Electron beam selective melting equipment and method fused with online CT detection system

Abstract

The invention provides electron beam selective melting equipment and method fused with an online CT (computed tomography) detection system, which are characterized in that an industrial CT system is fused in an EBSM (electron beam selective melting) process, and the purpose of printing a workpiece while detecting the workpiece is achieved. Through the designed rotating platform, the Y-axis moving device and the Z-axis moving device, the radiation source and the detector have six degrees of freedom, namely, the radiation source and the detector can move in the X direction, the Y direction and the Z direction, the centers of the radiation source, the detector and a machined workpiece are kept on the same straight line all the time, and the imaging accuracy is guaranteed. The EBSM machining process is monitored in real time, all-around information of internal defects of parts can be visually and accurately expressed, the defect information is stored in a defect database set in a computer system, and then a computer simulates and simulates to search and optimize the optimal parameters of the defects and stores the optimal parameters in the corresponding defect database. And if similar defects appear, the database can quickly identify the defects and feed back a signal for improving the defects to the electron beam equipment in time, so that the similar defects during printing are avoided. Certainly, workpieces with high quality requirements can be printed again, so that the time for integrally printing the workpieces due to the fact that the defects are not found in time, the processing cost and production raw materials are saved.

Description

Technical Field

[0001] The present invention relates to the field of metal additive manufacturing, and in particular to online monitoring of an electron beam selective melting process by an industrial CT system, and identification, marking and prevention of defects occurring during a printing process. Background Art

[0002] With the rapid development of aerospace, biomedicine, microelectronics, transportation and defense industries, metal manufacturing parts are becoming increasingly complex and their precision requirements are becoming higher and higher. Traditional welding processes are difficult to adapt to the development trend of high-tech manufacturing fields. Electron beam selective melting technology (ESBM) is a technology developed by additive manufacturing technology in the 21st century. This technology is based on the principle of discrete stacking. It uses electron beam as a heat source and selectively melts metal powder under computer control, melting layer by layer, stacking layer by layer, and finally forming dense three-dimensional metal parts. However, in the process of processing and forming metal parts in additive manufacturing, there are still severe technical challenges and several common basic problems that need to be solved urgently. For example, there are often defects such as cracks, holes and slag inclusions inside the processed parts. They not only have a certain impact on the performance and service life of the workpiece, but also threaten the safety of the machine. However, there is no complete method for online prevention and detection of these defects.

[0003] Therefore, "industrial computed tomography" (industrial CT for short) came into being in this context. Industrial CT imaging technology is a non-destructive testing technology that reconstructs the internal structure image of an object based on external projection data. This technology can detect internal defects of an object non-contactly and non-destructively to obtain a non-overlapping digital image. This technology can not only obtain the three-dimensional spatial information of internal defects of parts, but also can intuitively and accurately express the full range of information of internal defects of parts. By integrating the industrial CT system into EBSM, the defects appearing in EBSM are identified and marked, and the parameters of the electron beam equipment are adjusted to timely improve the quality problems caused by defects. This not only improves the quality of processed parts, reduces the high production costs and long processing cycles caused by the quality of the parts after the defects are formed, but also saves the defects that have appeared in the processing process to the defect database set by the computer. When the parts are processed again, if similar defects appear, the computer system will quickly identify and mark them based on the defect database, and at the same time feedback the best industrial parameters to optimize the defect to the electron beam equipment, so as to deal with defects in a timely manner, save production costs, and reduce processing cycles. Summary of the invention

[0004] The present invention provides an electron beam selective melting device and method integrated with an online CT detection system, and an industrial CT system is integrated into the EBSM process. The device can monitor the EBSM process in real time, intuitively and accurately express the full range of information on internal defects of parts, reduce various losses caused by the failure to find defects in time and resulting in substandard quality of processed parts, improve the production quality of EBSM and shorten the processing cycle. To achieve the above purpose, the present invention adopts the following technical solutions.

[0005] The first step is to pour the metal powder to be printed into the powder bin under vacuum, and at the same time start the computer system that controls the radiation source and detector, putting it in the pre-preparation stage.

[0006] In the second step, the metal powder flowing from the powder bin is sent to the forming platform using the powder spreading mechanism, and the electron gun is started to emit a small electron beam to pre-sinter and fix the powder bed. The preheating of the powder is stopped after it reaches the optimal temperature.

[0007] In the third step, after preheating the powder, the composite equipment starts to work, the electron gun starts to lower the beam, and the forming processing platform drops to a certain height. The drop height is the thickness of the powder layer and the height of the processed part. At this time, the electron gun is turned off and the industrial CT scanning mode is turned on. Before the CT mode is turned on, the radiation source and the detector need to adjust the spatial position according to the shape and size of the formed workpiece, so that the focal spot of the radiation source, the rotation center of the processed workpiece, and the center of the detector are as close to a straight line as possible, which ensures that the two-dimensional slice image of the workpiece is located in the center.

[0008] The fourth step is to adjust the position of the radiation source and detector by controlling the rotating platform, Y and Z axis mechanical motion devices, and then the industrial CT system starts. The radiation source emits X-rays to pass through the formed workpieces, and then the detector receives the X-rays passing through the workpieces, and converts them into electrical signals and transmits them to the data acquisition and signal processing system to form a two-dimensional slice image. At the same time, the computer system controls the uniform rotation of the rotating table, so that the X-rays scan the formed workpieces in all directions, thus forming multiple continuous two-dimensional slice images. These slice images are then reconstructed into a three-dimensional model through the corresponding algorithm, and the defects inside the workpieces can be clearly observed.

[0009] Step 5: After the workpiece is reconstructed, if there are defects in the workpiece, they will be identified and marked in the 3D image through the machine deep learning algorithm and saved in the computer's defect database. This will not only facilitate accurate identification during re-processing, but also play a preventive role in advance. In addition, according to the optimized processing parameters in the defect database, the same defects can be prevented from occurring in the unprocessed parts (for workpieces with stricter quality requirements, the processed parts can be reprinted, saving printing time). If there are no defects or minor defects in the workpiece (the quality requirements for the workpiece are not high), turn off the industrial CT system and the rotating platform, continue to start the electron gun down beam, and complete the processing of the remaining parts.

[0010] Step 6: Repeat steps 3, 4 and 5 until the entire printing process is completed. During the process, you can decide whether to print based on the quality requirements of the workpiece.

[0011] In order to complete the above technical solution, the present invention adopts the following method: The invention is characterized in that it includes a rotating platform, an industrial CT system, and a movable mechanical device. After the electron beam processes a workpiece of a certain height, the ray source and the detector are turned on, and the electron gun is stopped from beaming down. At the same time, the movable mechanical device is adjusted so that the ray source, the detector, and the center of the processed workpiece are in the same straight line. The X-ray passes through the formed workpiece, and the detector receives the X-ray after passing through the workpiece to form a two-dimensional slice image. At this time, the computer controls the rotating platform to rotate (the rotating platform can not only rotate, but also the Z-axis mechanical device can move left and right on it), so that the X-ray scans the processed workpiece in all directions, and thus forms multiple two-dimensional slice images. Multiple continuous two-dimensional slices are constructed into a three-dimensional model through corresponding algorithms, that is, the internal structure of the processed workpiece can be clearly observed, and then the defects are identified and marked through the machine deep learning algorithm, and the defects appearing in the three-dimensional model are saved in the computer system defect database to avoid the same defects in the next printing. At the same time, according to the defects that have appeared, the electron beam processing parameters are improved, which plays a role in real-time monitoring of defects. Of course, for workpieces with high processing quality requirements, printing can be stopped at any time and reprinted, which also avoids the losses caused by unqualified quality after the workpiece is fully processed, such as waste of raw materials and increased production cycle. If there are no defects or minor defects (the quality requirements for the workpiece are not high), the industrial CT system and the rotating platform are turned off, and the electron gun is started. That is, the electron beam will scan a part every time it processes a part, and the processing of each part can be detected in real time until the whole part is fully formed and the quality meets the required requirements.

[0012] The rotating platform has a structure similar to a slide rail. When the industrial CT system is turned on, the movable mechanical device on it can be moved left and right to adjust the position of the radiation source and the detector in the X-axis direction. At the same time, the rotating platform is the largest carrier of the entire mechanical device. Its greatest function is to continuously rotate at a uniform speed to ensure that the X-rays scan the processed parts in all directions. When the platform rotates, the radiation source and the detector rotate under the control of the rotating platform, and the forming cylinder does not rotate.

[0013] There are two sets of movable mechanical devices, which control the movement of the ray source and the detector on the Y axis and the Z axis respectively. There is a relative motion relationship between the two sets of movable devices and the rotating platform, so that the ray source and the detector have 6 degrees of freedom, that is, they can move in the X, Y, and Z directions.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides an electron beam selective melting device and method integrated with an online CT detection system, which utilizes the advantages of industrial CT detection. In the EBSM process, a ray source and a detector are used to scan the processed parts online, and then the defects are identified, marked and saved, which can not only improve the production quality of the processed parts, save costs, and reduce the processing cycle, but also store the defect database. According to different types of defects, the computer system will feedback the corresponding processing parameters for improving the defects to the EBSM process, and prevent and avoid the defects that have already occurred. Compared with the structure of the traditional single electron beam device, the beneficial effects are as follows.

[0015] The rotating platform not only supports the entire mechanical device, but also can rotate at a constant speed to scan the workpiece in all directions after the radiation source is started. It also serves as a slide rail to allow the mechanical moving device above to move left and right on it to adjust the position of the radiation source and detector in the X-axis direction.

[0016] There are two sets of movable mechanical devices, which control the movement of the radiation source and the detector on the Y-axis and the Z-axis respectively. There is a relative motion relationship between these two sets of movable devices and the rotating platform, so that the radiation source and the detector have six degrees of freedom in six directions. Under the precise control of the motor, they can adjust their own position according to the size and shape of the processed parts.

[0017] During the EBSM process, the defects of the workpiece can be monitored online, thereby improving the quality of the processed parts, and all existing defects can be concentrated in the set database. When the parts are processed again, the electron beam equipment will optimize and improve the defects according to the database to prevent the same defects from occurring in the processed parts.

[0018] Figure 1 The present invention provides an electron beam selective melting device and method integrated with an online CT detection system.

[0019] Numbers in the figure: 1. Electron gun; 2. Filament; 3. Electron beam; 4. Electron beam focusing coil; 5. Electron beam deflection coil; 6. Powder bin; 7. Powder spreading mechanism; 8. Detector; 9. Y-axis moving device; 10. Z-axis moving device; 11. Vacuum chamber; 12. Temperature protection cover; 13. Radiation source; 14. Forming cylinder; 15. Rotating platform. DETAILED DESCRIPTION

[0020] Now the invention is further described in detail with reference to the accompanying drawings. The above drawings are simplified schematic diagrams, which only illustrate the basic structure of the invention in a schematic manner, and therefore only show the components related to the invention.

[0021] The present invention provides an electron beam selective melting device and method integrated with an online CT detection system, comprising an electron gun 1, a filament 2, a powder bin 6, a powder spreading mechanism 7, a detector 8, a Y-axis moving device 9, a Z-axis moving device 10, a ray source 13, and a rotating platform 15.

[0022] First, put the metal powder to be printed into the powder bin 6. After the equipment starts working, the metal powder flows down from the powder bin 6, and is evenly spread on the working platform by the powder spreading device 7, and then sent to the forming platform under the temperature protection cover 12 for preheating. The powder bed is pre-sintered and fixed by starting the electron gun 1 to emit a small electron beam 3, and the powder is preheated to reduce the powder collapse phenomenon. After the preheating is completed, the composite equipment starts working, starts the electron gun down beam, controls the processing platform to descend to a certain height, and the descending height is the forming height of the processed workpiece. After forming a certain height, the electron gun is turned off, that is, the down beam is stopped and the industrial CT detection scanning mode is turned on to achieve the function of processing and detecting at the same time. Before turning on, the focus of the radiation source, the center of rotation and the center of the detector should be as close to a straight line as possible, so that the subsequent processed workpiece is located in the center of the image, mainly by adjusting the rotating platform 15, the Y-axis moving device 9, and the Z-axis moving device 10. The ray source 13 and the detector 8 can be adjusted and moved in the three directions of the X, Y, and Z axes. After adjusting the positions of the various equipment, the ray source emits X-rays to pass through the formed processed samples, and the detector receives the X-rays passing through the workpieces and converts them into electrical signals to transmit to the data acquisition and signal processing system. At the same time, the rotating table 15 is controlled to rotate at a uniform speed, so that the X-rays can scan the processed parts in all directions to form multiple two-dimensional slice images. After the multiple continuous two-dimensional slice images are processed by the corresponding algorithm, the three-dimensional model can be reconstructed, and the defects inside the processed parts can be clearly observed. For the defects that have appeared, they are saved in a database set up in the computer system, and then the computer simulation is simulated to find the best industrial parameters for optimizing the defects and save them in the corresponding defect library to prevent the remaining unprocessed parts from having the same defects. When reprocessing the parts, if similar defects appear, the database can quickly identify them and timely feedback the signal of improving the defects to the electron beam equipment to avoid the same defects when printing. Of course, for workpieces with high quality requirements, the parts can be reprinted, saving the time and production cost of printing the entire parts due to the failure to find defects in time. When the quality requirements for the workpiece are not high, and there are no defects or relatively small defects, the industrial CT system and the rotating platform are turned off, the electron gun beam is started, and the EBSM processing process is circulated until the entire printing process is finally completed. In the meantime, the decision to print can be made based on the quality requirements for the workpiece.

[0023] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An electron beam selective melting device and method integrated with an online CT detection system, characterized in that: It includes a rotating platform, a movable mechanical device, and an industrial CT system. The metal powder flows down from the powder bin, and is evenly spread on the working platform through the powder spreading device, and then sent to the forming platform under the temperature protection cover for preheating. After the preheating is completed, the composite equipment starts to work, starts the electron gun beam and controls the processing platform to descend to a certain height. The descending height is the forming height of the processed workpiece. After forming to a certain height, the electron gun beam is turned off and the industrial CT scanning detection mode is turned on at the same time. The workpiece is processed and inspected at the same time, realizing the role of real-time monitoring of EBSM. Before the industrial CT system is turned on, the focus of the radiation source, the rotation center, and the center of the detector are first placed on the same straight line as much as possible. The radiation source and the detector can be moved in the three directions of X, Y, and Z axes mainly by adjusting the rotating platform, Y, and Z axis moving mechanical devices. After adjusting the positions of each device, the ray source is started to emit X-rays through the formed workpieces. Then the detector receives the X-rays passing through the workpieces and converts them into electrical signals to transmit to the data acquisition and signal processing system. The computer system controls the uniform rotation of the rotating platform so that the X-rays can scan the formed workpieces in all directions and form multiple continuous two-dimensional slice images. These two-dimensional slice images can be reconstructed into three-dimensional models after the corresponding algorithms. At this time, the defects inside the workpieces can be clearly observed. After marking the defects, save them to the defect database set in the computer system and use simulation software to find the best electron beam processing parameters to optimize the defects, and save these optimized parameter data to the corresponding defect library. When the workpiece is processed next time, if similar defects appear, the database can quickly identify them and promptly feedback the signal to improve the defects to the electron beam equipment to avoid the same defects in printing. When the quality requirements for the workpiece are not high, and there are no defects or relatively small defects, the industrial CT system and the rotating platform are turned off, and the electron gun beam is continued to be started, the EBSM processing process is circulated, and online inspection is performed while processing. The above steps are repeated until the entire printing process is finally completed. In the middle, whether to continue printing can be decided based on the quality of the workpiece.

2. According to claim 1, an electron beam selective melting device and method integrated with an online CT detection system, characterized in that: The industrial CT system is integrated into the EBSM process, and the printing and detection are carried out simultaneously, that is, the EBSM processing process is monitored in real time, and the all-round information of the internal defects of the parts is expressed intuitively and accurately. The defects are identified and marked in the three-dimensional image through the machine deep learning algorithm, and then the simulation software is used to find the best electron beam processing parameters to optimize the defects and save them in the corresponding defect library. This not only facilitates the accurate identification of the defects of the processed parts next time, but also prevents the same defects from occurring in the unprocessed parts according to the optimized parameter data in the defect database (for parts with strict quality requirements, the equipment can be stopped immediately, that is, the processed parts can be reprinted, shortening the processing cycle). If no defects or relatively minor defects occur (when the workpiece quality requirements are not high), the industrial CT system and the rotating platform are turned off, and the electron gun beam is continued to be started. The above steps of processing and detection are repeated to complete the processing of the remaining parts. This not only reduces the financial losses caused by the substandard quality of the processed parts due to the failure to find defects in time, but also shortens the processing cycle and saves raw materials for production.

3. According to claim 1, an electron beam selective melting device and method integrated with an online CT detection system, characterized in that: The rotating platform has a structure similar to a slide rail. When the industrial CT system is turned on, the mobile mechanical device above can move left and right on the platform to adjust the position of the radiation source and the detector in the X-axis direction. At the same time, as the largest carrier of the entire mechanical device, the rotating platform can rotate continuously at a constant speed, thus ensuring that the X-rays can scan the processed parts in all directions. When the platform rotates, the radiation source and the detector rotate simultaneously under the control of the rotating platform, and the forming cylinder does not rotate.

4. According to claim 1, an electron beam selective melting device and method integrated with an online CT detection system, characterized in that: There are two sets of movable mechanical devices, which control the movement of the ray source and the detector on the Y axis and the Z axis respectively. There is a relative motion relationship between the two sets of movable devices and the rotating platform, so that the ray source and the detector have 6 degrees of freedom, that is, they can move in the X, Y, and Z directions.

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