SOLIDWORKS 2025 has a Plastics add-in for designers, and although it requires an additional subscription, it is well worth it if you do any plastic design. When your design starts going into high volume production, plastic is often the best choice as it cuts down on cost — and not only for materials. Because plastic is lighter weight, the company saves on shipping costs. Additionally, depending on the way you design the enclosure, you can save on assembly costs by adding features like bosses to replace spacers and snap hooks to replace fasteners.
The Plastics Add-In for SOLIDWORKS helps engineers and designers predict, analyze and optimize part and mold designs. Molds are incredibly expensive, so using this tool can prevent costly errors. The 2025 release introduces several enhancements which provide even more value for the user.
As a plastics designer, sink marks have been a particular sore point, soI am particularly interested in the new enhanced sink mark predictions. A new solver promises to provide more accurate predictions of sink mark locations and depths.
A sink mark is a shallow depression that appears on the surface of a plastic part, usually due to uneven cooling and/or shrinkage of the material. While sink marks are mostly a cosmetic defect, they can also affect the structural integrity of the part. In extreme cases, sink marks may lead to dimensional inaccuracies. This means that parts might not fit together properly or may not pass inspection. If the plastic material does not cool evenly, internal stress can develop, potentially making the part weaker or prone to cracking.
Additionally, customers often associate sink marks with cheap or low-quality manufacturing, which can hurt a brand’s reputation.
If your parts come out of the mold with sink marks, your options are to modify the mold or increase the cooling time — both of which add to production costs.
I have designed this small plastic part. I want to use the SOLIDWORKS Plastics Add-In to analyze it and verify that the design has no issues.
Before you start, verify that you have the SOLIDWORKS Plastics Add-Ins loaded and available.
If the Add-In is loaded, you will have a SOLIDWORKS Plastics ribbon available.
The 2025 release has expanded the number of plastic materials available, so it is worth browsing the available materials before you get started. Keep in mind that sometimes you can solve design issues, like sink marks, simply by selecting a different material.
The database can be viewed by material or by company.
The database doesn’t have all the information for each material, but it is a good starting point.
You can also add materials to your own user-defined database.
I usually consult matweb.com as my go-to resources for material specifications, and to verify the information.
Matweb has a new feature that allows you to export material data to a file that can be imported into SOLIDWORKS. It requires an annual subscription, but if you do a lot of design work it’s worthwhile.
When performing an analysis, start at the far left on the ribbon and move right. The first step is to launch a New Study and give your study a name. In this case, my part has only one material.
I specify the Shell Analysis procedure. The shell analysis is recommended for thin parts with moderate thickness variations and no narrow flow channels.
Next, I select the Green Check.
My browser updates to display the Plastics analysis tab.
Right click on the Simulation type and select Edit. You now have a list of the different simulation types available in the Plastics module.
[Note: The Cool and Warp analysis are available with the Premium license only.]
To check for sink marks, you should select the Fill + Pack simulation types. The Filling Phase simulates how molten plastic flows into the mold and highlights areas of uneven fill.
The Packing Phase analyzes material shrinkage and pressure distribution, which directly contributes to sink mark creation.
It is recommended to run a warp analysis after the fill and pack analysis to verify the design. Green check to complete the selection.
Even though I had a material applied in my SOLIDWORKS Part browser, I need to apply a material here.
Since I don’t know which vendor I will be using to manufacture my part, I opt to sort by Family and enable the Generic ABS+PC material.
Once I have verified my design and gone through design review, I will work with my company’s purchasing department to select a vendor to create the mold and produce the parts. At that point, the vendor will make recommendations of materials based on their supplies.
Normally, once I know which material will be used during production, I will run an analysis to check it again. I also will ask the vendor to perform an analysis, so I can compare my numbers to theirs.
You should see a green check next to the Injection Units and the Unit-1 Material to verify that the material has been assigned properly.
You need to set the location where the plastic will be injected into the mold to form the part. Best practice is to place the injection point at the thickest location of the part to ensure consistent flow.
I try to select an injection point which can be camouflaged or doesn’t detract from the part’s cosmetic quality.
Avoid placing the injection point at vertices, corners, edges or thin walls, and try to select a location that promotes uniform filling. If your part is large or complex, you can use more than one injection point.
If you are unsure of where to place the injection point, SOLIDWORKS Plastics has an Injection Location Advisor. The Advisor is a great tool to identify the best injection point(s). It ensures optimal mold filling and reduces the likelihood of defects, like sink marks.
The Advisor works by evaluating the wall thickness, the part shape and symmetry to suggest an ideal injection point. It prioritizes even flow distribution to reduce air traps, weld lines and shrinkage issues.
The Advisor uses a color-coded flow pattern to indicate:
You can allow the Advisor to determine the optimum number of injection points or set a minimum number.
Red areas indicate places to stay away from when placing an injection point. The blue area at the base of the part is displayed to be the optimal area for an injection point.
Click the green check to exit the advisor.
The Advisor automatically places an injection point in the best location.
In SOLIDWORKS Plastics, meshing is a crucial step in the simulation process because it transforms the 3D model into smaller computational elements. These elements allow the software to accurately analyze plastic flow, pressure, temperature distribution and potential defects during the injection molding process.
The mesh divides the plastic part into thousands (or millions) of small triangular or tetrahedral elements. This allows the simulation to calculate how molten plastic flows through each section of the mold cavity.
Depending on the size of the part, you may want to increase or decrease the size of the mesh. A finer mesh captures more details and provides precise results, such as predicting sink marks, air traps and warpage. A coarser mesh runs faster but may miss small design defects.
You have the ability to refine the mesh to focus on critical areas, such as ribs or thin walls.
There are three types of mesh available in SOLIDWORKS Plastics:
- Shell Mesh (midplane and surface) is used for thin-walled parts, such as plastic housings.
- Solid Mesh (tetrahedral elements) is used for thicker parts.
- Hybrid Mesh is used when you have a part with a combination of thin walls and thick sections.
Because this is a thin-walled part, we see Shell Mesh in the Browser. Right click and select Create Mesh.
You can also select Create Mesh from the ribbon.
By default, SOLIDWORKS uses the average mesh size. The finer the mesh, the longer the analysis will take.
You need to balance the amount of time you want to wait for analysis results versus the accuracy of the results.
SOLIDWORKS provides you with an estimated number of triangles based on the mesh size selected, to give you an idea of the amount of time the analysis will take.
The advanced mesh control allows a finer mesh only in areas where high detail is needed, such as thin walls, ribs, bosses, gate locations, sharp corners and small features. It can also be used to prevent excessive meshing in less critical areas.
I selected the faces for the bosses and ribs and designated a larger mesh for those areas.
Finally, I clicked the Create button to generate the mesh.
It took only a few seconds for SOLIDWORKS to generate this mesh.
You can see the mesh on the boss and ribs is slightly larger than the mesh on the rest of the part. At this point, I have an opportunity to adjust my settings or accept them by choosing the green check.
Less than a minute later, SOLIDWORKS provided me with an analysis of my part.
The summary looks like this:
For the report, you can generate images or an AVI.
The report can be saved as a Word document, Power Point or HTML file.
The real magic happens when you highlight the word analysis at the top of the browser, right click and select Run.
You can also run the analysis from the ribbon.
SOLIDWORKS then performs a complete analysis of your part.
It took about 10 minutes for Solidworks to finish the analysis based on my settings. This new release has sped up the calculation time significantly.
You can review some of the results from the ribbon.
To see potential sink marks, I highlight sink marks in the Available Results list.
SOLIDWORKS provides me with a colored image to see where potential sink marks might happen.
I was not expecting to see sink marks in those locations. Thanks to SOLIDWORKS I can return to the drawing board and modify my design. This will save my company money and help me create a more robust part.
By simulating real-world injection molding conditions, SOLIDWORKS Plastics helps designers develop high-quality, manufacturable plastic parts, faster and more efficiently.
Contact your local SOLIDWORKS reseller for a demo or arrange for a trial period so you can take SOLIDWORKS Plastics for a test drive. If you are regularly designing plastic parts, this is a critical tool and a must-have for your design process.
Elise Moss has worked for the past thirty years as a mechanical designer in Silicon Valley, primarily creating sheet metal designs. She has written articles for Autodesk’s Toplines magazine, AUGI’s PaperSpace, engineersrule.com, DigitalCAD.com and Tenlinks.com. She is President of Moss Designs, creating custom applications and designs for corporate clients. She has taught CAD classes at DeAnza College, Silicon Valley College, and for Autodesk resellers. She teaches CAD at Laney College in Oakland and Santa Clara University in Santa Clara. She holds a BS in Mechanical Engineering from San Jose State University.