In this tutorial you can learn how to use a metal mandrel, prepreg carbon fiber and shrink tape to produce a bespoke carbon fiber tube using the roll wrapping process.
The roll wrapping process is used by composite manufacturers to produce high strength carbon fiber tubes, either with a basic unfinished appearance or with a cosmetic finished appearance. Indeed, Cubicarbon carry one of the largest range of roll wrapped carbon fiber tubes available to buy online. Sometimes however, the need arises for a carbon fiber tube of very specific dimensions, fiber type/orientation or appearance.
Explained below are the materials and processes used in the tutorial.
1. Metal mandrel
The roll wrapping process involves wrapping prepreg carbon fiber around a metal mandrel and so the starting point is to have a metal mandrel of the correct diameter for the size tube that you want to create. Because the carbon fiber will be wrapped around the outside of the mandrel, the mandrel itself needs to have an outside diameter that matches the inside diameter of the carbon fiber tube you will use it to make. The outside diameter of your carbon fiber tube will be determined by the amount of reinforcement (the number of layers) you wrap around the mandrel.
If you want to produce a tapered carbon fiber tube then you will most likely need to use a lathe to turn down a solid aluminum rod to create a tapered mandrel.
Once you have a correctly sized mandrel, ensure it is completely clean and as smooth as possible to aid with extraction. The mandrel should then be thoroughly prepared with a high temperature chemical release agent, such as Easy-Lease.
2. Prepreg carbon fiber
Although in theory it may be possible to use alternative types of reinforcements, such as a dry fabric wetted out with an epoxy resin, in practice only prepreg carbon fiber offers the precision and ease of handling required for the roll wrapping process.
By altering the layup to include more or less woven layers or by changing or alternating the orientation of the unidirectional plies allows the performance of the tube to be precisely optimized for its specific use. For example, a tube for a prop-shaft will encounter primarily torsional forces and so the unidirectional fiber can be aligned off-axis, at 45° for example, specifically to handle these forces.
3. Composites shrink tape
Once the prepreg carbon fiber reinforcement has been wrapped around the mandrel as tightly as possible, the reinforcement is then tightly wrapped with a composites shrink tape to provide further consolidation.
When applying the shrink tape it is important to ensure there is lots of overlap. Each wrap of the tape advances only a few millimeters down the tube. Although time consuming to do by hand, having lots of overlap in this way will provide much more consolidation pressure when the tape contracts during the cure.
4. Oven cure
Besides the mandrel, having an oven to cure the tube in is likely to be the main limiting factor when considering the roll wrapping process outside of a full production environment. However, unlike other prepreg processes, the roll wrapping process does not require precise temperature control or the multi-step 'ramp and soak' cure cycles often needed. Nor does the process require an active vacuum line into the oven. Therefore, the only requirements for an oven to cure a roll wrapped tubes are basic temperature control and sufficient size to fit the tube in. Depending on the size of the tube you want to make, anything from a domestic oven to a powder-coating oven could be used.