Investigation into laser refurbishment and transformation hardening of cast iron forming dies for the automotive industry

Abstract

Forming dies used in the automotive industry are shaped as such that they impart a predetermined contour or a profile to the workpiece. Due to subsequent assembly requirements of sheet-formed body structure components, the dimensional accuracy of the components is of vital importance. The dimensional accuracy of the forming dies is, therefore, of equal importance. The sheet metal forming process involves severe contact conditions, with the draw die radius generally being the most affected zone. Due to intense local tribological conditions, wear damage is observed. The possible laser refurbishment of wear damaged cast iron die radii as well as laser transformation hardening of these areas have been investigated. The refurbishment is seen as a remedy to an existing problem and transformation hardening as a precautionary wear-inhibiting solution to the problem. Due to the high carbon content of the cast iron and the dilution—although low—obtained during the cladding process, the resulting build-up susceptibility to cracking can be high. A stainless steel buffer layer between the die substrate and the overlay material was introduced. It was found that the H11 overlay material hardness complied with the specific requirement. The laser transformation hardening was studied at different parameter sets to obtain the required surface hardness, and laser hardening was successfully implemented on a forming die that was put in service.