According to the molding method, plastics can be divided into thermoplastic and thermosetting plastics. Thermosetting plastics, such as bakelite powder, are pressed under heating and pressure for permanent molding. The Glulam mold is periodically subjected to pressure and continuously heated at 150-200 ℃. Thermoplastic plastics, such as PVC, are usually molded by injection mold. The plastic is heated in a separate heating chamber, and then injected into the colder mold cavity in a softened state to apply pressure, so as to make it cold and hard.

塑料模具的制造成本高，材料费用只占模具成本 小部分，因此选 用钢材时，应优先选 用工艺性能好，性能稳定和使用寿命较长的钢种，具体对塑料模具提出如下要求：

The manufacturing cost of plastic mold is high, and the material cost only accounts for a small part of the mold cost. Therefore, when selecting steel, priority should be given to the steel with good process performance, stable performance and long service life

1. 机械加工性能优良：塑料模具的型腔的几何形状非常复杂，而且要求加工深孔，深沟等难加工部位，钢材必须具有易切削的性能，在选择钢材时，如果其他条件都能满足，是这一条件是选定时的依据。

1. Excellent machining performance: the geometric shape of the cavity of the plastic mold is very complex, and it is required to process deep holes, deep grooves and other difficult parts. The steel must have the performance of free cutting. When selecting the steel, if other conditions can be met, this condition is the basis for the final selection.

2. 抛光性能优良：无论何种塑料模具，其型腔的允许表面粗糙度极小，几乎都要求能做到镜面光泽，而要达到镜面光泽，钢材必须具有好的硬度，钢材中的杂物要尽量少，而且不能有气泡存在，并且显微组织均匀，在大量生产中用的模具，表面粗糙度也是重要条件。

Two Excellent polishing performance: no matter what kind of plastic mold, the allowable surface roughness of its cavity is very small, almost all requirements can achieve the mirror luster, and to achieve the mirror luster, the steel must have good hardness, first of all, the impurities in the steel should be as little as possible, and there should be no bubbles, and the microstructure is uniform. The surface roughness of the mold used in mass production is also an important factor One.

3. 良好的表面腐蚀加工性：很多模具要求成型的塑件表面为各种其他物质的花纹，如皮革，绸纹，布纹，精细图案等，这就要求钢材的质地细而均匀，否则腐蚀后的效果不佳。

3. Good surface corrosion processability: many molds require that the surface of molded plastic parts be various patterns of other substances, such as leather, silk, cloth, fine patterns, etc., which requires that the texture of steel is fine and uniform, otherwise the effect after corrosion is not good.

4. 耐磨性和韧性好：塑料模具是长期承受热交变负荷的，而且又是长期经受摩擦的，如仅考虑耐摩擦的一面，而不考虑期受热交变负荷的一面，使用冷冲模具的高碳高合金钢制造时，必然会出现韧性不足而引起开裂。

4. Good wear resistance and toughness: plastic mold is subject to long-term heat alternating load and long-term friction. If only the side of friction resistance is considered, and the side of periodic heat alternating load is not considered, when high carbon and high alloy steel of cold stamping die is used for manufacturing, it is bound to have insufficient toughness and cause cracking.

5. 淬火性能好，变形小：塑料模具的型腔部分大部分都必须进行热处理，这就要求钢材具有较好的淬透性和很小变形，一般热塑性塑料成型用模具，采用调质，预硬化等处理即可，而热固性塑料成型用模具则必须淬硬。

5. Good quenching performance and small deformation: most of the cavity parts of the plastic mold must be heat treated, which requires the steel to have good hardenability and small deformation. Generally, the mold for thermoplastic molding can be quenched, tempered and pre hardened, while the mold for thermosetting plastic molding must be hardened.