“Am I going to get trapped air in the mold?” “Where will the air traps be?”
- “Air traps” are areas in the mold where air cannot escape during the molding process. Since the mold halves are designed one for one, meaning the mold halves touch, the air that is captured in the mold cavity when the mold is closed must be pushed out once the plastic starts filling the cavity. The mold must be able to adequately evacuate that air both in volume and in a short period of time.
- Air traps cause issues such as short shots and more dramatically burn marks. Burn marks are very dark spots on the plastic part in which the air, more specifically, the oxygen literally explodes and causes carbonization of the plastic. Additionally, these small explosions erode away the steel of the mold, eventually leading to costly repair.
SOLIDWORKS Plastics filling simulation.
How The Solution Helps
- Having the ability to identify and predict where the air traps will be BEFORE the mold is created allows you to adjust both the part design and/or the mold design. The whole idea is to do this exercise before the mold steel is cut. Completing this exercise after the fact is very costly and kills timing of getting the mold into production.
- Air traps that are on the parting line can be identified and edge vents can accurately placed in the mold during the build process.
- Air traps that are internal to the part can be identified and changes to that design can take place by relocating the gate or modifying part design features. Additionally, exact placement of an ejector pin at the air trap location to allow that pin to be vented.
- If neither of the above options are feasible, then the identification of the air trap can be incorporated into the mold design by making sure there is space cleared out and void of waterlines and ejector pins to insert a porous metal, which is designed to allow air to escape through the face of the mold.
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