Conformal preheating electron beam selective melting electron optical system and design method thereof

Abstract

The invention discloses a shape follow-up preheating electron beam selective melting electron optical system and a design method thereof. The shape follow-up preheating electron beam selective melting electron optical system comprises an electron beam forming unit and an electron beam focusing deflection unit. The electron beam forming unit comprises a central cathode and an annular cathode sleeving the outer side of the central cathode, suppression electrodes are arranged between the central cathode and the annular cathode and on the outer side of the annular cathode, an acceleration electrode is arranged on one side of a whole formed by the central cathode, the annular cathode and the suppression electrodes, and an electron beam focusing deflection unit is arranged on one side of the acceleration electrode; the electron beam focusing deflection unit comprises a collecting lens, an objective lens and a deflector which are sequentially arranged, the collecting lens and the objective lens are hollow and are respectively provided with a collecting lens coil and an objective lens coil, a plurality of deflector coils are uniformly distributed on the inner side of the deflector, and a second anastigmatism device is arranged in the inner side space of the collecting lens; a plurality of second anastigmatism device coils are uniformly distributed on the inner side of the second anastigmatism device, a first anastigmatism device is arranged in the inner side space of the second anastigmatism device, and a plurality of first anastigmatism device coils are uniformly distributed on the inner side of the first anastigmatism device.

Description

Technical Field

[0001] This invention relates to the field of electron beam additive manufacturing, and in particular to a conformal preheating electron beam selective melting electron optical system and its design 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 rapid scanning of the electron beam across the metal powder bed causes the powder layer to experience a sharp rise and fall in temperature, creating a very large temperature gradient on the forming surface. This generates stress and strain within the machined part, leading to anisotropy in its microstructure and causing problems such as internal cracks, defects, and coarse microstructure. Therefore, temperature field control is one of the key technologies for ensuring the machining performance of parts processed by selective electron beam melting.

[0004] Traditional powder bed temperature control methods involve preheating the powder bed, including rapid electron beam scanning preheating, substrate preheating, and laser-assisted preheating, to control the powder bed temperature within a certain range. While substrate preheating provides uniform temperature control, it is slow and energy-intensive. Laser-assisted preheating, although fast-responding, is costly and complex. Direct electron beam preheating achieves rapid, localized, and precise temperature control while improving electron beam energy utilization. Patent document (CN119609154A) describes a scheme using two high-frequency scanning electron guns to preheat and melt titanium-aluminum powder; one gun is used for preheating, and the other for melting. Patent document (CN105798301A) proposes splitting the electron beam into two beams: a high-energy beam for melting and a low-energy beam for heating. Both of these methods use a single electron beam for scanning-assisted preheating, which leads to poor uniformity of the preheating temperature field due to point-by-point scanning. Furthermore, this method requires an additional electric gun or splitting of the electron beam, which inevitably increases the number and complexity of electron optical components, as well as the difficulty and cost of the scanning control system.

[0005] Therefore, improving the preheating method of single electron beam point-by-point scanning will improve the uniformity of the preheating temperature field, thereby improving the internal microstructure and mechanical properties of the processed parts. Summary of the Invention

[0006] The purpose of this invention is to provide a conformal preheating electron beam selective melting electron optical system and its design method, so as to solve the problem of poor uniformity of the preheating temperature field caused by the use of a single electron beam for point-by-point scanning in current electron beam selective melting.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A conformal preheating electron beam selective melting electron optical system includes an electron beam forming unit and an electron beam focusing and deflection unit connected to the electron beam forming unit; The electron beam forming unit includes a central cathode and an annular cathode sleeved outside the central cathode. A suppression electrode is provided between the central cathode and the annular cathode and outside the annular cathode. An accelerating electrode is provided on one side of the integral formed by the central cathode, the annular cathode and the suppression electrode. An electron beam focusing and deflection unit is provided on one side of the accelerating electrode. The electron beam focusing and deflection unit includes a condenser lens, an objective lens, and a deflector arranged sequentially. The condenser lens and the objective lens are hollow inside and are respectively provided with a condenser lens coil and an objective lens coil. A plurality of deflector coils are evenly distributed on the inner side of the deflector. A second astigmatism reducer is provided in the inner space of the condenser lens. A plurality of second astigmatism reducer coils are evenly distributed on the inner side of the second astigmatism reducer. A first astigmatism reducer is provided in the inner space of the second astigmatism reducer. A plurality of first astigmatism reducer coils are evenly distributed on the inner side of the first astigmatism reducer.

[0008] Furthermore, the accelerating electrode includes an outer suction electrode, an outer first accelerating electrode, an outer converging electrode, and an outer second accelerating electrode arranged sequentially, and an inner suction electrode, an inner first accelerating electrode, an inner converging electrode, and an inner second accelerating electrode are respectively arranged on the inner side of the outer suction electrode, the outer first accelerating electrode, the outer converging electrode, and the outer second accelerating electrode.

[0009] Furthermore, the first astigmatism reducer is physically connected to the second accelerating electrode, and the two are at the same potential.

[0010] Furthermore, both the central cathode and the annular cathode are tungsten filament thermal emission cathodes.

[0011] A design method for a conformal preheated electron beam selective melting electron optical system includes: Step 1: Design of electron beam forming unit The central electron beam emitted by the central cathode is used for melting and forming, while the annular electron beam emitted by the annular cathode is used for preheating the powder bed. The central electron beam is always located within the annular region surrounded by the annular electron beam, thus increasing the potential V of the central cathode. cc and the potential V of the annular cathode co Both are set to 0V, and a negative potential V is applied to the suppressor relative to the center cathode and the annular cathode. supThe suppressor electrode is used to adjust the current magnitude of the central electron beam and the ring electron beam, while the accelerating electrode is used to accelerate the central electron beam emitted by the central cathode and the ring electron beam emitted by the ring cathode to the required electron beam energy. Step 2: Design of the electron beam focusing and deflection unit The objective lens and deflector are used for focusing and scanning the central electron beam and the annular electron beam, respectively. The second astigmatism reducer is used for adjusting the roundness of the annular electron beam, the first astigmatism reducer is used for adjusting the roundness of the central electron beam, and the condenser lens is used to adjust the size of the preheated area of ​​the annular electron beam on the molten plane. The first astigmatism reducer is used to shield the focusing effect of the condenser lens on the central electron beam. Step 3: Determine the excitation parameters of the electron beam forming unit electrodes First, the central electron beam emitted by the central cathode is calculated. The trajectory of the central electron beam is calculated using numerical calculation methods. The accelerating electrode is adjusted so that the central electron beam becomes a collimated electron beam after passing through the accelerating electrode. The annular electron beam emitted by the annular cathode is calculated. The trajectory of the annular electron beam is calculated using numerical calculation methods. Then, the accelerating electrode is adjusted so that the annular electron beam becomes a collimated electron beam after passing through the accelerating electrode. Step 4: Determine the excitation parameters of the electron beam focusing and deflection unit Calculate the beam spot of the central electron beam when only the objective lens is on, adjust the current excitation of the objective lens coil to focus the beam spot of the central electron beam, adjust the current excitation of the deflector coil to shift the beam spot of the central electron beam to a predetermined position, and adjust the excitation of the objective lens coil and the first astigmatism correction coil to improve the roundness of the beam spot of the central electron beam; calculate the beam spot of the annular electron beam, and adjust the excitation of the condenser lens coil and the second astigmatism correction coil to make the beam spot of the annular electron beam meet the requirements of the preheating area.

[0012] Furthermore, the accelerating electrode includes an outer suction electrode, an outer first accelerating electrode, an outer converging electrode, and an outer second accelerating electrode arranged sequentially, and an inner suction electrode, an inner first accelerating electrode, an inner converging electrode, and an inner second accelerating electrode are respectively arranged on the inner side of the outer suction electrode, the outer first accelerating electrode, the outer converging electrode, and the outer second accelerating electrode.

[0013] Furthermore, the trajectory of the central electron beam emitted by the central cathode is calculated using a numerical calculation method, and the accelerating electrode is adjusted so that the central electron beam is collimated after passing through the accelerating electrode. Specifically: The potential V of the central cathode cc Set to 0V, the potential of the suppressor V sup A negative potential V is applied relative to the central cathode sup Then, the potential V of the inner absorption electrode is set sequentially. ie The potential V of the inner first accelerating electrode i1 The potential V of the inner second accelerating electrodei2 The potential V of the inner second accelerating electrode i2 The final energy of the central electron beam is determined by calculating its trajectory using numerical methods, and then the potential V of the inner converging electrode is adjusted. ig This ensures that the central electron beam becomes a collimated electron beam after passing through the inner second accelerating electrode.

[0014] Furthermore, the calculation of the annular electron beam emitted by the annular cathode involves using a numerical calculation method to calculate the trajectory of the annular electron beam, and then adjusting the accelerating electrode to make the annular electron beam collimated after passing through the accelerating electrode. Specifically: The potential V of the annular cathode co Set to 0V, the potential of the suppressor V sup A negative potential V is applied relative to the annular cathode sup Then, the potential V of the outer absorption electrode is set sequentially. oe The potential V of the first accelerating electrode on the outer side o1 The potential V of the outer second accelerating electrode o2 The potential V of the outer second accelerating electrode o2 The final energy of the ring electron beam is determined by numerical calculation of its trajectory, followed by adjustment of the potential V of the outer converging electrode. og This causes the ring-shaped electron beam to become a collimated electron beam after passing through the outer second accelerating electrode.

[0015] Furthermore, the calculation only considers the beam spot of the central electron beam when the objective lens is on. Adjusting the current excitation of the objective lens coil focuses the beam spot, adjusting the current excitation of the deflector coil shifts the beam spot to a predetermined position, and adjusting the excitation of the objective lens coil and the first astigmatism corrector coil improves the roundness of the central electron beam spot. Specifically: Using the initial parameters of the central electron beam as a condition, a numerical calculation method is employed to calculate the beam spot of the central electron beam on the molten plane when only the objective lens is turned on. The current excitation of the objective lens coil is adjusted to minimize the beam spot of the central electron beam on the molten plane. At this point, the current excitation I of the objective lens coil is... ol This is called focused incentive, in focused incentive I ol Next, turn on the deflector, calculate the beam spot of the central electron beam, and adjust the current excitation of the deflector coil to shift the beam spot of the central electron beam to the corner position of the desired forming area. At this time, the current excitation I of the deflector coil is... def This is called maximum deflection excitation. Adjusting the current excitation of the objective lens coil improves the beam circularity of the central electron beam. At this point, the current excitation I of the objective lens coil... old This is called dynamic focus incentive, and finally, in dynamic focus incentive I... old and maximum deflection excitation I defThe first astigmatism canceller is activated, the beam spot of the central electron beam is calculated, and the current excitation I in the x-direction of the first astigmatism canceller coil is adjusted. stig1x and y-direction current excitation I stig1y Improve the beam spot roundness of the central electron beam.

[0016] Furthermore, the calculation of the annular electron beam spot, and the adjustment of the excitation of the condenser coil and the second astigmatism correction coil to ensure that the annular electron beam spot meets the preheating region requirements, specifically involves: Turn on the condenser lens and, using the initial parameters of the annular electron beam as conditions, calculate the beam spot of the annular electron beam on the molten plane using a numerical calculation method. Adjust the current excitation I of the condenser lens coil. cl Second astigmatism canceller coil x-direction current excitation I stig2x and y-direction current excitation I stig2y Improve the roundness of the annular electron beam spot.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention addresses the problem of poor uniformity of the preheating temperature field in existing electron beam selective melting (EPM) processes involving point-to-point scanning. It proposes a conformal preheating EPM system and its design method, employing an electron beam forming unit with a central cathode and an annular cathode, along with a focusing and deflection system. In this process, the central electron beam emitted from the central cathode is used to melt the metal powder, while the annular electron beam emitted from the annular cathode forms an annular preheating region that follows the central electron beam. This approach improves the uniformity of the temperature field in the surrounding area during the central electron beam melting process. Furthermore, the proposed electron beam focusing and deflection system incorporates a shielding tube structure within the condenser lens, allowing for adjustment of the size of the annular electron beam's preheating region without affecting the beam spot of the central electron beam. This significantly facilitates the control of the preheating temperature field. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a schematic diagram of an electron beam emitting unit; Figure 2 This is a schematic diagram of the combination of the electron beam emitting unit and the focusing deflection unit; Figure 3 This is a flowchart for determining the excitation parameters of the electron beam focusing and deflection unit; Figure 4 This is a diagram showing the trajectory calculation results of the central electron beam and the annular electron beam after passing through the second accelerating electrode in an example of the present invention. Figure 5This is a diagram of the initial coordinate points of the initial plane center electron beam and the ring electron beam; Figure 6 This is a diagram showing the coordinates of the electron beam at the center of the molten plane and the annular electron beam when they are not deflected. Figure 7 It is a diagram showing the coordinates of the central electron beam and the annular electron beam deflected to the corner of the molten plane; Figure 8 This is a diagram showing the coordinates of the electron beams as the central electron beam and the annular electron beam deflect to the corner of the molten plane, and how the excitation of the condenser and the second astigmatism reducer increases the inner and outer diameters of the annular electron beam.

[0020] Among them, 101 is the central cathode; 102 is the annular cathode; 103 is the suppressor electrode; 104 is the accelerating electrode; 1041 is the outer absorption electrode; 1042 is the outer first accelerating electrode; 1043 is the outer converging electrode; 1044 is the outer second accelerating electrode; 1045 is the inner absorption electrode; 1046 is the inner first accelerating electrode; 1047 is the inner converging electrode; 1048 is the inner second accelerating electrode; 201 is the condenser lens; 2011 is the condenser lens coil; 202 is the second astigmatism reducer; 2021 is the second astigmatism reducer coil; 203 is the objective lens; 2031 is the objective lens coil; 204 is the deflector; 2041 is the deflector coil; 205 is the first astigmatism reducer; 2051 is the first astigmatism reducer coil; 301 is the central electron beam; and 302 is the annular electron beam. Detailed Implementation

[0021] 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.

[0022] 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 non-exclusive inclusion.

[0023] Example 1 This invention provides a conformal preheating electron beam selective melting electron optical system, including an electron beam forming unit and an electron beam focusing and deflection unit connected to the electron beam forming unit; The electron beam forming unit includes a central cathode 101 and an annular cathode 102 sleeved outside the central cathode 101. A suppression electrode 103 is provided between the central cathode 101 and the annular cathode 102 and outside the annular cathode 102. An accelerating electrode 104 is provided on one side of the integral formed by the central cathode 101, the annular cathode 102 and the suppression electrode 103. An electron beam focusing deflection unit is provided on one side of the accelerating electrode 104. The accelerating electrode 104 includes an outer absorption electrode 1041, an outer first accelerating electrode 1042, an outer converging electrode 1043 and an outer second accelerating electrode 1044 arranged sequentially. An inner absorption electrode 1045, an inner first accelerating electrode 1046, an inner converging electrode 1047 and an inner second accelerating electrode 1048 are respectively provided on the inner sides of the outer absorption electrode 1041, the outer first accelerating electrode 1042, the outer converging electrode 1043 and the outer second accelerating electrode 1044. The electron beam focusing and deflection unit includes a condenser lens 201, an objective lens 203, and a deflector 204 arranged sequentially. The condenser lens 201 and the objective lens 203 are hollow inside and are respectively provided with a condenser lens coil 2011 and an objective lens coil 2031. A plurality of deflector coils 2041 are evenly distributed on the inner side of the deflector 204. A second astigmatism corrector 202 is provided in the inner space of the condenser lens 201. A plurality of second astigmatism corrector coils 2021 are evenly distributed on the inner side of the second astigmatism corrector 202. A first astigmatism corrector 205 is provided in the inner space of the second astigmatism corrector 202. A plurality of first astigmatism corrector coils 2051 are evenly distributed on the inner side of the first astigmatism corrector 205. The second astigmatism corrector 205 is physically connected to the second accelerating electrode 1048, and the two are at the same potential.

[0024] Example 2 A design method for a conformal preheating electron beam selective melting electron optical system, specifically including the design of an electron beam forming unit and an electron beam focusing and deflection unit, as well as the determination of the excitation parameters of the electron beam forming unit and the electron beam focusing and deflection unit.

[0025] Step 1: Design of the electron beam forming unit. To avoid the problem of uneven preheating temperature field caused by point-by-point scanning of a single electron beam, this invention designs an electron beam forming unit structure with a central cathode and a ring cathode, as follows: Figure 1As shown. Specifically, it includes a central cathode 101, an annular cathode 102, a suppressor electrode 103, and an accelerating electrode 104. Both the central cathode 101 and the annular cathode 102 are tungsten filament thermal emission cathodes. The central electron beam 301 emitted by the central cathode 101 is used for melting and forming, while the annular electron beam 302 emitted by the annular cathode 102 is used for preheating the powder bed. The central electron beam 301 is always located within the annular region surrounded by the annular electron beam 302, thus ensuring uniform temperature around the melting area, i.e., conformal preheating. During the design process, the potential V of the central cathode 101 is... cc The potential V of the annular cathode 102 co Both are set to 0V, and a negative potential V is applied to the suppression electrode 103 relative to the central cathode 101 and the annular cathode 102. sup (where V) sup <0), the suppression electrode 103 is mainly used to adjust the current magnitude of the electron beam emitted by the central cathode 101 and the annular cathode 102. The accelerating electrode 104 is used to accelerate the central electron beam 301 emitted by the central cathode 101 and the annular electron beam 302 emitted by the annular cathode 102 to the required electron beam energy. The accelerating electrode 104 can be further subdivided into an outer absorption electrode 1041, an outer first accelerating electrode 1042, an outer converging electrode 1043, an outer second accelerating electrode 1044, an inner absorption electrode 1045, an inner first accelerating electrode 1046, an inner converging electrode 1047, and an inner second accelerating electrode 1048. Among them, the outer converging electrode 1043 and the inner converging electrode 1047 are used for converging the annular electron beam 302 and the central electron beam 301, respectively, and the remaining electrodes of the accelerating electrode 104 are used for accelerating the electron beam.

[0026] Step two, design of the electron beam focusing and deflection unit. To ensure the annular electron beam can follow the central electron beam during the forming process and undergo conformal preheating, the electron beam focusing and deflection unit is designed as follows: Figure 2The structure shown is as follows. The electron beam focusing and deflection unit mainly includes components such as a condenser lens 201 and condenser lens coil 2011, a second astigmatism reducer 202 and second astigmatism reducer coil 2021, an objective lens 203 and objective lens coil 2031, a deflector 204 and deflector coil 2041, and a first astigmatism reducer 205 and first astigmatism reducer coil 2051. Among them, the objective lens 203 and the deflector 204 are used for focusing and scanning the central electron beam 301 and the annular electron beam 302, respectively; the second astigmatism reducer 202 is used for adjusting the roundness of the annular electron beam 302; the first astigmatism reducer 205 is used for adjusting the roundness of the central electron beam 301; and the condenser lens 201 is used to adjust the size of the preheating area of ​​the annular electron beam 302 on the molten plane. In order to ensure that the focusing effect of the condenser 201 on the annular electron beam 302 does not affect the central electron beam 301, the first astigmatism reducer 205 is required to shield the focusing effect of the condenser 201 on the central electron beam 301. The first astigmatism reducer 205 should be made of a high permeability material and should be physically connected to the inner second accelerating electrode 1048, with both being at the same potential.

[0027] Step 3: Determining the excitation parameters of the electron beam forming unit electrodes. First, calculate the central electron beam 301 emitted by the central cathode 101, and then determine the potential V of the central cathode 101. cc Set to 0V, the potential V of the suppressor 103 sup A negative potential (V) is applied relative to the central cathode 101. sup <0), then sequentially set the potential V of the inner absorption electrode 1045. ie The potential V of the inner first accelerating electrode 1046 i1 The potential V of the inner second accelerating electrode 1048 i2 The potential V of the inner second accelerating electrode 1048 i2 The final energy of the central electron beam 301 is determined. The trajectory of the central electron beam 301 is calculated using numerical methods, and then the potential V of the inner converging electrode 1047 is adjusted. ig This ensures that the central electron beam 301 is collimated after passing through the inner second accelerating electrode 1048. Next, the annular electron beam 302 emitted by the annular cathode 102 is calculated, and the potential V of the annular cathode 102 is... co Set to 0V, the potential V of the suppressor 103 sup A negative potential (V) is applied relative to the annular cathode 102. sup <0), and then sequentially set the potential V of the outer absorption electrode 1041. oe The potential V of the outer first accelerating electrode 1042 o1 The potential V of the outer second accelerating electrode 1044 o2 The potential V of the outer second accelerating electrode 1044 o2The final energy of the ring electron beam 302 is determined. The trajectory of the ring electron beam 302 is calculated using numerical methods, and then the potential V of the outer converging electrode 1043 is adjusted. og This makes the annular electron beam 302 collimated after passing through the outer second accelerating electrode 1044.

[0028] Step four: Determining the excitation parameters of the electron beam focusing and deflection unit. The process is as follows: Figure 3 As shown, firstly, the coordinates, slope, and other parameters of the central electron beam 301 are used as initial parameters. A numerical calculation method is then used to calculate the beam spot of the central electron beam 301 on the molten plane when only the objective lens 203 is turned on. The current excitation of the objective lens coil 2031 is adjusted to minimize the beam spot of the central electron beam 301 on the molten plane. At this point, the current excitation I of the objective lens coil 2031 is... ol This is called focused motivation, and then focused motivation I ol Next, turn on the deflector 204, calculate the beam spot of the central electron beam 301, and adjust the current excitation of the deflector coil 2041 to shift the beam spot of the central electron beam 301 to the corner position of the desired forming area. At this time, the current excitation I of the deflector coil 2041 is... def This is called the maximum deflection excitation. Since deflection disrupts the rotational symmetry of the central electron beam 301, causing the beam spot to become elliptical, the current excitation of the objective coil 2031 needs to be finely adjusted to improve the roundness of the central electron beam 301 (i.e., to minimize the difference between the major and minor axes of the ellipse of the central electron beam 301). At this point, the current excitation I of the objective coil 2031... old This is called dynamic focus incentive, and finally, in dynamic focus incentive I... old and maximum deflection excitation I def The first astigmatism canceller 205 is activated, the beam spot of the central electron beam 301 is calculated, and the x-direction current excitation I of the first astigmatism canceller coil 2051 is adjusted. stig1x and y-direction current excitation I stig1y Improve the circularity of the central electron beam 301. Next, turn on the condenser lens 201, and use the coordinates, slope, and other parameters of the annular electron beam 302 as initial parameters. Calculate the beam spot of the annular electron beam 302 on the molten plane using numerical calculation methods, and adjust the current excitation I of the condenser lens coil 2011. cl Second astigmatism canceller coil 2021x direction current excitation I stig2x and y-direction current excitation I stig2yImprove the roundness of the annular electron beam 302 (i.e., minimize the difference between the major and minor axes of the elliptical ring of the annular electron beam 302). Since the first astigmatism reducer 205 installed inside the condenser 201 can shield the influence of the condenser 201 on the central electron beam 301, adjusting the current excitation of the condenser coil 2011 and the current excitation of the second astigmatism reducer coil 2021 has no effect on the beam spot of the central electron beam.

[0029] Example 3 by Figure 1 The process of determining the electrode excitation parameters of the electron beam forming unit is illustrated using the electron beam forming unit shown as an example. The calculation model requires the central electron beam 301 and the annular electron beam 302 to be accelerated to 100 keV. First, the potential V of the central cathode 101 is set... cc Set to 0V, suppressor electrode 103 potential set to -100V, inner pull-in electrode 1045 potential V ie Set to 50kV, inner first accelerating electrode potential 1046V i1 and the potential V of the inner second accelerating electrode 1048 i2 All are set to 100kV. When the potential V of the inner converging electrode 1047 is adjusted... ig At 46 kV, the central electron beam becomes a collimated electron beam after passing the inner second accelerating electrode 1048. Then, the annular electron beam 302 emitted by the annular cathode 102 is calculated. The potential V of the annular cathode 102 is... co Set to 0V, external electrode draw-in potential 1041V oe Set to 50kV, outer first accelerating electrode 1042V o1 and the potential V of the second accelerating electrode on the outside 1044 o2 All are set to 100kV. When the potential V of the outer converging electrode 1043 is adjusted... og At 56 kV, the central electron beam 301 becomes a collimated electron beam after passing the outer second accelerating electrode 1044. The calculated trajectories of the central electron beam 301 and the annular electron beam 302 are as follows: Figure 4 As shown.

[0030] Example 4 by Figure 2The electron beam focusing and deflection unit shown is used as an example to illustrate the process of determining the excitation parameters of the electron beam focusing and deflection unit. The calculation model requires the scanning range of the molten region of the central electron beam 301 to be 150mm × 150mm. First, the initial conditions (i.e., electron coordinates, slope, etc.) when the central electron beam 301 enters the focusing and deflection unit are determined. To illustrate the calculation process, this example directly provides the initial conditions of the central electron beam 301. It is assumed that the initial coordinates of the central electron beam 301 are uniformly distributed within a circular region with a radius of 0.1mm, and the initial coordinates of the annular electron beam 302 are uniformly distributed within an annular region with an inner radius of 5.5mm and an outer radius of 6.5mm. Figure 5 As shown. The initial slopes of the central electron beam 301 and the annular electron beam 302 are both within the range of 0-0.0001 and are uniformly distributed. The initial plane is located at z=0mm, the molten plane is located at z=1000mm, the condenser lens 201 is located at z=100mm, the first astigmatism reducer 205 and the second astigmatism reducer 202 are both located at z=200mm, the objective lens 203 is located at z=500mm, and the deflector 204 is located at z=600mm. According to step four, firstly, the objective lens 203 is turned on to calculate the beam spot of the central electron beam on the molten plane, and the current excitation of the objective lens coil 2031 is adjusted to focus the central electron beam 301 on the molten plane. At this time, the focusing excitation I of the objective lens coil 2031 is determined. ol The λ is 0.85 Å. The diameter of the central electron beam 301 is 0.22 mm, and the outer diameter of the annular electron beam 302 is 14.40 mm, while the inner diameter is 12.26 mm. Figure 6 As shown. Then, the current excitation of the deflector coil 2041 is adjusted so that the central electron beam 301 is deflected to the corner of the scanning range of the molten plane, i.e., at the position of x=75mm, y=75mm. At this time, the maximum deflection excitation I of the deflector coil 2041 is determined. def =1.288A, then adjust the current excitation of objective coil 2031 and first astigmatism reducer coil 2051 to improve the roundness of the central electron beam 301 on the molten plane, and finally determine the dynamic focusing current excitation I of objective coil 2031. old =0.82A, the current excitation I in the x-direction of the first astigmatism canceller coil 2051 stig1x =0A, current excitation I in the y direction stig1y =4A. When I old =0.82A, I def At 1.288A, this example also calculated the beam spot of the annular electron beam 302. To improve the roundness of the annular electron beam 302, it is necessary to adjust the current excitation I of the condenser coil 2011. cl =0A, the current excitation I in the x-direction of the second astigmatism canceller coil 2021 stig2x =0.6A, current excitation I in the y directionstig2y =-0.8A, at this time the central electron beam 301 and the annular electron beam 302 are as follows Figure 7 As shown, the diameter of the central electron beam 301 is 0.25 mm, and the outer diameter of the annular electron beam 302 is 14.44 mm, while the inner diameter is 12.30 mm.

[0031] Example 5 Furthermore, the beam spot size of the annular electron beam 302 can be adjusted independently. In Example 4, when I old =0.82A, I def When the current excitation I of the condenser lens coil 2011 is 1.288A, adjust the current excitation I. cl =0.7A, the current excitation I in the x-direction of the second astigmatism canceller coil 2021 stig2x =-0.2A, current excitation I in the y direction stig2y At 0A, the outer diameter of the annular electron beam 302 increases to 19.12 mm, and the inner diameter increases to 16.62 mm, while the diameter of the central electron beam 301 remains at 0.25 mm. Figure 8 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. A conformal preheating electron beam selective melting electron optical system, characterized by, The electron beam forming unit and the electron beam focusing and deflecting unit connected with the electron beam forming unit are comprised; The electron beam forming unit comprises a center cathode (101) and a ring cathode (102) sleeved outside the center cathode (101), a suppressor (103) is arranged between the center cathode (101) and the ring cathode (102) and outside the ring cathode (102), an accelerating electrode (104) is arranged on one side of the whole formed by the center cathode (101), the ring cathode (102) and the suppressor (103), and the electron beam focusing and deflecting unit is arranged on one side of the accelerating electrode (104); The electron beam focusing and deflecting unit comprises a condenser (201), an objective lens (203) and a deflector (204) arranged in sequence, the condenser (201) and the objective lens (203) are hollow inside and are respectively provided with condenser coils (2011) and objective lens coils (2031), a plurality of deflector coils (2041) are uniformly distributed on the inner side of the deflector (204), a second stigmator (202) is arranged in the space on the inner side of the condenser (201), a plurality of second stigmator coils (2021) are uniformly distributed on the inner side of the second stigmator (202), a first stigmator (205) is arranged in the space on the inner side of the second stigmator (202), and a plurality of first stigmator coils (2051) are uniformly distributed on the inner side of the first stigmator (205).

2. A conformal preheating electron beam selective melting electron optical system according to claim 1, characterized in that, The accelerating electrode (104) comprises an outer suction electrode (1041), an outer first accelerating electrode (1042), an outer converging electrode (1043) and an outer second accelerating electrode (1044) arranged in sequence, and the inner sides of the outer suction electrode (1041), the outer first accelerating electrode (1042), the outer converging electrode (1043) and the outer second accelerating electrode (1044) are respectively provided with an inner suction electrode (1045), an inner first accelerating electrode (1046), an inner converging electrode (1047) and an inner second accelerating electrode (1048).

3. A conformal preheating electron beam selective melting electron optical system according to claim 2, characterized in that, The first stigmator (205) is physically connected with the second accelerating electrode (1048) and both are equipotential.

4. A conformal preheating electron beam selective melting electron optical system according to claim 1, characterized in that, The center cathode (101) and the ring cathode (102) are both tungsten filament thermionic cathodes.

5. A method of designing a conformal preheating electron beam selective melting electron optical system as claimed in claim 1, characterized in that, The method comprises the following steps: Step one: design the electron beam forming unit The center electron beam (301) emitted by the center cathode (101) is used for fusion forming, the ring electron beam (302) emitted by the ring cathode (102) is used for preheating of the powder bed, and the center electron beam (301) is always located in the ring area surrounded by the ring electron beam (302), the potential V cc of the center cathode (101) and the potential V co of the ring cathode (102) are both set to 0V, a negative potential V sup is applied to the suppressor (103) relative to the center cathode (101) and the ring cathode (102), the suppressor (103) is used for adjusting the current size of the center electron beam (301) and the ring electron beam (302), and the accelerating electrode (104) is used for accelerating the center electron beam (301) emitted by the center cathode (101) and the ring electron beam (302) emitted by the ring cathode (102) to the required electron beam energy. Step two: design the electron beam focusing and deflecting unit The objective lens (203) and the deflector (204) are respectively used for focusing and scanning of the center electron beam (301) and the ring electron beam (302), the second stigmator (202) is used for roundness adjustment of the ring electron beam (302), the first stigmator (205) is used for roundness adjustment of the center electron beam (301), the condenser (201) is used for adjusting the size of the preheating area of the ring electron beam (302) on the melting plane, and the first stigmator (205) is used for shielding the converging effect of the condenser (201) on the center electron beam (301); Step three: determine the electrode excitation parameters of the electron beam forming unit First, the center electron beam (301) emitted by the center cathode (101) is calculated, the trajectory of the center electron beam (301) is calculated by using a numerical calculation method, and the accelerating electrode (104) is adjusted so that the center electron beam (301) is a collimated electron beam after passing through the accelerating electrode (104); the annular electron beam (302) emitted by the annular cathode (102) is calculated, the trajectory of the annular electron beam (302) is calculated by using a numerical calculation method, and then the accelerating electrode (104) is adjusted so that the annular electron beam (302) is a collimated electron beam after passing through the accelerating electrode (104); Step four: determine the electron beam focusing and deflection unit excitation parameter The beam spot of the center electron beam (301) when only the objective lens (203) is turned on is calculated, the current excitation of the objective lens coil (2031) is adjusted to focus the beam spot of the center electron beam (301), the current excitation of the deflector coil (2041) is adjusted to deflect the beam spot of the center electron beam (301) to a predetermined position, the excitation of the objective lens coil (2031) and the first stigmator coil (2051) is adjusted to improve the roundness of the beam spot of the center electron beam (301); the beam spot of the annular electron beam (302) is calculated, and the excitation of the condenser lens coil (2011) and the excitation of the second stigmator coil (2021) are adjusted to make the beam spot of the annular electron beam (302) meet the preheating area requirement.

6. The method of designing a conformal preheat electron beam selective melting electron optical system of claim 5, wherein, The accelerating electrode (104) comprises an outer side suction electrode (1041), an outer side first accelerating electrode (1042), an outer side converging electrode (1043) and an outer side second accelerating electrode (1044) arranged in sequence, and the inner sides of the outer side suction electrode (1041), the outer side first accelerating electrode (1042), the outer side converging electrode (1043) and the outer side second accelerating electrode (1044) are respectively provided with an inner side suction electrode (1045), an inner side first accelerating electrode (1046), an inner side converging electrode (1047) and an inner side second accelerating electrode (1048).

7. The method of designing a conformal preheat electron beam selective melting electron optical system according to claim 6, wherein, The center electron beam (301) emitted by the center cathode (101) is calculated, the trajectory of the center electron beam (301) is calculated by using a numerical calculation method, and the accelerating electrode (104) is adjusted so that the center electron beam (301) is a collimated electron beam after passing through the accelerating electrode (104), specifically: The potential V of the center cathode (101) is set to 0 V cc The potential V of the suppressor electrode (103) is set to 0 V sup A negative potential V is applied to the center cathode (101) sup Then, the potential V of the inner side extraction electrode (1045) is set to 0 V ie The potential V of the inner side first acceleration electrode (1046) is set to 0 V i1 The potential V of the inner side second acceleration electrode (1048) is set to 0 V i2 The potential V of the inner side second acceleration electrode (1048) is set to 0 V i2 The potential V of the inner side convergence electrode (1047) is adjusted by numerical calculation method to determine the final energy of the center electron beam (301) ig So that the center electron beam (301) becomes a collimated electron beam after passing through the inner side second acceleration electrode (1048).

8. The method of designing a conformal preheat electron beam selective melting electron optical system of claim 6, wherein, The annular electron beam (302) emitted by the annular cathode (102) is calculated, the trajectory of the annular electron beam (302) is calculated by using a numerical calculation method, and then the accelerating electrode (104) is adjusted so that the annular electron beam (302) is a collimated electron beam after passing through the accelerating electrode (104), specifically: The potential V of the ring-shaped cathode (102) is set to 0 V co The potential V of the suppressor (103) is set to 0 V sup A negative potential V is applied to the ring-shaped cathode (102) sup Then, the potential V of the outer side extraction electrode (1041) is set to 0 V oe The potential V of the outer side first acceleration electrode (1042) is set to 0 V o1 The potential V of the outer side second acceleration electrode (1044) is set to 0 V o2 The potential V of the outer side second acceleration electrode (1044) is set to 0 V o2 The potential V of the outer side convergence electrode (1043) is set to 0 V og The potential V of the outer side convergence electrode (1043) is set to 0 V 9. The method of designing a conformal preheat electron beam selective melting electron optical system of claim 6, wherein, The beam spot of the center electron beam (301) when only the objective lens (203) is turned on is calculated, the current excitation of the objective lens coil (2031) is adjusted to focus the beam spot of the center electron beam (301), the current excitation of the deflector coil (2041) is adjusted to deflect the beam spot of the center electron beam (301) to a predetermined position, the excitation of the objective lens coil (2031) and the first stigmator coil (2051) is adjusted to improve the roundness of the beam spot of the center electron beam (301), specifically: Using the initial parameters of the central electron beam (301) as a condition, the beam spot of the central electron beam (301) on the molten plane is calculated numerically when only the objective lens (203) is turned on. The current excitation of the objective lens coil (2031) is adjusted to minimize the beam spot of the central electron beam (301) on the molten plane. At this time, the current excitation I of the objective lens coil (2031) is... ol This is called focused incentive, in focused incentive I ol Next, turn on the deflector (204), calculate the beam spot of the central electron beam (301), and adjust the current excitation of the deflector coil (2041) to shift the beam spot of the central electron beam (301) to the corner position of the required forming area. At this time, the current excitation I of the deflector coil (2041) is... def This is called maximum deflection excitation. Adjusting the current excitation of the objective coil (2031) improves the beam spot circularity of the central electron beam (301). At this time, the current excitation I of the objective coil (2031) is... old This is called dynamic focus incentive, and finally, in dynamic focus incentive I... old and maximum deflection excitation I def The first astigmatism canceller (205) is activated, the beam spot of the central electron beam (301) is calculated, and the x-direction current excitation I of the first astigmatism canceller coil (2051) is adjusted. stig1x and y-direction current excitation I stig1y Improve the beam spot roundness of the central electron beam (301).

10. The method of designing a conformal preheat electron beam selective melting electron optical system of claim 6, wherein, The calculation of the beam spot of the annular electron beam (302) adjusts the excitation of the condenser coil (2011) and the excitation of the second stigmator coil (2021) to make the beam spot of the annular electron beam (302) meet the preheating area requirement, specifically: The condenser (201) is turned on, and the beam spot of the annular electron beam (302) on the melting plane is calculated by numerical calculation method with the initial parameters of the annular electron beam (302) as the condition, and the current excitation I of the condenser coil (2011) is adjusted cl and the x-direction current excitation I of the second stigmator coil (2021) stig2x and the y-direction current excitation I stig2y The roundness of the annular electron beam (302) is improved.

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