Roughness and ejection force of injection mold surface

In the injection molding process, the conventional process is to open the mold and eject the molded product that has been cooled and solidified to a certain strength after being injected into the mold cavity, so as to take out the molded product.

When releasing the molded product from the cavity, or ejecting it from the core and taking it out, the surface temperature is higher than room temperature because the cavity and core are usually steel and the molded product is made of thermoplastic resin status. The surfaces of the cavity and core are machined or polished to a certain surface roughness. Also, in general, its hardness and strength are higher than those of thermoplastic resin molded products. Examining this state from a physical point of view, it can be inferred that the frictional resistance caused by the surface roughness of the cavity and the core will greatly affect the release of the molded product from the cavity and the core.

The rougher the surface roughness of the cavity and core, the greater the coefficient of friction. Depending on the hardness and self-lubricating properties of the resin, the degree of influence varies. The relationship between the surface roughness of the cavity, the core, and the coefficient of friction with the resin material should also be taken into consideration when considering the release of the molded product. The following are reference values for experimental data.