bluuebunny/crossref_metadata_2025 huggingface dataset:
The Importance of Including Size Effect When Modeling Slot Milling
Authors: Melkote S. N. , Endres W. J.
Published: February 2008

This paper presents a detailed mechanistic force analysis that includes size effect for slot milling operations. Existing studies of the milling process have modeled the slot end milling operation as a simple geometric extension of peripheral end milling models with constant values for the specific energies used to predict forces for a given cutter geometry and cutting conditions. This paper addresses the limitations of this approach for accurate predictions of the instantaneous cutting force variation, particularly for steady-state slotting with four-flute cutters. It is shown through a comparison of model simulations and experimental results that significantly improved predictions of the cutting force variation are obtained by properly accounting for the size effect in slotting. The dependence of the cutting force variation on axial depth of cut and helix angle is demonstrated. Practical implications of selecting helix angle and axial depth of cut based on the improved slot end milling model are also discussed. Modeling approaches other than the mechanistic approach considered here are also noted in this light.
Experimental Validation of a Dynamic Workpiece Steady Control Method for Traverse Grinding
Authors: Gao Yongsheng
Published: February 2008

In order to achieve high accuracy and surface quality during traverse grinding of long, slender workpieces, multiple workpiece steadies with soft supporting pads should be used. Due to the complex interaction between the workpiece and the steadies and also the deflection of the pads the control of the steadies becomes difficult. Previous work has proposed and examined the potential for a dynamic workpiece steady control method. In this study, the use for workpiece steadies is further discussed and accuracy testing for the workpiece measurement system presented. The results of the experimental validation tests show that the dynamic workpiece steady control method together with the iterative pad position design algorithm is efficient and effective in achieving required workpiece accuracy and surface quality. The control model for the traverse grinding system using workpiece steadies is verified by agreement between the results obtained experimentally and those obtained theoretically. Necessary measures for further improvement are also discussed.
Finite Element Analysis of Heat Flow in Dual-Beam Laser Welded Tailored Blanks
Authors: Liu Yu-Ning , Kannatey-Asibu E.
Published: February 2008

A two-dimensional moving adaptive finite element analysis is presented for dual-beam laser welded tailored blanks. The phase change effect, temperature dependence of material properties, and convection and radiation heat transfer are considered. The simulation results show that welding with a dual-beam system to induce preheating reduces cooling rates effectively. The cooling rate in the thin blank is observed to be slightly higher than that in the thick blank at a given temperature. For example, at 650°C, 2 mm away from the weld centerline, the cooling rates are calculated to be 362°C/sec and 373°C/sec in the thick (2 mm) and thin (0.8 mm) blanks, respectively, for a welding speed of 1.5 cm/sec and beam power of 900 W on mild steel. For the same welding conditions, but with a preheating power of 400 W and inter-beam spacing of 1 cm, the cooling rates reduce to 212°C/sec and 228°C/sec in the thick and thin blanks, respectively. Experiments undertaken for verification show close correlation between the simulation and experimental results.
Thermal and Design Sensitivity Analyses for Cooling System of Injection Mold, Part 1: Thermal Analysis
Authors: Park S. J. , Kwon T. H.
Published: February 2008

In recent years, increased attention has been paid to the design of cooling systems in injection molding, as it becomes clear that the cooling system affects significantly both productivity and part quality. In designing the cooling system of a mold efficiently in terms of rapid and uniform cooling, it would be desirable for mold designers to have an optimal CAD system. For this optimal design, one needs capabilities of both a thermal analysis (to be discussed in Part 1) and a corresponding DSA (to be presented in Part II) for the 3-d mold heat transfer during the cooling stage of an injection molding process. It was found that seemingly negligible inaccuracy in the thermal analysis result sometimes leads to meaningless DSA result. With a successful DSA being an intermediate goal towards optimum design, we have improved the thermal analysis system based on the modified BEM in terms of accuracy and developed rigorous treatments of B.C.s appropriate for DSA by considering the following issues: (i) numerical convergency, (ii) the series solution in part thermal analysis, iii) treatment of tip surface of line elements, (iv) treatment of coolant, and (v) treatment of mold exterior surface. Using two examples, this paper amply demonstrates the importance of these issues.
Optimum Blank Shapes for Prismatic Cup Drawing—Consideration of Friction and Material Anisotropy
Authors: Lo Sy-Wei , Lee Jing-Yeong
Published: February 2008

A theory employing the concept of potential flow and an easily implemented numerical method are developed. It can offer a preliminary prediction of the optimum blank shape with a little computational effort. The effects of the material anisotropy and the interfacial friction between the workpiece and blank holder on the material flow can be modeled by superimposing a “sink” or “source” term in the potential field. Variations in the cup wall thickness are considered. Both convex and non-convex punch profiles are studied. Generally speaking, the contours of the present theory are smoother than the solutions from the slip-line method. The discrepancy of the optimum blank contours between the plane strain and anisotropic cases is more significant for polygon and irregular cup drawing. The influence of friction on the optimum blank contour is not negligible.
Automatic Tuning and Regulation of Injection Molding by the Virtual Search Method
Authors: Ivester R. , Danai K.
Published: February 2008

Methodical specification of process inputs for injection molding is hindered by the absence of accurate analytical models. For these processes, the input variables are assigned either by trial and error, based on heuristic knowledge of an experienced operator, or by statistical Design of Experiments (DOE) methods which construct a comprehensive empirical model between the inputs and part quality attributes. In this paper, an iterative method of input selection (tuning) referred to as the Virtual Search Method (VSM) is introduced that conducts most of the search for appropriate machine inputs in a ‘virtual’ environment provided by an approximate input-output (I-O) model. VSM applies the inputs to the process only when it has exhausted the search based on the current I-O model. It evaluates the quality of inputs from the search and updates the I-O model for the next round of search based on measurements of part quality attributes (e.g., size tolerances and surface integrity) after each process iteration. According to this strategy, VSM updates the model only when needed, and thus selectively develops the model as required for tuning the process. This approach has been shown to lead to shorter tuning sessions than required by DOE methods.
Chatter in the Strip Rolling Process, Part 2: Dynamic Rolling Experiments
Authors: Yun I-S. , Ehmann K. F. , Wilson W. R. D.
Published: February 2008

This paper presents the results of dynamic rolling experiments examining the variations in rolling force, back tension and roll gap in response to a sinusoidal dynamic component of various frequencies being superimposed on the roll gap or back tension. Comparisons between the experimental results and the corresponding simulation results are also presented to investigate the validity of the new dynamic model of the rolling process presented in Part 1 of this paper.
A Systematic Approach for Analyzing the Fixturability of Parts for Machining
Authors: Ong S. K. , Nee A. Y. C.
Published: February 2008

Design for manufacturability (DFM) is a growing concern in the academia as well as the industry. However, an evaluation of the manufacturability of the features on a part is incomplete without considering the work-holding requirements of and the pre-processes that have been performed on the part (i.e., the initial state of the part before machining could be a casting or a prismatic block). A feature on a part, which has been evaluated to be manufacturable in its own right, might not be achievable when it is being machined together with other features in a set-up, if the part cannot be properly fixtured during the machining of this set-up. In this paper, the authors proposed a fuzzy set based fixturability evaluation procedure for establishing fixturing relations between the features on a part and assessing the suitability of these features for use as fixturing features during the machining of other features on the part. The overall fixturability of a part as a whole is evaluated after a set-up plan has been formulated for producing it and a fixture configuration and a fixturability index have been found for each of the set-ups in this set-up plan. Although the methodology has been formulated for machining features of prismatic parts, the approach is also applicable to castings and non-prismatic parts. The fuzzy membership functions for assessing the fixturing properties of features are generic to features that are found on castings and prismatic parts.
A Comprehensive Identification of Tool Failure and Chatter Using a Parallel Multi-ART2 Neural Network
Authors: Li X. Q. , Wong Y. S. , Nee A. Y. C.
Published: February 2008

Tool failure and chatter are two major problems during machining. To detect and distinguish the occurrences of these two abnormal conditions, a novel parallel multi-ART2 neural network has been developed. An advantage of this network is more reliable identification of a variety of complex patterns. This is due to the sharing of multi-input feature information by its multiple ART2 subnetworks which allow for finer vigilance thresholds. Using the maximum frequency-band coherence function of two acceleration signals and the relative weighted frequency-band power ratio of an acoustic emission signal as input feature information, the network has been found to identify various tool failure and chatter states in turning operations with a total of 96.4% success rate over a wide range of cutting conditions, compared to that of 80.4% obtainable with the single-ART2 neural network.
Design Evaluation of Sheet Metal Joints for Dimensional Integrity
Authors: Ceglarek D. , Shi J.
Published: February 2008

The design of joints between parts is one of the most critical issues in the design of sheet metal assemblies. This paper presents a new part-to-part joint design evaluation index developed for dimensional control of sheet metal assemblies. The proposed index provides a new analytical tool to address the dimensional capabilities of an assembly process in the early product design stage. It covers the three basic types of joints, which encompass the whole domain of joints used in sheet metal assembly. The part-to-part interactions for each type of joint are studied, and an analytical model is provided. Two evaluation indices, (1) product joint design evaluation and (2) critical part determination, are developed. The developed methodology is demonstrated using two industrial design examples of sport-utility automotive bodies.
Sheet Metal Joint Configurations and Their Variation Characteristics
Authors: Liu S. Charles , Hu S. Jack
Published: February 2008

In sheet metal assembly, joints are designed to facilitate welding the parts. The three basic joints used in sheet metal assemblies are lap (slip) joints, butt joints, and butt-lap (corner) joints. Each joint configuration has its own variation characteristics. However, the currently available variation analysis methods, such as worst case analysis, root sum squares, etc., are not applicable to deformable sheet metal because they are based on rigid bodies. This paper analyzes the variation characteristics of simple assemblies constructed from the three basic joints, using Mechanistic Variation Simulation. Mechanistic Variation Simulation combines engineering structural models with statistical analysis in predicting deformable sheet metal assembly variation. Furthermore, the variation characteristics of the boxes constructed from the three basic joints are also evaluated. The developed models and analysis provide an improved understanding of sheet metal product design and process design.
Analyzing the Probabilities of Natural Resting for a Component With a Virtual Resting Face
Authors: Ngoi B. K. A. , Lim L. E. N. , Lee S. S. G.
Published: February 2008

This paper introduces a new approach to predicting the natural resting behavior of a part of irregular prismatic cross-sectional shape. The methods proposed by Boothroyd, Redford, Poli, and Murch (1972) and Boothroyd and Ho (1977), successfully analyzed parts whose centers of gravity were located at the geometric center. The hypothesis presented here employs the centroid solid angle of parts of irregular cross-sectional shape with virtual resting faces, such as the L-section. It postulates that the probability of the respective natural resting surfaces of a part coming to rest is directly proportional to the centroid solid angle and inversely proportional to the height of the center of gravity from that surface. The proposed hypothesis is compared with the Energy Barrier Method and experimental results obtained from drop-tests of the L-shaped part. The theoretical results agree well with the experimental results, with the maximum deviation not exceeding 6 percent.
Design and Implementation of a Tube Wall Thickness Measurement System
Authors: Ludwick S. J. , Jenkins H. E. , Kurfess T. R.
Published: February 2008

This paper describes the design and implementation of a gage for measuring the wall thickness of hot rolled steel tubing at an actual production facility. The design is based upon a statistical analysis of the tube samples, and upon the economic realities of mill operating conditions. Issues relating to time constraints, uneven sample preparation, a mill operating environment, and differences between gage operators are addressed. The gage records more data from the tubes than could be taken manually, and therefore allows the accompanying software to apply unique algorithms for the calculation of hexing and eccentricity in each sample. All results are recorded and stored in a database for continuous use in statistical process control.
Process Mean Shift Detection Using Prediction Error Analysis
Authors: Hu S. J. , Liu Y. G.
Published: February 2008

Autocorrelation in 100 percent measurement data results in false alarms when the traditional control charts, such as X and R charts, are applied in process monitoring. A popular approach proposed in the literature is based on prediction error analysis (PEA), i.e., using time series models to remove the autocorrelation, and then applying the control charts to the residuals, or prediction errors. This paper uses a step function type mean shift as an example to investigate the effect of prediction error analysis on the speed of mean shift detection. The use of PEA results in two changes in the 100 percent measurement data: (1) change in the variance, and (2) change in the magnitude of the mean shift. Both changes affect the speed of mean shift detection. These effects are model parameter dependent and are obtained quantitatively for AR(1) and ARMA(2,1) models. Simulations and examples from automobile body assembly processes are used to demonstrate these effects. It is shown that depending on the parameters of the AMRA models, the speed of detection could be increased or decreased significantly.
Manufactured Part Modeling for Characterization of Geometric Variations of Automotive Spaceframe Extrusions
Authors: Wang Yu (Michael) , Gupta S. , Hulting F. L. , Fussell P. S.
Published: February 2008

This article presents a method for characterizing geometric shape variations in manufactured automotive spaceframe extrusions using measurement data obtained by a Coordinate Measurement Machine (CMM). With a manufacturing perspective, a modeling scheme is proposed for representing the actual shape of the extrusions. Systematic deviations in the geometry of the parts from their theoretically perfect design description models are described by the critical parameters of their manufactured part models (MPMs), which are constructed by fitting CMM data through an optimization. The manufactured part model can then be interpreted in a meaningful way for improving bending process as well as quantifying the process capability. An application of the methodology is illustrated through the analysis of experimental data for rotary draw bent extrusions used in the aluminum intensive automobiles.
An Investigation of the Cutting Process for Chip Breaking Monitoring in Turning of Steels
Authors: Grzesik W. , Bernat P.
Published: February 2008

This paper presents some results of an experimental study on chip breaking monitoring when turning steels with chip forming inserts. In the first part of this study the recognition of chip forms by means of cutting force analysis in the frequency domain is described. Generally, the present work is concerned with the use of the interface control factor for determining the transition from unacceptable chip forms to the chip breaking. For this purpose experiments under approximately orthogonal machining conditions including measuring the shear strain, the cutting energy and the average interface temperature are carried out. The obtained results confirmed that the initiation of acceptable chip breaking for a wide range of cutting conditions and the three steels used could be predicted in terms of an appropriate energy consumption rate. An architecture for on-line cutting state monitoring system based on signal processing procedure in the frequency domain is developed and the performance of the system is experimentally evaluated.
An Analytical and Experimental Study of Cleaning With Moving Waterjets
Authors: Meng P. , Geskin E. S. , Leu M. C. , Li F. , Tismeneskiy L.
Published: February 2008

A mathematical model of cleaning with moving waterjet is established by considering the structure of waterjet and applying Springer’s semi-empirical model on material erosion due to impact of water droplets. Based on this model, the cleaning width as a function of travel speed, standoff distance, water pressure, and nozzle radius is derived. Also derived is the relation of the critical cleaning standoff distance to travel speed, water pressure, and nozzle radius. The validity of the derived relations is verified by conducting moving waterjet experiments with varied cleaning system parameters.
Improving Laser Cutting Quality for Two-Dimensional Contoured Paths
Authors: Di Pietro P. , Yao Y. Lawrence
Published: February 2008

Quality improvements in laser cutting of mild steel have been achieved by a newly developed model-based optimization strategy and its application to one-dimensional cut has been reported early. The specific aims of this paper are to assure quality of cut when cornering and generating small diameter holes. Such routines encompass a large proportion of all features processed on laser cutting systems, and therefore their successful production is significant. Currently, extensive trial-and-error based experimentation is needed in order to improve quality for these routines. Thus model-based optimization has the benefit of reducing this time-exhaustive step whilst leading to an optimal solution. Nonlinear power adaptation profiles are generated via the optimization strategy in order to stabilize cutting front temperatures. Uniform temperatures produce better quality by reducing (i) kerf widening effects, (ii) heat-affected zone extents, and (iii) workpiece self-burning effects. Experimental results are presented, and it is demonstrated that such process manipulation can produce significant quality improvements. In addition, predicted heat-affected zones correlate closely to those actually obtained. The process manipulation is successfully implemented in an industrial laser cutting system under laboratory condition.
Noncontact Ultrasonic Sensing for Seam Tracking in Arc Welding Processes
Authors: Zhang S. B. , Zhang Y. M. , Kovacevic R.
Published: February 2008

A novel seam tracking technology based on high frequency ultrasound is developed in order to achieve high accuracy in weld seam identification. The transmission efficiency of the ultrasound is critical for obtaining a sufficient echo amplitude. Since the transmission efficiency is determined by the difference in impedance between the piezoelectric ceramic and air, match layers are designed to optimize the transmission efficiency by matching impedance. Since the air impedance depends on the density and velocity of the ultrasound, which both depend on the temperature, the optimization has been done for a wide bandwidth. Also, the receiving circuit is designed so that its resonance frequency matches the frequency of the ultrasound. As a result, the sensitivity of the noncontact ultrasonic sensor is improved 80-fold. By properly designing the focal length of the transducer, a high resolution ultrasound beam, 0.5 mm in diameter, is achieved. Based on the proposed sensing technology, a noncontact seam tracking system has been developed. Applications of the developed system in gas tungsten arc welding (GTAW) and CO2 gas metal arc welding (GMAW) processes show that a tracking accuracy of 0.5 mm is guaranteed despite the arc light, spatter, high temperature, joint configuration, small gap, etc.
Analysis of Resin Transfer Molding With High Permeability Layers
Authors: Tari M. J. , Imbert J. P. , Lin M. Y. , Lavine A. S. , Hahn H. T.
Published: February 2008

In resin transfer molding (RTM) a high permeability layer (HPL) is placed on top of the fiber mat lay-up to reduce mold filling time and increase the ultimate distance resin can be drawn into the mold. HPL’s are particularly useful in vacuum bag resin transfer molding (VBRTM), where driving pressures are relatively low. When compared to traditional closed mold RTM, VBRTM has the advantages of low capital costs and short start up time. The goal of the current research is to investigate how an HPL can be used to improve quality and process efficiency for parts of complex geometry made by both conventional and vacuum bag RTM. As a first step towards this goal, the effect of the HPL on the flow field has been studied through analysis, experiment and simulation. As expected, the use of the HPL creates a transverse (i.e., top-to-bottom) flow in the fiber mat, facilitating mold filling. The thickness of the HPL has been varied to determine the effects on the flow front. The experimental results validate the capability of the simulation to model two-dimensional flow in a porous medium with heterogeneous permeability.
Shape Deposition Manufacturing With Microcasting: Processing, Thermal and Mechanical Issues
Authors: Amon C. H. , Beuth J. L. , Weiss L. E. , Merz R. , Prinz F. B.
Published: February 2008

Shape deposition manufacturing (SDM) is a solid freeform fabrication (SFF) methodology for automatically building up material layers to form three-dimensional, complex-shaped, multi-material structures. Microcasting is a molten metal droplet deposition process which is able to create fully dense metal layers with controlled microstructures. SDM combines microcasting with other intermediate processing operations, such as CNC machining and shot peening, to create high quality metal parts. In this paper, a description is given of SDM and the microcasting process. An overview of thermal and mechanical issues associated with SDM and microcasting is presented, including the control of interlayer metallurgical bonding through substrate remelting, the control of cooling rates of both the substrate and the deposited material and the minimization of residual thermal stress effects. Thermal models are used to study the issue of localized remelting of previously deposited material by newly deposited molten droplets to achieve metallurgical bonding. Mechanical modeling provides insight into residual stress build-up during part manufacture and residual stress-driven debonding between deposited layers.
A Slip-Line Field for Ploughing During Orthogonal Cutting
Authors: Waldorf D. J. , DeVor R. E. , Kapoor S. G.
Published: February 2008

Under normal machining conditions, the cutting forces are primarily due to the bulk shearing of the workpiece material in a narrow zone called the shear zone. However, under finishing conditions, when the uncut chip thickness is of the order of the cutting edge radius, a ploughing component of the forces becomes significant as compared to the shear forces. Predicting forces under these conditions requires an estimate of ploughing. A slip-line field is developed to model the ploughing components of the cutting force. The field is based on other slip-line fields developed for a rigid wedge sliding on a half-space and for negative rake angle orthogonal cutting. It incorporates the observed phenomena of a small stable build-up of material adhered to the edge and a raised prow of material formed ahead of the edge. The model shows how ploughing forces are related to cutter edge radius—a larger edge causing larger ploughing forces. A series of experiments were run on 6061-T6 aluminum using tools with different edge radii—including some exaggerated in size—and different levels of uncut chip thickness. Resulting force measurements match well to predictions using the proposed slip-line field. The results show great promise for understanding and quantifying the effects of edge radius and worn tool on cutting forces.
An Empirical Tool Force Model for Precision Machining
Authors: Arcona C. , Dow Th. A.
Published: February 2008

The accuracy of precision machining operations could be improved through tool force feedback. Tool force is ideally suited for use in a control algorithm because it contains information on the instantaneous depth of cut, feed rate and condition of the tool. A tool force model that could form the basis of this new control technique has been developed. By measuring the shear angle from micrographs of chip cross sections, equations for the forces due to chip formation and the friction between the chip and the tool have been written. Furthermore, the effects of elastic deformation of the workpiece (spring back) on chip formation and the measured forces, which can be significant in precision machining, have been included in the model. Machining experiments were conducted with a 0 deg rake diamond tool and four metals that are commonly diamond turned. For machining with newly lapped as well as worn tools, the calculated forces were in excellent agreement with the measured values for the array of workpiece materials.
Analysis of Contact Mechanics for a Circular Filamentary Brush/Workpart System
Authors: Shia C.-Y. , Stango R. J. , Heinrich S. M.
Published: February 2008

This paper addresses the contact problem associated with the filament/workpart interaction that arises during brushing processes. A discretized model of a filament within the brushing tool is developed by employing Lagrange’s equations in conjunction with special constraint equations that are appropriate for the impact and impending large displacement of a flexible fiber whose tip traverses a flat, rigid surface. This formulation leads to the identification of five nondimensional parameters which fully characterize the filament/workpart contact problem. A damping mechanism is also included which can be used for modeling complex filament interactions that arise during the actual brushing operation. Special consideration is given to examining the initial filament/workpart impact and the subsequent forces that are generated along the contact region. Initial velocity of the filament is determined by employing an inelastic impact mechanics analysis. Time-varying transient response of the filament is then obtained by employing a predictor-corrector technique in conjunction with a finite difference method. Overall brush force is computed by a superposition of filament contact forces exerted onto the workpart surface. Numerical results are reported and compared with experimentally obtained data for an actual brush/workpart system.
Rapid Tooling for Sheet Metal Forming Using Profiled Edge Laminations—Design Principles and Demonstration
Authors: Walczyk D. F. , Hardt D. E.
Published: February 2008

Sheet metal forming dies constructed of laminations offer advantages over more conventional tooling fabrication methods (e.g. CNC-machining) in terms of tooling accessibility, reduced limitations on die geometry and faster fabrication with harder die materials. Furthermore, the recently introduced Profiled Edge Lamination (PEL) tooling method improves upon other lamination-based tooling methods. Adoption of this promising rapid tooling method by industry is being hindered by the lack of formal analysis, design principles, and manufacturing requirements needed to construct dies in such a manner. Therefore, the propensity for delamination of the die is discussed and preventive measures are suggested. The basic machining instructions, i.e., an array of points and directional vectors for each lamination, are outlined for both compound and planar profiled-edge bevels. Laser, AWJ and flute-edge endmilling are experimentally identified as the most promising methods for machining bevels. Development of a stand-alone PEL fabrication machine is suggested over retrofitting commercially-available 5-axis machines. Finally, the general procedure for creating PEL dies is implemented in the construction of a matched set of sheet metal forming tools. These tools are used to successfully stamp a sheet metal part out of draw-quality steel.
The Ring Test for P/M Materials
Authors: Dutton R. E. , Goetz R. L. , Shamasundar S. , Semiatin S. L.
Published: February 2008

The application of the ring test to assess die-workpiece interface friction during forging of powder metallurgical materials has been investigated. As for fully dense materials, the change in internal diameter as a function of height reduction was used to quantify friction. To this end, calibration curves were generated by conducting finite element method (FEM) simulations of ring forging with different friction factors. The method was validated by conducting isothermal, hot compression tests on rings of an alpha-two titanium aluminide alloy with starting densities of 75, 85, or 100 percent of full theoretical density. Comparison of the test data to the calibration curves revealed somewhat higher friction factors for the porous materials (as compared to the fully dense material) for both lubricated and unlubricated interface conditions. Furthermore, the accuracy of the FEM simulations of the ring test was confirmed by good agreement between measured and predicted density distributions and load-stroke curves for tests on the porous titanium aluminide material.
Three-Dimensional Finite Element Analysis for the Stamping of a Motorcycle Oil Tank
Authors: Chen Fuh-Kuo , Chiang Bai-Hong
Published: February 2008

The three-dimensional finite element analysis was performed to determine an optimum die design and the corresponding sheet-blank shape for stamping a part of motorcycle oil tank. To save the computation time, an equivalent drawbead model was adopted to replace the actual drawbead shape in the finite element simulations. The forming limit diagram constructed from stretching tests was also used in conjunction with the finite element results to predict the occurrence of fracture. The optimum die design and the corresponding sheet-blank shape obtained from the finite element analysis was validated by the achievement of defect-free production panels. The advantage of using the finite element analysis for the stamping die design was thereby confirmed.
Optimal Open-Loop Ram Velocity Profiles for Isothermal Forging: A Variational Approach
Authors: Berg J. M. , Frazier W. Garth , Chaudhary A. , Banda S. S.
Published: February 2008

This paper considers the problem of selecting the ram velocity profile in an isothermal forging, to best obtain a desired material microstructure. This is to be accomplished by tracking a prescribed strain rate profile. A weighting function, reflecting the rate at which the microstructure is transforming, describes the relative importance of different parts of the billet. Finding the optimal solution generally requires a search over an infinite-dimensional function space. However, for a certain class of forgings the task reduces to solving a single ordinary differential equation. The result is a globally optimal and unique ram velocity profile. The method is demonstrated for the simulated forging of a TiAl turbine disk.
Sensor Location Optimization for Fault Diagnosis in Multi-Fixture Assembly Systems
Authors: Khan A. , Ceglarek D. , Ni J.
Published: February 2008

The effectiveness of fault diagnosis in assembly is contingent on the effectiveness of the sensor measurement of assembled parts. Using a diagnosability enhancement methodology for a single fixture, a means to achieve an optimal sensor configuration for a multi-fixture assembly of sheet metal parts is proposed. A Hierarchical Group description of the assembly is used to build a State-Transition representation which, with fixture CAD information, is used in multi-level hierarchical optimization to arrive at the optima. A defined Coverage Effectiveness Index quantifies fault isolation performance. The index also serves to evaluate the performance effectiveness of the measurement station location and change in the sensor number. The approach has significant utility in automotive body assembly where system complexity makes the choice of sensor location vital to fault isolation performance. Examples using multi-fixture simulated and industrial automotive body assembly sequences are provided to illustrate the methodology.
An Integrated Model of the Material Handling System and Unit Load Design Problem
Authors: Noble J. S. , Klein C. M. , Midha A.
Published: February 2008

Material flow system design problems (i.e. facility layout, material handling equipment selection and specification, flow path design, unit load sizing, cell design, warehousing, routing, etc.) have been predominately modelled independently in the past. Independent consideration of each design problem has reduced the solution complexity, but in the process has caused a loss in problem reality. This paper reviews recent developments in integrated approaches to material flow design and presents a model which integrates material handling equipment selection and specification (including material handling interface equipment) and path/load dependent unit load size. The formulation is solved using the meta-heuristic procedure of tabu search to find good solutions to the more realistic (and more complex) model formulation.
Bifurcation and Catastrophes in Metal-Cutting Processes
Authors: Shi Hanmin , Wang Xibing , Lu Tao
Published: February 2008

Based on a theoretical model and the Principle of Minimum Energy [1, 2, 3] the bifurcation and catastrophes in a non-free cutting process are theoretically predicted and experimentally verified. The phenomena lead to the complexity of a cutting process with very strong non-linearity and may be the source of the difficulties in its control.
The Correlation Between the Cutting Fluid Pressure Distribution and the Topography of Tool Wear in BTA Drilling
Authors: Astakhov V. P. , Karam S. Abi , Osman M. O. M.
Published: February 2008

This paper investigates experimentally the correlation between the cutting fluid pressure distribution in the bottom clearance (the space enclosed by the bottom of the hole being drilled from one side and the flanks of the drill head from the other) and the flank wear of BTA drills. Two types of BTA drills were studied representing two basic drill designs in the current use: single- and multi-edge drilling heads. Experiments included the study of the bottom clearance topology, the measurements of the cutting fluid pressure distribution in the bottom clearance, and the study of the tool wear topology. The results reveal the notable correlation between the cutting fluid pressure distribution in the bottom clearance and the topography of tool wear.
Impact Fracture of Screws for Disassembly
Authors: Studny D. , Rittel D. , Zussman E.
Published: February 2008

Environmental legislation urges manufacturers to develop effective technologies to cope with obsolete products. The goal is to optimize the disassembly procedure (cost, efficiency) with emphasis on potential recycling. In this work we adopt a destructive approach to product disassembly as an alternative to reverse assembly. Specifically we investigate unsupported screwed assemblies for which the screw head is protruding. Disassembly consist of breaking this head by applying side impact. The transient forces are measured by means of an instrumented bar. Experiments were conducted on various screw diameters and materials to assess the feasibility of this process. Typical design parameters (energy, time and forces) were measured. The fracture mechanism(s) was characterized by fractographic analysis. Results are presented and potential applications of this technique to efficient disassembly are discussed. The results are integrated into the preliminary design of robotic disassembler.
Tool Path Generation Using C-Space for 5-Axis Control Machining
Authors: Morishige K. , Takeuchi Y. , Kase K.
Published: February 2008

The paper deals with the method of tool path generation for 5-axis control machining using a ball end mill. 5-axis control machining has been used for aircraft parts as well as for complicated shapes such as mold and dies. However, most of the present CAM systems for 5-axis control machining have limited functions in terms of tool collision, workpiece shapes and machining methods. For that reason, in many cases the optimal cutter location (CL) data cannot be obtained or considerable time is consumed. To solve this problem, we applied a 3-dimensional configuration space (C-Space) and showed the relationship between all tool positions and postures and the existence of tool collision. The method of tool path generation devised in the study enables users to generate CL data reflecting their own machining strategy such as smooth change in tool posture and the state of machining without considering the gouging. The validity of this method was experimentally confirmed by successfully milling an impeller without tool collision occurring.
Analysis of Burr Formation Mechanism in Orthogonal Cutting
Authors: Hashimura M. , Chang Y. P. , Dornfeld David
Published: February 2008

To prevent problems caused by burrs in machining, reduction and control of burr size is desirable. This paper presents a basic framework for and conceptual understanding of the burr formation process based upon the material properties of the workpiece. In order to verify this framework and explain the basic phenomena in the burr formation process, the deformation at the edge of the workpiece was analyzed using a finite element method (FEM). Micro-machining tests under an optical microscope and a scanning electron microscope using Al-2024-O material were also done to observe the burr formation process. The feed rate and tool edge radius were varied and the resulting burr formation observed. FEM analysis of burr formation in the 2024 material and observation of the deformation at the workpiece edge in the micro-machining tests verified the proposed conceptual understanding of the burr formation process. For the experimental conditions examined, all of the burrs in Al-2024-O were “negative” burrs, that is, edge breakout. As the feed was increased two effects were observed. One effect was an increase in the resulting burr thickness. Another effect, which was observed during the burr initiation stage while machining with a sharp tool, was an increase in both the distance and depth of the initial pivoting point of the burr from the tool edge.
The Design and Analysis of a Polypropylene Hub CBN Wheel to Suppress Grinding Chatter
Authors: McFarland D. M. , Bailey G. E. , Howes T. D.
Published: February 2008

This research investigated the addition of flexibility into a CBN grinding wheel to suppress regenerative chatter, and illustrates some design features that should be present in such a wheel. Flexibility was added by replacing the hub of an aluminumhub CBN grinding wheel with polypropylene, decreasing the bulk stiffness to approximately 12 percent of its original value. Experiments showed that the modified wheel met the design requirements and suppressed chatter, but exhibited increased forced vibration at two frequencies. When the polypropylene between the flanges was replaced by an aluminum insert, one forced vibration disappeared. There is evidence that such a flexible wheel with a homogeneous rim would outperform a standard aluminum hub wheel.
A Definition of the Topography of Grit-Blasted Surfaces for Plasma Sprayed Alumina Coatings
Authors: Griffiths B. J. , Gawne D. T. , Dong G.
Published: February 2008

This paper describes the topographical implications of grit blasted surfaces on plasma sprayed alumina. The transition of the grit blasted surface from raw material to correctly blasted is described in terms of surface heights, height distribution, spacings and texture. The influence of embedded grit is shown to be significant. The individual particles of alumina impacting the surface are classified into two types, these being disc splats and splash splats. Their deposition relationships with regard to surface topography and adhesion is explained with reference to the two types of splat.
A Finite Element Study of Electromagnetic Riveting
Authors: Repetto E. A. , Radovitzky R. , Ortiz M. , Lundquist R. C. , Sandstrom D. R.
Published: February 2008

Electromagnetic riveting, used in some aerospace assembly processes, involves rapid deformation, leading to the finished rivet configuration. Analysis of this process is described for the case of an aluminum rivet joining typical aluminum structural elements. The analysis is based on a finite element method that includes the effects of heating, due to rapid plastic deformation of the material, on the material properties. Useful details of material deformation and thermal history and the final rivet and structure configuration and states of stress and strain are obtained. These results have significant implications in the design, implementation, and improvement of practical fastening processes in the aerospace industry.
Buckling Analysis of a Heated Steel Strip in a Continuous Annealing Furnace
Authors: Luo H. , Dunbar W. S. , Moore J. E.
Published: February 2008

Thermal buckling is a problem that arises in the operation of continuous annealing lines for thin steel strips. In this paper finite element analysis (FEA) is carried out on the furnace buckling of thin steel strips. The results obtained agree very well with observations of furnace buckling made in actual operation. It has been quantitatively shown that the main cause of furnace buckling is the combined effect of high heating temperature coupled with line tension on a strip. This finding is based on the comparison of numerical results with the experimental data collected at a continuous annealing line of Armco Ashland Works in Texas. The analysis has revealed the need for accurate control and monitoring of annealing line heating system in order to avoid buckling of thin steel strips. In addition, the results presented, herein, could be useful in the design of a heating system that ensures buckling free operation.
Deposition Strategies and Resulting Part Stiffnesses in Fused Deposition Modeling
Authors: Kulkarni P. , Dutta D.
Published: February 2008

In the Fused Deposition Modeling (FDM) process, the choice of deposition strategy plays an important role. In this paper, the effects of different deposition paths on this deposition based LM process are investigated. Some variations on the current deposition strategies are also proposed. The stiffness of parts manufactured by the different strategies is experimentally determined. It is then compared with an analytical model developed using laminate analysis. A good conformance of the laminate model to the experimental results suggests that the laminate model can be used as a design aide to help the designer tailor the deposition strategy to the stiffness requirements.
A Finite Element Scheme for Determining the Shaped Rail Slider Flying Characteristics With Experimental Confirmation
Authors: Peng Jih-Ping , Hardie Cal E.
Published: February 2008

A rapidly convergent finite element approach to determining the air bearing slider flying attitude is developed in the present investigation. The air flow between the slider and the disk is modeled by the generalized Reynolds equation. The equilibrium equation for the slider flying attitude includes both the suspension stiffness and the preload. These coupled, nonlinear equations are linearized by the Newton-Raphson method. Solutions are obtained by applying the Galerkin finite element method to the governing equations. The flying characteristics of a sub-ambient pressure shaped rail slider are studied using this proposed approach. The accuracy of the numerical solution is confirmed by comparison with experimental measurements.
Inlet Pressure Effects on the Thermohydrodynamic Performance of a Large Tilting Pad Journal Bearing
Authors: Ha Hyun Cheon , Kim Ho Jong , Kim Kyung Woong
Published: February 2008

Inlet pressure effects on the thermohydrodynamic performance of a 4-pad large tilting pad journal bearing are investigated both theoretically and experimentally. The theory takes into account the inlet pressure and the three-dimensional variation of oil viscosity and eddy viscosity. Film pressure, film thickness, bearing metal temperature, load capacity, and eccentricity are measured by experiments. A noticeable inlet pressure rise is observed at the entrance of pads. It is shown that the inlet pressure increases not only the film pressure and the load capacity but also the supply flow rate, while it decreases the mixing and bearing surface temperature. The bearing characteristics predicted by the turbulent thermohydrodynamic theory, including the inlet pressure, are in good agreement with the experimental results. Therefore it can be suggested that the inlet pressure must be taken into account in theoretical calculations in order to predict the thermohydrodynamic performance of large tilting pad journal bearings accurately.
A Porous Media Model for Thin Film Lubrication
Authors: Tichy J. A.
Published: February 2008

A rheological model has been developed which can be applied to boundary lubrication. The model is applicable to thin films in which the molecular length scale is the same order as the film thickness. The micro structure is simulated by porous layers attached to the contact surfaces. The model contains three material properties: (1) viscosity, (2) the thickness of the porous layer, and (3) a porosity parameter. A modified Reynolds equation is developed. Behavior in two types of contacts is calculated: squeezing flow between crossed cylinders (Chan and Horn’s, 1985 drainage experiment) and a one-dimensional converging wedge contact. The effect of the layer thickness parameter is to increase the load and reduce the friction coefficient. Increasing the porosity parameter value tends to reduce the magnitude of the load increase.