Deviations in geometry of miniature gears fabricated by wire electrical discharge machining

Functional performance of a gear during its service life depends on its manufacturing quality which is decided by the amount of deviations in the gear geometry. Most of the conventional miniature gear manufacturing processes (i.e. stamping, hobbing, powder-metallurgy, extrusion, die-casting) are unable to meet the very high quality requirements of miniature gears used in highly precise and sophisticated equipments such as devices used in MEMS, NEMS and timer mechanisms, robots, micro-motors, micro-pumps etc. Present work was undertaken to explore the use of wire electrical discharge machining (WEDM) as a superior alternative miniature gear manufacturing process. This paper reports on the deviations in macro-geometry (i.e. span, tooth thickness, dimensions over two-balls) and micro-geometry (single pitch deviation, runout, and surface finish) of WEDMed miniature external spur gears (having 9.8 mm outside diameter with 12 teeth) made of brass. The best quality WEDMed miniature gear had very less macro-geometry and micro-geometry deviations and belongs to American Gear Manufacturers Association (AGMA) quality range 8-11. The average surface roughness and maximum surface roughness were 1 μm and 6.4 μm respectively. The SEM images indicate tooth surfaces free from surface defects. Attempt was made to find the probable causes of deviations in geometry of WEDMed miniature gears. Comparative study of the WEDMed miniature gear with the hobbed gear was also done. The findings of the present work prove that using appropriate process parameters WEDM can manufacture superior quality miniature gears than by any conventional process.