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2 Stamping
Stamping is a kind of plastic forming process in which a part is produced by means of the plastic forming of the material under the action of a die．Stamping is usually carried out under cold state, so it is also called cold stamping. Heat stamping is used only when the blank thickness is greater than 8-100mm. The blank material for stamping is usually in the form sheet or strip, and therefore it is also called sheet metal forming. Some non-metal sheets (such as plywood, mica sheet, asbestos, leather) can also be formed by stamping.
Stamping is widely used in various metalworking industry, and it plays a crucial role in the industries for manufacturing automobiles, instruments, military parts and household electrical appliances, etc.
The process，equipment and die are the three foundational problems that needed to be studied in stamping.The characteristics of the sheet metal forming are as follows:
(1) High material utilization.
(2) Capacity to produce thin-walled parts of complex shape.
(3) Good interchangeability of stamping parts precision in shape and dimension.
(4) Parts with lightweight，high strength and fine rigidity can be obtained.
(5) High productivity, easy to operate and to realize mechanization and automatization.
The manufacture of the stamping die is costly, and therefore it only fits to mass production. For the manufacture of products in small batch and rich variety, the simple stamping die and the new equipment such as a stamping machining center, are usually adopted to meet he market demands.
The materials for sheet metal stamping include mild steel, copper, aluminum, magnesium alloy and high-plasticity alloy steel, etc.
Stamping equipment includes plate shear and punching press. The former shears plate into strips with a definite width, which would be pressed later. The later can be used both in shearing and forming.
There are various processes of stamping forming with different working patterns and names, but these processes are similar to each other in plastic deformation．There are following conspicuous characteristics in stamping：
(1) The force per unit area perpendicular to the blank surface is not large but is enough to cause the material plastic deformation. It is much less than the inner stresses on the plate plane directions．In most cases stamping forming can be treated approximately as that of the plane stress state to simplify vastly the theoretical deformation mechanics analysis and the calculation of the process parameters.
(2) Due to the small relative thickness，the anti-instability capability of the blank is weak under compressive stress．As a result，the stamping process is difficult to proceed successfully without using the anti-instability device (such as blank holder)．Therefore the variety of the stamping processes dominated by tensile stress are more than those dominated by compressive stress．
(3) During stamping forming，the inner stress of the blank is equal to or sometimes less than the yield stress of the material．In this point，the stamping is different from the bulk forming. During stamping forming，the influence of the hydrostatic pressure of the stress state in the deformation zone to the forming limit and the deformation resistance is not so important as to the bulk forming．In some circumstances，such influence may be neglected．Even in the case when this influence should be considered，the treating method is also different from that of bulk forming.
(4) In stamping forming，the restrain action of the die to the blank is not severe as in the case of the bulk forming(such as die forging)．In bulk forming, the constraint forming is proceeded by the die with exactly the same shape of the part．Whereas in stamping，in most cases，the blank has a certain degree of freedom, only one surface of the blank contacts with the die．In some extra cases, such as the forming of the suspended region of sphere or cone，and curling at the end of tube, neither sides of the blank on the deforming zone contact with the die. The deformation in these regions are caused and controlled the die applying an external force to its adjacent area.