Virtual injection molding part III: Using simulation software to find the processing window

When moldmakers commit the mold to steel without any idea of the processing window it can create a big problem, according to Matt Proske, applications manager for Sigma Plastic Services Inc. When a tool shop does consider the processing window, it’s called building a mold “steel safe,” and Proske said that a “cultural change will have to occur in this industry” in order to reduce the time is takes to qualify a mold. “The tool maker builds a tool and the molder takes three months to find a process window,” he said. “With Sigmasoft, we do the mold design and process development prior to the mold build.”
 
Typically, there’s been reluctance on the part of mold manufacturers to invest in technology outside the realm of actual moldmaking, i.e. high-speed machines, mold design software, etc. Many entrepreneurial companies have given up on trying to sell to the moldmakers, and instead go straight to the OEMs. After seeing the benefits of a new technology, often the OEM will persuade the moldmaker or molder to implement the technology.

Getting moldmakers to understand the value of Sigmasoft process simulation software requires getting them to understand how long it takes to get a new mold into production and get parts that are production quality. “How would your life be different if you already knew what the process is and would that make a difference in your business?” Proske asks moldmakers. “Understanding the mold and the process is critical because they are married. If the mold is developed with a wide processing window, you can’t make good parts. If you have the process window dialed in before you start the mold, you will understand how the mold will behave in the actual molding process. Then all you need to do is repeat that simulation. Your understanding of the mold before you put it into the molding machine will save time in validating a medical process, for example.”

Shorter trial time, faster cycles
Simulation can be used to shorten trial and error time, but that is just one aspect of the Sigmasoft simulation program. It can be used to shorten cycle time as well.  “All molders do is rent time on their molding machine,” said Christof Heisser, president of Sigma Plastic Services. “Another aspect of utilizing simulation is that if you optimize productivity, you’ll use less material in the runner, less energy, have less environmental impact and can justify the cost of the software.”

In an ideal world, the part designer asks ‘how do I have to make this?’ and gets the moldmaker involved in a way that’s cost effective, and they talk to the molder about equipment, Heisser explained. “We have three cubicles, and they always throw things over the wall to the next guy. The design guy doesn’t consider the process; the moldmaker might have some consideration for the process. With Sigmasoft mold process simulation, even before they have a real mold, the molder can tell us if this mold will work. It becomes a good communication tool to prove a feature such as wall thickness. You have never found this out through a designer alone. We have to make sure all three of these parties understand, a) process simulation is possible for the moldmaker and designer, and b) stay in touch with the designer.”

Turning dials vs. adhering to process
Simulation software can be used as a communications tool between the mold design engineer and the processor to convey information such as the ideal processing temperature of the mold. “If you convey this with pictures – such as if you do this, that will happen with respect to injection speeds, temperature, you’ll get better results,” noted Heisser. “I have molders tell me, ‘I can’t control what my operator does, so when things go outside the parameters they turn dials.’ Internal communication can clarify the process.”
 
MGS’s Klotz agreed. “We make fewer iterations when qualifying a mold,” he said. “You can establish the process window, but I would argue that we’re still in an era when the old guard processing technicians – the non-scientific guys – are not convinced with regard to simulation data analysis. It’s important that the knob-turners understand this new technology. Simulation gives you a starting point that could very well be closer to your starting point than you would have been without simulation. And it saves you money, but you can’t apply a monetary value to that. If we give you a starting point and you do one or two sampling runs rather than four or five, you don’t actually know how much money you’ve saved.”
 
Simulation software can also be used for customer communication. “The moldmaker can provide suggestions prior to cutting mold steel ‘If you can change the design a bit here, you’ll have better cycle time and reduce the price’ for example,” Heisser said.  “You can also take that a step further – if the moldmaker uses the process simulation software, and the moldmaker’s competition doesn’t, it can be a competitive edge.”
 
Klotz began a review of simulation software several years ago and found that Sigmasoft has done a good job in the area of helping moldmakers determine first, whether a mold-specific feature is viable, and provides a basis for confirming that to the customer. “Secondly, where there are violations of the part design, but the customer has to have it that way, we can use our simulation analysis to back up why we think there will be a problem,” said Klotz. “If they won’t budge and down the road there’s a problem, we know who will foot the bill for the engineering change.”

From a business standpoint, John Berg, director of marketing for MGS, said that the company’s recent investment in Sigmasoft is “one of many investments we have been making in new technologies which also includes 5-axis machining, path verification, and automation among others.”
 
SIGMA’s Proske sees those types of investments as a necessity in today’s plastics processing community. “You can either change or close up shop. People who care and want to make money, and want to sustain their business, wouldn’t hesitate to invest in new technology,” he said. “[Moldmaking] is a very traditional industry and very conservative. But Sigmasoft could be a true game changer. The moldmakers will eventually forced into it by competitors or customers, then it becomes a true business tool.”

MGS Manufacturing Group likes the results Sigmasoft provides, and recently purchased that software. However, according to Kevin Klotz, simulation engineer for MGS, simulation software has evolved technically over the past two decades to provide a greater level of understanding the implications of mold design and processing aspects.

“Simulation software can be a key component in mold design and build, however that’s relatively new for most mold shops,” Klotz said. “Simulation software is making headway into that area from my experience most of the simulation software hasn’t been perfected to the point that mold makers are comfortable with it. Moldmakers are a unique bunch – they’re perfectionists and the software isn’t perfect. Many assumptions must be made, the data analyzed and decisions made based on the analysis.”

MGS also uses simulation to help it determine if a specific mold design will have the ability to meet the customer’s desired cycle time. “A lot of upfront issues don’t reveal themselves until the mold is done,” Klotz noted. “If you don’t understand the goals of the customer, such as their cycle-time requirements, you might not make the right decisions regarding things such as core/cavity configuration, which mold steels to use and where to put the necessary water for optimum processing. In one instance, we were able to get the cycle time on a multi-cavity mold for a medical device customer down to 9 seconds from 14 seconds just by knowing that each cavity needed a needle bubbler to get a trickle of water to the core. In that case, we were successful because we ran simulation on that tool as part of the mold design process. However, we don’t want to put extensive materials into the mold if we don’t have to. The goal is to spend our dollars and resources wisely, and that’s where simulation plays a part.”

While simulation is critical to mold design, Klotz said that it isn’t necessary to perform simulation and analysis on every mold the company builds. “Some parts are basic, and we can’t perform simulation on those types of straightforward molds due to financial constraints,” he said. “We look at the part and then apply simulation and analysis where it’s necessary and where the most benefit will be derived. There’s also time constraints on some molds in that the time line just doesn’t allow for all the ‘what if’ scenarios to be performed.”

Ultimately, said Klotz, the analyst is the most critical part of the software simulation process. “Customers often come to us and says ‘let’s try this’ or ‘what if we do that?’ and we run a number of scenarios that result in a lot of data that then has to be analyzed to make sure that it’s all interpreted correctly,” he added. “What is the data telling you and how does it apply to your application?”

Sigma’s Proske said that simulation is the one thing that can impact all areas of mold manufacturing and molding process development, which makes it a valuable tool. “You can become a change agent – that’s scary but start small and grow it,” he said. “People totally underestimate what they can do with mold simulation. If you implement it correctly, you can make money in every aspect of your business, and we have hard numbers to prove this for you.”