The effect of micro/nano particle size on the thermal, tribological properties and the performances of coated composite tools
Abstract
In metal cutting, selecting an appropriate cutting tool is a critical factor for obtaining a good surface integrity on the machined surface and achieving high efficiency of the process. Tribological and thermal properties such as coefficient of friction and thermal conductivity of the cutting tool are important in determining mechanical and thermal fields which contribute to both the surface integrity of the machined part and the efficiency of the process. In the case of coated composite tools, size of dispersed particulates is considered as an important factor in determining both tribological and thermal properties of the cutting tool. However, very few studies provide fundamental understanding of the relationships between the particulate size and other properties in composite tools. The main objective of this research is to develop a new scientific methodology of determining and analyzing important fundamental variables for high performance cutting tool design and optimization. The first part of this research investigates the effect of dispersed particulate sizes on thermal conductivity of coated composite tools. Then, a statistical model is used for determining a relationship of coefficient of friction as a function of thermal conductivity and surface roughness and hardness of the workpiece. Then, a fully coupled thermalstress finite element model of orthogonal cutting is constructed for doing sensitivity analysis of the effects of thermal conductivity and coefficient of friction on mechanical and thermal fields. Results show stress and temperature distributions as affected by different values of thermal conductivities and coefficients of frictions. The results also show residual stress at different depths on the machined surface, generated from cutting tools with different thermal conductivities and coefficients of frictions. Since tool life is a criterion for evaluating a cutting tool’s performance, a statistical model is developed for determining the relationships of the tool life to the thermal conductivity, the coefficient of friction and the cutting process variables such as speed, feed, and depth of cut. Superfinish hard turning composite tools at different dispersed particulate sizes, in micro/nano range, and two types of hardened steels are used in this research. For coated composite tools, cBN-TiN coated on WC substrate tools with different dispersed cBN particle sizes are used. The cBN-TiN composite tool is synthesized in a two-step process of electrostatic spray coating (ESC) of cBN particles on tungsten carbide substrate to form a porous powder coating, and followed by chemical vapor infiltration (CVI) of ceramic binder (TiN). The materials tested are hardened steel of AISI 4340 and AISI 52100. A new methodology is developed in this study for providing basic understanding of the effects of both tribological and thermal properties to the performances of the tools and the cutting process efficiency. This new methodology would be useful in determining and analyzing important composite coating variables for the design of high performance cutting tools.
Degree
Ph.D.
Advisors
Liu, Purdue University.
Subject Area
Mechanical engineering|Materials science
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