For stamping dies, wear resistance is an important factor in determining the life of the die. The wear resistance of steel depends on the condition of the hard point phase, such as carbide and the hardness of the substrate. The higher the hardness of both and the more the number of carbides, the better the wear resistance. The materials for stamping die manufacturing include steel, steel junction carbide, cemented carbide, zinc-based alloy, polymer material, aluminium bronze, high and low melting point alloy and so on. Most of the materials used to manufacture stamping dies are mainly steel.
Common materials used for the working parts of dies are carbon tool steel, low-alloy tool steel, high-carbon high-chromium or medium-chromium tool steel, medium-carbon alloy steel, high-speed steel, matrix steel, and as carbide and steel cemented carbide. It is also necessary to consider the influence of factors such as thickness, shape, size and precision requirements of the workpiece on the selection of die materials.
This article will introduce how to choose the right material for stamping dies to extend the die life.
1. Low-alloy tool steel
Low-alloy tool steel is based on carbon tool steel with the addition of the right amount of alloying elements. Compared with carbon tool steel, it reduces the tendency of cracking and quenching deformation, improves steel’s hardenability, and improves wear resistance. Low-alloy steel used in the manufacture of molds are CrWMn, 9Mn2V, 7CrSiMnMoV (code CH-1), 6CrNiSiMnMoV (code GD), etc.
2. Carbon tool steel
In the mould, more applications of carbon tool steel for T8A, T10A, etc., the advantages of good processing performance, cheap. But the hardenability and red hardness are poor, heat treatment deformation, and low load-bearing capacity.
3. High-speed steel
High-speed steel has the highest hardness, wear resistance and compressive strength of the mould steel and high load-bearing capacity. Commonly used in the mould are W18Cr4V (code 8-4-1) and fewer tungsten W6Mo5Cr4V2 (code 6-5-4-2, the U.S. grade M2) to improve the toughness of the development of reduced carbon vanadium high-speed steel 6W6Mo5Cr4V (code 6W6 or low carbon M2). High-speed steel also needs to be re-forged to improve its carbide distribution.
4. High-carbon medium chromium tool steel
High-carbon medium-chromium tool steels are Cr4W2MoV, Cr6WV, Cr5MoV, etc. They have low chromium content, less eutectic carbide, uniform carbide distribution, small heat treatment deformation, good hardenability and dimensional stability. Compared with the relatively serious high-carbon high chromium steel carbide segregation, the performance has improved.
5. High-carbon, high-chromium tool steel
Commonly used high-carbon high-chromium tool steels are Cr12 and Cr12MoV, and Cr12Mo1V1 (code D2). They have good hardenability, hardenability and wear resistance, and heat treatment deformation is very small. For high wear-resistant micro-deformation tool steel, load-bearing capacity is second only to high-speed steel. But carbide segregation is serious and must be repeatedly upsetting (axial upsetting, radial pulling) to change forging to reduce carbide’s unevenness and improve performance.
6. Cemented carbide and steel cemented carbide
The hardness and wear resistance of cemented carbide are higher than any other die steel, but the bending strength and toughness are poor. The cemented carbide used for mould is tungsten cobalt type. The cemented carbide with lower cobalt content can be used for the mould with a small impact and a high requirement of wear resistance. Carbides with higher cobalt content can be used for dies with high impact.
7. Base steel
In the basic composition of high-speed steel, add a small number of other elements and appropriate increase or decrease the carbon content to improve steel performance. Such steel grades are collectively known as matrix steel. They not only have the characteristics of high-speed steel, with certain wear resistance and hardness, and fatigue strength and toughness are better than high-speed steel. For high strength and toughness of cold working tool steel, material costs are lower than high-speed steel. The commonly used matrix steel in the mold are 6Cr4W3Mo2VNb (code 65Nb), 7Cr7Mo2V2Si (code LD), 5Cr4Mo3SiMnVAL (code 012AL), etc.
Stamping mold working parts material requirements
Stamping dies are subjected to vibration, impact, friction, high pressure and tensile, bending and other loads, but also at higher temperatures (such as cold extrusion), working conditions are particularly complex, prone to wear, fatigue, fracture, deformation and other phenomena. Therefore, the requirements for the materials of the working parts of the die are higher than those of ordinary parts. Because the working conditions of various types of stamping dies are different, so the requirements for the materials of working parts of dies are also different.
1. Requirements of cold extrusion die materials
The working parts of the die are required to have high strength and hardness, high wear resistance, and certain toughness to avoid impact breakage. Because of the extrusion will produce a large temperature rise, so it should also have a certain amount of heat-resistant fatigue and thermal hardness.
2. Punching die material requirements
For thin plate punching die working parts with high wear resistance and hardness, and for thick plate punching die in addition to high wear resistance, compressive yield point, in order to prevent die fracture or chipping, should also have a high fracture resistance, high bending strength and toughness.
3. Deep drawing die material requirements
The requirements of mold work parts material have good anti-adhesion (anti-bite), high wear resistance and hardness, certain toughness and good cutting performance, and heat treatment deformation should be small.
To sum up.
So, among almost all the mold failure factors, the material selection and heat treatment of the mold has about 70% of the proportion, which becomes the main factor of the mold life length. Therefore, in the whole process of mold design and manufacturing, the selection of mold materials and heat treatment technology is particularly important.