Rapid manufacturing technologies tend to be focused primarily on making prototype and sometimes production parts. But Linear Mold and Engineering in Livonia, Mich., is one of the first firms in this country to apply “rapid” technologies to making tooling components as well as parts.
This producer of injection molds and prototype tooling has 52 employees and six CNC machines. It also has a custom injection molding business with five presses of 110 to 700 tons.
Linear Mold is now making lifters, slides, slide-assembly components, and “cashew” gates using rapid-tooling technology. The company uses a Direct Metal Laser Sintering (DMLS) process from EOS GmbH of Germany. Linear Mold bought its first DMLS machine two and a half years ago and a second machine in April 2007. “Our primary intent in purchasing the DMLS machine was to sell metal parts to the medical and aerospace industries. But we are finding increasing use for it in our own toolmaking,” says Linear Mold president John Tenbusch. The firm has used the DMLS process to make more than 75 metal inserts for use in epoxy or aluminum injection molds. “We grow all of the mold components using DMLS except the cavity and core blocks,” Tenbusch says.
Linear Mold uses an EOS Eosint DMLS machine that builds up, or “grows,” the piece layer by layer in an additive process. It uses a laser to sinter layers as thin as 0.02 mm of metal powders (stainless steel or a nickel-bronze alloy ) as fine as 20 microns.
DMLS can create features such as holes and threads during the build, eliminating secondary operations such as drilling and tapping. Reaming holes for ejector pins is still required, but DMLS avoids the step of drilling the holes first.
Traditional moldmaking requires EDM for ribs or sharp corners. “Using DMLS inserts with these features grown as part of the insert allows us to cut the cavity and core blocks very quickly,” says Tenbusch. “This is much quicker than cutting ribs or detailed areas.”
The inserts are built to net shape on all sides, thereby reducing secondary CNC machining. “Cashew”-style tunnel-gate inserts can be made in one piece, unlike with standard machining, and internal baffles can be added in hard-to-cool lifters or slides.
“We are achieving significant cost and time savings with DMLS,” says Tenbusch. “It depends on the complexity of the part, but our cost savings average anywhere from 15% to 30% versus EDM. The more EDM operations that a component would require, the greater the savings we gain with DMLS.”
The bigger benefit is the “tremendous” time savings, says Tenbusch. Linear Mold built a four-cavity family mold for an auto headrest guide and button in three weeks. Traditional CNC methods would have taken five weeks. In another job, Linear Mold built a tool with 24 DMLS inserts, 10 of which would have required EDM.