How to Drop Forge Wheel Hub?

The forgings of wheel hub type are often made by means of drop forging processes realized on presses. Due to the necessity of lightweight structure, wheel hubs are often manufactured by aluminum forging. Forming of drop forged wheel hub is a specific hot forging process and it differs from steel forging process.

The big changeability of aluminum alloys properties within the range of the applied forming parameters results in difficulties in the process design. The majority of aluminum alloys’ forgings are made by means of forging process with flash. The degree of complex forging geometry decides about the amount of heating and type of the applied tooling. The forgings with a complex geometry, ribbed, which need a precise preforming, are forged in preforming impression, and next, after the damages removing and reheating they are forged in forming impression. In the forming process of less complex forgings, which are made in small series, the application of preforming impression is usually omitted. Preforming operation is made in forming impression with several  millimeters of underfilling. After the damages removing and reheating, it is finally made in the same impression. In case of enlarged forgings, the preforms are rarely used despite difficulties in their obtaining. For the preforming of material, enlarging and rolling impressions are not applied. The operation of this type causes fast lowering of material temperature and the overlapping creation as a result forging with rotation at the same time. Because of that, workpiece in the form of a bar with the section close to the biggest forging section is used.

In Fig. 1, shape and dimensions of the wheel hub forging formed on hammer are presented. Drop forging is made of 6061 aluminum alloy.

Fig. 1. The wheel hub forging made by means of forging on hammer; forging inclinations 7°, not given radii R3

Fig. 2. Other phases of the wheel hub drop forging forming process on hammer: a) charge, b) upsetting, c) forging in preforming impression, d) forging in forming impression, e) final forged parts, f) flash

As a charge for forging of part presented in Fig. 1 is a bar of circular section of dimensions Ø45x115 mm. The schema of a typical forging process on hammer of the discussed forging consists of the following phases: