Thermal aspects of grinding for surface integrity

Yongqing Ju, Purdue University

Abstract

Thermal aspects of grinding are analyzed in detail since it is argued that temperature controls the effect of grinding on workpiece surface integrity. Transient and steady state heat partition in sliding contact is discussed in detail. This leads to a complete thermal model for heat partition and temperatures in surface grinding. Numerical predictions of the model are shown to agree with experimental results available in the literature. Effects of grinding conditions including real contact area ratio, thermal properties, feeds and speeds, and type of cut (down or up grinding) on heat partition and workpiece temperature are studied systematically. It is shown that the presence of the fluid inside the grinding zone can reduce the heat flux into the workpiece and workpiece temperature significantly. It is also found that some ratios of workpiece velocity to wheel velocity result in high temperatures and therefore should be avoided. This result provides a basis for the difference between conventional and creep-feed grinding regions. After obtaining temperature, an efficient and robust FFT approach is developed to obtain the thermal stress field induced by moving heat sources. Study of the 'hot spot' problem shows that the effect of hot spots on surface displacement and stress is small suggesting that grinding thermal stress is induced by the global temperature while local temperature controls metallurgical phase transformations. It is also shown that thermal stress is dominant on the global scale while the global scale mechanical stress is insignificant. Thus, the superior thermal properties of CBN compared to Al$\rm\sb2O\sb3$ leads to low temperature and less deleterious residual stresses. Finally, spectral analysis is performed to evaluate contact behavior of the finished surface. This analysis shows that a good grinding process improves not only the magnitude of the surface roughness but the frequency content as well.

Degree

Ph.D.

Advisors

Farris, Purdue University.

Subject Area

Mechanical engineering|Aerospace materials|Mechanics

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