SIMULATING INJECTION MOLDING

Proper planning ensures strength and performance.

by Benny Foreman and Bruce Sumpter

BENNY: Hey, Bruce — I’ve been thinking about this whole visualization thing and ...

BRUCE: Whew … That’s a relief! I know you had your heart set on that bright red motorcycle you were ‘visualizing’ last time, and I’ve been trying to come up with a way to break it to you that …

BENNY: Not that kind of visualization, Bruce. In the last issue of Solutions, we talked about using Pro/E®’s visualization tools to create virtual prototypes. Well, I was thinking about how working with plastics can get pretty complex. So this time, I thought our readers might be interested in hearing more about some of the other tools we use, like Moldflow Plastics Advisers®.

BRUCE: That’s a great idea.Where Pro/ENGINEER’s visualization tools focus on the design of a part or assembly, Moldflow extends visualization and virtual prototyping to the actual material being used.

BENNY: And with so many advances in plastics, and more and more metal-to-plastic conversions, it’s a timely discussion.

BRUCE: True. Today, plastic is used in some pretty demanding applications, and the advantages are huge. Compared to metal, plastic is lightweight, can provide nearly the same structural strength and increased design options, can eliminate secondary operations like painting or welding, has greater resistance to chemicals, is quieter and can yield improved speed-tomarket. It’s a beautiful thing!

CHOOSING THE RIGHT GATE LOCATION: Gate Location
Analysis ranks areas by color and number, and pinpoints
potential problem locations.

WATCHING FOR PRESSURE DROP: Identifying areas with
large pressure or temperature gradients shows which areas
are likely to cause problems in molding.

BENNY: But with all the advantages of plastics, there is also a lot to consider. For starters, what should the GATE configuration be, and where should it be located? What is the FILL PATTERN? What about PRESSURE and TEMPERATURE DISTRIBUTION? What can we do to ensure the integrity of any WELD LINES, and minimize or eliminate MELD LINES? What’s the WALL THICKNESS at critical stress points? How quickly does the plastic COOL? What about SHRINKAGE? How can we eliminate WARPING? What’s the risk for AIR TRAPS and SINK MARKS? Most importantly, what impact do all of these issues have on the STRENGTH and PERFORMANCE of the part or assembly?

BRUCE: I’m exhausted just thinking about it. But you’re absolutely right. Plastics are the material of choice for more and more applications, and ensuring the best possible results means addressing these questions on the front end, before the plastic gets poured. That’s where visualization and analysis tools like Moldflow come in, right?

BENNY: Right. Of course, the assumption is that Moldflow users, like you and me, are knowledgeable about plastics and understand that balancing the complexities of the material can be sort-of like choreographing and performing a delicate dance.

BRUCE: A delicate dance?

BENNY: You know what I mean — working with plastics takes specialized knowledge. A subtle change to one parameter can dramatically impact another. Fortunately, from chemistry through design and manufacturing, plastics is a core area of expertise for RL Hudson, and that expertise is one of the key benefits we bring to our customers.

BRUCE: Absolutely! And the beauty of Moldflow is that it lets us simulate injection molding in the design phase so we can help ensure efficient and effective manufacturability as well as maximum strength and performance.

BENNY: That’s right. Moldflow’s Part Adviser includes a Material/Process Adviser that can be used to rank potential materials that may be used in manufacturing a part. Once the material has been identified, then Gate Location Analysis identifies the best and worst potential position for the gate, and even provides detailed feedback on why.

BRUCE: Hey, Benny. When we’ve been asked to evaluate parts produced by a competitor because there’s an issue, isn’t it amazing how many times the main culprit has been poor gate location?

BENNY: It sure is. In fact, that’s a great example of where material expertise in plastics really comes into play — at the design stage first, but it has to be present at the mold and manufacturing levels, too. One of the first parts we evaluated using Moldflow was a part that was threaded on the inside, with a flange at its base that was supposed to fit flush against another plate. The flange was warping because the part wasn’t cooling properly. Guess what? The problem was with the gating. When the plastic hit the threads, it raced down one side faster than the other, causing uneven cooling. We redesigned the gate configuration to balance the flow, which balanced the cooling process, which eliminated the warping.

BRUCE: Ahhh. Delicate dance. Well choreographed. Problem solved.

BENNY: Exactly.

BRUCE: The next part of the analysis focuses on Fill Confidence, which analyzes cavity pressures, temperatures and injection short shots, to identify areas where filling problems may occur. Then,using that data,the system generates a Quality Prediction, which can help identify issues that could dramatically reduce strength and performance, or result in outright failure.

BENNY: This is where things like Weld Lines and Air Trap locations can be visualized and evaluated for potential design changes. Moldflow Part Adviser also provides Sink Mark Analysis that can help identify the location and severity of sink marks. Finally, Moldflow’s Cooling Quality Analysis can identify areas where there may be too much heat. In doing so, it gives us the opportunity to improve the design to create better cooling characteristics.

BRUCE: Now, that’s cool!

BENNY: It sure is. Together with the visualization and virtual prototyping power in Pro/E, it’s definitely key to ensuring quality. Adding Moldflow to the process is like putting a part or assembly through a virtual test run. Hey Bruce, speaking of cool stuff and test runs … want to go for a spin on my new motorcycle?

BRUCE: Are you serious?

BENNY: Yep.

BRUCE: Sweet!

If you have questions about Pro/E or any other design engineering topic, please email Benny and Bruce at benny&bruce@rlhudson.com.

Pro/E® and Pro/ENGINEER® are registered trademarks of Parametric Technology Corporation (PTC). Moldflow® and Moldflow Plastics Advisers® are registered trademarks of Moldflow Corporation.

Solutions 1Q08

SIMULATING INJECTION MOLDING

Proper planning ensures strength and performance.