Let’s discuss one of the potential pitfall of designing for the process of injection molding. Melting plastic pellets and molding them into a part seems like a rather simple endeavor; however, it’s sometimes anything but. There are many factors to consider, and this month, we are going to talk about one of the more common: sink marks.

What is Sink?

 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.

How to Avoid Sink?

  1. Core out the solid sections of your part to reduce thick areas.
  2.              * If you require the strength of a solid part, try using cross hatched rib patterns inside of the cored out area to increase strength and avoid sink marks

  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.
      * Click here for a quide to recommend wall thickness by resin

Have any further questions about sink or enhancing your Injection Molding project?  Call your Sales Manager at 770-901-3200 to discuss your project today!