Flashless (Enclosed Impression Die) Forging

Flashless Forging

Impression die forging is sometimes performed in totally enclosed impressions. The process is used to produce a near-net or net shape forging. The dies make no provision for flash because the process does not depend on the formation of flash to achieve complete filling. Actually, a thin fin or ring of flash may form in the clearance between the upper punch and die, but it is easily removed by blasting or tumbling operations, and does not require a trim die. The process is therefore called "flashless forging", and is sometimes called "enclosed die forging".

Enclosed dies are illustrated in Figure 5-14. In some cases the lower die may be split, allowing as-forged undercuts. Split die arrangements are illustrated in Figure 5-15.

The absence of flash is an obvious advantage for flashless forging over the conventional impression die process, but the process imposes additional requirements. For example, flashless forging is usually accomplished in one operation, and does not allow for progressive development of difficult-to-forge features through several stages of metal flow. In addition, the volume of metal in the workpiece must be controlled within very narrow limits to achieve complete filling of the cavity without developing extreme pressures. It takes some very well controlled preforming steps to accomplish this precise weight control in the final die.

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Precision Forgings vs. Conventional Forgings?

Precision Forgings differ from Conventional Forgings in many ways.  While Conventional forgings are typically machined on all surfaces, a Precision Forging is often characterized by very slight draft angles (0 to 1 degree), thin cross-sections, close tolerances, small radii, and excellent surface finishes.
While the tooling for a precision forging is typically more costly to produce and maintain, the advantages of precision forgings over conventional forgings pay multiple dividends.  The net or near-net shape of the precision forging can greatly reduce machining times and produce a part that is nearly ready to put right into service.  Additionally, the optimal grain structure of a precision forging increases fatigue life, and produces superior stress and inter-granular corrosion resistance.