Kinematics of die filling during upsetting of the head of a steel self-tapping screw

Abstract

The aim of the work is to determine the kinematics of filling the die when upsetting the head of a steel self-tapping screw. It is noted that a significant part of the wire from ferrous metals is used for the manufacture of hardware products in the form of screws. For the analysis of the form change, a self-tapping screw made of 15Gps steel was selected. The process modeling was performed by the finite element method using the DEFORM software package. The distribution of the degree of deformation for the final position of the tool during the formation of the workpiece is presented. The contour of the center of forming and the accumulation of plastic deformations along the upsetting of the workpiece are given. The maximum strain up to a value of 2.70 is localized in the central part of the head with the spread of the zone of increased deformation in the transverse direction. A zone of increased deformations is identified in the area of the free surface and adjacent to it to the contact surface of the lower half-stamp. The distribution of the mean normal stress is shown. The highest values up to +504 MPa are observed in the zone of the free surface, not constrained by the action of the tool. Under real production conditions, the screw head profile was measured and recorded in coordinate form. For comparison, the calculated data obtained in solving the problem are given. Differences at small values of the current axial coordinate indicate a shift in the area of increased metal broadening in the calculated version closer to the upper half-stamp. The localization of tool wear in the real process is fixed. It is noted that the location of this zone corresponds to the position of the region where the highest level of plastic deformation is established by calculations, which corresponds to one of the variants of wear theories.