Substrate assembly for laser additive manufacturing and additive manufacturing process method

Abstract

The invention provides a substrate assembly for laser additive manufacturing and an additive manufacturing process method. The substrate assembly for laser additive manufacturing comprises a first substrate, a second substrate, an electromagnet, a first lifting assembly and a second lifting assembly. A placement groove is formed in the top surface of the first substrate; the second substrate is placed in the placing groove, and the top surface of the second substrate is flush with the top surface of the first substrate; the two electromagnets are placed in the placing groove and located on the two sides of the second base plate. The first lifting assembly comprises a first driving unit and a heating lifting rod, and the first driving unit is connected with the heating lifting rod; the heating lifting rod is connected with the bottom surface of the second substrate; the second lifting assembly is connected with the electromagnet. By arranging the structure that the second substrate is embedded into the first substrate, the cost can be saved, the structure is simpler and the energy consumption is lower only by applying the magnetic field to the second substrate and heating the second substrate, the second substrate can be continuously used after the thickness of the second substrate is continuously reduced due to machining through lifting of the second substrate, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular, to a substrate assembly for laser additive manufacturing and an additive manufacturing process method. Background Art

[0002] In the field of additive manufacturing, the laser powder bed fusion (LPBF) technology scans a metal powder bed with a laser beam of high energy density, causing the powder to melt and solidify layer by layer, and finally forming a three-dimensional solid part. It has better quality and performance, and has advantages such as high forming freedom and short manufacturing cycle, and is applicable to the additive manufacturing of metals such as copper alloys, iron alloys, titanium alloys, aluminum alloys, and nickel-based alloys. In the LPBF technology, the metal powder melts under the action of the laser to form a molten pool, and the melted metal rapidly cools to the ambient temperature. The rapid heating, melting, and solidification of the molten pool form relatively large residual stresses, which in turn lead to the formation of metallurgical defects (porosity and cracks). Therefore, improving the quality of the formed parts, especially reducing the crack and porosity defects of difficult-to-machine materials, is of great significance for the development of laser additive manufacturing technology.

[0003] To solve the above problems, in the prior art, some people have proposed applying a magnetic field during the LPBF process. By using the stirring effect of the magnetic field on the molten pool to change the mass and heat transfer process, the purpose of improving the quality of the deposited layer, accelerating the escape of gas, breaking solid-phase dendrites, refining grains, and improving performance can be achieved. However, the LPBF forming process is carried out in a closed cavity. The existing magnetic field device and the substrate are independently arranged, and the magnetic field device is installed outside the substrate, which will increase the overall volume of the LPBF device and increase the equipment cost. Summary of the Invention

[0004] In view of this, the present invention provides a substrate assembly for laser additive manufacturing and an additive manufacturing process method to solve the technical problem that the existing magnetic field device and the first substrate are independently arranged, and the magnetic field device is installed outside the first substrate, which will increase the overall volume of the LPBF device and increase the equipment cost.

[0005] The technical solution of the present invention is realized as follows: In a first aspect, the present invention provides a substrate assembly for laser additive manufacturing, including a first substrate, a second substrate, an electromagnet, a first lifting assembly, and a second lifting assembly, wherein: A placement groove is provided on the top surface of the first substrate, and a receiving cavity for receiving the first lifting assembly and the second lifting assembly is provided inside the first substrate, and the receiving cavity is located below the placement groove; The second substrate is placed in the placement groove, and the top surface of the second substrate is flush with the top surface of the first substrate; There are two electromagnets, and the two electromagnets are placed in the placement groove and located on both sides of the second substrate; The first lifting assembly includes a first driving unit and a heating lifting rod. The first driving unit is installed at the bottom of the accommodating cavity and is connected to the heating lifting rod for driving the heating lifting rod to move in a direction perpendicular to the second substrate; the heating lifting rod is connected to the bottom surface of the second substrate; The second lifting assembly is installed in the accommodating cavity and is connected to the electromagnet for driving the electromagnet to move in a direction perpendicular to the second substrate.

[0006] Based on the above technical solutions, preferably, the first driving unit includes a bottom support frame, a mounting frame, a first driving member, a first transmission mechanism, a support rod, a screw rod, and a connecting rod. The bottom support frame is installed at the bottom of the accommodating cavity, the mounting frame is fixed to the side wall of the support rod, the first driving member is installed on the mounting frame, the first transmission mechanism is connected to the first driving member, the support rod is installed on the bottom support frame, one end of the screw rod is threadedly connected to the first transmission mechanism, the other end of the screw rod is connected to the middle of the connecting rod, and both ends of the connecting rod are respectively connected to the two heating lifting rods.

[0007] Based on the above technical solutions, preferably, the first transmission mechanism includes a transmission shaft, two bearings, two driving bevel gears, and two driven bevel gears; there are four heating lifting rods, and the four heating lifting rods are respectively arranged at the four corners of the second substrate and symmetrically installed; the two bearings are installed on the mounting frame; the transmission shaft is installed in the two bearings, and the first driving member is drivingly connected to the transmission shaft; the two driving bevel gears are installed on the transmission shaft; the two driven bevel gears are respectively rotatably installed on the two support rods and are axially limited to each other, and the driven bevel gear is threadedly connected to the screw rod and meshes with the driving bevel gear.

[0008] Based on the above technical solutions, preferably, the second lifting assembly includes a bottom support rod, a support frame, a second driving member, and a second transmission mechanism; the bottom support rod includes a fixed section and a movable section, the fixed section is installed on the bottom support frame, the movable section is connected to the second substrate and is slidably installed in the fixed section; the support frame is sleeved on the bottom support rod, and both ends of the support frame are provided with fixing parts for fixing the electromagnet; the second driving member is installed on the support frame and is connected to the second transmission mechanism; the second transmission mechanism is connected to the fixed section for driving the support frame to slide along the bottom support rod.

[0009] On the basis of the above technical solutions, preferably, the second transmission mechanism includes a driving gear and a rack. The driving gear is connected to the second driving member. The rack is installed on the fixed section and its length direction is parallel to the height direction of the support rod. The rack meshes with the driving gear.

[0010] On the basis of the above technical solutions, preferably, a driving frame and a clamping plate are provided on the support frame. The driving frame includes a horizontal plate and a vertical plate connected to each other. The second driving member is installed on the horizontal plate. The vertical plate is arranged parallel to the height direction of the bottom support rod. The clamping plate is arranged parallel to the vertical plate and there is a gap between the two. The rack is located in the gap.

[0011] Second, the present invention provides an additive manufacturing process method, using the laser additive manufacturing substrate assembly described in the first aspect, including: Drive the heating lifting rod to move in a direction perpendicular to the second substrate through the first driving unit, and drive the electromagnet to move in a direction perpendicular to the second substrate through the second lifting assembly, so that the upper surfaces of the second substrate, the electromagnet and the first substrate are on the same horizontal plane; Set the laser power, scanning rate, scanning spacing and layer thickness of the laser beam according to the size of the formed part and the material used; Lay a layer of metal powder on the surface of the second substrate according to the layer thickness; Start the heating device of the heating support rod to heat the second substrate and the metal powder layer; After the temperatures of the second substrate and the metal powder layer are stabilized at 200~500 °C, according to the set process parameters such as laser power, scanning rate, scanning spacing, etc., the laser beam selectively melts the metal powder to form a molten pool. After the molten pool solidifies, a molten track is formed, and the tracks are overlapped to form a layer; After the current layer is scanned, the first substrate descends by a layer thickness; Repeat the above process until the formed part is manufactured.

[0012] On the basis of the above technical solutions, preferably, setting the laser power, scanning rate and scanning spacing of the laser beam and the layer thickness of the metal powder layer according to the size of the formed part and the material used specifically includes: setting the laser power to 100~600 W, the scanning speed to 100~1000 mm / s, the scanning spacing to 40~100 μm, and the layer thickness to 20~70 μm.

[0013] On the basis of the above technical solutions, preferably, after the step of layer-by-layer deposition until the manufacturing of the formed part is completed, the method further includes: removing the second substrate, separating the formed part from the surface of the second substrate, and milling the surface of the second substrate. When it is used again, install the second substrate and start the first driving unit to drive the heating lifting rod in a direction perpendicular to the second substrate, so that the upper surface of the second substrate rises to be flush with the upper surface of the first substrate.

[0014] On the basis of the above technical solutions, preferably, before the temperature of the second substrate and the metal powder layer stabilizes at 200-500 °C and the laser beam selectively melts the metal powder to form a molten pool, the method further includes: the second lifting assembly raises the electromagnet by a height of one layer thickness.

[0015] The substrate assembly for laser additive manufacturing and the additive manufacturing process method of the present invention have the following beneficial effects compared with the prior art: (1) By providing a placement groove on the top surface, the second substrate is placed in the placement groove, and the top surface of the second substrate is flush with the top surface of the first substrate, so that the second substrate is embedded in the first substrate. For small, precision and complex parts with customized requirements, in the case where the forming area required for the actual part is small and the forming cylinder is large, this structure can save costs, and the magnetic field and heating device applied only to the second substrate are simpler and have lower energy consumption; through the adjustment of the second substrate by the first lifting assembly, it can be ensured that the upper surfaces of the second substrate and the first substrate are on the same horizontal plane. At the same time, the lifting of the second substrate can enable the second substrate to continue to be used after its thickness is continuously reduced due to machining, reducing costs; by heating the heating lifting rod, the heat can be quickly conducted to the second substrate, thereby avoiding a too large temperature gradient, reducing thermal stress, improving the forming performance of the material, and improving the forming quality. (2) By adjusting the height of the electromagnet through the second lifting assembly, it can be ensured that the laid metal powder layer is always within the magnetic field action range to achieve a stable magnetic induction intensity effect. Through the regulation of the molten pool by the magnetic field, it can effectively accelerate the gas escape, break the solid-phase dendrites, promote the non-spontaneous nucleation of the molten pool, refine the grains, reduce the temperature gradient, inhibit stress cracking, improve the formability and increase the strength and toughness. (3) By respectively arranging the four heating lifting rods at the four corners of the second substrate and symmetrically installing them, the heating can be ensured to be uniform, avoiding a too large temperature gradient, thereby reducing thermal stress, improving the forming performance of the material, and improving the forming quality. The first driving member drives the transmission shaft to rotate, thereby driving two driving helical gears to rotate. The driving helical gears drive the driven helical gears to rotate. The driven helical gears drive the screw to rotate through a thread. Since both ends of the connecting rod fixed to the screw are limited by two heating lifting rods, the screw can only move linearly along the axial direction of the driven helical gear, thereby realizing the lifting of the heating lifting rods; through the meshing of the driving helical gear and the driven helical gear, the locking of the driven helical gear and the screw can be realized, ensuring that when the first driving member does not work, the overall mechanism does not rotate, so that the second substrate remains stable; (4) The rack is installed on the fixed section and its length direction is parallel to the height direction of the support rod. The rack meshes with the driving gear. The second driving member drives the driving gear to rotate, and the driving gear moves on the rack, so as to move together with the second driving member and the support frame, realizing the lifting of the electromagnet; (5) While preheating the second substrate, magnetic perturbation is supplemented to regulate the solidification and crystallization process and the solid-state phase transformation process, promote grain refinement and reduce the content of brittle phases, improve the tissue toughness while reducing the ductile-brittle transition temperature, and thus can solve the cracking problem faced by the LPBF formed alloy at a lower preheating temperature (200 °C); (6) By setting the laser power to 100 - 600 W, the scanning speed to 100 - 1000 mm / s, the scanning spacing to 40 - 100 μm, and the layer thickness to 20 - 70 μm, under the above parameters, the processing quality of LPBF is relatively good, which can reduce the influence of processing parameters on the processing quality, and obtain the results of the influence of the magnetic field and heating temperature on the porosity and cracks of the formed parts, and the accuracy and reliability of the results are better; (7) It is applicable to laser powder bed melting of almost all metal materials such as stainless steel, copper alloy, superalloy, and light alloys (titanium alloy, aluminum alloy, magnesium alloy, titanium aluminide intermetallic compound), and at the same time, the substrate can be conveniently installed in equipment of different models. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic structural diagram of the substrate assembly for laser additive manufacturing in the embodiment of the present invention; Figure 2 It is a schematic structural diagram of the substrate assembly for laser additive manufacturing (removing the first substrate) in the embodiment of the present invention; Figure 3 Schematic diagram of the structure of the first lifting component in the embodiment of the present invention; Figure 4 Schematic diagram of the structure of the second lifting component in the embodiment of the present invention; Figure 5 For the present invention Figure 4 Partial enlarged view of part A therein; Figure 6 Schematic diagram of the structure of the second transmission mechanism in the embodiment of the present invention; Figure 7 Schematic diagram of the principle of arrangement one (a) and arrangement two (b) of the electromagnet in the embodiment of the present invention; Figure 8 Schematic diagram of the process flow of the additive manufacturing process method in the embodiment of the present invention; Figure 9 Metallographic photos of the longitudinal sections of specimen 1 (a) and 2 (b) in the comparative example; Figure 10 Metallographic photos of the longitudinal sections of specimen 3 (c) and 4 (d) in the comparative example; Figure 11 Metallographic photo of the longitudinal section of specimen 5 (e) in the comparative example; Figure 12 Metallographic photo of the longitudinal section of specimen 6 in Example 1; Figure 13 Metallographic photos of the longitudinal sections of specimen 7 (a) and specimen 8 (b) in Example 2; Figure 14 Metallographic photos of the longitudinal sections of specimen 9 (c) and specimen 10 (d) in Example 2; Figure 15 Metallographic photos of the longitudinal sections of specimen 11 (a) and specimen 12 (b) in Example 3; Figure 16 Metallographic photos of the longitudinal sections of specimen 13 (c) and specimen 14 (d) in Example 3.

[0018] Explanation of reference numerals: 1 - first substrate, 2 - second substrate, 3 - electromagnet, 4 - first lifting component, 5 - second lifting component; 41 - first driving unit, 411 - bottom support frame, 412 - mounting frame, 413 - first driving member, 414 - first transmission mechanism, 4141 - transmission shaft, 4142 - bearing, 4143 - driving helical gear, 4144 - driven helical gear, 415 - support rod, 416 - screw rod, 417 - connecting rod, 42 - heating lifting rod; 51 - Bottom support rod, 511 - Fixed section, 512 - Movable section, 52 - Support frame, 53 - Second driving member, 54 - Second transmission mechanism, 541 - Driving gear, 542 - Rack, 55 - Driving frame, 551 - Horizontal plate, 552 - Vertical plate, 56 - Clamping plate. Specific embodiments

[0019] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0020] Refer to Figures 1-7 As shown, in the first - aspect embodiment of the present invention, a substrate assembly for laser additive manufacturing is proposed, including a first substrate 1, a second substrate 2, an electromagnet 3, a first lifting assembly 4, and a second lifting assembly 5, wherein: A placement groove is provided on the top surface of the first substrate 1, and a receiving cavity for accommodating the first lifting assembly 4 and the second lifting assembly 5 is provided inside the first substrate 1, and the receiving cavity is located below the placement groove; The second substrate 2 is placed in the placement groove, and the top surface of the second substrate 2 is flush with the top surface of the first substrate 1; There are two electromagnets 3. The two electromagnets 3 are placed in the placement groove and on both sides of the second substrate 2. The electromagnet 3 and the second substrate 2 are embedded in the placement groove; the electromagnet 3 can be energized with direct current or alternating current; the magnetic poles of the two electromagnets 3 are opposite. When energized with direct current, since the direct - current is constant, the magnetic field generated by the direct - current electromagnet 3 is stable and does not change with time; when energized with alternating current, the magnetic field of the alternating - current electromagnet 3 changes periodically with the change of the alternating current; The first lifting assembly 4 includes a first driving unit 41 and a heating lifting rod 42. The first driving unit 41 is installed at the bottom of the accommodation cavity and is connected to the heating lifting rod 42 for driving the heating lifting rod 42 to move in a direction perpendicular to the second substrate 2. The heating lifting rod 42 is connected to the bottom surface of the second substrate 2. One end of the heating lifting rod 42 is fixed at the bottom of the accommodation cavity, and the other end can be lifted. The lifted end is fixedly connected to the bottom surface of the second substrate 2. The heating lifting rod 42 is made of iron-chromium-aluminum electrothermal alloy with a relatively high thermal conductivity (52.7 KJ / m·h·°C), and is connected to a current controller. Heat insulation coatings are applied to the connection part of the heating lifting rod 42 and the four side surfaces of the second substrate 2. After laying metal powder on the surface of the second substrate 2, the current controller can be turned on to heat the heating lifting rod 42. The heat insulation coating can effectively reduce heat loss and can quickly conduct heat to the second substrate 2, thereby realizing rapid heating and ensuring uniform heating. At the same time, the heat insulation coating at the connection part effectively reduces the loss caused by high temperature to the moving mechanism. The second lifting assembly 5 is installed in the accommodation cavity and is connected to the electromagnet 3 for driving the electromagnet 3 to move in a direction perpendicular to the second substrate 2.

[0021] It should be noted that for small, precision, complex parts with customized requirements, when the forming area required for the actual part is small and the forming cylinder is relatively large, the structure of setting a second substrate 2 with a smaller area embedded in the first substrate 1 can save costs. Moreover, the magnetic field and heating device applied only to the second substrate 2 are simpler and consume less energy. Through the adjustment of the second substrate 2 by the first lifting assembly 4, it can be ensured that the upper surfaces of the second substrate 2, the first substrate 1, and the forming cylinder are on the same horizontal plane. At the same time, after removing the part from the second substrate 2, mechanical processing needs to be performed on the upper surface, which will reduce the thickness of the second substrate 2. The first lifting assembly 4 can lift the second substrate 2 after the thickness of the second substrate 2 continuously decreases, so that the second substrate 2 can continue to be used, avoiding waste caused by the inability to use due to the reduction of the thickness of the second substrate 2, reducing costs, and avoiding the impact of the loss of the second substrate 2 caused by milling on the quality of the formed parts after repeated use of the substrate.

[0022] The substrate assembly for laser additive manufacturing proposed in this embodiment has a placement groove provided on the top surface of the first substrate 1. The second substrate 2 is placed in the placement groove, and the top surface of the second substrate 2 is flush with the top surface of the first substrate 1. The structure of setting the second substrate 2 embedded in the first substrate 1 can save costs, and the magnetic field and heating device applied only to the second substrate 2 are simpler and have lower energy consumption. Through the adjustment of the second substrate 2 by the first lifting assembly 4, it can be ensured that the upper surfaces of the second substrate 2 and the first substrate 1 are on the same horizontal plane. At the same time, the lifting of the second substrate 2 allows the second substrate 2 to continue to be used after its thickness is continuously reduced due to machining, reducing costs; by heating the heating lifting rod 42, heat can be quickly conducted to the second substrate 2, thereby avoiding a situation of too large a temperature gradient, reducing thermal stress, improving the forming performance of the material, and improving the forming quality; by adjusting the height of the electromagnet 3 through the second lifting assembly 5, it can be ensured that the laid metal powder layer is always within the magnetic field action range to achieve a stable magnetic induction intensity effect. Through the regulation of the molten pool by the magnetic field, it can effectively accelerate the escape of gas, break solid-phase dendrites, promote non-spontaneous nucleation of the molten pool, refine grains, reduce the temperature gradient, inhibit stress cracking, improve formability, and improve strength and toughness.

[0023] In some embodiments, the first driving unit 41 includes a bottom support frame 411, a mounting frame 412, a first driving member 413, a first transmission mechanism 414, a support rod 415, a screw rod 416, and a connecting rod 417. The bottom support frame 411 is installed at the bottom of the accommodation cavity, the mounting frame 412 is fixed to the side wall of the support rod 415, the first driving member 413 is installed on the mounting frame 412, the first transmission mechanism 414 is connected to the first driving member 413, the support rod 415 is installed on the bottom support frame 411, one end of the screw rod 416 is threadedly connected to the first transmission mechanism 414, the other end of the screw rod 416 is connected to the middle of the connecting rod 417, and both ends of the connecting rod 417 are respectively connected to two of the heating lifting rods 42. By driving the first transmission mechanism 414 by the first driving member 413 to drive the screw rod 416 to rotate, since the other end of the screw rod 416 is connected to the middle of the connecting rod 417, and both ends of the connecting rod 417 are respectively connected to two of the heating lifting rods 42, the screw rod 416 and the connecting rod 417 are fixedly installed, and the connecting rod 417 can only move linearly along the axis of the screw rod 416 together with the screw rod 416, thereby realizing the lifting of the heating lifting rod 42.

[0024] In some embodiments, the first transmission mechanism 414 includes a transmission shaft 4141, two bearings 4142, two driving helical gears 4143 and two driven helical gears 4144; there are four heating lifting rods 42, and the four heating lifting rods 42 are respectively arranged at the four corners of the second substrate 2 and symmetrically installed; the two bearings 4142 are installed on the mounting frame 412; the transmission shaft 4141 is installed in the two bearings 4142, and the first driving member 413 is drivingly connected to the transmission shaft 4141; the two driving helical gears 4143 are installed on the transmission shaft 4141; the two driven helical gears 4144 are respectively rotatably installed on the two support rods 415 and are axially limited to each other, and the driven helical gear 4144 is threadedly connected to the screw 416 and meshes with the driving helical gear 4143. By arranging the four heating lifting rods 42 at the four corners of the second substrate 2 and symmetrically installing them, the heating can be ensured to be uniform, the situation of too large temperature gradient can be avoided, thereby reducing thermal stress, improving the forming performance of the material, and improving the forming quality; the first driving member 413 drives the transmission shaft 4141 to rotate, thereby driving the two driving helical gears 4143 to rotate. The driving helical gear 4143 drives the driven helical gear 4144 to rotate. The driven helical gear 4144 drives the screw 416 to rotate through the thread. Since both ends of the connecting rod 417 fixed to the screw 416 are limited by the two heating lifting rods 42, the screw 416 can only move linearly along the axis of the driven helical gear 4144, thereby realizing the lifting of the heating lifting rod 42; through the meshing of the driving helical gear 4143 and the driven helical gear 4144, it is ensured that when the first driving member 413 does not work, the driven helical gear 4144 and the screw 416 can be locked, and the overall mechanism does not rotate, so that the second substrate 2 remains stable. The first driving member 413 can adopt a motor. In actual design, the number of teeth of the driving helical gear 4143 and the driven helical gear 4144 are set to be the same. The driving helical gear 4143 and the driven helical gear 4144 should be selected with more teeth, which can improve the contact ratio and make the transmission smooth; the thread specification of the screw 416 should make the pitch as small as possible on the premise of maintaining good self-locking performance to ensure the accuracy when adjusting the height of the second substrate 2.

[0025] In some embodiments, the second lifting assembly 5 includes a bottom support rod 51, a support frame 52, a second driving member 53, and a second transmission mechanism 54; the bottom support rod 51 includes a fixed section 511 and a movable section 512, the fixed section 511 is installed on the bottom support frame 411, and the movable section 512 is connected to the second substrate 2 and slidably installed in the fixed section 511; the support frame 52 is sleeved on the bottom support rod 51, and both ends of the support frame 52 are provided with fixing portions for fixing the electromagnet 3; the second driving member 53 is installed on the support frame 52 and connected to the second transmission mechanism 54; the second transmission mechanism 54 is connected to the fixed section 511 and is used to drive the support frame 52 to slide along the bottom support rod 51. By driving the second transmission mechanism 54 with the second driving member 53, the support frame 52 is driven to slide along the bottom support rod 51, and the fixed section 511 of the bottom support rod 51 is installed on the bottom support frame 411, and the movable section 512 is connected to the second substrate 2 and slidably installed in the fixed section 511. When the second substrate is lifted or lowered, the movable section 512 of the bottom support rod 51 moves together with the second substrate 2, and the movement of the support frame 52 is independent of the lifting and lowering of the second substrate 2, without interference with each other, improving the reliability and stability of the device.

[0026] In some embodiments, the second transmission mechanism 54 includes a driving gear 541 and a rack 542, the driving gear 541 is connected to the second driving member 53, the rack 542 is installed on the fixed section 511 and its length direction is parallel to the height direction of the support rod 415, and the rack 542 meshes with the driving gear 541. By the rack 542 being installed on the fixed section 511 and its length direction being parallel to the height direction of the support rod 415, the rack 542 meshing with the driving gear 541, the second driving member 53 drives the driving gear 541 to rotate, and the driving gear 541 moves on the rack 542, so as to move together with the second driving member 53 and the support frame 52 to realize the lifting and lowering of the electromagnet 3. The second driving member 53 can adopt a motor.

[0027] In some further embodiments, a driving frame 55 and a clamping plate 56 are provided on the support frame 52. The driving frame 55 includes a horizontal plate 551 and a vertical plate 552 which are connected to each other. The second driving member 53 is installed on the horizontal plate 551, and the vertical plate 552 is arranged parallel to the height direction of the bottom support rod 51; the clamping plate 56 is arranged parallel to the vertical plate 552 and there is a gap between the two, and the rack 542 is located in the gap. The output shaft of the second driving member 53 is rotatably installed on the vertical plate 552 and the clamping plate 56, and then the driving gear 541 is installed on the output shaft of the second driving member 53 and is located between the vertical plate 552 and the clamping plate 56. The rack 542 is located in the gap between the clamping plate 56 and the vertical plate 552, and the two sides of the rack 542 are guided by the clamping plate 56 and the vertical plate 552, so that the rolling of the driving gear 541 on the rack 542 is more stable and reliable, improving the reliability and stability of the device.

[0028] The working principle of the substrate assembly for laser additive manufacturing in this embodiment is as follows: After the second substrate 2 is installed, the first lifting assembly 4 is used to adjust the second substrate 2 to be horizontal with the first substrate 1. After the metal powder is laid on the surface of the second substrate 2, the current controller is turned on to preheat the second substrate 2; at this time, there is already a powder height of one layer thickness on the surface of the second substrate 2, and the initial position of the electromagnet 3 is horizontal with the second substrate 2. It is necessary to use the second lifting assembly 5 to raise the electromagnet 3 by one layer thickness to ensure that the laid powder layer is within the action range of the magnetic field; after the laser beam completes one layer of scanning, the first substrate 1 descends by one layer height, so that the overall forming plane descends by one layer height; after the formed part is manufactured, the part is separated from the surface of the second substrate 2. If the second substrate 2 still needs to be used, after milling the surface of the second substrate 2, the second substrate 2 is reinstalled to the first lifting assembly 4. Since the thickness of the second substrate 2 decreases, it is necessary to use the first lifting assembly 4 to adjust the height of the second substrate 2 again until it is horizontal with the first substrate 1; When the height of the second substrate 2 needs to be adjusted, by starting the first driving member 413, after the transmission shaft 4141 rotates, the driving helical gear 4143 is driven to rotate, the driven helical gear 4144 is driven to rotate, the screw 416 is driven to rotate, the heating lifting rod 42 is driven to lift, and then the second substrate 2 is driven to perform a height adjustment; when the height of the electromagnet 3 needs to be adjusted, by starting the second driving member 53 to drive the driving gear 541 to rotate, the driving gear 541 rolls on the rack 542, driving the driving gear 541 and the second driving member 53 as a whole to move upward, driving the support frame 52 connected to the second driving member 53 to move, and then driving the electromagnet 3 to complete a height adjustment.

[0029] Based on the same concept, in the second aspect embodiment of the present invention, in combination with Figure 8As shown, a method for additive manufacturing process is provided, which uses the substrate assembly for laser additive manufacturing described in the first aspect, including: Step S1: Drive the heating lifting rod 42 to move in a direction perpendicular to the second substrate 2 through the first driving unit 41, and drive the electromagnet 3 to move in a direction perpendicular to the second substrate 2 through the second lifting assembly 5, so that the upper surfaces of the second substrate 2, the electromagnet 3 and the first substrate 1 are on the same horizontal plane; Step S2: Set process parameters such as the laser power, scanning rate, and scanning spacing of the laser beam, as well as motion parameters such as the layer thickness of the metal powder layer, according to the size and material of the formed part; Step S3: Lay a layer of metal powder layer on the surface of the second substrate 2 according to the layer thickness; Step S4: Start the heating device of the heating support rod 415 to heat the second substrate 2 and the metal powder layer; Step S5: After the temperatures of the second substrate 2 and the metal powder layer are stabilized at 200 - 500 °C, according to the set process parameters such as laser power, scanning rate, and scanning spacing, the laser beam selectively melts the metal powder to form a molten pool, and after the molten pool solidifies, a molten channel is formed, and the channels overlap to form a layer; Step S6: After the current layer is scanned, the first substrate 1 is lowered as a whole by a layer thickness; Step S7: Repeat steps S3 - S6 until the part manufacturing is completed.

[0030] The additive manufacturing process method proposed in this embodiment preheats the second substrate and is supplemented with magnetic perturbation while regulating the solidification and crystallization process and the solid-state phase transformation process, promoting grain refinement and reducing the content of brittle phases, improving the tissue toughness while reducing the ductile-brittle transition temperature, and thus can solve the cracking problem faced by LPBF formed alloys at a lower preheating temperature (200 °C).

[0031] In some embodiments, setting the process parameters such as the laser power, scanning rate, and scanning spacing of the laser beam, as well as the motion parameters such as the layer thickness of the metal powder layer according to the size and material of the formed part specifically includes: setting the laser power to 100 - 600 W, the scanning speed to 100 - 1000 mm / s, the layer thickness to 20 - 70 μm, and the scanning spacing to 40 - 100 μm. Under the above parameters, the processing quality of LPBF is relatively good, which can reduce the influence of processing parameters on the processing quality, and obtain the results of the influence of the magnetic field and heating temperature on the porosity and cracks of the formed part, and the accuracy and reliability of the results are better.

[0032] In some embodiments, in step S7, after the forming part is manufactured, the following steps are further included: removing the second substrate 2, separating the part from the surface of the second substrate 2, and milling the surface of the second substrate 2. When it is used again, install the second substrate 2, start the first driving unit 41 to drive the heating lifting rod 42 in a direction perpendicular to the second substrate 2, so that the upper surface of the second substrate 2 rises to the same plane as the upper surface of the first substrate 1. After the part is formed, remove the second substrate 2, separate the part from the surface of the second substrate 2, and mill the surface of the second substrate 2. At this time, the thickness of the second substrate 2 decreases. When it needs to be used again, install the second substrate 2, start the first driving unit 41, and make the upper surface of the second substrate 2 rise to be horizontal with the upper surface of the first substrate 1. By adopting this technical solution, it is possible to avoid the waste caused by the loss of the second substrate 2 due to milling after repeated use of the second substrate 2, reduce the use cost, and avoid the influence of the loss of the second substrate 2 due to milling after repeated use of the substrate on the quality of the formed part.

[0033] In some embodiments, in step S5, after the temperature of the second substrate 2 and the metal powder layer is stabilized at 200 - 500 °C and before the laser beam selectively melts the metal powder to form a molten pool, the following steps are further included: the second lifting assembly 5 raises the electromagnet 3 by a height of one layer thickness. Through the above operations, it is ensured that the next layer of metal powder layer to be laid is in the magnetic field action area, and the magnetic induction intensity generated by the electromagnet 3 on the surface of the formed part remains stable, ensuring the quality of the formed part.

[0034] The present invention conducts verification experiments on the effects of the above methods, and sets a comparative example, Example 1, Example 2, and Example 3 respectively.

[0035] Comparative Example The Ti - 43Al - 9V - 0.5Y powder with a particle size of 15 - 53 μm is dried in a VO - 6050T vacuum drying oven at 100 °C for 2 h, taken out and added to the powder feeder. The TC4 titanium alloy second substrate 2 is polished and sandblasted and then installed on the first substrate 1, and the upper surface of the second substrate 2 is adjusted to be horizontal with the upper surface of the first substrate 1. The process parameters used in the experiment are shown in Table 1 and are started according to the set laser scanning path. Without preheating of the second substrate 2 and magnetic field assistance, the laser power, scanning speed, layer thickness, and scanning spacing are respectively changed, and specimens 1 - 5 are prepared by LPBF to prepare Ti - 43Al - 9V - 0.5Y alloy.

[0036] Table 1 。

[0037] Example 1 Only the heating device is turned on, and the preheating temperature is 400 °C. Other parameters are the same as those of Specimen 2. Under this condition, Specimens 6 of Ti-43Al-9V-0.5Y alloy are prepared by LPBF, and the parameter settings are shown in Table 1 above.

[0038] Example 2 In Example 2, the process parameters used are shown in Table 2. Compared with the comparative example, the heating and magnetic field devices are turned on, the preheating temperature is 200 °C, and the magnetic induction intensity is set to gradually increase (0.05 - 0.16 T). Other process parameters are the same. Under this condition, Specimens 7 - 10 of Ti-43Al-9V-0.5Y alloy are prepared by LPBF.

[0039] Table 2 。

[0040] Example 3 In Example 3, the process parameters used are shown in Table 3. Compared with the comparative example, only the magnetic induction intensity is changed to 0.16 T, and the preheating temperature is 200 °C. Other process parameters are the same. Under this condition, Specimens 11 - 14 of Ti-43Al-9V-0.5Y alloy are prepared by LPBF.

[0041] Table 3

[0042] Subsequently, the samples 1 to 14 prepared in Example 1, the comparative example, Example 2, and Example 3 were separated from the second substrate 2 by wire electrical discharge machining. The image method was used to analyze the porosity and crack density of the specimens. Before measurement, the cross-section and longitudinal section of the specimens were ground and polished using the standard metallographic preparation method. Then, a Leica DM ILM optical microscope (Optical microscope, OM) was used to observe the two sections and 20 different metallographic photos were taken on each section. The Image-Pro Plus 6.0 image analysis software was used to process the metallographic photos, and the porosity and crack density were statistically analyzed. The software calculated the area by identifying the pores (gas pores and unfused holes). The porosity is the ratio of the area of the gas pores and unfused holes in each metallographic photo to the total area of the metallographic photo. The length of the cracks was measured using the measurement tool in the software, and then the total length of the cracks was obtained. The crack density is the ratio of the total length of the cracks in each metallographic photo to the total area of the metallographic photo. The obtained results are shown in Table 4. And the metallographic photos of the longitudinal sections of the specimens in Example 1, the comparative example, Example 2, and Example 3 are respectively as Figures 7 to 14 shown.

[0043] Table 4

[0044] Comparing Example 1 with the comparative example, it can be seen that the effect of reducing the number of pores and cracks is not obvious only under the action of heating. Comparing the comparative example, Example 2 and Example 3, it can be seen that through the combined action of magnetic field and heating, the present invention reduces the number of pores and cracks in the LPBF-formed Ti-43Al-9V-0.5Y alloy. On the one hand, the preheating effect of the heating device on the second substrate 2 and the powder reduces the thermal stress and temperature gradient during the forming process. On the other hand, an additional steady magnetic field is introduced during the LPBF forming process. The magnetic field acts on the endogenous thermal current at the solid-liquid interface to generate a thermoelectromagnetic force (thermoelectromagnetic effect), regulates the flow of the molten pool melt, accelerates the escape of gas, and thus reduces the number of pores. In addition, while the second substrate 2 is preheated, magnetic perturbation is supplemented to regulate the solidification crystallization process and the solid-state phase transformation process, promote grain refinement and reduce the content of the brittle B2 phase, improve the tissue toughness while reducing the ductile-brittle transition temperature, and thus can solve the cracking problem faced by the LPBF-formed Ti-43Al-9V-0.5Y alloy at a lower preheating temperature (200 °C).

[0045] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A substrate assembly for laser additive manufacturing, characterized in that, It includes a first substrate, a second substrate, an electromagnet, a first lifting assembly, and a second lifting assembly, where: A placement groove is provided on the top surface of the first substrate, and a receiving cavity for accommodating the first lifting assembly and the second lifting assembly is provided inside the first substrate, and the receiving cavity is located below the placement groove; The second substrate is placed in the placement groove, and the top surface of the second substrate is flush with the top surface of the first substrate; There are two electromagnets, and the two electromagnets are placed in the placement groove and located on both sides of the second substrate; The first lifting assembly includes a first driving unit and a heating lifting rod. The first driving unit is installed at the bottom of the receiving cavity and is connected to the heating lifting rod for driving the heating lifting rod to move in a direction perpendicular to the second substrate; the heating lifting rod is connected to the bottom surface of the second substrate; The second lifting assembly is installed in the receiving cavity and is connected to the electromagnet for driving the electromagnet to move in a direction perpendicular to the second substrate.

2. The substrate assembly for laser additive manufacturing according to claim 1, wherein The first driving unit includes a bottom support frame, a mounting frame, a first driving member, a first transmission mechanism, a support rod, a screw rod, and a connecting rod. The bottom support frame is installed at the bottom of the receiving cavity, the mounting frame is fixed to the side wall of the support rod, the first driving member is installed on the mounting frame, the first transmission mechanism is connected to the first driving member, the support rod is installed on the bottom support frame, one end of the screw rod is threadedly connected to the first transmission mechanism, the other end of the screw rod is connected to the middle of the connecting rod, and both ends of the connecting rod are respectively connected to the two heating lifting rods.

3. The substrate assembly for laser additive manufacturing according to claim 2, wherein The first transmission mechanism includes a transmission shaft, two bearings, two driving bevel gears, and two driven bevel gears; there are four heating lifting rods, and the four heating lifting rods are respectively arranged at the four corners of the second substrate and symmetrically installed; the two bearings are installed on the mounting frame; the transmission shaft is installed in the two bearings, and the first driving member is drivingly connected to the transmission shaft; the two driving bevel gears are installed on the transmission shaft; the two driven bevel gears are respectively rotatably installed on the two support rods and are axially limited to each other, and the driven bevel gear is threadedly connected to the screw rod and meshes with the driving bevel gear.

4. The substrate assembly for laser additive manufacturing according to claim 1, wherein The second lifting assembly includes a bottom support rod, a support frame, a second driving member, and a second transmission mechanism; the bottom support rod includes a fixed section and a movable section, the fixed section is installed on the bottom support frame, the movable section is connected to the second substrate and is slidably installed in the fixed section; the support frame is sleeved on the bottom support rod, and fixing parts for fixing the electromagnet are provided at both ends of the support frame; the second driving member is installed on the support frame and is connected to the second transmission mechanism; the second transmission mechanism is connected to the fixed section for driving the support frame to slide along the bottom support rod.

5. The substrate assembly for laser additive manufacturing according to claim 4, characterized in that, The second transmission mechanism includes a driving gear and a rack, the driving gear is connected to the second driving member, the rack is installed on the fixed section and its length direction is parallel to the height direction of the support rod, and the rack meshes with the driving gear.

6. The substrate assembly for laser additive manufacturing according to claim 5, characterized in that, A driving frame and a clamping plate are provided on the support frame, and the driving frame includes a horizontal plate and a vertical plate connected to each other. The second driving member is installed on the horizontal plate, and the vertical plate is arranged parallel to the height direction of the bottom support rod; the clamping plate is arranged parallel to the vertical plate and a gap is provided between the two, and the rack is located in the gap.

7. An additive manufacturing process method, which uses the substrate assembly for laser additive manufacturing as described in any one of claims 1-6, characterized in that, include: The heating lifting rod is driven to move in a direction perpendicular to the second substrate by a first driving unit, and the electromagnet is driven to move in a direction perpendicular to the second substrate by a second lifting assembly, so that the upper surfaces of the second substrate, the electromagnet and the first substrate are in the same horizontal plane; Setting the laser power, scanning rate and scanning spacing of the laser beam and the layer thickness of the metal powder layer according to the size of the formed part and the material used; Laying a metal powder layer on the surface of the second substrate according to the layer thickness; Starting a heating device for heating the support rod to heat the second substrate and the metal powder layer; After the temperature of the second substrate and the metal powder layer is stabilized at 200-500 °C, the laser beam selectively melts the metal powder to form a molten pool according to the set process parameters such as laser power, scanning rate, and scanning spacing. After the molten pool solidifies, a molten channel is formed, and the channels overlap to form a layer. After the current layer is scanned, the first substrate is lowered by one layer thickness; Repeat the above process until the formed part is completed.

8. The additive manufacturing process method according to claim 7, wherein The laser power, scanning rate and scanning spacing of the laser beam and the layer thickness of the metal powder layer are set according to the size of the formed part and the material used, specifically including: setting the laser power to 100-600 W, the scanning speed to 100-1000 mm / s, the scanning spacing to 40-100 μm, and the layer thickness to 20-70 μm.

9. The additive manufacturing process method according to claim 7, characterized in that, After the layer-by-layer deposition is completed until the formed part is manufactured, the process further includes: removing the second substrate, separating the part from the surface of the second substrate, and milling the surface of the second substrate. When it is used again, the second substrate is installed, and the first driving unit is started to drive the heating lifting rod in a direction perpendicular to the second substrate so that the upper surface of the second substrate rises to be flush with the upper surface of the first substrate.

10. The additive manufacturing process method according to claim 7, characterized in that, After the temperature of the second substrate and the metal powder layer is stabilized at 200-500° C. and before the laser beam selectively melts the metal powder to form a molten pool, the method further includes: a second lifting component raising the electromagnet to a height of a layer thickness.

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