Plastic mold processing principles and process requirements

   Before the processing and manufacturing of plastic molds, a complete process diagram is usually prepared to determine the processing techniques and machining accuracy for each step. This is the prerequisite for ensuring the successful production of plastic molds and is also an essential factor in ensuring the quality of the molds produced. Today, we will focus on explaining the processing principles of plastic molds and some principles of machining accuracy, as well as the factors that need to be considered during design.

1. Principle of machining allowance

For workpieces requiring heat treatment, the material preparation size for the shape before heat treatment should have a grinding allowance of 0.25mm added to each side;

2. For the parts of the mold core and insert that require CNC rough machining, a single-sided allowance of 0.2mm should be reserved;

3. For rough milling on a fitter's milling machine, a single-sided allowance of 0.3-0.5mm should be reserved for the overall shape. For workpieces that require grinding after wire cutting, a single-sided allowance of 0.05mm should be reserved for the forming part, and a single-sided grinding allowance of 0.1mm should be reserved for the roughing of the overall shape;

4. After CNC finishing and electric pulse treatment, mirror polishing is required, with a polishing allowance of 0.03mm on one side.

II. Requirements for machining accuracy

The manufacturing accuracy of mold dimensions should be within the range of 0.005 to 0.02mm; the perpendicularity requirement is within the range of 0.01 to 0.02mm; the coaxiality requirement is within the range of 0.01 to 0.03mm; and the parallelism requirement for the upper and lower planes of the moving and stationary mold parting surfaces is within the range of 0.01 to 0.03mm.

After mold closing, the gap between the parting surfaces should be less than the overflow value of the molded plastic. The parallelism of the mating surfaces of the remaining templates is required to be within the range of 0.01~0.02mm; the mating accuracy of the fixed parts is generally selected within the range of 0.01~0.02mm; if there is no requirement for insertion or the impact on dimensions is not significant, a double-sided gap fit of 0.01~0.02mm can be adopted for small cores; the mating accuracy of the sliding parts is generally selected from three types: H7/e6, H7/f7, and H7/g6.

Note: If there are inserts with hanging steps on the mirror surface, the fit should not be too tight. Otherwise, when the inserts are knocked back from the front, the tool used for knocking may easily damage the mirror surface. If it does not affect the product dimensions, a clearance fit of 0.01~0.02mm on both sides can be adopted.

Label: Plastic mold manufacturing