the first principle for deciding on the parting line is to assure the plastic part’s appearance. Because during molding, the parting plane may easily lead to welding marks or overflow, it is hard to clean the mold, so a better choice of the parting plane is to help to form smooth, rounded corners on the plastic part.
The first place to know the best parting line to use for an injection molded product is the mold design. In some parts, the choice is obvious while it might not be so clear in some places. This section will address the importance of parting lines in plastic design.
The first consideration is to determine the opening direction of the mold relative to the part. Machinists call this factor “the line of draw.” It is very important in determining how the design of the part will look like. It also helps to know which sides to add the features of the product. Apart from this, it also helps to determine how the vestiges left by the two halves of the injection molded product will look like on the final product.
Another factor that is important when determining the parting line is where to place components on the part. This is because the shrinking of plastic while it cools might shift the position of the part in the mold. This could displace the functional features of the part, rendering it useless. Also, the machinists should ensure the shrinking part doesn’t shrink too hard to avoid difficult ejection.
One way to ensure the components stay in the right place is to draft the walls of the injection molded part away from the parting line. The more draft, the less the probability of the features falling apart.
Another good way to determine the part line in injection molding is with checking the Design for Manufacturability (DfM) of your product. Apart from suggesting the best positions for your part line, it also helps to check for defects and optimize your part for manufacture. This will help provide economic options to manufacturing your part.