3.4 Process Tradeoffs

When a product that has been traditionally made by some other process is being designed for forging, or when an existing product is being redesigned for forging, the design must focus on the function that is to be performed and avoid the tendency merely to replicate the former shape.

Designing for function, rather than form, will enable the designer to realize the full benefits of forging. It will help, in many cases, to avoid costly overdesign. As noted above, in functional design the various features of the forging are tailored to the mechanical requirements of each feature.

The end product contains the minimum amount of material, minimizing weight and reducing cost. The stamping mentioned below would have a constant thickness while the forging thickness could be varied to develop less weight for essentially the same part.

In most design programs, more than one manufacturing process may be employed, but one process will be optimum. Therefore, identifying the optimum process is a critical step in a the development of a product.

A second factor, often overlooked, is the profound effect of the manufacturing process on the shape of a product. For example:

  • The features of a steel stamping are essentially uniform in thickness because the stamping is made from sheet stock of uniform thickness. A forging that performs the same function can have varying thicknesses tailored to the mechanical requirements of each feature.
  • A weldment often requires special built-up features at joints, such as flanges and bevels, to develop adequate weld strength. A forging is a monolithic structure, and does not need those features.

In both categories, the finished forgings often weigh less than the part being replaced.

A third factor is the opportunity to combine two or more parts that are being separately manufactured and assembled. Often, substantial cost savings and product improvement can be realized by redesigning into one forging. The tractor drawbar hitch and steering knuckle, shown in Figure 3-2, illustrate successful parts combinations.

The following summaries identify the critical factors for choosing among the available forging processes and for comparing forging with alternate processes. It is worth repeating that these decisions are often best made in concurrent engineering teams.

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