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Pity the poor luxury car owner. Many of the accoutrements that were once reserved for high-priced conveyances have, through better design and more efficient manufacturing processes, made their way down to the masses. Automatic climate control, six-way power seats and even navigation systems can be found on such plebeian rides as Accords and Camrys. Now Visteon has added soft-touch cockpits to the list of down-market luxuries with its new laminate insert molded (LIM) process.
Visteon’s engineers approached the development of the LIM process with several goals in mind: a softer feel than standard hard plastics without the expense and complexity of traditional foam-in-place techniques; parts integration that would enhance fit and finish and reduce squeaks and rattles; utilization of existing equipment (as opposed to shelling out for specialized production machines); and material choice that would allow for easy and complete recycling.
Immaculate Injection. The process begins with the formation of the instrument panel insert: the part that will make up the soft-touch surface. A trilaminate flat sheet stock is used. It consists of (1) a cover skin of thermoplastic olefin (TPO), (2) a 2-mm layer of polypropylene cross-linked foam, and (3) a back skin of polypropylene. This sheet is heated to near its melting point, then vacuum formed into a net shape. The result is trimmed in a robotic cutting cell using high-pressure water, then placed by robot in a horizontal 2500-ton standard-issue injection molding press.
The machine shoots mold-in-color polypropylene underneath the insert which forms hard areas around the glove box door, steering column cover, and center stack and fashions an integrated defroster grill. The design of the valve gating prevents the injected plastic from flowing over the insert and creates sharp definition between the hard and soft areas. Mike Pavlowski, advanced manufacturing engineering manager at Visteon, says, “Most similar processes produce panels that must be trimmed after the injection process, but this process produces a piece that goes right from the molding machine onto a rack and off to assembly.” And because the injected material is completely separate from the insert, a two-tone instrument panel can be produced without installing additional parts.
Material Concerns. Visteon claims that its LIM panels represent the first cost-effective alternative to foam-in-place polyurethane soft touch panels. Pavlowski cites the specially formulated TPO cover skin as one of the keys to the success of the process. Visteon co-developed the skin with ATC Inc. (Nashville, TN) to eliminate deformation of the exterior grain, which is a problem that has plagued TPO use in the past. (Pavlowski says that “some special things” were done to the thermal former to help maintain the grain, but is mum on the proprietary details.) The team also addressed TPO’s less-than-stellar scratch resistance performance by modifying the material to have a higher surface crystallinity, which places it on par with the touchstone for such applications: polycarbonate ABS.
So, why not just use tried-and-true polycarbonate ABS and save development time and money? One answer is recyclability. Because the materials used in the LIM panels are all olefins, they do not have to be separated before recycling. And by eliminating the expensive and time-consuming task of separation, Visteon greatly increases the chances that its panels will eventually be recycled. In fact, the company has developed a closed recycling loop in its plant in Saline, Michigan, that takes 100% of the offal, runner waste and scrap panels from the LIM process and molds it into glove box bins. Another answer is that the higher lubricity of polypropylene helps to reduce the squeaks that are traditional bane of instrument panels. And according to Pavlowski, an added benefit is that the material is highly conducive to vibration welding or the laser scoring that is being increasingly used to accommodate seamless airbags.
LIM in Action. Visteon has been using the LIM process to mass produce instrument panels for the Mazda Tribute SUV at its Saline plant since May 2001, and has been able to get away with using only one molding machine for the 50,000-unit annual volume. Pavlowski says that this is because this process is much simpler than foam-in-place and eliminates a lot of the tooling costs of the traditional method. He ticks off a few: no separate injection molds for the substrate retainer or the defroster grill, no vacuum forming tool for the skin or nickel shell necessary for a cast skin, and no polyurethane foaming machine.
However, while LIM panels are cheaper than their more luxurious foam-in-place counterparts, they still cannot beat the costs of more common hard panels, and that is a major obstacle in the path of increased adoption. But Visteon is hoping that OEMs will be willing to pay a little more to add pleasingly soft cockpits to future models.
The company’s pitch to OEM designers looking for more real estate for the ever-increasing array of in-dash gadgets is that the laminate used in LIM panels is significantly thinner than foam-in-place materials (5 mm vs. 12 mm), which provides a little more packaging space. (As well as more elbow room for assemblers.) And that since the defroster grill, registers and demisters can be integrated into the panel, the potential for fit and finish problems is diminished.
LIM is probably not going to revolutionize the way cockpits are made. Hard plastic is deemed to be just fine for lots of vehicles, and foam-in-place will still offer more luxury for the upper end, which can afford to pay a little more for components. But it adds one more option to the palette of technologies that OEMs can choose from and adds a hint of the sybarite in otherwise workaday machines.