Thermal Analysis of Large Area Additive Manufacturing Resistance Heating Composites for Out of Oven/Autoclave Applications

3D printing of carbon fiber (CF) reinforced composite has received growing attention because of the design flexibility, superior mechanical strength, improved thermal properties, and weight reduction. A potential field of application is the autoclave tooling industry which mostly requires the mold and dies fabricated using CF reinforced composites. However, the cost associated with tooling, heating, and cycle time in a conventional autoclave tooling process is relatively higher, thus losing the interest of using additively manufactured composite tools. This study represents an innovative method of the resistive heating of composite molds which does not require a room size oven for heating during the autoclave curing processing. Therefore, it has the potential to reduce the operating cost drastically. Using the wire coextrusion technology, CF reinforced Acrylonitrile Butadiene Styrene (ABS) with embedded resistance heating wire (nichrome) can be printed in the Big Area Additive Manufacturing (BAAM) machine at the manufacturing demonstration facility in Oak Ridge National Laboratory.

An integrated wire coextrusion tool allows the user to embed the nichrome wire to be embedded within every layer of the printed part. Embedded nichrome wires are used for the resistance heating by providing geometry and part-specific input electrical power. However, embedding the nichrome wire in every layer is may not an efficient scheme for heating up to the desired temperature. In the present study, we performed numerical analysis of the wire embedded bead. The following three different cases were considered for the numerical simulation: embedded wire (i) in every layer, (ii) by skipping one bead i.e. one bead with wire and other beads without the wire, and (iii) by skipping multiple beads after every wire embedded bead. The goal of this study is to determine the thermal behavior of the printed mold part. In autoclave tooling application, uniform temperature distribution at the surface of the mold part is needed to be maintained to achieve the uniform curing and solidification. Therefore, it is important to understand the temperature distribution on the mold surface by changing the spatial distance of the embedded wires. It is anticipated that the larger distance between increase the cold spot, on the other hand, close distance of the wire can create the unwanted localize heating, thus melting.

Numerical characterization of the three different wire embedding schemes helped to determine the best possible combination of the wire coextrusion during the printing process. Moreover, the characterization results helped to understand the thermal behavior of the resistance heating mold part. Constant thermal properties of the ABS/CF composite printed in BAAM were used for the simulation purpose. As the ABS/CF composite has a glass transition temperature of 108°C, thermal characterization was limited to 100°C to avoid the thermal deformation or bulging on the part surface. Simulated thermal behaviors of the wire embedded parts were then used to print and test composite molds panel for autoclave tooling application.