Stamping Service

Stamping and Sheet Metal Forming Service

Key words: Sheet metal stamping 

1.The article overview  Stamping is a kind of plastic forming process in which a part is  produced by means of the plastic forming the material under the action  of a die. Stamping is usually carried out under cold state, so it is also  called 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 of 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 fields of the 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 between stamping parts due to  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 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 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. 

2.Characteristics of stamping 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 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  varieties of the stamping processes dominated by tensile stress are more  than 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 severs 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  blank on the deforming zone contact with the die. The deformation in these  regions are caused and controlled by 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 form the bulk metal  forming: （1）．The importance or 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 per 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 state 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 modern 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 development, but also enhances the manufacturing technique of iron and steel industry, and provides a  reliable foundation for increasing sheet metal quality. 

3.Categories of stamping forming  Many deformation processes can be done by stamping, the basic  processes of the stamping can be divided into two kinds: cutting and  forming. Cutting is a shearing process that one part of the blank is cut from  the other. It mainly includes blanking, punching, trimming, parting and  shaving, where punching and blanking are the most widely used. Forming  is a process that one part of the blank has some displacement from the  other. It mainly includes deep drawing, bending, local forming, bulging,  flanging, necking, sizing and spinning. In substance, stamping forming is such that the plastic deformation  occurs in the deformation zone of the stamping blank caused by the external  force. The stress state and deformation characteristic of the deformation  zone are the basic factors to decide the properties of the stamping forming.  Based on the stress state and deformation characteristics of the  deformation zone, the forming methods can be divided into several  categories with the same forming properties and be studied  systematically. The deformation zone in almost all types of stamping forming is in  the plane stress state. Usually there is no force or only small force  applied on the blank surface. When is assumed that the stress  perpendicular to the blank surface equals to zero, two principal stresses  perpendicular to each other and act on the blank surface produce the  plastic deformation of the material. Due to the small thickness of the  blank, it is assumed approximately the two principal stresses distribute  uniformly along the thickness direction. Based on this analysis, the  stress state and the deformation characteristics of the deformation zone  in all kinds of stamping forming can be denoted by the points in the  coordinates of the plane principal stresses and the coordinates of the  corresponding plane principal strains.

4.Raw materials for stamping forming  There are a lot of raw materials used in stamping forming, and the  properties of these materials may have large difference. The stamping  forming can be succeeded only by determining the stamping method, the  forming parameters and the die structures according to the properties and  characteristics of the raw materials. The deformation of the blank during  stamping forming has been investigated quite thoroughly. The  relationships between the material properties decided by the chemistry  component and structure of the material and the stamping forming has been  established clearly. Not only the proper material can be selected based  on the working condition and usage demand, but also the new material can  be developed according to the demands of the blank properties during  processing the stamping part. This is an important domain in stamping  forming research. The research on the material properties for stamping  forming is as follows: （1）．Definition of the stamping property of the material. （2）．Method to judge the stamping property of the material, find  parameters to express the definitely material property of the stamping  forming, establish the relationship between the property parameters and  the practical stamping forming, and investigate the testing methods of  the property parameters. （ 3 ）． Establish the relationship among the chemical component,  structure, manufacturing process and stamping property. The raw materials for stamping forming mainly include various metals  and nonmetal plate. Sheet metal includes both ferrous and nonferrous  metals. Although a lot of sheet metals are used in stamping forming, the  most widely used materials are steel, stainless steel, aluminum alloy and  various composite metal plates. 

5.Stamping forming property of sheet metal and its assessing method  The stamping forming property of the sheet metal is the adaptation  capability of the sheet metal to stamping forming. It has crucial meaning  to the investigation of the stamping forming property of the sheet metal.  In order to produce stamping forming parts with most scientific, economic and rational stamping forming process and forming parameters, it is  necessary to understand clearly the properties of the sheet metal, so as  to utilize the potential of the sheet metal fully in the production. On  the other hand, to select plate material accurately and rationally in  accordance with the characteristics of the shape and dimension of the  stamping forming part and its forming technique is also necessary so that  a scientific understanding and accurate judgment to the stamping forming  properties of the sheet metal may be achieved. There are direct and indirect testing methods to assess the stamping property of the sheet metal.  Practicality stamping test is the most direct method to assess  stamping forming property of the sheet metal. This test is done exactly  in the same condition as actual production by using the practical  equipment and dies. Surely, this test result is most reliable. But this  kind of assessing method is not comprehensively applicable, and cannot  be shared as a commonly used standard between factories. The simulation test is a kind of assessing method that after  simplifying and summing up actual stamping forming methods, as well as  eliminating many trivial factors, the stamping properties of the sheet  metal are assessed, based on simplified axial-symmetric forming method  under the same deformation and stress states between the testing plate  and the actual forming states. In order to guarantee the reliability and  generality of simulation results, a lot of factors are regulated in detail,  such as the shape and dimension of tools for test, blank dimension and  testing conditions(stamping velocity, lubrication method and blank  holding force, etc).  Indirect testing method is also called basic testing method its  characteristic is to connect analysis and research on fundamental  property and principle of the sheet metal during plastic deformation, and  with the plastic deformation parameters of the sheet metal in actual  stamping forming, and then to establish the relationship between the  indirect testing results(indirect testing value) and the actual stamping  forming property (forming parameters). Because the shape and dimension  of the specimen and the loading pattern of the indirect testing are different from the actual stamping forming, the deformation  characteristics and stress states of the indirect test are different from  those of the actual one. So, the results obtained form the indirect test  are not the stamping forming parameters, but are the fundamental  parameters that can be used to represent the stamping forming property  of the sheet metal.