Powder metallurgy is a well-established, cost effective manufacturing method for the production of automotive components.  The industry has targeted transmission gearing as the next major product application.  The end user community will benefit from the lower product acquisition cost associated with this net shape manufacturing process.  The transmission plants will not have to upgrade or replace aging manufacturing equipment thereby reducing the capital investment needed for the next transmission program.  Due to the lower core density in these PM gears the transmission will feature lower mass thereby improving gas mileage and NVH while maintaining the reliability of wrought steel gearing.  Process modeling will allow new transmission designs to take advantage of these cost effective PM gears without the need for another lengthy development program. 

The program is designed to evaluate gear processing issues that are unique to PM gears with the goal to further improve the performance of PM gears in order to meet the powertrain performance requirements.  The lower hardenability (lack of high manganese in the PM alloy compositions) and surface porosity are known features of PM gears that must be overcome in order to serve powertrain needs.  The program commenced in 2008.

Program Objectives 

(1) Quantify the contribution of post-PM processes on critical performance characteristics, e.g., contact fatigue, bending fatigue, dimensional accuracy
(2) Develop a PM gear post-PM process model

Scope

The program will focus on four post-PM processing treatments:

(1) Surface densification – type of process and processing conditions (depth of densification, control of root densification, dimensional accuracy, need for additional processing, process production rate)
(2) Surface treatments – shot peen (conventional versus multi-pass, intensity, shot size, surface finish, residual surface stresses); isotropic finishing (alone or after shot peen, surface finish); coatings (DLC, WC-graphite, graphite/MoS₂)
(3) Heat treatment – case carburizing (gas versus vacuum, cycle parameters, case depth, residual surface stresses, metallurgical features); through hardening (carbon content, temper cycle, grain size, residual surface stresses)
(4) Gear root geometry – classic involute root shape versus full fillet radius (FEA analysis versus AGMA analysis method); ground versus wire EDM (effect of manufacturing process parameters, surface finish)