What is Metal Forming?
Metal forming refers to the plastic deformation of a metal to end up with a useful geometry. The change in geometry is achieved by using force that exceeds the metal’s yield strength. Metal forming can also be referred to the bending, stretching and/or compression of a metal by force, to achieve the desired geometry. The more the force applied, the more the magnitude of bending, although these two are not directly proportional. Metal forming differs with elastic deformation in that, in elastic deformation, a substance will return back to its original geometry once the force is released while it will not resume its original geometry in metal forming. The latter happens because the deformation passes a certain point called its yield strength. In deed, plastic deformation is itself referred to as yielding.
Metal Forming at Different Temperatures
Although it is mentioned that an important factor in metal forming is force applied, it is important to understand that metals react differently to processes under different temperatures. Indeed, the same metal may have different properties under different temperatures as it is worked upon. Theory defines three temperature ranges at which one can form metals. These three include cold, warm and hot working.
- Cold working: in this case, metal forming occurs at room temperature or just above the room temperature. In this case, forming a given metal requires use of greater force in colder temperatures because the yield point is higher at lower temperature range. Care must be taken to avoid fracture during cold metal forming, because metals have limited ductility at cold working temperatures. They can only be deformed to a certain limited amount. Surface preparation is necessary to avoid fractures.
- Warm working: in this case, the temperature range is above that of cold working but below the metal’s recrystallization temperature. The force required to deform the metal will also be smaller as compared to the force used in cold working.
- Hot working: metal forming takes place at a temperature above the metal’s recrystallization temperature. In this case, much lesser force and power is required to form the metal compared to force and power required in other working processes above.
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