Research Of Rapid Prototyping System Based On 3D Scanning Electron Beam

Electron beam rapid prototyping technology is a novel processing method which can be considered as the combination of electron beam processing and rapid prototyping manufacturings. It has more advantages such as vacuum environment, high energy density, rapid scanning speed, precise control and parts rapid manufacturing without any molds, shorter design cycle and lower manufacturing cost. Therefore, this technique will be greatly developed in the automotive, aerospace and medical fields. However, only few related research works have been reported around the world. None has been published at home.In order to meet the requirement of rapid prototyping process, all related research works have been already investigated. Among them, some works must to be prepared before a new layer will be sintered. The works are, the electron beam focus position is unchanged during rapid prototyping process, the current sintered layer is moved down through the mechanical devices, the devices are made up of computer, control card, sensor, motor, drive gear and shaft etc. Their own shortcomings such as low precision, low efficiency and control singnal delaying can not be overcomed. Moreover, to accommodate those driving devices, the vacuum chamber size has to be increased.Studies on electron beam technique used for rapid prototyping are investigated in this paper. On the basis, to improve the processing accuracy and efficiency of tradional electron beam prototyping system, based on 3D scanning electron beam, one novel rapid prototyping technique is developed. In details, the height of the device is unchanged during processing and mechanical devices which the sintered workpiece is put on are replaced by new controlling software, and the software can control the current signals of X and Y deflecting coils and focusing coils which have been fixed in the direction of EB spreading path in the EB gun. The electron beam moving track in plane XY is controlled by deflecting coils, the focus position in the Z direction controlled by focusing coils, and the EB track in three dimentions can be controlled at the same time.Based on the common electron beam welding machine, the 3D scanning electron beam rapid prototyping system has been developed, and the hardware and software platforms are rebuilt. The hardware platform includes prototyping subsystem (Focusing and Scanning deflecting coils of EB welding machine), the control subsystem (Computer, Touch screen, PLC), temperature acquisition subsystem (Infrared Thermometer, Data Acquisition Card, Computer). Meanwhile, corresponding controlling software procedures are designed, they are electron beam processing operation, data automation processing of CAD model, temperature closed-loop control, and the serial communication between computer, touch screen, PLC and EB gun. The control system software interface can be friendly visited, be operated easily and safely.Slicing method of CAD model to be sintered is discussed. Different slicing methods are compared, and the direct slicing algorithm based on the second development of AutoCAD software is put forward. The slicing contour information saved in BMP format files can be collected by the direct slicing algorithm from any complicated CAD models, and the BMP files is feasible to read by corresponding Labview language program which can transfer slicing data from AutoCAD to Labview data file. Through in-depth research and analysis for the existing technique of scanning and hatching, a novel composite filling method, which combined contours offsetting and region hatching, has been put forward. The present way can make use of the property of high accuracy and eficiency in contours offsetting and region hatching. And it is adaptive for various technics in RP&M. In order to implement the proposed method, the slicing layer is divided into several small regions according to optimization rule, and contours offsetting is adopted in each small region. The group algorithm of intersections, which reduced the process of partition and increased the efficiency, is also used to relize the region hatching.Utilizing the effect of extremum temperature of molten pool caused by the interactive effect of electron beam with metal powder, the measurement methods of EB focus are studied. The factors of measurement methods are analyzed. During electron beam processing, the changing rules of metal powder molten pool temperature following focusing current are discovered. The peak of metal powder pool temperature corresponds to the transferring point of critical energy density in the dynamic focusing process of electron beam processing. Based on the characteristics of critical temperature, the measuring concept of dynamic focal spot of electron beam is put forward in the paper. The method of measuring dynamic focal spot of electron beam is invented to provide a new possibility for 3D scanning prototyping through changing fofus position of EB.Adaptive fuzzy PID temperature control technology of the sintering parts is used in the electron beam rapid prototyping process, the temperature signals of the sintered parts are obtained online and compared with the setting value, so as to get the error and the error change rate of the sintered parts temperature, which is acted as the two inputs of the adaptive fuzzy PID controller. The controller gives an appropriate control signal according to its inputs to adjust the electron beam current, and the closed loop control of rapid prototyping temperature is realized. The simulation and experiment results show that the better dynamic characteristic, control accuracy can be obtained if adaptive fuzzy PID rather than traditional PID or Fuzzy control technology is used in the electron beam rapid prototyping process.The mechanism of 3DSEB rapid prototyping is studied in this paper. The physical model of 3DSEB rapid prototyping is established and studied. The necessary conditions for one success sintering process must be met through the model theoretical analysis, which are EB scanning space must be smaller than the max sintering width and the max sintering depth at the same time. The effects of EB current, scanning time, scanning frequency and scanning point num on sintering depth are studied. The results show that the sintering depth increases with the increasing of EB current, scanning time, scanning frequency and scanning point num. And the effect of EB current on sintering depth is the most significant.Novel method to solve the uniformity of energy density distribution of the irregular scanning tracks is presentd in this paper. To avoid local energy over high, scanning points distribution must be varied properly, and the accuracy of sintering parts can be improved.The experiment results show that the accuracy can be better by decreasingthe point distribution density at the corner for irregular scanning tracks configuration.In this paper software system of 3DSEB rapid prototyping based on LABVIEW language and VISUAL LISP language has been developed. Software structure based on modular programming and visual programming technique is built in this paper. The whole software system is made up of five modules which are 3D model design and display; model slice data processing; slice data filling; EBW automatic operation and temperature closed-loop control module. The whole processing controlling software including temperature acquisition, data processing, EB focus track 3D location and temperature control are validated through 3DSEB experiment equipments and that is appreciated by sintering models such as the cylinder and four- plum column.