Optimization of additive manufacturing for the production of short carbon fiber-reinforced polyamide/Ti-6Al-4V hybrid parts

The present work is aimed at utilizing an adapted version of the Fused-Filament Fabrication process as a means to produce hybrid joints comprised of sandblasted, rolled Ti-6Al-4V substrates and additively manufactured short carbon fiber-reinforced polyamide (PA-CF). Layer height (h), printing speed (v) and printing bed temperature (Tbed) for the coating layer (i.e. initial layer with unreinforced polyamide) were varied. Using the ultimate single-lap shear strength (ULSS) of the produced joints as a response, linear and polynomial regressions were fit to the experimental dataset using an approach based on Machine Learning. The linear model achieved a better accuracy, with a test R2 of 0.76. It was possible to conclude that the ULSS is strongly dependent on the actual coating layer height (hreal), which in turn depends on h and v. The optimal set of parameters resulted in an ULSS of 23.9 ± 2.0 MPa. Additionally, specimens for a three-point bending test based on the ISO 14679:1997 were produced and tested to further evaluate the influence of coating layer on mechanical behavior of hybrid joints, this time focusing exclusively on their interphase component. For this test, v did not play a statistically significant role, whereas h did.