Die Casting Mold Performance Requirements
Pressure casting can cast parts with complex shapes, high precision, small surface roughness and good mechanical properties. Therefore, the die casting mold should have the following performance requirements:
(1) Large high temperature strength and toughness
The die-casting mold is subjected to high temperature, high pressure and thermal stress when molten metal is injected, and is easily deformed or even cracked. Therefore, the mold material should have sufficient high temperature strength and toughness and high hardness at the working temperature. Toolox materials have the advantages of high strength, high toughness (up to 100J or more toughness) and high hardness. Toolox44 is the world’s hardest pre-hardened tool steel (HRC45-48). The Royal Swedish Institute of Technology claims that Toolox is the perfect combination of high hardness and high toughness.
(2) Excellent high temperature wear resistance, oxidation resistance and tempering stability
When the high-temperature molten metal is injected into the mold at high speed and demoulded after casting, a large friction effect is generated. To ensure long-term use of the mold, the mold should have high wear resistance at the working temperature. A large number of continuously produced die-casting molds should maintain their high hardness for a long time under a certain temperature, and should not stick to the mold and produce no scale. Therefore, the mold should also have good oxidation resistance and tempering stability.
(3) Good thermal fatigue performance
The surface of the die-casting mold is repeatedly heated and cooled by high temperature, and continuously expands and contracts to generate alternating thermal stress. When this stress exceeds the elastic limit of the mold material, repeated plastic deformation occurs, causing thermal fatigue. At the same time, the surface of the mold is subject to corrosion and oxidation of molten metal for a long time, and fine cracks are gradually generated. In most cases, thermal fatigue is the most important factor determining the life of the die-casting mold.
(4) High resistance to melt damage
As the size of the die casting machine increases, the die casting pressure also increases, from 20 to 30 MPa for low pressure to 150 to 500 MPa for high pressure. High temperature and high pressure casting can produce obvious melt damage, and the mold should have greater resistance to this. For this reason, the mold material must have a large high-temperature strength, a small affinity for the molten metal, the mold indicates a small roughness, and a protective layer such as an appropriate oxidation mold, a nitride layer, or the like, without the decarburization layer.
(5) Good hardenability and small heat treatment deformation
Generally, a die-casting mold is manufactured by engraving a cavity of an annealed mold material, and then heat-treating to obtain a desired hardness, or heat-treating the mold material to obtain a desired hardness, and then engraving the cavity. The manufacturing method of the post-cavity cavity post-heat treatment has high hardness and strength, and is not easy to cause melt loss and thermal fatigue. No matter which method is used for heat treatment, it is necessary to obtain uniform hardness, so it is required to have good hardenability. In particular, heat treatment is performed after the cavity is first engraved, and a material having a small heat treatment deformation is used, which is especially true for a mold having a large size. important.
(6) Good machinability and grinding
The die-casting mold cavity is made by cutting, so the mold material should have good machinability. It must be pointed out that materials with good wear resistance are generally poorly cut. This is the case with many die steels, which, although annealed, have a harder base portion. Add hard carbides, which are generally difficult to cut.
In order to obtain a smoother die-casting part, the surface roughness of the mold cavity surface is required to be small, so that the mold material should also have good polishing performance.
(7) The internal organization of the material is uniform and free of defects.
The structure of the mold material should be uniform, free of defects and less directional, otherwise it will not only affect the crack, strength and thermal fatigue properties of the mold, but also affect the heat treatment deformation.