Identifying Sink Marks Using SOLIDWORKS Plastics

   By Suman Sudhakaren on August 27, 2019

Sink Marks appear during the cooling process with injection molding and can be easily identified using SOLIDWORKS Plastics. Detecting them during the design phase saves time and money by avoiding manufacturing defects. Let’s dive in to the ways in which you can utilize this software to easily spot the errors that cause these marks.

  1. Getting Started
  2. Shell Mesh
  3. Material Specification
  4. Process Parameters and Flow Pattern
  5. Fill Time Plot
  6. Analysis

1. Getting Started

A plastics handle with ribs and mounting pins is used here to illustrate the workflow in SOLIDWORKS Plastics. Sink marks are common for such parts with ribs attached to the surface body. After enabling the SOLIDWORKS Plastics add-in via Tools->Add-Ins, you can use either the Getting Started Wizard or directly go to the Plastics tab to manually set up the analysis.

SolidWorks Sink MarksFigure 1 – SOLIDWORKS Plastics

Since the interface is the same, changes made in the CAD model can be quickly analyzed without worrying about file translation.

SolidWorks Plastics Getting Started WizardFigure 5 – Plastics Getting Started Wizard

2. Shell Mesh

A shell mesh of 2mm is used. Mesh refinement can be used for critical areas. If needed, a shell mesh can be converted into a solidmesh for better accuracy. For simple parts such as this handle, a shell mesh is okay to use.

Shell MeshFigure 2 – Shell Mesh for Plastic Handle

3. Material Specification

Next in the Plastics Manager Tree is material specification. You can define different materials for cavity, inserts and mold as required. ABS, a generic material is used in this case. Users can also custom define a material of their choice.

Polymer Material DatabaseFigure 3 – Polymer Material Database

4. Process Parameters and Flow Pattern

The process parameters option allows users to set parameters for the filling, packing and warping phases of the process. For this analysis, you can leave parameters at their default values and set up the injection location in the Boundary conditions. You can let the software automatically add an injection location and predict the flow pattern. The image below shows the predicted flow pattern for an injection location at the center of the inner edge.

Predict flow patternFigure 4 – Predict Flow Pattern using Automatically added Injection Location

If the predicted flow pattern is not acceptable, users can delete and manually add a new location as shown below. Once the location is finalized, a right mouse click on the flow option will solve the analysis.

User Defined injection Location

Figure 5 – User defined Injection Location

5. Fill Time Plot

At the completion of analysis, a fill time plot is automatically displayed. On the right side of the graphical screen, Results Adviser is displayed. Results Adviser explains the result plots in detail. The green light in the adviser panel lights up to indicate the part can be successfully filled. It shows an injection pressure of 28.6Mpa is required to fill this part. Fill time plot displays profile of the plastics melt as it flows. The animation toolbar in results property manager can be used to animate the filling process.preview-full-Animation Fill

Figure 6 –  Fill Plot

6. Plastics Analysis

The Sink marks occur during the cooling process and appears as depressions on the surface of the molded part. SOLIDWORKS Plastics analysis predicts the sink marks and displays them in fill analysis as shown in Figure 7. The bands of color mark each rib of the part from the outside. Modifying the draft angle and rib thickness at the base would help to minimize potential sink marks in the part.

sink mark
Figure 7 – Sink Mark

Besides the many other flow results, such as volumetric shrinkage and shear rate at end of fill, weld line and air trap locations are of importance. These can be viewed by enabling the check boxes for these in the results property manager as shown below. By knowing the air trap location, you can minimize the potential for the dieseling effect by providing adequate venting or modifying the design to avoid abrupt thickness differences in the part.

Weld lines

Figure 8 – Weld Lines and Air Traps

To minimize the sink marks, a design change can be made to the ribs. Adding a design configuration with the modified rib thickness and fillet radii, a new analysis can be quickly run. Users don’t need to setup analysis from scratch. Using the copy settings option in SOLIDWORKS Plastics, material and process parameters can be copied easily to different configurations to quickly run the analysis. This helps when analyzing different design iterations to find out the optimum design.

The Plastics avisor also includes a nominal wall thickness advisor that queries the geometry and determines the overall nominal wall thickness and the model and percentage deviation from this nominal value. This is important as a uniform wall thickness leads to uniform filling patterns, pressure distributions, optimized cycle times and reduced warping.

Once the analysis is completed, you can use the automated report generation tools to share the simulation results in either Word or PowerPoint format. 

>> View SOLIDWORKS Plastics Product Matrix

SOLIDWORKS Plastics is the essential addition to SOLIDWORKS to ensure that 3D printing plastic prototypes is a smooth and efficient process. Defects waste time, money and materials which leads to slower production. Producing prototypes faster will always be a competitive advantage which makes refining your design stage to find issues before they are printed is the key to proactively decreasing time-to-market. 

Ready to solidify your design process? Learn more by watching our webinar “Practical Part Design Using SOLIDWORKS Plastics”!

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Suman Sudhakaren

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