Thermosetting plastics such as electric wood powder are pressed and permanently formed under heating and pressure. The electric wood mold is subjected to pressure periodically and continuously heated at a temperature of 150-200 ℃.

Thermoplastic materials, such as polyvinyl chloride, are generally molded by injection molding. The plastic is heated in a separate heating chamber and then injected into a cooler mold in a softened state, applying pressure to make it cold hard to form.

The normal operating temperature for injection molding is 120-180 ℃, with some as high as 260 ℃. But during operation, the water-cooled cavity is usually used, so the degree of heat, force, and wear is relatively light. Only some varieties, such as plastics containing chlorine and fluorine, release harmful gases during compression, which have a significant corrosive effect on the mold cavity.

According to the working conditions and characteristics of precision plastic molds, the following requirements are proposed for the steel used in plastic molds:

① Steel materials need to be very pure to obtain a highly glossy processing surface. Therefore, it is required to have fewer inclusions, less segregation, a dense structure, and high surface hardness;

② The surface should be wear-resistant and corrosion-resistant, requiring a certain degree of surface hardening layer, generally above 45HRC, and the surface smoothness should be maintained unchanged for a long time;

③ Has sufficient strength and toughness to withstand loads without deformation or damage;

④ Heat treatment has minimal deformation to ensure interchangeability and precision of fit;

⑤ Has good electrical machining ability.