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)Part 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 the 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 plan 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 the point, the stamping is different from the bulk forming. During stamping forming, the influence of the hydro-static 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 he same shape of the part. whereas in stamping, in most case, the blank has a certain degree of freedom, only one of the suspended 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 region is caused and controlled the die applying an external force to its adjacent area.

Due to the characteristics of stamping deformation and mechanics mentioned above, the stamping technique is different from the bulk metal forming:
(1) The importance of the strength and rigidity of the die in stamping forming is less than that in bulk forming because the blank can be formed without applying large pressure unit area on its surface. Instead, the techniques of the simple die and the pneumatic and hydraulic forming are developed.
(2)Due to the plane stress or simple strain in comparison with bulk forming, more research on deformation or force and power parameters has been done, stamping forming can be performed by more reasonable scientific methods. Based on the real time measurement and analysis on the sheet metal properties and stamping parameters, by means of computer and some modem testing apparatus research on the intellectualized control of stamping process is also in proceeding.
(3)It is shown that there is a close relationship between stamping forming and raw material. The research on the properties of the stamping forming, that is, forming ability and shape stability, has become a key point in stamping technology. The research on the properties of the sheet metal stamping not only meets the need of the stamping technology development, but also enhance the manufacturing technique of iron and steel industry, and provides a reliable foundation for increasing sheet metal quality.