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Predicting Injection Pressure with SolidWorks Plastics

Ricky Huynh

By Chris Ma

Recently, I was able to attend a 2 day plastics seminar at California State University, Chico that covered the chemistry of different plastics, how plastics are used for different applications, and how to use an injection molding machine. With the addition of SolidWorks Plastics in our analysis arsenal, the class was a great way to get exposure to the type of training that those in the mold industry get. But by far, the best part was actually getting to use the injection molding machine.

On day 2, the instructors gave me some basic instruction on how to operate the machine and then let me loose. After several tries and almost blowing up a machine when I hit the max injection pressure of 50MPa, I got a plastic part I could take home (fig. 1).

                                          Predicting Injection Pressure: Finished Part

Figure 1. My Finished Part

You might notice some flashing around the runners in figure 1. Flashing is when plastic flows out of its intended channel and in between the two halves of the mold. The instructors told me this happens when a mold doesn’t seal due to insufficient clamping force in the machine, or due to excessive wear of the mold halves. Turns out in this case it was a combination of both.

Back in the office the next week we got to talking about the class and how we could integrate SolidWorks Plastics into the curriculum. The most obvious way that we came up was being able to help students visualize how the plastic would flow in the mold and how to predict the injection pressure before actually running the machine. (And to prevent blowing up the machine like I almost did.)

To do this, we built a SolidWorks model (fig. 2) that matched the part we molded and using SolidWorks Plastics Advanced 2014, set up an analysis with the same parameters used in my first molding attempt:

  • Material = High Density Polyethylene (HDPE)
  • Fill time = 30 s
  • Mold Temperature = 58 °C
  • Melt Temperature = 230 °C
  • Injection Pressure Limit = 55 MPa (Assumed that there is a small margin of safety in the machine)

                                                      Predicting Injection Pressure - Figure 2. SolidWorks Model of Sample Part

 Figure 2. SolidWorks Model of Sample Part

The results from the analysis were spot-on. The software reported a maximum injection pressure of 50 MPa (fig. 3) which is almost exactly what we saw in the lab and noted some additional considerations which we also experienced:

  • I may have some problems filling this part because I was so close to the injection pressure limit.
  • The clamping force required to keep the mold halves was close to the clamping force limit which could lead to the flashing. (Again another thing that we saw in the physical test.)

                                                  Predicting Injection Pressure - Pressure Plot in SolidWorks Plastics

 Figure 3. Pressure Plot in SolidWorks Plastics

I would like to thank Professors Joe Greene and Daren Otten at Cal State Chico for giving us the opportunity to take their Introduction to Plastics seminar and use their state-of-the art plastics lab. If you are interested in learning more about plastics and the plastics industry in their 2 day seminar, you can contact Joe Greene by email at jpgreene@csuchico.edu or Daren Otten at dmotten@csuchico.edu.

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