW tool, and the developed advanced numerical model might be used to find optimum tool rake angle for other aluminum alloys.

Commentary by Dr. Valentin Fuster
2007;():659-664. doi:10.1115/IMECE2007-42550.

A hybrid numerical and experimental study was undertaken to evaluate the performance of as Friction Stir Welded (FSW) and Superplastically Formed Friction Stir Welded (SPF-FSW) Titanium joints. This paper presents the numerical models which were developed to simulate mechanical response of as FSW and SPF-FSW joints. The simulation results were then compared to experimentally determined behavior characteristics of the joints to assess the validity of the modeling approach. It was found that the numerical modeling approach presented here have simulated successfully the tensile behavior of a FSW joint agreeing with the experimental results. This method also adequately simulated the tensile behavior of a SPF-FSW joint, but due to geometrical influences, there are discrepancies between the numerical results and experimental observations.

Commentary by Dr. Valentin Fuster
2007;():665-668. doi:10.1115/IMECE2007-42673.

Weldability is a critical enabler for application of new grades of steel, which have found widespread applications in the auto industry to meet new safety regulations and reduce weight of vehicles. There are a wide variety of these grades of steel which are being used across the industry. Even within a OEM the number of material and gauge combinations becomes quite large. This requires a considerable amount of testing to prove out welding feasibility of these steels. This paper discusses the use of a finite element method (FEM) to model spot welding of DP600 and correlates the results with experiments. Improved accuracy and confidence in these tools can provide a way to better understand the physics of the process and improve the weldability of these steels in a cost effective manner.

Commentary by Dr. Valentin Fuster
2007;():669-675. doi:10.1115/IMECE2007-42675.

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are getting popular with superior mechanical properties and weight advantages compared to mild steel materials. These new materials have significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application in future vehicle programs. Due to high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for DP600, and DP780 steels are discussed. DP600 steels were joined with two different weld equipments and three different electrodes and their influence on mechanical properties are discussed. Development work on the effect of weld tips on button size, and shrinkage voids due to different welding variables is discussed. DP780 EG steel (1.0 mm) is also joined to itself. The weld lobes, mechanical properties (tensile shear and cross tension), cross-section examination, and microhardness of 1.0 mm DP780 EG to 1.0 mm DP780 EG weld joint results are discussed.

Commentary by Dr. Valentin Fuster
2007;():677-687. doi:10.1115/IMECE2007-42721.

Modal vibration testing and static flexure testing at the macromechanical level combined with numerical finite element (FE) models have been used to indirectly determine the elastic moduli of 6111 aluminum alloy base metal and spot friction welded (SFW) joints which have been formed at different processing times. It was observed that the frequency (and the corresponding apparent stiffness) of the joint oscillates at low amplitudes as processing time increases. For each vibration mode, the amplitude of the oscillation in the frequency vs. processing time is only a few percent of the mean frequency with 99% confidence level, while the corresponding lap shear strength increases monotonically by a factor of about 8 as the processing time increases. Due to the scatter in the damping data it is difficult to detect any significant trends. Comparison of predicted modal frequencies and static load-displacement response of SFW joints at the macromechanical level with the corresponding measured responses seems to indicate that the weld zone is not as stiff as the base metal, but more detailed micromechanical analysis is required before definite conclusions can be drawn. In addition, studies of microstructural characteristics and Vickers microhardness distributions across the weld zone for the SFW samples reveals the formation of a partial metallurgical bond in the direction of flow, which is governed by the tool used, whereas the hardness distribution in the weld zone depends on the processing time.

Commentary by Dr. Valentin Fuster
2007;():689-697. doi:10.1115/IMECE2007-42929.

Ultrasonic metal welding (USW) is a promising joining method for aluminum automotive body construction applications. During USW, aluminum weldments are joined together by applying high frequency vibrations while holding the parts together with a moderate clamping force. In an effort to further the development of USW for high volume robotic body construction applications, a reliability and maintainability study was performed using a robotic welding cell installed in the Ford Research and Innovation Center. The robot was equipped with a modified Sonobond ultrasonic metal welder, which was mounted on a C-frame. The study consisted of welding fully overlapped 550 mm × 350 mm × 0.9mm thick AA6111-T4 aluminum panels with 330 welds on each panel until 100,000 welds were made. Consistency in welder operation was monitored by welding fully overlapped AA6111-T4 aluminum strips (25mm wide × 550 mm long × 0.9mm thick) at the end of each day’s welding and then tensile testing the strips in a T-peel configuration. There was no statistical difference in average T-peel strength over the course of the 100,000 weld study. There was also no degradation noted in lap shear failure loads between samples welded at the end of the 100,000 weld study and those generated before initiation of the study. Reliability of the USW process during this study was monitored by periodic inspection of the robot and welder joints, attachments, fittings, tip, anvil, clamps, cables, etc. Only very minor wear of the welder tip and anvil contact surfaces were noted after the study was completed. However, during the study, after 82,000 welds a small piece of aluminum was removed from between the tip grooves, even though the weld strength was unaffected by the presence of the aluminum. There were no failures of any mechanical or electrical parts during the study. In addition, primary voltage and current signals of the ultrasonic welder’s power controller were periodically recorded during the weld study and it was determined that there was no change in the electrical behavior of the welder.

Commentary by Dr. Valentin Fuster
2007;():699-703. doi:10.1115/IMECE2007-43415.

In response to demands for improved safety standards and fuel economy, automotive OEMs have shown an increased interest for using light weight materials with greater strength. Advanced High Strength Steels (AHSS) have gained popularity due to their superior mechanical properties and weight advantages, as compared to mild steel materials. Welding of AHSS materials remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. Currently, various fusion welding processes such as Metal Inert Gas (MIG), Laser and Laser Hybrid are used on mild steel applications. The Laser and Laser Hybrid weld processes continue to gain popularity in automotive applications due to their ability to provide structural integrity and manufacturing efficiency. In laser welding, only a light source is used to join materials together. In laser hybrid, both a light source and metal filler are used to join the materials. In this paper, the laser hybrid joining process on AHSS materials (DP780 and Boron) is investigated. Influence of heat from Laser Hybrid welding process and its effect on the steel is discussed.

Commentary by Dr. Valentin Fuster
2007;():705-713. doi:10.1115/IMECE2007-43419.

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years as new safety and fuel economy regulations are enacted. These new steels pose significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. In this paper, Gas Metal Arc Welding (GMAW) of uncoated DP 600 and boron (coated and uncoated boron) steels were investigated. In the first study, 2.0 mm DP 600 and 2.0 mm uncoated boron lap joints (Joint #1 and #2) were investigated. In the second study, 1.00 mm DP 600 and 2.0 mm USIBOR (aluminized coated boron) lap joints (Joint # 3 and #4) were investigated. Static and fatigue tests were conducted on the four joint configurations. The effects of steel stack-ups and microhardness distribution along the tensile stress flow direction of the joints on fatigue performance defined by fatigue life as well as crack initiation site and propagation path were analyzed. Metallurgical properties of the dissimilar metal lap joints were evaluated using optical microscopy. The boron steel shows a significant drop in hardness at the heat affected zone (HAZ) as compared to the DP600 steel side. It was found that for the 2.0 mm DP600 and 2.0 mm boron steel dissimilar joint, fatigue life of the joint is better when boron steel was on the top of the joint (Joint #2). However, in the case of 1.0 mm DP 600 and 2.0 mm USIBOR lap joint, the fatigue life of the joint is better when 1.0 mm DP 600 was on the top of the joint (Joint # 3). Ductility of boron steel and significant HAZ softening in boron steel are believed to be the key factors for the fatigue failure at the boron steel side (in all four joint configurations).

Commentary by Dr. Valentin Fuster
2007;():715-723. doi:10.1115/IMECE2007-43423.

The development of lightweight vehicles, in particular aluminum intensive vehicles, require significant manufacturing process development for joining and assembling aluminum structures. Currently, 5xxx and 6xxx aluminum alloys are being used in various structural applications in a number of lightweight vehicles worldwide. Various joining methods, such as GMAW (it is also referred as Metal Inert Gas Welding), Laser and adhesive bonding have been investigated as technology enablers for high volume joining of 5xxx, and 6xxx series alloys. In this study, GMA welding was used to join 5754 non-heat-treatable alloy sheet and 6063-T6 heat treatable extrusion products. The objective of this study was to develop optimum weld process parameters for non-heat-treatable 5754 aluminum and heat treatble 6063-T6 alloys. For both the alloys, the lap joint configuration was used. The GMA welding equipment used in this study was an OTC/Daihen CPD-350 welding systems and DR-4000 pulse power supply. In the first phase of the experiments for 5754 aluminum alloy, the factors selected for the experiment were power input (torch speed, voltage, current, wire feed), pulse frequency, gas flow rate and surface condition. A full factorial design of experiment (DOE) was conducted (DOE #1) to understand the main and interaction effects on lap joint failure and weld penetration. Based on the results from phase 1 results, surface condition was eliminated in the phase 2 experiments. In phase 2 experiments for heat treatable alloys 6063 T6, the factors selected were power input (torch speed, voltage, current, wire feed), pulse frequency, gas flow rate, torch angle, and arc intensity. A partial factorial DOE was conducted (DOE # 2) primarily to understand the main effects and some two level interaction effects. For both phase 1 (non-heat treatable alloy 5754) and phase 2 (heat treatable alloy 6063-T6) experiments, the factors influence on the mechanical properties of the lap joint, metallurgy (weld penetration) and micro hardness were evaluated. Post weld analysis indicates for non heat treatable alloy 5754, power input and gas flow rate are the two signficant factors (statistically) based on lap shear load to failure and weld penentration data. For heat treatable alloy 6063, power input was the significant factor on joint load to failure, however, for weld penetration, power input, pulse frequency and gas flow rate were the significant factors. Based on the joint strength and weld penetration, optimum weld process factors were determined for both non-heat treatable alloy 5754 and heat treatble alloy 6063 T6.

Commentary by Dr. Valentin Fuster
2007;():725-726. doi:10.1115/IMECE2007-43567.

Composite structures in an aircraft are susceptible to impact damage, which can occur during manufacture, service or maintenance. Recent studies show that impacts with ground support equipment are the major cause of in-service damage to composite structures in an aircraft. Other sources of impact include collision with birds, runway stones or ballistic impacts. These impacts can produce various types of damage, including fiber breakage, matrix cracking, delamination, and interfacial debonding. The results of such damage can have detrimental effects on the overall structural performance and safety. A comprehensive structural health monitoring (SHM) system provides a means to significantly reduce life-cycle costs of aerospace vehicles by providing accurate diagnostics and prognostics of structural damage to reduce unnecessary inspections and support vehicle life extension. The main objective of this paper is to develop a methodology to detect and identify the damage sources and their severity in composite laminates subjected to low velocity impact using wave propagation methods. When damage occurs in a material due to mechanical load or impact, an acoustic wave emits and propagates through the material. The material chosen for this work is a 12″ long and 12″ wide, +/− 60 degree braided composite. Two edges of the plate were fixed by clamping the plate between two steel bars and secured by bolts spaced 1″ apart, while the other two edges were free, as shown in Figure 1. In order to characterize the wave propagation and damage process, two resonant type AE sensors and four accelerometers were mounted on the specimen. The specimen was then tapped lightly with a hand-held acoustic impact hammer at several different chosen locations, and stress wave signals were monitored using a commercial dynamic signal process system which contains software capable of detecting impact source location. The impact force was kept to a minimum initially such that no damage occurred in the specimen. After this initial test, the specimens were subjected to low velocity impact using drop weight impact machine with 0.5 inch spherical indenter. The impact force was increased by a number of times until substantial damage observed while monitoring signals generated from the specimen. After each incremental impact, both acoustic hammer tapping test and nondestructive inspection such as ultrasonic C-scan and/or X-ray radiography were carried out to delineate the damage source and severity. Figure 2 is an example of C-Scan of the composite plate after a series of impacts with various drop heights. Recorded signals were analyzed to determine the origin of the source and its severity. The impact hammer produced both an extensional wave and a flexural wave in these composite plate specimens. Because of dispersive characteristics of the flexural wave, the first arrival time of the extensional wave was used for source location algorithm. Besides the source location, discussion will be given on parameters such as amplitude, energy, frequency, number of events related with impact force, and damage size in detail. As an example, Figure 3 is a plot of the measured damage size as a function of the dead-weight drop height for tests conducted on various panels. As expected, the size of the damage increases with amount of drop height (or impact energy). Thus, based on C-scan measurements, critical threshold impact height of approximately 5″ is identified for “any measurable” damage to occur. The corresponding magnitude of the impact energy is ∼ 108 in-lb. On the other hand, the critical threshold for any visual damage to be detected is approximately 502 in-lb for the laminate material investigated. In summary, a methodology has been developed for estimating the damage severity from the amplitude of the signal received. The approach entails constructing design curves relating the size of the damage to impact energy, and establishing relationships between impact energy and the magnitude of the signal. These relationships can then be used to predict the estimated size of the damage based on the amplitude of the arriving signal. A critical threshold impact energy has been identified below which “no measurable” damage occurs. Three regions of damage growth, namely, a decreasing rate with magnitude of impact energy. A constant damage growth rate characterizes the steady-state region, while damage size increases almost exponentially with impact energy in the tertiary region potentially leading to catastrophic failure.

Commentary by Dr. Valentin Fuster
2007;():727-729. doi:10.1115/IMECE2007-43588.

Simplex optimization algorithm was applied to predict the fiber orientations of the scarf repair patch for a given quasi-isotropic panel to maximize strength retention of the repair. The optimal stacking sequence of the repair patch avoids 0 degree plies in the direction of the load. Such a stacking sequence prolongs the life of the adhesive and results in a predicted 13% strength increase as compared to the traditional ply-by-ply replacement. The second optimization problem solved was one of finding the least favorable stacking sequence of the repair patch. Such stacking sequence inserts stiff plies into the patch and leads to the failure of the repair patch as early as 20% below the reference failure load of the repair patch with traditional ply-by-ply replacement. The strength prediction model consisted of nonlinear constitutive modeling of adhesive behavior and fiber failure prediction loads in the adherents based on critical failure volume (CFV) (see [8]) strength prediction method. Benchmark analysis was performed on the virgin, scarfed, and repaired (ply-by-ply replacement) panels and was in good agreement with experimental data.

Commentary by Dr. Valentin Fuster
2007;():731-737. doi:10.1115/IMECE2007-44007.

This paper presents ultrasonic assisted friction stir welding (UaFSW), which is suggested to improve the weld quality and efficiency as a hybrid welding system. Ultrasonic-assisted processes have been coupled with tooling in various manufacturing processes to enhance the performance of conventional machining and bonding processes. For successful and effective implementation of the UaFSW, we must first consider how to integrate ultrasonics into the friction stir welding equipment. To solve this problem, we designed an ultrasonic horn to vibrate the FSW tool and transmit ultrasonic energy into the workpiece. Using a numerical modal and harmonic analysis, we fabricated and analyzed the ultrasonic horn under specific design considerations. Force was measured and compared during ultrasonic assisted and conventional friction stir welding. The mechanical properties of the workpieces were also investigated.

Topics: Friction , Welding , Design
Commentary by Dr. Valentin Fuster
2007;():739-744. doi:10.1115/IMECE2007-44115.

Fiber-reinforced polymer (FRP) composites are increasingly used in structural systems, replacing structural steel and aluminum. It is now well established that adhesive bonding is the most efficient mean of joining composites. Unfortunately, analytical models available in the literature offer design equations mainly applicable to balanced adhesive joints; where the two adherends are identical. In many practical applications, however, FRP composites are used (joined) in conjunction with other materials. This paper presents a simplified model that accurately predicts the behaviour of adhesive joints between different adherends. In this model, exponentially small terms are removed from the analytical solution, greatly simplifying the solution. The resulting design equations provide an accurate method of the design and analyzing of adhesive joints. The model applies to single-lap, single-strap and stiffener-plate joints, where shear and peel stresses are present. Furthermore, the model is easily extended to determine the energy release rate in adhesive joints. Results from the analytical model closely agree with finite element results, which are obtained in a fraction of the time and effort required for a non-linear finite element analysis.

Commentary by Dr. Valentin Fuster

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