Precision metal stamping is one of the most widely used manufacturing processes in various industrial applications with high production efficiency, low material consumption, because it is fast, precise, repeatable, and a multi-purpose, low-cost metal forming process, which is suitable for the production of large quantities of parts and products, and is convenient for mechanization and automation.
Correct selection of metal stamping materials
Stamping material is an important factor affecting part quality and die life. When complex parts are manufactured by metal stamping, the best raw materials must be selected for your application. Especially in the early stage of product design and development, the materials must be fully evaluated to ensure that the materials have the performance suitable for the product requirements.
How to choose the right metal stamping materials?
The selection of stamping materials shall consider the use requirements, stamping process requirements and economy of stamping parts.
According to the use requirements of stamping parts
The selected materials shall enable the stamping parts to work normally in the use of the equipment and ensure the service life. Therefore, the selected materials shall meet the corresponding performance requirements according to the service conditions of the stamping parts:
- Tensile Strength
- thermal conductivity
- corrosion resistance
According to stamping process requirements
For any kind of stamping structural parts, the selected materials shall be able to stably form qualified products without cracking or wrinkling according to the requirements of their stamping process, especially deep drawing parts, bending parts, or other complex and high precision stamping structural parts. This is the most basic and important material selection requirements.
According to economic requirements
The selected materials shall meet the requirements of service performance and stamping process, with low price, convenient source and good economy, so as to reduce the cost of stamping parts.
Characteristics of stamping materials and stamping formability
Yield strength, tensile strength and yield ratio
The tensile strength is the basic element for calculating the punching force. When the yield strength and tensile strength are high, the stamping forming force is large, the forming difficulty is increased, and the life of the die will be reduced. If the yield strength is high, the deformation of elastic recovery is also large when the stamping part is separated from the die and unloaded after the stamping forming, which affects the dimensional accuracy of the stamping part.
If the elongation of sheet metal is large, it is beneficial to all elongation stamping. When the elongation is large, the forming limit of bulging and flanging is also large. Therefore, most high-quality stamping steels have high uniform elongation.
Work hardening value (n)
The drawing forming of stainless steel plate can reach the product shape only after several times of processing. During the drawing process, the material will be hardened, which is generally called work hardening. The reason for the formation of work hardening is that after the material is subjected to a plastic deformation, the load force applied in the same direction will make its yield point rise, thus increasing the necessary deformation resistance to resist the re generation of plastic deformation. The falling point is the initial point of permanent deformation caused by exceeding the elastic deformation area. As known from the tensile test, it is the point where the stretching behavior is still going on without increasing the load.
What does the work hardening coefficient mean?
Materials with high （n） values have the following behaviors:
(1) Continuous processing will cause hardening of materials and reduction of elongation, making processing difficult.
(2) Continuing machining will restrain local deformation and obtain consistent deformation.
Materials with low （n） values have the following behaviors:
Continued processing will cause local deformation, weak parts and even breakage.
Therefore, the elongation type forming requires the sheet metal to have a large n value.
Generally speaking, the lower the hardness, the better the plasticity. However, the hardness of the material is on the high side. If the carbide spheroidization rate is above 90%, a good blanking surface can also be obtained. On the contrary, if the hardness of the material is low but the spheroidization is not sufficient, the blanking surface will be torn. Therefore, hardness is a macro indicator to judge whether it is suitable for shearing, while metal structure (uniformity and spheroidization degree of carbide) is a micro indicator to judge whether it is suitable for blanking.
Plastic strain ratio (r)
It is a parameter representing the anisotropic properties of the sheet. As the plate has to go through rolling and annealing processes in the manufacturing process, the result is that the plate forms a texture structure with the crystal orientation tending to be consistent, which is anisotropic in the macro view. The r value mainly affects the drawing performance. The plate has a large r value, and its drawing performance is also good.
The microstructure of low carbon steel is composed of soft ferrite as the matrix and a small amount of pearlite. Pearlite is a fine mixture of ferrite and cementite, in which cementite accounts for 12%. Ferrite has good plasticity, while cementite is hard and brittle. From the point of view of materials with the same carbon content, the plasticity can be improved and the quality of blanking surface can be improved with the spheroidization of carbide.
When some plates (such as stainless steel plate and brass plate) are deep drawn, due to the effect of residual stress formed during deep drawing, longitudinal cracking will occur on the side wall of cylindrical parts after deep drawing. This cracking phenomenon may occur immediately after demoulding, or after a period of time, or during the use of stamping parts, so it is called age splitting.
Cylinder deep extension test (LDR value)
The cylinder deep drawing test is one of the most basic methods to evaluate the deep drawing property of sheet metal. The purpose of this test is to obtain the limit drawing ratio (LDR) of metal materials. The larger the LDR value is, the better the elongation of the material is.
Common materials for stamping
The most commonly used metal materials in stamping production (including ferrous metals and non-ferrous metals), among which ferrous metals mainly include ordinary carbon structural steel, high-quality carbon structural steel, alloy structural steel, carbon tool steel, stainless steel, electrical silicon steel, etc; Nonferrous metals mainly include pure copper, brass, bronze, aluminum, etc;
The supply status of metal materials for stamping is generally sheet and strip of various specifications. The sheet can be used for the production of engineering dies, and the strip (coil) can be used for the mass automatic feeding production of continuous dies, as well as the production of engineering dies.
For the grades, specifications, properties and stamping applications of various materials, refer to the following links:
Relevant manuals and standards can also be consulted.