Improved Broaching Steel Technology

摘要

Helical broaching is a highly efficient machining technology used to cut tooth profiles in annulus planetary gears used in car and truck automatic transmissions. The operational costs largely depend on the life of the expensive broach bar, with rapid tooth wear rates leading to very high broaching costs. The wear rate of the broach bar teeth is dependent upon factors including the broach bar material, tooth design, surface treatments, lubricants and the properties of the gear blank material/condition. A laboratory broach machine was developed to study the impact of these variables on the wear rate and life of the broach tool material. Extensive testing has been performed utilizing this test, with an emphasis on the effects of the gear blank material on the life of the broach tool. Effects of base material composition, hardness and microstructure on the life of the broach tool have been studied in detail. Testing results reveal the current typical ferrite/pearlite microstructure of gear broach blanks can cause high tool wear rates, whereas a non-pearlitic structure can result in a 100% to 500% improvement in broach tool life. Tested steels include both carburizing (SAE 5120, 8620, 5130, etc.) and induction hardening (SAE 1050, 1552, 5150, etc.) grades, with ferrite/pearlite, ferrite/bainite and martensitic structures. This paper describes the laboratory broach test, a summary of the testing performed, significant findings resulting from the test and the metallurgical correlations between the base material and the broach tool life.