A Fracture Mechanics Approach to the Prediction of Tool Wear in Dry High Speed Machining of Aluminum Cast Alloys: Part 2 — Model Calibration and Verification

Experimental study has been carried out to establish the effect of cutting conditions (speed, feed, and depth of cut) on the cutting forces and time variation of carbide tool wear data in high-speed machining (face milling) of Al-Si cast alloys that are commonly used in the automotive industry. The experimental setup and force measurement system are described. The test results are used to calibrate and validate the fracture mechanics-based tool wear model developed in Part 1 of this work. The model calibration is conducted for two combinations of cutting speed and a feed rate, which represent a lower and upper limit of the range of cutting conditions. The calibrated model is then validated for a wide range of cutting conditions. This validation is performed by comparing the experimental tool wear data with the tool wear predicted by calibrated cutting tool wear model. The prediction errors were found to be less then 7%, demonstrating the accuracy of the object oriented finite element (OOFE) modeling of the crack propagation process in the cobalt binder. It also demonstrates its capability in capturing the physics of the wear process. This is attributed to the fact that the OOF model incorporates the real microstructure of the tool material.

Modelling Transient Behavior of a Mechanical System Including a Rolling and Sliding Contact

The friction and wear of rolling and sliding contacts are critical factors for the operation of machine elements such as bearings, gears, and cam mechanisms. In precision machines, for example, the main concern is to compensate for frictional losses, so as to improve control accuracy. In other applications it is often desirable to minimize friction losses to improve efficiency, though sometimes high friction is desired to prevent sliding and wear. The aim of this study is to simulate the behavior of a test equipment and show that simulations can be used to study and optimize mechanical systems that include rolling and sliding contact. Simulations can be used to study the system as a whole, as well as the contact conditions. The test equipment and the measurement procedure used are described. In the simulations, a contact model designed to handle transient contact conditions is integrated into a system model. The results show that the contact strongly influences the system. The simulations show that the use of a contact model allows the simulation of systems that contain contacts with different amounts of slip, and that such simulations can be used to study the contact as well as the system. Surface roughness influences the contact stiffness and is included in the simulations.

Scuffing Failure Due to an Abrasive Contaminant and Filter Suitability in High Pressure Injection Fuel System

The field studies have revealed that there is an unprecedented high failure rate of rotary diesel fuel injection pump (RDFIP). The presence of rigid abrasive contaminant between the plunger and sleeve of hydraulic head assembly of RDFIP causes scuffing failure. The abrasive contaminant is modeled as a spherically shaped rigid particle. The contaminant is envisioned to penetrate into the sleeve while positioning itself in rubbing contact with the plunger. Excessive temperature rise known as flash temperature between the particle-plunger interface is used as an indication of whether scuffing would take place. Flash temperature is determined by incorporating operating speed of pump, particle size, minimum film thickness, fuel properties, thermomechanical and surface properties of plunger and sleeve. Thermomechanical properties are determined through material composition of plunger and sleeve by spectroscopic techniques. Coordinate measuring machine is used to determine the radial clearance between the plunger and sleeve. Three high-pressure injection pumps are taken as case study for obtaining experimental data. This experimental data is used as an input in our theoretical model for the determination of flash temperature duly analyzing partial and diametric penetration of the abrasive contaminant. The model uses flash temperature in conjunction with the material properties to determine the critical particle size that may result in scuffing failure. The exact rating of fuel filter based on the critical particle size of the contaminant producing scuffing failure in the plunger and sleeve of hydraulic head assembly of RDFIP is also determined. The range of critical particle size initiating significant abrasive wear is determined and validated with the experimental results available in literature.

Numerical Analysis for Influence of Plastic and Elastic Deformation of Rough Surfaces on PEHL for Line Contacts

In the present paper, analysis of elasto-plasto-hydrodynamic lubrication (PEHL) in the line contact is carried out to investigate the effect of heavily loaded roll-over on the change in profile of indents. The pressure and film thickness profiles are obtained to solve the Reynolds and film thickness equations simultaneously. And, both the elastic and plastic deformations of the contact, featured with an indent, have been considered. A multi-grid numerical algorithm used in EHL of line contacts is modified and then used for the oil lubricated rolling contacts. In the program, stress and plastic deformation of the indent profile are calculated with the hardening plastic stress-strain relationship according to the theories of plasticity when pressure excesses the yield stress. The results, with and without considering plastic deformation, are compared to show the different influences on the pressure and film thickness. Analysis shows that since the plastic deformation will change the surface roughness, it will significantly change the pressure but film thickness.

Study on Tribological Properties of Cadmium Dialkyl-Dithiophosphyl-ldithiophosphate Additive

An cadmium dialkyl-dithiophosphyl-dithiophosphate additive was synthesized. A four-ball tester was used to evaluate the tribological performance of the additive in mineral base oil under different loads, compared with commercial additives. The results show that it exhibits excellent antiwear and load-carrying capacities and better than these additives. The surface analytical tools such as Auger Electron Spectrometer (AES), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) were used to investigate the topography, the contents and the depth profile of some typical elements on the rubbing surface of worn scar. Smooth and light topography of worn scar further confirms that the additive showed good antiwear capacities, the results of Auger electron spectrometer and energy dispersive X-ray analysis indicate that tribochemically protective films consists of cadmium compouds, sulfides, sulphates and phosphates were formed on the rubbing surface, which contribute to improving the tribological properties of lubricants. Particularly, the results from depth profile indicate that a large amounts of cadmium are rich in outer layer of surface, which play an important role in improving antiwear properties of oils. Finally, the antiwear mechanism of the additive were proposed.

Modeling the Motion of Slurry Nanoparticles During Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) has emerged as a commonly used method for achieving global surface planarization of micro-/nano-scale systems during fabrication. During CMP, the wafer to be polished is pressed against a rotating polymeric pad that is flooded with slurry. The motion of the wafer surface against the asperities of the pad and the abrasive nanoscale particles in the slurry causes the surface of the wafer to be polished to an atomically smooth level. Past studies have shown that the wear distribution is a function of the distribution of slurry particles in the wafer/pad interface, and thus it is desirable to model the migration of particles in order to predict the wear of the wafer surface. The current study involves the creation and simulation of a mathematical model which predicts the paths of slurry particles in a Lagrangian reference frame. The model predicts the effects of the various forces on each particle to determine its motion. The model also accounts for interparticle collisions and wafer/particle and pad/particle collisions. It is expected that the particle motion that is predicted from this model will allow for a more accurate correlation of the wafer surface wear distribution.

New Mathematical Model for the Form Factor of Involute Spur Gear’s Teeth

In this paper, a theoretical research is made on the influence of the friction force, the profile shift coefficient and the radial component of the normal force in the Form Factor applicable to the stress on spur gears’ teeth. A Gear’s FEM model was establish with the best approach to the real physical models, for the validation of the New Form Factor Model elaborated and then, the stress calculation in gear tooth root. Finally Using FEA and Multiple Lineal Regression, a new expression for the calculation of the stress concentration coefficient in the feet of the tooth, in function of the number of teeth and of the correction coefficient, was found.

Research on the Identification of Nonlinear Internal Damping and Kinematical Joint Damping of Mechanical Systems

A simultaneous identification method of the nonlinear internal damping of alloy material and the Coulomb friction in the kinematical joints in a mechanical system is put forward in this paper. The free vibration differential equation of a vibration system with these two kinds of damping is established. According to the free vibration response signal, the nonlinear internal damping characteristic curve and the Coulomb friction are got by using the moving rectangle window method. Several types of the nonlinear damping models are investigated in simulations. The validity and accuracy of the proposed method are illustrated by the good simulation results, in which the computing accuracy of the nonlinear internal damping is higher than that of the Coulomb damping in kinematical joints.

Cast In-Situ Al (Mg,Mo)-Al2O3 (MoO3) Composite: Characterization and Tribological Behavior

Aluminum alloy-based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO3) in molten aluminum at the processing temperature of 850 °C. During processing, displacement reaction between molten aluminum and MoO3 particles, results in formation of alumina particles in-situ also releases molybdenum into molten aluminum. A part of this molybdenum forms solid -solution with aluminum and the remaining part reacts with aluminum to form intermetallic phase Mo(Al1−xFex)12 of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in-situ, by molten aluminum and help to retain these particles inside the melt. The mechanical properties (ultimate tensile stress, yield stress, percentage elongation and hardness) of the cast in-situ composite are relatively higher than those observed either in cast commercial aluminum or in cast Al-Mo alloys. The wear and friction of the resulting cast in-situ Al(Mg, Mo)Al2O3(MoO3) composites have been investigated using a pin-on-disc wear testing machine, at different normal loads of 9.8, 14.7, 19.6, 24.5, 29.4, 34.3 and 39.2 N and a constant sliding speed of 1.05 m/s, under dry sliding conditions. The results indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar load and sliding conditions. Beyond about 30-35 N loads, there appears to be a higher rate of increase in the wear rate in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or cast Al-Mo alloy. The coefficient of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or cast Al-Mo alloy remain more or less the same. Beyond a critical normal load of about 30-35 N, the coefficient of friction decreases with increasing normal load in all the three materials.

An Exploratory Study on the Analysis of Electron Triboemission Data

The authors have carried out extensive measurements of electron triboemission from the scratching of selected ceramics and of semiconductors in high vacuum. Although the origin of triboemission is not clear, the authors suggest that some triboemission features relate to worn surface evolution. A bibliographic review is presented on analysis of electron triboemission data. Time-domain and frequency-domain discussion of the burst-type triboemission outputs are presented. This paper briefly summarizes key findings on triboemission and presents measurements of electron triboemission from an alumina ball and a diamond cone scratching alumina and sapphire disks. An exploratory study is focused on frequency analysis of data. The feasibility of investigating randomness vs. deterministic origin is explored for the triboemission outputs. Because key triboemission features are yet to be explained, the proposed data analysis can be a tool for such understanding.