Efeito do ângulo da fieira na geometria e propriedades mecânicas de barras trefiladas

Abstract

In cold drawing of metallic bars most of the plastic flow is caused by compressive forces which arise from the reaction of the metal to the die. Due to the characteristics of the process this flow is not homogeneous along the cross section of the bar and is influenced by the die geometry. This inhomogeneous deformation generates residual stresses in the bars, which can produce a change in size and straightness during subsequent processes of cutting, grinding and heat treatment. This work presents an analysis of the influence of the die geometry and number of drawing passes on the final geometry and mechanical properties of drawn bars of SAE 1045 steel. Eight experiments were performed, with die angles of 12º, 18º, 30º and 40º, bearing lengths from 3,51mm to 7,09mm, and 01 or 02 passes of drawing. Measurements of straightness, roundness and diameter, microhardness and tensile tests were performed on the bars. Also were made measurements of straightness of shock absorbers rods after the induction hardening process. This study has shown that the die angle has a strong influence on the final geometry of the drawn bars; dies with high entry angle (30º and 40º) resulted in better values of straightness than dies with smaller angles (12º and 18º). Dies with high entry angle also resulted in less variation between the bearing diameter and the final diameter of the bar. It was also observed a strong relation between the straightness of the drawn bars and the straightness of the shock absorbers rods after the induction hardening process, where drawn bars with better straightness resulted in a better straightness of the shock absorbers rods after the induction hardening process.