Development of a Fully Automatic Precision Warm Forging Cell for the Production of Variable or Constant Ratio Steering Racks

This paper describes the development of a fully automatic Precision Warm Forging Cell to produce Variable or Constant Ratio steering racks at a cycle time of 12 seconds. Racks are forged in a unique closed cavity multi-element forging die (Bishop Y-Forge Die) that uses a combination of mechanically and hydraulically loaded tooling elements to generate the required forming loads. The racks produced in this process are essentially free of flash and require no finish machining of the teeth or the rack faces (Y-faces) that contact the rack pad. Racks may have a specific “high point on centre” or “rise/fall pattern”, or both, and an accuracy of ± 0.010mm on centre to ± 0.025mm at full lock is achieved. As-forged tooth mesh quality achieved is DIN Class 9 or better. The Cpk of all critical rack forged dimensions exceeds 1.67.