How to Avoid Sink Marks with SOLIDWORKS Plastics

Article by Aditya Chandurkar updated January 11, 2016

Article

Ejected mold parts often have cavities or pits on the surface, they are called Sink Marks. The physical appearance of these marks are fairly small but are strikingly visible as they reflect light in different direction on the part’s surface.  Sink marks do not affect the physical strength, longevity and functioning of the molded part but are distinguished as quality defects.

Plastic part with Sink Marks

Plastic part with Sink Marks

Causes

  • High volumetric shrinkage
  • Insufficient material compensation
  • Early gate freeze-off
  • Short packing or cooling time
  • High melt and mold temperatures
  • Thicker wall thickness
  • Injection Material

Solution for Sink Marks

Using SOLIDWORKS Plastics simulation software, designers and engineers can detect mold part defects such as sinks marks well before the part is manufactured, reducing expense mold rework.

Some remedies are listed below to rectify the sink mark issue using Plastics analysis tools early in the design process:

Optimize packing profile

The most effective way to eliminate sink marks is to set the packing pressure at an optimum value. This can be done easily with SOLIDWORKS Plastics simulation Post processing tools.

injection moulding pressure

Post Processing tool- Packing Pressure

Modify Part Design

Sink marks often occur due to relatively thicker wall thickness of the molded part. SOLIDWORKS Plastics is nicely integrated with SOLIDWORKS 3D CAD package allowing users to quickly change part geometry such as wall thickness values or dimensions such as height, width, length by simply switching tabs in the SOLIDWORKS real estate. This results in huge time saving due to elimination of importing file from different packages for analysis purposes.

Changing Material Injection Location

The best part about SOLIDWORKS Plastics is that it allows the user to simulate multiple what-if scenarios to reach an acceptable result, changing the injection location allows sections of the molded part to be packed before the thinner sections where the material get frozen and sink marks occur.

Injection Location

Injection Location Setup

Optimize the runner balancing system

For family mold layout, it is important that all mold cavities fill up at the same time with the same injection pressure and material. Incorrect runner balance system can cause premature gate freeze off.  Using SOLIDWORKS Plastics, the runner system can be set and Plastics iterative algorithm figures out the optimum value so that the runner system is balanced throughout the board.

Runner Balancing

Runner Balancing Tool Setup

Learn more about SOLIDWORKS Plastics

SOLIDWORKS Plastics brings easy-to-use injection molding simulation directly to the designers of plastic parts and injection molds, as well as advanced CAE analysis.  You can quickly evaluate manufacturability while you design, to eliminate costly mold rework, improve part quality, and accelerate time to market.

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Aditya Chandurkar