As customer’s quality awareness for the product improving, many manufacturers have high requirements for the mold and mold material. Hard mold collectively refers to plastic die/mold core and cavity with hardness over 50HRC. Generally, allowed hardness is about 50HRC, and now more common domestic die/mold hardness are in 48-52HRC. Hard plastic molded products are mainly small products, such as our most common thin-walled mold, disposable cutlery mold, nylon plastic mold, wine box mold etc.
The biggest characteristic of hard mold is its high hardness which ensures longer life. Universally hard mold life can reach more than 1 million shots. It is relatively very cost-effective for some big products. It can be used to improve plastic parts profit by improving the mold production.
The process for hard mold is different from other plastic mold. Considering its hardness is about 50 HRC which is very difficult for machining, the first step is to rough machining and remain a few millimeters allowance for the surface. After rough finish, it is heat treatment. The common technique is vacuum hardening. To make the plastic mold hardness reach to 50 HRC. Because the steel has deformation after heat treatment, we need air cooling three days before starting fine machining work. Due to the high hardness, it is very difficult for finishing, especially for CNC milling tool, while the plastic mold processing progress will be slower. We will give priority to spark discharge machining.
Since there has some scrap rate for the mold heat treated, it is high risk to make hard mold than make a common mold in a general way. But need to decide according to actual situation. For plastic hard mold/die, the most common steels are mainly H13, S136, 2344 and so on.