Forging, one of the oldest know metalworking processes, is the art of shaping metal by using localized compressive forces. The different types of forging include: hot, cold, press, upset, automatic, roll, net-shape forging, and induction forging. Forged parts can range in weight from less than a kilogram to 170 metric tons. Forged parts usually require further processing to achieve a finished part.
Pros and Cons
As an advantage forging can offer the designer several basic performance advantages such as directional strength forging, which refines the grain structure and develops the optimum grain flow, which imparts desirable directional properties such as tensile strength, ductility, impact toughness, fracture toughness and fatigue strength. Structural integrity forgings are free from internal voids and porosity. The process achieves consistent material uniformity, which results in uniform mechanical properties and a uniform, predictable response to heat treatment. The forging process maximizes impact toughness, fracture toughness and fatigue strength, through proper deformation and grain flow, combined with high material uniformity. These properties are particularly advantageous in safety related applications, such as aerospace structural components and automotive components. The features of a forging can be made with varying cross sections and thicknesses to provide the optimum amount of material for the anticipated load. This capability, plus the high mechanical properties of forgings, often allows designers to minimize component part weight, especially when compared with castings and assemblies of sheet metal stampings. Forging eliminates internal voids and gas pockets that can weaken metal parts. By dispersing segregation of alloys or nonmetallics, forging provides superior chemical uniformity. Predictable structural integrity reduces part inspection requirements, simplifies heat-treating and machining, and ensures optimum part performance under field-load conditions.
The disadvantages of forging include the fact that the required temperature can easily cause the iron to oxidise; the presence of oxide of iron offers great resistance to the welding and renders difficulty for the metals to join with one another; during the operation of the welding, which ought to be done in the open air, the oxidation cannot be prevented. The welder, in order to minimise the oxidation, employs some sand or borax, but in both cases a silicate is formed, which is very fusible and must be removed by hammering. The inconvenience of the oxidation makes the forging unsuitable for articles of small and thin dimensions, such as tools, wires, etc, because the oxidation being too rapid, the metal burns but does not weld. The necessity of hammering makes it also difficult to apply forging to various objects by reason of their form or the difficulty of their removal; for instance, tubes, cisterns, or objects of a voluminous form. It is in such cases, where the forge is insufficient, or the application difficult, that welding by fusion is resorted to. This means that secondary machining will most likely be needed to obtain a finished part.