Going back to basics, it's important to remember that the mold is the shaped hollow into which the plastic will be injected. You can remove more of the mold so it can be filled with more plastic, but you can't add back to the mold so that it requires less plastic. Changes to molds must be "steel safe", meaning you are taking away metal from the mold rather than trying to add to it.

The older a mold is, and the more wear it has, the more carefully you will need to consider any modifications. The overall cost of modifying a mold which is nearing the end of its useful life may be greater than replacing it with a new mold.

Cutting changes into molds can only be done to certain minimum depths. Any modifications to a mold must be millable to that minimum depth or they cannot reasonably be made. For these changes which cannot reasonably be milled, a new mold will be required.

Because parting lines indicate where the two halves of the mold meet, changes which affect parting lines will usually affect gating (how plastic gets into the mold) and venting (where air gets out as plastic fills the mold). These additional changes and their effect on how plastic flows through the mold can make mold modifications too broad or simply impossible to accomplish and a new mold will be needed.

Because undercuts usually require a special action to eject parts from the molds, such changes in design are usually better suited to a new mold rather than attempting to modify an existing mold.

With decades of experience and expertise in the plastics industry, Bennett Plastics is ready to help you design and create your products and bring them to market. Contact us today to see how we can partner with you.