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07/09/2007 - Forging

The term forgino indicate the fabrication process in which the piece is obtained by means of the action of compression forces applied by various kind of tools and dies. It’s one of the oldest method the man knows, dating back to 4000 B.C. and initially used for the production of coins and jewels.
The simplest forging is that made by the blacksmith with hammer and anvil, but the majority of industrial processes needs dies and special equipments like hammers and presses (Figure 1). In forging, the metal flux and its structure can be controlled, in this way parts with good mechanical properties can be obtained and then used for high stress application like crankshafts, connecting rods (Figure 2), landing gears and turbine shafts.
Forging can be conducted both at high and low temperatures. In the first case, pieces with good dimensional tolerances and surface finishing can be obtained, but higher forging forces are needed. In the second case the magnitude of the forces is lower, but the surface finishing and the tolerances are no good as in hot forging.
Forging can be made in open dies (by means of hammering and rotation) or in closed dies. In this case the piece assume the shape of the die cavity, that is shaped to reproduce the external shape of the component (Figure 3).
The thin quantity of metal that come out of the die plays a very important role, cooling down very quickly and the subjecting the internal material to high pressures that make die filling easy.
Typically forging needs the following passages. The raw piece is cut from a bar and the inserted in the lower die. Then a series of forgings brings the piece to its final configuration (Figure 4). The final operation it’s the elimination of the residuals from the finished piece.

Figure 2: Connecting rods obtained by forging.

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