Wire Electrical Discharge Machining of Micro-Involute Gears.

Abstract

Micro-involute spur gears with a module of less than 0.1 are fabricated by wire electrical discharge machining instead of conventional rack cutting since rack cutters with a fine module are very difficult to fabricate. This paper shows that undercutting of involute tooth profile occurs when the module of the microgear is small because the width of tooth fillet becomes smaller than the diameter of a tool with a circular section, namely the sum of the diameter of wire and the gap of electrical discharge. The relation between the diameter of wire and the limit module that a micro-involute gear can be machined without undercutting is also derived. A micro-involute gear 0.024 in module, 0.280 mm in diameter, and having 9 in number of teeth was machined with a tungsten wire 25 μm in diameter, and the machined gear had a tooth profile error less than 1 μm but no undercutting as theoretically expected.