The newest generation of wax injection equipment can reproduce details as small as one-hundredth of a millimeter in a single channel mold with a very high degree of repeatability. Still, we can see defects in wax patterns that appear to be air bubbles. These defects can be reproduced in a wide range of waxes, molds and injection setups. Such defects are hard to explain since the wax was degassed in the tank and a high vacuum was inside the mold during injection. These facts make outgassing from the wax in the mold or other gas-related problems like venting improbable causes of this new class of defects. This paper describes a search for the real cause of these wax pattern defects. It will show how the geometry of the defect and other laboratory experiments point to what is called the triboelectric effect as the cause of these bubbles, not air. In short, these defects are caused by the electrostatic repulsion on the injection fronts due to their tribocharging.

Author(s): Andrea Giaccherini