Analysis of surface defects on industrial casting tools for automotive applications after machine hammer peening

Abstract

Abstract The increased usage of advanced high strength steels (AHSS) as material for car body parts leads to a continuous reduction of car weight and thus a lowering of CO 2 emissions. This weight reduction results from higher yield and tensile strength of AHSS than conventional steel grades. However, the higher strength of AHSS leads to higher loadings of the forming tools. To increase the wear resistance of the tool surfaces, mechanical surface treatments are used. In this work, the incremental forming of EN-JS2070 deep drawing tools by means of machine hammer peening (MHP) is investigated. In the past, small surface defects were observed after MHP of nodular cast iron EN-JS2070. The cause for the occurrence of these surface defects is unknown. The aim of this work is the investigation and description of the logical relationship between the cause and effect of MHP process parameters and the surface defects on nodular cast iron EN-JS2070. The surface defects occurred independent of the chosen MHP parameter setup at one critical zone on the hammered deep drawing tools and the investigated microstructure showed the existence of shrink holes, which were primarily responsible for the occurrence of the surface defects after MHP.