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What kind of materials are used in car molds?

Update:27-04-2020
Summary:

According to the service life requirements of automobil […]

According to the service life requirements of automobile cold punching molds: under normal use and maintenance, 500,000 qualified parts can be produced in multiple batches and small batches. Therefore, the performance and quality of the mold material have a great influence on the service life of the mold. Therefore, the research and development of mold materials have always been valued by mold steel manufacturers and have been rapidly developed.
1. Current status of mold materials
In recent years, China's die steel production technology has developed rapidly, and the materials used to manufacture cold stamping die are mainly divided into the following categories:
(1) High carbon and low alloy cold work die steel, such as: 9SiCr, 7CrSiMnMoV, 8Cr2MnWMoVS, etc.
(2) Anti-wear cold working die steel, such as: 6Cr4W3Mo2VNb, Cr12, Cr12MoV, Cr12Mo1V1, etc.
3) Impact-resistant cold work die steel, such as: 4CrW2Si, 5CrW2Si, 6CrW2Si, etc.
(4) High-speed steel for cold work molds, such as: W6Mo5Cr4V2, W12Mo3Cr4V3N, W9Mo3Cr4V, etc.

2. The performance of automotive mold materials
(1) Requirements for the use of punching die materials
The materials for thin plate punching dies are required to have high abrasion resistance and hardness. In addition to the high wear resistance and compressive yield point for thick plate punching dies, in order to prevent die breakage or chipping, they should High fracture resistance and toughness.
(2) Use requirements for drawing and shaping die materials
The material of mold working parts is required to have high wear resistance and hardness, certain strength and toughness, good cutting performance, good adhesion resistance (bite resistance), and small deformation during heat treatment.
Cr12MoV: belongs to high-carbon high-chromium steel, which contains a large amount of carbides and high alloy martensite. The steel has high hardness and high wear resistance, and its hardness and wear resistance are higher than that of molybdenum chromium cast iron. The vanadium contained in it can refine the grain and increase the toughness, and can form a high hardness VC to further increase the wear resistance of the steel; chromium also gives the steel high hardenability and tempering stability. After the overall quenching, 1 to 2 tempers are required, and the heat treatment time is longer. The hardness after fire can reach HRC 60-62. However, the amount of deformation after heat treatment is greater than that of air-cooled steel, which eliminates the difficulty of deformation and easily reduces the accuracy of the mold. The method of producing Cr12MoV die steel is forging, which has a high production cost. At the same time, due to the limitations of the forging process, Cr12MoV steel can only be forged in blocks, and the inserts need to be assembled when manufacturing the mold, which increases the labor intensity of the fitter and extends the mold. The manufacturing cycle increases costs. At the same time, because its hardness is higher than that of air-cooled steel, the tool wears more during processing, which increases the cutting time and cost. In addition, due to the large amount of Cr, a large number of eutectic carbides precipitated during the crystallization of the molten steel form a brittle zone of ribbon or network carbides, which has poor plasticity and toughness, and cracks are easy to initiate and propagate here, often becoming cracks The main reason for its occurrence is to reduce its service life. When repairing it, due to poor welding performance, it is not possible to directly cold weld the surface. After heating and heat preservation for a period of time, welding the surface is a waste of repair time.

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Cast air-cooled steel: It is a high-carbon low-alloy steel that is replaced by casting. The manganese contained in the steel gives the steel higher strength and hardness, and improves the hardenability of the steel. The method of heat treatment is also surface quenching, and then the purpose of quenching is achieved by air cooling, which saves a lot of time and cost. The hardness after fire can reach above HRC 55, no other processing is required, so the deformation is very small, and the amount of deformation gradually decreases with the increase of quenching temperature. After the surface cooling of the air-cooled steel, there is a high toughness matrix as a liner under the hardened layer, the toughness is higher than Cr12MoV, and it is not easy to produce cracking and chipping during work. However, as the cast air-cooled steel cannot be cast as a whole, before machining the mold, a fitter needs to splice the inserts and then machine them. The labor intensity of the fitter is increased, which extends the manufacturing cycle and increases the manufacturing cost. However, because it can be made into a near-mold type using foam board, it can save casting costs and some processing costs, and can also reduce some costs. The hardness is higher than that of molybdenum-chromium cast iron, and the tool wears more during processing, which increases the cutting time and increases the processing cost. In addition, the air-cooled steel has good welding performance, so that the mold obtains a higher service life. If there are deviations in the manufacturing, repair welding can be directly performed, and the desired effect can be achieved after grinding and trimming, which saves a lot of maintenance time.

Based on the above performance introduction, the materials suitable for drawing punches, concave dies, and clamping rings are molybdenum chromium cast iron and Cr12MoV; the materials suitable for shaping dies are molybdenum chromium cast iron, Cr12MoV, cast air-cooled steel; The material is Cr12MoV, as-cast air-cooled steel.

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