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The direct ink writing (DIW) technique utilizing a single-screw mixing exhibits the capability of fabricating functionally graded materials (FGMs) featuring continuous gradients. Nevertheless, the vast array of parameters involved in the printing process and the absence of standard values and suitable matching relationships between individual parameters are factors that negatively impact print quality. This, in turn, hampers the potential application of FGMs across a multitude of fields. Thus, the primary objective of this study was to devise a process parameter model that can facilitate the setup of additional control parameters. To this end, the parametric model was constructed on the basis of the correlation between volumetric flow and pressure in each zone, and took into consideration all structural parameters of the prototype and material property parameters. Moreover, the digital image processing was employed to analyze and compare the printing results of FGM samples fabricated using different screw speeds across three groups. The analysis revealed that for stacking quality, deviations from the optimal screw speed resulted in understacking or overstacking. Furthermore, unsuitable screw speeds led to inconsistencies between the printed material information and the expected results. [ABSTRACT FROM AUTHOR]

We offer the possibility of implementing a lab-made extruder for direct ink writing (DIW) into a conventional fused deposition modelling (FDM) 3D printer. The ink extruder was designed to comply with various requirements including the possibility of using multiple syringe volumes, ease of assembly, compatibility with numerous commercial FDM printers, ink retraction and ink flow control and the ability to extrude inks with a wide range of viscosities (ink yield stresses from 135 to 1100 Pa). The load in the extruder was attained by combining a stepper motor and a gear reduction system. The reduction system was connected to a trapezoidal threaded spindle through a rigid coupler. The movement of the spindle was transmitted to the plunger of a syringe that contained the ink (with volumes ranging from 3 to 30 mL), by means of a linear guide system. Most of the extruder parts were printed with the same FDM printer to which the DIW extruder ended attached to. The DIW extruder wiring connections were simply made by using the E-axis connectors available in the FDM printer. Modifications of the FDM printer software required for the correct control of the DIW extruder were also relatively simple, avoiding firmware modification. This simplicity made the two DIW and FDM heads easily interchangeable, thus amplifying the functionality of a conventional FDM printer. The cost of this new DIW extruder is approx. 100€. [ABSTRACT FROM AUTHOR]