On surface integrity of miniature spur gears manufactured by wire electrical discharge machining

This paper reports about investigations on some important aspects of surface integrity of the miniature spur gears manufactured by wire electrical discharge machining (WEDM) process. The investigations included study of variation of form errors (deviations in profile and lead) and surface roughness with discharge energy parameters, i.e., voltage and/or pulse-on time for the miniature gears. The effect of WEDM process on flank surface topography, bearing length parameters, microstructure, and microhardness for the best quality miniature gear were also studied. The manufactured miniature gears were of external spur type having 9.8 mm as outside diameter, 4.9-mm thickness, 0.7 mm as module, 12 teeth, and were made of brass. It was found that combination of low discharge energy parameters resulted in better form accuracy, surface finish, and microstructure ensuring enhanced service life and better functional characteristics of the WEDMed miniature gears. The best quality miniature gear had form errors (i.e., lead and profile deviations) as low as 5.4 μm, very little variation in the actual surface topography from the theoretical one, an average surface roughness of 1 μm, and maximum surface roughness within the entire evaluation length as 6.4 μm, showed consistent surface finish measured by other surface roughness parameters, good bearing area curve, and crack-free gear tooth surface without significant alteration in microhardness. Results of the present work demonstrate the superiority of the WEDM process over the conventional miniature gear manufacturing processes.