Abstract
The final objective of this study is to establish the optimized manufacturing method of herringbone microgrooves for fluid dynamic spindles. In this article, two kinds of fundamental coining experiments of a simple indentation are carried out to create microgrooves of 5〜10μm depth. In order to compare the coining performance, two kinds of materials are used. One is an austenitic stainless steel (SUS303) of the wrought material and the other is also an austenitic stainless steel (SUS304L) of metal injection molded (MIM) material which has 5% porosity. In experiment-1, a flat head punch with three micro projections of 10μm height is pushed into a hexahedral specimen with or without the ultrasonic vibration. The groove depth of the MIM material increases in proportion to the punch load in the static indentation and its maximum value is about 80% larger than that of the wrought material. The imparting of the ultrasonic vibration is effective to increase the amount of groove depth especially for the MIM material under the lower punch load. In experiment-2, a circular punch and a circular anvil are statically pushed into a cylindrical specimen to produce 18 parallel grooves with an equal pitch in the circumferential direction. The groove profiles become almost uniform and the burr formation at tips of groove shoulder is effectively suppressed under the excessive amount of die indentation.
