Faster cycle times and consistent, repeatable part quality are the keys to successful injection molding, said speakers at a technical seminar at Arburg Inc.'s technology center in Elgin.
“Cycle time, lower part cost keeps you ahead of the competition,” said Martin Neff, Arburg's Midwest sales and engineering manager.
About 130 people attended the seminar, held Nov. 9. Other speakers addressed scientific molding, hot runners, multishot cube molds and in-mold sensors.
Neff said the injection molding machine has become the central controller of quality.
“Each machine nowadays has a lot of monitoring functions already incorporated,” said Neff. “The press controls all auxiliary machines, robots and functions such as temperature control. So I have a real quality-control system and I do real quality control at the press.”
Neff, who works out of the Elgin facility, also outlined machinery drive technology, from hydraulic to hybrid to all-electric. There is no single best solution, he said: “You need to look at your part family before you decide.”
Arburg can build modular machines, where the customer chooses which type of power to run each function.
Arburg ran two all-electric injection presses at the seminar. An Allrounder Edrive, with 110 tons of clamping force, molded medical syringe barrels on an eight-second cycle using an edge-gated Heitec hot runner. Arburg has positioned the Edrive as an entry-level all-electric.
The other press, a 110-ton Alldrive, was molding medical fittings from liquid silicone rubber, using an Elmet mold and LSR dosing system. Cycle time for the four-cavity mold: 28 seconds.
Susan Montgomery, president of Priamus System Technologies LLC, detailed the Brunswick, Ohio, company's Fillcontrol platform that makes sure the mold is completely filled with plastic, and the related BlueLine hardware. Fillcontrol is a new modular concept with four modules, using mold-cavity pressure and temperature sensors to measure viscosity, fill time, shear stress of the melt, and part compression and shrinkage.
One key function is to detect the melt front from the mold-fill stage to pack and hold. The system also can do sequential control of valve gates.
“The nice thing about these systems is they are machine-independent,” Montgomery said, adding that this means Fillcontrol can be used on presses in far-flung global factories. “We are looking at long-term part consistency,” she said.
John Bozzelli delivered a rousing, riff-laden talk on making identical parts out of multicavity molds. He got into how plastic flows, as the polymer molecules slide past each other under pressure from the press. Viscosity is very much impacted by shear rate, he said, and that means changing pressure — not temperature — is the way to change viscosity.
Bozzelli is CEO of Injection Molding Solutions in Midland, Mich.
Arburg seminar attendees got a grounding in multishot turning-cube molds from David Nolan, North American sales manager for German toolmaker Foboha GmbH. Cube molds can run parts with two or more materials and do in-mold assembly.
Nolan showed videos of 180-degree stack turning molds, a 90-degree turning cube and other layouts.
Because the tool has more than one mold face and injection units, you can pump out large-cavitation multicomponent parts on a smaller press than would normally be needed.
“There's some incredible potential for volumes with this process,” he said.
On the hot-runner front, smaller sizes, engineering resins and difficult gate locations are a challenge, said Paul Boettger of Technoject Machinery Corp., which represents Heitec hot runners from Germany.
Historically, it was tough to make a hot runner to handle tiny parts of less than 5 grams, Boettger said. But now they can handle parts less than a single gram.
“These parts are becoming more and more difficult to direct gate,” he said.
That puts a challenge on hot-runner makers to develop shorter nozzles with smaller nozzle spacing. Using a flat nozzle, Heitec can do minimal nozzle spacing of 4.5 millimeters, suitable for parts that weigh less than 1 gram. He showed a slide of a mold for toothpicks.
Deciding where to locate the gate is important, to hide the gate vestige, Boettger said.