At Rock West Composites in Salt Lake City, Utah, technicians have multiple ways to fabricate carbon fiber parts. Some parts are fabricated with traditional manual layups while others are braided. Over in Europe, there is a truck manufacturer that relies on pultrusion to fabricate large rails on which trailers can be built. Some say pultrusion is the best method for carbon fiber fabricating. Is it?
Pultrusion is process that relies on pulling carbon fiber threads impregnated with resin through a die. It is a form of continuous fabrication that can be automated to some extent. It appears to be the ideal method for creating some kinds of carbon fiber pieces. However, it does have its limitations. Pultrusion is not the best fabrication method for every application.
Basics of Pultrusion
The term ‘pultrusion’ is a combination of the words ‘pull’ and ‘extrusion’. In your typical extrusion process, material is pushed through a die in order to form the desired shape. Pultrusion is just the opposite. Material is pulled through the die instead.
To create a trailer frame rail using pultrusion, fabricators would start with a machine containing multiple spools of carbon fiber thread. The number of spools and threads would be determined by the specifications of the part in question. Each of those threads would be fed into a chamber that impregnates them with epoxy resin.
The threads are also confined into a smaller space as they pass through the resin chamber. They then pass through a stationary die that also applies the heat that induces resin polymerization. The die is shaped in such a way as to form the finished part. Finally, the material passes through the other side of the die where it cools and cures in motion.
A Continuous Process
As previously explained, pultrusion is a continuous process. In other words, once begun it continues until spools are empty. It is theoretically possible to fabricate miles of carbon fiber parts as long as you have large enough spools. The obvious advantage here is efficiency.
Continuous fabricating allows for manufacturing large volumes of parts using a single machine and a single die. Engineers are not constantly setting up new dies on new machines for successive runs. There is also no time spent manually fabricating as everything is done by the pultrusion machine.
Such automation offers the triple advantages of speed, consistency, and virtually no waste. Yet pultrusion is only appropriate for simple parts for which structural integrity is limited to a single direction. It is not suitable for more complex parts with complicated shapes requiring increased integrity at multiple points.
Ideal for Truck Rails
Knowing what we know about pultrusion, it is completely reasonable that a trailer manufacturer would find it the best process for fabricating frame rails. Carbon fiber frame rails are of a uniform shape that can be easily fabricated with a stationary die. Frame rails are also rather long. The advantage of pultrusion is that its continuous nature affords the opportunity to make exceptionally long pieces without compromising strength.
You can certainly make frame rails a lot more efficiently with pultrusion than you can with manual layups. Pultrusion is also less expensive compared to 3D printing. It would be cost prohibitive for that same truck manufacturer to set aside pultrusion in favor of newer, 3D printing technology.
So, is pultrusion the best carbon fiber fabrication method? For some parts, yes. But it is not the best choice for every application. Like most things in manufacturing, fabricators have to look at a wide variety of factors to determine which fabricating process is most appropriate.