Micro structuring of coated tools for dry sheet metal forming of Aluminium alloys

Sheet metal forming is characterised by strong frictional forces involving an increase of the temperature and a tendency to adhesion. Consequently, use of lubricants is essential yet, especially for forming of Aluminium alloys. Furthermore, lubricant reduces tool wear. However, for economical and ecological reasons, dry forming is highly desired. Avoiding the application of lubrication requires a reduction of the coefficient of friction and the tendency for adhesion in dry forming processes. One approach is to increase the nominal surface pressure by micro structuring the tool. Additionally, different carbon based layers (a]C:H:Si and CVD diamond) are applied on the tool to reduce wear and tendency to adhesion. For using a a]C:H:Si layer, uncoated steel drawing tools are micro structured with calottes by milling. Because of a higher thickness of CVD diamond layers, calottes have to be generated directly in the coating using ablating processes like electrical discharge machining. To emulate the tribological system of a sheet metal forming process and characterise it, strip drawing tests are done. For a]C:H:Si coated drawing tools, the test results show a significant reduction of the coefficient of friction in micro structured, compared to polished drawing tools. To further increase the wear resistance of the tool it is intended to apply CVD diamond layers on steel tools as soon as the process is operational.