Research On Focus Current Compensation Of Powder Bed Electron Beam Additive Manufacturing Equipment

The powder bed electron beam additive manufacturing equipment that uses metal powder as the raw material,electron beam as the processing heat source,is widely used in the field of additive manufacturing,but it has the disadvantage of small size of molded parts.In order for the powder bed electron beam additive manufacturing equipment to be able to form large-size parts,it is necessary to increase the deflection angle of the electron beam.The increase of the deflection angle will cause serious defocusing of the electron beam,and the defocusing will cause the electron beam spot on the working plane.The energy density of the electron beam is changed,which seriously affects the processing effect of the electron beam.Therefore,it is necessary to compensate the focusing current and correct the defocus of the electron beam during the processing of the equipment to improve the accuracy and quality of the equipment processing large-size parts.This article first introduces the types and development status of common additive manufacturing technologies in the industry.Theoretical analysis and simulation verification of the electron beam selective melting technology involved in this topic are carried out,and the causes of electron beam defocusing are classified;Intrinsic defocus and additional defocus in the process of beam processing give different correction methods;experiments have verified that intrinsic defocus is the main cause of defocus when the electron beam is deflected at a large angle,and the compensation is collected through characteristic parameter experiments.The characteristic parameters of the focusing current,the method of calculating the compensation focusing current in the working plane based on the characteristic parameters is given;the feasibility of the inherent defocus correction method and the compensation focusing current algorithm is verified by the verification experiment;the multi-phase winding deflection coil is used as an additive The deflection coil of the manufacturing equipment provides a decomposition method of the regular 2n polygonal scanning trajectory and the excitation electromotive force;the use of multi-phase coil windings can increase the scanning range of the electron beam and reduce the additional defocusing phenomenon caused by the uneven deflection magnetic field.Improve the accuracy of parts with larger forming sizes;for the dynamic compensation of the focus current control problem,a fuzzy PID control algorithm is proposed to control the main focus system.The simulation experiment proves that the focus system using fuzzy PID control has high stability and sensitivity,Can effectively ensure the stability of the main focus magnetic field,using the ultra-microcrystalline iron core as the magnetic core of the deflection coil and the focus coil can ensure the synchronization of the deflection response and the focus correction response under high frequency conditions,and ensure the deflection of the electron beam.The accuracy of dynamic defocus correction: By optimizing the winding circuit of the secondary focusing coil,the correction performance of the secondary focusing coil for electron beam defocusing under variable frequency conditions is improved.The subject research shows that by compensating the focus current value,the quality of the electron beam spot can be effectively improved,and the processing accuracy of the additive manufacturing equipment and the quality of the part forming can be improved.The dynamic compensation of the focus current during the electron beam processing can provide a technical guarantee for the future use of powder bed additive manufacturing equipment to form large-size parts.