How You Can Predict Manufacturing Defects in Injection Molding

Shawn Wasserman (SW): Hi, this is Shawn Wasserman, Simulation Editor of Engineering.com. I'm here with Peter Rucinsky at SolidWorks World in Phoenix, Arizona. First off, could you just tell us a little bit about SolidWorks World, and how SolidWorks Plastics falls into it?

Peter Rucinsky (PR): We have a very large presence with plastics this year at the show, somewhere on the order of about 10 different presentations that are focused on SolidWorks Plastics, from hands-on training sessions, to sessions that help you learn the basics of SolidWorks Plastics, to sessions that take you into very in-depth detail demonstrations of some quite advanced functionality of the product.

SW: You mentioned the release of SolidWorks Plastics 2015 recently. Could you explain to me your favorite benefits?

PR: We came up with a number of new features and enhancements in Plastics 2015. 

One of the first ones I'd like to talk about is eDrawings support. This is the platform that's used to communicate design information or simulation results. You can run a simulation in SolidWorks Plastics and dump some of those results to eDrawings and make them freely shared among colleagues or key members of the plastics design to manufacturing team. 

Another one of my really favorite features, it's called the Nominal Wall Thickness Advisor. The cardinal rule that you want to follow in the design of an injection molded plastic part is to maintain uniform wall thickness. Meaning, you don't want to have sections of your part that are too thin, you don't want to have sections of your part that are too thick. 

We incorporated a tool into Plastics 2015 which allows a user to identify their average nominal wall thickness and then find areas that might cause problems because of the fact that they're too thin or they're too thick. We give our users a very simple traffic light plot to do that. Green is good; yellow, proceed with caution; red, probably not a good thing, meaning you might want to go back and make some design changes to eliminate those red areas.

We have three basic flavors of SolidWorks Plastics. Plastics Standard, Plastics Professional and Plastics Premium. The breakdown between those three packages is the amount of functionality available. Plastics Standard, we target specifically at plastics part designers. If we talk about Professional and Premium, that's when you get into some of the advanced mold design technology as well as the advanced cooling and warpage technology. 

In general, your average plastics part designer doesn't really need to go that deep into a simulation. There's a lot of tools that we have in Plastics Standard that are geared towards the plastics part designer, which basically gives them a thumbs up or a thumbs down on whether or not they're heading in the right direction for their fundamental design. 

SW: Could you run through the process of a typical filling analysis?

PR: There's four basic phases of the injection molding process, what we call filling, packing, cooling and shrinkage, or warpage. The first thing that I would do as a designer is run a basic filling analysis. This answers the question, "Will my part fill?" 

If my part will fill, the second question we might want to answer is, "Are there going to be any problems?" For example, something like weld lines or air traps. So that gives a designer some pretty important information upfront on whether or not their part will be easily manufacturable. If it is, great, they can move on to the next step; if it's not, they can make some design changes to try to improve manufacturability. 

The second phase of the process is what we call the packing phase, and that's where we pack enough plastic into the injection mold cavity to compensate for the shrinkage that occurs after the cavity is filled with plastic. This just provides a deeper level of detail into what happens during the process. After the part is packed out, we go into the cooling phase -- so every injection mold has some type of cooling system built into it -- and it's actually the longest phase of the process. It's very important to analyze that phase to determine whether or not, for example, a poor cooling line design might cause some part warpage problems down the road. 

Once we've optimized the cooling system design, we go into predicting whether or not the molded part will warp, which is a very common problem with injection molded plastic parts. If the part warps, we can identify the causes of that part warpage; again, make some design changes to try to alleviate those problems; run another simulation and see what happens. 

So that's the basic process. We run filling, packing, cooling, and warpage and by doing that, when you actually cut your tools to make your mold, you can be certain that when you put the mold in the machine, it will work right the first time. That's really the ultimate goal of running the SolidWorks Plastics simulations.