Calibration Dependencies and Accuracy Assessment of a Silicone Rubber 3D Printer

Abstract

Silicone rubbers are relatively new in additive manufacturing, with only a few commercial printing services and reports on custom-built printers available. Publications and standards on calibration and accuracy assessment are especially lacking. In this study, the printhead calibration process of a custom-built silicone printer is explained, and a set of test objects is proposed and evaluated. The printer in use is based on an open-source filament printer, capable of multi-material printing with silicone rubbers and thermoplastic polymers. Three different high-viscosity single-component liquid silicone rubbers and one polylactic acid thermoplastic filament were used as printing materials. First, the calibration process of the silicone printhead was conducted, and the dependency of the dosing accuracy on silicone viscosity, nozzle diameter and extrusion speed was evaluated. Second, various test specimens were proposed and printed to characterize the accuracy and geometric limitations of this printer. These test parts contained features such as thin walls, slender towers, small holes and slots, unsupported overhangs and bridges. It was concluded that silicone viscosity strongly affects geometric inaccuracies. Design recommendations were deducted from the results, advising for wall thicknesses above 1 mm, slenderness ratios below 2, bridging lengths below 2 mm and unsupported overhang angles below 30°.

3D-Printed multi-material liver model with simultaneous mechanical and radiological tissue-mimicking features for improved realism

“…This is challenging, as all the previously tested single-component printing silicones are an order of magnitude stiffer according to their technical datasheets [ 38 ] . However, prior printing experience with the system [ 37 , 38 ] suggests that lower infill structures can make printed objects macroscopically softer than the bulk printing material, but printing infill structures below 40% silicone volume fraction is often unreliable in terms of printing success. 92 Furthermore, preliminary experience of printing a viscous fluid into an infill structure has shown to increase viscous macroscopic mechanical behavior upon deformation.…”

“…The material chosen to print the shell and infill structure of the liver model was the softest available single-component liquid silicone rubber already tested with the system [ 38 ] , namely the Elkem AMSil 20101 (Elkem Silicones SAS, Lyon, France) [ 41 ] . This material starts curing upon contact with air, with skin formation within 10 min and full crosslinking within 24 h after deposition at room temperature.…”

“…It is described in more technical detail in refs. [ 37 ] and [ 38 ] . The two halves of the fluid extruder are operable independently.…”

“…Both fluid extruder halves were calibrated to their respective material along the calibration process described in ref. [ 38 ] to ensure accurate dosing. After extruder calibration, the liver model ( Figure 4A ), three tensile testing specimens matching the liver model’s internal structure ( Figure 4B ) and three silicone-only benchmark specimens were printed.…”

“…In recent publications, a custom-built prototype printer [ 37 ] was described that combines fused filament fabrication (FFF) and direct ink writing (DIW) technologies. The capabilities of this system in terms of printable geometries [ 38 ] have also been explored.…”