Vacuum heat treatment of punching die

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The clutch plates are punched from 65Mn quenched strip steel. The parts are produced in large batches, with an annual output of more than 2 million pieces, requiring high smoothness and small punching burrs, so the blanking punching die is required to have a long life. At present, the one-time sharpening life of the mold is only 3000~5000 pieces, which greatly affects the quality and production efficiency of the product. Since there are many factors that affect the quality, production efficiency and service life of the mold, in order to improve the service life of the mold, the principles of systems engineering must be applied to comprehensively analyze the various factors that affect the life of the mold, and find the main factors. Usually the mold structure, mold material and heat treatment process have a great influence on the service life of the mold.

Mold structure
The blanking gap is the most important technical parameter in the design and manufacture of blanking die. It not only affects the blanking force, discharge force and ejector force, but also affects the dimensional accuracy of the blanking part, the life of the die, the manufacturing process and the cost. . The size of the blanking gap mainly depends on the thickness and hardness of the sheet. The material of the transmission plate is 65Mn, and the hardness is as high as 45-48 HRC. The original blanking gap is 6% to 8% of the thickness of the plate, and the bright band on the section of the blanking part accounts for a large proportion, and the burr is serious. Through the gap optimization test analysis, it is believed that the original die gap is too small and the punching burr is high, and the reasonable punching gap should be 18%-20% of the plate thickness.

Mold material
The mold material is an important factor affecting the test life of the mold. The original mold core and punch materials are all Cr12. The main failure mode is the dimensional excess caused by friction and wear, indicating that the hardness of the material in use is not high and the wear resistance is insufficient. . Due to the high carbon content of Cr12, there are a large number of carbides, the block is large and the distribution is uneven, and the quality of forging and heat treatment is not easy to control. At present, this material has been gradually replaced by high-speed steel such as Cr12MoV and W6MoSCr4V2. As a mature cutting tool material, W6MoSCr4V2 high-speed steel has been widely used in blanking dies with satisfactory results. CW50 is a steel-bonded cemented carbide material developed in the 1970s, with high hardness and excellent wear resistance.

CW50 steel-bonded cemented carbide material is sintered by powder metallurgy method. It has forgeability, machinability, and can be strengthened by heat treatment. Its performance is between alloy tool steel and cemented carbide, and its wear resistance is better than Alloy tool steel. Therefore, CW50 steel-bonded cemented carbide is selected as the die material, and W6Mo5Cr4V2 high-speed steel is selected as the punch and punch and die material.

Heat treatment process:
Heat treatment of W6MoSCr4V2 high speed steel. At the same time, in order to reduce the deformation and avoid oxidation and decarburization of the mold surface, quenching and tempering are carried out in a double-chamber vacuum quenching furnace. The tempering process (low quenching and low tempering process) is quenching oil at 1120~1180 ℃, and tempering twice at 190~220 ℃. The quenching and tempering structure is tempered martensite plus alloy carbide + a small amount of retained austenite. The hardness is 57~61HRC.

Since CW50 has excellent hardenability (can be hardened by air cooling), the cooling rate of annealing should be ≤20 °C/h. The annealed structure is spherical and point-like pearlite plus WC. Hard phase, the hardness is 30~35 HRC. CW50 quenching and tempering are carried out in a vacuum quenching furnace. The process is quenching oil at 1020~1080℃ and tempering at 180~200℃ twice. The quenched and tempered microstructure is tempered martensite plus WC hard phase with uniform distribution, and the hardness is 64~66 HRC.

Select a reasonable blanking gap, use W6MO5Gr4V2 high-speed steel as punch and punch and die material, GW50 steel-bonded cemented carbide as die material, and adopt corresponding vacuum heat treatment process, so that the clutch transmission plate blanking punching die can be used. The service life is significantly improved, reaching more than 20 times that of the original mold.

Equipment selection: The VOGQ series vacuum air quenching furnace produced by SIMUWU is a high-quality product for handling this kind of process. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum quenching process. With more than ten years of sales and manufacturing experience, it is exported to developed regions in Europe, America and Asia. It is a widely acclaimed vacuum furnace product.