Steel is a staple in the design of heavy-duty equipment and vehicles that carry heavy loads for a living. But that doesn’t mean these machines can’t stand to shed a few pounds here and there, especially if it means increasing fuel efficiency or upping payload capacity at no penalty to durability.
“Cat is really good at building things out of steel. And when you don’t have plate, and bar, and tube available, we like steel castings too,” Jeff Jensen, Ph.D., Advanced Materials Technology Specialist for Caterpillar Inc., said at a recent conference devoted to advanced lightweight materials. “We’re really good at welding steel together as a company; that’s what we know how to do, that’s what we like to do, that’s what our plants can do. So to get people to think about other ways of putting things together can be a challenge.”
According to Jensen, lightweighting opportunities at the heavy-equipment maker typically fall into two categories: loading and hauling applications. “Lightweighting doesn’t always make sense,” he said, noting that the company’s track-type tractors, for example, are not likely candidates for lightweight initiatives because “you need a lot of mass to push a lot of dirt.”
Likewise, large wheel loaders “are not great candidates” because they need to go into a pile of material, lift it up, and drop it over the side of a truck. “If we start taking weight out of the rear structure by going to more aluminum castings, for example, all you’re going to do is have to add more counterweight, or live with lifting less dirt,” Jensen said.
In the area of polymers and composites, Cat is advancing usage in “light structures” such as hoods and other body components. One example is a three-piece, RIM-DCPD (reaction injection molded dicyclopentadiene) bonded hood assembly for backhoe loaders.
Other examples can be found on the company’s new on-road offering—the CT660 Class 8 vocational truck, which is designed to work as a transit mixer, refuse hauler, and dump truck, among other applications. The CT660 features a Metton LMR (liquid molding resin) hood and fender extensions made of a flexible rubber composite material.
“There are probably more opportunities” in the polymers/composites space, Jensen admitted. “We do have some people [internally] that are trying to help our designers think about how to implement plastics where it’s appropriate. And we are starting to add some better in-house capability, getting some of our own tools internally. But really the key to implementing more of this [plastics] is design analysis and validation; in the steel space, we have decades to know what the fatigue life is going to be of the structure. We’re not as comfortable in this space.”
Bonded structures is another area in which Caterpillar is starting to develop more capability, according to Jensen, acknowledging that the aerospace and automotive industries have been working with the technology for some time. One reason for this increased interest is better appearances—the ability to displace stitch-welds that are very noticeable on Cat’s trademark glossy black and yellow bodies, he said.
Cost reduction is another driver, by eliminating post-weld grinding, as is the ability to use thinner-gauge steel, Jensen noted. “Again, this [technology] kind of changes the skillset required if you’re going to do these assemblies in-house; it’s more of an assembly instead of a welding operation now,” he said. “Personally, I’m pretty excited about opportunities for joining dissimilar materials.”
Higher-strength steels also are being pursued as a lightweighting technology at Caterpillar, Jensen said, as is aluminum, which could play a larger role in certain applications. For example, when talking about lightweighting opportunities for hauling applications, he noted that “typically we do a lot of ferrous castings today. There are opportunities to go to aluminum castings.”
The new CT660 vocational truck makes good use of the nonferrous metal. Its aluminum-alloy cab weighs about 250 lb (113 kg) less than conventional steel cabs, which could translate into larger payloads or better fuel efficiency. Discussing some of the main differences between the CT660 and its International counterpart, Gary Blood, Product Manager for Cat Vocational Trucks, noted that the aluminum cab is sourced from the same supplier as the PayStar’s cab, but “everything about it except the roof cap and the back panel is totally different.”
Though such efforts are gaining more traction at Caterpillar, the top priority in the design of its heavy equipment and vehicles was made clear at a media ride-and-drive event for the CT660 this fall. Blood explained to SAE Magazines that Cat works with its suppliers to select optimized components—for example, Hendrickson with the Primaax air suspension—to take out weight without sacrificing durability.
“It’s little wars—not a grand-scale war—that keep trimming that weight down,” Blood said. But the main takeaway from Blood was this: “Stoutness trumps lightweight.”