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Powder Metallurgy is a proven technology to produce high strength gears for the automotive industry. Advances in powder production, compaction, and sintering combined with double pressing have enabled overall part densities up to 7.5 g/cm3 in spur gears. However, helical gears are more difficult to produce to these same densities because the geometry does not lend itself to the DP/DS process. Described in this paper is a P/M parts making technology capable of producing single pressed and sintered helical gears with densities greater than 7.4 g/cm3. Description of a prototype run will be presented with the resulting sintered part densities and part-to-part variability. To further enhance the gear performance and gear tolerance of these helical gears, the gears were subsequently surface densified via rolling. Improvements in the surface density and gear quality will be described.

Powder Metallurgy is an efficient manufacturing process for the production of gearing and similar net shape components. Because of limitations arising from the inherent porosity and limited alloy systems available, the traditional uses for P/M gearing was in relatively low stress applications. The recent introduction of new compaction techniques and new alloy materials has produced P/M components with significantly higher yield and tensile strengths approaching the strength levels of wrought gearing materials. This paper will review the new P/M processes and materials and their suitability for gear type applications. Mechanical property comparisons will be made to the common automotive gearing materials including ductile and malleable cast irons and wrought low alloy steels.

Malleable and ductile cast irons are used extensively in gearing and high strength applications within automotive power train applications. Advantages of malleable and ductile cast irons are low material cost with mechanical properties that meet or exceed the requirements of the intended application(s). One disadvantage of the malleable cast iron is the extensive heat treating required to obtain the proper microstructure and mechanical properties. Both malleable and ductile iron components require extensive machining to produce the finished component. The combination of heat treating and extensive machining often results in a component that is costly to manufacture. Recent advances in the Powder Metallurgy (P/M) process including high strength material systems and high density processing have achieved mechanical properties that meet or exceed the level achieved with the current malleable and ductile cast iron materials.

Turbine hubs for automatic transmission torque converters are ideal candidates for the powder metallurgy (P/M) process. The complex shape of turbine hubs is costly to produce via conventional forging and machining operations. Increases in engine size and torque requirements by automotive designers require turbine hubs to possess high levels of mechanical properties. High density P/M manufacturing techniques, in combination with high performance ferrous material produces components capable of replacing a forged and machined turbine hub. This paper will review the conversion of a conventionally forged and machined turbine hub used in a high torque automatic transmission to a single pressed and single sintered P/M turbine hub. The material used for the P/M hub was an MPIF FD-0405. Warm compaction processing achieved significantly increased overall sintered densities in the highly stressed internal spline region.