3D Printhead for Composite Materials

The emergence of additive manufacturing technologies in the 1980s paved the way for the development of contemporary 3D printers. These technologies are revolutionizing engineering design and have the potential to transform the manufacturing industry.

New composite filaments are emerging, including towpreg filaments, which are thermoplastics impregnated with continuous carbon fibers. These composite filaments have an ultra-high strength-to-weight ratio. However, the printing of these composite filaments requires specialized 3D printheads. As such, advances in 3D printing technology are critical to the realization of these benefits.

This capstone focuses on designing and building an advanced 3D printhead for composite filament printing. This undertaking is based off an existing 3D printhead that was designed by PhD student Nicholas Elderfield. Our printhead minimizes the filament cut length, allowing shorter filament paths, and leading to greater flexibility in the designs and G-code. Furthermore, the printhead is mounted on a 6-axis robot arm to maximize overall component strength.

Furthermore, the configuration of this printhead enables the reinforcement of internal ribbing and other inserts with carbon fiber filament for high performance applications, such as the automotive and aerospace industries. Ultimately, the aim is to print composite parts with strength that is comparable to injection molded and compression molded components. Enabling the additive manufacturing of complex functional components is expected to offer low-cost prototyping, replacement parts, and small series production.

The CFP-500 is effective because it is designed to enhance the effect of the technologies it combines.

Printing continuous carbon fiber infused filaments increases component strength, but can be a limitation if the cut length is long as it limits the scope of components that can be printed. The CFP-500 minimizes this cut length making it more effective.

Mounting the printhead on a robotic arm allows for the printing over double curved surfaces and around metallic inserts. However, this is severely limited if the nozzle shape and size impact the ability of the printhead to enter small spaces. The CFP-500 maximizes the effective length of the nozzle allowing it to reach into small spaces and enhance the effect of having 6-axes of freedom.

Additionally, the project scope determined clear guidelines that would need to be achieved to ensure that the design solution was effective. By achieving or coming close to all of the success criteria as shown below, the design solution has proven to be effective.

The CFP-500’s designs were validated through extensive engineering analysis and in-lab testing. The team worked closely with the project stakeholders to ensure smooth integration of the printhead with the robotic arm. By performing engineering calculations, seeking and receiving feedback, and conducting tests, the printhead evolved into a functional prototype. Key testing and engineering analysis is highlighted below.

Analysis & Testing

Feed Motor

To evaluate if the 25 mm pancake stepper motor was a viable option, a 40 mm NEMA17 stepper motor was current limited to output the same torque as the 25 mm pancake motor. Lab testing confirmed that the reduced torque was sufficient to extrude the composite filament. Thereby, validating our motor selection.

Cutting Mechanism

Kinetic and kinematic analysis of the cutting link was crucial to ensuring that sufficient force was supplied to cut the filament. The analysis on the left shows the kinetic model of the pneumatic link and a comparison between the angle of the cutting link and the cutting force applied. These calculations validated that the cutting force supplied is adequate.

Microscopy

The photo on the left shows the machined slot in the cutting blade. The smooth finish shown serves to minimize wear on cutting link.

The photo on the right shows the edge of cut filament. The clean cut with minimal fraying of filament demonstrates that the cutting mechanism is effective.

Heat Dissipation

Standard 3D printers use a heat sink and fan to remove heat and protect heat sensitive components. On the left, the progression of heat sink designs for the CFP-500 can be seen. Due to the nozzle’s unique length, it was determined that this distance could be optimized as a heat break, removing the need for a heat sink. This hypothesis was validated using a series of heat transfer calculations. Through the CFP-500’s first prints, the heat break has worked effectively to dissipate heat and protect the heat sensitive components.

The feasibility of the design solution was demonstrated in the manufactured product. After the design process was completed, the CFP-500 was fully manufactured. While elaborate test prints were not able to be completed, simple test prints were conducted, and the major systems all proved to be functional.