In this paper, we describe form rolling of microgrooves (herringbone grooves) on the surface of cylindrical metal specimens used for fluid dynamic bearings. A new reciprocating form rolling machine for the form rolling of microgrooves on metal shafts is deigned and constructed. The materials used are austenitic stainless steel SUS303 and aluminum alloy 6061 with a diameter of 10 mm. The gap between a couple of flat dies is set in the resolution of micrometers. Form rolling performance is checked for two types of die combination : in one type, the upper die has a flat surface and the lower die has herringbone grooves on its surface (flat/corrugated dies); in the other type, both upper and lower die surfaces have herringbone grooves (corrugated/corrugated dies). The depth of grooves does not become uniform in the circumferential direction when using the former die combination, while the latter die combination is effective in producing uniform microgrooves 10 μm deep. It is also found that burrs generated at the tip of projections can be restrained by making the bottom shape of grooves round. Finite element simulation results for the form rolling of microgrooves are in qualitative agreement with the experimental observations.
