Effects of extrusion parameters in the printing stability: evaluation in an innovative 3D printer containing a vertical co-rotating twin screw extrusion unit

Abstract

The study of die swell phenomenon in Material Extrusion Additive Manufacturing (MEX-AM) technologies holds great importance in order to maintain the control over the extruded beads diameter to ensure surface quality, dimensional precision, adhesion between adjacent beads (intra and inter), as well mechanical properties on manufactured parts. This paper addresses an experimental procedure to analyze the influence of extrusion parameters on the die swell phenomenon on extruded beads printed from a 3D customized equipment containing a customized co-rotating vertical twin-screw extrusion unit (Co-TSE AM). In this context, an analytical estimation of shear rate in the screws and die was performed; a design of experiments (DOE) was conducted to evaluate the influence of factors as of screw rotational speed (40 rpm and 80 rpm), output rate (20 g/h and 40 g/h), and nozzle diameter (0.4 mm and 0.6 mm) on the die swell ratio (DSR); and scanning electron microscopy (SEM) was employed to assess the morphology in the cross-sectional area of the beads, as well as qualitative aspects of surface texture. Additionally, print line experiments were conducted to examine the influence of platform speed and standoff distance on bead width and bead height. It was observed that the DSR average varied between 1.28 and 1.67. Output rate and nozzle diameter are the parameters that most strongly influence DSR. Screw rotational speed has not significant influence on the thermomechanical environment that influences material swelling. The bead width and bead height are differently influenced by the standoff distance and print platform speed.