Lubricant free forming with tailored tribological conditions

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The results of the first and the second project phase show that the direct contact during dry deep drawing leads to intensive interactions between tool and sheet surface. With conventional tools, lubricant-free deep drawing causes increasing forming forces, local wear occurrence and failure in form of cracks depending on the sheet material. This motivates the development of surface modifications which reduce friction as well as wear and thus, help to control the material flow. As approach in the first and second project phases, amorphous carbon based coatings and laser based surface modifications have been developed and analyzed regarding their tribological behavior. Reduction of friction and wear is achieved by ta-C and a-C:H coatings while a laser based heat treatment and microstructuring are applied to control the material flow in the deep drawing process. Promising surface modifications have been applied on blank holder and die in order to realize a dry deep drawing of rectangular cups. Under dry conditions, the application of ta-C coatings leads to a reduced forming force and increased surface quality of the cups for steel and aluminum alloys in comparison to cups drawn with uncoated tools. This demonstrates the feasibility of dry deep drawing with the help of the measures chosen in this research project. However, it is not clear how the tribological behavior of the developed modifications changes at long sliding distances. Thus, the main objective of the third project phase is the investigation of run-in and wear behavior of the surface modifications under varied load conditions. This knowledge will be used in order to increase the wear resistance. Regarding the coating process, coating designs and deposition parameters will be adapted to improve the wear behavior of the coatings. In addition, laser based measures in terms of heat treatment, microstructuring and smoothing will be developed and analyzed. A heat treatment of coated surfaces could reduce critical residual stresses while microstructures are able to collect wear particles and keep them away from the contact zone. Challenging sheet properties which are associated with increasing contact and shear stresses will be investigated as well. This will prove whether the selected measures enable dry deep drawing for a broad range of applications.