A study on the effect of process parameters on feature resolution in 3D inkjet printing

Among the existing additive manufacturing (AM) technologies, 3D inkjet printing (3D-IJP), also known as material jetting, enables fabrication of intricate multi-materials parts with resolution and accuracy in the order of few microns. In 3D-IJP, a piezo-based printhead generates tiny droplets on a substrate which merge upon impact. The printing is followed by a curing step to solidify the wet printed layer before continuing with the next layer. The resulting print quality is governed by numerous process parameters. The aim of this investigation is to determine the influence of the process parameters UV-exposure time and print-velocity on the achievable feature resolution of the 3D printed part based on the USAF MIL-STD-150A resolution test chart. The trials were conducted on a 3D inkjet printer and a transparent UV-curable ink was used. This study showed that the USAF test coupon serves well to study the effect of printing parameters on feature resolution qualitatively. Several heights (0.5 mm to 2 mm) of the USAF test chart group 0 have been printed. Each group is made of three vertical and three horizontal lines. The printed lines were assessed based on a three-level grading system (partial merge = 2 of 3 adjacent lines merged, full merge = 3 of 3 lines merged, or no merging). ... mehrThe specimens were printed on a base layer printed with the same material in order to decouple the obtained results from the substrate properties. The applied aspect ratios (1 to 7.13) did not have any influence on the merging behavior, while a longer UV-exposure was able to resolve smaller features. The improvement of feature resolution by lowering the print-velocity was not as significant as when increasing the UV-exposure time and could only be observed for the lines perpendicular to print direction. The smallest resolvable element printed in this investigation was 353.55 µm for lines in print direction which were subject to a curing of 100 ms exposure time at 4 W/cm2 UV-irradiance. The closest distance that could be resolved for the lines perpendicular to the print direction without any merging was 396.85 µm.