Mechanical characterization and analysis of FDM 3D printed copper samples

Abstract

Additive manufacturing, specifically 3D printing, technology has revolutionized the design, creation, and building of parts and engineering objects. The fused deposition modeling (FDM) or UV-cured resin-based 3D printings are widely used techniques for rapid prototyping today. The prototypes are typically made of various thermoplastics such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polyethylene terephthalate glycol (PETG) with each thermoplastic having different properties. However, FDM or resin-based 3D printing cannot manufacture metal parts due to some inherent engineering challenges, such as the requirement of the extremely high melting temperature of the metals, making metal filaments, and involved complex thermal management. This thesis research has explored and studied the possibility of manufacturing metal parts using an ordinary FDM 3D printer, a specialized kiln, and PLA-Cu filament with 80% - 90% of copper (Cu) contents. The parts were debound and sintered in the kiln to burn off the PLA, which allowed the Cu to bond to create pure Cu parts. The 3D printing flow rates, debinding and sintering times in the kiln were varied to understand the effect of these parameters on the material characteristics and mechanical strength of the printed Cu samples. The ASTM D638 samples were 3D printed at three flow rates: 133%, 135%, and 140% in an FDM printer and debound and sintered at three different times: 3 hour debind 3 hour sinter, 3 hour debind 4 hour sinter, and 3 hour debind 5 hour sinter. The dimensions and weight of the samples were measured before and after sintering. Samples were polished and etched using a 5-step polishing method with different grinding grits (coarse to ultrafine) and etched with ferric chloride. Grain boundaries and surface qualities of the 3D printed and sintered samples were observed under a high-precision material microscope, stored, and compared with the cold-rolled annealed copper samples. The tensile strength of the samples was evaluated using Universal Testing Machine (UTM). The results show that the 135% 3-hour debind and 4- hour sinter provided the best overall results for the least amount of void within the sample, nicer grain boundaries and mechanical strength. The average stress vs strain value for cold rolled annealed copper is 220.6 Mpa. The results from the tensile testing came out to have a maximum of 39.107 MPa in the 133% flow rate 3 hour debind 4 hour sinter. The second highest stress value came from the 135% flow rate 3 hour debind 4 hour sintering time group at 37.29 Mpa. While the quality and material grain boundaries are comparable with cold-rolled annealed samples, the mechanical characteristics are far off. Nonetheless, the overall aspect of making copper parts from conventional FDM-based 3D printing technology is promising. The findings of this research will contribute to understanding and better utilization of FDM-based 3D printed Cu and general metal parts for future engineering endeavors.