Research Of The Effects Of Grinding Force On Mechanism Of White Layer Formation In Grinding Of Quench Bearing Steels

Superhard and difficult-to-machine materials are widely used in industry fields. Some ultrahard mini-metallurgical structure layers, named"white layers", often form on the machined surface during machining processes. White layer brings incipient faults to the security of the parts, and reduces the performances and life spans of the products. So it should be wiped off during the fine machining. Compared with other processing method, grinding has clear advantage on inhibiting the white layer's formation. In this paper, the effects of grinding force on the formation mechanism of white layer are studied systematically by experiment analysis, theoretical calculation and numerical simulation. The influences of the plastic deformation and the contact stress caused by grinding force on the white layer's formation are analyzed. In addition, the optimum value of the grinding parameters is obtained. The main studies include:(1)The grinding force and the grinding white layer are analyzed deeply on the basis of the experiment. An effective experimental program is designed by orthogonal experimental method. The influencing factors of white layer's formation are discussed. The variable tendency about grinding force and grinding white layer with the grinding parameters is analyzed. It is found that the thickness of white layer increases with the wheel speed and the cutting depth. However, when the table speed is increasing, the white layer increases slowly at first, but decreases sharply as follow.(2)A new numerical simulation technique of surface grinding process is proposed. The maximum total equivalent plastic strain and the equivalent Von Mises stress on the grinding surface can be acquired from this simulate results. It can be showed that the total equivalent plastic strain increases with the grinding force when the effect of temperature is not noticeable, and the severe plastic strain lead to more white layers. A larger contact stress caused by the grinding force can reduce the phase transformation temperature and thus it speeds up the phase transform of the materials. In addition, the high temperatures on grinding surface cause theα→γtransformation. High workpiece surface temperatures combined with the grinding forces result in the severe deformation of martensite structures, and the dislocation in grain may entwist each other at the same time. The grain fracture severely and refine. The formation of white layer is the common results of grinding heat and severe plastic deformation.(3)An empirical formula for the thickness of white layer is constructed by using a lot of experimental data. The formula is of high accuracy and can predict the thickness of white layer very well. The optimum value about grinding parameters can be acquired when the thickness of white layer is minimum by optimization method. The optimize results shows very good correlation with the visual analysis.This study is significant in improving difficult-to-machine materials'surface quality, and it has the academic value and practical value.