Automotive 'Oscar' goes to two-color IP

To get more than one color in this massive automotive part, collaborators found the answer in two-shot—simultaneous, not sequential.

Molded-in-color instrument panels are becoming more prevalent in the automotive market, but until recently, these large structural parts were molded in a single color. To achieve a two-tone look, painting was the only option.

The landscape has changed, thanks to a collaborative design process between Ford, Tier One supplier Visteon, material supplier Advanced Composites, machinery manufacturer Husky, moldmaker Lamko Tool & Mold, and hot runner supplier Synventive Molding Solutions. Together, this team produced a two-color IP without paint in a concept-to-production time of less than six months, while at the same time developing a simultaneous shot process that reduces costs. Not surprisingly, SPE’s Automotive Div. acknowledged this application as the Process/Enabling Technology winner in its 34th annual Innovation Awards program (a.k.a. the Automotive Oscars) held in Livonia, MI last month.

As is more common today, design innovation often requires an eye toward manufacturability. This achievement is not only a design first, but also a lesson in the integrated approach. Designers worked together with processing engineers and equipment suppliers to make their vision happen.

Two-shot Kept Simple

Robert Stammler, engineering manager at Visteon’s Saline, MI plant, explains how the concept of a simultaneous two-shot process was born. "We wanted to be able to produce a two-color IP that didn’t require paint, but doing so with traditional two-shot tooling would have been cost prohibitive. By simplifying the process and the tool, we were able to shoot both materials at about the same time without any rotating mechanisms or complicated cores. In addition, there was minimal risk to our OEM customer, Ford, because even if the process didn’t work, we could still produce a one-color IP in the same tool and paint it."The process did work, and produced good parts off the tool by the seventh shot, a direct result of close collaboration. Trials were conducted at Husky’s Detroit Technical Center, where Husky provided a two-shot press, its QD1650, an 1800-ton QuadLoc dual-material machine. Because the tool was simplified compared to a traditional two-shot mold, the part could be fabricated on a press that was about half the tonnage and 3.5 times less costly than a traditional approach.

The tool itself contains no rotating mechanisms or complicated cores, and costs roughly 50% less than a comparable two-shot tool with two cavities and two cores. What’s more, Stammler says that cycle times are 10% to 15% less than sequential two-shot, and scrap rates are significantly lower. "We’ve been in production since September, and the only scrap occurs when we change color. Even then, it’s minimal."

The Secret to Less Scrap, Lower Emissions

In effect, two colors are injected into the mold at nearly the same time so that both materials reach the end of fill at exactly the same time. Flow fronts are controlled by opening and closing valve gates based on screw position feedback from each injection unit using Husky’s Polaris controls. Rather than trying to achieve a clean line between the two colors, uneven knitlines are placed in areas that will eventually be covered by finish panels on the final IP.

Advanced Composites compounds the 20% talc-filled TPO material for high scratch resistance, low gloss, and a Class A surface. According to Rob Morgan, a general manager, this grade has been on the market for about five years, and 15 of the 18 molded-in-color IPs now on vehicles use it. "About 4 million vehicles of the 16 million made in the U.S. annually contain one of our TPO materials," says Morgan. Visteon’s prior experience with the material bolstered the choice, along with the material’s reputation for resisting scratches.To predict how the two TPO shots would flow, and how (and when) those flow fronts would meet within the mold, Visteon used Moldflow MPI software as a base, and then adapted the simulation for its simultaneous injection process. Stammler adds that having the software in-house has helped Visteon’s designers to create more accurate simulations, and has also given them enough knowledge to perform this kind of adaptation.

Cost reductions over a painted two-tone version begin with less scrap and eliminating a secondary operation, bringing a direct labor savings of 12.9% per IP. Indirectly, Visteon estimates saving about $240,000 a year on related labor costs. Bypassing the paint operation also wipes out 3.6 tons of VOC emissions annually.