Investigations on ironing parameters in screw extrusion additive manufacturing (SEAM)

Additive Manufacturing (AM) is a novel manufacturing process that enables the physical realization of a given 3D model via layered deposition. Material extrusion (MEX) is one of the most widely used forms of the various AM techniques, in which the screw extrusion-based AM (SEAM) processing offers the most versatile characteristics, in terms of material handling and flow rate capacities. It involves continuous extrusion of the semi-solid material via an extruder screw. Ironing is a common practice in MEX techniques, to maintain z-height and improve the surface morphologies while deposition. Most commercially used nozzles for MEX are thin-walled, such that the ratio of the nozzle width to the diameter (w/d) is close to 1. In this research, investigations on the ironing effect during screw extrusion-based material deposition are explored using a set of wider nozzles (w/d as high as 40). Special emphasis is laid on the deposited surface finish, interlayer strength, and geometrical conformance of the extrusion. The nozzle diameter and the stand-off distance (SOD) are also independently varied. It is found that the best dimensional stability is achieved when the SOD is set between 75 % and 100 % of the nozzle diameter. Ironing improved the surface finish and the interlayer strength in all instances, with an average improvement of 50 % and 200 %, respectively.