Gear-cutting tool for screw-compressor rotors - (Built-up hob)

A built-up hob for a screw-compressor rotor is proposed. The hob is compose d of cutter blades and a hob head. The blade is cut out from a tempered pla nar plate of high speed tool steel by wire-cut electrodischarge machining ( EDM). During the wire cutting process, the wire electrode has a fixed angle to ensure both the side and the end relief angle of the cutting edge, so t hat the rake face regrinding sharpens the Cutting edge without changing the profile of the rake face. In other words, theoretically, the hob has no ac curacy deterioration due to rake face regrinding. The formulae of rack toot h profile are derived from the female rotor tooth profile expressed by nume rical formulae. Next, the fundamental helicoid of the hob and the profile o f the cutting edge of the blade are calculated. The hob was fabricated and the rotor hobbing was carried out.