# Railways NTPC (Technical Ability) Metal Forming, Casting and Cutting Metal Forming

Metal Forming

Category : Railways

Metal Forming

• Metal forming is a general term for a large group that includes a wide variety of manufacturing processes. Metal forming processes are characteristic in that the metal being processed is plastically deformed to shape it into a desired geometry.
• In order to plastically deform a metal, a force must be applied that will exceed the yield strength of the material. When low amounts of stress are applied to a metal it will change its geometry slightly, in correspondence to the force that is exerted. Basically it will compress, stretch, and/or bend a small amount.
• The magnitude of the amount will be directly proportional to the*force applied. Also the material will return to its original geometry once the force is released. Think of stretching a rubber band, then releasing it, and having it go back to its original shape. This is called elastic deformation.
• Once the stress on a metal increases past a certain point, it no longer deforms elastically, but starts to undergo plastic deformation. In plastic deformation, the geometric change in the material is no longer directly proportional to stress and geometric changes remain After the stress is released; meaning that the material does not recover its shape.
• The actual level of stress applied to a metal where elastic deformation turns to plastic deformation is called the proportional limit, and is often difficult to determine exactly. The .002 offset convention is usually used to determine the yield point, which is taken for practical purposes as the stress level where plastic deformation, (yielding), begins to occur
• Forming, or metal forming, is the metalworking process of fashioning metal parts and objects through mechanical deformation; the work-piece is reshaped without adding or removing material, and its mass remains unchanged.
• Forming operates on the materials science principle of plastic deformation, where the physical shape of a material is permanently deformed.
• Metal forming tends to have more uniform characteristics across its sub-processes than its contemporary processes, cutting and joining.
• On the industrial scale, forming is characterized by:

$-$Very high required loads and stresses, between 50 and $2500\,\text{N/m}{{\text{m}}^{\text{2}}}$ (7-360 ksi)

$-$Large, heavy, and expensive machinery in order to accommodate such high stresses and loads

$-$Production runs with many parts, to maximize the economy of production and compensate for the expense of the machine tools

• Forming processes tend to be typified by differences effective stresses. These categories and descriptions are highly simplified, since the stresses operating at a local level in any given process are very complex and may involve many varieties of stresses operating simultaneously, or it may involve stresses which change over the course of the operation.
• Compressive forming involves those processes where the primary means of plastic deformation is uni-or multiaxial compressive loading.

$-$Rolling, where the material is passed through a pair of rollers

$-$Extrusion, where the material is pushed through an orifice

$-$Die forming, where the material is stamped by a press around or onto a die

$-$Forging, where the material is shaped by localized compressive forces

• Tensile forming involves those processes where the primary means of plastic deformation is uni-or multiaxial tensile stress.

$-$Stretching, where a tensile load is applied along the longitudinal axis of the work piece

$-$Expanding, where the circumference of a hollow body is increased by tangential loading

$-$Recessing, where depressions and holes are formed through tensile loading

• Combined tensile and compressive forming
• This category of forming processes involves those operations where the primary means of plastic deformation involves both tensile stresses and compressive loads.

$-$Pulling through a die

$-$Deep drawing

$-$Spinning

$-$Flange forming

$-$Upset bulging

This category of forming processes involves those operations where the primary means of plastic deformation is a bending load.

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##### Notes - Metal Forming

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