Carbon Fiber Wheel Tubs

As a whole, creating composite pieces can be an intimidating process that often hesitates individuals from experimenting with them. The reality of the composite portion is very simple, but the preparation steps that go into creating a composite part the most challenging.

Why Carbon Composites?

There are an array of reasons that people choose composites for their manufacturing process. Below are some examples of these.

• Strength to Weight Ratio

• Manufacturing Complex Geometry

• Appearance

• Heat Resistance

While rebuilding the front end of my BMW E30, I decided to showcase my ability to work with composites by manufacturing a set of one-off wheel tubs. The wheel tubs were designed in SolidWorks to match the remaining strut towers and new tubing profile.

To bring the concept to reality, I created the desired profile, often referred to as a “plug”. I found the best way to produce large and complex profiles by producing 3D printed parts. With the correct equipment, settings, and set-up, 3D printing provides accurate parts, require minimal finishing, and create a smooth surface.

To reduce print time and the amount of material used, the wheel tub was 3D printed as a skin. This was then mounted to a wood board and backfilled with expanding foam. Once cured, the expanding foam was trimmed, a coat of body filler was applied, and sprayed with a High Build Primer. After the primer cured, the surface was wet sanded (400 grit) and cleaned. I then applied 3 coats of Wax and 3 coats of PVA.

In a conventual application, the male portion of the skin would be used to create a female mold. Since this was a one-off part, I used the “plug” as the mold surface instead. While skipping the mold step saves time and material costs, it unfortunately prohibits the use to vacuum bagging as it can deform the part. In this case, it was acceptable, as all of the curves were very subtle and did not require vacuum to prevent the carbon layers from lifting off the mold surface.

The wheel tubs are constructed from four layers of 3K 2x2 Twill Weave Carbon Fiber. With the passenger wheel tub being within immediate contact with the turbine housing and wastegate, I applied RDR-3350 High Impact/High Temperature resin to prevent damage. This resin was post cured to withstand temperatures of 500 degrees Fahrenheit. Once resin was applied to each layer, an additional layer of Peel Ply was used to soak up excess resin and create a consistent texture on the bottom surface.

After 24-48 hours, the wheel tube was removed from the mold. This process involved prying from different directions with Tapered Wedges. Once removed, the part was trimmed, post treated for maximum temperature resistance, finish sanded to remove surface imperfections, and painted with four layers of High Quality Clear Coat for maximum UV protection. At last, the wheel tubs were installed onto the front end using 8 M5 machine screws.