bluuebunny/crossref_metadata_2025 huggingface dataset:
Workholding Stability in Shoe Centerless Grinding
Authors: Zhang Bi , Gan Zhongxue , Yang Yanhua , Howes Trevor D.
Published: February 2008

The workholding stability problem has been one of the critical issues in shoe centerless grinding since it can directly affect the grinding process, and therefore cause the surface quality and the dimensional accuracies of a workpiece to deteriorate. In order to solve the problem, this paper investigates the underlying workholding mechanism of a shoe centerless grinding system, and proposes theoretical models to predict the driving capability of the system. The models are verified by an experimental study. It is made clear that workholding stability is achievable if the driving capability of the drivehead is matched by the constraint capability of the workholding system. Based on the models, workholding stability conditions are established that can serve as a guideline to the manufacturing industry.
Design and Simulation of an Entry Edge Guide Control System for Tandem Cold Mills
Authors: Guo Remn-Min , Loen M. V.
Published: February 2008

A new entry edge guide control system for cold mills was designed using a dual-mode control system. One control loop regulated the cylinder pressure to prevent machine damage due to pressure surge while the other loop provided edge guide position control. The target control level was ±1.59 mm accuracy for a maximum operating strip speed of 530 mpm with coil sidewall location variations of ±12.5 mm/sec. A mathematical model was developed to simulate the dynamic behavior of the control system using the state space design method. The control system features two PID controllers, two hydraulic proportional valves, and a digital edge sensor. The PID tuning constants and the hydraulic proportional valves were specified by simulation results considering system response and signal noise. Data from 35 coils was used to investigate control performance. The results show that the average standard error is entirely acceptable. The majority of the coils are expected to have tracking errors less than the required accuracy.
Finite Element Geometry Creation Using Three-Dimensional Laser Profilometry
Authors: Jordache N. , Pandit S. M. , Cronin K. M.
Published: February 2008

Obtaining a complete view of a general 3D object has been of increasing importance in topographical measurements. This is particularly useful in 3D solid modeling, robotic 3D vision, quality control, numerically controlled machining, dimensional measurement and control for sheet metal forming, and other industrial applications. In this paper we use a phase-measuring technique initially developed for conventional interferometry to create a digitized map of a formed sheet metal surface. The resulting mesh data are converted into nodes and elements and imported into a finite element package for structural analysis via a translator. The procedure yields significant time savings in the part geometry modeling task for objects with complex surfaces which need a finite element analysis. Necessary theoretical review is provided for those with laser profilometry backgrounds and no prior FEA experience as well as FEA analysts without prior laser profilometry background. The paper aims at developing an awareness of combining these two existing technologies to advance product engineering analysis.
Theoretical Analysis of Externally Pressurized Porous Foil Bearings—Part I: In the Case of Smooth Surface Porous Shaft
Authors: Hashimoto H.
Published: February 2008

In this paper, the theoretical analysis for the hybrid performance of externally pressurized foil bearings with a hollow porous shaft is described. In the analysis, in order to save computation time and to improve the convergency of solutions, the two-dimensional modified Reynolds equation considering the added flow through hollow porous shaft is reduced to the ordinary differential equation by expanding the film pressure to the Fourier series with respect to the axial coordinate. The reduced Reynolds equation and the equilibrium equation for the perfectly flexible foil are solved iteratively by the finite element technique. The numerical solutions for the pressure and film thickness distributions between the foil and the shaft are obtained for a wide range of bearing width-to-diameter ratio under the various combinations of dimensionless supply pressure, dimensionless permeability of porous shaft and dimensionless wrap angle of foil, and the hybrid performance of foil bearings are examined theoretically. It is found from the numerical results that the bearing width has the significant effect on the pressure and film thickness distributions between the foil and the shaft.
Slider/Disk Interaction During the Landing Process
Authors: Leo H.-L. , Chapman S. R. , Crone R. M.
Published: February 2008

In rigid disk drives, slider/disk interface (SDI) wear should ideally occur only during the start/stop (S/S) process. Good S/S wear performance is crucial, but often difficult to achieve. This is due in part to a lack of understanding of slider/disk interaction during the S/S process. The intent of this study is to provide a thorough theoretical model to aid in our understanding of the slider/disk interaction during the landing process. In contrast to assessments in the literature, this model includes more rigorous surface characterization, the statistical nature of summit interaction, and the nonlinear rarefaction effects in the modified Reynolds equation. In this paper, we present results of a baseline slider/disk configuration, together with a crown sensitivity study.
Theory Versus Experiment for the Rotordynamic Characteristics of a Smooth Annular Gas Seal at Eccentric Positions
Authors: Alexander C. R. , Childs D. W. , Yang Z.
Published: February 2008

Experimental results are presented for the rotordynamic coefficients of a smooth gas seal at eccentricity ratios out to 0.5. The effects of speed, inlet pressure, pressure ratio, fluid prerotation, and eccentricity are investigated. The experimental results show that direct stiffness KXX decreases significantly, while direct damping and cross-coupled stiffness increase with increasing eccentricity. The whirl-frequency ratio, which is a measure of rotordynamic instability, increases with increasing eccentricity at 5000 rpm with fluid prerotation. At 16,000 rpm, the whirl-frequency ratio is insensitive to changes in the eccentricity. Hence, the results show that eccentric operation of a gas seal tends to destabilize a rotor operating at low speeds with preswirled flow. At higher speeds, eccentric operation has no significant impact on rotordynamic stability. The test results show that the customary, eccentricity-independent, model for rotordynamic coefficients is only valid out to an eccentricity ratio of 0.2~0.3. For larger eccentricity ratios, the dependency of rotordynamic coefficients on the static eccentricity ratio needs to be accounted for. Experimental results are compared to predictions for static and dynamic characteristics based on an analysis by Yang (1993). In general, the theoretical results reasonably predict these results; however, theory overpredicts direct stiffness, fails to indicate the decrease in KXX that occurs with increasing eccentricity, and incorrectly predicts the direction of change in KXX with changing pressure ratio. Also, direct damping is substantially underpredicted for low preswirl values and low supply pressures, but the predictions improve as either of these parameters increase.
A New Rolling Contact Surface and “No Run-In” Performance Bearings
Authors: Zhou Rao S. , Hashimoto Fukuo
Published: February 2008

Plasticity indexes are usually used to describe the elastic-plastic deformation properties of a rough surface. The contact surfaces of any new rolling element bearing always change during the bearing run-in period until arriving upon a relatively stable surface texture. In this paper, a new random isotropic surface with very low plasticity index is proposed and created for the surfaces of rolling elements bearings. From both the calculated surface parameters and the run-in torque test results, the special rolling contact surfaces demonstrated “No Run-In” characteristics. Lower running torque is obtained from bearing tests and longer fatigue life is also expected by the subsurface stress analysis.
Frictional Heating of Tribological Contacts
Authors: Bos J. , Moes H.
Published: February 2008

Wherever friction occurs, mechanical energy is transformed into heat. The maximum surface temperature associated with this heating can have an important influence on the tribological behavior of the contacting components. For band contacts the partitioning of heat has already been studied extensively; however, for circular and elliptic contacts only approximate solutions exist. In this work a numerical algorithm is described to solve the steady state heat partitioning and the associated flash temperatures for arbitrary shaped contacts by matching the surface temperatures of the two contacting solids at all points inside the contact area. For uniform and semi-ellipsoidal shaped heat source distributions, representing EHL conditions and dry or boundary lubrication conditions respectively, function fits for practical use are presented giving the flash temperature as a function of the Pe´clet numbers of the contacting solids, the conductivity ratio, and the aspect ratio of the contact ellipse. These function fits are based on asymptotic solutions for small and large Pe´clet numbers and are valid for the entire range of Pe´clet numbers. By comparison with numerical results they are shown to be accurate within 5%, even for the situation of opposing surface velocities.
Two-Dimensional Models of Boundary and Mixed Friction at a Line Contact
Authors: Polycarpou Andreas A. , Soom Andres
Published: February 2008

Two-dimensional dynamic friction models at a lubricated line contact, operating in boundary and mixed lubrication regimes, are developed. The friction coefficient is shown to be a function of the sliding velocity and the instantaneous separation of the sliding bodies, normal to the sliding direction. The models are based on unsteady friction experiments carried out under constant normal loads and under time-varying sliding velocities. The normal motions at the sliding contact were detected indirectly by contact resistance measurements. The contact resistance is related to the theoretical central film thickness for smooth surfaces. An advanced system identification technique (Minimum Model Error) is implemented to identify the most important terms in a number of nonlinear friction models. Two friction models are then nondimensionalized and parameterized. The validity and range of application of the models are then tested, by comparing them with experiments and with selected models proposed by other researchers.
Elastohydrodynamic Analysis of Reverse Pumping in Rotary Lip Seals With Microasperities
Authors: Salant Richard F. , Flaherty Andrew L.
Published: February 2008

An elastohydrodynamic analysis of a rotary lip seal containing microasperities, incorporating both the fluid mechanics of the lubricating film and the elastic behavior of the lip, has been performed numerically. The results indicate that some asperity patterns generate reverse pumping that prevents leakage through the seal. Other asperity patterns are found to generate negative reverse pumping that enhances leakage. In all cases considered, the asperities also hydrodynamically generate sufficiently high pressures to provide load support and maintain the integrity of the film.
Evaluating Surface Roughness From Contact Vibrations
Authors: Hess Daniel P. , Wagh Nitish J.
Published: February 2008

This paper examines the relationship between the contact dynamics and the composite surface roughness of two bodies in planar contact. Measurements of the natural contact frequency are obtained for a range of surface roughness levels and normal loads from an apparatus which isolates the contact dynamics of two steel blocks from all other system dynamics. The normal contact dynamics of the contacting components are modeled with a single-degree-of-freedom system which incorporates the Greenwood and Williamson surface roughness model. Analytical and empirical expressions relating the normal natural contact frequency and roughness parameters, such as the standard deviation of asperity heights and the average roughness value, are developed. Both theory and experiments show that the contact frequency increases with a decrease in the composite roughness and vice versa; a power law relation between the contact frequency and the roughness parameters is found in most cases. The results of this work indicate that it may be possible to use contact vibration as a means for assessing or monitoring composite roughness parameters of surfaces in contact.
Oil Drop Formation at the Outlet of an Elastohydrodynamic Lubricated Point Contact
Authors: Larsson Per-Olof , Jacobson Bo , Ho¨glund Erik
Published: February 2008

The loss of lubricant from grease-lubricated bearing surfaces is determined by a number of different mechanisms such as side-flow out of the contacts, evaporation, drop formation, oxidation etc. Some of the drops formed behind a rolling element in a bearing will be onrolled by the next rolling element but some will be lost from the bearing. This loss of lubricant is dependent to a high degree on the speed of the air flow through the bearing and is one of the reasons for early failure of grease lubrication in bearings operating in strong, axial air streams. To evaluate the most important parameters in drop formation, the droplets being thrown out from the outlet of an elastohydrodynamic contact were analyzed using picture processing and statistical methods. An empirical model has been built to describe mathematically the principal factors involved in the volume flow thrown out into the air at the outlet side of the Hertzian contact area. For example, drops in a ball bearing will contribute to the inlet feed of oil for the next ball if it is not lost by sideways flow out from the bearing.
Slider Overcoats for Enhanced Interface Durability in Magnetic Recording Applications
Authors: Ganapathi S. K. , Riener Timothy A.
Published: February 2008

The effects on tribological performance of air bearing surface overcoats on magnetic recording sliders are presented. Both component level and disk drive level testing indicate that significant performance enhancements are afforded by the overcoat, and that both stiction/friction and wear of the head/disk interface are reduced, thus increasing interface durability. The degradation in electrical performance of the heads due to the presence of the overcoat is shown to be consistent with that predicted by the Wallace equation. In addition, it is shown that the performance enhancements of the overcoat are achieved only in the presence of lubricant on the disk surface, suggesting that the overcoat lubricant interaction may be more benign than the interaction of the lubricant with the slider material.
Numerical Simulation of a Ball Impacting and Rebounding a Lubricated Surface
Authors: Larsson Roland , Ho¨glund Erik
Published: February 2008

The case of a ball bouncing on a flat surface covered by a thin lubricant layer is analyzed theoretically. Both impact and rebound are studied. A Newtonian lubricant and perfect elastic solids are assumed. As long as the ball approaches the flat surface the pressure in the contact increases and a lubricant entrapment is formed at the center of the contact. When the ball begins to leave the surface, cavitation occurs. At the periphery of the contact a pressure spike is formed. Just before the ball leaves the lubricated surface, very high pressure values arise at and near the contact center. These results are compared with the case of nonlubricated impact. It is found that the pressure in the contact at lubricated impact is higher than in the case of dry impact. Due to the elastic and damping properties of the lubricant film and the impacting surfaces, a time delay is observed between the time of maximum impact force and minimum film thickness. Comparing the theoretical results with experimental results, presented by other authors, shows good correlations.
Feasibility Study of Abrasive-Waterjet Milling of Fiber-Reinforced Plastics
Authors: Hocheng H. , Tsai H. Y. , Shiue J. J. , Wang B.
Published: February 2008

Composite materials are ideal for structural applications where high strength-to-weight and stiffness-to-weight ratios are required. Currently, linear cutting of composite materials has been increasingly practiced in industry and milling will be an important technology for wider applications of the materials and the benefit of onestation operation integrating linear and surface machining. Abrasive waterjet is adequate for machining of composite materials thanks to minimum thermal or mechanical stresses induced. The present paper discusses the feasibility of milling of composite materials by abrasive waterjet; it studies the basic mechanism of chip formation, single-pass milling, double-pass milling followed by the repeatable surface generation by multiple-pass milling. The mechanisms of material removal-deformation wear and cutting wear are studied first. High volume removal rate as well as a neat surface are desired. The major parameters affecting material removal rate are hydraulic pressure, standoff distance, traverse rate and abrasive flow rate. Dimensional analysis shows these significant parameters in machining and the results are compared with the theory of material erosion. The single-pass milling tests of carbon/epoxy are then conducted. The milling characteristics determining the generation of an extended surface are depth, width and width-to-depth ratio. The following dimensional analysis constructs the correlation between parameters and the surface characteristics. Based on the results of single-pass milling tests, the paper discusses the double-pass milling specifically considering the effect of lateral feed increments. The study then extends to six-pass milling. The obtained surface roughness from the sixpass milling is expressed as a function of the width-to-depth ratio and the lateral increment. With the knowledge of the volume removal rate and the surface roughness as well as the effects of the major process parameters, one can proceed to design a milling operation by abrasive waterjet.
Real-Time Sensing of Sag Geometry During GTA Welding
Authors: Zhang Y. M. , Kovacevic R.
Published: February 2008

Seam tracking and weld penetration control are two fundamental issues in automated welding. Although the seam tracking technique has matured, the latter still remains a unique unsolved problem. It was found that the full penetration status during GTA welding can be determined with sufficient accuracy using the sag depression. To achieve a new full penetration sensing technique, a structured-light 3D vision system is developed to extract the sag geometry behind the pool. The laser stripe, which is the intersection of the structured-light and weldment, is thinned and then used to acquire the sag geometry. To reduce possible control delay, a small distance is selected between the pool rear and laser stripe. An adaptive dynamic search for rapid thinning of the stripe and the maximum principle of slope difference for unbiased recognition of sag border were proposed to develop an effective real-time image processing algorithm for sag geometry acquisition. Experiments have shown that the proposed sensor and image algorithm can provide reliable feedback information of sag geometry for the full penetration control system.
Real-Time Image Processing for Monitoring of Free Weld Pool Surface
Authors: Kovacevic R. , Zhang Y. M.
Published: February 2008

The arc weld pool is always deformed by plasma jet. In a previous study, a novel sensing mechanism was proposed to sense the free weld pool surface. The specular reflection of pulsed laser stripes from the mirror-like pool surface was captured by a CCD camera. The distorted laser stripes clearly depicted the 3D shape of the free pool surface. To monitor and control the welding process, the on-line acquisition of the reflection pattern is required. In this work, the captured image is analyzed to identify the torch and electrode. The weld pool edges are then detected. Because of the interference of the torch and electrode, the acquired pool boundary may be incomplete. To acquire the complete pool boundary, models have been fitted using the edge points. Finally, the stripes reflected from the weld pool are detected. Currently, the reflection pattern and pool boundary are being related to the weld penetration and used to control the weld penetration.
Burr Minimization in Face Milling: A Geometric Approach
Authors: Narayanaswami R. , Dornfeld D.
Published: February 2008

Experimental studies indicate that two types of burrs occur in face milling–primary and secondary burr, which are sensitive to the depth of cut and cutter exit angle. The primary burr is much larger in size compared to the secondary burr and needs to be removed by a deburring operation subsequent to machining, for effective performance of precision parts. In this paper we present a strategy for minimizing burrs in face milling. We develop a representation in a CAD framework to parametrize the edges of a part into primary and secondary burr zones. We present an algorithm which minimizes the primary burrs along the edges of the part, using a variety of objective functions reflective of deburring complexity. The parameters varied in the optimization process are of a geometric nature, affecting the cutter exit angle, and include cutter approach angle, cutter center position and the cutter radius.
Identification of Cutter Axis Tilt in End Milling
Authors: Zheng Li , Liang S. Y.
Published: February 2008

The scope of the paper is to discuss the identification of cutter axis tilt in end milling process via cutting force analysis. Cutter axis tilt redistributes the chip load among flutes thereby generating minor frequency components of cutting forces. These minor components can be utilized to infer the tilt geometry during the cutting action. This study involved the mathematical representation of chip thickness variation due to tilt, the modeling of local forces in relation to instantaneous chip thickness, the formulation of total cutting forces through convolution integration in the angle domain, the derivation of dynamic force components in the frequency domain, and the solution for tilt geometry from the dynamic cutting forces. Results show that the tilt magnitude and orientation can be estimated given the dynamic cutting force components along with the tool/work geometry, cutting parameters, and machining configuration. Numerical simulation results confirmed the validity of the angle domain convolution approach, and the end milling experimental data agreed with the analytical model.
Manipulation of Uncertainties in the Determination of Optimal Machining Conditions Under Multiple Criteria
Authors: Chen Li , Rao S. S.
Published: February 2008

In any real-world manufacturing situation, the problem of determining the optimum machining conditions involves not only empirical data but also imprecise information. Uncertain factors may need to be considered in the computational optimization process due to fuzziness present in the empirical equations and experimental data used. To manipulate the uncertainties in the optimization process, a fuzzy model is introduced and investigated. The fuzzy model quantifies the degree of certainty (or uncertainty) in the range 0 to 1. A numerical example is considered to illustrate the computational approach. The overall impact of the uncertain factors on the optimization process is assessed by comparing the present numerical results with those given by the traditional approach.
Cycle-Time Reduction in Machining by Recursive Constraint Bounding
Authors: Ivester R. , Danai K. , Malkin S.
Published: February 2008

Modeling uncertainty in machining, caused by modeling inaccuracy, noise and process time-variability due to tool wear, hinders application of traditional optimization to minimize cost or production time. Process time-variability can be overcome by adaptive control optimization (ACO) to improve machine settings in reference to process feedback so as to satisfy constraints associated with part quality and machine capability. However, ACO systems rely on process models to define the optimal conditions, so they are still affected by modeling inaccuracy and noise. This paper presents the method of Recursive Constraint Bounding (RCB2) which is designed to cope with modeling uncertainty as well as process time-variability. RCB2 uses a model, similar to other ACO methods. However, it considers confidence levels and noise buffers to account for degrees of inaccuracy and randomness associated with each modeled constraint. RCB2 assesses optimality by measuring the slack in individual constraints after each part is completed (cycle), and then redefines the constraints to yield more aggressive machine settings for the next cycle. The application of RCB2 is demonstrated here in reducing cycle-time for internal cylindrical plunge grinding.
Correlation Between Acoustic Emission and Wear of Multi-Layer Ceramic Coated Carbide Tools
Authors: Cho S.-S. , Komvopoulos K.
Published: February 2008

Acoustic emission (AE) was used to monitor the machining process and tool condition during turning of AISI 4340 steel with uncoated, two-layer (TiC/Al2O3) coated, and three-layer (TiC/Al2O3/TiN) coated cemented WC-Co tools. The experiments were performed at four different feedrates and constant cutting speed and depth of cut. The variation of the AE signal with cutting time is interpreted in light of the dominant mechanisms, rates, and patterns of wear and the contact friction conditions at the tool/workpiece and tool/chip interfaces. Correlations between intrinsic frequencies and AE sources are identified by examining the root-mean-square, dominant amplitude, type, and count rate of the AE signals. It is shown that AE frequencies in the range of 50–100 kHz are primarily due to plastic deformation in the near-surface tool regions and the primary, secondary, and tertiary shear zones of the workpiece, whereas cracking leading to coating delamination and WC grain pull-out generates frequencies in the range of 170–200 kHz. The tool life estimated from the root-meansquare of the AE signal is shown to be in good agreement with that determined from measurements of the maximum wearland width on the tool nose. The obtained results demonstrate that AE is an effective technique for in-process wear monitoring and wear mechanism identification of multi-layer ceramic coated tools.
An Investigation of Variable Spindle Speed Face Milling for Tool-Work Structures With Complex Dynamics, Part 2: Physical Explanation
Authors: Radulescu R. , Kapoor S. G. , DeVor R. E.
Published: February 2008

Part 2 of this paper focuses on the explanation, both on theoretical grounds and through model simulations, of why the technique of variable spindle speed machining is an effective tool for increasing the quality and productivity of machining operations. In particular, Part 2 explains why, by disturbing the regenerative and forced vibration excitation frequencies which generate large amplitudes of vibration during constant speed machining, variable speed machining has the potential to reduce the vibration of the tool-work system and be robust with respect to the cutting process dynamics. The explanation is based on the work done by the cutting forces, the chip load variation, tool-work displacements, cutting forces, and workpiece surface error generated by both constant and variable speed machining. By investigating the effects of regeneration and forced vibration during variable speed machining on the vibration of tool-work systems having different cutter diameter-to-workpiece width ratios, it has been shown that variable speed machining is also robust with respect to the geometry of the tool-work system. This work concludes that variable speed machining is safer to use than constant speed machining when the effects of the tool-work dynamics and geometry on the vibration of the cutting process are hard to determine.
Analysis of Front End Bending in Plate Rolling by The Finite Element Method
Authors: Park B. H. , Hwang S. M.
Published: February 2008

This paper deals with the problem of the front end bending arising in plate rolling. The problem, which is caused by unbalanced rolling, is investigated by the finite element simulation technique. Discussions are made on the effect of various unbalanced rolling conditions on the deformation of the front end. In particular, an empirical model is developed for the prediction of the curvature of the front end rolled under the presence of the roll speed difference.
Thermal Modeling of Deposit Solidification in Uniform Droplet Spray Forming
Authors: Acquaviva P. , Chen Chen-An , Chun Jung-Hoon , Ando Teiichi
Published: February 2008

In spray forming, the deposit thermal state is a key parameter which influences the microstructural evolution upon and after droplet impact onto the deposit. The uniform droplet spray (UDS) forming process has been developed to enable precise control of the droplet and deposit thermal state and the resultant material microstructure. By having a uniform droplet size throughout the spray, all the droplets deposited onto the substrate will have the same thermal state upon impact, allowing for precise control of the solidification process. This paper describes a one-dimensional, finite difference model that predicts the temperature and liquid fraction of the deposit during the UDS process. The model employs an explicit temperature-enthalpy method to incorporate a variety of solidification models. Experiments were conducted using Sn-15 wt percent Pb binary alloy. Temperatures were measured in the deposit and acceptable agreement with the simulation was obtained. Modeling has shown that the deposit thermal state is highly dependent on variations in spray conditions, which are predicted using droplet trajectory and droplet thermal models. Using the droplet and deposit models, the relationship between UDS process parameters and material microstructure can be understood.
Elastic-Plastic Finite Element Analysis of Deep Drawing Processes by Membrane and Shell Elements
Authors: Shim H. B. , Yang D. Y.
Published: February 2008

Both cylindrical cup drawing and square cup drawing are analyzed using both membrane analysis and shell analysis by the elastic-plastic finite element method. An incremental formulation incorporating the effect of large deformation and anisotropy is used for the analysis of elastic-plastic non-steady deformation. The corresponding experiments are carried out to show the validity of the analysis. Comparisons are made in punch load and distribution of thickness strain between the membrane analysis and the shell analysis for both cylindrical and square cup drawing processes. In punch load, both methods of analysis show very little difference and also show generally good agreement with the experiment. For the cylindrical cup deep drawing, the computed thickness strain of a membrane analysis, however, shows a wide difference with the experiment. In the shell analysis, the thickness strain shows good agreement with the experiment. For the square cup deep drawing, both membrane and shell analysis show a wide difference with experiment, this may be attributable to the ignorance of the shear deformation. Concludingly, it has been shown that the membrane approach shows a limitation for the deep drawing process in which the effect of bending is not negligible and more exact information on the thickness strain distribution is required.
A Probabilistic View of Problems in Form Error Estimation
Authors: Yang Tai-Hung , Jackman J.
Published: February 2008

Form error estimation techniques based on discrete point measurements can lead to significant errors in form tolerance evaluation. By modeling surface profiles as random variables, we show how sample size and fitting techniques affect form error estimation. Depending on the surface characteristics, typical sampling techniques can result in estimation errors of as much as 50 percent. Another issue raised in the fitting approach is the metric p selection for the fitting objective. We show that for p = 2 and p = ∞, the selection does not appear to significantly affect the estimation of form errors.
An Air Layer Modeling Approach for Air and Air/Vacuum Bearings
Authors: Pitarresi J. M. , Haller K. A.
Published: February 2008

Air layer supported bearing pads, or “air bearings” as they are commonly called, are popular because of their high load capacity and low in-plane coefficient of friction, making them well suited for supporting moving, high accuracy manufacturing stages. Air/vacuum bearings enhance these capabilities by giving the bearing pad load resistance capacity in both the upward and downward directions. Consequently, it is desirable to know how to model the air layer between the bearing pad and the bearing surface. In this paper, a simple finite element modeling approach is presented for investigating the vibrational characteristics of an air layer supported bearing. It was found that by modeling the air layer as a bed of uniform springs who’s stiffness is determined by load-displacement tests of the bearing, a reasonable representation of the response can be obtained. For a bearing supported by air without vacuum, the dynamic response was very similar to that of a freely supported bearing. The addition of vacuum to an air bearing was found to significantly lower its fundamental frequency which could lead to unwanted resonance problems.
Applications of D-H Notation in Machining and On-Line Measurement of Roller-Gear Cams on 5-Axis Machine Tools
Authors: Lin Psang Dain , Lee Ming Far
Published: February 2008

A kinematic model is presented to aid in the design of cam-profiles and determine the NC data equations using Denavit-Hartenberg (D-H) notation to produce and to measure the dimension accuracy of roller-gear cams on 5-axis machine tools. First, cam profiles are determined based on the conjugate surface theory. Then, D-H notation is employed in the derivation of machine tool ability functions and in the generation of the desired cutter/measuring-probe location matrices. The desired NC data equations are obtained by solving the link variables of the machine tool by equating the machine tool ability function with the tool location matrices. The resultant cutting speed and material-removal rate during machining are also investigated. To verify the validity of this methodology, a designed roller-gear cam was machined and its surfaces were measured through the on-line measurement system equipped with a touch-trigger probe on a 5-axis machine tool. This methodology combines the cam design, machining, and measurement techniques, thus making the production process more flexible, automatic, and controllable.
In-process Evaluation of the Overall Machining Performance in Finish-Turning via Single Data Source
Authors: Fang X. D. , Yao Y. L.
Published: February 2008

Sensor fusion often uses multiple sensors to evaluate a single quantity. The work presented in this paper attempts to use information from a single sensor to estimate overall machining performance (characterized by cutting forces, chip breakability, surface roughness, and dimensional deviation due to tool wear). In particular, the performance is aimed at reflecting the in-process changes of the above-named quantities with respect to tool wear progression (major flank, crater and minor flank wear). 3-D cutting force measured by a tool dynamometer is fully utilized by aggregating multivariate time series models and neural network techniques. Dispersion analysis is used to extract signal features which correlate well with progressive tool wear. The results have shown the effectiveness of the proposed method which also has the obvious merit of simplicity.
A New Method to Detect Regenerative Chatter Using Spectral Analysis, Part 1: Basic Study on Criteria for Detection of Chatter
Authors: Kondo E. , Ota H. , Kawai T.
Published: February 2008

The purpose of this study is to introduce a new criterion for detecting regenerative chatter by application of spectral analysis. From the regenerative chatter theory, it can be seen that the vibration amplitude perpendicular to a workpiece surface comes equal to the amplitude of surface undulation at the stability limit. So the regenerative chatter theory is applied to the criterion introduced in this study to detect regenerative chatter. Validity of this criterion was examined by using numerical simulations assumed to be orthogonal, and then experiments for verification of criterion validity were carried out using the regenerative chatter of a turning workpiece in orthogonal cutting. We concluded that this criterion is reliable enough to detect regenerative chatter.
An Enhanced Cutting Force Model for Face Milling With Variable Cutter Feed Motion and Complex Workpiece Geometry
Authors: Gu F. , Kapoor S. G. , DeVor R. E. , Bandyopadhyay P.
Published: February 2008

An enhanced model for the prediction of static cutting forces in face milling is presented. The key features of the model include the ability to handle complex work-piece geometry, two-dimensional cutter feed paths, multiple pass machining, and effects of machine set-up errors. A two-dimensional boundary representation scheme is used to describe the workpiece geometry which may contain holes, slots, and other complex geometrical features. Variable cutter feed paths are represented by a combination of linear and circular arcs. In view of this and the complex workpiece geometry, a new algorithm for cutter-workpiece engagement determination is developed. Several sources of machine set-up error such as spindle and cutter axis tilt, and cutter center offset runout are modeled and their individual as well as combined effects on key machining process variables such as the axial and the radial depth of cut illustrated. Results of model verification experiments are reported for different workpiece geometry and cutter feed paths. A comparison of the predicted and measured forces shows good agreement.
Cutting Tool Temperatures in Contour Turning: Transient Analysis and Experimental Verification
Authors: Stephenson D. A. , Jen T.-C. , Lavine A. S.
Published: February 2008

This paper describes a model for predicting cutting tool temperatures under transient conditions. It is applicable to processes such as contour turning, in which the cutting speed, feed rate, and depth of cut may vary continuously with time. The model is intended for use in process development and trouble shooting. Therefore, emphasis is given in the model development to enable rapid computation and to avoid the need to specify parameters such as thermal contact resistances and convection coefficients which are not known in practice. Experiments were conducted to validate the predictive model. The model predictions with two different boundary conditions bound the experimental results. An example is presented which shows the utility of the model for process planning.
Investigation on Cutting Temperature in Turning by a Tool-Work Thermocouple Technique
Authors: Leshock C. E. , Shin Y. C.
Published: February 2008

Tool-chip interface temperature is analyzed experimentally during turning of 4140 steel alloy and Inconel 718 with tungsten carbide tools using a tool-work thermocouple technique. The experimental results are compared with Loewen and Shaw’s analytical results. Based on the experimental results, an empirical model relating the tool face temperature to cutting conditions is established for 4140 steel alloys with tungsten carbide tools. Finally, the tool-chip interface is investigated with flank and crater wear to determine the effect of tool face temperature on these tool wear mechanisms.
Mechanisms of Material Removal in the Precision Production Grinding of Ceramics
Authors: Subramanian K. , Ramanath S. , Tricard M.
Published: February 2008

Grinding of ceramics is often treated as coarse grinding dominated by brittle fracture or fine grinding, at very low removal rates, dominated by plastic deformation. Through a set of experimental observations and analysis, it is shown that in grinding of ceramics the abrasive/work interaction can be treated similar to well known chip formation models. Such an approach permits the coexistence of ductile deformation and brittle fracture during the grinding of ceramics. When the grinding process is managed such that the brittle fracture is minimized, while maximizing the plastic deformation optimum results are achieved. In this regard it is conceivable to design ceramic grinding cycles, where the rough grinding cycle focuses on surface generation to achieve high material removal rate and productivity while minimizing brittle fracture and the finish grinding cycle focuses on surface generation which maximizes plastic deformation while still minimizing brittle fracture. While the above accounts for only one of four interactions in the grinding zone (viz) abrasive/work interaction, it is also necessary to address the other three interactions (viz) chip/bond, chip/work and bond/work interactions. The later considerations for ceramics grinding are identical to well established practices in metal grinding. When such grinding cycle optimization is carried out taking simultaneously into account the aspects of machine tool, grinding wheel, work material and operational factors, significant progress can be made in the grinding of ceramics. The results obtained through such systems approach are also described in this paper.
Extension of the Backward Tracing Scheme of the Rigid-Plastic FEM in Three-Dimensional Deformation
Authors: Kang B. S. , Lee J. H. , Choi H. H.
Published: February 2008

Preform design is one of the critical fields in metal forming. The finite element method (FEM) has been effective in designing preforms and process sequence, for which the backward tracing scheme of the rigid-plastic FEM has been explored. In this work a program using the backward tracing scheme of the rigid-plastic FEM is developed for three-dimensional plastic deformation, which is an extension of the scheme from two-dimensional cases. The calculation of friction between workpiece and die, and handling of boundary conditions during backward tracing require sophisticated treatment. The developed program is applied to upsetting of a rectangular block and to side pressing of a cylindrical workpiece. The results of the two applications show feasibility of the program on three-dimensional plastic deformation.
Feedback Interpolators for CNC Machine Tools
Authors: Lo Chih-Ching
Published: February 2008

This paper presents interpolators that are capable of generating 2D curves in general implicit forms and 3D curves in general parametric forms. In contrast to the existing interpolators, which utilize complicated algorithms to meet the interpolation requirements such as maintaining high accuracy and constant feedrate, the proposed interpolators utilize a simple algorithm and a feedback action which corrects the interpolation results to meet the interpolation requirements.
Prediction of Thermally Induced Time-Variant Machine Tool Error Maps Using a Fuzzy Artmap Neural Network
Authors: Srinivasa N. , Ziegert J. C.
Published: February 2008

A novel approach to on-line learning and prediction of time-variant machine tool error maps is proposed. These error maps are measured using a fast calibration device called the laser ball-bar (LBB) that directly measures the total positioning errors at the cutting tool using trilateration. The learning and prediction of these error maps is achieved using a Fuzzy ARTMAP neural network by treating the problem as an incremental approximation of a functional mapping between thermal sensor readings and the associated positional errors at each location of the cutting tool. Experimental measurements of the positional errors for a two axis turning center were performed using the LBB over two separate thermal duty cycles. The Fuzzy ARTMAP was trained on-line using the data collected over the first thermal duty cycle, which simulated machining of large workpieces with several hours of machining, inspection and set-up time. The network was made to predict the error map of the machine for a new thermal duty cycle that simulated machining of a range of short and long workpieces with shorter machining and set-up times. Results of these predictions show that the LBB and Fuzzy ARTMAP combination is a fast and accurate method for real-time error compensation in machine tools. This method overcomes drawbacks in currently methodologies including high cost and excessive downtime to calibrate machine tools. Application of the Fuzzy ARTMAP to continuous process improvement is discussed.
Dynamic Estimation of Full Penetration Using Geometry of Adjacent Weld Pools
Authors: Zhang Y. M. , Li L. , Kovacevic R.
Published: February 2008

Control of weld penetration is currently one of the most important and crucial research issues in the area of welding. The weld pool can provide accurate and instantaneous information about the weld penetration, however, the establishment and confirmation of the correlation between weld pool and weld penetration require numerous accurate measurements and suitable geometrical modeling of weld pool. A normalized model is proposed to characterize the weld pool two-dimensionally. More than 6,000 weld pools are measured from experiments using a developed real-time weld pool sensing system. A data analysis shows that the weld penetration is correlated with the weld pool which is specified by the three characteristic parameters proposed in the study. However, the correlation is nonlinear. To approximate the complicated nonlinearity, neural networks are used. Comparative modeling trails show that the weld penetration can be more accurately calculated if the adjacent weld pools are also used. This implies that the correlation between the weld penetration and weld pool is dynamic. Hence, an on-line nonlinear dynamic estimation system is developed to estimate the weld penetration.
The Design of a Large Single-Screw Melt Extruder Using a Quasi Two-Dimensional Conducting Screw Computer Model
Authors: Jones D. R. Samuel , Ghoshdastidar P. S. , Muju M. K. , Das Manab K.
Published: February 2008

This paper describes a computer-aided design study for a large (5000 kg/hr) single-screw melt extruder processing 0.2 MFI LDPE using a quasi 2D steady-state non-Newtonian flow and heat transfer model that takes into account screw conduction. The effect of different screw materials has also been investigated.
Analytical Stability Prediction and Design of Variable Pitch Cutters
Authors: Altıntas¸ Y. , Engin S. , Budak E.
Published: February 2008

An analytical prediction of stability lobes for milling cutters with variable pitch angles is presented. The method requires cutting constants, number of teeth, and transfer function of cutter mounted on the machine tool as inputs to a chatter stability expression. The stability is formulated by transforming time varying directional cutting constants into time invariant constants. Constant regenerative time delay in uniform cutters is transformed into nonuniform multiple regenerative time delay for variable pitch cutters. The chatter free axial depth of cut is solved from the eigenvalues of stability expression, whereas the spindle speed is identified from regenerative phase delays. The proposed technique has been verified with extensive cutting tests and time domain simulations. The practical use of the analytical solution is demonstrated by an optimal tooth spacing design application which increases the chatter free depth of cuts significantly.