Rotor Form Machining and its Form Cutter Calculation for Dry Screw Vacuum Pumps

The rapid and high-precision machining of rotors is the key technology to improve the performance and reduce the production cost for dry screw vacuum pumps. In this study, the mathematical model for the form cutter profile generation is proposed employing the contact line method, which is based on a novel forming machine with the adjustable vertical position and tilt angle of cutters. We analyze the influence of the position parameters(initial rotation angle, solution range parameter, center distance, oblique angle, and tilt angle) on the cutter profile.Resultsshow that an overlarge oblique angle leads to the concave phenomenon, and a too narrow oblique angle results in interference in cutter profiles. An overlarge tilt angle also gives rise to the concave phenomenon, while a too-small tilt angle causes the unfeasible solution of cutter profiles. Additionally, with the increase of the solution range parameter, center distance, and initial angle, the cutter radius effectively increases while an overlarge center distance results in the unfeasible cutter profile. During the design of form cutter position parameters, oblique angle,tilt angle, and center distance should be selected carefully to avoid interference, concave, and unfeasible solution phenomenon for cutter profiles. To improve the cutter radius, the solution range parameter could be reasonably increased. The proposed method could be effectively applied to calculate the form cutter profile for the fixed-pitch or stepped variable-pitch screw vacuum pumps.