Recently, there was an extended discussion on a Linkedin Group—Plastic Injection Molding—on the value of the various material flow/mold filling analysis software such as Moldflow, MoldEx 3D, Sigmasoft, and Cimetron. Those participating in the conversation noted the greater accuracy of these software programs, but at the same time emphasized the need of operators of these software programs to analyze and understand the data.
Peter Van Damme, managing director for PVD Engineering (www.pvd-engineering.be) in Belgium, noted, “Most [material flow] simulation software is capable of calculating in a very accurate way. The only problem is that the operator must really understand plastics product design, mould design and what happens in production,” he wrote. “If the operator doesn’t have these skills then you get only nice pictures, which everybody can make when he knows how to work with the software.”
Another person in the group wrote: “The skill is understanding and interpreting the results, similar to a doctor checking an x-ray. We can quite quickly train an engineer to be competent at using the software but it takes much longer to build up an understanding of the results.”
Others in the conversation noted the “garbage in, garbage out” scenario, noting that most of these software packages are “quite accurate providing you use the correct material grade and do not use generic materials,” wrote Gary Blenkinsop, a manager at a major OEM in the UK. “Warpage analysis is much more accurate if you model in the 3D mould cooling circuits.”
As moldmakers tend to be reluctant adopters of some types of technology—specifically mold filling software—many have failed to see the value in these engineering tools. John Linder, a third-generation moldmaker and director of engineering for Chemtech Plastics (www.chemtechplastics.com) in Elgin, IL, agreed to an interview with PlasticsToday on this topic, using his 40 years' experience to explain the benefits of mold filling simulation to the moldmaking community. Chemtech uses MoldEx 3D simulation software.
One barrier for many mold manufacturing companies investing in mold filling software is that it requires someone with the know-how to interpret the results of the analysis. It doesn’t always have to be someone with knowledge of mold design and molding. Linder pointed out that he worked for an OEM during his career, and they had an analyst that didn’t know moldmaking or mold design, but could have written the code book for the software.
“Back then we worked with parts that had no uniform wall thicknesses so there was no nominal wall and the analysts had to mesh the model so the software could run the analysis,” explained Linder. “If the model wasn’t meshed well or wasn’t a good model, or they selected the wrong value for the nominal wall, you got less than valid information.”
Today, however, Linder said that the mold filling software takes the 3D model and preforms the meshing. “The software can look at varying wall thickness and run the analysis,” he said. “The results are more accurate and faster. Our guy only spends a half-hour to an hour setting up the simulation. If you have a good model, you’ll get good information. Then you need someone who understands how the software works to interpret that information correctly.”
Another obstacle for mold manufacturers is the cost of the initial investment in the mold filling simulation software. “To get a good package you’ll spend 25 to 30 grand – cost is part of it, but the other part is they don’t see the value in it,” Linder said. “They’re all quick to go out and buy new high-speed fancy toys equipment to create a high-horsepower system, but they can’t design fast enough to keep all the equipment busy because they don’t have enough people, and they’re not willing to make the investment because typically there’s no return to the moldmaker. The captive molders are the ones that will most likely embrace the benefits of mold simulation. Here at Chemtech, while we’re a custom molder, we start everything from the standpoint of the mold filling analysis.”
Linder gave one example of a simulation used to design and develop a three-plate mold with for a part with multiple living hinges. The simulation helped Linder to control when and where the plastic flowed into and across the hinges. “We have virtually simulated a valve gate hot runner manifold with various gate closing times,” he added. “In some cases more than 10 simulations were required before the optimum gate locations could be determined.”
Linder explained that being able to accurately predict warpage conditions can be a major benefit to moldmakers, both in terms of being able to modify the mold (windage) in advance so that the plastic warps to the desired shape and size, and being able to share the warpage prediction with the customer so that product design changes can be considered if critical dimensions are identified as a high-level risk.
“You used to be able to reason with the product engineer and could talk your way out of warpage,” said Linder, “and you’d give them a long list of deviation requests and they’d relent. Today they won’t do that. Today it’s, 'Here’s the drawing, make it to print." You’ve got to figure out warpage up front or you’ll be making tools multiple times.”
Linder understands the value of knowing molding processing when designing a mold, and the benefits that value engineering using mold filling software provides.
“However,” he noted, “buying mold filling software is almost counter-productive to the moldmaker. It’s an investment they don’t get a lot of return on unless they’re held responsible by their customers for warpage, shrinkage, etc. Too often, the sum total for a moldmaker when bidding a job is ‘how low can you go?’ Then it takes a savvy sales person to sell the customer on value vs. price.”
