Extrusion-based Additive Manufacturing of Silicone Elastomer Parts

Additive Manufacturing;Soft Materials;3D Printing;Silicone;Soft Robotics;Pneumatic Actuators;Mechanical Engineering;Engineering;Mechanical Engineering

Plott, JeffreyZhu, Bizhong ;

University of Michigan

关键词: Additive Manufacturing;    Soft Materials;    3D Printing;    Silicone;    Soft Robotics;    Pneumatic Actuators;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/140816/plottjs_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The extrusion-based additive manufacturing (AM) of moisture-cured silicone elastomer parts with minimal voids and high strength, elongation, and fatigue life is presented.Due to the soft deformable nature of silicone, AM is technically challenging; as each layer is extruded, it compresses and deforms previous layers, making process parameter selection difficult and dependent on the AM scenario. This research aims to close this knowledge gap and improve the capabilities of silicone AM. First, a process parameter selection approach to achieve high strength voidless wall structures through previous layer deformation is presented.Effects of flowrate, layer height, and distance between adjacent silicone lines on the vertical layer deformation and void generation are shown.The results are then applied to create hollow sphere-like balloons and finger pneumatic actuators. The sphere-like balloons exhibited diametric expansion between 152 and 207% with burst stress between 1.46 and 2.55 MPa (comparable to the base material properties) while the pneumatic finger actuators fully articulated over 30,000 cycles before failure.To quantify the strength impact of internal voids and infill direction on silicone AM parts, the tensile strength are failure modes are investigated in tensile test specimens with various infill directions (0°, ±45°, and 90° relative to the tensile direction) and internal void sizes. These strength results are then compared to baseline silicone specimens. The AM specimens with ±45° and 90° infill direction and either the minimal or small voids had the strongest tensile strength (average between 1.44 and 1.51 MPa). This strength is close to that of the sheet stamped specimens which had an average tensile strength of 1.63 MPa. As voids became larger and more elongated in shape, the average tensile strength significantly reduced to 1.15 and 0.90 MPa for specimens with ±45° and 90° infill direction, respectively. Counterintuitively, specimens with 0° infill direction were consistently the weakest due to the tangency voids and sharp corners resulting from the tool path. To maximize the tensile strength, it is important to select process parameters which minimize the elongated voids, infill tangency voids, and surface edges. If these conditions can be achieved, the infill direction does not play a significant role.Finally, to increase the maximum possible height of silicone AM parts, the tangential and normal forces imparted by the AM process were studied to investigate the effects of three key process parameters: volumetric flow rate, nozzle tip inner diameter, and layer height.The interaction between the nozzle tip and extruded silicone bead is controlled to either prevent any interaction, flatten the top surface of the extruded silicone, or immerse the nozzle in the extruded silicone. Results showed that tangential and normal forces strongly depend on this interaction. Specifically, forces remained low (less than 0.2 mN) if the nozzle tip did not contact with the extruded silicone bead but quickly grew to over 1 mN once the nozzle interaction with extruded silicone came into effect. To reduce these tangential and normal forces, process parameters should be selected to prevent the nozzle tip from dragging through the deposited silicone while maintaining sufficient line width for structural integrity. These findings create a foundational understanding of the extrusion-based AM of silicone and other soft materials. The results presented can be implemented to enable control strategies which may greatly expand the design freedoms for producing compliant, stretchable, and functional custom silicone parts.