| In recent years,the preparation of conformal structures on curved surfaces by Direct Ink Writing(DIW)technology has important application prospects,such as conformal antennas,curved circuits,flexible sensors,etc.However,the preparation capability of traditional threeaxis printing in curved areas is insufficient,with defects such as long build time,low part strength,and surface step effect.In order to break through the above limitations of three-axis printing and prepare structural samples with high conformality,this paper develops a directwrite 3D printing platform based on multi-degree-of-freedom robotic arms,and verifies the stability and reliability of the built platform by experimentally discussing the performance of different robotic arms in 3D printing application scenarios.Subsequently,an innovative multiangle process study using silicone rubber material was conducted to systematically analyze the influence of the nozzle on the print line geometry and the molding effect of multilayer structures under the guide angle and tilt angle,and to derive a multi-angle process law to improve the conformability of samples.The main work of this paper is as follows:(1)Feasibility study for multi-degree-of-freedom robotic arm direct-write 3D printing platform,design and build multi-degree-of-freedom motion module,pneumatic extrusion module,and upper computer control module.The PDMS silicone rubber is used as the printing paste to characterize its rheological properties,and this is used to design the pneumatic extrusion module,which can control the material extrusion amount online by the upper computer program.The printing performance of the multi-degree-of-freedom robotic arm is discussed in terms of singularity and positioning accuracy analysis.The motion simulation of the industrial robotic arm KR210 was used to avoid singularity positions,and then the programming rules of the printing program were designed for KR210 control commands,and complete silicon foam samples were successfully printed.However,this industrial robotic arm has some limitations in printing complex structures due to its low accuracy.The 3D printing study was continued with a collaborative robotic arm UR5 with higher positioning accuracy.The motion accuracy of the UR5 was calibrated and measured with the help of a laser tracker,and actual printing experiments were conducted,which showed that the samples were well formed and could meet the process study requirements.The flow of silicone material in the nozzle was analyzed by Polyflow,a fluid simulation software,and the results showed that the flow of material in the conical nozzle was smoother;later,simulations were conducted for various angular nozzles with different force conditions,and it was found that the different gravity and inertia forces did not affect the line extrusion.(2)Innovative nozzle multi-angle process was proposed and studied in direct writing printing to improve sample conformability,i.e.,regular shape of line cross-section,consistent line width,low line collapse,etc.The baseline printing parameters such as printing speed,extrusion air pressure and layer thickness were determined through orthogonal experiments,and the process laws were derived.The printhead angle is then decomposed into Lead Angle and Tilt Angle according to the printing direction,and the path planning software module is developed for generating the printing program.The results show that: 1)when the nozzle Lead Angle is greater than 0°,the consistency of the silicone foam line width is higher,the line crosssectional shape is more regular,and the line collapse problem is improved as the Lead Angle increases;while the nozzle Lead Angle is less than 0°,the sample forming effect becomes worse.2)The line cross-sectional shape of the printed lines at the Tilt Angle is regular,but it is prone to distortion and poor straightness;the Tilt Angle also does not improve the line collapse problem and has an uncontrollable impact on the mechanical properties of the silicon foam samples.3)The results of printing curved silicon foam on a spherical substrate with a spherical substrate based on the multi-angle process rule of high conformality for flat surfaces show that the silicon foam printed with a printhead Lead Angle greater than 0° has better structural conformability.The results show that the conformality of the structure is better when the nozzle Lead Angle is greater than 0°,which provides guidance for applications requiring high conformality,such as curved sensors and conformal antennas. |
