The surface/subsurface damage of engineering ceramics after machining has a great influence on the service performance of parts. In order to obtain a high grinding surface quality of engineering ceramics, and take silicon nitride ceramic as a research object, a series of grinding experiments were carried out. The effects of grinding parameters on longitudinal crack propagation depth and the surface residual stress of silicon nitride ceramics were analyzed by grinding experiments, and the residual stress at the location of crack propagation was obtained. The variation in the grinding temperature under different grinding parameters was explored. The influences of the grinding temperature on crack propagation depth and surface residual stress were clarified, the distribution of residual stress along the depth direction was discussed, and the relationship between the residual stress and crack propagation was revealed. The results show that the residual compressive stress on the surface of silicon nitride ceramics decreases with the increase in the depth of crack propagation and the degree of surface brittle spalling. The residual stress at the location of the crack propagation was residual tensile stress. The crack propagation depth increased with the increase in the residual tensile stress. The research provides a reference for the realization of high-quality surfaces in the grinding of silicon nitride ceramics.

The processing quality of steel bar thread has a large influence on its performance. Using the traditional thread processing technology, it is difficult to meet the requirements of steel bar thread processing with large diameter and high strength. A technical process for HRB500 high-strength steel bar thread processing, including face milling, rib stripping, chamfering, necking formation, and thread rolling, was proposed. The influences of cutting parameters on the cutting force of steel bar surface in face milling were analyzed by the finite element method. For the necking formation process, the effect of springback amount on necking formation was studied. The main parameters in rolling formation were analyzed and calculated, including extrusion pressure, rolling speed, and rolling feed. Experiments for uniaxial tensile of the processed high-strength steel bar threads were carried out. The results showed that cutting depth has the largest influence on the cutting force; the second is feed rate. The effect of the spindle speed was lowest during the face milling. After the necking formation process, the values of the maximum springback amount along the X, Y, and Z directions were 0.05 mm, 0.06 mm, and 0.98 mm, respectively. The finished thread met the precision and quality requirements of a grade I joint. This study provides a high-quality processing technology for large-diameter and high-strength steel bar threads.