Multi-objective optimization of processing parameters for ultrasonic surface rolling 12Cr2Ni4A gear steel based on an improved gray correlation analysis

To improve the efficiency of gear machining and fatigue strength under heavy load and alternating stress, the surface integrity of 12Cr2Ni4A gear steel after ultrasonic surface rolling was investigated, and an improved gray correlation analysis for machining parameters was proposed to achieve optimal surface integrity. First, the influence law and sensitivity of rolling pressure, feed rate, and spindle speed on residual stress, hardness, and surface roughness R-a were analyzed. Subsequently, in combination with the analytic hierarchy process, the gray correlation analysis method was improved by correcting the weight distribution of rolling pressure, feed rate, spindle speed, residual stress, hardness, and surface roughness. Then, a model was built to predict the surface integrity and gray correlation degree by applying the nonlinear fitting. The results showed that rolling pressure, feed rate, and spindle speed had decreasing effects on surface integrity in decreasing order. The optimum surface integrity was achieved with a surface roughness of 0.32 mu m, a Vickers hardness of 615, and a residual stress of - 650.12 MPa at a rolling pressure of 320 N, a feed rate of 0.2 mm/r, and a spindle speed of 125 r/min. The reasonable selection of optimum process parameters was beneficial in improving the surface integrity of the machined surface.