Mold making, cooling, gating for LSR discussed

Oak Brook, Ill. — IMTECH attendees got a dose of hard metal at the inaugural IMTECH conference: precision side valve gating, conformal cooling and tooling for liquid silicone rubber.

Donald Hickel, regional sales manager of Männer USA Inc., said valve gating is a high-precision technology, and that added advantages come from side gating.

"The big benefit here is compact mold design," he said.

Männer USA is a unit of Germany-based Otto Männer GmbH, owned by the publicly traded Barnes Group Inc.

Hickel said Männer got into valve gate nozzles to meet customer demand for better high-cavitation molds. The company offers the Edgeline hot runner valve gate nozzle for side injection.

Medical parts like syringes and other applications that can have no outside gate vestige are the most common uses of side valve gating.

Hickel said Edgeline, now in its third generation, "has been used extensively in Europe. And one of my goals is to bring it the United States."

"The whole focus of the Edgeline is to be able to produce higher part density, higher cavitation in certain applications," he said.

Otto Männer makes hot runners, molds and micromolding systems.

The tool design session was Aug. 2 at IMTECH in Oak Brook.

Another speaker, Rick Finnie, president of M.R. Mold & Engineering Corp., a mold maker in Brea, Calif., outlined the challenges of LSR molding.

A big one is flash.

"Silicone flashes so easily that it's very difficult to stop the flash," he said. "It's surprisingly hard to get this [flash] eliminated completely."

LSR processing is the opposite of injection molding, since silicone is kept cool and then cured in a heated tool. And that creates unique problems, like backrind, Finnie said. Backrind is distortion of the parting line, usually from too much heat in the tool and overpacking. It's a gap and a groove in the part — Finnie recalls the Super Balls of his youth, that had that feature around the ball.

Silicone can rip, tear or deform. Parts can be hard to get out of the mold, he said.

Another danger is called air trap, where the air super heats and burns the silicone. "There's so many places that can trap air in a part," Finnie said.

LSR has some advantages over thermoplastics, such as in part design, but the product has to be designed for silicone from the start, Finnie said.

For example, undercuts can be molded in if it's done correctly. Weld lines are not an issue with silicone, he said, since "it bonds back to itself very well."

LSR also replicates the texture of the mold. "We're going to start making a lot of lenses out of silicone rather than PC or acrylic. It's going to become very, very popular, making lenses out of silicone," Finnie said.

Conformal cooling got a workout at IMTECH.

David Baucus, senior product manager at DME, said the unit of Milacron Holdings Corp. looks at the how cooling fits into the total cycle through process control. He discussed DME's TruCool mold inserts, made by direct metal laser melting, a 3D printing process.

"We are going to give complete process window control through thermal control of your entire process," Baucus said.

Conformal cooling uses mold cooling channels that mimic the geometric surfaces of the mold and part. DME designs the mold inserts specifically for each application. Baucus said it can use a variety of 3D metal additives, such as maraging steel, stainless steel, aluminum and beryllium copper.

"Depending on your application, we use the technology that's appropriate to you," he said.

Baucus said conformal cooling can pay for itself, depending on the part, in reduced part costs, faster cycle time, increased part quality and more throughput.

For 3D printing of conformal inserts, Baucus said, DME brings people experienced in molds, many with 20 years of experience. "If you go down the street to a 3D manufacturer, they they do not know what they don't know, basically," he said.

Reiner Westhoff, managing director of the Menden, Germany-based Contura MTC GmbH that makes conformal inserts for molds, also made a presentation at IMTECH.