Research Of Deflection Scanning System For Electron Beam Selective Melting

The technology of the electron beam selective melting has wide application prospect in t he aerospace fields and themedical fields for its high precision molding while the fast and hig h-accuracy deflection of the electron beam scanning system is the key to the melting technolo gy. This paper focuses on the scanning system of the electron beam selective melting. Based on the ZD60-6A CV500L vacuum electron beam welding machine, the deflection scanning system has been built through both the software and hardware design and the deflection coil has been designed as well. The construction of the electron beam welding machine makes it possible that the electron beam selective melting can be used in rapid prototyping.The design deflection coil with multi-pole structure can improve the uniformity of magnetic field. The influence of the coil structure and the core material on the deflection angle and the magnetic field uniformity of coil has been studied through three-dimensional electromagnetic simulation. The result shows that the increase in the number of the cores can significantly expand the deflection angle and the uniformity of magnetic field also improves with the coil pole number. For 24 pole coils, the fluctuation of magnetic flux density is less than 1% along the deflection direction of the electron beam within a distance of 2.5mm to the coil center. Comparing the 24 core and non-core deflection coil with unit current, the core coil has the deflection angle of 1.19°in X direction and a deflection angle of 1.17°in Y direction while the non-core coil has the deflection angle of 0.37°in X direction and a deflection angle of 0.38°in Y direction.The rapid deflection scanning control system has been built for the electron beam selective melting based on FPGA. Through the slicing algorithm, the control system is able to cut the 3D models into thin slices with detailed information. The system can be switched among three modes of ready, preheat and melt conveniently and the scanning frequency of electron beam can be adjusted from 0 to 20kHz, which can accurately control the electron beam deflection scanning.Through pentagram scanning test, an absolute error limit of 0.28mm is achieved and an absolute error limit of 0.62mm was obtained through the scanning of a disk. As a result, the scanning system of the electron beam selective melting has a high scanning precision. The system can achieve high precision rapid prototyping with appropriate process parameters.