Drop Forging - Closed die (Impression die)

Closed die drop forging sometimes referred to as impression die forging comprises of a die on the anvil which resembles a mould, the ram which falls and strikes the top of the work piece can also be equipped with a die. The metal work piece is heated and placed on the lower die while the ram falls down forcing the metal to fill the contours of the die blocks. The ram may impact the work several times to ensure all of the contours are filled, with all the pressure put on the work piece its common place to get metal flow between the dies called flash, however the flash due to its decreased size cools relatively quickly and therefore helps block or reduce further flow between the dies. This flash will have to be trimmed off once forging is complete.

Advantages

• Hot forging prevents work hardening associated with cold forming


• Parts of sizes up to 25 tons can be produced with closed die forging


• Closed die forging can produce near net shapes that will require only a small amount of finishing


• Economic for large runs of product


• Forging provides superior mechanical properties over castings due to the internal grain structure formation in forged parts

Disadvantages

• Not very economical for short runs due to the high cost of die production


• The business set up cost of drop forging is very high, not only are the machines and furnaces costly but special building provisions must be in place to cope with the powerful vibrations caused by drop forging. A special foundation must be laid to deal with this environment


• Drop forging presents a dangerous working environment