CARBON-BASED COATINGS FOR DRY SHEET-METAL WORKING

This paper describes recent advances in the coating of tools for formi ng processes such as deep drawing or clinching of aluminium and stainl ess-steel sheets. Various carbon-based coatings, prepared by PECVD (RF and pulsed-DC mode) and by reactive DC magnetron sputtering have been investigated with respect to hardness, abrasive wear resistance, adhe sion properties and tribological behaviour under forming conditions. T he softer and less wear-resistant coatings exhibited the lowest adhesi ve wear and friction against aluminium and stainless-steel counterpart s. Application tests with coated tools were carried out under near pro duction conditions. Correlation of mechanical test results with the fi lm behaviour under service shows that for the dry forming of stainless steel, a high abrasive wear resistance of the hydrocarbon coating is necessary. No cold welding of the steel sheets on the tools was found, so the aim of dry working is reached by these coatings. For forming o f aluminium, only softer a-C:H coatings showed satisfying anti-galling properties. In particular, in the case of aluminium working with a hi gh degree of form change, there is a need for coatings with further im proved anti-galling properties. (C) 1998 Elsevier Science S.A.