On Micro-Geometry of Miniature Gears Manufactured by Wire Electrical Discharge Machining

This article presents the investigations on micro-geometry of fine pitch miniature spur gears manufactured by wire electrical discharge machining (WEDM). Effects of voltage, pulse-on time, pulse-off time, wire feed rate and cutting speed on total profile and accumulated pitch errors were studied using one-factor-at-a-time approach. The miniature gears had a module of 0.7mm, outside diameter 9.8mm, face width 4.9mm, and were made of brass. The best quality manufactured gear had DIN quality number of 6 and 8, respectively, for pitch and profile with average and maximum surface roughness values of 1 mu m and 6.4 mu m, respectively, establishing WEDM as a superior process for miniature gear manufacturing. It was observed that wire-lag and irregular shaped craters produced by high discharge energy parameters are responsible for micro-geometry errors of miniature gears manufactured by WEDM. Use of low voltage and pulse-on time, avoiding high pulse-off time, maximum values of wire feed rate and cutting speed are recommended to manufacture the high quality miniature gears by efficient and stable WEDM. This study found 5-15V for voltage, 0.6-1.0 mu s for pulse-on time, 90-170 mu s for pulse-off time, 9-15m/min for wire feed rate, and 100% cutting speed as the optimum settings for further investigations.