Effects of ball burnishing on surface properties of SKD11 mold steel

Abstract

Burnishing is an energy-efficient technology to enhance the surface of mechanical parts. Metallic parts’ surfaces with hardness up to 65 HRC can be enhanced with a hydrostatic burnishing tool. This paper presents the effects of the hydrostatic burnishing on surface residual stress of the SKD11 mold steel by conducting the five-parameter orthogonal experiments using Taguchi Method. Results showed that burnishing force played the most significant role in the improvement of the magnitude of the compressive residual stresses, while the feed and the number of passes played less significant roles. Besides, the effect of burnishing direction and burnishing speed could be neglected. Single-factor experiments were conducted to provide further demonstrations of the influences of burnishing feed and number of passes on the surface properties and the results corresponded well with the orthogonal experiments in general. The single-factor experiments also showed that with the increase of burnishing feed, the surface hardness firstly experienced steady decrease and then decreased dramatically. However, the surface roughness firstly experienced steady increase and then increased dramatically. The surface hardness increased initially, but then followed a decreasing trend with the increase of the number of passes. The distribution of residual stress in the direction at an angle of 45° to the burnishing direction was related with the parity of the number of passes.