bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent Flow Foil Bearings for Cryogenic Applications
Authors: San Andres Luis
Published: February 2008

Fluid film foil bearings are an innovative bearing technology proposed for rotor support in cryogenic turbomachinery. These bearings offer system life and rotor speeds currently unachievable with rolling element bearings alone. An isothermal analysis for the turbulent bulk-flow of a variable properties liquid in a foil bearing with a simple elastic matrix is introduced. Numerical predictions compare the static and dynamic force performance of a three pad foil bearing with a rigid surface bearing for a high speed application in liquid oxygen. The major advantages of the foil bearing are immediately apparent, namely linearity in the load versus eccentricity curve, uniform rotordynamic coefficients, and overall unsurpassed stability conditions. The effects of excitation frequency and the foil structural damping on the dynamic force coefficients are discussed.
Linear Stability Analysis of Short Porous Journal Bearings—Use of the Brinkman Model
Authors: Lin Jaw-Ren , Hwang Chi-Chuan
Published: February 2008

On the basis of a Brinkman model (BM), this paper predicts that the effects of viscous shear stresses on the linear stability of short porous journal bearings are apparent and not negligible. Compared with those of the slip-flow model (SFM) and the Darcy model (DM), the viscous shear effects provide a significant increase in the stability threshold speeds of short porous journal bearings.
Polymer/Metal Conformal Sliding Contact With Forced Convective Cooling
Authors: Haverstick J. K. , Ovaert T. C.
Published: February 2008

A model for predicting the onset of severe wear for a conformal polymer/metal sliding contact with forced convective cooling has been developed. Finite difference techniques were used for the solution of the bulk contact temperature for the two-dimensional model. The flash temperature was calculated assuming a limiting-case annular, stationary heat source. The limiting load for a given set of operating conditions was solved iteratively, assuming a relationship between strength and temperature, for a heat-resistant polymer, polyethersulphone (PES). An experimental apparatus was constructed, and specimens were tested near the predicted points of wear instability. In addition, specimens were examined using a scanning electron microscope (SEM), and at the most severe operating conditions, signs of thermal softening and gross material transfer were evident. A discussion of model is made in light of the predicted and experimental results.
Rheological Models for Thin Film EHL Contacts
Authors: Jang Siyoul , Tichy John
Published: February 2008

Rheological behavior in concentrated contacts has been studied extensively. In certain conditions such as a rough concentrated contact or sliding of nominally flat surfaces, films may be of molecular (nanometer) scale. The question arises as to whether the application of any viscous fluid model is appropriate. In this study, elastohydrodynamic lubrication analysis is performed on three candidate rheological models: (1) the classical case of viscosity variation with pressure, (2) an isoviscous model which idealizes porous layers on the solid surfaces representing the molecular microstructure, and (3) an isoviscous model which includes van der Waals and solvation surface forces. The latter two models predict behavior similar to classical behavior. The study is not sufficiently sensitive to determine which model best predicts experimental results, but some credence must be given to the latter two because experimental evidence suggests that Reynolds’ equation is not valid for molecularly thin films.
The Slippery Sheet
Authors: Benson R. C.
Published: February 2008

An analysis is presented to describe how a sliding sheet might entrain air that lubricates the interface. Closed-form results are obtained for a wide, slightly curled, elastic sheet sliding on an incompressible layer of air. Example results are calculated for a paper sheet typically used in copiers, and an approximate model for mixed lubrication is developed.
Boric Acid as an Additive for Core-Drilling of Alumina
Authors: Liang H. , Jahanmir S.
Published: February 2008

Interactions between chemical compounds added to cutting fluids and the workpiece surface in the cutting zone can have pronounced effects on the material removal process during abrasive machining. These interactions can influence the coefficient of friction, the wear of the abrasive grit, and the mechanical properties of the workpiece, thus affecting the machining rate. Experiments were conducted on sapphire and a high-purity polycrystalline alumina to evaluate the chemomechanical effects of boric acid mixed with distilled water. The machining tests were performed on a precision drill with metal-bonded diamond core-drills. Following the experiments, the drilled surfaces and the debris were examined by scanning electron microscopy to elucidate the material removal process. The results indicated that addition of boric acid to distilled water increases the rate of drilling of polycrystalline alumina by a factor of two. But, boric acid was found to be ineffective in improving the drilling rate of single crystal alumina, i.e., sapphire. Based on the results it is postulated that boric acid interacts with the amorphous oxide grain boundary phase in the polycrystalline alumina promoting intergranular fracture; thereby, increasing the drilling rate.
Die Shape Optimal Design in Bimetal Extrusion by the Finite Element Method
Authors: Byon S. M. , Hwang S. M.
Published: February 2008

A new approach to die shape optimal design in bimetal extrusion of rods is presented. In this approach, the design problem is formulated as a constrained optimization problem incorporated with the finite element model, and optimization of the die shape is conducted on the basis of the design sensitivities. The approach is applied to the determination of the optimal die shapes for several combinations of the core and sleeve materials.
A Fast Electro-Optical Sensing System for Measuring Thermal Response of a Rotating Roll Without Generating Contact Noise
Authors: Tseng A. A. , Chaidilokpattanakul C. , Chen J. S. , Westgate C. R.
Published: February 2008

A non-contact sensing system has been developed to measure the temperature response of a rapidly rotating roll under spray cooling encountered in metal rolling processes. A thin-film sensor with a fast response time, on the order of microseconds, has been designed and fabricated to measure the roll surface temperatures. To eliminate contact noise, an electro-optical data acquisition system has been developed to provide fast acquiring rate without physical contact to the rotating roll. The system has been implemented on a roll simulator to demonstrate sensor reliability and system feasibility. Also, using the measured temperatures as boundary conditions, a numerical calculation has been performed to provide the temperature distributions of the roll and the corresponding heat transfer coefficients of the spray cooling. Results indicate that the cyclic peak value of the heat transfer coefficient varies from 75 to 100 kW/m2 -K directly under the impingement of the spray jet. These values are consistent with the existing literature.
Automated Generation of Fixture Configuration Design
Authors: Rong Yiming (Kevin) , Bai Yong
Published: February 2008

Flexible fixturing is a necessary aspect of Flexible Manufacturing Systems (FMS) and Computer-Integrated Manufacturing Systems (CIMS). Modular fixtures are most widely used in industry for job and batch production. Computer-Aided Fixture Design (CAFD) has become a research focus in implementing FMS and CIMS. Fixture configuration design is an important issue in the domain of CAFD. A review of the current research in CAFD indicates that a major problem impeding the automated generation of fixture configurations is the lack of studies on fixture structures. This paper investigates fundamental structures of dowel-pin based modular fixtures and fixturing characteristics of commonly used modular fixture elements. A Modular Fixture Element Assembly Relationship Graph (MFEARG) is designed to represent combination relationships between fixture elements. Based on MFEARG, algorithms are developed to search all suitable fixturing unit candidates and mount them into appropriate positions on a baseplate with interference checking. A prototype system for automated design of dowel-pin modular fixture configurations is presented in this paper. Fixture design examples are given at the end of the paper.
Prediction of Strip Profile in Rolling Process Using Influence Coefficients and Boussinesq’s Equations
Authors: Guo Remn-Min
Published: February 2008

A simplified numerical method is proposed in this article to predict strip profile. The mill is simulated by beams (rolls) on the infinite elastic half space (between rolls and strip). The roll deflection and indentation are calculated using the influence coefficients and Boussinesq’s equations respectively. The roll contours in the contact zone can be expressed in terms of the influence coefficient and indentation matrices. Compatibility equations are derived by matching two surface profiles in the contact zone. Equilibrium equations ensure force and moment balance of the strip and each roll. A complete linear system is established by assembling compatibility and equilibrium equations. The contact rolling pressure distribution and the rigid motion of the roll chocks can be solved. Roll surface contours and strip profiles can be further calculated accordingly.
Experimental and Computational Study of the Quenching of Carbon Steel
Authors: Wang K. F. , Chandrasekar S. , Yang H. T. Y.
Published: February 2008

An investigation of the quenching of 1080 carbon steel cylinders has been carried out to determine the validity of a quenching process model for carbon steels. The process model included a description of the austenite-pearlite and austenite-martensite transformations in carbon steels, temperature-dependent material properties, and an elastic-plastic stress analysis. The model was simulated using the finite element method (FEM). An experimental study of the quenching of 1080 steel cylinders in water and two types of polymeric quenchants has also been carried out. The temperatures at three points within the cylinder during quenching were measured using thermocouples. The hardness and residual stress distributions along a cross-section of the quenched cylinders were determined using a Rockwell hardness test and an X-ray diffraction technique, respectively. The temperature-time histories, residual stress, and hardness distributions predicted from the FEM simulation of the quenching model were found to be in good agreement with the corresponding measurements. The quenching process simulation described in the study appears to be a promising tool for the design of heat-treatment process parameters for carbon steels.
Analysis of Residual Stresses and Metallurgical Phase Changes in Centrifugally Cast Bi-Metal Grinding Rolls
Authors: Narasimha Murthy Y. V. L. , Venkata Rao G. , Krishna Iyer P.
Published: February 2008

A mathematical model was developed for computing the metallurgical phase transformations and residual stresses in centrifugal casting of bi-metal grinding rolls used for coal pulverizing. The model considers variation of thermo-mechanical properties of material with temperature, effects of phase changes and metallurgical phase transformations. Rolls idealized as having infinite cylindrical geometry and the actual finite conical geometry are analysed for cases of air and water jet cooling of the centrifuging die. As expected an increase in the martensitic fraction is obtained on the grinding surface due to water jet cooling. The study indicates that the large size rolls analysed herein have higher martensitic fraction as compared to small size roll. Simplified analysis model is developed for usage in parametric studies involving various sizes for initial sizing of the rolls.
Analysis of Filament Deformation for a Freely Rotating Cup Brush
Authors: Stango R. J. , Shia Chih-Yuan
Published: February 2008

In this paper, a mechanics formulation is outlined and used for evaluating the steady-state, large deflection of a slender member subjected to displacement-dependent centrifugal load. The problem is examined within the context of rotating filamentary cup brushes that are used in surface finishing operations. Several parameters which are closely related to the machining performance and service life of cup brushes are identified and reported, including filament tip spatial distribution and orientation, filament stress, and the steady-state configuration of the working surface of the cup brush during free rotation. Numerical results indicate that filament inertia forces can lead to significant fiber displacement and stress and thus, must be included as an integral part of the design of rotary cup brushes.
Simultaneous Consideration of Process Development and Die Design for Cold Forming a Fuel Injector Nozzle
Authors: Seth S. , Shivpuri R.
Published: February 2008

Higher strength and tighter dimensional tolerance is desired for the injector nozzles to attain high injection pressures for lower NOx and particulate emissions. Cold forming is an alternate method which can provide these characteristics replacing the present machining operation. Upset tests were carried out to study the flow stress properties for selecting a suitable material for this part. A knowledge-based system was used to design the die angles and a multi-stage cold forming sequence process to manufacture the injector nozzle. Finite Element Modeling was used to do the punch design and to optimize the punch loads and punch pressures for each stage of the forming process. Initial sequence design was modified based on the results of numerical modeling. The tooling was designed and experimentation was done to verify the formability and material flow.
Use of a Quality Loss Function to Select Statistical Tolerances
Authors: Vasseur H. , Kurfess T. R. , Cagan J.
Published: February 2008

In this paper, we present a method for the selection of processes to manufacture various parts of an assembly by establishing a compromise between product quality and part manufacturing cost. We quantify the impact the precision of a part characteristic has on the overall quality of a product by using a standard Taguchi loss function. Part manufacturing cost is modeled as a function of process precision (i.e., standard deviation of the output characteristic) as opposed to previous models where manufacturing cost is a function of part tolerance. This approach is more realistic and does not assume, a priori, a relationship between conventional tolerance and process spread. Rather than allocating conventional tolerances on the assembly parts, we use statistical tolerances that are more pertinent when using a quality loss function. The model adopted makes it possible to investigate the relationship between optimum quality loss and tolerance variations. As expected, the optimum quality loss generally decreases when the tolerance increases. Exceptions may be encountered when changes of process occur. The manufacture of a simple three component assembly is studied to illustrate the findings.
Profile Recognition and Mensuration in Machine Vision
Authors: Pandit S. M. , Guo R.
Published: February 2008

This paper presents a systematic profile recognition and mensuration approach in machine vision. It can be utilized to recognize and measure the profiles of industrial parts in an automated manufacturing process by machine vision systems. A new method of profile representation by sampling the data from the object boundary in a digital image is presented. Autoregressive (AR) models are used to code the sampled data of the profiles into AR coefficients for profile recognition. Characterization of the profiles is accomplished by the Data Dependent Systems (DDS) methodology. The AR coefficients and characteristic roots help construct the AR and DDS descriptors to characterize the signatures of the profiles. The frequency domain information about the profiles can be extracted by DDS analysis. The measurement of the profile variation is obtained from the DDS results using optical mensuration method. Neural network and feature weighting method are utilized as reasoning machines for recognition. The illustrative examples in which the profile sampled data are corrupted by noise show that the profile recognition and mensuration approach is very effective and robust in a typical noisy environment on the shop floor.
New Statistical Moments for Diagnostics of Rolling Element Bearings
Authors: Honarvar F. , Martin H. R.
Published: February 2008

Statistical moment analysis has proven to be a very effective technique for diagnosis of rolling element bearings. The fourth normalized central statistical moment, kurtosis, has been the major parameter in this method. In this paper it will be shown that the third normalized statistical moment can be as effective as kurtosis if the data is initially rectified. The advantage of this moment over the traditional kurtosis value is its lesser susceptibility to spurious vibrations, which is considered to be one of the shortcomings of higher statistical moments including kurtosis. The sensitivity of this moment to changes of load and speed is also less than kurtosis. The proposed method can also be applied to higher odd statistical moments.
Computer Animation of 3-D Chip Formation in Oblique Machining
Authors: Fang X. D. , Fang Y. J. , Hamidnia S.
Published: February 2008

This paper presents details of developing a computer animation system for chip formation in oblique machining process. The 3-D chip animation model developed integrates chip flow equation, chip curling patterns, chip geometrical features and mathematical expression for 3-D helix surface. Based on the input conditions (chip breaker parameters and cutting conditions), a computer program is developed to convert the parametric prediction into a series of dynamic graphs demonstrating chip formation process. The methodology presented in this paper may provide an assistance for the machine operator to choose the machining conditions or for the process planning designer to evaluate the chip control effect.
Analysis of a Compliant Honing Tool for Brushing Cylindrical Surfaces
Authors: Shia Chih-Yuan , Stango R. J.
Published: February 2008

In this paper, a mechanics-based model is developed and I used for analyzing the steady-state configuration of brush fibers during concentric brushing of a cylindrical surface. The geometry of the problem is generalized in order to facilitate the analysis of flexible honing tools, that is, brushing tools having a spherical volume of abrasive compound attached at the end of each fiber. The integrity of the model is evaluated by examining two special cases that have a known solution, namely, (i) quasistatic contact, and (ii) dynamic contact associated with successively reduced fiber stiffness. In each case, correct results are obtained for the contact forces generated at the interface of the filament tip/cylindrical workpart surface. Also, special attention is given to examining the role that brush rotational speed plays in the response of each fiber of the honing tool, including filament/workpart contact force, torque, and filament stress.
Thermal Stresses in a Circular Cylinder with Temperature Dependent Properties
Authors: Ali Z. , Alam M. K.
Published: February 2008

The thermal stresses in a long circular cylinder are analyzed by two approximate methods. An interpolation formula is then used to develop a semi-empirical solution for thermal stresses which is then validated by a test case of a nondimensional temperature profile with temperature dependent modulus of elasticity, coefficient of thermal expansion and Poisson’s ratio. The interpolation formula is compared with the numerical solution by a finite element code (ABAQUS). It is shown that the interpolated approximation compares well with the finite element solution for a range of parameters that are typical for processing of billets.
A Model for the Prediction of Surface Flatness in Face Milling
Authors: Gu F. , Melkote S. N. , Kapoor S. G. , DeVor R. E.
Published: February 2008

This paper presents a new model for the prediction of surface flatness errors in face milling. The model includes the effects of machining conditions, elastic deformation of the cutter-spindle and workpiece-fixture assemblies, static spindle axis tilt and axially inclined tool path. A new method called equivalent flexibility influence coefficient method is used to compute the elastic deflection of the cutter-spindle and workpiece-fixture assembly at the points of cutting force application. Single insert and multi-insert face milling experiments are conducted to evaluate the predictive ability of the surface flatness model. A comparison of the model predictions and measurements shows good agreement. The influence of static spindle axis tilt on the surface flatness error is found to be very significant. It is shown that care needs to be exercised in comparing the model predictions based on elastic deflection of the machining system and spindle axis tilt with the surface flatness error measurements due to the fact that these measurements may be inflated by inclusion of the surface roughness.
Perturbation Methods in Nonlinear Dynamics—Applications to Machining Dynamics
Authors: Nayfeh Ali H. , Chin Char-Ming , Pratt Jon
Published: February 2008

The role of perturbation methods and bifurcation theory in predicting the stability and complicated dynamics of machining is discussed using a nonlinear single-degree-of-freedom model that accounts for the regenerative effect, linear structural damping, quadratic and cubic nonlinear stiffness of the machine tool, and linear, quadratic, and cubic regenerative terms. Using the width of cut w as a bifurcation parameter, we find, using linear theory, that disturbances decay with time and hence chatter does not occur if w < wc and disturbances grow exponentially with time and hence chatter occurs if w > wc. In other words, as w increases past wc, a Hopf bifurcation occurs leading to the birth of a limit cycle. Using the method of multiple scales, we obtained the normal form of the Hopf bifurcation by including the effects of the quadratic and cubic nonlinearities. This normal form indicates that the bifurcation is supercritical; that is, local disturbances decay for w < wc and result in small limit cycles (periodic motions) for w > wc. Using a six-term harmonic-balance solution, we generated a bifurcation diagram describing the variation of the amplitude of the fundamental harmonic with the width of cut. Using a combination of Floquet theory and Hill’s determinant, we ascertained the stability of the periodic solutions. There are two cyclic-fold bifurcations, resulting in large-amplitude periodic solutions, hysteresis, jumps, and subcritical instability. As the width of cut w increases, the periodic solutions undergo a secondary Hopf bifurcation, leading to a two-period quasiperiodic motion (a two-torus). The periodic and quasiperiodic solutions are verified using numerical simulation. As w increases further, the torus doubles. Then, the doubled torus breaks down, resulting in a chaotic motion. The different attractors are identified by using phase portraits, Poincare´ sections, and power spectra. The results indicate the importance of including the nonlinear stiffness terms.
Improvement of Machinability of Sintered Composite-type Alloyed Steel Powder
Authors: Yamaguchi Katsumi , Nakamoto Takeshi , Kitano Masayuki , Suzuki Masakuni , Abraha Petros A.
Published: February 2008

Composite-type alloyed steel powder has drawn great attention in recent years due to the rapid increase of high strength materials. A typical powder consisting of iron with nickel and molybdenum as an additive which adheres to the surface of iron particles is used. This type of sintered alloyed steel causes excessive tool wear. The purpose of this study is to improve the machinability of the sintered alloyed steel by adding nonmetallic materials. Experiments show that the addition of 3% glass to the sintered alloyed steel increases the tool life 100 times. In order to clarify the mechanisms of the increase of tool life, the worn face of the cutting tool is examined by an Electron Probe Microanalyzer (EPMA). The analysis shows that the glass additive acts as a protective film and lubricant when cutting with silicon nitride and tungsten carbide tools, respectively.
Injection Forging of Industrial Components From Thick-Walled Tubes
Authors: Colla D. , Petersen S. B. , Balendra R. , Martins P. A. F.
Published: February 2008

Traditional forging techniques are limited to the manufacture of components from solid materials; tubes may only be formed with a form of internal support to prevent the collapse of the work-material under axial forces. There is, however, the scope for achieving sufficiently large plastic deformation of tubes by injection into a diecavity; the extend of such deformation may be enlarged by preforming. The preform is designed to prevent the onset of one of the previously-identified modes of failure; the geometry of the preform was generated using a finite element model which was conditioned on the basis of a large set of experimental results. This paper discusses the possibility of applying the injection forging process in order to allow the complete forming of a geometrically complex tubular component in a single station. The work is supported by finite element modelling in conjunction with metal experiments in aluminum. Metallographic observations and micro-hardness measurements were performed to validate the approach.
Simulation of the Hot Ring Rolling Process by Using a Thermo-Coupled Three-Dimensional Rigid-Viscoplastic Finite Element Method
Authors: Xu S. G. , Weinmann K. J. , Yang D. Y. , Lian J. C.
Published: February 2008

During hot metal forming, the temperature variation and plastic deformation affect each other considerably. In the present investigation, ring rolling of hot steel is simulated by using a three-dimensional thermo-coupled rigid-viscoplastic finite element method. A new term is added to the functional in the variational approach to consider the influence of the frictional torque of the mandrel bearing, and the coupled thermal-mechanical simulation is performed by the iteration between the rigid-viscoplastic finite element analysis and the thermal finite element analysis. Since the deformation region and the severe temperature changes are restricted to the vicinity of the roll gap, only a ring segment and parts of the rolls are analyzed using a steady-state treatment to save computation time. Roll force and torque, width spread, temperature distributions, the distributions of strain and strain rate and the distributions of relative velocity and stress at the roll surfaces are obtained. The results show that the angular velocity of the driven roll has a significant influence on the temperature variations in the ring and the rolls, to which attention should be paid in the design of the process. The method presented can also be used to analyze other forming processes such as unsymmetrical plate rolling, symmetric rolling, and extrusion.
A Variational Method of Robust Fixture Configuration Design for 3-D Workpieces
Authors: Cai Wayne , Hu S. Jack , Yuan J. X.
Published: February 2008

Fixtures are used to locate and hold workpieces during manufacturing. Because workpiece surface errors and fixture set-up errors (called source errors) always exist, the fixtured workpiece will consequently have position and/or orientation errors (called resultant errors). In this paper, we develop a variational method for robust fixture configuration design to minimize workpiece resultant errors due to source errors. We utilize both first-order and second-order workpiece geometry information to deal with two types of source errors, i.e., infinitesimal errors and small errors. Using the proposed variational approach, other fundamental fixture design issues, such as deterministic locating and total fixturing, can be regarded as integral parts of the robust design. Closed-form analytical solutions are derived and numerical examples are shown. By employing the nonlinear programming technique, simulation software called RFixDesign is developed. This paper presents a new procedure for robust fixture configuration design that contributes especially to fixture designs where deformation is not influential.
Generation of Periodic Trajectories for Optimal Robot Excitation
Authors: Swevers J. , Ganseman C. , De Schutter J. , Van Brussel H.
Published: February 2008

This paper describes the parameterization of robot excitation trajectories for optimal robot identification based on finite Fourier series. The coefficients of the Fourier series are optimized for minimal sensitivity of the identification to measurement disturbances, which is measured as the condition number of a regression matrix, taking into account motion constraints in joint and cartesian space. This approach allows obtaining small condition numbers with few coefficients for each joint, which simplifies the optimization problem significantly. The periodicity of the resulting trajectories and the fact that one has total control over their frequency content, are additional features of the presented parameterization approach. They allow further optimization of the excitation experiments through time domain data averaging and optimal selection of the excitation bandwidth, which both help the reduction of the disturbance level on the measurements, and therefore improve the identification accuracy.
A Methodology to Improve Manufacturing Precision in the Presence of Workpiece Imperfections
Authors: Lee Neville , Joneja Ajay
Published: February 2008

In modern manufacturing applications of products such as LCD’s, semiconductor wafers, and thin film heads, the workpiece has to be processed in multiple steps. The quality and yield of the products depends on how precisely the workpiece is aligned in each setup. The effect of imperfections of the workpiece on the manufacturing precision are analyzed, and our analysis shows that the imperfections of the workpiece can be a major cause of tolerance problems. A methodology that can help to greatly reduce the sensitivity of imperfections in the workpiece has been proposed. The methodology is applied to the 2-D domain, and is substantiated by characterization and analysis of samples from the LCD industry.
Mechanics of Saw-Tooth Chip Formation in Metal Cutting
Authors: Vyas A. , Shaw M. C.
Published: February 2008

The saw-tooth chip was the last of the major types to be identified. This occurred in 1954 during machining studies of titanium alloys which were then being considered for aerospace applications because of their large strength-to-weight ratio and corrosion resistance. This is a type of chip that forms when very hard brittle materials are machined at high speeds and feeds. Since this is an area of machining which will be of increasing interest in the future, particularly in hard turning, it is important that the mechanism and mechanics of this type of chip formation be better understood. At present, there are two theories concerning the basic origin of saw-tooth chips. The first to appear assumed they are of thermal origin while the second assumes they arise due to the periodic development of cracks in the original surface of the work. The thesis presented here is that the root cause for saw-tooth chip formations is cyclic cracking. This is followed by a discussion of extensive experimental data that supports this point of view.
Mid-Surfaces of Profile-based Freeforms for Mold Design
Authors: Fischer A. , Smolin A. , Elber G.
Published: February 2008

Mid-surfaces of complex thin objects are commonly used in CAD applications for the analysis of casting and injection molding. However, geometrical representation in CAD typically takes the form of a solid representation rather than a mid-surface; therefore, a process for extracting the mid-surface is essential. Contemporary methods for extracting mid-surfaces are based on numerical computations using offsetting techniques or Voronoi diagram processes where the data is discrete and piecewise linear. These algorithms usually have high computational complexity, and their accuracy is not guaranteed. Furthermore, the geometry and topology of the object are not always preserved. To overcome these problems, this paper proposes a new approach for extracting a mid-surface from a freeform thin object. The proposed method reduces the mid-surface problem into a parametrization problem that is based on a matching technique in which a nonlinear optimization function is defined and solved according to mid-surface criteria. Then, the resulting mid-surface is dictated by a reparametrization process. The algorithm is implemented for freeform ruled, swept, and rotational surfaces, that are commonly used in engineering products. Reducing the problem to the profile curves of these surfaces alleviates the computational complexity of the 3D case and restricts it to a 2D case. Error is controlled globally through an iterative refinement process that utilizes continuous symbolic computations on the parametric representation. The feasibility of the proposed method is demonstrated through several examples.
A Comparison of Rapid Fabrication Methods for Sheet Metal Forming Dies
Authors: Walczyk D. F. , Hardt D. E.
Published: February 2008

The need for rapid, low-cost die fabrication and modification methods is greater than ever in the sheet metal forming sector of industry. Consequently, three fabrication methods, suitable for rapid die development schemes, are being compared experimentally based on cost, lead-time, shape resolution and flexibility issues. The candidate methods include CNC-machining a solid billet of material (standard method), assembling and clamping an array of profiled-edge laminations (PEL), and configuring and clamping a matrix of closely-packed pins (discrete die). A matched-set of forming dies was made using each of the candidate fabrication methods for stamping an FEA-verified benchmark part out of steel sheet. Based on the stamping experiments, a PEL die is shown to be similar to CNC-machined dies except that most tooling accessibility problems are eliminated, die geometry limitations are reduced and faster fabrication is possible for harder tool materials. When compared with CNC-machined dies, the discrete die method limits part shape fidelity, maximum forming loads, die geometry and blankholder incorporation. However, the discrete die method excels over the other two methods in terms of lower cost and faster fabrication time. The results of this study make a strong case for the sheet metal forming sector of industry to actively implement the PEL and discrete die methods in their manufacturing operations.
Dimensional Measurement Data Analysis, Part 2: Minimum Zone Evaluation
Authors: Choi W. , Kurfess T. R.
Published: February 2008

Modern inspection systems such as coordinate measurement machines generate discrete three dimensional coordinates representing points from the surface of a manufactured part. These coordinates must be compared to a target or nominal geometry to determine if the part conforms to specification. Quite often a least squares fit or a min-max fit are employed to determine the part geometry. However, as described in Part 1 of this paper, acceptable deviations are often specified as tolerance zones about the nominal geometry. Part 1 of this paper presents a zone fitting algorithm having an objective of placing the sampled data points within a specified tolerance zone. If all of the points fit within the zone, the part is passed. This pass/fail result does not provide information as to the quality of the part. The question that is not answered is “Did the points just fit into the tolerance zone, or did the points fit with ample space remaining?” This question is important as it informs production personnel whether their processes are operating well within specifications or just barely within specifications. In this part of the paper, the zone fitting method developed in Part 1 of this paper is extended to a minimum zone evaluation. This can be formulated as a one dimensional search for the critical value of the zone fitting objective function. The minimum zone evaluation algorithm developed in this paper can be applied to an arbitrary geometry profile evaluation. A number of examples are presented to demonstrate its capabilities.
Modeling Surface Texture in the Peripheral Milling Process Using Neural Network, Spline, and Fractal Methods with Evidence of Chaos
Authors: Stark G. A. , Moon K. S.
Published: February 2008

Modeling texture of milled surfaces using analytic methods requires explicit knowledge of a large number of variables some of which change during machining. These include dynamically changing tool runout, deflection, workpiece material properties, displacement of the workpiece within its fixture and others. Due to the complexity of all factors combined, an alternative approach is presented utilizing the ability of neural networks and fractals to implicitly account for these combined conditions. In the initial model, predicted surface points are first connected using splines to model 3D surface maps. Results are presented over varying several cutting parameters. Then, replacing splines, an improved fractal method is presented that determines fractal characteristics of milled surfaces to model more representative surface profiles on a small scale. The fractal character of surfaces as manifested by the fractal dimension provides evidence of chaos in milling.
Effects of the Feedline and the Hydrostatic Pocket Depth on the Flow Pattern and Pressure Distribution
Authors: Braun M. J. , Dzodzo M.
Published: February 2008

The paper treats on a comparative basis the development of the flow and pressure maps in deep, and respectively, shallow hydrostatic bearing pockets. The numerical simulation uses a dimensionless formulation of the Navier-Stokes equations written for a body fitted coordinates system, and applied through a collocated grid. The present work is a continuation of the simulations performed by Braun et al. (1993, 1994a, 1994b) to cases where the length and diameter of the restrictor feedline is of consequence to the flow in both the shallow and the deep pocket. The model includes the coupling between the pocket flow and a finite length feedline flow, on one hand, and the pocket and the adjacent lands on the other hand. Geometrically, all pockets have the same projected footprint, lands length, and capillary feedline. This numerical study uses the Reynolds number Re based on the runner velocity (laminar range only), and the inlet jet strength F as the dynamic similarity parameters, while the dimensionless clearance C is used as a geometric parameter. The flow structures, and the physical reasons underlying the causes of the pressure variation inside the deep and shallow pockets [either longitudinally (radially) or transversally (circum-ferentially)], are discussed quantitatively and comparatively. It is further shown that the transversal pressure distributions under the runner are highly dependent on whether the flow is dominated by the rotation of the runner (hydrodynamic effects), or by the strength of the hydrostatic jet (F). Finally the longitudinal pressure curves in the depth of the pocket, and restrictor are presented and the nature of their variation discussed. The back step and Rayleigh step effects are also discussed on a comparative basis for the two types of pockets, and in conjunction with the Couette, and the jet dominated flow. The modification of the central vortical zones of the deep pockets into oblong vortical zones for the shallow pockets is presented, and its consequences are discussed.
Development of a New Tip Assembly for Lateral Force Microscopy and Its Application to Thin Film Magnetic Media
Authors: Lu C.-J. , Jiang Zhaoguo , Bogy D. B. , Miyamoto T.
Published: February 2008

In a Lateral Force Microscope (LFM), appropriate spring constants of the tip assembly are essential for obtaining proper normal loads for wear or scratch tests and good lateral force signals. We developed a new tip assembly design for which the lateral and normal springs can be changed independently. It was installed on a LFM where two optical heads are used to detect the lateral and normal deflections of the tip assembly for simultaneous measurements of the surface topography and friction force. Reliable calibration procedures for the LFM are presented. The LFM was used to measure the lateral forces in wear tests under various normal forces for thin film magnetic disks with and without a carbon overcoat. The friction coefficient is constant in the load range where there is no wear and increases with normal load after the tip starts to damage the surface. The carbon-coated disk has a lower friction coefficient and can support larger normal loads without wear.
On the Transitions in the Lubrication of Concentrated Contacts
Authors: Schipper D. J. , de Gee A. W. J.
Published: February 2008

Friction experiments on lubricated concentrated contracts were performed to study; (a) the transitions between the different lubrication modes when operating in the lubricants liquid-state regime and (b) the frictional behavior of these contacts, under conditions of full-film lubrication, taking into account the lubricants liquid-state and solid-state behavior. On the basis of these results a flow diagram is presented for lubricated concentrated contacts, from which the lubrication mode as well as the frictional behavior can be obtained as a function of the operational conditions, under which these contacts are functioning.
Boundary and Mixed Friction in the Presence of Dynamic Normal Loads: Part I—System Model
Authors: Polycarpou Andreas A. , Soom Andres
Published: February 2008

The instantaneous normal motion between bodies in a sliding contact is an important variable in determining dynamic friction under unsteady sliding conditions. In order to model friction under dynamic conditions, it is therefore necessary to combine a dynamic model of the sliding system with an accurate model of the friction process. In the present work, the nonlinear normal dynamics of a friction test apparatus are described by a linearized model at a particular steady loading and sliding condition in a mixed or boundary-lubricated regime. The geometry is a line contact. The Hertzian bulk contact compliance and film and asperity damping and stiffness characteristics are included as discrete elements. In Part I of the paper, a fifth-order model is developed for the normal dynamics of the system, using both the Eigensystem Realization Algorithm (ERA) and classical experimental modal analysis techniques. In Part II, this system model is combined with a friction model, developed independently, to describe dynamic friction forces under both harmonic and impulsive applied normal loads.
The Development and Implementation of Discrete Texture for the Improvement of Tribological Performance
Authors: Li Yufeng , Menon Aric K.
Published: February 2008

The bearing area of conventional texture on magnetic recording disk surfaces shows a tendency of increase with a decrease in surface height. This is believed to be a major reason for the increase of head/disk friction with the accumulation of CSS cycles. In view of this, a novel type of texture is developed in this study. This type of texture consists of discrete pillar-shaped asperities, whose height and shape can be optimized to reduce friction build-up and wear depth during CSS operation. It also allows lower asperity height to reduce take-off velocity and glide height. In addition, it is suitable for landing zone texturing. The discrete texture remarkably outperforms mechanical texture during CSS tests.
A Study of the Mechanism of Lubrication in Porous Journal Bearings: Effects of Dimensionless Oil-Feed Pressure on Frictional Characteristics
Authors: Kaneko Satoru , Hashimoto Yuji
Published: February 2008

The frictional characteristics of a porous bronze bearing are investigated experimentally under hydrodynamic and mixed lubrication conditions. The results show that under the same value of dimensionless oil-feed pressure pˆs, the relationship between the coefficient of friction μ and the Sommerfeld number S can be represented by a single friction curve extending from the hydrodynamic regime to the mixed regime. With decreasing S, μ decreases in the hydrodynamic regime and then steeply increases in the initial stage of the mixed regime. However, at lower values of S, μ becomes steady and its value remains almost the same for various pˆs. The value of S at the transition point from the hydrodynamic regime to the mixed regime is significantly affected by pˆs, becoming smaller for higher pˆs. To estimate μ in the mixed regime, a simple frictional model is proposed on the basis of the assumption that the load supported by the fluid film and the coefficient of fluid friction in the mixed regime are determined by the oil film extent and that they are the same as those at the transition point. The calculated values of μ based on the model are found to approximately agree with the experimental results.
Transparent Pin Wear Test on Thin-Film Magnetic Disk
Authors: Kawakubo Youichi , Yahisa Yotsuo
Published: February 2008

Pin-on-disk wear tests on thin-film magnetic disks were performed using transparent materials. Quartz glass (QG), transparent zirconia (TZ), sapphire (SA), and synthesized diamond (DI) were used as pin materials. In addition to friction, sliding condition and pin wear were continuously monitored with video camera. Simultaneous friction measurement and video monitoring showed that friction dropped when wear debris intruded between pin and disk surfaces. Pin wear, from the measured diameter of wear scar on spherical pins, increased in the order of DI, SA, QG, and TZ. This order of pin wear does not coincide with that of the pin bulk hardness. Disk lifetime increased in the order of TZ, QG, SA, and DI, and the smaller the pin wear, the longer the disk lifetime.
Transient Analysis of Tilt Pad Journal Bearings Including Effects of Pad Flexibility and Fluid Film Temperature
Authors: Gadangi R. K. , Palazzolo A. B.
Published: February 2008

The paper considers vibration response of spinning shafts supported by flexible tilt pad journal bearings, to large mass imbalance (blade loss). A time transient study of the tilt pad journal bearing with thermal effects and without pad deformations, and with pad deformations and without thermal effects, is performed. Influence of the inclusion of thermal effects on the journal center’s orbit, the minimum film thickness, and the maximum film temperature is evaluated, and also the influence of pad deformations due to the fluid film forces on the journal center’s orbit and the minimum film thickness is studied. Inclusion of thermal effects had little effect on the orbit, while the inclusion of pad deformations had considerable effect on the journal orbit and the minimum film thickness. Three cases are studied in this paper; static load without imbalance, static load with low imbalance, and static load with high imbalance.