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Drop Forging Design Considerations

For the advantages of drop forging, it is always used to make metal parts. Drop forging design is the first step for starting a new part, and such design will follow the application and assembling of products. And drop forging products will be compressed in a closed die upper and lower dies to get desired shapes, after that we will see trimming around the products, which will be cut in punching machine, then forging blanks will be born. So before put into production, designer should consider in a whole way for following aspects:

Parting line

The forging dies will decide the postion of parting line around the edges of drop forgings. So it is a important thing to determine the position of parting line. The choice of parting line will directly affect waste material, machining allowance. Designer should indicate the position of parting line in the forging drawing clearly. It is better that the parting line lies in one plane perpendicular to the axis of the die motion. It can be located such that one die half will be completely flat, and the line will surround the largest projected area of the piece. The angle of the surface at the parting line from the primary parting plane should not exceed 75°, in general, the shallower the angles,the better it will be. It is crucial for designer to select the parting line such that no undercuts are in either die impression, since the forging must be ejected out of the die after it is made. The parting line location can be changed to control the grain direction given the above recommendations are fulfilled.


The forging must be designed such that it will be adequate to remove the forging from the dies, we call this draft. Generally, all forged surfaces which are parallel to the die motion will be tapered. This taper is helpful for metals flow into deeper die cavities, so that we could take full advantages of materials and ontain good inside properties. We specify the draft using the angle with respect to the die-motion axis. It is conventional to specify a standard draft angle for all affected surfaces on a drop forging. Also, it is used to calling for matching draft on both die halves to make surfaces of unequal depth meet at the parting line. Low-draft and no-draft forging can be produced in aluminum and brass. This is done in cases when reduction or elimination of draft yields significant benefits. Normally, the drafe angle of closed die drop forging is around 5°。

Machining allowance

Machining allowance is refer to the tolerance gaps beween forging blanks and finished parts as it is impossibe to forge to final size tolerance and have to meet by machining. Machining allowance should allow for the worst-case buildup of draft and for all tolerances. Extra metal should be provided to at the critical machined surfaces away from the grain-flow pattern that in the flash region close to the parting line. In most cases, machine allowance should be left at 0.06 inch for each machine surface.

Wall thickness

For the limits of drop forging process, it could not forge parts in all wall thickness. In general, designer should determine maximum wall thickness according to manufacturing capabilities. And maximum wall thickness is about 10 inch. And 0.4 inch should be considered as the minimum wall thickness. It is not available to forged thin parts, which can be stamped.


Traditionally, the surface of drop forgings will be better than investment casting parts. Typical surface roughness of drop forging components should be at Ra6.3. For better surface rougness, it could be reached by machining.

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