Study On The Light Field Control In The Field Of Laser Additive Manufacturing

In laser selective melting additive manufacturing,the fundamental mode Gaussian beam is often used as the energy source.Conventional optical systems have high energy density in the center of the focused spot,resulting in a large temperature gradient between the center and the edge of the molten pool.The center region of the molten pool is overheated,leading to the vaporization.While the powder in the edge area is incompletely melted,causing the inferior quality of the forming.In this paper,aiming at improving the quality and stability of laser selective melting additive manufacturing,the optical field control research of laser additive manufacturing optical system is carried out.The main research work is as follows:(1)The light field control scheme of the four-focus combined rectangular spot is designed.The controlled phase distribution of the four-focus combination rectangular spot is designed by superimposing two tilted phases each in X and Y directions.At the same time,the improved GS algorithm is used to design the flat-top rectangular spot.The uniformity of the optical and temperature fields of the flat-top rectangular spot and the four-focus combination rectangular spot are close to each other,which puts up a better performance compared with the Gaussian focused spot.By changing the size of the incident spot,the off-center distance of the incident light,and the distance of the output panel out of focus,the anti-distortion characteristic of the four-focus combined rectangular spot is significantly improved compared with that of the flattopped circular spot.(2)The light field control scheme based on the polarization combination of the fundamental Gaussian beam and the vortex beams with different topological charges to obtain a near flat-topped distribution is proposed,and the flat-topped-like round spot is obtained in the experiment.The improved G-S algorithm is used to design the flat-topped round spot.The uniformity of the optical and temperature fields of the flat-topped round spot and the flattopped-like round spot are close to each other.And the anti-distortion characteristic of the flattopped-like round spot is significantly improved compared with that of the flat-topped circular spot.(3)The optical field control scheme based on the vortex beam generated by the spiral phase plate is studied,and the experimental research on the laser selective melting is carried out.Theoretical simulation revealed that the larger the topological charge of the vortex beam,the larger the central zero-intensity region of the focused beam,and the vortex beam also is of better anti-distortion characteristic.Because of the zero-intensity region in the center,the uniformity of the temperature field distribution acting on the material is substantially improved over the fundamental mode Gaussian beam.Experiments on laser selective melting of Al7075 powder were carried out using both the vortex beam with topological charge number 1 and a fundamental mode Gaussian beam.The roughness of the samples obtained by the vortex beam with topological charge number 1 was lower than those obtained by the Gaussian beam under different laser powers and other identical experimental conditions.