Behavior of DLC coatings in lubricant free cold massive forming of aluminum

Capability of diamond-like carbon coatings to permit lubricant free cold massive forming of aluminum is tested by forced-in tests featuring high deformation degree. The frictional behavior during penetration into AA6016 material is tested for PVD a-C as well as PECVD a-C:H and a-C:H:Si coatings in comparison to uncoated 1.3343 tool steel. Also tendency to workpiece material take-up by tool surfaces and roughness of formed surfaces are analyzed. Though uncoated punches show less material take-up and provide lower friction during forming, high potential of diamond-like carbon coatings, particularly a-C:H coatings, for lubricant free cold massive forming of aluminum is proved. Significantly lower surface roughness both in axial and circumferential directions in produced bores is measured for use of a-C:H coated punches compared to uncoated punches and hydrogen free or silicon doped diamond-like carbon coatings. Also in contrast to uncoated punches no change of surface quality is observed for repeated testing. Friction and material take-up are highest for a-C:H:Si coated punches. Strong degradation of bore surface quality is observed for repeated testing with a-C coated punches.