Dry Deep Drawing of Aluminum and the Influence of Sheet Metal Roughness

Dry forming processes are associated with major challenges, especially when it comes to aluminum as the workpiece material. Major losses in process quality and robustness occur when lubricants are spared. This is due to the high adhesion tendency of aluminum towards common tool materials. Nanoscopically smooth coatings based on amorphous hydrocarbons (a-C:H) can significantly reduce wear. Further preliminary investigations have shown that a reduction of the roughness of a mill-finished sheet results in a significant improvement with regard to the friction and wear behavior in the strip drawing test. These tests are now transferred to a real workpiece. First, the different zones of the deep drawing process are modeled in the strip drawing test and coefficients of friction are derived. Flawless deep drawing tests can be carried out with nanoscopically smooth a-C:H coatings. By polishing the sheets and using the a-C:H coated tools without further surface treatment, the dry friction and wear are reduced, but compared with experiments on smoothened a-C:H coatings, the necessary process forces are higher and may lead to rupture of the aluminum sheet.