Case Study: Differential Gear Set

Process: Powder forging
Secondary Processes: Carburized, quenched & tempered
Surface Hardness: 58–62 HRC
Materials: Pre-alloyed low-alloy steel PF-4620 and modified PF-4620
Density: 7.80 g/cc³ minimum for each component

Differential Gear Set
2016 Grand Prize: Differential Gear Set

End Use and Function

The above five components—a side gear, two pinion gears, a locking side gear, and a locking plate—comprise a powder forged electronic locking differential gear set. The parts go into the rear axle differential of the Ford F-150 light truck; the first time powder forged differential gears have been used in such an application.

Fabrication

All five components are made of pre-alloyed low-alloy steel (PF-4620 and PF-4620 modified for the locking plate), produced to a minimum density of 7.80 g/cm3, and delivered in the carburized, quenched, and tempered condition with a surface hardness of 58–62 HRC. The case profile and core hardness is unique for each component. Net-shape forging yields the external cam teeth on the locking plate, side gears with AGMA Class 6 internal splines, pinions with AGMA Class 7 bevel gear teeth, and dog teeth on both locking parts that are held to a 0.2 mm profile tolerance. Minimal machining operations are performed on thrust bearing surfaces, internal bore on the pinions, end faces on the locking plate, and chamfers on the pinion and side gears.

Results

The higher performance delivered by the powder forged differential gears compared with that of competing metal-forming processes will help usher in downsized gear systems, satisfying a critical need in future automotive design.