Many industries, including automotive, aerospace, and robotics are using additive parts made of carbon fiber. These parts are popular for the strength-to-volume ratio they offer.

But the use of carbon in additive materials may not always produce a part with the desired look and feel. Parts 3D printed with carbon composites can display a non-uniform appearance, for example, show wrinkles, ridges, or even voids. According to some 3D printing vendors, this effect can be the result of imprecise consolidation of the carbon fiber plies in the material.  Depending on the part, these effects could be considered defects and affect part performance.

3D Systems application engineers have been working on a way to reduce the chance of such defects. They use stereolithography (SL) along with the company’s SL materials.  SL often produces parts with good feature detail that need minimal post-processing.

The engineers use two components in the SL machine. One is a sacrificial internal tool (the mandrel), and the other is a reusable external tool (the shell).

The engineers design a mandrel to be hollow so that there is an open channel the carbon fiber travels through during the vacuum process. Pressure is applied to the internal surface of the mandrel pushing outward, while the external surface of the shell pushes inwards. The vacuum process ensures that the exterior surface of the mandrel will be imparted on the inside of the part while the interior surface of the shell will be imparted to the exterior of the part. The equal pressure applied externally and internally helps consolidate the carbon fiber plies, delivering smooth, well-detailed features.

In most cases, the recommended wall thickness of the mandrel is about 2 mm. It can be helpful to design mandrel extensions or grips. The grips assist in sealing the vacuum bag, and make it easier to remove the mandrel from the final part interior. You can also design the mandrel to break in a specific way for easier extraction from the final part.