Composite Fabrication: What is Pultrusion and How Does It Work?

1. Composite Fabrication: What is Pultrusion and How Does It Work? There are multiple methods for transforming raw carbon fiber into usable, carbon fiber reinforced plastic (CFRP) parts. Carbon fiber fabricators can choose manual layups or braiding. They can also choose a process known as pultrusion. This post will explain what pultrusion is and why some fabricators might choose it over other methods. The word 'pultrusion' is a portmanteau word – a new word that is created by combining elements of two or more base words. Pultrusion comes from the words 'pull' and 'extrusion'. Knowing this should help you understand the basics of how the process works. Pultrusion 101 An extrusion process is one that takes a material and forces it through a die by pushing. What comes out the other end is perfectly shaped. It need only be trimmed and finished before moving on to the next step. Pultrusion is a very similar process. Its main difference is that material is pulled through the die rather than pushed. Pultrusion is also a continuous process. Unlike injection molding, which injects a new round of material into a die with every cycle, pultrusion begins with a continuous roll of either carbon fiber fabric or thread. The rolls are loaded onto pultrusion machines in much the same way spools are loaded onto a sewing machine. The carbon fiber material is then fed over the top of a tension roller and down under a second tension roller that carries it through a resin impregnator. The saturated material then runs through a die that gives the finished product its desired shape. The die is generally heated in order to begin the curing process. Finally, the material exits the die and is attached to a pull mechanism. Then the machine is turned on and allowed to run. It continuously pulls impregnated and shaped CFRP material that will fully cure down the line. The material can be cut to size at any point after exiting the die. Repetition and Automation What has been described here is a basic explanation of how pultrusion works. Now let us talk about its practical use. According to a Plastics Today article published in late December (2019), Germany's Carbon Truck & Trailer GmbH relies on pultrusion to fabricate truck chassis. They chose the process because of its repetition and automation capabilities.

2. Since truck chassis are not geometrically complex, they are an ideal candidate for pultrusion. The company's pultruders can be set up to run continuously, with stoppages necessary only to reload empty spools and refill resin reservoirs. And because the process is continuous, it is also repeatable. The material that exits during the first few minutes of operation is identical to what exits the system two hours later. As you might have guessed, this repeatability allows for automation as well. Producing truck chassis with pultrusion does not require a large team of workers staffing an assembly line. All you need is a single protrusion system and a small staff to monitor output and replenish materials. Not for Every Application Pultrusion is an effective fabrication method for non-complex parts that require repeatability and consistency. And because it can be automated, pultrusion represents a fast and cost-effective way to mass produce parts using continuous carbon fiber material. Having said that, pultrusion is not appropriate for every application. For example, it does not work for complex geometric shapes. It also does not work well for exceptionally large parts, like airplane wing panels, for example. When you are building something on a large scale or with complex geometry, you need other processes. Fabricators choose manual layups, braiding, spinning, and other processes for those jobs.