We started manufacturing parts made with carbon fiber, but this wasn't our first choice. This post describes some of the reasoning behind creating parts using an additive 3D printing process with carbon fiber and how we came to love it.
A quick primer
Originally we envisioned creating parts in aluminum (t6061-t6) via a subtractive milling process. If you aren't familiar this process is called CNC or Computer Numerical Controlled Milling. A block of solid metal is precision milled (cut) to form the parts or shapes required. The parts are designed in CAD and then CAM software is used to defined how the milling takes place. The output of CAM (called gcode) is sent to a milling machine, and the shape is created. The process is similar for turning (lathe) work, etc. Parts come out shiny (in the case of aluminum at least). Our milling machine is made by Tormach.
Additive manufacturing is literally the opposite. You start with nothing and add layers to make a shape or part. It's called "industrial 3d printing" because of the tolerances and strength the final part has. In our case we will be speaking about FDM additive (there are other kinds like SLS, etc). In this process layer upon layer of filament is created to produce the final part. Typical the materials are thermoplastics and additives like carbon fiber or kevlar. In our case it's Nylon (called Onyx in our case) with carbon fiber chunks it it, as well as strategically placed layers of carbon fiber for strength - called Composites. Parts come out matte black. Our industrial 3d printer is made by Markforged and prints these composite parts using a unique dual extruder design.
Why carbon fiber vs metal?
As we began to make and test parts we noticed that the time required in tooling, setup, and pure operator time would be significant to produce a wide variety of similar but different parts. But we always assumed that additive manufacturing couldn't make parts good enough. Ultimately, we found that Markforged machines and processes could in fact make an amazingly durable, high quality, sweet looking, functional parts. Additive manufacturing techniques make it easy to have a digital inventory where slightly different parts have low impact, and are financially viable. Plus, we were free to design unique shapes and have many parts in our inventory vs a few. That said, going forward we will choose the right tool for the job, and if we need to use subtractive for some parts, or even a combination of the two we can. Ultimate freedom to make amazing products for our customers!
Carbon fiber parts
As the term suggests, we actually use carbon fiber as a composite in two forms - one as a chopped component in the filament itself (Onyx nylon filament) and two as layers of pure carbon fiber filament woven into the body of the part to add strength in strategic ways. This allows for strong, durable and extremely lightweight parts. The material characteristics are well suited to our use case - harsh environments with UV exposure, hot/cold, dirt, grime, fuel, etc. About the only thing it's not good for is being full-time submerged in water or extreme heat like engine bay or exhaust components. In those cases we might choose subtractive to make the parts.
In FDM industrial 3D printing, parts will have isotropic strength characteristics. Simply put, this means they are inherently weaker in 1 of the 3 dimensions they are constructed in. But, weaving carbon fiber filament into the part drastically reduces this effect, allowing for incredible tensile strength. Thus these composite parts end up well suited to a huge variety of use cases in the overland and off-road communities.
A pattern of how the continuous carbon fiber is inlaid into the part to increase strength.
Designing for this additive process required new skills and an eye towards specifically making the parts so they exhibit the best characteristics outlined above, and were cost effective. We also needed to ensure we could use more advanced techniques like adding heat-set threaded inserts, embedding magnets, or threaded nuts into the parts as needed. For instance, our Molle inserts have stainless steel nylock nuts inserted into the part surrounded by continuous carbon fiber. These nuts resist twisting, sheer, and pull-out.
section view of a part where a threaded stainless steel nut is inserted into the printing process and captured for maximum strength
Wrapping it all up
So there you have it in the gory details - how we embraced additive manufacturing to create strong, durable, functional, and cost effective parts for you, our customer. We live in an incredible time, and we will continue to innovate and adopt these new technologies as it makes sense.