Metals are converted into various usable products of desired shape and size using different manufacturing processes such as casting, machining, welding or metal forming (rolling, forging. extruding, etc). Metal forming of metals involves deforming a metal plastically into various. desired shapes and sizes under the effect of externally applied forces. The stresses induced during the deformation process are greater than the yield strength, but less than the fracture strength of the metal. The type of loading may be tensile, compressive, bending or shearing or a combination of these. Also, the operation of deforming the metal may be carried out either in cold state or in hot state of the metal using mechanical means such as press, die and rolls. The process of metal forming is also called mechanical working of metals. The formability of a metal indicates the response and suitability of the metal for plastic deformation processes. Metals behave differently at different temperatures and also respond differently to i different deforming processes. Hence, all such factors should be considered in deciding the overall formability of a metal.
Metal forming operations, such as rolling, forging, drawing, extruding , have come up as high productivity processes as compared to other metal working processes like casting, welding or machining and they also generally ensure high dimensional accuracy. good surface finish with no waste of material in the form of chips, etc. and are, therefore. economical also. These processes are capable of producing items with specified physical and metallurgical properties. A large variety of metal forming processes have been developed for various specific applications, but in view of the applied forces on the job during working, these processes can be broadly categorized as follows.
(a) Direct-compression type processessuch as forging and rolling, wherein the force. is applied to the surface of the job and the metal flows at right angles to the direction of compression
(b) Indirect-compression processessuch as wife drawing, tube drawing, extrusion and deep drawing wherein primary applied forces are generally tensile but the indirect compressive forces developed by the reaction of the job with die reach high alues. and the metal flows under the action of a combined stress state which includes very high compressive forces in at least one of the principal directions
(c) Tension type processessuch as stretch forming of sheet metal under the application of tensile forces when the sheet metal is wrapped to the contour of a die
(d) Beading processesinvolve the application of bending moments to the sheet metal or other metal structurals such as rod, wire or angle
(e) Shearing processesinvolve the application of shearing forces of adequate magnitude to rupture the metal in the plane of shear
The process of forming a metal may take place any time it is subjected to loads (or stresses) that are greater than its yield point’, or in other words, when the deformation stress moves from the elastic range to the plastic range Metal forming may be ‘cold’ or ‘hot’; cold forming or cold-working is carried out at room temperature or below the recrystallization temperature of the metal and the hot forming or hot-working is done above the recrystallization temperature but below the melting point of the metal. The hot working is preferred for primary solid-state shaping processes such as forging, rolling, extruding, etc. because the power (or forces) required in shaping the hot metals is lower and larger reductions in the size of the metal are easily and economically possible without its cracking. Hot-working gives high production rate of products of various sizes and shapes from the original ingot received from steel plants. It also generally does not bring noticeable changes in the properties of metal (i.e. hardness and ductility, etc.). The cold-working, however, causes more noticeable changes in the mechanical properties by increasing the tensile strength and yield strength of cold worked metal with a corresponding loss in the ductility of metal.
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