Two trends at opposite ends of the automotive market are pushing development of polycarbonate (PC) plastic windows as a replacement for traditional glass in some situations. For expensive, niche, speciality vehicles, designers are taking advantage of the plastic’s ability to create complex shapes that would be nearly impossible with glass. And in the mass market, the demand for lower vehicle weights at a time when window openings are getting larger, has made glass a target for weight watchers.
David Loren, glazing segment manager for polycarbonates at Covestro LLC spoke with Today’s Motor Vehicles about advanced composites technologies and the potential impact PC glazing will have on vehicle designs in the near future.
Today’s Motor Vehicles (TMV): Glass is a proven technology in automotive. How can new materials compete?
David Loren (DL): It’s an exciting time in automotive, where automakers are faced with new challenges – lightweighting, efficiency, corporate average fuel economy (CAFE) regulations, efficiency – but at the same time, they have to make vehicles that consumers want.
It’s not just about lightweighting, and it’s not just about styling. Where you truly hit a homerun is when you can combine the two. Right now, everything’s on the table for the companies. They’re more open to considering new technologies and materials than ever before.
TMV: What are some PC material uses showing up in vehicles today?
DL: We’re having a lot of success with aesthetic offerings, appliques on roofs, side trims, and other types of components. We can lower weight and offer more design freedom in PC compared to painted metal.
With appliques, particularly on the roof, it offers a shiny, glass-like appearance that extends the visual look of glass. It draws windows and windscreens into the vehicle exterior and gives the side of a vehicle a rich, luxurious look.
The trick is to deliver an optimized PC material that can give a rich, consistent, homogeneous, color – maintaining high lot-to-lot consistency and improved productivity from carefully controlled viscosity.
TMV: Weight savings are key to every product today. What other advantages do PC trim items have?
DL: You get shape for free with polycarbonate. You’re building an injection mold anyway. Build it any shape you want, and you’re going to have the same basic cost.
What’s also helped in manufacturing is part consolidation. We can mold in attachments, glue tracks, fastener rings, and other features that optimize the part for assembly.
We’re seeing companies consolidate parts and cut weight, especially with smaller cars. A few years ago, small cars were all about keeping costs down. Now, they have many of the features, textures, appearances, and luxuries that used to be associated with a higher-end vehicle. You still need to keep costs down, so plastics are playing a larger role.
TMV: A handful of vehicles have used PC windows (rear windows on the Smart FourTwo), but the trend hasn’t moved mainstream. What are the prospects for PC glazing?
DL: In late 2015, Europe changed its glazing regulations to essentially make polycarbonates legal for the entire vehicle. The big push there was the addition of the windscreen. Regulators did a 3-year, in-depth study that included using PC windows in several police vehicles. The target for that was vandalism – resisting bricks thrown at police cars to break windows. They bounce off of PC windows instead of shattering them. The vehicles passed all of the safety and durability tests, so we’re seeing a lot of movement in Europe. U.S. regulators are watching those results, so we see some movement here.
The demand is there. Every year, the concept vehicles at the auto shows have bigger daylight openings – huge panoramic roofs, wraparound windscreens that tie into side windows, wider windows. In most cases, you can’t do that, cost- or weight-effectively, with glass.
TMV: Is design freedome the primary reason automakers are considering PC, or are there other advantages?
DL: On any glazing, first and foremost, you get upward of 50% mass reduction. If it’s a one-to-one replacement, it is 50%. Typically, by the time you factor in reinforcements and some of the other intricacies of installation, there’s more opportunity for mass reduction.
When you design the part to be PC, and you consolidate parts, weight savings can add up quickly. Aesthetically, PC supports those wider openings, and you can get rid of seams. Seams are the enemy of styling, designers hate the look of them. And seams are the enemy of engineering because they have to seal them.
If you can take a single piece of glazed PC material and run it from the windscreen to the panoramic roof to the rear of the vehicle, you’re eliminating a lot of seams.
The technology is there so those cool auto show concept vehicles can be brought into reality with the added benefit of mass reduction.
TMV: What’s standing in the way of greater adoption?
DL: Glass is a great technology. It’s been around forever. There are applications where it makes economic sense to use glass. However, when you factor in styling, part complexity, fragility, and mass reduction, you start seeing the benefits for polycarbonates. But there are many applications that are in glass and should stay in glass.
There’s a familiarity with glass for most engineers, and we’re working to provide that for polycarbonates. Good simulation software, the ability to predict performance, is key. We have in-house CAD expertise, our technical experts do full studies on how PC materials are going to behave in different thermal environments and how they’re going to behave with different wind loads.
We replaced an existing glass panoramic roof to show a customer how a PC option would work. Our computational tools predicted roof leaks, using the existing seals, between 70mph and 75mph, and our test vehicle leaked at 73mph. That gave us a lot of confidence in our design tools, and it told us that if we’d been able to re-engineer the seal on the roof to optimize the use of the PC material, we could have improved noise performance compared to glass.