Injection molding is about to become a whole lot more fashionable, thanks to a new system that can incorporate real fabrics into molded electronics enclosures. Developed by Dow Plastics Inclosia Solutions, the system could dramatically change the look and feel of everyday consumer electronics. Imagine blue-suede cell phones, denim-covered PDAs, or leopard-skin MP3 players. "The choices are limited only by the designer's imagination and the consumer's desires," says Inclosia business development manager Tom Tarnowski.
Designed to support high-volume production, the EXO Overmolding System combines aspects of in-mold-decorating (IMD) and two-shot injection molding. The process starts with the robotic placement of pre-cut fabric in a two-shot injection mold. Once the molding starts, the first shot covers the back of the fabric with a thermoplastic substrate, which also forms the enclosure's structural wall. The second shot then encapsulates the edges of the back-molded fabric. Tarnowski notes that the fabric stays on the outside of the enclosure, so there are no issues with EMI shielding. And the method works with all the engineering thermoplastics and elastomers normally used for enclosures—including polycarbonate, PC/ABS, and thermoplastic urethanes.
Inclosia certainly isn't the only practitioner of either IMD or two-shot molding. "Both technologies are well-known," Tarnowski acknowledges. But EXO does break some new ground. For example, the system operates at the high-injection pressures needed to fill thinwall parts—sometimes in excess of 20,000 psi. Earlier methods for incorporating in-mold textiles, such as the back-molding process used for large automotive interior parts, require elaborate steps to lessen molding pressures so as not to crush or shoot through the textile. "We've done a lot of work to understand how to avoid damaging the fabric at high pressures, "Tarnowski says. Inclosia engineers have also figured out a way to keep the plastic melt from the second shot from working its way between the fabric and the substrate applied during the first shot, he adds.
And unlike IMD methods that try to mimic fabric, EXO doesn't require specialized flocked films. Ashe breaks out a thick book of swatches, Tarnowski reports that EXO works with a huge variety of standard fabrics—everything from animal prints to the rugged textiles used for automotive seating. It also can handle leather and vinyl. "Most covering materials bond well to the thermoplastics used in electronic enclosures," Tarnowski points out. For those materials that don't stick, Dow has developed non-woven backing material that can promote adhesion—or, in some cases, protect more delicate fabrics from the injected plastic.
EXO offers a wide range of design possibilities. Tarnowski lugs around a large case filled with prototype phones, PDAs, and notebook computers. Taken together, they show EXO's ability to accommodate all sorts of form factors and part features. The prototypes also illustrate how the process can combine fabrics with both rigid and flexible thermoplastics. This capability can be found on the first commercial EXO product—a thermoplastic, elastomer, and synthetic leather case for Hewlett-Packard PDAs.
Expect EXO parts to cost more than their unswaddled plastic counterparts. Tarnowski describes the cost of the new process as "IMD plus two-shot-molding." And then there's the cost of the fabrics, which tend to be sold by the yard rather than the pound. "Fabric isn't cheap, but the cost is only moderately above printed graphics," Tarnowski says. Anyway, extra investment in enclosures promises to buy something of increasing value: attention in the crowded electronics marketplace. With more and more electronic products failing to stand out based on functionality alone, the look and feel of their housings matters more than ever. "Enclosures have become an important way to differentiate and brand electronics products," says Tarnowski.
The EXO Overmolding System is available only on enclosures produced by Inclosia, whose manufacturing partners operate molding and assembly facilities in North America, Europe, and Asia.