Core-back/MuCell pairing adds strength but takes out weight for automakers

Engel's two-platen injection molding machine

Advances in core-back technology are being made to help automakers realize significant weight reductions to improve fuel economy. For example, recent industrial trials announced by Mazda using MuCell have demonstrated the capability to mold parts with weight reductions of up to 30%, and the company announced it will begin using the technology on 2011 model year cars.

In core-back expansion molding, once the foamed resin has filled the mold, the volume of the mold is increased, causing the foam to expand. This results in stiffer plastic parts, with low density and good rigidity, which can be made with less resin. Through a series of industry trials, the combination of these two processes has demonstrated the possibility of redesigning parts in order to achieve dramatic weight savings in structural applications like IP retainers and door panel liners. But Trexel and Engel officials say the process combination is potentially applicable to a wide range of automotive applications.

“When you combine core-back and the MuCell process, you can essentially saturate the polymer with SCF, or gas in its supercritical state, while keeping the mold closed under pressure, and then precisely open the mold to get maximum expansion,” says David Bernstein, president of Trexel. “You get a much thicker part, but one that is much less dense—as much as 75%."

To succeed with core-back, precision molding machine technology is needed. Engel’s duo 1000-ton machine reportedly provides the ability to precisely control both position and clamp force by using its patented design concept for two-platen machines. “We offer the only two-platen injection molding machine that has no contact with the tiebars, allowing frictionless movement to better control speed and precision,” says Steve Braig, president of Engel’s North American operations.

Engel’s duo machines also feature a patented Platen Parallelism Control system. This allows users to control all four corners of the mold’s positioning individually, which, when using the core-back process, allows the tool to be opened for the material expansion part of the process with complete precision. “As a result, we can achieve the necessary precision for running the combined process and achieving dimensionally accurate results,” says Braig.

Bernstein adds, "Core-back technology is being given an entirely new purpose with the MuCell process, and we see a major quality and cost-savings opportunity for our customers.”—[email protected]