Process performance of precision stamping materials
Stamping material is suitable for stamping and forming, which involves material properties such as hardness, tensile strength and shear strength. The good stamping performance of a material means that it is easy to be processed by stamping, the degree of ultimate deformation in one stamping process and the total degree of ultimate deformation is high, the productivity is high, the high-quality stamping parts are easily obtained, and the die life is long, etc.
Performance requirements of precision stamping materials
The stamping material is an important factor affecting the quality of the parts and the life of the die. Currently, the materials available for stamping are not only low carbon steel but also stainless steel, aluminium and aluminium alloy, and copper and copper alloy. Generally, the materials with carbon content <0.25% and tensile strength less than 650N/mm² are the main ones. For example, cold rolled steel SPCC (JIS) or 1010 (SAE).
Stamping performance requirements for metal materials.
1、Have good mechanical properties and large deformation capacity.
The mechanical properties of metal materials are tensile strength, yield strength, elongation, hardness, and plastic strain ratio.
2、With the ideal metallographic structure
The metallographic organization is the microscopic quality characteristics of the material. Its main symbol is carburized body or carbide spheroidization degree
Introduction of common precision stamping materials
Hot-rolled steel is a kind of high-quality carbon structural steel with a carbon content of about 0.10%~0.15%, low carbon steel.
Hot-rolled steel for stamping has the following three types.
(1) SPHC – is the representative steel grade of hot-rolled steel.
(2) SPHD – which has better tensile properties compared to SPHC.
Advantages of hot-rolling
It can destroy the ingot’s casting organization, refine the steel’s grain, and eliminate the defects of the microstructure, thus making the steel dense and improving its mechanical properties. This improvement is mainly reflected along the rolling direction so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded together under high temperature and pressure.
One is that after hot rolling, the non-metallic inclusions inside the steel (mainly sulfides and oxides, and silicates) are pressed into thin sheets, and delamination (interlayer) occurs. Delamination greatly deteriorates the performance of the steel in tension along the thickness direction, and there is a risk of interlayer tearing during weld shrinkage. The local strain induced by weld shrinkage often reaches several times the yield point strain, much larger than the load-induced strain.
The second is the residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress in the absence of external forces; a variety of cross-sectional hot-rolled steel sections have such residual stresses; generally, the larger the section size of the steel, the greater the residual stress. Although the residual stress is self-balancing, the performance of steel members under the action of external forces still has a certain impact. Such as deformation, stability, fatigue resistance, and other aspects may have a negative effect.
Cold-rolled steel is also a high-quality carbon structural steel, with a carbon content of about 0.08% to 0.12%, and is low-carbon steel.
Cold-rolled steel for stamping has the following three types.
(1) SPCC – is the representative steel grade of cold-rolled steel.
(2) SPCD – has better tensile properties compared to SPCC.
(3) SPCE – has better tensile properties compared to SPCC.
-Compared with SPHC, its tensile properties are better.
Advantages of cold-rolled: 1. Cold-rolled products are accurate in size and uniform in thickness, and the thickness difference between the sheets and coils is generally no more than 0.01-0.03mm or less, which can fully meet the requirements of high-precision tolerances; 2. Very thin strips (up to 0.001mm or less) that cannot be produced by hot-rolling.
Disadvantages of cold-rolling.
1, the forming process does not undergo thermal plastic compression. However, there are still residual stresses in the cross-section, which must impact the steel’s overall and local flexural properties.
2, cold-rolled section style is generally an open section, making the free torsional stiffness of the section low. Easily twisted in bending, bending and torsional buckling when compressed, with poor torsional resistance.
The main differences between hot-rolled and cold-rolled are
1, cold-rolled forming steel allows local buckling of the cross-section to make full use of the bearing capacity of the bar after buckling, while hot-rolled sections do not allow local buckling of the cross-section. 2, hot-rolled and cold-rolled sections of residual stress are generated for different reasons, so the distribution on the cross-section is also very different. Cold-formed thin-walled sections of residual stress distribution on the cross-section are bending type, while hot-rolled sections or welded sections of residual stress distribution are film type.
Stainless steel is the chromium content of 11% or more high-alloy steel; its main characteristics are corrosion resistance and heat resistance, stainless and surface brilliance. The stainless steel used in stamping and forming is ferritic, austenitic, and martensitic stainless steel.
The stamping performance of ferritic stainless steel is close to that of cold-rolled steel sheets, and the production process of this stainless steel sheet can also use hot rolling, cold rolling and annealing methods to obtain the weave structure so that the r value reaches about 1.2 to 1.8, and therefore has good deep-drawing properties. But its hardening index is about 0.2 or so; elongation is about 0.25 to 0.3 or so, less than austenitic stainless steel, so its elongation class stamping and forming performance is poor.
Advantages of stainless steel
Stainless steel offers many advantages for users of architectural/decorative metals. Major advantages include its high corrosion resistance, which allows it to be used in harsh environments. It is fire-resistant, resisting scaling and maintaining strength at high temperatures.
Copper and Copper Alloys
Copper and copper alloys can be classified into two categories according to their manufacturing methods: drawn copper (spreading copper) and cast copper; the representative characteristics of copper and copper alloys are as follows:
(1) good thermal conductivity and electrical conductivity;
(2) good machinability in cutting;
(3) non-magnetic function
(4) No embrittlement at low temperatures;
(5) Corrosion resistance;
(6) Good flexibility
(7) beautiful colour tone, easy to tinning.
Aluminum and aluminium alloy
Aluminium and aluminium alloy materials can be divided into two categories according to their manufacturing and forming processes: extension and casting. The difference between heat-treated and non-heat-treated alloys lies in the different methods of controlling the strength of the material. Non-heat treated alloys control the strength of the material by adjusting the degree of cold working, generally speaking, the higher the degree of cold working, the higher the strength of the material. Heat-treated alloys are heat-treated by quenching and ageing treatment to obtain the required strength.
(1): beautiful appearance
(2): large strength-to-weight ratio
(3): excellent processability
(4): good overall
(5): corrosion resistance
(6): low-temperature characteristics
(7): good electrical conductivity (8): good thermal conductivity
(9): good reflectivity