Sink marks are a common potential pitfall of designing for the process of injection molding in many cases without the correct design tools sink marks are unavoidable.

Melting plastic pellets and molding them into a part seems like a rather simple endeavor although, sometimes can be anything but. A sink mark is a local surface depression or void that typically occurs in moldings with thicker sections. They are also common in locations above ribs, bosses, or internal fillets. As the plastic cools at different rates in the mold, the surface hardens but leaves the thicker areas in the center still molten. As the thicker areas cool, they contract and leave depressions in the surface of the part; sometimes the part may even warp completely

Sink marks can be avoided by:
  1. Core out the solid sections of your part to reduce thick areas.
  3. As a rule of thumb,  make sure that all bosses and locating & support ribs are no more than 60% of the thickness of your nominal wall.
  4. Modeling your part in Soildworks through the design process.
If you have any questions with regard to the injection moulding process and creating injection mould through the EDM machining Process please feel free to contact ALNO product Services for more information.

Sink | Marks | Injection | Moulding | EDM | Machining