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Pennsylvania conference takes deep dive into technical aspects of molding

Bill Bregar | PLASTICS NEWS

A plastics technical conference at the Pennsylvania State University campus in the city of Eric had a little bit of something for everyone, from tool design and hot runners to molding technology.

Doug Espinoza, manager of RJG Inc.'s TZero program, for example, explained how the consulting company helps link engineering and production to create a tool launch that's right the first time -- by spending time and effort before cutting steel. He advised molders to document and validate the processes involved in molding a part.

"Half the battle is knowing what is happening in the mold," he said.

People in manufacturing these days know to avoid setting up silos of work functions, where departments toss projects over the wall. But Espinosa said TZero uses a documented, organized plan to foster communication when designing an injection mold.

Training and education are the keys, and the missing links at many companies, he said, displaying detailed flow charts to track progress and encourage teamwork.

"Get out there, get folks together and do some problem-solving," he said.

TZero helps design experiments to go through a list of hypotheses. "We can be on the plant floor for two weeks, getting people out of problems," Espinoza said.

TZero uses molding simulation, as RJG is licensed to use Sigmasoft, Moldex3D and Autodesk Moldflow Insight. Espinoza reviewed part design and mold design, where he said "cooling is a big factor."

Measuring machine performance is very important and can sometimes give simulation a bad rap, he said. TZero experts prefer to get real data.

"Don't just use the machine spec and its inputs. You have to have actual machine inputs," Espinoza said.

And changes in resin viscosity can impact part quality, which is why he recommends monitoring the history of mold cavity pressure, using's RJG's Decoupled II and Decoupled III processes.

Hot runners
The Innovation and Emerging Technologies Conference, which attracted 185 attendees for 30 presentations, included two speakers discussing hot runner control.

Marcel Fenner, technical manager and president of Priamus System Technologies LLC, said balancing of high-cavitation molds is necessary to prevent uneven filling. Reasons for variations include different positions of the thermocouples and other factors.

"The biggest one is variation in the viscosity of the resin," he said.

Priamus, working with Synventive -- its sister company under Barnes Group Inc. -- has developed technology that electronically handles hot runner tip temperatures. Fenner said that gives precise part length and part weight in multicavity molds -- even in family molds, which are inherently unbalanced.

Shear rate differences created in a hot runner system often are the cause of blow imbalances related to changes in viscosity, said Eric Gerber, an engineer at Sigma Plastic Services Inc. in Schaumburg, Ill. Other factors that affect melt flow rate include flow length, pressure within the mold cavity and temperature in the mold or the hot runner manifold.

Paul Maguire, president and CEO of Riverdale Global in Aston, Pa., said that liquid color gives 100 percent color distribution in the melt. He outlined Riverdale's RGInfinity system that automatically refills the color container when the fluid level is low.

Maguire also described a system where processors can refill their own drums and custom-mix color in-house, which he joked is the "Home Depot method."

Injection/compression
Trevor Pruden, technical and engineering manager at Arburg Inc. in Rocky Hill, Conn., said injection/compression molding -- or "coining" -- molds parts with low physical stresses that are constant through the entire part. Coining can prevent sink marks and minimize warpage and can be used with a wide variety of materials, such as thermoplastics, powder injection molding and liquid silicone rubber, he said.

That makes coining a good way to make some types of parts, such as LED optical lenses and semi-crystalline polymers, he said.

Dan Spohr, of Wittmann Battenfeld Inc. in Torrington, Conn., said it's a good idea to replace older robots with new ones that can perform movements in parallel with injection press functions. For instance, an old robot may need to make separate judgments to be sure the part is located on the end-of-arm tooling, then remove the part from the molding area, and finally OK'ing the machine to close again, can consume three seconds in those tasks. "A new robot can be less than one second," he said.

"This is where molders make their money. You want that mold-open time to be as short as possible," he said.

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