Impact of online mixing via KSM on the accuracy of ingredient deposition in manufacturing FGMs

•3D printer mounted with KSM was utilized to form FGMs with smooth gradient.•Two factors that affect deposition accuracy are mixing delay and variable ratios.•Dynamically changing ratios causes asynchronous transport and inhomogeneous mixing.•Mechanical properties are susceptible to deposition accuracy and mixing efficiency.•Compared to original KSM, modified KSM can effectively improve gradient forming. Integrating online mixing into extrusion-based 3D printing has vastly magnified its capability to form functionally graded materials (FGMs). However, insufficient insights into the complex hydrodynamic behavior during online mixing will directly incur the failure of FGMs. Here, computational fluid dynamics (CFD) tools were leveraged to analyze the viscoelastic flow behavior during varying ratios. The main goal of this work is to clarify the effect of non-constant flow on the ingredient deposition for achieving the accurate forming of FGMs with smooth gradients. Visualization analysis of online mixing found that the velocity gradient contributed to the formation of smooth gradients, but there were long transition delays and asynchronous transport. Therefore, a 2–4 shunt modified Kenics static mixer (KSM) was designed to improve the mixing efficiency and compensate for the mixing delay. Using modified KSM, FGMs with smooth gradient were successfully prepared and used to test mechanical properties, whose outcome verifies the validity of the simulation model and the modified structure. Based on the advantage of KSM with a 2–4 shunt in the accurate deposition of smooth gradients, it promises to be popularized for fabricating FGMs with complex anisotropic gradients. [Display omitted]