A patent applied by Swedish ARCAM company in 1994, The developed technique is called electron beam melting forming technology (Electron Beam Melting), ARCAM is also the first company in the world to commercialize electronic beam manufacturing, And the first generation of equipment was introduced in 2003.Since then, the Massachusetts Institute of Technology, NASA and other have developed their own rapid manufacturing system based on electron beam.
Electron Beam Solid Freeform Fabrication (EBSFF) developed by Massachusetts Institute of Technology. EBSFF technology uses wire supply forming material two by electron beam melting metal wire, electron beam fixed, metal wire by wire feeding device and a movable working table, and the lens technology, electron beam freeform fabrication, the influence of many factors, such as electron beam, acceleration the voltage, current, focusing deflection scanning, working distance, workpiece speed, wire feed speed, range, feeding angle, wire end from the workpiece height, wire length etc.. These factors play an important role in the geometrical parameters of the fused section, and it is very difficult to distinguish the single factor.
Selective melting of Swedish ARCAM company and Tsinghua University developed electron beam (EBSM) metal powder by electron beam melting shop on the work table, similar and selective laser melting technology, to achieve real-time melting by electron beam deflection, the technique does not need 2D moving parts, fast scanning can be achieved in metal powder forming.
The principle of electron beam selective melting (EBSM)
Similar selective laser sintering and selective laser melting technology, electron beam selective melting technology (EBSM) is a kind of high energy electron beam bombardment high selective metal powder, rapid manufacturing technology which makes the melting powder forming materials.
The process of EBSM Technology: first in the powder plane spreading a layer of powder; then, the electron beam under the control of a computer in accordance with the contour information of molten metal powder in selective, electron beam bombardment by melting together, and has the following parts forming and bonding layers stacked until the whole parts are melting completed; finally, the removal of excess powder will be required for 3D products.
The real time scanning signal of the upper computer is transmitted to the deflection coil through digital to analog conversion and power amplification, and the electronic beam deflects under the magnetic field produced by the corresponding deflection voltage to achieve selective melting. After a dozen years of research, some orthogonal experiments have been carried out on some technological parameters such as electron beam current, focusing current, action time, powder thickness, accelerating voltage and scanning mode. The action time has the greatest influence on molding.
The advantages of electron beam selective melting
Electron beam direct metal forming technology by high energy electron beam processing as heat source, scanning forming can be performed by manipulating the magnetic deflection coil, no mechanical inertia, vacuum environment and electron beam has also can avoid the metal powder in liquid phase sintering or melting process is oxidation.
Compared with laser, electron beam has the advantages of high energy utilization, large depth of action, high material absorption rate, stability and low operation and maintenance cost. The advantage of EBM technology is the high efficiency of forming process, small deformation of parts, no metal support during the forming process, and more compact microstructure.
The focusing control of the electron beam is faster and more sensitive. The deflection of the laser requires the use of a vibrating mirror. The speed of the galvanometer is very high when the laser is scanning at high speed. When the laser power is large, the oscillating mirror needs more complicated cooling system, and the weight of the galvanometer is also increased significantly. As a result, the scanning speed of the laser will be limited when the power scanning is used.
When scanning the larger forming range, the focal length of the laser is difficult to change rapidly. The deflection and focus of the electron beam are accomplished by a magnetic field. The deflection and focus length of the electron beam can be controlled sensitively and quickly by changing the intensity and direction of the electrical signal.
The electron beam deflection focusing system is not disturbed by metal evaporation. When the metal is fused with a laser and electron beam, the metal vapor will diffuse throughout the forming space and be plated with metal film on any surface of the contact. The electron beam deflection focusing is completed in the magnetic field, so it is not affected by the evaporation of metals. The optical devices such as lasers, mirrors and so on are easy to be polluted by evaporation.
The main problems of electron beam selective melting
The vacuum pumping process in the powder is easy to flow away, resulting in pollution of the vacuum system; but there is a special problem that powder scattering phenomenon, the reason is that the electron beam has a larger kinetic energy, heating, heating when high speed metal atoms to bombardment, electronic part of the kinetic energy is directly converted into kinetic energy of powder particle.
When the powder flow is better, the powder particles will be pushed the formation of electron beam scattered phenomenon. The basic principle is to prevent cooking powder to improve the stability of powder bed, overcome beam thrust, there are four main measures: reduce the flowability of powders for preheating powder, preheat the molding plate, optimization of electron beam scanning. Therefore, the powder material has been difficult to be the object of the vacuum electron beam equipment, and the research on the process parameters is seldom reported.
The powder is easy to be broken in the electron beam under the action of the phenomenon of electron beam domain different powder system can withstand the current value (sodium current) and electron beam scanning speed (the speed of its domain value) criterion, and based on the mixed powder.
The EBM molding chamber must be of high vacuum in order to ensure the normal operation of the equipment, which makes the EBM Technology.