M. C. Perkins, Peerless-Winsmith Inc., Springville, NY
The use of austemper heat treatment on ductile iron gearing produces a gear with greatly increased static load capacity and wear-resistance; however, the austempering process causes dimensional changes in the gear that may affect critical features such as bore size, keyway position, tooth profile, and pitch-line run-out. Selection of austempering conditions and alloy content affect the amount of growth and distortion that takes place during heat treatment. This paper discusses the results of a 2-level, 2-factor, fractional factorial experiment analyzing the dimensional growth of austempered ductile iron worm-wheels. The goal of the experiment is to determine specific material and process conditions required in order for austemper heat treatment to be used and the effect on the manufacturing plan regarding whether subsequent finishing operations will be required to achieve the desired quality for use in finished product. Because the mass of the gear directly affects the amount of growth and distortion that occurs, the results of a short study on the effect of worm-wheel size are also briefly discussed.
Summary: The magnitude and variation of dimensional distortion due to austemper heat treatment of ductile iron wormwheels is examined using a two-level, two-factor, fractional factorial designed experiment. The effect of austempering temperature and alloy content of the iron is investigated.
