Steel for plastic mold making covers a wide range, from ordinary steel to dedicated steel. This was more evident in the early days of plastic molds, and it is now becoming more advanced.
The dedicated steel has its own system. The chemical composition of the mold steel is basically the same as that of the alloy tool steel, but its metallurgical quality is higher, its processing is better, and it is beneficial to heat treatment.
Plastic mold steel has strict performance requirements and is difficult to heat treat.
In order to avoid the deformation or other heat treatment problems of the mold parts during the toughening process, it is more common for the mold steel to be supplied to the market in pre-hardening.
Plastic products with petrochemical products as raw materials have different degrees of corrosivity, so corrosion-resistant steel is also used more for this kind of injection molding.
With the application of pre-hardened steel and non-quenched and tempered steel, handy cutting is also a feature of plastic mold steel.
Selection and heat treatment of mold steel
Among the manufacturing costs of plastic molds, processing and polishing account for 70% to 80%. Therefore, when selecting mold steel, it is necessary to improve the processing performance of the molds while ensuring the performance requirements of the molds.
The selection method can be carried out as follows:
- according to the type and quality requirements of plastic products.
- According to the production batch of plastic parts. When other factors are determined, the smaller the production batch is, the lower the wear resistance and service life requirements of the mold will be. Therefore, steel with low performance can be selected. For small batches, quenched and tempered steel or carbon steel can be used. For medium batches (300,000 to 1 million shoting), P20, 5NiSCa, SM2, etc. can be selected; for larger batches, 5NiSCa, PMS, etc.
- Select according to the size and accuracy requirements of plastic parts. For large-scale high-precision injection molds, like plastic cap mold , when the production volume of plastic parts is large, pre-hardened steel is used to prevent heat treatment deformation.
- Select according to the complexity of plastic parts. Mold maker should fully consider the processing technology of the mold, try to choose materials that are easy to cut, and it has small heat treatment deformation and good wear resistance.