Akron, Ohio — Micromolding of LSR parts is a challenge, speakers from Kipe Molds Inc. and Starlim North America Corp., told attendees at the International Silicone Conference.
Starlim, a major LSR molder, uses heavily modified Engel LSR injection presses for its molding, according to John Timmerman, vice president of marketing and sales at Starlim North America in London, Ontario.
For micromolding, the company uses an all-electric press with a clamping force of 10 tons. Timmerman said the machine was designed for micromolding of LSR including two-component molding of thermoplastics and LSR, or two LSR materials. The maximum pellet size is 2 to 4 millimeters, which qualify as micropellets, he said.
Most of Starlim's existing molds are made by EDM, but the company had to come up with a new way to cut the micromolds, Timmerman said. The mold base was the only thing that did not change.
“That was quite an education for ourselves,” he said.
Micromolding is a world apart. He said Starlim uses CT scan technology to see the interior of the parts. And they are tiny. Timmerman showed a slide of two-component micro part smaller than the size of a penny, with tiny holes.
But Starlim set the bar high.
“Our goal with this and the reason it took us so long — seven years — was to have a fully automatic, fully flashless production, without the need for full inspection,” Timmerman said.
Dana King, director of business development for Kipe Molds in Placentia, Calif., said LSR micromolding magnifies issues like material compressibility, mixing and changes in viscosity and flow rate from shear. Pot life is a major issue for very small parts, because you will have more material waiting to be molded than with regular-sized parts, he said.
King said that Kipe Molds and a customer developed the MicroDeck, and Kipe Molds holds a license to manufacture it. The goal: create micro parts, weighing a thousandth of a gram, without having a substantial runner, and with no flash.
He said the MicroDeck uses a servo-actuated plunger instead of a standard micro-screw, in a first-in, first-out process, with a premixed material cartridge.