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The experience of the mold factory, the defects in the mold heat treatment

update:18-03-2021
abstract:

1. There are soft spots on the mold surface There are s […]

1. There are soft spots on the mold surface
There are soft spots on the surface of the mold after heat treatment, which will affect the wear resistance of the mold and reduce the service life of the mold.
cause
1) There are oxide scales, rust spots and local decarburization on the surface of the mold before heat treatment.
2) After the mold is quenched and heated, the cooling and quenching medium is improperly selected, and there are too many impurities or aging in the quenching medium.

2. Poor organization of the mold before heat treatment
The final spheroidization structure of the mold is coarse and uneven, and the spheroidization is imperfect. The structure has mesh, band and chain carbides, which will make the mold easy to crack after quenching and cause the mold to be scrapped.
cause
1) There is severe carbide segregation in the original structure of the die steel material.
2) Poor forging process, such as high forging heating temperature, small deformation, high stop forging temperature, slow cooling rate after forging, etc., so that the forging structure is coarse and there are network, band and chain carbides, which make the ball It is difficult to eliminate during chemical annealing.
3) Poor spheroidizing annealing process, such as too high or too low annealing temperature, short isothermal annealing time, etc., can cause uneven spheroidizing annealing organization or poor spheroidization.

3. Quenching cracks in the mold
Cracking of the mold after quenching is the biggest defect in the heat treatment process of the mold, which will cause the processed mold to be scrapped and cause great losses in production and economy.
Causes
1) The mold material has serious network carbide segregation.
2) There is mechanical processing or cold plastic deformation stress in the mold.
3) Improper heat treatment of the mold (heating or cooling too fast, improper selection of quenching cooling medium, too low cooling temperature, too long cooling time, etc.).
4) The mold shape is complex, the thickness is uneven, with sharp corners and threaded holes, etc., which make the thermal stress and the structural stress too large.

4. Coarse structure after mold quenching
The coarse structure of the mold after quenching will seriously affect the mechanical properties of the mold, and the mold will be broken during use, which will seriously affect the service life of the mold.
Causes
1) Die steel is confused, the actual steel quenching temperature is much lower than the required quenching temperature of the mold material (such as GCr15 steel as 3Cr2W8V steel).
2) The die steel is not properly spheroidized before quenching, and the spheroidizing structure is poor.
3) The mold quenching heating temperature is too high or the holding time is too long.
4) Improper placement of the mold in the furnace may cause overheating in the area close to the electrode or heating element.
5) For molds with large section changes, the quenching and heating process parameters are not properly selected, resulting in overheating at thin sections and sharp corners.

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