The basic performance requirements of steel for plastic injection mould are generally summarized as follows:

(1) Sufficient surface hardness and abrasion resistance: the hardness of plastic mould is generally below 50~60 HRC, and the mould after heat treatment shall have sufficient surface hardness to ensure that the mould has sufficient rigidity. 

Because the filling and flowing of the plastic in the mold must bear large pressure stress and friction, the mold is required to maintain the accuracy of the shape and the stability of the dimensional accuracy to ensure that the mold has sufficient service life. The wear resistance of the die depends on the chemical composition and heat treatment hardness of the steel, so improving the hardness of the die is beneficial to improving the wear resistance.

(2) Good machining performance: select the steel that is easy to cut and can obtain high-precision parts after machining. For this purpose, medium carbon steel and medium carbon alloy steel are the most commonly used, which is especially important for large moulds. For parts requiring electric spark machining, it is also required that the burn hardened layer of the steel grade is thin.

(3) Excellent polishing performance: high-quality plastic products require small roughness value of cavity surface. Therefore, the working surface of injection molding parts needs to be polished to mirror surface, Ra ≤ 0.05 μ m. Steel hardness of 35~40 HRC is preferred, and hard surface will make polishing difficult. For this purpose, the selected steel shall have less impurities, uniform and dense microstructure, no fiber directivity, and no pitting or orange peel defects during polishing.

(4) Good thermal stability: the shape of plastic injection mold parts is often complicated and difficult to process after quenching. Therefore, materials with good thermal stability shall be selected as far as possible to reduce the linear expansion coefficient, heat treatment deformation, dimensional change rate caused by temperature difference, metallographic structure and mold size stability after heat treatment, So as to ensure the dimensional accuracy and surface roughness of the die.

(5) Good wear resistance and fatigue resistance: the injection mold cavity is not only washed by the high pressure plastic melt, but also affected by the cold and hot alternating temperature stress. Ordinary high carbon alloy steel can be heat-treated to obtain high hardness, but the toughness is poor, easy to form surface cracks, so it should not be used. The selected steel type shall enable the injection mould to reduce the times of polishing and trimming, maintain the dimensional accuracy of the mould cavity for a long time and achieve the service life of batch production.

We undertake relevant design business and processing of injection molding products. We have experience in mold design of complicated structure and high grade (such as automobile, digital, mobile phone, laptop, DVD shell mold, etc.).