There are three mainstream material-conversion options: machining from tubing, machining from bar or machining from a forging. The majority of manufacturers use some type of forging technique coupled with machining. We continually look to improve process efficiency in order to improve material efficiency and reduce the downstream effects of distortion due to conversion-induced stresses.
All types of forging processes are used, including high-speed, high-volume processes like Hatebur and Sakamura presses; inline multi-step presses with optional ring expanders; or individual forge operations on larger parts, which include expansion mills like an SMS Meer (formerly Wagner) ring-rolling unit. Shaped forgings significantly reduce the material losses, but sometimes a “pot” forging is prescribed for thin-wall parts where multiple parts are machined from one forging to reduce distortion. In the end, the forging process selected must provide the best overall value and not impact downstream operations.
There are a number of parts that are cooled in a controlled manner after forging or given a quench and temper to impart final properties. Sometimes this is coupled with selective induction hardening at critical fatigue areas or when a rolling contact surface is present. Automotive wheel-hub units that incorporate a bearing race are a prime example.