Precision grinding of screw rotors using CNC method

A precision grinding method for screw rotors using a computer numerical control (CNC) grinding wheel dressing is presented in this study. A mathematical model for screw rotor grinding is developed for a prototype based on the new screw rotor grinding machine SK7032. A spatial contact curve equation for screw rotor grinding is proposed, which includes three parameters: center distance, swivel angle, initial phase angle. A parameterized program was designed by the contact curve equation, and the grinding wheel axial-section profiles were calculated for different parameters. With the calculation results, the grinding wheel profile errors were analyzed, and the maximum influence of the grinding wheel profile error was swivel angle. The minimum influence was the initial phase angle, but the position of grinding wheel profiles can be changed and the interference between the screw rotor and the grinding wheel can be avoided by its changing. A segmentation dressing method for the grinding wheel was designed based on a variable center distance, and the reasonable interval value was studied. A male rotor grinding experiment was conducted on SK7032, and the rotor profile error was measured on the gear tester P65. The results reveal that the screw rotor profile errors can be controlled within ±10 μm.