CW Blog

Long-lead-time tooling is a common limiting factor in aerospace development. A joint venture program between Bell (Fort Worth, Texas, U.S.) and Thermwood Corp. (Dale, Ind., U.S.) recently explored a solution, resulting in what Thermwood claims may be “the largest 3D printed autoclave-capable tool ever made.” 

Bell enlisted Thermwood to print a closed cavity helicopter blade mold measuring approximately 20 feet long, 14 inches wide, and 17 inches high. The tooling needed to meet several requirements: It must be printed in one continuous run for vacuum integrity, its surface finish must be 32 RMS or better, and it must be able to withstand 90 psi at 360°F. Tight tolerances were also required to ensure proper mating of the two blade mold halves.

When I joined CompositesWorld as editor-in-chief in the fall of 2006, I was coming off of a 10-year stint as editor and eventually publisher of a trade publication that served the injection molding industry. As I transitioned to my new job at CW, I anticipated some modest crossover in materials and manufacturing concepts between injection molding and composites. Both industries are polymer-based, and there are principles of robust injection molding manufacturing that, I assumed, must have application in composites manufacturing as well.

My assumptions, of course, turned out to be wrong. Injection molding is a machinery-intensive, fast-cycle process that uses thermoplastics almost exclusively. The name of the game is speed (measured in seconds), consistency, repeatability and tight, highly automated process control. In composites, I discovered a vast and complex world composed of multiple fiber types, fiber formats, resin types, tooling types and process types. And although machinery is important in composites fabrication, it is not the centerpiece of fabrication. Further, the highly engineered, multi-ply, quasi-isotropic nature of composites manufacturing depends, in many cases, on touch labor of the type that would be unheard of in injection molding. 

In April 2016, I authored a column titled “Can we make recycled carbon fiber sexy?”. It was written after I had seen a roof panel on a BMW i8 at the North American International Auto Show in Detroit that was made from a visible, clear-coated carbon fiber mat, recovered and repurposed from cuttings in BMW’s composites manufacturing process. It demonstrated significant forward thinking at the time, as all other examples of visible carbon fiber on display at the show were woven fabrics, yielding the classic carbon fiber “look” under their clear finishes.

A lot has transpired since then, as various composites recycling technologies have matured and spawned multiple entrants. Composites recycling has also attracted investment from venture capital funds as well as strategic investors, such as Hexcel (Stamford, CT, US) taking an equity position in Carbon Conversions Inc. (Lake City, SC, US) in 2016, and the December 2018 announcement of Mitsubishi Corp. (Tokyo, Japan) taking a 25% stake in ELG Carbon Fibre Ltd. (Coseley, UK). Perhaps most significant is the growing list of end-use applications incorporating recycled composite materials, from manhole covers to park benches to materials for 3D printing, among others.

Composites have been used in fire resistant applications for decades. Generally, inorganic fibers (e.g., glass, carbon, basalt, ceramic) and inorganic matrix materials (e.g., ceramic/carbon, metals, polysialate/geopolymers) do not burn and most can withstand high temperatures. However, when most organic fibers and polymer matrices are exposed to high temperatures and fire, they will decompose into:

A composite’s fire performance is measured by a variety of characteristics, including:

My latest blog, about HIA Velo bicycles, concerned the use of high molecular weight polypropylene (HMWPP) combined with carbon fiber for more durable bicycle frames. But there’s more to cover on this topic: bicycle rims (wheels) that combine carbon and HMWPP for greater toughness. I recently had the opportunity to speak with Ray Scruggs, the founder, owner, and product designer of Derby Rims LLC (San Anselmo, CA, US). The company is named for Scruggs’ nickname (derby), which came from his participation in friendly mountain bike gatherings, or derbys, in the California mountains.

Scruggs began designing and testing carbon fiber bicycle rims in 2012, and sold his first mountain bike rims, which were wider than any available at the time, in 2013. Says Scruggs, “My carbon fiber rim designs had much improved thicker, more durable upper rim walls and tire retention safety over existing carbon rims.” He adds that advanced riders recognized the advantages of improvements in width, durability and safety. Scruggs continued investing all proceeds from rim sales back into the business, while continuing his day job testing and developing business software. He explains that he filed patent applications for new designs for self-protection but adds “My designs were immediately closely copied by nearly every carbon fiber rim brand.”