These composite leaf half-springs were built by Thunder Composite Technologies for a prototype self-contained, remote-controlled, battery-electric tank developed by General Dynamics. The leaf springs were manufactured through Thunder Composites’ automated, continuous pultrusion process. Photo credit, all images: Thunder Composite Technologies
Historically, land defense has been a difficult market for composites to break into, which relied instead on legacy tank designs and materials. “To enter this market, you really need to offer an automated, cost-competitive system, or unique, low-cost tools that can be automated. They are looking for weight savings, but they don’t have the big budgets to develop unique systems [to replace the manual layup tooling currently available]says Andrew Glover, President of Thunder Composite Technologies Ltd. (Windsor, Canada) and owner/engineering director of parent company Harbor Technologies (Windsor).
He continues: “The defense industry for land systems is completely different from the aerospace defense market, which is already in the composites business. The defense industry is actually very similar in nature to the heavy truck market, and some vehicle platforms use some of the same steel tools. For example, tooling from a particular tractor-trailer roof structure could be used in defense for a similar part on a defense vehicle.
Building on more than a decade of experience in high-volume automated processes for automotive composites, Thunder Composite Technologies recently achieved its goal of entering the defense market, developing a suspension system and a composite leaf half-spring for an all-electric self-contained tank. platform for global aerospace and defense company General Dynamics (Reston, Virginia, USA).
Entry into the automotive industry: automated and continuous composite processes
Harbor Technologies is a family-owned company that has been building automated systems for a variety of manufacturing processes for over 50 years, with customers in automotive, aerospace, defense, medical, manufacturing nuclear parts and more.
Composites manufacturing company Thunder Composite Technologies was established in 2009, offering engineering, prototyping, production and machining of composite components, as well as automation and mold manufacturing equipment through Harbor Technologies. For automation equipment, Glover says the company can either develop a custom automated line for in-house production or deliver systems for production at a customer’s facility.
Thunder Composite Technologies uses its automated pultrusion and RTM to design and manufacture leaf springs (top), tie rods (bottom) and other components for the automotive and defense markets.
Together, Harbor Technologies and Thunder Composite Technologies operate from four production facilities, with approximately 80,000 square feet of manufacturing space. “It’s a complete turnkey package. Not only do we design and manufacture the product, but we design, manufacture and construct the entire production systemsays Glover.
This emphasis on automation along with the company’s proximity to Detroit, Michigan, USA, allowed it to quickly enter the market for prototyping and production of automotive composites with leaf springs, followed steering axles, stabilizer bars, etc.
Glover explains that for its main leaf spring components, Thunder Composite Technologies uses a patented process it calls hybrid pultrusion – essentially, an automated system for continuously pultrude composite parts with variable thickness. The process is said to be highly scalable, enabling high volumes at relatively low cost, with cycle times as short as three to four minutes per part, depending on the application.
The system begins with a traditional pultrusion process, producing a part of uniform thickness from continuous fibers and with a high fiber to resin ratio. This uniform pultruded “core” is moved into a secondary system, which wraps wetted continuous rovings around the original part, resulting in a stronger part with customizable material performance based on application requirements. This secondary stage is similar to a filament winding system, says Glover, but with more control. “The whole system travels [along the part], and it is a CNC controlled system. We are able to selectively add individual bits on the central structure, at any degree of angle that we determine in the software. A heated mold moves along the system and pulls material through it to harden the finished part.
To optimize its composite leaf spring designs, Thunder Composite Technologies has developed software to reverse engineer steel leaf springs. The mechanical properties of the steel part are entered into the software, which then produces a digital model of a comparable composite leaf spring, taking into account the new material properties and optimizing to avoid failures. “What’s special about our system is that it reduces the amount of engineering, so we’re coming right out of the gate with a really close product that can be used in spring applications,” says Glover.
Using this software and its hybrid pultrusion process, Thunder Composite Technologies has produced composite leaf springs and half leaf springs for a variety of applications and customers in the automotive market.
Eventually, the opportunity arose to translate this knowledge and experience to the land defense market.
Opportunity for composites in next-generation defense vehicles
Thunder Composites says next-generation land defense systems are designed to be smaller, more portable, battery-powered and self-contained — and may provide more opportunities for composites to enter the market.
Glover explains that next-generation defense vehicles are being developed that look and function differently than traditional manned tanks, and that’s where the opportunity exists for composites. “They will be entirely electric and autonomous, piloted by remote control. Vehicles become smaller, stealthier, and you no longer have to worry about vehicle survivability when you eliminate the human factor. The payload is radically different,” he says.
Like the commercial automobile market, land defense vehicles can also benefit from the weight reduction that composites offer, however, Glover explains, the goal is less to save fuel or range, but to carry more effectively tanks by land or air. “You can make it light enough to carry several in a transport vehicle at once,” he notes.
In recent years, “we have become a reference in the defense market for companies wishing to transform a steel component into a composite”, he says. One project produced by Thunder Composites was a series of carbon fiber composite oil pans for defense vehicles, which Glover said included a unique resin system to enable high performance at high temperatures. The part was constructed via a low-vacuum resin transfer molding (RTM) system developed by Thunder Composite Technologies which, Glover notes, uses relatively inexpensive tooling and can achieve a Class A finish.
In late 2018, Thunder Composite Technologies was approached by General Dynamics to design and build a complete suspension assembly for a prototype 10-ton remote-controlled battery electric tank, including eight composite leaf spring half-springs per vehicle built with fiber composites of glass via the company’s hybrid pultrusion process. Completed in 2021, the package mixes steel, aluminum and composite components, all designed, manufactured and machined by Thunder Composite Technologies in-house.
Thunder Composite Technologies designed the entire suspension package for the General Dynamics Land Systems prototype, including the composite leaf springs.
Thunder Composite Technologies and Harbor Technologies anticipate that additional opportunities for composites will arise as the land defense market continues to shift towards portable and autonomous vehicles, and automated processes will be essential.
Meanwhile, companies continue to develop automated processes for their automotive and defense composites customers. For example, Glover states: “We are developing a solution entirely Automatique, continued process to make coil springs, and we can make coils of any size with quick change tooling. We see this market as just huge,” he says. “We’ve been working on the system since probably 2012, and it’s finally at the engineering stage when we’re ready to start production on the system.”