Research On Forming Quality Analysis And Toolpath Optimization Of Three-dimensional Concrete Printing

3D Concrete(cement mortar)Printing(3DCP)has become the research frontier and hot spot of the construction industry due to its characteristics as non-template construction,efficient automation and more freedom of achievable complex geometries.However,the current 3DCP technology has always been recognized for the quality problems of printed components,including forming quality,mechanical(strength,durability,etc.)quality,etc.The mentioned forming quality problem generally refers to two aspects-a)The geometric error in the shape and size of printed components,that is,the geometric quality issue;and b)The imperfection in the surface roughness of printed components,that is,the surface quality issue.This forming quality problem has restricted the practical application and development of the 3DCP technology to some extent.This dissertation performs research for the practical demand of good 3DCP forming quality with the main research outputs described as follows:(1)Preliminary establishment of the factor influence mechanism and assessment method of the 3DCP forming qualityThe coupling influences of factors on the forming quality of 3DCP components were qualitatively analysed.There were three decisive factors-material property,process parameter and planned toolpath,and two restrictive factors-hardware performance and component design parameter.The factor influence mechanism of the forming quality was preliminarily established.Based on the Geometric Dimensioning and Tolerancing(GD&T)system,a control-variable experiment was designed to quantitively investigate the factor influences on the forming quality of planes and corners.Four characteristics of the factor influence mechanism were observed.Consequently,the printing process capability was established according to key features of a component to predict the forming quality,and the forming quality assessment model of physically printed components was also established for quantitive assessment.(2)Development of the theory with toolpath optimization algorithms of volumetric 3DCPConsidering the influence of toolpath on the forming quality of complex geometries,an innovative volumetric 3DCP theory was proposed.This theory replaced the accumulation of lines of constant cross-sections with an ordered combination of voxels with variable crosssections.Volumetric toolpath optimization algorithms were then designed for both the singlepath volumetric pattern parts and the multi-path volumetric solid parts.These included a voxel positioning line-based variable layer-thickness slicing optimization algorithm,and a Voronoi graph-based variable width toolpath planning optimization algorithm.The mathematical solution was accomplished for the voxels of square(rectangle)cross-sections.(3)Development of an optimised process under multi-parameter collaborative control mechanism for volumetric 3DCPA volumetric 3DCP software and hardware prototype system with independent intellectual property rights was developed for the voxels of square cross-section.The system could achieve a multi-dimensional linkage control of the XYZ motions of the motion module with the material extrusion,the nozzle steering,and the nozzle size varying of the extrusion module.To put to use,matching relationships of selected key process parameters were experimentally fitted to develop a multi-parameter collaborative control mechanism.These key process parameters referred to nozzle size,nozzle travel speed,material extrusion rate and toolpath curvature radius.During the process experiments,a material mix was applied in consistence with the common workability requirements of printed concrete.Key process details as gantry motion jitter,singlepath key points,multi-path surface smoothness were also optimised.This dissertation has finished a systematic research on the improvement of the 3DCP forming quality.The obtained research outputs will provide effective references for promoting practical applications of the 3DCP technology and the high-quality development of the construction industry.