Minimizing voids in continuous carbon fiber-reinforced composites made by robotic 3D printing

This study focuses on optimizing the process parameters for continuous carbon fiber-reinforced composites made by robotic 3D printing to minimize defects such as delamination, gaps, fiber entanglement, non-linear tape consolidation, and voids. The specimens were manufactured by the ABB IRB 1200-05/0.9 6-axis robot with a custom-built 3D print head. Two printing directions were explored, x and y-axis printing. The max change in printing height for x and y-axis printing directions were 25.4 μm (0.001 inches) and 63.5 μm (0.0025 inches), respectively. X-axis printing was the optimal print direction due to its low variation in end effector height and more uniform tape deposition. The coefficient of variation for x and y-axis printing was 0.39 and 1.88, respectively. Gaps formed due to tension build-up resulting from the motion of the print head relative to the laminated tape. This tension caused the tape to warp and become narrower than its nominal width. When printing a single tape at 10.1 mm/s, the width of the printed tape was less than its nominal width. Due to this observation, a minimum tape raster offset (TRO) of 5.50 mm was selected. The micrograph of a 5.50 mm TRO specimen revealed overlaps at each adjacent tape interface. These overlaps resulted in large void formation between overlapping layers. Coupons printed with larger TRO values showed increasingly larger gaps between adjacent tapes.