Investigation and implementation for forming lead screw by through-feed rolling process with active rotation

Abstract

A through-feed rolling process with active rotation for manufacturing lead screw has been developed, where the speed matching and stable motion between workpiece and the rolling die during the whole rolling process can be ensured. Its process control, die structure and rolling equipment are relatively simple, and the accuracy of pitch for rolled lead screw can be effectively ensured. The motion characteristic during through-feed rolling process was analyzed, and then the general design criteria for the die were set up. The feasibility of the through-feed rolling process with active rotation was verified by experiment and finite element method (FEM). The verified results indicated that the error of lead-screw pitch between experimental value and designed value is about 0.125 %, and the error between the FEM value and the experimental and designed values is less than 1 %. According to the deformation characteristics of lead screw rolling and the distribution of field variables, the workpiece can be divided into non-deformation zone, entry-angle zone (incremental forming zone), correction zone, exit-angle zone, and full-formed zone. The same position of workpiece will undergo those five forming states in turn. The FEM results indicated that the effective stress and effective strain both gradually increase from the entry-angel zone to the correction zone, and the strain in the exit-angle zone and full-deformed zone are almost quite; the effective stress and effective strain in thread root are larger, and both gradually decrease along thread flank to thread crest; the distributions of stress and strain have a certain periodicity along the axial direction. The results in this study provide a basis for high-efficiency and precise rolling forming of threaded parts with large diameter such as the lead screw.