Patrick Kwon

Predictive Models for Flank Wear on Coated Inserts

The purpose of this paper is to develop predictive models for flank wear that explicitly incorporate cutting temperature and the physical properties of coatings and work materials. The development of such models can minimizes time-consuming machining experiments in predicting tool life by establishing flank wear models that can be applied to wide classes of coated inserts and work materials. To develop such models, a set of experiments was performed to understand the effect on flank wear due the morphology and amount of the second phase in work materials. The plain carbon steels of AlSl designation 1018, 1045, 1065, 1070, and 1095 in hot-rolled (pearlitic) and/or spherodized conditions were turned. The inserts with a single coating of TiN, TiCN, or Al 2 O 3 were used in the cutting experiments. The temperature history at a remote location on the rake face was measured during cutting by using an infrared pyrometer with a fiber optic attachment. This temperature information was used to estimate the steady-state tool-chip interface temperatures using the inverse estimation scheme by Yen and Wright (1986). The results were then used to predict the work-tool interface temperature using the scheme suggested by Oxley (1989). The results of this experiment showed that, for the spherodized steels, flank wear per sliding distance (the flank wear rate) increased with the cementite content. For the hot-rolled (pearlitic) steels, no conclusive evidence was found that correlates the flank wear rate with the cementite content. However, for pearlitic steels the wear rates, in general, were shown to increase with the flank temperature while for spherodized steels the rates decrease with the flank temperature. The reason for these trends can be explained by the microstructural difference between pearlitic and spherodized steels; therefore, the semi-empirical models of two-body and three-body wear developed by Rabonowicz (1967) and Rabinowicz et al. (1972) can be applied to describe the flank wear process.

Making process visible: A grammatical approach to managing design processes

This paper presents a novel framework for managing design processes using a formal grammar as the theoretical foundation to represent, manipulate and execute design processes. The grammatical approach allows designers to represent a complex activity concisely with a small number of higher-level tasks and to explore alternative processes within a space of feasible alternatives. These capabilities allow the engineers to visualize the design process so that they can fully understand the alternative methods before making any design decisions. The framework, called MIDAS, includes separate layers for process specification and execution. Using the process specification layer, designers can capture the overall design process and each designer can understand his or her task with respect to the whole design process. In the process execution layer, design tasks are executed according to the information in specification layer so that designers can be informed of the current design status, alternative design methods, and their impacts in a whole design process. The framework has the potential to improve design productivity by accessing, reusing, and revising previous processes for a similar design. We use a gearbox design process to demonstrate the framework.

Effective moduli of high volume fraction particulate composites

Abstract Predictions using current micromechanics theories for the effective moduli of particulate-reinforced composites tend to break down at high volume fractions of the reinforcing phase. The predictions are usually well below experimentally measured values of the Youngs modulus for volume fractions exceeding about 0.6. In this paper, the concept of contiguity, which is a measure of phase continuity, is applied to Mori—Tanaka micromechanics theory. It is shown that contiguity of the second phase increases with volume fraction, leading eventually to a reversal in the roles of the inclusion and matrix. In powder metallurgy practice, it is well known that at high volume fractions, sintering and consolidation of the reinforcement make it increasingly continuous and more like the matrix phase, while the former matrix tends to become more like the inclusion phase. The concept of contiguity applied to micromechanics theory results in very good agreement between the predicted Youngs modulus and experimental data on tungsten carbide particulate-reinforced cobalt.

Macroscopic Analysis of Axisymmetric Functionally Gradient Materials Under Thermal Loading

The axisymmetric functionally gradient materials (FGMs) subject to nonuniform temperature variations were studied with the combined use of homogenization and inhomogeneous eigenstrained media analysis. The material properties and the temperature variations were assumed to depend on the radial coordinate only. The inhomogeneous material properties of the FGM cylinder can be obtained by modulating the concentration level of spherical alumina particles in an aluminum matrix. The resulting stresses due to the temperature variation are presented for numerous distribution functions of alumina particles. It is shown that the particle distribution extensively influences the intensity and profile of the thermal stresses.

The fabrication of smooth, sub-millimeter open channels and internal channels in ceramics and ceramic composites without machining

Internal channels for the flow of fuel, medicine or cooling fluids are of interest in many technical applications. For example, a variety of electronic devices require cooling for proper functioning [1–3]. In particular, cooling channels for some recent computers are about 7.8 mm in diameter [1], and development is underway of cooling “microchannels” that range from several hundred microns in diameter down to about 100 microns [2, 3]. Although ceramics such as alumina and aluminum nitride are used for electronic packaging and substrates [4], it is difficult to incorporate cooling channels into ceramics via machining. The authors and co-workers have fabricated internal channels in a variety of ceramic materials, including alumina, zirconia, and hydroxyapatite [5–7] as part of a broader study of microwave processing of ceramics which has included sintering [8–11], binder burnout [12], crack healing [13], modeling of refractory heating [14, 15], thermal etching [16] and joining of ceramics [5–7]. The joined ceramics included specimens with open channels machined into their outer surfaces, so that closed internal channels were formed when two specimens with surface channels were joined [5–7]. This study extends the authors’ previous work by fabricating the channels without the need for machining. The channels in this study were “stamped” into alumina and alumina/partially stabilized zirconia (PSZ) composite powder compacts during hard-die pressing. The powder compacts then were sintered to form open channels with roughly semi-circular cross-sections and diameters of about 200 microns. The sintered specimens were polished and bonded together to produce channels that penetrated the bulk of the joined specimens. The channel fabrication technique discussed in this paper is analogous to the “soft lithography” microfabrication techniques used for polymeric materials, as reviewed by Xia and Whitesides [17]. Soft lithography, which involves molding and stamping, was developed as a less expensive and more versatile alternative to standard photolithography for microfabrication in polymeric materials [17]. Also, just as photolithography can be used for polymeric materials, it also can produce shallow channels of various shapes in single crystal alumina, with channel dimensions of up to several hundred microns across and chan-

Crater Wear Evolution in Multilayer Coated Carbides During Machining Using Confocal Microscopy

Abstract Steady-state turning experiments were carried out with multilayer coated inserts consisting of TiN/Al2O3/TiCN deposited on a carbide substrate. Confocal microscopy was used for the first time to observe the topography of crater wear evolution in multilayer coated inserts. A hump made of TiN coating next to a growing crater of Al2O3, traces of attached steel, and the maximum depth regions have been identified. Scoring marks were also detected in the TiN layer, indicating the presence of abrasion wear. Interestingly, the crater depth was stagnant once it reached the Al2O3 layer, and the wear progresses by broadening the area of exposed Al2O3. It was concluded that the effectiveness of multilayer coated tools comes from the dissolution resistance of the Al2O3 layer, which delays depth growth and develops the wear front into a wider area. Confocal microsocopy was found to be a valuable tool to obtain wear topography for multilayer coated tools.

Tool wear mechanisms in machining

Most of tool wear studies are classified as empirical (e.g. Taylors equation); thus, they do not bring out the physical nature of the wear phenomenon. Consequently, tool life in general cannot be predicted by extending the result from one study. By understanding the physics behind the process, the important wear mechanisms can be identified. By constructing a wear model for each wear mechanism with more fundamental quantities such as materials properties, these models can be combined and extended to estimate tool life. This should be the ultimate goal of tool wear research in machining. However, a major gap exists between the current understandings of tool wear and the ultimate goal of tool wear research. This paper will describe how cutting tools are being worn down during machining based on the physics behind tool wear.

Dissolution Profile of Tool Material Into Chip Lattice

The dissolution hypothesis of tool wear is rearticulated as a boundary condition for the transfer of tool components to the chips bulk via diffusion. In this setting, dissolution wear is defined more generally as the combined events of tool decomposition at the interface and the subsequent mass transfer of decomposed elements into the chip region. Chemical equilibrium is invoked for the distribution of tool species at the tool-chip interface. Under a linear-diffusion hypothesis, one would expect an exponentially decaying concentration profile of tool species in the chip. However, a humped concentration profile has been found experimentally by Suhramanian et al. in 1993. In this paper, the Frank-Turnbull mechanism is proposed to explain the humped concentration profile of tool constituents into the chip. This mechanism is defined by the interaction between interstitial impurities and vacancies to form substitutional impurities, and it introduces a quadratic nonlinearity in the advection-diffusion-reaction equations. The present approach is semi-empirical in that, while the interstitial- and suhstitutional impurity distributions are solved from the equations, the vacancy distribution is constructed so that the final substitutional-impurity distribution agrees with the observed data. The present interpretation of the Frank-Turnbull mechanism in the wear process is illustrated by finite-element simulations.