Tribological Performance of Textured Micro Forming Dies

Abstract

Aim of this work is the tribological investigation of micro structured surfaces generated by micro milling and the performance testing of a micro structured micro deep drawing die. Three samples exhibiting different micro structured surfaces with arithmetical mean heights Sa in a range of 148 nm to 741 nm were manufactured by micro milling. The surface texture is determined by the process parameters of the micro milling operation. Tribological properties of the micro structured surfaces were investigated by means of a ball-on-plate micro tribometer and compared to those of a polished reference sample (Sa = 24 nm), a clear dependence of the frictional properties on the surface roughness was found. Lowest friction μ =0.26 was achieved for the sample with a roughness Sa = 148 nm. Surfaces with higher or lower roughness provoked increased friction in tribological testing being associated with an interlocking of surfaceâ s asperities or dominant adhesion, respectively. Subsequently, micro structures were machined into the surface of a micro deep drawing die for drawing of rectangular micro cups. The performance of this die was tested in deep drawing experiments against a polished reference die by means of achievable drawing ratio. At this stage the full advantage of the micro structuring of die surfaces was not achieved, yet. Still particular challenges within the micro regime, e.g. alignment of punch and die as well as blank positioning, have to be improved.