UNIFIED APPROACH AND INTERACTIVE PROGRAM FOR THERMAL ANALYSIS OF VARIOUS MANUFACTURING PROCESSES WITH APPLICATION TO MACHINING

Analytical approach to thermal aspects of various manufacturing processes, such as machining, grinding, polishing, welding, heat treatment, laser processing, and tribology was used by many researchers between the late 1930s and early 1940s. That was the golden period when Blok introduced the heat partition concept in 1937; Jaeger developed the heat source method in 1942; and Rosenthal introduced the moving heat source theory in 1946. Starting from the Fourier's partial differential equation (PDE) of heat conduction, researchers have addressed various manufacturing processes using different approaches, namely, separation of variables, Fourier transform, Laplace transform, Bessel function, and Green's function methods. Consequently, it has become difficult to conceive a unified analytical approach of the various manufacturing processes based on the review of the literature as one approach differs from the other quite significantly and integration of them would be a formidable task, if not an impossible task. In contrast, using the Jaeger's classical heat source method and appropriate heat source (shape, size, and distribution) we developed a unified analytical approach to address the thermal aspects of various manufacturing processes. Such an approach, to the best of our knowledge, has never been attempted before and lends itself to the development of a user friendly interactive programming software that can be extremely valuable in practice. In this paper, we used Jaeger's classical heat source method, modified Hahn's oblique moving heat source for the shear plane heat source, Blok's ingenious heat partition method, and Chao and Trigger's functional analysis approach to illustrate the analysis of the temperature distribution in the work material, chip, and cutting tool in machining.     

A GEOMETRICAL APPROACH FOR REDUCTION OF TOOL SHAPE DEGENERATION IN ELECTRIC DISCHARGE MACHINING (EDM)

In this study, the geometric wear characteristics of tool electrodes were obtained for various pulse time, discharge current and machining depth settings in electric discharge machining. Different forms of protrusions were machined on the front surface of the tool to reduce the geometric wear. Significant reductions in original tool geometric wear characteristics (front wear, side wear and edge wear) were obtained with the use of square cross-section protrusions. The dimensions of the square cross-section protrusions were modeled mathematically in terms of machining parameters used in the experiments.     

考虑应变梯度效应的低碳钢试样单向拉伸尺寸效应理论研究

采用二阶应变梯度塑性理论，得出伸长率、峰值应力后工程应力应变曲线和真应力应变曲线的解析解，结果表明三者均具有尺寸效应。将低碳钢试样的单轴拉伸简化为轴向的一维问题。采用拉伸过程中体积不变假设及平衡条件，将应变梯度引入屈服函数，得到伸长率、平均应变及真应变的解析式。理论结果完全反映伸长率与标定长度呈反比的客观事实。工程应力应变曲线尺寸效应可以在数值结果中找到佐证。拉应变局部化是三者尺寸效应的本质原因。     

ON THE NATURE OF MACHINING CRACKS IN GROUND CERAMICS: PART II, COMPARISON TO OTHER SILICON NITRIDES AND DAMAGE MAPS

The size and severity of grinding machining cracks in a sintered reaction bonded silicon nitride are compared to data for other silicon nitrides. Crack sizes follow a similar trend with grinding wheel grit size despite differences in microstructures, strengths, and fracture toughnesses. Silicon nitrides with enhanced fracture toughness actually develop deeper machining cracks than in less tough silicon nitrides. Machining damage maps for silicon nitride are presented.