Sink marks, depth result

The Sink marks, depth result indicates the location and depth of sink marks (and voids) likely to be caused by features on the opposite face of the surface.

Sink marks can occur in moldings with thicker sections, or at locations opposite ribs, bosses or internal fillets. The Sink marks, depth result only indicates sink marks likely to be caused by features on the opposite face of the surface.

The Sink marks, depth result plot is generated by a Pack analysis using Midplane analysis technology.

Using this result

Sink marks appear as depressions on the surface of a molded part. These depressions are typically very small; however they are often quite visible, because they reflect light in different directions to the part. The visibility of sink marks is a function of the color of the part as well as its surface texture so depth is only one criterion. Although sink marks do not affect part strength or function, they are perceived to be severe quality defects.

Sink marks are caused mainly by thermal contraction (shrinkage) during cooling. For example, areas where a rib meets the top surface will cool slower than other regions due to restricted local contact with the colder mold surface. This in turn will cause higher shrinkage which effectively pulls the cooling plastic away from the mold surface to create depressions on the surface of a molded part.

What to do next

After identifying sink marks on your model, consider the following actions to remove them:
  • Alter part design to avoid thick sections and reduce the thickness of any extrusions, or conceal the sink marks within the design.
  • Increase the packing pressure/packing time.
  • Relocate the gate to or near a thicker section. This allows these sections to be packed before the thinner sections freeze.
  • Increase the size of gates and runners to delay the gate freeze-off time. This will allow more material to be packed into the cavity.
  • Decrease the melt and mold temperature.
  • Use a material with a lower viscosity.
Note: Changes such as these can only be made using a licensed Autodesk Simulation Moldflow Adviser or Autodesk Simulation Moldflow Insight product.