| Three-dimensional Printing(3DP)technique has been applied to 3D Printing sand molds,providing a new manufacturing method for the foundry industry.However,it still has low molding accuracy and low material utilization rate in single batch printing.The main reasons of the low forming parts accuracy are stratification of step error and adhesive penetration error.This thesis focuses on how to measure and reduce the error of the two parameters so as to improve the forming precision,and how to increase the number of parts in a single batch print so as to increase the material utilization,the research work completed is as follows:(1)Due to the difference in step errors generated by different triangular slices during stratification,this thesis studies the defined upward triangular slices and downward triangular slices according to the changes in angle between normal vector direction of triangular slices and forming direction.By analyzing the position error of the boundary formed by the two-dimensional projection of the triangle and the bonding of the binder to the sand in the simulation experiment,the interaction law between the step error and the penetration error is found,and the offset error formula of the upward triangle and downward triangle are derived after integrating the step and penetration error.The sample models are designed for printing experiments,and the measured offset errors are compared with the offset error calculated by the offset error formula.The validity of the offset error formula is verified.(2)Aiming at the optimization of forming parameters in 3DP technique,the forming accuracy formula are established based on the triangle offset error formula.Comparing the forming error calculated by the forming accuracy formula with the actual measured forming error,the validity of the forming accuracy formula is proved.The multi-objective optimization model is established,which takes the thickness and forming direction as variables and the forming precision and forming efficiency as objectives.The NSGA-Ⅱalgorithm is used to solve the multi-objective optimization model so as to settle the optimization problem of forming parameters in 3DP technique,The effectiveness of the algorithm is verified by experiments.(3)Aiming at the low rate of material utilization in 3DP technique,the center layout algorithm is proposed.The algorithm includes STL model projection algorithm and center layout strategy.The projection algorithm of STL model calculates the minimum irregular outer frame of the model in the projection plane and converts the 3D layout into 2d layout.The central layout strategy realizes the central layout by defining the layout rings and the layout points as the reference position of model movement.According to the layout parameter experiments,the layout parameters of the example experiments are given,and the applicability of the center layout algorithm for different types of parts is verified by the example experiments.(4)The optimization of forming parameters and the layout of parts in 3DP process are combined and verified further..The STL model layout software is developed according to the central layout algorithm.In this software,the molding parameters of the models are optimized according to the optimal solution calculated by the optimization algorithm,and then the layout tests are carried out.designing The three samples containing the characteristics of curved surface and plane are designed which are used for the layout and molding parameters optimization experiments.The results show that the model of optimal molding precision compared with the model of optimal molding efficiency,the forming precision of former is better than that of latter.The effectiveness of both the forming parameter optimization algorithm and the central layout algorithm is verified. |
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