Optimization of process parameters for the manufacture of 3D printed biopolymer composite for medical implants

Abstract

One of the most applied additive manufacturing processes for fabricating functional parts from composite polymers is fused filament fabrication. Carbon fiber-reinforced composites have been widely used for many applications, especially in medical implants. Due to their better stiffness and strength-to-weight ratio compared to metallic materials. Although fused fabrication filament is now a well-established additive manufacturing process for producing parts from these materials. However, it is still limited in its applicability in the industry due to inherent problems, such as significant residual stresses. Residual stresses negatively affect the mechanical properties and dimensional accuracy of additively built products. The effect of residual stresses cannot be corrected by post-processing like heat treatment. As a result, determining input process parameter combinations that result in minimal residual stresses is crucial. In this study, Digimat-AM 2020 software was used in prediction of residual stresses, deflection and build time for different process parameters. In fused filament fabrication process, printing temperature, layer height, and print speed are very critical to mechanical properties. These parameters were varied based on the literature and material manufacturer. Minitab 2018 software was used to determine the influence of process parameters on the mechanical properties of fused filament fabrication of CF/PA12 composite hip joint implant. Experiments were done to validate the results. The grey relational Taguchi method was used to obtain the optimal process parameters. The significance of the process parameters on the part characteristics was determined using an analysis of variance. Taguchi’s results showed that the optimal factor setting levels required for minimizing part deflection, residual stresses, and printing time differed. However, Grey relation analysis showed that optimal factors were: a printing temperature (255◦C), a layer thickness (0.3 mm), and a print speed (50 mm/s). From the results, printing temperature had the strongest influence on the part characteristics. Experimental results showed a near convergence of the observed deflection, residual stresses, and printing time values with a percentage difference of 8.34 %, 2.5 %, and 4.61 %, compared to simulated results. The surface roughness of the 3D printed hip implant were: 1.51 µm, 1.5 µm, and 1.61 µm. These values were within the acceptable range of below 2 µm for better bone-to-implant contact. From the tensile test, the average values of ultimate strength, compressive strength, Young’s modulus, and percentage elongation of the printed CF/PA12 hip joint implant were 71.48 MPa, 135.8 MPa, 7.54 GPa, and 1.86 %, respectively. In addition, the fatigue life for all investigated loadings was greater than or equal to 105 cycles. These results were within the acceptable range of cortical bone and hip implant performance properties. The fused filament fabrication method was found to work well with CF/ PA12 composite, making it possible to produce hip implants with acceptable mechanical integrity.