While it is true that almost any shape not involving back-draft can be forged, the wise engineer will attempt to create forging designs that excel in simplicity – as simplicity of design is synonomous with plastic moulding production engineering.
The life of forging dies is governed by the complexity of the part being forged, and as both die-steel and die-makers are at a premium it behooves the engineer to use forgings only where necessary, and then design irreplaceable forgings for maxi- mum manufacturing economy.
Simplicity, as applied to forging design does not mean a forging of simple con- figuration, but rather one that will be simple to forge. Forging simplicity is obtained by eliminating sharp corners, small fillets, highly irregular sections and other forging evils that contribute to die breakage and increased forging time.
Small weight sacrifices are sometimes necessary to obtain forging simplicity, for absolute minimum corner radii, draft angles, web depths and rib thickness are obtainable only at the expense of complicated lengthy forging operations and shortened die-life.
Forged members will support higher unit loads than metal shapes produced by other methods, owing to their close, uniform grain structure. The repeated pounding and/or extreme pressure required to produce a forging insures a closely compacted grain structure, free from the “sponginess” some- times found in castings; while the fact that the forging is formed from a heated metal bar or “billet” insures a well-defined, continuous grain.
The forging process involves the shaping of heated metal to the desired form in a forging hammer, which essentially comprises a power-driven reciprocating ram in opposition to an anvil, with the actual forging being formed by cavities machined into metal dies attached to ram and anvil. The forging is made from a metal bar or “billet” having a volume sufficient to make the required part, and heated to the plastic condition.
This heated billet is placed in the cavity of the lower die, and the upper die-half driven against the bar by the force of a mechanical action or power cylinder augmented by the weight of the descending ram. The force of the impact causes the bar to “flow” into the shape of the die cavities, and the blows of the ram are continued until the metal is forged into the proper shape to completely fill the die impressions.
The completed forging is then removed, another heated bar placed in the lower die, and the shaping of another part begun. Before beginning the design of a new forging, it is advisable to investigate existing company forgings to ascertain if it will be possible to use an existing rough-forging by a slight amount of additional machining. This is frequently the case, and may result in considerable savings in die cost and delivery time.
Further, when a number of similar forgings are designed, it may be practicable to combine two or more within the envelope of one rough forging by providing additional stock for surfaces required on only one of the forgings. In many cases, the slight in- crease in machining cost will be justified by the savings in die expense and forge shop time.
Additional die and forging costs may often be saved by designing a single rough- forging for both “hands” of a part that must be made in both left and right-hand forms. In such cases the right-hand is an exact mirror image of the left-hand form, and one rough forging can often serve for both by slight additional machining, removal of one of a pair of lugs or bosses from each “hand”, or the like. An arrangement frequently used with small forgings is to design the rough- forging to form both “hands” of the part by sawing into halves. This may not appreciably reduce die-cost, but certainly reduces forging time.