Designing of screw impressions in the helical rolling of balls

The paper presents the results of the studies undertaken to investigate the helical rolling process for producing balls in modified helical impressions. In the first part of the paper, the helical rolling process for producing balls is discussed and the effect of selected technological parameters on the quality of formed parts is described. Next, the methods for sizing of helical impressions are discussed and a modified version of the tool design process is proposed. In the subsequent part of the paper, the results of the conducted experimental tests of rolling balls in traditional helical impressions are presented, and then the results of the performed numerical simulations of rolling balls in single and double impressions developed using the modified method are described. The numerical analysis of the process was conducted based on the finite element method (FEM), using the commercially available software package Simufact Forming version 11.0. The simulations were performed in the three-dimensional state of strain and in their course the following were determined: the geometry of the balls being rolled, metal flow kinematics in the helical impression, and force parameters of the process. The obtained results confirmed the validity of using the proposed modified tool sizing method in the helical rolling of balls.