3.5.1 Development of a Typical Shape

The shape of a forging, as with most other products, is driven by its function, material and manufacturing processes. The sequence of events in determining the shape is similar to the events for products made by any other process.

  1. Identify the functional surfaces and features, including those that relate to end use and those that relate to machining or heat treating.
  2. Add material to develop the required mechanical properties.
  3. Complete the form in a manner that will optimize the product to the selected alloy, forging process and finish machining process.


This sequence of events can best be seen by following a simple forgeable shape through the forging process. The finished drawing for a typical forged part consisting of a disk, hub and rim is shown in cross-section in Figure 3-4. This part can be made in a variety of alloys by several forging processes. In this case, the impression die process has been chosen. Note that the locating surface and chucking surface for the first machining operation are indicated. These notations will enable the forging company to deliver a part that the user can finish machine with minimum difficulty. Figure 3-5 shows the part after forging and trimming operations and prior to machining. Figure 3-6 shows the part in the forging die after it has been forged to shape, prior to ejection and trimming. Note that there is a web of material inside the hub hole, formed by plugs in both the upper and lower die members. There is draft on the walls of the hub to facilitate release of the plugs.

Figure 3-4 Cross Section of a finished part consisting of a disk, hub and rim.
Figure 3-5 The part in Figure 3-4 after forging and trimming operations and prior to machining.

Figure 3-7 shows the part in the trim and pierce die at the start of the trim and pierce operation. In Figure 3-8, the part has been pushed down over the lower die, trimming the flash from the perimeter and piercing the hole in the hub. Piercing operations impose high forces on the forging, and may distort the forging somewhat, requiring a subsequent straightening operation. (See Appendix A Tolerances For Impression Die Forgings and Appendix D Specialized Tolerances for Precision Aluminum Forgings.)

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The shape of a forging, as with most other products, is driven by its function, material and manufacturing processes. The sequence of events in determining the shape is similar to the events for products made by any other process.

  1. Identify the functional surfaces and features, including those that relate to end use and those that relate to machining or heat treating.
  2. Add material to develop the required mechanical properties.
  3. Complete the form in a manner that will optimize the product to the selected alloy, forging process and finish machining process.


This sequence of events can best be seen by following a simple forgeable shape through the forging process. The finished drawing for a typical forged part consisting of a disk, hub and rim is shown in cross-section in Figure 3-4. This part can be made in a variety of alloys by several forging processes. In this case, the impression die process has been chosen. Note that the locating surface and chucking surface for the first machining operation are indicated. These notations will enable the forging company to deliver a part that the user can finish machine with minimum difficulty. Figure 3-5 shows the part after forging and trimming operations and prior to machining. Figure 3-6 shows the part in the forging die after it has been forged to shape, prior to ejection and trimming. Note that there is a web of material inside the hub hole, formed by plugs in both the upper and lower die members. There is draft on the walls of the hub to facilitate release of the plugs.

Figure 3-4 Cross Section of a finished part consisting of a disk, hub and rim.
Figure 3-5 The part in Figure 3-4 after forging and trimming operations and prior to machining.

Figure 3-7 shows the part in the trim and pierce die at the start of the trim and pierce operation. In Figure 3-8, the part has been pushed down over the lower die, trimming the flash from the perimeter and piercing the hole in the hub. Piercing operations impose high forces on the forging, and may distort the forging somewhat, requiring a subsequent straightening operation. (See Appendix A Tolerances For Impression Die Forgings and Appendix D Specialized Tolerances for Precision Aluminum Forgings.)

Return to Table of Contents

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The shape of a forging, as with most other products, is driven by its function, material and manufacturing processes. The sequence of events in determining the shape is similar to the events for products made by any other process.

  1. Identify the functional surfaces and features, including those that relate to end use and those that relate to machining or heat treating.
  2. Add material to develop the required mechanical properties.
  3. Complete the form in a manner that will optimize the product to the selected alloy, forging process and finish machining process.


This sequence of events can best be seen by following a simple forgeable shape through the forging process. The finished drawing for a typical forged part consisting of a disk, hub and rim is shown in cross-section in Figure 3-4. This part can be made in a variety of alloys by several forging processes. In this case, the impression die process has been chosen. Note that the locating surface and chucking surface for the first machining operation are indicated. These notations will enable the forging company to deliver a part that the user can finish machine with minimum difficulty. Figure 3-5 shows the part after forging and trimming operations and prior to machining. Figure 3-6 shows the part in the forging die after it has been forged to shape, prior to ejection and trimming. Note that there is a web of material inside the hub hole, formed by plugs in both the upper and lower die members. There is draft on the walls of the hub to facilitate release of the plugs.

Figure 3-4 Cross Section of a finished part consisting of a disk, hub and rim.
Figure 3-5 The part in Figure 3-4 after forging and trimming operations and prior to machining.

Figure 3-7 shows the part in the trim and pierce die at the start of the trim and pierce operation. In Figure 3-8, the part has been pushed down over the lower die, trimming the flash from the perimeter and piercing the hole in the hub. Piercing operations impose high forces on the forging, and may distort the forging somewhat, requiring a subsequent straightening operation. (See Appendix A Tolerances For Impression Die Forgings and Appendix D Specialized Tolerances for Precision Aluminum Forgings.)

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