The Quantification of Galling in Forming Operations of Hot Dip Galvanized Sheet Metal under Laboratory Conditions

In the sheet metal forming industry, tools are subject to mechanical, thermal, chemical and tribological loads. One of the major problems in forming operations of hot-dip galvanized sheet metal is galling (build-up of zinc flakes on the tool). This phenomenon develops gradually as an adhesion on the tool surface. The adhesive wear leads to high rejection and reworking costs for large car body forming tools. Due to economic aspects and the easy castability, the forming tools are made of cast iron. These materials tend to high adhesive wear. The aim of this project is to find a three-dimensional surface parameter, which describes a tribologically advantageous surface of forming tools in order to reduce galling. An additional objective is to optimize tool materials, heat treatment and surface coating. The evaluation of galling under laboratory conditions is based on strip drawing tests. The characterization of tool materials was executed for grey cast iron (EN-GJL-200/250) and nodular cast iron (EN-GJS-700). Investigations demonstrate that the processing methods and test parameters like sliding speed and temperature have a significant influence on galling. Three-dimensional surface parameters have also shown an effect on galling.