Electron beam selective melting electron beam spot measurement and calibration device and method

Abstract

The invention discloses an electron beam spot measurement and calibration device and method for electron beam selective melting. The device comprises an electron beam emission unit, a focusing deflection unit, a melting forming area, an electron beam spot measurement module and an electron beam spot calibration unit. The electron beam emission unit is used for forming high-energy large-beam electron beams, the focusing deflection unit is used for focusing the high-energy large-beam electron beams into fine electron beam spots and scanning the fine electron beam spots, and the electron beam spot measurement module is located above a melting forming area and used for measuring current density distribution of the electron beam spots. A plurality of measurement calibration positions which are distributed at equal intervals in a two-dimensional mode are arranged in the melting forming area, all the measurement calibration positions jointly form coordinates of the beam spot measurement system, and the electron beam spot calibration unit is used for controlling the electron beam spot measurement module and the focusing deflection unit. According to the invention, accurate measurement of beam spot current density distribution at a fixed position is realized, and thermal damage of a high-energy large-beam electron beam to the small-hole diaphragm and the Faraday cup is also avoided.

Description

Technical Field

[0001] This invention relates to the field of electron beam additive manufacturing, and more specifically to an electron beam selective melting electron beam spot measurement and calibration device and method. Background Technology

[0002] Selective electron beam melting (SEBLM) is an additive manufacturing technology that uses an electron beam as a heat source. Compared with additive manufacturing technology that uses a laser as a heat source, SEBLM has higher energy density and energy utilization, and is particularly suitable for processing high-temperature refractory alloys such as tungsten, molybdenum, tantalum, and niobium, as well as complex aerospace structures.

[0003] In selective electron beam melting (SEBLM), the distribution and size of the electron beam spot on the forming plane are decisive factors affecting the final precision of the formed part. Measuring and correcting the electron beam spot size before SEBLM is crucial for ensuring beam quality and the machining accuracy of the formed part.

[0004] Currently, in selective electron beam melting (SEBLM) technology, the beam spot diameter is typically on the order of hundreds of micrometers. Furthermore, electron beams have high accelerating voltage, large current, and high beam spot energy density. Traditional knife-edge-based beam spot measurement methods are prone to melting and deformation of the knife edge under high-energy-density electron beam irradiation, affecting the accuracy of beam spot measurement. Chinese patent application CN118330706A discloses an electron beam spot calibration device and method, employing two calibration plates. The upper plate uses an array of coarse holes for coarse calibration, while the lower plate uses an array of fine holes for fine calibration. The electron beam is scanned through the calibration holes, and the current signal collected by the calibration holes is extracted and converted into an image signal. Based on image processing methods, beam spot size information is extracted. Then, the coil current parameters of the deflector, objective lens, and astigmatism reducer are adjusted, and the above process is repeated until the electron beam calibration is complete. This method is suitable for calibrating the beam spot at a fixed location. However, for high-power-density electron beams, the melting damage caused by the beam spot to the calibration aperture is not considered. When measuring small-sized beam spots, the processing accuracy of the array apertures on the upper and lower plates and the assembly accuracy between the upper and lower plates are very high, which is not conducive to the measurement and calibration of small-sized beam spots. In order to protect the current measuring device from damage by high-power-density electron beams, the literature "Transient Data Acquisition and Preprocessing of Vacuum High-Energy Electron Beams" mentions a method for measuring the power density of vacuum high-energy electron beams. This method uses a Faraday cylinder with an aperture size much smaller than the cross-sectional size of the beam spot. The electron beam is rapidly scanned within a small angular range and the electron beam covers the Faraday cylinder. Then, the current of the Faraday cylinder under different scanning signals is collected. Since the position of the electron beam corresponds one-to-one with the scanning signal, the beam spot power density distribution in a two-dimensional plane can be established. Chinese patent application CN117169950A discloses a method for measuring the beam spot of a high-power electron beam. The method involves scanning the electron beam in a circular trajectory of a certain diameter. Simultaneously, a Faraday cup is positioned and moved along the x-direction, and another Faraday cup is positioned and moved along the y-direction. During the electron beam scanning process, the currents of the two Faraday cups in the x and y directions are collected and converted into voltage signals. Based on the coordinates of the Faraday cups and the corresponding voltage signals, the two-dimensional distribution of the electron beam spot can be obtained. In the second and third methods for measuring beam spot power density distribution, to prevent high-temperature damage to the Faraday cups from the high-power-density electron beam, both employ rapid scanning of the electron beam to shorten the contact time between the electron beam and the Faraday cup, thus avoiding burn-out of the Faraday cups during the measurement process.

[0005] However, during the aforementioned measurement process, the Faraday cup collects the electron beam current. Since the electron beam is constantly moving within a two-dimensional plane, the minute movements of the electron beam have a more significant impact on the beam spot distribution, especially at large deflection angles. This means that the beam spot power density distribution established using a fixed-position Faraday cup cannot accurately reflect the beam spot's power density distribution, resulting in measurement errors. Therefore, measuring the beam spot current density distribution while avoiding high-temperature damage to the Faraday cup and ensuring the electron beam's stable position is crucial for improving the measurement and calibration accuracy of the electron beam spot, as well as further enhancing the precision and quality of part forming. Summary of the Invention

[0006] To address the problem that the electron beam current collected by the Faraday cup in existing high-power electron beam spot measurement methods is not accurate enough to reflect the local current density within the electron beam spot due to electron beam scanning movement, this invention provides an electron beam selective melting electron beam spot measurement and calibration device and method to improve the measurement and calibration accuracy of electron beam spots.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An electron beam selective melting electron beam spot measurement and calibration device includes an electron beam emitting unit, a focusing and deflection unit, a melting and forming region, an electron beam spot measurement module, and an electron beam spot calibration unit; The electron beam emitting unit is used to form a high-energy, high-current electron beam. The focusing and deflecting unit is used to focus the high-energy, high-current electron beam into a small electron beam spot and scan it. The electron beam spot measurement module is located above the melting and forming area and is used to measure the current density distribution of the electron beam spot. The melting and forming area is provided with m×m two-dimensional equidistant measurement and calibration positions. All measurement and calibration positions together constitute the coordinates of the beam spot measurement system. The electron beam spot measurement module includes a high-precision displacement stage, an aluminum plate, a Faraday cup, a camera, a pinhole aperture, and a support. The aluminum plate, the pinhole aperture, and the Faraday cup are fixed on the high-precision displacement stage by the support. The camera is located directly above the corner of the beam spot measurement system coordinates. The pinhole aperture has a square hole with a side length of ΔL at its center. The electron beam spot calibration unit is used to control the movement of the high-precision displacement stage, collect the position coordinate data of the high-precision displacement stage, collect the current signal of the Faraday cup, calculate the beam spot contour size, and adjust the excitation of the focusing and deflecting unit.

[0008] Furthermore, the electron beam emitting unit includes a cathode, a suppressor, and an accelerating electrode. The cathode is used to emit an electron beam, the suppressor is used to control the on and off of the electron beam, and the accelerating electrode is used to regulate the energy of the electron beam. The focusing and deflection unit includes an astigmatism reducer, an objective lens, and a deflector. The astigmatism reducer is used to adjust the beam spot uniformity, the objective lens is used to adjust the beam spot focusing state and adjust the beam spot size, and the deflector is used for deflection scanning of the electron beam in the melting and forming region.

[0009] Furthermore, the electron beam spot calibration unit includes a data acquisition module, a host computer, and an excitation signal control module. The data acquisition module is used to acquire the position coordinate data of the high-precision displacement stage and the current signal of the Faraday cup. The host computer is used to control the movement of the high-precision displacement stage and calculate the beam spot profile size. The excitation signal control module is used to adjust the excitation of the astigmatism reducer, objective lens, and deflector.

[0010] A method for measuring and calibrating electron beam spots in selective electron beam melting includes the following steps: Step 1: Turn on the electron beam emitting unit and form a focused deflection beam by adjusting the excitation of the electron beam emitting unit and the focusing deflection unit; Step 2: Determine the preliminary dimensions of the focusing deflection beam profile using the electron beam spot measurement module; Step 3: Establish the beam spot current density distribution and calculate the fine dimensions of the focusing deflection beam spot profile using the electron beam spot measurement module; Step 4: Calibrate the focusing deflection beam profile size using the electron beam calibration unit.

[0011] Furthermore, the electron beam emitting unit includes a cathode, a suppressor, and an accelerating electrode. The cathode is used to emit an electron beam, the suppressor is used to control the on and off of the electron beam, and the accelerating electrode is used to regulate the energy of the electron beam. The focusing and deflection unit includes an astigmatism reducer, an objective lens, and a deflector. The astigmatism reducer is used to adjust the beam spot uniformity, the objective lens is used to adjust the beam spot focusing state and adjust the beam spot size, and the deflector is used for deflection scanning of the electron beam in the melting and forming region. The electron beam spot calibration unit includes a data acquisition module, a host computer, and an excitation signal control module. The data acquisition module is used to acquire the position coordinate data of the high-precision displacement stage and the current signal of the Faraday cup. The host computer is used to control the movement of the high-precision displacement stage and calculate the beam spot profile size. The excitation signal control module is used to adjust the excitation of the astigmatism reducer, objective lens, and deflector.

[0012] Furthermore, step one specifically includes: The cathode, suppressor, and accelerating electrode of the electron beam emitting unit are turned on to obtain a high-energy, high-current electron beam. m×m two-dimensional, equally spaced measurement and calibration positions are selected within the melting and forming region. The objective lens and deflector are turned on, and the excitation of the deflector is adjusted to deflect the electron beam to near measurement and calibration position A within the melting and forming region. Then, the excitation of the objective lens is adjusted to focus the electron beam into a small spot, melting the powder bed metal. The excitation of the suppressor, objective lens, and deflector at this point is recorded. Then, the excitation of the suppressor is adjusted to turn off the electron beam, and the excitation of the objective lens and deflector is kept constant. At this point, there is no electron beam spot on the forming plane.

[0013] Furthermore, step two specifically involves: Set the measurement calibration position A of the melting and forming area in step one as the initial position of the beam spot measurement system coordinates, and position the camera directly above the initial position of the beam spot measurement system coordinates. Reset the high-precision displacement stage to the initial position of the beam spot measurement system coordinates. Use the high-precision displacement stage to move the support to the powder bed metal melting area in step one, ensuring that the aluminum sheet is directly above the measurement calibration position A. Record the position coordinates (x0, y0) of the high-precision displacement stage at this time. Then adjust the excitation of the suppression electrode to the excitation of the suppression electrode recorded in step one. At this time, the electron beam irradiates the aluminum sheet, and waits for the Faraday cup below the aluminum sheet to be detected. Once a stable current is detected, the excitation of the suppressor is adjusted to turn off the electron beam. The support is moved to the initial position of the beam spot measurement system coordinates. The camera's focal length is adjusted so that a complete and clear image of the aluminum sheet appears in its field of view. The melting point dimensions L1 and L2, as well as the distances s1 and s2 of the melting point center relative to the aluminum sheet boundary, are captured and measured by the camera. The melting point dimensions are used as the preliminary dimensions of the beam spot profile, and the melting point center position is used as the beam spot center position. Then, a small aperture of a certain size is selected to measure the beam spot current density distribution, and a square area is selected as the measurement area for the beam spot current density distribution.

[0014] Furthermore, step three specifically includes: A high-precision displacement stage is used to move the pinhole aperture to the corner of a square region. The high-precision displacement stage is controlled to move the pinhole aperture point by point along the x and y directions with a step size of ΔL, and the dwell time at each point is Δt, thus scanning the square region. When the pinhole aperture dwells at a certain point, a pulse excitation with a pulse width Δts ≤ Δt is applied to the suppressor electrode. The excitation magnitude is the same as the excitation of the suppressor electrode recorded in step one. During the time Δt, an electron beam passes through the pinhole and is collected by the Faraday cup located below the pinhole aperture. The current signal collected by the Faraday cup is transmitted to the host computer through the data acquisition module. The host computer establishes the beam spot current density distribution based on the current and coordinates of each sampling point, and normalizes the beam spot current density distribution. Based on the normalized current density distribution, the effective area contour and beam spot contour size are determined, and the coordinates (X, Y, Δt) of discrete points on the effective area contour line are extracted. e Y e), where e=1…N, N is the number of discrete points on the contour line, and the coordinates (X) are obtained by averaging the x and y coordinates of all discrete points on the contour line. m Y m Using the new coordinates of the beam spot center, the electron beam spot distribution exhibits rotational symmetry under the action of a rotationally symmetric system. When the electron beam is deflected, its rotational symmetry is disrupted, and the beam spot distribution becomes approximately elliptical. The beam spot profile size can be calculated using the following formula:

[0015] In the formula, a and b are the major and minor semi-axis of the elliptical profile of the clump spot; eig represents the eigenvalue of the solution matrix; and Cov represents the covariance.

[0016] Furthermore, the determination of the effective region contour of the beam spot is based on two criteria, specifically: The first method is to select the region enclosed by n times the maximum value of the normalized current density distribution as the effective region of the electron beam spot, where 0 < n < 1; The second method involves selecting an annular region as the effective region of the electron beam spot, where the current contained in the annular region is n times the total current of the beam spot, where 0 < n < 1.

[0017] Furthermore, step four specifically involves: The beam spot center coordinates (X) calculated in step three are used to... m Y m The beam spot center coordinates are compared with the designed deflection position coordinates. If the deviation between the beam spot center coordinates and the designed deflection position coordinates meets the design requirements, then the deflector excitation value at this time is set as the deflector excitation calibration value at the measurement position. If the deviation between the beam spot center coordinates and the designed deflection position coordinates does not meet the design requirements, then the deflector excitation value is finely adjusted through the excitation signal control module, and the beam spot current density distribution is measured again and the beam spot center coordinates (X) are calculated. m Y m ), until the deviation between the beam spot center coordinates and the designed deflection position coordinates meets the design requirements, and the final deflector excitation value after fine adjustment is set as the deflector excitation calibration value at the measurement position; Under the deflector calibration excitation, the beam spot diameter calculated in step three is compared with the design size. If the beam spot diameter and beam spot uniformity meet the design requirements, the objective lens excitation and astigmatism correction excitation at this time are set as calibration values. If they do not meet the design requirements, the objective lens excitation is first adjusted through the excitation signal control module, and the beam spot current density distribution is measured again and the beam spot diameter is calculated until the objective lens excitation that minimizes the beam spot diameter is found. Under the excitation of this objective lens, the astigmatism excitation is adjusted by the excitation signal control module, the beam spot current density distribution is measured again and the major and minor semi-axis of the profile is calculated until the astigmatism excitation that makes the beam spot uniformity best is found, and the astigmatism excitation at this time is set as the astigmatism excitation calibration value at the measurement position. Under the excitation of the astigmatism reducer calibration, the objective lens excitation is finely adjusted until the beam spot diameter meets the design size requirements. The objective lens excitation at this point is set as the objective lens excitation calibration value at the measurement position, and the beam spot calibration at the measurement calibration position selected in step one is completed. Then, the beam spot at the remaining positions is measured and calibrated in sequence to obtain the curves of the calibration excitation of the deflector, objective lens, and astigmatism reducer as the beam spot position. Based on the curves, the deflector excitation, objective lens excitation, and astigmatism reducer excitation required to deflect the electron beam to any position in the melting and forming region are calculated using the interpolation method and symmetry. The beam spot diameter remains consistent throughout the melting and forming region, and the beam spot calibration is completed.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: In existing electron beam spot measurement methods using pinholes and Faraday cups, to avoid the Faraday cup being burned by the high-power electron beam during the measurement process, the electron beam is often rapidly scanned through the pinhole and Faraday cup to reduce the irradiation time. In this method, the electron beam is always moving in a two-dimensional plane, so the current collected by the Faraday cup cannot accurately reflect the distribution of the beam spot at a fixed position.

[0019] The beam spot measurement and calibration device proposed in this invention, for measuring and calibrating an electron beam spot deflected to a fixed position, employs a pinhole aperture and Faraday cup to collect beam spot current point-by-point, establishing the beam spot circuit density distribution and calculating the beam spot profile size. Then, the objective lens and astigmatism reducer are adjusted to excite and calibrate the beam spot. During the point-by-point current acquisition process, when the electron beam deflects to a certain position, the deflector excitation remains unchanged. The electron beam is turned off and on by applying pulse excitation to the suppressor, achieving accurate measurement of the beam spot current density distribution at a fixed position while avoiding thermal damage to the pinhole aperture and Faraday cup from the high-energy, high-current electron beam. This is of great significance for improving the calibration and melting accuracy of the electron beam spot. Attached Figure Description

[0020] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the overall device for measuring and calibrating electron beam selection melting electron beam spots; Figure 2 This is a schematic diagram of the electron beam spot measurement module. Figure 3 This is a schematic diagram of the two-dimensional, equally spaced measurement and calibration positions within the selected melting and forming area; Figure 4 This is a schematic diagram showing the preliminary dimensions of the beam spot profile; Figure 5 This is a schematic diagram of the movement of the aperture during the beam spot current density distribution measurement process; Figure 6 This is a schematic diagram illustrating the fine-grained dimension determination of the beam spot profile; Figure 7 This refers to the beam spot measurement calibration area and measurement calibration location selected in Example 2; Figure 8 This is a schematic diagram of the suppression pole pulse excitation in Example 2; Figure 9 It is the relative positional relationship between the calibrated deflector excitation and the beam spot deviation from the center of the melting and forming region; Figure 10 It is the relative positional relationship between the calibrated objective lens excitation and the beam spot deviation from the center of the fused forming region; Figure 11 It is the relative positional relationship between the calibrated astigmatism deflector excitation and the beam spot deviation from the center of the melt-forming region; Figure 12 It is the relative positional relationship between the calibrated beam spot size and the beam spot's deviation from the center of the melt-forming region; Figure 13 These are the beam spot current density distributions and effective beam spot region contours at eight different locations in Example 2 after calibration. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0024] Example 1 An electron beam selective melting electron beam spot measurement and calibration device, such as Figure 1 As shown, it includes: an electron beam emission unit 100, a focusing and deflection unit 200, a melting and forming region 300, an electron beam spot measurement module 400, and an electron beam spot calibration unit 500.

[0025] The electron beam emitting unit 100 is used to form a high-energy, high-current electron beam, specifically including: a cathode 101, a suppressor 102, an accelerating electrode 103, etc. The cathode 101 is the emission source of the electron beam, the suppressor 102 is used to control the on and off of the electron beam, and the accelerating electrode 103 is used to regulate the energy of the electron beam. The focusing and deflecting unit 200 is used to focus the high-energy, high-current electron beam into a small beam spot and scan it, specifically including: an astigmatism reducer 201, an objective lens 202, a deflector 203, etc. The astigmatism reducer 201 is used to adjust the beam. To ensure beam uniformity, the objective lens 202 is used to adjust the beam spot focusing state and size. The deflector 203 is used for deflection scanning of the electron beam in the melting and forming region. The electron beam spot measurement module 400 is used to measure the electron beam spot current density distribution. The electron beam spot measurement module 400 is located above the melting and forming region 300 and is used to measure the electron beam spot current density distribution. Within the melting and forming region 300, m×m two-dimensional equidistant measurement calibration positions are selected. These positions constitute the beam spot measurement system coordinates 301, such as... Figure 2 As shown, the electron beam spot measurement module 400 specifically includes: a high-precision displacement stage 401, an aluminum plate 402, a Faraday cup 403, a camera 404, a pinhole aperture 405, and a bracket 406, etc. The aluminum plate 402, the pinhole aperture 405, and the Faraday cup 403 are fixed on the high-precision displacement stage 401 by the bracket 406. Figure 2 and 3As shown, the camera 404 is located directly above the corner of the beam spot measurement system coordinate 301, and the pinhole aperture 405 has a square hole with a side length of ΔL at its center; the electronic beam spot calibration unit 500 is used to control the movement of the high-precision displacement stage 401, acquire the position coordinate data of the high-precision displacement stage 401, acquire the current signal of the Faraday cup 403, calculate the beam spot profile size, and adjust the excitation of the focusing deflection unit 200. Specifically, it includes: a data acquisition module 501, a host computer 502, and an excitation signal control module 503.

[0026] To achieve the measurement and calibration of the electron beam spot, the following steps are taken: Step 1: Activate the electron beam emitting unit 100 and form a focused deflection beam spot. Activate the cathode 101, suppressor 102, and accelerating electrode 103 of the electron beam emitting unit 100 to obtain a high-energy, high-current electron beam. Select m×m two-dimensional, equally spaced measurement and calibration positions within the melting and forming region 300, such as... Figure 3 As shown, objective lens 202 and deflector 203 are then turned on, and the excitation of deflector 203 is adjusted to deflect the electron beam in the molten forming region 300 to near a certain measurement calibration position, as shown. Figure 3 The position at (1,1) can also be any one of the four corner positions among the aforementioned m×m two-dimensional equally spaced measurement and calibration positions, for example... Figure 3 In the middle (1, m), or (m, m), or (m, 1), then adjust the excitation of objective lens 202 to focus the electron beam into a small spot and melt the powder bed metal. Record the excitation of suppressor 102, objective lens 202 and deflector 203 at this time. Then adjust the excitation of suppressor 102 to turn off the electron beam and fix the excitation of objective lens 202 and deflector 203 unchanged. At this time, there is no electron beam spot on the forming plane.

[0027] Step 2: Determine the preliminary dimensions of the beam spot profile. Set position (1, 1) in the melting and forming area 300 from Step 1 as the initial position of the beam spot measurement system coordinates 301, and position camera 404 directly above the initial position of the beam spot measurement system coordinates 301. Reset the high-precision displacement stage 401 to the initial position of the beam spot measurement system coordinates 301. Use the high-precision displacement stage 401 to move the support 406 carrying the aluminum sheet 402, the pinhole aperture 405, and the Faraday cup 403 to the powder bed metal melting area from Step 1, ensuring that the aluminum sheet 402 is directly above position (1, 1) from Step 1. Record the position coordinates (x0, y0) of the high-precision displacement stage 401 at this time. Then adjust the excitation of the suppression electrode 102 to the excitation of the suppression electrode 102 recorded in Step 1. At this time, the electron beam irradiates the aluminum sheet 402. When the Faraday cup 403 below the aluminum sheet 402 detects a stable current, it indicates that the area of ​​the aluminum sheet 402 irradiated by the electron beam has been melted. Then, the excitation of the suppressor 102 is adjusted to turn off the electron beam. The support 406, carrying the aluminum sheet 402, the pinhole aperture 405, and the Faraday cup 403, is moved to the initial position of the beam spot measurement system coordinates. The focal length of the camera 404 is adjusted so that a complete and clear image of the aluminum sheet 402 appears in the field of view of the camera 404. The melting point dimensions L1 and L2, as well as the distances s1 and s2 of the melting point center relative to the boundary of the aluminum sheet 402, are captured and measured by the camera 404. Figure 4 As shown, the melting point size is used as the initial size of the beam spot profile, and the center position of the melting point is used as the center position of the beam spot. Since the position coordinates (x1, y1) of the apex of the aluminum sheet 402 relative to the initial position of the beam spot measurement system are known during the design of the beam spot measurement system, the coordinates of the center position of the beam spot are (x0+x1+s1, y0+y1+s2). Then, a small aperture 405 of a certain size is selected to measure the beam spot current density distribution (408). When selecting the small aperture 405, the aperture size ΔL should be ensured to be ≤0.05*(L1+L2). A square region (407) is selected as the measurement area for the beam spot current density distribution. When selecting, the side length L of the square region 407 should be ≥(L1+L2), and the center of the square region 407 coincides with the center position of the beam spot.

[0028] Step 3: Establish the beam spot current density distribution and calculate the fine dimensions of the beam spot profile. Use the high-precision displacement stage 401 to move the pinhole aperture 405 to the corner of the square region 407. Then control the high-precision displacement stage 401 to... Figure 5The aperture 405 is moved point-by-point along the x and y directions in steps of ΔL, with a dwell time of Δt at each point, thus scanning the square region 407. When the aperture 405 dwells at a certain point, a pulse excitation with a turn-on voltage pulse width Δts ≤ Δt is applied to the suppressor 102. The excitation magnitude is the same as the excitation of the suppressor 102 recorded in step one. During the time Δt, an electron beam passes through the aperture and is collected by the Faraday cup 403 located below the aperture 405. By reducing Δt, the time the electron beam irradiates the aperture 405 can be reduced, avoiding the risk of damage to the aperture 405 and the Faraday cup 403 from the high temperature of the electron beam. The current signal collected by the Faraday cup 403 is transmitted to the host computer 502 through the data acquisition module 501. The host computer 502 establishes a beam spot current density distribution 408 based on the current and coordinates of each sampling point and normalizes the beam spot current density distribution 408. The effective region contour and size of the electron beam spot can be determined based on the normalized current density distribution. This invention provides two methods for determining the effective region contour. First, the region enclosed by n times (0 < n < 1) the maximum value of the normalized current density distribution is selected as the effective region 409 of the electron beam spot. Second, an annular region is selected as the effective region 409 of the electron beam spot, where the current contained in this annular region is n times (0 < n < 1) the total current of the beam spot. Then, the coordinates (X, X) of discrete points on the effective region contour line are extracted. e Y e ), where e=1…N, and N is the number of discrete points on the contour line, such as Figure 6 As shown. The coordinates (X, Y) are obtained by averaging the x and y coordinates of all discrete points on the contour line. m Y m () serves as the new coordinate for the center position of the beam spot. Under the action of a rotationally symmetric system, the electron beam spot distribution exhibits rotational symmetry. When the electron beam is deflected, its rotational symmetry is disrupted, and the beam spot distribution can be approximated as an ellipse. Therefore, the beam spot profile size can be calculated using formula (1): (1) In the formula: a and b are the major and minor semi-axis of the elliptical profile of the beam spot; eig represents the eigenvalue of the solution matrix; Cov represents the covariance; (a+b) is defined as the beam spot diameter; (ab) is defined as the beam spot uniformity. The closer (ab) is to 0, the better the beam spot uniformity, and vice versa.

[0029] Step 4: Calibrate the beam spot profile size. First, convert the beam spot center coordinates (X, Y, Z) calculated in Step 3 to... m Y mThe beam spot center coordinates are compared with the designed deflection position coordinates. If the deviation between the beam spot center coordinates and the designed deflection position coordinates meets the design requirements, then the deflector excitation value at this time is set as the deflector excitation calibration value at the measurement position. If the deviation between the beam spot center coordinates and the designed deflection position coordinates does not meet the design requirements, then the deflector excitation value is finely adjusted by the excitation signal control module 503, and the beam spot current density distribution is measured again and the beam spot center coordinates (X) are calculated. m Y m The process continues until the deviation between the beam spot center coordinates and the designed deflection position coordinates meets the design requirements. The final deflector excitation value after fine-tuning is then set as the deflector excitation calibration value at the measurement position. Next, under deflector calibration excitation, the beam spot diameter calculated in step three is compared with the design dimensions. If both the beam spot diameter and beam spot uniformity meet the design requirements, the objective lens excitation and astigmatism correction excitation at this point are set as calibration values. If they do not meet the design requirements, the objective lens excitation is first adjusted via the excitation signal control module 503, and the beam spot current density distribution is measured again, and the beam spot diameter is calculated until the objective lens excitation that minimizes the beam spot diameter is found. Under this objective lens excitation, the astigmatism correction excitation is adjusted via the excitation signal control module 503, and the beam spot current density distribution is measured again, and the major and minor semi-axes of the profile are calculated until the astigmatism correction excitation that maximizes beam spot uniformity is found. The astigmatism correction excitation at this point is then set as the astigmatism correction excitation calibration value at the measurement position. Finally, under the astigmatism correction calibration excitation, the objective lens excitation is fine-tuned until the beam spot diameter meets the design size requirements. This objective lens excitation value is then set as the calibration value for the objective lens excitation at the measurement position. At this point, the beam spot calibration at the measurement calibration position selected in step one is complete. Then, the remaining positions are measured and calibrated sequentially, yielding curves of the calibration excitation of deflector 203, objective lens 202, astigmatism correction 201, etc., as a function of the beam spot position. Based on these curves, using interpolation and symmetry, the deflector excitation, objective lens excitation, and astigmatism correction excitation required to deflect the electron beam to any position in the melting and forming region can be calculated, ensuring a consistent beam spot diameter throughout the entire melting and forming region. This completes the beam spot calibration.

[0030] Example 2 This example illustrates the beam spot measurement process. According to Figure 1An electron gun was designed for the electron beam selection, melting, electron beam spot measurement, and calibration device. This electron gun is used to generate an electron beam with an accelerating energy of 100 keV and a beam current of 11 mA. The turn-off voltage Vsup of the suppressor relative to the cathode is -800V, meaning that electron beam emission occurs when the voltage Vsup ≥ -800V. The designed device has a melting and forming area of ​​350mm × 350mm, and the designed beam spot size requires a beam spot diameter ds ≤ 0.1mm. According to step one, 15 × 15 two-dimensional, equally spaced measurement and calibration positions are selected within the melting and forming area. Due to the symmetry of the electron beam scanning area, only one quadrant needs to be selected for measurement and calibration. In this example, the first quadrant is selected, with a measurement and calibration area of ​​175mm × 175mm and a measurement and calibration position spacing of 25mm, totaling 7 × 7 = 49 positions. Figure 7 As shown. According to step two, the selected aluminum sheet has a length, width, and height of 10mm, 10mm, and 1mm, respectively. The selected aperture center square hole is 5μm × 5μm, the aperture thickness is 0.5mm, and the selected beam spot current density distribution measurement area is 0.5mm × 0.5mm. According to step three, the high-precision displacement stage's movement step size ΔL is set to 5μm, the peak-to-peak value of the suppressor pulse excitation is set to -800V to 0V, the turn-on voltage pulse width Δts is set to Δts = 50μs, the turn-off voltage pulse width Δte is set to Δte = 450μs, and the suppressor pulse excitation is as follows. Figure 8 As shown.

[0031] Example 3 To illustrate the beam spot calibration process, this example describes the process based on the measured current density distribution. The selected beam spot positions are located at eight equidistant points on the line connecting the coordinates (0mm, 0mm) to (175mm, 175mm) of the measurement and calibration area in Example 1 (e.g., ...). Figure 7(As shown by the dashed line), starting from the (0mm, 0mm) position, the beam spot is calibrated sequentially at 8 positions. In this example, the region enclosed by 0.1 times the maximum value of the normalized current density distribution is selected as the effective region of the electron beam spot. For example, for the beam spot at the (0mm, 0mm) position, the calibration values ​​for the deflector excitation are: x-direction 0A, y-direction 0A, the calibration value for the objective lens excitation is 0.9438A, and the calibration values ​​for the astigmatism reducer excitation are: x-direction 0A, y-direction 0A. The effective region of the beam spot has a major semi-axis of 0.0353mm, a minor semi-axis of 0.0349mm, a diameter of 0.0702mm, and a uniformity of 0.0004mm. For the beam spot at the (175mm, 175mm) position, the calibration values ​​for the deflector excitation are: 1.8606A in the x-direction and 1.8350A in the y-direction; the calibration value for the objective excitation is 0.9108A; and the calibration values ​​for the astigmatism reducer excitation are: 8A in the x-direction and 20A in the y-direction. The semi-major axis of the effective beam spot region is 0.0375mm, the semi-minor axis is 0.0326mm, the diameter is 0.0701mm, and the uniformity is 0.0049mm. The beam spot calibration results for eight equidistant positions along the line from (0mm, 0mm) to (175mm, 175mm) are as follows: Figures 9 to 13 As shown. From Figure 9 It can be seen that the calibrated deflector excitation and the relative position of the beam spot deviating from the center of the melt-forming region are approximately linearly related. Figure 10 and Figure 11 It can be seen that the excitation of the calibrated objective lens and the excitation of the astigmatism corrector have a non-linear relationship. Under calibrated excitation, when the beam spot scans along the line connecting (0mm, 0mm) to (175mm, 175mm), the beam spot diameter can be maintained around 0.07mm, and the beam spot is uniform. Figure 12 and Figure 13 As shown.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit its scope of protection. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading the present invention, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, but these changes, modifications or equivalent substitutions are all within the scope of protection of the pending claims of the invention.

Claims

1. An electron beam selective melting electron beam spot measurement and calibration apparatus, characterized by, The electron beam emitting unit (100), the focusing and deflecting unit (200), the melting forming area (300), the electron beam spot measuring module (400) and the electron beam spot calibration unit (500) are included. The electron beam emitting unit (100) is used for forming a high-energy large beam current electron beam, the focusing and deflecting unit (200) is used for focusing the high-energy large beam current electron beam into a fine electron beam spot and scanning, the electron beam spot measuring module (400) is located above the melting forming area (300) and is used for measuring the electron beam spot current density distribution, m*m two-dimensional equidistantly distributed measuring calibration positions are arranged in the melting forming area (300), and all the measuring calibration positions jointly constitute a beam spot measuring system coordinate (301), the electron beam spot measuring module (400) includes a high-precision displacement table (401), an aluminum sheet (402), a Faraday cup (403), a camera (404), a pinhole diaphragm (405) and a support (406), the aluminum sheet (402), the pinhole diaphragm (405) and the Faraday cup (403) are fixed on the high-precision displacement table (401) through the support (406), the camera (404) is located directly above a corner position of the beam spot measuring system coordinate (301), a square hole with a side length of ΔL is formed in the center of the pinhole diaphragm (405), and the electron beam spot calibration unit (500) is used for controlling the movement of the high-precision displacement table (401), collecting position coordinate data of the high-precision displacement table (401), collecting a current signal of the Faraday cup (403), calculating a beam spot profile size and adjusting excitation of the focusing and deflecting unit (200).

2. A device for electron beam spot measurement and calibration for electron beam selective melting according to claim 1, characterized in that The electron beam emitting unit (100) includes a cathode (101), a suppressor (102) and an accelerating electrode (103), the cathode (101) is used for emitting an electron beam, the suppressor (102) is used for controlling the opening and closing of the electron beam, and the accelerating electrode (103) is used for regulating the energy of the electron beam. The focusing and deflecting unit (200) includes an anastigmat (201), an objective lens (202) and a deflector (203), the anastigmat (201) is used for adjusting the beam spot uniformity, the objective lens (202) is used for adjusting the focusing state of the beam spot and adjusting the beam spot size, and the deflector (203) is used for deflecting and scanning the electron beam in the melting forming area.

3. An electron beam spot measurement and calibration apparatus for electron beam selective melting as claimed in claim 2, wherein, The electron beam spot calibration unit (500) includes a data acquisition module (501), an upper computer (502) and an excitation signal control module (503), the data acquisition module (501) is used for collecting position coordinate data of the high-precision displacement table (401) and collecting a current signal of the Faraday cup (403), the upper computer (502) is used for controlling the movement of the high-precision displacement table (401) and calculating a beam spot profile size, and the excitation signal control module (503) is used for adjusting the excitation of the anastigmat (201), the objective lens (202) and the deflector (203).

4. A method for electron beam spot measurement and calibration of electron beam selective melting based on the apparatus for electron beam spot measurement and calibration of electron beam selective melting according to claim 1, characterized in that The method comprises the following steps: Step one: turn on the electron beam emitting unit (100), form a focused and deflected beam spot by adjusting the excitation of the electron beam emitting unit (100) and the focusing and deflecting unit (200). Step two: determine the preliminary size of the focused deflected beam spot profile by the electron beam spot measurement module (400); Step three: establish the beam spot current density distribution and calculate the fine size of the focused deflected beam spot profile by the electron beam spot measurement module (400); Step four: calibrate the size of the focused deflected beam spot profile by the electron beam spot calibration unit (500).

5. A method of electron beam spot measurement and calibration for electron beam selective melting as claimed in claim 4, wherein, The electron beam emission unit (100) includes a cathode (101), a suppressor (102), and an acceleration electrode (103), the cathode (101) is used for emitting an electron beam, the suppressor (102) is used for controlling the opening and closing of the electron beam, and the acceleration electrode (103) is used for regulating the energy of the electron beam; The focusing and deflection unit (200) includes an anastigmat (201), an objective lens (202), and a deflector (203), the anastigmat (201) is used for adjusting the beam spot uniformity, the objective lens (202) is used for adjusting the focusing state of the beam spot and adjusting the beam spot size, and the deflector (203) is used for deflection scanning of the electron beam in the melting forming area; The electron beam spot calibration unit (500) includes a data acquisition module (501), an upper computer (502), and an excitation signal control module (503), the data acquisition module (501) is used for acquiring the position coordinate data of the high-precision displacement table (401) and the current signal of the Faraday cup (403), the upper computer (502) is used for controlling the movement of the high-precision displacement table (401) and calculating the beam spot profile size, and the excitation signal control module (503) is used for adjusting the excitation of the anastigmat (201), the objective lens (202), and the deflector (203).

6. A method of electron beam spot measurement and calibration for electron beam selective melting as claimed in claim 5, wherein, The step one is specifically: Turn on the cathode (101), the suppressor (102), and the acceleration electrode (103) of the electron beam emission unit (100) to obtain a high-energy large-current electron beam, select m×m two-dimensional equidistant distribution measurement calibration positions in the melting forming area (300), turn on the objective lens (202) and the deflector (203), adjust the excitation of the deflector (203) to deflect the electron beam to the vicinity of the measurement calibration position A in the melting forming area (300), then adjust the excitation of the objective lens (202) to focus the electron beam into a micro beam spot, melt the powder bed metal, record the excitation of the suppressor (102), the objective lens (202), and the deflector (203) at this time, then adjust the excitation of the suppressor (102) to turn off the electron beam, and fix the excitation of the objective lens (202) and the deflector (203) unchanged, at this time, the forming plane has no electron beam spot.

7. A method of electron beam spot measurement and calibration for electron beam selective melting as claimed in claim 6, wherein, The step two is specifically: The measurement calibration position A of the melt forming area (300) in step one is set as the initial position of the beam spot measurement system coordinates (301), the camera (404) is located directly above the initial position of the beam spot measurement system coordinates (301), the high-precision displacement table (401) is reset to the initial position of the beam spot measurement system coordinates (301), the support (406) is moved to the position of the melt of the powder bed metal in step one by using the high-precision displacement table (401), and the aluminum sheet (402) is ensured to be directly above the measurement calibration position A, and the position coordinates (x0, y0) of the high-precision displacement table (401) at this time are recorded. Then, the excitation of the suppressor (102) is adjusted to the excitation of the suppressor (102) recorded in step one, and the electron beam irradiates the aluminum sheet (402) at this time. After the Faraday cup (403) below the aluminum sheet (402) detects a stable current, the excitation of the suppressor (102) is adjusted to turn off the electron beam. The support (406) is moved to the initial position of the beam spot measurement system coordinates, the focal length of the camera (404) is adjusted so that a complete and clear image of the aluminum sheet (402) appears in the field of view of the camera (404), the melt point sizes L1 and L2 and the distances s1 and s2 of the melt point center relative to the boundary of the aluminum sheet (402) are photographed and measured by the camera (404), the melt point sizes are taken as the preliminary sizes of the beam spot profile, and the melt point center position is taken as the beam spot center position. Then, a small aperture diaphragm (405) of a certain size is selected for beam spot current density distribution (408) measurement, and a square region (407) is selected as the measurement region of the beam spot current density distribution.

8. A method of electron beam spot measurement and calibration for electron beam selective melting as claimed in claim 7, wherein, The step three is specifically: The high-precision displacement table (401) is used to move the pinhole diaphragm (405) to the corner of the square area (407), the high-precision displacement table (401) is controlled to move the pinhole diaphragm (405) point by point along x and y directions with a step of ΔL, and the dwell time of each point is Δt, the scanning of the square area (407) is realized, when the pinhole diaphragm (405) stays at a point, a pulse excitation with an opening voltage pulse width of Δts≤Δt is applied to the suppressor (102), the excitation size is the excitation of the suppressor (102) recorded in step one, during the time of Δt, the electron beam passes through the pinhole and is collected by the Faraday cup (403) located below the pinhole diaphragm (405), the current signal collected by the Faraday cup (403) is transmitted to the upper computer (502) through the data acquisition module (501), the upper computer (502) establishes the beam spot current density distribution (408) according to the current and coordinates of each sampling point, and the beam spot current density distribution (408) is normalized, according to the normalized current density distribution, the effective area profile and the beam spot profile size are determined, and the coordinates (X e , Y e ) of the discrete points on the effective area profile line are extracted, wherein e=1…N, N is the number of discrete points on the profile line, the coordinates (X m , Y m ) obtained by averaging the x coordinates and y coordinates of all discrete points on the profile line are taken as the new coordinates of the beam spot center position, under the action of the rotationally symmetric system, the electron beam spot distribution has rotational symmetry, when the electron beam is deflected, the rotational symmetry is destroyed, the beam spot distribution is approximately elliptical, and the beam spot profile size is calculated by the following formula: In the formula, a and b are the long semi-axis and the short semi-axis of the beam spot elliptical profile; eig represents the eigenvalue of the solution matrix; Cov represents the covariance.

9. A method of electron beam spot measurement and calibration for electron beam selective melting as claimed in claim 8, wherein, The determination of the effective region profile of the beam spot includes two kinds, which are specifically: The first kind is that a region surrounded by n times of the maximum normalized current density distribution is selected as the effective region (409) of the electron beam spot, and 0 The second kind is that a ring region is selected as the effective region (409) of the electron beam spot, and the current contained in the ring region is n times of the total current of the beam spot, and 0 10. A method of electron beam spot measurement and calibration for electron beam selective melting as claimed in claim 8, wherein, The step four is specifically: The beam spot center coordinates (X) calculated in step three are used to... m Y m The beam spot center coordinates are compared with the designed deflection position coordinates. If the deviation between the beam spot center coordinates and the designed deflection position coordinates meets the design requirements, the deflector excitation value at this time is set as the deflector excitation calibration value at the measurement position. If the deviation between the beam spot center coordinates and the designed deflection position coordinates does not meet the design requirements, the deflector excitation value is finely adjusted by the excitation signal control module (503), and the beam spot current density distribution is measured again and the beam spot center coordinates (X) are calculated. m Y m ), until the deviation between the beam spot center coordinates and the designed deflection position coordinates meets the design requirements, and the final deflector excitation value after fine adjustment is set as the deflector excitation calibration value at the measurement position; Under the calibration excitation of the deflector, the beam spot diameter calculated in step three is compared with the design size. If the beam spot diameter and the beam spot uniformity both meet the design requirements, the objective lens excitation and the stigmator excitation at this time are defined as the calibration values. If the design requirements are not met, the objective lens excitation is adjusted by the excitation signal control module (503), the beam spot current density distribution is measured again, and the beam spot diameter is calculated until the objective lens excitation that makes the beam spot diameter minimum is found; Under the objective lens excitation, the stigmator excitation is adjusted by the excitation signal control module (503), the beam spot current density distribution is measured again, and the long semi-axis and the short semi-axis of the profile are calculated until the stigmator excitation that makes the beam spot uniformity best is found. The stigmator excitation at this time is defined as the calibration value of the stigmator excitation at the measurement position. Under the calibration excitation of the stigmator, the fine-tuning objective excitation is performed until the beam spot diameter meets the design size requirement, the objective excitation at this time is defined as the objective excitation calibration value at the measurement position, the beam spot calibration at the measurement calibration position selected in step one is completed, then the beam spots at the remaining positions are measured and calibrated in turn, and the calibration excitation curves of the deflector (203), the objective (202) and the stigmator (201) with the beam spot position are obtained. According to the curves, the interpolation method and the symmetry are used to calculate the deflector excitation, the objective excitation and the stigmator excitation required when the electron beam is deflected to any position in the melting forming area, and the beam spot diameter remains consistent in the entire melting forming area, and the beam spot calibration is completed.

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