Surface and Infill optimization of binder based 3D-printed (FGF) biodegradable Mg-0.6Ca-alloy implant prototypes

Abstract text (incl. figure legends and references)

Introduction

Fused Granular Fabrication (FGF) is a binder based 3D-printing technique which enable manufacturing of complex shaped parts, even with hollow infill structure at dense shell or scaffold like strut structures (Fig. 1).

Figure 1: 3D-printed Mg-alloy scaffold.

For the 3D-printing process, feedstock granules made from spherical metal powder and polymer binder components are needed. Identical feedstock is used for Metal Injection Molding (MIM) a near net shape industrial mass production technique.

Objectives

Aim of this investigation is the optimization of the 3D-printed surface morphology and the infill quality of the dense matrix of a 3D-printed implant. Both is in need for optimal performance of bone implants which are placed close to tendons and ligaments – smooth surface roughness and homogeneous metal morphology. The MIM processing was used as a reference route within this study.

Materials & Methods

Spherical Mg- and Mg-10Ca-powder of particle size below 45 µm as well as polymer binder components (wax, stearic acid, PPcoPE) were used for the feedstock preparation in a planetary mixer. The 3D-printing was performed using an AIM3D ExAM255 machine. Sintering was done using a hot wall furnace (MUT, RRO350-900). All details of processing and sintering are publishes elsewhere [1].

Results

As shown in Fig. 2a, optimization of printing parameters using a 0.3 mm nozzle at 0.09 mm layer high and 6 mm/s printing speed results in significant enhancement of the specimens surface quality and density (see x-ray in Figure 2b).

Fig. 2

Conclusion

It could be demonstrated that binder based 3D-printing technique is able to produce parts with smooth surface roughness and a pore free matrix, obtaining no delamination or density differences using fine powder, thin printing nozzle and minimum layer highness. Further investigations will focus on additional electro- and laser-polishing.

Reference

1 Wolff, M. et al, 2016, MIM of Magnesium and Its Alloys, Metals, 6, 118.