The manufacturing method of the cavity is also cold extrusion, hot extrusion, electric discharge machining and welding. Among them, the cold extrusion method is suitable for small molds, especially multi-cavity molds, to ensure the consistency of each cavity.
For large volume cavities, it can be manufactured by machining combined with welding. When blow molding products are required to have high dimensional accuracy, it is necessary to use a profile milling method to manufacture the cavity. The shrinkage rate should be considered when designing the cavity size.
For machined cavities, the shrinkage rate includes the shrinkage of the blow molded product and the shrinkage of the mold after the processing; for the cast cavity, the shrinkage of the mold material during casting is also considered. The final stage of cavity manufacturing is polishing, Sandblasting or etching.
Before etching, especially when it is necessary to etch a fine pattern, the scales and marks generated by cutting, electric discharge machining, grinding or extrusion processing are removed to ensure a certain degree of smoothness. Unless the production batch is large, the mold cavity generally does not need to be hardened, and the metal is rarely plated (such as chrome plating).
If the cavity is to be hardened or chrome-plated, it should be done after etching. Most of the steel inserts, tie rods, guide columns and guide sleeves are made of steel or copper-bismuth alloy by mechanical processing, and are also hardened.