Rapid surface quality assessment of green 3D printed metal-binder parts

Mixtures made of a solid metal powder and a viscous polymeric binder are increasingly used in material Extrusion Additive Manufacturing (EAM) processes. The EAM process adopts the relative movement of an extruder head to a build table, to deposit thin strands of the mixture and build a 3D object layer by layer. In this study, EAM process was applied to produce 3D printed square plate-shaped parts of stainless steel 316 L at the green state, i.e. before debinding and sintering. The 3D printing experiments were designed by considering various independent process parameters: extrusion velocity ve, table velocity vt, layer height h and hatch spacing Da. The surface characteristics of as printed (green) square plate-shaped parts were investigated by a rapid, high-resolution optical imaging technique. The obtained images were analyzed to model the effect of the process parameters on the surface uniformity Ui and space filling Fi. The proposed methodology can be also used as a process monitoring technique. The study has demonstrated that the layer height h has the most relevant effect on the infill quality and should be set at a low value for good quality. However, a combination of the other parameters can be found that yields a compromise between infill surface quality and build up rate.