Effects Of Process Parameters On The Quality Of FDM 3D Printing

3D printing,also known as additive manufacturing,has been widely used in aerospace,medical,and art fields due to its highly customized and rapid prototyping characteristics.However,printing dimensional accuracy and surface quality are still inadequate compared to traditional processing and molding methods,and there are few standardized evaluations on printing quality,which limit the popularization and application of 3D printing to some extent.In this work,the printing quality of fused deposition modeling of PLA（poly（lactic acid））filament was investigated.and the relationships between material-process-structure-performance were considered,including changes of the cross-section and interface adhesion between accumulated or contiguous filaments undergoing thermal processing.The effects of process parameters（nozzle temperature,extrusion rate,layer height or distances between nozzle and forming surface/platform,nozzle speed or printing speed）on printing quality,including surface roughness,dimensional and mechanical properties,was studied based on experimental measurement results and quantitative analysis.The main research contents and conclusions are as follows.（1）The effect of process parameters on the diameter of a filament printing.First PLA filament heated by the nozzle,the PLA filament transfers into viscous flow or elastomeric state;then the filament cooled by air,and changes in the shape and size of the diameter after contact with the printing platform was discussed.The diameter d₂ of the filament after extrusion from the nozzle was calculated by printing specimens measurements and numerical simulations,and the extrusion expansion ratio B（B=d₂/D_N）of the filament through the nozzle was studied.The influence of the printing speed on the diameter d₃ and d₄ when contacting the platform was obtained.It was found that:（i）the diameter of the filament becomes larger after extrusion near the nozzle,and the extrusion expansion ratio B decreases with the increase of the nozzle temperature and the decrease of extrusion speed;（ii）the tensile shrinkage of the filament is related to d3 which increases with the increase of the printing speed;（iii）the single filament forming diameter d4,i.e.,the actual the width of the deposition path,The size error is reduced by 73.9%through process parameter adjustment.（2）The effect of process parameters on interface adhesion of the printed filament were discussed.A scanning electron microscopy,an optical microscopy and the mechanical property testing machine were used to investigate the effects of nozzle temperature,layer thickness,and extrusion ratio（ratio of extrusion speed to printing speed）on the interface/section shape and bonding properties between adjacent filaments.A parameter of the interlayer fusion ratio was defined to represent the fusion adhesion between adjacent filaments during the printing process.According experimental and calculated quantitative results,it is shown that:（i）increasing the nozzle temperature and extrusion ratio,decreasing the printing layer height are helpful to improve the fusion performance;（ii）there are voids between neighboring filaments during printing,the SEM results showed that increasing the nozzle temperature and decreasing printing layer height reduce the void size and shape,;（iii）the extension test results that 3D printed specimens have the highest tensile strength when printing direction was the same as tensile axial,and decreasing the layer thickness and route distance improved the mechanical properties.（3）Based on the study of single filament and adjacent filaments printing,the influence of printing route（product structure）on print quality was investigated.Products with different tilt angles and different cross-sectional shape contours were designed to study the effects of path planning and printing parameters on print accuracy and surface roughness.It was found that:（i）the excursion of the route decreased printing shape precision and even caused printing layer warpage.With the increase of excursion,the dimension accuracy and surface quality decreased;（ii）the parameter of print layer thickness had obvious influence on the printing quality of tilted structure products.Reducing print layer thickness significantly improved the molding quality.The influence of nozzle temperature and extrusion ratio on the molding quality is limited.In summary,the whole process of FDM printing,including filament extrusion,interface adhesion between 3D printed filaments,and accumulated layer by layer to form final products,was studied.The effects of polymer viscoelasticity,printing process parameters and its route（product structure）on printing quality（dimensional and mechanical properties,shape accuracy and surface roughness）are discussed.Optimized process parameters were obtained and its effects were verified through experiments,numerical simulations,and orthogonal experimental analysis.The results can provide reference for improving the quality of 3D printing.