Study On The Preparation And Shape Control Strategy Of Zirconia Ceramics Parts By Stereolithography 3D Printing

The ceramic parts prepared by stereolithography(SL-3D)technology have the characteristics of good surface quality,high molding precision and excellent mechanical properties,etc.This technology has a broad application prospect in the field of precision manufacturing of ceramic parts with personalized,complex structure,high precision and high performance.Starting from the key problems of 3D printing technology of ceramics,this study aimed at the forming,debinding and sintering process of SL-3D printing technology,and established the prediction model of parts cracking in the debinding process,which provided a valuable reference for the rapid manufacturing of complex ceramic parts and promotes the development of ceramic 3D printing technology.This paper carried out the following three aspects of research.Firstly,the influences of laser power and forming strategy on the dimensional accuracy,density and mechanical properties of parts were studied systematically,and the optimal laser power and the principle of selecting forming strategy according to the shape of parts are determined.Secondly,the effects of different debinding processes on the weight,shape and density of the debinded parts were studied,and the optimal debinding atmosphere and temperature were obtained.At the same time,taking the hardness and fracture toughness as the main evaluation indexes,the influences of sintering process on the mechanical properties of the parts were found and the optimal sintering temperature and holding time were determined.Finally,the mechanism of deformation and cracking in the process of debinding were analyzed,and based on the lamination theory,the maximum thermal stress was calculated and compared with the maximum stress of material to predict whether the parts would crack in the debinding process.The effects of forming strategies(laser power and forming direction)on the dimensional accuracy and mechanical properties of parts were studied.Firstly,based on the Gaussian beam and Lambert-Beer law,the influence of laser power on the dimensional accuracy of different forming directions were analyzed,and the dimensional change and shrinkage of parts after forming,debinding and sintering were studied,and the shrinkage scale factor was determined.It was found that the size shrinkage of the laminated surface was larger than that of the laser scanning surface,that was to say,the reasonable selection of forming strategy was of great significance to the manufacturing of high-precision parts.Secondly,the influence of different laser power on the weight,density and porosity of parts were analyzed.It was found that the weight reduction of debinding process accounts for 97.6%of the total weight reduction of sintering preparation process,while the density increased of sintering process accounts for 86.9%of the total density increased of sintering preparation process.It could be seen that the debinding process was the process of organic matter removal,and the sintering process was the process of part densification and mechanical properties improvement.Finally,through the analysis of the influence of laser power on the dimensional accuracy and mechanical properties of the parts,and 360 mW was determined as the optimal laser power.The SL-3D printing of ZrO2 bearing and gear wers realized with the relative density no less than 97%,the hardness of 13.1 GPa,the fracture toughness of 5.62 MPa-m1/2,and the flexural strength of 1044 MPa.The effects of debinding(debinding atmosphere and debinding temperature)and sintering(sintering temperature and holding time)process on the dimensional accuracy and mechanical properties of parts were studied.Firstly,the influences of the debinding process in nitrogen,argon,argon before air and air atmosphere on the weight,size and density of the debinded parts was studied,and the debinding effect under different debinding processes and the matching principle between the part characteristics and the reasonable debinding process were clarified.When the weight reduction degree(the amount of debinding)and the size shrinkage stability(the amount of the shrinkage)in debinding process were taken as the measurement indexes,the air atmosphere debinding effect was the best,and the density of debinded parts was smaller at the same time which was more conducive to the decomposition and escape of organic matters.Secondly,the influence of debinding temperature on dimensional accuracy and mechanical properties of parts were studied.The results show that the weight of the debinded parts decreases with the increase of debinding temperature.With the increase of debinding temperature,the size of parts shown the same change trend.When the temperature was lower than 1050?,the size of parts basically remains unchanged,and when the temperature was higher than 1150?,the size of parts rapidly shrunk.Meanwhile,when the debinding temperature was lower than 1050?,the density of the parts remained basically unchanged,while when the debinding temperature was higher than 1150 ?,the density of the parts increased rapidly.Finally,the influence of the sintering temperature and holding time on the hardness and fracture toughness of the ZrO2 parts under different laser power were studied,and the optimal sintering process of ZrO2 parts was determined as the sintering temperature of 1500? and the holding time of 120 min.At this time,the average values of hardness and fracture toughness of the parts were 13.15 GPa and 5.64 MPa·m1/2,respectively.The deformation and cracking mechanism of parts in sintering preparation process were analyzed.Based on the lamination theory,the thermal stress prediction model of ZrO2 parts in debinding process was established,and the shape control strategy in sintering process were put forward,and the SL-3D printing preparation of precise and complex ceramic parts were realized.Firstly,the deformation and cracking mechanism of ZrO2 parts in debinding process were analyzed,and the main factors influencing deformation were found by experiments.It was found that the gravity of the part itself was the main factor affecting the deformation during the debinding process,and the change of the material components in the debinding process made the coefficient of thermal expansion and the modulus of elasticity changed,which leads to the deformation of the part and the internal thermal stress.When the maximum stress that the material can bear was exceeded,the parts would crack.Secondly,based on the lamination theory,the strain was divided into horizontal strain and vertical strain to establish the thermal stress prediction model in debinding process.Combined with the stress balance equation,the maximum thermal stress of parts during the debinding with 1150? in air atmosphere was calculated,and compared with the stress that ZrO2 materials can bear,it was determined that ZrO2 parts will not crack.Finally,based on the process optimization of forming,debinding and sintering process and the analysis of deformation and cracking mechanism,the shape control strategy of ZrO2 parts in the sintering preparation process was proposed,and the rapid manufacturing of precise and complex ceramic parts was realized with the surface roughness(Ra)of parts after polishing was 0.365 ?m.