Witness marks are a function of the injection molding process and these molding defects cannot be completely eliminated. Their effect on the look and performance of the part can be controlled by using good design practices, including the following:
Disguise the location of the witness within some other feature of the part
Use a submarine gate to relocate the witness location to an unobtrusive area
Use a fan gate to distribute the resin over a wider area with less pressure
Use multiple, smaller runners to distribute resin and pressure
Place the witness in an area that can be easily accessed for post-machining or sanding
Please note that all of these approaches to fixing molding defects could compromise other areas of the part design and finished molded products, so we advise consulting with the injection molder well in advance.
