The durability of injection molds has a great deal to do with the materials used. Therefore, attention must be paid to the selection of mold materials. In general, mold materials should have the following properties:

(1) High wear resistance

In order to increase the rigidity and mechanical properties of plastic parts, glass fiber is widely used in plastic formulations, and inorganic fillers are used to reinforce them. After adding these additives, they enter the mold cavity at a high speed along with the molten material, causing great friction to the cavity of the mold. If the mold material does not wear, it is easy to cause excessive wear of the cavity, therefore, the material for making such a mold should have better wear resistance.

(2) High corrosion resistance

Many plastic additives, such as flame retardants, and even the chemical action of the frit itself will corrode the mold cavity. When the plastic material is mixed with abrasive fillers and reinforcing materials, it is more likely to increase the damage of the mold. In this regard, it is preferable to use corrosion-resistant steel, or perform surface plating on the mold, chrome plating or nickel plating.

(3) Good thermal conductivity

In injection molding, good mold temperature control has a great impact on the quality of plastic parts, especially when processing semi-crystalline thermoplastics. In general, copper alloys have much better thermal conductivity than alloy steels, but their elastic modulus, hardness, and durability are lower. The lack of thermal conductivity of the steel can be compensated by the cooling system.

(4) Good dimensional stability

During the molding operation of the injection mold, the temperature of the mold cavity should reach 300° C. or more, and the temperature difference is so large that it can easily cause a microscopic change in the cavity structure, resulting in a change in the size of the mold and making the size of the plastic part unstable. Therefore, an appropriate selection can be made. Tempered tool steel, ie heat treated steel. In order to increase the hardness and wear resistance, the mold is generally heat treated. However, this heat treatment should minimize the impact on the size of the mold. The pre-hardened steel that can be machined can be used. This steel does not require heat treatment after machining.

(5) Good polishing performance

The inner wall of the mold cavity is very demanding and the roughness is very small, so as to meet the requirements of the good glossiness of the plastic surface. In this regard, the mold cavity is generally polished, and the brighter the surface, the better. For this reason, the mold material is required to be easy Polishing, the selected material should not be trapped with impurities and pores and other defects.

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