The use of extrusion technology in commercial vehicle manufacturing
Aluminum extrusions are a proven technology, as they are very popular on a wide variety of commercial vehicles — from Class 8 tractors and trailers to delivery vans and utility vehicles. The diversity of vehicles that use aluminum extrusions validates the value proposition of extrusions in regards to lightweighting, corrosion resistance, maintenance, ease of integration, and structural efficiency.
Extrusions in Commercial Vehicles
Class 8 Tractors and Trailers
Class 8 semi-trucks are also known as tractors, which originates from the Latin word "trahere", meaning “to pull. ”The sales volume of tractors per year pales in comparison to the general automotive market for cars, SUVs, and light duty trucks. For example, the Toyota RAV4 model alone had higher sales (399,941) in 2022 than the entire Class 8 truck market, which sold a total of 309,615 tractors.
Another difference from the automotive market is the availability of information about the materials used. Cars are often disassembled by benchmarking firms in order to analyze the internal components and materials used, and this information is made publicly available. On the other hand, there is no known company that does the same sort of benchmarking in the commercial trucking sector, and if there is, the data is not published. Commercial truck OEMs very sparingly share the material make-up of their trucks. It is known that there are some extrusions in tractors, such as small mounting brackets, yet these parts are not often visible. The most prominent extrusion on a commercial truck is the side protection beam on the electric tractor. It is possible that car manufacturers were inspired to use an extruded profile on their electric tractors based on the automotive industry’s use of extruded rockers for vehicle crash safety and battery protection.
Side protection extrusion on tractor
Extrusions can be found literally all around in various trailer designs, whether they are of an enclosed or flatbed type. The front of the trailers tend to use extrusions as corner beams, and the walls are generally manufactured in a standard post and sheet construction. Other areas that use extrusions are the floor, side wear band, cross-members beneath the floor, landing gear, and doors and hinges. If there is a ramp, extruded materials lighten the ramp’s weight for ease of handling and can also incorporate slip-resistant grip features into their profile design to prevent accidents.
At the Technology and Maintenance Council’s 2023 Transportation Technology Meeting and Exhibition, trailer manufacturers were surveyed about their usage of extrusions. Most OEMs pointed to lightweighting as the primary value. An example is the cross members below the floor, such as a weight-sensitive refrigerated trailer (referred to as a “reefer”), in which the cross members are extruded aluminum. For a typical dry van that is not often weight-sensitive, the cross members are stamped steel. For a trailer that contains many cross members, the difference between aluminum and steel is substantial, yet the cost is as well.
The reefer trailer construction requires the typical structural and durability standards. However, it also has requirements for thermal management, mold, and moisture. As a result, aluminum is often selected in place of wood for the flooring, because it will not mold or absorb moisture and is easier to clean.
Aluminum floor and skid plate on a utility trailer
Within an enclosed trailer, there are often load securement systems, which use extrusions on slide mechanisms and the beams. In this case, extrusions have the ability to provide specific geometries that make it easy for users to adjust the location of the securement devices. In addition, the low density of the aluminum minimizes the weight penalty.
Flatbed trailers also use a lot of extrusions. Extrusions are used throughout the flatbed trailer, including a large, strong extruded beam down the center of the platform to support the load.
Utility and Work Trucks
Many variations of work utility and work trucks are on display, highlighting the various ways in which each one is customized to meet a user’s needs. Most work truck beds are built with drawers and enclosures full of tools and materials, all designed to meet the specific requirements of the job. Extrusions are great for these systems because they are lightweight, durable, don’t rust, and most importantly are easy to customize with tight geometrical tolerances.
Lightweighting is a key attribute to extrusions in work trucks, too. These trucks boast a 45% lower weight than a steel bed design. While one might expect the aluminum dump bed to have reduced durability to steel, aluminum manufacturers prove this otherwise. They have demonstrated that sand, gravel, and even large rocks can be dropped from an end loader into the truck, without damage to the truck bed.
Extruded rocker for an electric delivery van
A carryover from automotive design to commercial vehicles is the multi-hollow rocker structures for electric delivery trucks. Extruded rockers are common now on light duty electric vehicles, as a separate component, or as a battery box surround. The picture above shows a section of an extruded rocker used on an electric delivery van. The rocker structure is critical to absorb crash energy to protect the passenger compartment. In electric vehicles, it is used to protect the battery system as well.
Some electric delivery van with a lightweight aluminum and composite body. The vehicle also includes aluminum honeycomb shelving in the cargo area.
Material Selection in Commercial Trucking
The majority of the structural extruded products in ground transportation, trucks, and cars utilize 6000 series alloys. In commercial vehicles, most products highlight the use of 6061-T6, because of its all-around performance, ease of fabrication and welding, and general corrosion performance. Better corrosion performance was noted for 6063 alloys, and better extrudability in 6005A. However, after speaking with a number of commercial trailer engineers, it was clear that 6061 was preferred. This is likely due to its commercial availability, which is a major consideration as the trailer market is very cost competitive.
Aluminum battery housing use 6000 series alloys
There are many references in trucking to advanced high strength steels being used in various components, from frame rails to the body structure. Most frame rails are 120 ksi (827 Mpa), yet 160 ksi (1,100 Mpa) rails are now available. On the other hand, there is no known use of 7000 series aluminum sheet or extrusions being used to provide similar high strength, while cutting additional weight. The reason is likely due to the cost and value of 7000 series aluminum, along with limited supply.
Fuel efficiency alone is not a motivating factor for commercial OEMs to focus on lightweighting. It takes about 2,000 lbs (907 kg) of weight reduction to cut fuel by 1%. With such little benefit in terms of fuel economy, lightweighting initiatives are motivated by the ability to carry more goods on each trip. This concept is explored more deeply in an objective study on Class 8 tractor and trailer lightweighting, published by the North American Council for Freight Efficiency.
Moving forward, the trucking market is seeking alternative propulsion solutions to reduce diesel fuel usage or even avoid it completely. Electrification activities are in full swing, yet are facing significant hurdles as the charging levels are high and the infrastructure is non-existent. Battery electric Class 8 tractors are about 5,000 lbs (2,268 kg) heavier than diesel counterparts. Even in trailers, there are a couple of solutions in development that could capture energy from the trailer axle to store and power the refrigeration unit. This adds weight to the trailer, on the order of hundreds of pounds, which could spur more lightweighting efforts. The trucking market will continue to innovate as already seen with load stabilizers and lifting booms, and aluminum extrusions are proven as a low risk, cost competitive, and durable material to achieve lightweighting and performance goals.