Research On High-precision Large-angle Election Beam Deflection Scanning System

In order to meet the forming requirements of large-sized metal parts,the metal powder bed electron beam additive manufacturing technology needs to expand the electron beam deflection angle,which will increase the electron beam astigmatism.The non-uniformity of the magnetic field inside the conventional two-phase winding deflection scanning device will increase the additional astigmatism.The additional defocusing can exceed the focus correction capability of the partial scan system.Therefore,astigmatism is the main factor restricting the wide-angle scanning of the electron beam.Therefore,improving the uniformity of the internal magnetic field of the deflection scanning device is beneficial to reduce astigmatism,improve the scanning range of the electron beam and the precision of large-size forming.This paper first summarizes the research status of electron beam selective melting technology and equipment at home and abroad.The working principle of the electron beam deflection scanning system is expounded.The causes of the deflection error and defocusing caused by the electron beam during the large-angle deflection are analyzed.The methods of dynamic focusing and deflection error correction are given.A multi-phase winding deflection device capable of improving the uniformity of the magnetic field is designed.The influence of winding phase number on the uniformity of the magnetic field is analyzed by electromagnetic field simulation.And make a physical object for measurement.The results show that the magnetic field uniformity of the deflection coil increases with the increase of the number of winding phases,which can effectively reduce the astigmatism.The multi-phase winding can expand the scanning range without increasing the excitation current.The integrated structure of the focus correction winding and the multi-phase winding deflection device is used to correct astigmatism and reduce the dynamic loss caused by the mutual inductance effect.Aiming at the problem that the multiphase winding combined magnetomotive force and partial magnetomotive force do not correspond to each other,the control of the deflection system is uncertain.A decomposition method based on the principle of circular deflection trajectory is proposed and converted into the decomposition of the phase winding excitation current,and the corresponding functional relationship is obtained.The multi-phase winding deflection scanning device designed in this paper improves the uniformity of the deflection magnetic field,while reducing the additional defocus,and has a wider scanning range;using the principle of circular deflection scanning trajectory decomposition can obtain a one-to-one corresponding partial excitation current,which is multi-phase The winding deflection scanning device lays the foundation for digital control.