Characterization of surface profile of shot peened cemented tungsten carbide dies with micro valleys and their lubrication performance in cold forging

摘要

To improve tribological characteristics of dies for cold forging, micro valleys were formed on surface of cemented tungsten carbide dies by shot peening. The mean period of the surface roughness profile (RSm) of the shot peened (SP) die was approximately 1/3 times shorter that of the conventional mechanical polished (MP) die. The distribution of peaks and valleys of the surface profile (Rsk) was close to symmetric in the SP die (Rsk = 0), while it was skewed toward peaks in the MP die (Rsk < 0). The lubrication performance of the SP and MP dies was investigated by cold ring compression test of a titanium workpiece. The surface roughness was dominant factor for the friction in the test with rough finish dies. On the other hand, the SP die with mirror finish reduced the friction at a high reduction in height in the test. The lubricant trapped area of the end surface of the compressed titanium workpiece with the SP die was wider than that with the MP die. It was found that the SP die with mirror finish was effective to confine larger amount of the lubricant within micro valleys on the surface up to high reduction in height in the test.