bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of Variable Spindle Speed Face Milling for Tool-Work Structures With Complex Dynamics, Part 1: Simulation Results
Authors: Radulescu R. , Kapoor S. G. , DeVor R. E.
Published: February 2008

A mechanistic dynamic model is used to simulate a face milling process during constant and variable speed machining. The model can be used to predict the optimum speed trajectory that can provide a low level of vibration and consequently a large productivity rate and a small surface error. The model is used to investigate the vibration of face milling processes that have one, or multiple coupled modes of vibration acting throughout the cut. For cutting processes having one dominant mode of vibration, the model predicts that variable speed machining is especially effective over constant speed machining when the tool-work system changes its dominant mode of vibration throughout the cut, or when the tool-work system has several modes of vibration coming from component parts that are cut in the same time. For cutting processes having multiple dominant modes of vibration, the model predicts that variable speed machining is especially effective over constant speed machining when the tool-work modes of vibration are unequal and moderately coupled to each other. Also, the model suggests that for tool-work systems having complex geometries with dynamics hard to predict, variable speed machining is safer to use than constant speed machining when trying to achieve high productivity rates. This is due to the fact that variable speed machining is robust with respect to the dynamics of the tool-work system. Finally, the model predictions are in good agreement with the experiment.
Far-Field Initial Response of Acoustic Emission From Cracking in a Weldment
Authors: Fang C.-K. , Kannatey-Asibu E. , Barber J. R.
Published: February 2008

An analytical expression is developed for the relationship between far-field acoustic emission (AE) signal and the propagation of a finite plane crack due to a nonuniform residual stress in a weldment. The AE sensor is situated at the boundary parallel to the crack surface. The quasi-static crack opening displacement (COD) rate is used as the source function. The AE initial response on a traction-free surface is obtained as a function of instantaneous crack length and speed. A closed-form expression is obtained for the normal surface displacement at the epicenter when the crack propagates at uniform speed for a finite duration between initiation and arrest. Results from an earlier analysis of the (variable) speed of crack propagation in a weldment are used to develop a more exact numerical prediction of the surface motion. The effects of initial crack length and bluntness on AE surface motion are investigated in both time and frequency domains.
Three-Dimensional Finite Element Analysis of Sheet-Metal Bending With Complex Die Geometry
Authors: Chou I-Nan , Hung Chinghua
Published: February 2008

The purpose of this research was to find manufacturing processing conditions that would prevent the occurrence of fractures in a sheet-metal bending product. The finite element code ABAQUS was used to analyze the tensile strain at the particular point where fractures frequently occur. First an optimal combination of factors was sought using the method of controlling parameters. The analysis showed that the three factors, r2, r4, and the coefficient of friction, which are typical controlling factors, cannot be used to reduce the tensile strain at the critical point efficiently. A preform design was then applied to solve the problem of fracturing. By using a two-step bending operation, we successfully moved the highest tensile strain away from the critical point and also reduced the magnitude of this strain.
Variation Simulation for Deformable Sheet Metal Assemblies Using Finite Element Methods
Authors: Liu S. Charles , Hu S. Jack
Published: February 2008

Traditional variation analysis methods, such as Root Sum Square method and Monte Carlo simulation, are not applicable to sheet metal assemblies because of possible part deformation during the assembly process. This paper proposes the use of finite element methods (FEM) in developing mechanistic variation simulation models for deformable sheet metal parts with complex two or three dimensional free form surfaces. Mechanistic variation simulation provides improved analysis by combining engineering structure models and statistical analysis in predicting the assembly variation. Direct Monte Carlo simulation in FEM is very time consuming, because hundreds or thousands of FEM runs are required to obtain a realistic assembly distribution. An alternative method, based on the Method of Influence Coefficients, is developed to improve the computational efficiency, producing improvements by several orders of magnitude. Simulations from both methods yield almost identical results. An example illustrates the developed methods used for evaluating sheet metal assembly variation. The new approaches provide an improved understanding of sheet metal assembly processes.
5-Axis Freeform Surface Milling Using Piecewise Ruled Surface Approximation
Authors: Elber G. , Fish R.
Published: February 2008

This paper presents a 5-axis side milling scheme for freeform surfaces based on automatic piecewise ruled surface approximation. With this scheme, resulting surface finish is accurate and pleasing, and has a smaller scallop height compared to ball-end milling. The ruled surface approximation can be made arbitrarily precise resulting in an overall fast milling operation that satisfies tight tolerances, and smoother surface finish. The class of surfaces that can take advantage of this type of 5-axis milling operation includes both convex and saddle-like (hyperbolic) shapes.
Error Compensation for Sculptured Surface Productions by the Application of Control-Surface Strategy Using Predicted Machining Errors
Authors: Lim Ee Meng , Menq Chia-Hsiang
Published: February 2008

In this paper, the principle and effectiveness of the control-surface strategy in machining-error compensation for end milling processes are studied. Using this strategy, two new approaches, namely the direct compensation approach and the sensitivity function approach, are proposed. When compared to existing approaches, there are two major improvements in the proposed approaches. First, machining errors caused by tool deflection are estimated from a developed surface generation model. This eliminates the time and costs required to design and conduct the actual machining experiments and dimensional inspections. Second, the effectiveness of the proposed approaches is improved either by increasing the number of times the strategy is been used or by selecting the appropriate shifted distance based on the estimated machining-error curve. The effectiveness of the proposed error-compensation approaches is verified from simulations and experimental results for a 2D sculptured surface. By using computer aided design tool, this surface generation model can be easily applied to the problems in which the designed surfaces are complex 3D sculptured by considering more complicated chip geometry model. These proposed approaches can also be integrated into an integrated framework for machining path planning in which prediction and compensation of dimensional errors take place in the process development phase rather than in the manufacturing phase of the production cycle.
On a Method for Die Container Design in Completely Closed Die Forging
Authors: Ibhadode A. O. A.
Published: February 2008

Relatively simple design equations are derived for selecting container external diameter in completely closed die forging, using die expansion as a basis. The method imposes a theoretical lower limit on the tolerance than can be specified on the maximum diameter of a forging. The method can be used for axisymmetric shapes such as solid and hollow cylinders, +-, U-, H-, and T-shapes.
Magnetic Float Polishing of Ceramics
Authors: Raghunandan M. , Umehara N. , Noori-Khajavi A. , Komanduri R.
Published: February 2008

Magnetic float polishing is a new technique developed for efficient finishing of advanced ceramics. The equipment for this application thus far has been developed on the basis of empirical designs and trial and error experimental approach which can be costly and time consuming. In the work reported here both analytical (FEM simulation) and experimental approaches were taken to determine such design parameters as the variation of magnetic float stiffness with buoyant force and variation of buoyant force with the gap between the magnet and the float. The agreement between the experimental and analytical results is found to be excellent. Consequently, it is possible to simulate different designs without actually building different equipment for the performance evaluation. Also, the effect of ball circulation speed in magnetic float polishing is discussed qualitatively for assessing the conditions for high removal rates and/or best finish. Such an approach can facilitate the development of operating conditions maps for magnetic float polishing.
Refined Friction Modeling for Simple Upsetting
Authors: Hsu Tze-Chi , Lee Chung-Hung
Published: February 2008

A refined model for friction in lubricated simple upsetting processes which takes account of the different lubrication regimes which may occur at the workpiece/tooling interface is developed. The refined friction model considers not only the full film situation but also the mixed and boundary lubrication condition. The load carrying capacity of the lubricant in the mixed lubrication regime is evaluated by using the average flow model to treat the influence of surface roughness on lubricant flow. The mechanics of asperity contact is governed by a semi-empirical boundary model in which the plastic deformation of the workpiece is considered. The lubricant film thickness is then determined by using a shooting method to ensure that the interface pressure is partially supported by the asperity contact and partially supported by the lubricant film. The refined friction model is then combined with a rigid-plasticity finite element code to analyze the simple upsetting processes. Numerical results using the coupled codes such as the distribution of the friction stress and normal pressure, the geometry and surface topography of the deformed workpiece are compared with previous numerical and experimental investigation under different lubrication conditions. The simulation results are in good agreement with the experimental data.
Robust Tolerance Design With the Integer Programming Approach
Authors: Feng Chang-Xue (Jack) , Kusiak A.
Published: February 2008

The quality loss function incorporates the cost of tolerances, however, it does not consider the manufacturing cost and design constraints. In this paper, a stochastic integer programming (SIP) approach is presented for simultaneous selection of tolerances and manufacturing processes. A direct link between the minimum manufacturing cost and the required level of manufacturing yield is established through the process capability index Cpk. As the tolerances in SIP are discrete, the solution generated is acceptable for manufacturing. It is shown that the integer programming models are applicable in the quality loss function and six sigma design approaches. The SIP approach is illustrated with a classical example of nonlinear tolerance design. The comparison of the proposed SIP approach, the Taguchi method, and the conventional mathematical models in tolerance synthesis is presented.
Centerless Grinding Systems Stability
Authors: Epureanu B. I. , Montoya F. M. , Garcia C. L.
Published: February 2008

In this paper, the steady state dynamics of a centerless grinding machine and work piece has been examined. A model of a centerless grinding system which allows both the deflection of the work piece center and the deformation of the grinding machine frame has been developed. Two instabilities are demarcated • work piece surface generation instability, and • grinding process instability. Both the generation and the grinding stability of self-excited vibrations are investigated. Stability limits are defined using the characteristic equations of the system. The main factors that influence the limit of stability of the machine, and the transversal profile of the work piece have been shown to be • the relative position of the grinding wheel, regulating wheel and support blade of the work piece; • the width of the grinding wheel; • the harmonic response of the grinding machine frame.
Laser Weld Penetration Estimation Using Temperature Measurements
Authors: Lankalapalli K. N. , Tu J. F. , Leong K. H. , Gartner M.
Published: February 2008

Penetration depth is an important factor critical to the quality of a laser weld. This paper presents a 3D heat conduction model with a moving line source to correlate the temperature measured on the bottom surface of the workpiece to the weld penetration, weld bead width and welding speed. Temperatures on the bottom surface of the workpiece are measured using infrared thermocouples located behind the laser beam. The averaging effect due to the temperature measurement spot size is analyzed. This paper provides a model-based approach for laser weld penetration monitoring instead of a pure empirical correlation between a measured signal (e.g., acoustic, infrared) and the penetration depth. Experiments were conducted to compare the depth estimation based on the model to bead-on-plate welds on low carbon steel plates of varying thickness at different laser power levels and speeds. It is shown that the temperature on the bottom surface is a consistent indicator of penetration depth and that the correlation is also sensitive to the sensor location as well as other process conditions such as weld shape, width, and the plate thickness. The proposed model is computationally efficient and is suitable for on-line process monitoring application.
An Experimental Investigation of the Survivability and Friction Characteristics of Tin-Coated and Polymer-Laminated Steels
Authors: Jaworski J. , Schmid S. R. , Wang J. E.
Published: February 2008

The food and beverage container industry is of immense economic importance, and being an established technology, is also fiercely competitive. In the manufacturing process for metal containers, a time consuming and therefore expensive process involves the spray of a food-contact safe polymer coating onto the can before filling. This process can be eliminated using a pre-laminated metal workpiece as long as the polymer will survive the manufacturing operations involved in can making. The most demanding operation in can making is the ironing process because of the high pressures involved as well as the necessary generation of new surface. This paper presents experimental results on the ironing of steels with tin and lacquer coatings and polyester laminate, and addresses tribological characteristics as well as survivability issues with these workpieces. The experimental apparatus used, a specially fabricated ironing simulator, allowed variation of die angles using titanium carbide tooling inserts. The polyester laminate is found to perform very well at low die angles without lubricants, suggesting that this is a viable option for can manufacture.
Dimensional Measurement Data Analysis, Part 1: A Zone Fitting Algorithm
Authors: Choi W. , Kurfess T. R.
Published: February 2008

Measured data taken from Coordinate Measuring Machines (CMMs) are in the form of Cartesian coordinates of points from a part surface. In order to interpret the data, a numerical analysis must be performed on them. Currently, data fitting techniques such as a least squares fit or a min-max fit are employed to compare the measured points to the design model. As the objectives of the various techniques differ, they often yield conflicting results. Since this discrepancy may lead to a different conclusions in the process dimensional inspection, it is critical that inspection procedures are based on well defined criteria that employ the appropriate technique to achieve the desired inspection goals. If tolerances are represented by tolerance zones, a zone fitting algorithm, introduced in this paper, provides a more consistent means of verify conformance to the tolerance zone. It determines whether a set of measured points fits into a specified tolerance zone. If the point set can fit into the zone, a rigid body transformation placing the points inside the zone is returned. The algorithm is numerically stable and addresses a general type of tolerance zone. The examples demonstrate that the zone fitting algorithm is more consistent compared to the least squares fit and the min-max fit in tolerance zone conformance verification. A subsequent paper (Part 2) addresses the determination of a minimum zone that extends inspection from a pass/fail mode to a quality analysis operation.
Kinematics Analysis of the Chipping Process Using the Circular Diamond Saw Blade
Authors: Jerro H. D. , Pang S. S. , Yang C. , Mirshams R. A.
Published: February 2008

One of the primary goals in the design of a diamond blade cutting system is to reduce the cutting force. By understanding the fundamentals of the kinematics of the sawing operation, these forces can be lowered and even optimized with respect to the machining parameters. In this work the material chipping geometries have been mathematically defined and derived through kinematic analysis. These geometries are bounded by four curves and depend on the parameters: depth of cut h, blade diameter D, transverse rate of the workpiece νT, peripheral speed of the saw blade νP, and grit spacing λ. From these chipping geometries, chip area and thickness relations have been obtained. A relation for the mean chip thickness to grit spacing ratio (tc/λ) has also been obtained as a function of the nondimensional machining parameter ratios, h/D and νT/νP. The effects of these parameters on tc were also investigated. It was found that increasing ω and D, reduces the chip thickness. Contrarily, increasing νT, λ, and h, increases the magnitude of the chip thickness. A review of older chipping models was performed, comparing well with the developed model. The results show an excellent agreement between the new model and the older ones. However, at moderately small to large h/D values the new model yields a more exact result. Thus, for h/D values greater than 0.08, it is recommended that the kinematic model be used to compute tc and other pertinent sawing parameters (i.e., grit force and grinding ratio) which are a function of tc.
System Modeling and Real-Time Simulator for Highly Model-Mixed Assembly Systems
Authors: Kuo Chung-Hsien , Huang Han-Pang , Wei Kuang C. , Tang Steve S. H.
Published: February 2008

In recent years, the automobile industry is facing more challenge than ever due to rapid model change requirements and demand fluctuations. Traditional fixed-type production systems are less capable in coping with the rapid change, while flexible production systems can better meet the requirement of low-volume production with model variations. Flexible machines integrated with model-mixed assembly lines form flexible assembly systems (FASs). In this paper, Colored Timed Petri Net (CTPN) is used to model a highly model-mixed automobile assembly system. Based on this CTPN model, a real-time simulator was developed along with different dispatching rules. Besides, the algorithm of balanced budget work standard (BWS) for a small batch production is developed for adjusting the loading balance of the operators in the highly model-mixed assembly lines. The simulator can be used as an effective tool for developing scheduling strategies.
Multiple Fault Detection and Isolation Using the Haar Transform, Part 1: Theory
Authors: Koh C. K. H. , Shi J. , Williams W. J. , Ni J.
Published: February 2008

Most manufacturing processes involve several process variables which interact with one another to produce a resultant action on the part. A fault is said to occur when any of these process variables deviate beyond their specified limits. An alarm is triggered when this happens. Low cost and less sophisticated detection schemes based on threshold bounds on the original measurements (without feature extraction) often suffer from high false alarm and missed detection rates when the process measurements are not properly conditioned. They are unable to detect frequency or phase shifted fault signals whose amplitudes remain within specifications. They also provide little or no information about the multiplicity (number of faults in the same process cycle) or location (the portion of the cycle where the fault was detected) of the fault condition. A method of overcoming these limitations is proposed in this paper. The Haar transform is used to generate sets of detection signals from the original measurements of process monitoring signals. By partitioning these signals into disjoint segments, mutually exclusive sets of Haar coefficients can be used to locate faults at different phases of the process. The lack of a priori information on fault condition is overcomed by using the Neyman-Pearson criteria for the uniformly most powerful form (UMP) of the likelihood ratio test (LRT).
Multiple Fault Detection and Isolation Using the Haar Transform, Part 2: Application to the Stamping Process
Authors: Koh C. K. H. , Shi J. , Williams W. J. , Ni J.
Published: February 2008

The sheet metal drawing operation is a complex manufacturing process involving more than forty process variables. The intricate interaction among these variables affect the forming tonnage which is measured by strain gages mounted on the press. A fault is said to occur when any of these process variables deviate beyond their specified limits. Current detection schemes based on thresholding do not fully exploit the information in the tonnage signals for the detection and isolation of multiple fault condition. It is thus an excellent case study for demonstrating the implementation of the detection methodology presented in Part 1. By partitioning the tonnage signature into disjoint segments, mutually exclusive sets of Haar coefficients can be used to isolate faults in each stage of the process.
Boundary and Mixed Friction in the Presence of Dynamic Normal Loads: Part II—Friction Transients
Authors: Polycarpou Andreas A. , Soom Andres
Published: February 2008

The normal dynamic model of the sliding system developed in Part I of this paper is combined with a friction model, obtained separately from the same apparatus, to provide estimates of the friction under dynamic loading conditions. The two-dimensional friction model, developed from measurements at constant normal load and slowly varying sliding speeds, includes the normal approach of the sliding bodies as a key variable. From the combined model, estimates of friction under harmonic loading and of friction transients associated with short duration impacts are compared with measurements. The very good agreement between estimates and measurements indicates that, while a good friction model is required, the crucial and most variable aspect of the modeling of dynamic friction is the representation of the normal dynamics of the sliding system.
The Double Dimple Magnetic Recording Head Suspension and Its Effect on Fly Height Variability
Authors: Harrison J. C. , Hanrahan K. P.
Published: February 2008

A gimbal forming modificaton is presented which, when implemented, leads to significant reduction in air bearing surface (ABS) static attitude and flying height variability within head-gimbal assembly (HGA) populations. The modification requires no additional parts or steps in the manufacture of the suspension assembly. An experimental test of the concept is described, along with the procedure on which it is based. The resulting reduction in product variability is obtained without measurement of (or tailoring to) the initial conditions of the constitutive parts of each HGA. A ≈ 50 percent reduction in static attitude variability, and a ≈ 33 percent reduction in flying variability, was experimentally shown to result from the adoption of the Double Dimple design concept, in all flying degrees of freedom.
Three-Dimensional Surface Characterization by Two-Dimensional Autoregressive Models
Authors: Hong Min S. , Ehmann Kornel F.
Published: February 2008

An attempt is made to characterize and synthesize engineered surfaces. The proposed method, based on two-dimensional difference equations and two-dimensional linear autoregressive models, is not only an analytical tool to characterize but also to generate/synthesize three-dimensional surfaces with desired properties. The developed method expresses important three-dimensional surface characteristics such as the autocorrelation or power spectrum density functions in terms of the two-dimensional autoregressive coefficients.
Cavitation in Normal Separation of Square and Circular Plates
Authors: Boedo S. , Booker J. F.
Published: February 2008

The “negative squeeze” lubrication problem is investigated by means of a mass-conservating finite element cavitation algorithm (described elsewhere) within the context of a dimensionless study of lubricant film behavior between rigid, parallel separating surfaces. Appropriate mesh geometries which capture spatial and temporal mixture density history and satisfy JFO conditions on the cavitation interface are determined. Present simulation results agree qualitatively with previous experiments, supporting the validity of the algorithm and its utility in the bearing design process.
Initial Temperature Evaluation for Flash Temperature Index of Gear Tooth
Authors: Deng Gang , Kato Masana , Maruyama Noboru , Morikawa Kunihiko , Hitomi Nobuteru
Published: February 2008

In the AGMA standard for the scoring resistance evaluation of gears, flash temperature is used as an index indicating the risk of scoring. The flash temperature is expressed as the sum of flash rise of temperature and initial temperature. In this research, the initial temperatures are measured for various gear sets in running by thermocouples which are mounted just beneath the working surface of pinion. The effects of gear dimensions, rotating speed, and lubrication conditions on the initial temperature are clarified. An experimental formula is proposed for estimating the initial temperature, which depends on the temperature of oil inlet, the frictional power loss, and the running conditions such as rotating speed, contact position, and the oil supply rate. The estimated initial temperatures are in good agreement with the measured values. The proposed method is available for the scoring resistance evaluation of the vehicle transmissions.
Conditions for Scuffing Failure of Ground and Superfinished Steel Disks at High Sliding Speeds Using a Gas Turbine Engine Oil
Authors: Patching M. J. , Kweh C. C. , Evans H. P. , Snidle R. W.
Published: February 2008

This paper describes the results of an experimental investigation to compare the scuffing performance of conventionally ground and superfinished hardened steel disks operating at sliding speeds of up to 26 m/s and lubricated with a gas turbine engine oil at a temperature of 100° C. The ground disks were finished in the axial direction to simulate the orientation of surface finish found on involute gears. Superfinishing was found to give a significant increase in the load at which scuffing occurred. Frictional traction was also measured in the experiments and was found to be significantly lower for the superfinished disks in the loading stages preceding scuffing failure.
Measurement of Physical Properties of Lubricants Under High Pressure by Brillouin Scattering in a Diamond Anvil Cell
Authors: Nakamura Y. , Fujishiro I. , Nishibe K. , Kawakami H.
Published: February 2008

Brillouin scattering spectra and their transverse mode were measured for paraffinic and naphthenic synthetic lubricants, employing a high-pressure diamond anvil cell (DAC). Sound velocity, density, refractive index, and shear modulus under high pressure were obtained. The density obtained from the thermodynamic relation was compared with that from Lorentz-Lorenz‘s formula. The densities were also compared with Dowson‘s density-pressure equation of lubricants. The sound velocity in the transverse mode and shear modulus were obtained for 5P4E up to 2.7 GPa. A slope change in the pressure-sound velocity diagram was confirmed at about 0.3 GPa, which may be associated with crystallizaton of 5P4E, observed through a diamond optical window in the DAC.
Investigation Into Relationship Between Friction Behavior and Plastic Deformation Using a Newly Devised Rolling-Type Tribometer
Authors: Dohda Kuniaki , Wang Zhrgang
Published: February 2008

A new rolling-type tribometer has been devised to investigate the effects on friction behavior of the average velocity of the lubricant at the inlet to the contact zone and the relative sliding velocity during deformation independently. This paper shows the principle of operation of the tribometer and deformation mode of the workpiece, especially considering the relationship between friction and bulk deformation. Experiments using mild steel strips with a dull surface showed that the friction stress on the friction roll, which has a smaller velocity than that of the traction roll, is mainly controlled by lubricating conditions on the friction roll side. The contact pressure is mainly decided by the friction conditions on the traction roll side. It was also revealed that, with an increase of the reduction in the workpiece thickness, the friction stress on the friction roll side remains constant when the friction roll is rotated. The friction stress increases when the friction roll is stopped after a certain reduction in the workpiece thickness.
Operating Characteristics of an Externally Pressurized Gas Lubricated Piston Ring
Authors: Yamamoto Minoru , Mori Haruo , Yoshikawa Tsuneo
Published: February 2008

An analytical model is presented to obtain the film thickness profile of an externally pressurized gas lubricated piston ring which is applied to an air compressor. In order to examine the effects of the ends of the ring, the analysis is based on the two-dimensional, transient, compressible Reynolds equation accounting for the ring deflection and the equilibrium condition of the ring in the clearance space between the piston and the cylinder bore. In the numerical simulation, the Reynolds equation is discretized by using a cell method. The resulting nonlinear system of equations is solved by the Newton-Raphson iteration method. The obtained results show that the piston ring keeps the lubricating film thickness within a narrow range of the design clearance over the entire circumferential area throughout one cycle of compressor operation.
EHD Analysis, Including Structural Inertia Effects and a Mass-Conserving Cavitation Model
Authors: Bonneau D. , Guines D. , Freˆne J. , Toplosky J.
Published: February 2008

The dynamic behavior of two elastic connecting-rod bearings is studied. The Newton-Raphson method and 8-node isoparametric elements for the lubrication analysis are used. For the structural analysis, 3-D elasticity assumptions are made and 20 nodes isoparametric elements are used. Inertia forces due to the kinematics of the structure are incorporated with the effects of the hydrodynamic pressures in the elastic deformations of the bearing. Comparisons with Goenka‘s results are presented for the General Motors connecting-rod bearing. A mass-conserving model used in conjunction with Murty‘s algorithm is presented for the transient evolution of the cavitation area. This model is applied for the EHD study of a Renault connecting-rod bearing.
Upstream Pumping of Radial Lip Seals by Tangentially Deforming, Rough Seal Surfaces
Authors: Van Bavel P. G. M. , Ruijl T. A. M. , Van Leeuwen H. J. , Muijderman E. A.
Published: February 2008

This paper aims at a theoretical explanation of the following two experimental observations of radial lip seals: fluid film formation and upstream pumping action. The origins of these observations are still poorly understood. A hydrodynamic analysis is presented for the fully flooded contact zone of a smooth shaft surface running against a rough seal surface. Four roughness structures are considered: one-dimensional sinusoidal and two-dimensional sinusoidal seal roughness structures both without and with a tangential seal surface displacement. The tangential seal surface displacement is chosen asymmetric with the axial position in the contact. It follows that the tangential deformation of the one- and two-dimensional seal roughness structures used in this paper can explain the aforementioned experimental observations and simulate the observed order of magnitude of load-carrying capacity, pump rate, and friction torque found in the literature.
A Study of Cross-Width Variations in the Two-Dimensional Foil Bearing Problem
Authors: Mu¨ftu¨ Sinan , Benson Richard C.
Published: February 2008

The foil bearing problem, common to magnetic tape recording, is modeled through numerical simulation. The emphasis is on the effects of cross-width changes in the system parameters. Air lubrication is modeled using the Reynolds equation including the first-order slip correction terms and compressibility. A segmented structural model is introduced for the tape displacements where the tape is modeled as a cylindrical shell in the wrap zone and as a plate in the straight segments between the guide pins and the tangency points. Tape inertia and transport effects are included by using the material time derivative of the displacements. An explicit time integration method is used for the tape equation in order to obtain a faster transient coupling algorithm. The Reynolds equation is solved with the alternating direction implicit (ADI) integration method. The effects of axial tape tension, guide shape variations and the tape width on the steady-state tape-guide separation are investigated. It is shown that small axial variations on the parameters mentioned can lead to important and unintended variations in tape-guide separation.
Transient Analysis of Plain and Tilt Pad Journal Bearings Including Fluid Film Temperature Effects
Authors: Gadangi R. K. , Palazzolo A. B. , Kim J.
Published: February 2008

The paper considers vibration response of spinning shafts supported by flexible fluid film bearings to sudden mass imbalance (blade loss). A time transient study of the plain journal bearing with thermal effects is performed. A comparison between three transient analyses is performed. The three transient analyses studied are, the full nonlinear analysis, linear analysis using dynamic coefficients, and pseudo transient analysis using static application of dynamic loads. The validity of the nonlinear transient analysis is checked by matching the lower unbalance results with the linear analysis and the static equilibrium position results with Newton-Raphson iterative scheme. A nonlinear transient analysis of the tilt pad journal bearing is also performed, and a comparison is drawn between the three approaches.
Friction Characteristics and Adhesion Force Under Low Normal Load
Authors: Ando Yasuhisa , Ishikawa Yuichi , Kitahara Tokio
Published: February 2008

The friction coefficient and adhesion force between steel balls and flat test pieces were measured during friction under low normal load in order to examine the tribological characteristics. First, the friction coefficients were measured under a constant normal load of 0.8 to 2350 μN, and the adhesion forces were measured before and after each friction. The result showed that the friction coefficient was highest at low normal loads, while the friction force divided by the sum of the normal load and the mean adhesion force was almost constant over the whole range of loads. Second, when the normal load was reduced gradually during friction, friction still acted when the normal load became negative and a pulling off force was applied to the surface. Thus an adhesion force acts during friction and this adhesion force affects the friction force in the same way as the normal load.
Wear Resistance of N+-Implanted Silicon Investigated by Scanning Probe Microscopy
Authors: Miyamoto T. , Yokohata T. , Miyake S. , Bogy D. B. , Kaneko R.
Published: February 2008

A scanning probe microscope with a 80 nm radius diamond tip was used to investigate the wear resistance of single-crystal silicon and N+-implanted silicon. The N+ implantation conditions were 35 to 150 keV and 5 × 1016 ions/cm2. The N+ concentration depth profile was analyzed by using secondary ion mass spectrometry, and the chemical structure of N+-implanted silicon was also analyzed by using x-ray photoelectron spectroscopy. The following results were obtained. The maximum N+ concentration on the ion-implanted silicon shifted further below the surface and the thickness of the high ion concentration region increased with the implantation energy. The high N+ concentration region using multiple energies of 35–150 keV during the same ion implantation process was wider than that for the N+-implanted silicon using a single energy. The wear resistance of ion-implanted silicon was higher than that of single-crystal silicon. The N+-implanted silicon using multiple energies during the same ion implantation process showed higher wear durability than that of the N+-implanted silicon using a single energy. The Si2p spectrum of the high N+ concentration region implied a structure similar to a Si3N4 film, which resulted in higher wear resistance.
Influence of Indent Geometry on Repeated Two-Dimensional Rolling Contact
Authors: Gupta V. , Bastias P. , Hahn G. T. , Rubin C. A.
Published: February 2008

A “two-body,” elasto-plastic finite element model is employed to simulate repeated rolling contact in the presence of a surface irregularity. It is shown that the maximum Mises stress and equivalent plastic strain values in the substrate are related to the height of the pressure spikes. The results of the finite element calculations are used to derive generalizations about the influence of the indent geometry on the pressure spikes, peak cyclic plastic strains and their location below the surface. These relations can serve as guidelines for designing the depth and properties of surface coatings and modified layers.
Misalignment Effect on the Static and Dynamic Characteristics of Hydrodynamic Journal Bearings
Authors: Qiu Z. L , Tieu A. K.
Published: February 2008

This paper solves the Reynolds equation by the finite difference method in a fixed coordinate system with the static load acted in the vertical direction. All static and dynamic characteristics (including load capacity, attitude angle, side flow, friction force, misaligned moments, and eight linear force coefficients) of a horizontally grooved bearing under different eccentricity and misalignment conditions are presented and compared with available experimental data. The effects of misalignment on all these bearing characteristics and on the stability of the rotor-bearing system are analyzed.
Analysis of a Gas Lubricated Hydrodynamic Thrust
Bearing
Authors: Hughes S. J. , Hogg S. I. , Jones T. V.
Published: February 2008

Experimental results from a gas thrust bearing test facility are reported in this paper. This fundamental investigation of the thermo-fluid dynamics of a gas lubricated bearing forms part of a wider programme aimed at their introduction into the aeroengine environment. The experiments provide the most detailed measurements to date of a hydrodynamic lubrication film which uses gas as a working fluid. The bearing tested was lubricated with air. The thrust pads had an outer radius of 0.125 m and during operation the clearance between the bearing surfaces was typically 10 μm. The design speed of the bearing was 10,000 rpm. Mean pad pressure and temperature distributions are presented for a range of bearing loads up to 3/4 kN, which were measured under steady operating conditions. Transient pressure and surface clearance measurements from fast response probes are also reported. These measurements show a complex relative motion of the bearing surfaces, the exact nature of which could only be determined from a more detailed set of surface clearance measurements than those in the present work. However, the transient pressure measurements show that these surface clearance fluctuations do not exert a strong influence on the lubrication film pressures, which can be considered to be essentially steady. The test data are compared with predictions obtained by solving Reynolds equation numerically, using a finite-volume based procedure. Thermal distortion of the bearing surface is not included in the model and this limits the agreement between measurements and calculations. The results suggest that this must be accounted for in the design of practical bearing systems, even though the lubrication film can be treated as isothermal. The measurements also show evidence of the inlet effects which raise the static pressure of the flow entering the bearing to above the ambient level.
Performance of a Powder Lubricated Journal Bearing With
WS2 Powder: Experimental Study
Authors: Heshmat H. , Brewe D. E.
Published: February 2008

Previous investigations have demonstrated the principle and feasibility of quasi-hydrodynamic lubrication using powders. With conventional lubricants, the hydrodynamic behavior of a journal bearing can be summarized in the form of a plot of friction coefficient against a nondimensional load parameter, usually referred to as a Stribeck curve. One of the main features of the curve is that, as the thickness of the lubricant film increases, the friction coefficient initially decreases until it reaches a minimum and then increases due to shearing of the lubricant film. Previous tests on a three pad journal bearing using molybdenum disulfide powder as the lubricant showed that its friction/load characteristics followed the Stribeck form. The experimental work reported herein describes further tests carried out on a three-pad journal bearing to evaluate its thermal stability and long term wear characteristics using tungsten disulfide powder as the lubricant. Dry tungsten disulfide powder lubricant has been shown to provide excellent wear resistance. Its friction properties are similar to molybdenum disulfide but it can be used at much higher temperatures. Bearing tests were carried out at speeds up to 30,000 rpm and loads up to 236 N. Over the load/speed range stable thermal operation was achieved. From friction torque measurements it was found that the coefficient of friction for the bearing was essentially constant over the range of loads and speeds. Unlike liquids, powders have a limiting shear strength property. When the limiting shear stress is reached in a powder flow, the powder essentially shears along a plane and does not flow in a viscous manner. The constant friction coefficient seen with the tungsten disulfide powder suggests that the powder had a low limiting shear strength and that this dominated the operation of the bearing in the tests. The total accumulated test time was more than eighteen hours. Periodically, the test journal and bearing pads were inspected but there was no measurable wear or visible damage.
Head-Disk Interface Performance With a Starved Liquid
Bearing—Analytical Solution to Reynolds Equation in the Near-Contact
Regime
Authors: Streator J. L.
Published: February 2008

Further increase in magnetic recording density requires a reduction in slider flying height. The current study employs the short-bearing approximation to determine analytically the static equilibrium configuration of a slider supported by a starved liquid bearing that operates between ideally smooth surfaces. The solution incorporates rheological behavior based on previously acquired data. The accuracy of the short-bearing approximation is assessed by determining how well the resulting solution satisfies the Reynolds equation. The analysis suggests a means of designing a slider to achieve head/medium spacings in the neighborhood of 20 nm.
Experimental Study of Freely Alignable Journal Bearings—Part 2:
Dynamic Characteristics
Authors: Qiu Z. L , Tieu A. K.
Published: February 2008

The traditional harmonic excitation method was modified to estimate 16 dynamic force coefficients of two misaligned journal bearings. To avoid the effects of different running conditions on the estimated coefficients, two harmonic forces with different frequencies were excited on the rotor simultaneously and all data were acquired during one test run. The excitation forces and their displacement responses were transferred to the frequency domain in which eight linear (complex) equations are derived. All 16 bearing force coefficients can then be obtained by solving these simultaneous linear equations through one operation. Applicable experimental procedures and data processing techniques are presented. The force coefficients of two circular journal bearings with two axial grooves each are estimated and correlate well with theoretical values when misalignment is considered. Various experimental errors are discussed and the uncertainty in the estimated coefficients is analyzed.
Three-Dimensional Measurement of Head Flying Height and Attitude
Using Image Processing of Fringe Patterns Formed by Michelson Laser
Interferometry
Authors: Mitsuya Yasunaga , Mitsui Akihito , Kawabe Yasuyuki , Lunde Lars
Published: February 2008

In-situ measurement of head flying height and attitude using image processing of fringe patterns formed by Michelson interferometry is studied. A wide laser beam is applied to illuminate the slider back surface and disk surface simultaneously to create interferometric fringe patterns. Employing the relationships arising between the two fringe patterns, the calculation procedure is formulated to yield the slider’s parallel, pitch and roll displacements. Experimental fringe patterns are captured in a single visual field by a high-speed CCD camera. Image processing for a higher signal-to-noise ratio, such as smoothing, filtering, amplification and ridge line extraction is then applied to the image data. Additionally, average processing with respect to multiple fringe lines to produce higher accuracy is successfully applied. Measured values of flying height and pitch and roll displacements are confirmed to be in good accordance with the calculation results, demonstrating excellent applicability of the present method down to the near-contact region.
Elastohydrodynamic Lubrication of Air-Lubricated
Rollers
Authors: Chang Y. B. , Chambers F. W. , Shelton J. J.
Published: February 2008

The lubricating air film between two rotating rollers in close contact was studied numerically. The numerical model used in this study accounts for the effects of air compressibility, material deformation, and the slip flow which occurs when the air film thickness is not much larger than the mean-free-path of the air molecules. The air film profiles and the pressure profiles for the nip region between the rollers were calculated. It was found that the calculated air film thicknesses are lower than predicted by the liquid elastohydrodynamic calculation. From this study, equations for the minimum air film thickness, the air film thickness at the center of contact, and the amount of air that passes through the nip were obtained. This study has application to the prediction of the amount of air entrained in a winding roll.
Measurements of Friction in Cold Metal Rolling
Authors: Tabary P. E. , Sutcliffe M. P. F. , Porral F. , Deneuville P.
Published: February 2008

Measurements of friction in rolling of aluminium strip on an experimental mill are described. Friction depended most strongly on the ratio Λ of the smooth film thickness to the combined roughness of the roll and strip, and on the reduction in strip thickness. Whether the greater roughness was on the roll or on the strip was found to be unimportant. Varying the oil temperature from 40 to 60°C was also found to be of secondary importance. Profilometry results suggested that friction was determined by the mean film thickness between the surfaces. At the slowest speeds and smallest films, friction was close to the value of 0.09 found in separate measurements in a disk machine of the boundary additive properties. At the highest speed the friction values, which were less than 0.01, could be explained by hydrodynamic lubrication. The transition between these two extremes occurred when the film thickness was of the order of the additive molecule length of 3 nm.