Avoid Molding Mistakes with Injection Molding Simulations

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By: Liz Lipply | September 29, 2016

As a kid I had a toy that purported to answer questions about the future. Wouldn’t it be great if we had a Magic 8 Ball® to answer life’s big questions? Should I marry this person? Should I buy this house? We would be able to make the decisions that get the happiest results.

While this is just a fantasy, when it comes to custom injection molding, actually there is a way to predict the future using plastic injection-molding simulation software. Enter the geometry of the part (via a CAD model), specify parameters such as the type of resin, locations of the feed system and vents, injection pressure and temperature, and then watch what happens. The goal is to anticipate problems via simulation, without incurring the significant cost of creating a mold. When we review the results, we may tweak certain parameters of the molding process and then run the simulation again. By optimizing the tool design, we can improve part quality, shorten cycle times, and above all, avoid the need to rework a mold. If necessary, we work with our customer to modify the design and resin selection to achieve the best results.

Here is a rundown of the useful ways simulation software can improve your design and lower manufacturing costs.

  • Filling animation. The software takes the molding process parameters and the part geometry and applies a computer model that predicts how the resin will flow into the part. The software shows the filling as an animation, so we can see how the part fills with resin over time. The goal is to fill the mold evenly at the same time.



  • Injection pressure. The software predicts the injection pressure at switch over, which is usually 99% of complete fill. Lower pressure is better as it facilitates manufacturing.

  • Cooling time. As the animation continues, we see the part cool. Colors indicate the various temperature ranges. Knowing how the molded part cools is helpful in specifying the packing/pressure hold time and predicting the speed of manufacturing.

  • Temperature at the flow front. As the resin fills the mold, the resin is cooling. You don’t want resin in areas of the mold to cool and harden before the rest of the part is filled, because that could introduce quality issues. The software predicts the temperature drop at the flow front. This type of information helps us strike a balance between fill time, injection pressure and other key process parameters.


  • Weld line formation. Where flow-fronts meet and knit together they form weld lines. Under some circumstances, weld lines may introduce points where stresses can collect, causing a weakness in the part or be a visual concern.
  • Warpage. After the filling simulation is complete, the software shows expected warpage, a common issue of complex part designs. The software gives us the option to exaggerate the warpage for easier understanding of deflection.

There are even more ways to use the software, but I think you get the point. Obviously, simulation software is no child’s toy. It is a powerful tool for reducing cost on your injection molded project. Consider involving a molding expert who can assist you with this type of analysis.  

Using software is only one way to save money on your project. There are several more, explained in our guide, “Seven Ways to Cut Costs on Injection Molded Parts.” Click the button to download your free PDF tip sheet.

Download the Tip Sheet Seven Ways to Cut Costs on Injection Molded Parts

If you’re ready to ask specific questions about your injection molded parts development process, complete a request for quote form. Or, if you prefer, call us at (330) 786-3000 for immediate attention.

(By the way, the lawyers want me to tell you that Magic 8 Ball® is a registered trademark of Mattel. Moldflow® is a trademark of Autodesk, Inc.)

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