Effects of cryo-cooling in grinding steels

Abstract

The grinding process is inherently characterised by high specific energy and high temperature, which are responsible for high wheel loading, increased grinding forces, reduced metal-removal rate, rapid wheel wear and deterioration in the quality of the ground surface through oxidation, the induction of tensile residual stress and micro-cracks. These problems become more acute when the product is of HSHR material and subjected to dynamic loading while functioning. Therefore, in industry the user should pay special attention to control and optimise all the significant parameters for minimising the afore-said problems, aiming at higher grindability, productivity and overall economy in grinding. The basic principles of controlling such high temperature are: (i) proper selection and optimisation of wheel and process parameters; (ii) the removal of heat from the grinding zone by the application of proper grinding fluid. Profuse cooling with conventional grinding fluids, even in the form of mist or jet, is virtually unable to solve the problem. However, cryogenic cooling by agents such as liquid nitrogen is expected to meet this challenge. In the present work, specimens of different steels, namely MS, HCS, cold- and hot-die steel and HSS, have been surface ground at different infeeds under dry conditions and with soluble oil and liquid nitrogen. The effects of such cryo-cooling relative to soluble oil and dry grinding have been investigated in respect of chip formation, grinding forces, specific energy, burning and surface characterisation. The experimental results indicate that the grinding temperature and burning decreased remarkably under cryo-cooling. Thermal damage of the ground surface has been reduced substantially by cryo-cooling, but to different degree in different steels. Cryo-cooling also enables retention of the wheel sharpness for a longer period and results in less force and specific energy being required.