Investigation of Tribological Systems for Dry Deep Drawing by Tailored Surfaces

Growing ambitions for efficient resource utilization and improving environmental standards stimulate the abandonment of environmentally harmful lubricants. However, dry forming leads to direct contact between tool and workpiece surface which causes increasing friction and wear. This paper presents a methodology for realization of lubricant free deep drawing processes. Dry deep drawing of a rectangular cup is investigated by a numerical simulation. First numerical results reveal the necessity of modifying the tribological system in order to realize dry deep drawing. Basic tribological investigations reveal increasing friction and intensive wear under dry conditions. Therefore, tailored surfaces are developed to improve the tribological properties without lubrication. By laser structuring various micro features were fabricated on the tool surface. Furthermore, tungsten doped hydrogenated amorphous carbon coatings (a-C:H:W) were deposited on the tool using unbalanced magnetron sputtering. The tribological behavior of these surface modifications were researched by a ring-on-disc-tribometer. The wear mechanisms during the dry sliding process are discussed depending on the micro features and coatings. The obtained test results help building the basic concept for generating tailored surfaces and subsequently to realize lubricant free deep drawing.