Don’t Sink the Boat

Sink marks are a common defect, in plastic injection molding, that are costly to fix, frustrating and not very pleasing! Reducing sink marks early in the design process using SOLIDWORKS Plastics achieves a better finished part. Before starting to cut steel for a mold plastics simulation software visualizes where sink marks could cause an issue. SOLIDWORKS and SOLIDWORKS Plastics aid in the design and analysis of plastic parts to identify sink marks and make design changes quickly before sending the model out to the mold makers.

Being able to see the preview of sink marks on your geometry before the construction of the mold is critical. The results are also color-coded (fig 1) to show the severity of the sink marks. Based on the results, modify the geometry, re-run the analysis to narrow down where problem areas still exist. Doing this shows a reduction of the defect with every iteration of geometry changes. Reducing the severity of sink marks is one step closer to a better-looking plastic part. Finding sink marks at the earliest stages of part design save thousands of dollars down the line.



The example (fig 2) shown has the possibility of sink marks. After the analysis has completed, looking at the results, shows the color changes to signify the area that has sink marks at the production level. Here notice the difference in color shades. The yellow area represents the possibility of sink marks. Making minor changes in the design will help reduce the sink marks.


Fixing sink marks is easy and intuitive with the use of SOLIDWORKS configurations. Noticing that not all the geometry in the plastic part (fig 2) has the same thickness, making changes to the part for more constant wall thickness will aide in eliminating sink marks. Consistent wall thickness parts reduce or completely wipe out the sink marks.


Going even further to understand how severe the sink mark is, a designer can measure the depth of the sink mark using the measurement tool.  Using the  “Measure” command gives the ability to make selections just by picking two locations on the part. The selection shows the depth of the sink (fig 4) directly on the geometry. Using configurations of the part, trying different senerios, helps achieve more consistent wall thickness and fewer sink marks.

By reducing sink marks, in plastics parts, early in the design process gives more confidence in final part design, before sending it to the mold makers. While making quick changes to part design may prevent sink marks, there could be many other defects in plastic part as well. SOLIDWORKS Plastics will help detect many different plastic part defects due to injection molding and optimize your designs to create a more ecstatically pleasing plastic part. For more information click here.



Jeff Osman

Jeff Osman

Jeff Osman has more than 23 years of experience in the mechanical CAD industry. As Senior Technical Sales Specialist Plastics NA, he is responsible for all technical Sales of SolidWorks products, focusing on SolidWorks Plastics, for North America and has been with SolidWorks for 19 years. Prior to joining SolidWorks, Jeff was a senior technical manager with Microcadam, a division of IBM. In addition, he has held several manufacturing positions with companies Processed Plastics, Plano Molding and Furnas/Siemens Electric.
Jeff Osman

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