| With the development of modern industrial manufacturing technology,additive manufacturing,as a new processing technology,has been widely used in industrial manufacturing,mold design,aerospace,automotive,medical and biological science and other fields,especially it provides a good solution for small batch,complex shape parts manufacturing.As a kind of additive manufacturing technology,selective laser sintering technology has the characteristics of simple manufacturing process,no additional support in the manufacturing process,one-time forming of special-shaped components,wide range of material selection,and recyclable materials.It has great advantages in small-scale manufacturing and high-end customized products,so it is widely used in the manufacture of products and parts.However,the selective laser sintering molding system based on this technology still has some problems such as low efficiency and low precision.On the basis of ensuring selective laser sintering molding,further research on how to improve the forming efficiency and precision of parts has become the focus of existing technology.In order to improve the forming efficiency,forming accuracy and shorten the forming time of selective laser sintering,this research uses a carbon dioxide laser as the heat source,and builds a selective laser sintering molding system consisting of laser flat-top line-shaped beam shaping system,laser galvanometer scanning system,micro-displacement drive system,dynamic focusing,control system,etc.Further,a more comprehensive theoretical and experimental research was carried out on the selective laser sintering molding technology of flat-top line-shaped beam laser dynamic focusing scanning.In order to improve the molding speed of products or parts,the laser circular spot was shaped into a flat-top line-shaped beam.Through the research and analysis of the current laser beam shaping theory and system,the theory and system of shaping the Gaussian laser beam into a flattop line-shaped beam were proposed to solve the problem of uneven beam energy when the point light source was shaped into a line light source.Compared with other flat-top line-shaped beam shaping methods,this method can effectively improve the beam quality of the line light source and reduce the influence of diffraction effects.A dynamic focusing driving system based on piezoelectric ceramics was proposed,and the flat top line beam was focused and switched by digital micromirror system,so as to improve the forming quality of machined parts.In order to eliminate the nonlinear influence of piezoelectric ceramics(PZT)on the displacement process of precision displacement device,mathematical modeling and theoretical analysis were carried out on each module of the system.The composite control method combining PID closed-loop control and creep compensation control was used to solve the nonlinear problem of the piezoelectric ceramic actuator in the driving process,so as to realize the precise control of the dynamic focusing.The structure and scanning principle of the laser galvanometer scanning system were studied,the causes of the error of the laser galvanometer scanning system and the correction method of graphic distortion during scanning were analyzed,and the error correction experiment was carried out to verify the feasibility of the correction method.Abaqus finite element software was used to establish the finite element simulation model of flat-top line-shaped beam sintering molding.Walnut shell /Co-PES powder was used as the material,considering thermal radiation,thermal convection,heat transfer and other factors,the multi-field coupling simulation study of flat-top line-shaped beam selective laser sintering process was conducted.The distribution of the morphology,temperature field and stress field of the flat-top line-shaped beam sinter cell in selective laser sintering was obtained.The effect of process parameters on the structure and heat transfer of the sinter cell in selective laser sintering process was studied,and the temperature field generated by the gaussian double ellipsoid heat source was compared.The temperature field and layer thickness of monolayer forming parts were measured by infrared thermal imager to verify the rationality of finite element simulation parameter setting,and the temperature distribution of sintering forming temperature field and the depth of sintering pool were consistent with the actual sintering forming situation.By solving the above key theoretical and technical problems,the experimental results show that the forming efficiency of the flat-top line laser dynamic focusing scanning system is nearly5 times higher than that of the Gaussian laser forming system,and the forming accuracy is higher than that of the Gaussian laser sintering system.Therefore,the system has great theoretical significance and practical application value for improving the precision and efficiency of selective laser sintering forming and promoting the development and popularization of selective laser sintering forming technology. |
