This project was brought to our custom composites manufacturing shop in Seattle, WA by an individual who wanted to add the first piece of custom carbon fiber to his Porsche. The requirements for this project were straight forward - a one-off, low cost replica of the OEM diffuser, in twill carbon without any finishing.
Materials: Melamine Board, Clay, TR Wax
One-off carbon fiber parts for customers with an existing OEM part almost always go the direction of a splash mold. The curvature and cutouts of this diffuser required creative flange construction. Acrylic and melamine were pieced together to match the curves. Any remaining gaps were filled with clay. For more information on the plug building process, check out our blogs on splash plug fabrication, machining a foam plug, and plug finishing.
Parts with fine detail, tight radii, or in this case deep fins, should be fiberglassed in two sessions. The first session lays in fiberglass tows and two to three half sheets that conform easily to the mold details. It is then left to cure for 12 to 24 hours. The second session lays in four to five full sheets to strengthen, or 'bulk' the mold. We had a tight time budget on this project so, despite the deep features of the part, we combined the two sessions into one. Predictably this turned out to be a mistake - poorly filled and lightly backed features are prone to leaking, which in turn makes for a poor infusion and part. The lesson here: cutting corners to save time in the mold making process will create additional work downstream, so do it right from the start. You can learn more about mold making best practices in our posts on spraying gelcoat, the mold lamination process, and how to finish your mold.
As mentioned in the previous section, the diffuser mold leaked significantly. Leaks in the mold or in the vacuum bag result in a very porous part. At its best, porosity looks like small pinholes in the resin dispersed across the part. At its worst, it can mean that entire features of the part are missing - particularly at a hard corner, like the edge/trim line of the part. Both cases require significant work in the finishing step to correct. Read our post on VARTM infusions for an in-depth look at this part of the process, and keep an eye out for our upcoming troubleshooting post on leak chasing during an infusion.
Materials: High Build Primer, Black Paint, Clear Coat, 3M Buffing and Polishing Compounds, Boss Perfecting Foam Pads
While difficult to see in the photos above, the porosity and feature-loss in the diffuser was beyond recoverable for a clear-gloss finish. Our customer's low budget wouldn't allow us to remake the mold and make another part, so we opted to Bondo™ the offending areas and paint the whole part black. Had there been less body work required we could have spot treated the areas with Bondo™ then misted them black paint to hide the imperfections, while keeping the rest with a clear-gloss finish. We'll write about that process in more detail in a later post. You can learn more about the intricacies of the finishing process in our posts on trimming carbon fiber, how to spray clear coat and buffing and polishing best practices.