Development of New Steels for Lightweight Construction

Due to increasing stringent restrictions concerning the exhaust emissions until the year 2020 the automobile manufacturers aim to reduce the CO2-emissions. In the past, the focus of weight reduction efforts was set on the car body and resulted in very case-specific solutions. Recent investigations show high potential for weight reduction of the powertrain. A very promising weight reduction concept is the intelligent lightweight design through multi-component processes. In actual terms this approach replaces the conventional gear concept by a high-strength gear ring and a wheel body using lightweight design structure. The teeth on the gear ring have to withstand high local loads in the tooth contact. The necessary interference fit has to be calculated with respect to the transferred torque value and the strength of the gear ring, especially tooth root strength. A central process of the multi-component gear design is the joining process of the single components that can be realized by a friction type press fit supported by the heat of the previous case hardening process. An important point is the effect of case-hardened depth on size change of the gear ring. The joined gears will be checked on a static torque test device in order to determine typically occurring failure modes and to pick promising variants with best gear performance.