Variable powder spot coaxial powder feeding structure and laser additive powder feeding method

Abstract

The application relates to the technical field of laser additive manufacturing, in particular to a coaxial powder feeding structure with variable powder spots and a laser additive powder feeding method, which comprises a first nozzle, the inner side of the first nozzle is provided with a first cavity, and the inside of the first nozzle is provided with a first powder feeding channel; a second nozzle is connected in the first cavity, the inner side of the second nozzle is provided with a second cavity; and a third nozzle is connected in the second cavity. The three nozzles are assembled in a nested mode to form a nozzle and form two independent powder feeding channels, the powder feeding pipe and the gas feeding pipe in the powder feeding component are respectively connected to one of the two powder feeding channels, that is, one kind of powder feeding and one kind of gas feeding, the media fed by the two powder feeding channels can be switched by changing the position of the powder feeding component, the switching of large powder spots and small powder spots is realized, the powder feeding pipe and the nozzle do not need to be disassembled, and the continuity of processing can be ensured.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology, and more specifically to a coaxial powder feeding structure with variable powder spots and a powder feeding method for laser additive manufacturing. Background Technology

[0002] Laser additive manufacturing technology has wide applications in the industrial field. In the laser additive manufacturing process, larger laser spots are often used to improve production efficiency. However, in precision printing, smaller laser spots are required. As the laser spot size changes, the powder spot size also needs to be adjusted to ensure powder utilization, thus enabling precision processing through small laser and powder spots.

[0003] The current common practice is to replace the powder feeding nozzle under the cladding head. Since the powder feeding nozzle needs to be connected to the powder inlet pipe and the cooling water pipe, they need to be removed one by one during replacement. Then the nozzle needs to be removed from the cladding head, a new nozzle needs to be replaced, and the powder inlet pipe and the cooling water pipe need to be reconnected before the powder spot position is adjusted. The operation is extremely inconvenient, seriously affects production efficiency, and cannot meet actual needs. Summary of the Invention

[0004] To address the technical problems existing in the powder feeding structure of the prior art, the first aspect of the present invention proposes a coaxial powder feeding structure with variable powder spots, comprising:

[0005] A first nozzle, wherein a first cavity is provided on the inner side of the first nozzle, and a first powder feeding channel is provided inside the first nozzle;

[0006] The second nozzle is connected to the first cavity, and the second nozzle has a second cavity inside it;

[0007] The third nozzle is connected to the second cavity, and a second powder feeding channel is formed between the inner wall of the second nozzle and the outer wall of the third nozzle. The inner side of the third nozzle is provided with a channel for the laser to pass through.

[0008] The powder feeding component includes a powder feeding pipe and an air feeding pipe;

[0009] The first nozzle is further provided with a connecting channel, the first end of which is connected to the powder inlet pipe or the air inlet pipe, and the second end is connected to the powder inlet end of the second powder feeding channel.

[0010] The powder feeding component is configured to switch between a first position and a second position. When the powder feeding component switches between the first position and the second position, the positions of the powder inlet pipe and the air inlet pipe are interchanged, so that the connection state of the first powder feeding channel, the second powder feeding channel and the corresponding powder inlet pipe or air inlet pipe is switched.

[0011] The powder spot formed by the first powder feeding channel is larger than the powder spot formed by the second powder feeding channel.

[0012] Preferably, the first cavity is larger in size at the first end of the first nozzle than at the second end, the second nozzle is assembled into the first cavity from the first end of the first nozzle, the second cavity is larger in size at the first end of the second nozzle than at the second end, the third nozzle is assembled into the second cavity from the first end of the second nozzle and connected to the first nozzle, and the third nozzle has a portion that extends beyond the end face of the first end of the first nozzle.

[0013] Preferably, the powder feeding component is constructed in an annular shape and connected to the outer wall of the third nozzle, and can be driven relative to the third nozzle along its axis. When the powder feeding component is driven around the axis of the third nozzle by a predetermined angle, the first position and the second position can be switched.

[0014] Preferably, the outer wall of the third nozzle is provided with a threaded connection structure, and a pressure plate is provided on the threaded connection structure. When the pressure plate is tightened on the threaded connection structure, it can press the powder feeding component, so that the powder feeding component is kept in the first position or the second position.

[0015] Preferably, the first end of the connecting channel is connected to the upper end face of the first nozzle, the first end of the first powder feeding channel is connected to the upper end face of the first nozzle, a gasket is provided between the powder feeding component and the first nozzle, and the gasket is provided with a plurality of through holes, the through holes being distributed corresponding to the connecting channel and the first powder feeding channel, and the through holes corresponding to the connecting channel and the through holes corresponding to the first powder feeding channel being distributed at equal intervals.

[0016] Preferably, the plane where the lower end face of the first nozzle is located is defined as the powder outflow end face, the outlet of the first powder feeding channel is located at the powder outflow end face, and the outlet of the second powder feeding channel is located at the powder outflow end face.

[0017] Preferably, the first powder feeding channel extends from the first end face of the first nozzle to the second end face, and the first powder feeding channel is configured to include a plurality of independent tubular channels distributed in an axisymmetric manner.

[0018] Preferably, the tubular channel is provided with a powder feeding pipe, and the bottom of the tubular channel is provided with a stepped groove, the outer diameter of the stepped groove being equal to the outer diameter of the powder feeding pipe.

[0019] Preferably, the inner wall surface of the second nozzle includes a first conical surface with a gradually decreasing inner diameter, and the outer wall surface of the third nozzle includes a second conical surface with a gradually decreasing inner diameter. An annular channel with a diameter gradually decreasing from the first end to the second end is formed between the first conical surface and the second conical surface. An annular cavity is provided above the annular channel, and the annular cavity is in communication with the connecting channel.

[0020] Preferably, the second nozzle has a first step at its second end, the first step being connected to the inner wall of the first nozzle and restricting the second nozzle from continuously moving toward the second end of the first nozzle, the third nozzle has a second step, the second step abutting against the first end face of the second nozzle and restricting the second nozzle from moving toward the first end of the first nozzle, and the third nozzle and the first nozzle are connected by bolts.

[0021] Preferably, a water-cooling cavity is provided between the second nozzle and the first nozzle, and the outer wall of the first nozzle is provided with a water inlet and a water outlet, which are connected to the water-cooling cavity.

[0022] A second aspect of this invention provides a technical solution: a powder feeding method for laser additive manufacturing, using the aforementioned coaxial powder feeding structure with variable powder spots, comprising the following steps:

[0023] Step 1: Based on the dimensions of the part to be additively manufactured, select either the first or second laser spot for additive manufacturing;

[0024] Step 2: According to the selected light spot type, switch the size of the powder spot, with the first powder spot corresponding to the first light spot and the second powder spot corresponding to the second light spot;

[0025] The steps for switching the size of the powder spot include:

[0026] Step a: Pause powder delivery and air delivery;

[0027] Step b: Rotate the powder feeding component to switch between the first and second positions. After switching, turn on the powder feeding and air supply to change the powder feeding status of the first and second powder feeding channels.

[0028] Compared with the prior art, the advantages of the present invention are as follows:

[0029] This application uses three nested nozzles to form a nozzle, which has a compact structure and can be applied to smaller working holes. The nozzle forms two independent powder feeding channels. The powder feeding pipe and air feeding pipe in the powder feeding component are respectively connected to one of the two powder feeding channels, that is, one for powder feeding and one for air feeding. By changing the position of the powder feeding component, the medium conveyed by the two powder feeding channels can be switched between each other, realizing the switching between large powder spots and small powder spots. There is no need to disassemble the powder feeding pipe and nozzle, which can ensure the continuity of processing. Attached Figure Description

[0030] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0031] Figure 1 This is a schematic diagram of the coaxial powder feeding structure with variable powder spots as shown in this invention;

[0032] Figure 2 This is an exploded view of the coaxial powder feeding structure with variable powder spots as shown in this invention;

[0033] Figure 3 This is a schematic diagram showing the distribution of the powder inlet pipe and the air inlet pipe as illustrated in this invention;

[0034] Figure 4 This is a cross-sectional view of the plane in which the first powder feeding channel shown in this invention is located;

[0035] Figure 5 This is a cross-sectional view of the plane in which the connecting channel shown in this invention is located;

[0036] Figure 6 This is a schematic diagram of the air delivery and powder delivery paths shown in this invention. Detailed Implementation

[0037] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0038] In the printing process of large-size parts, large-size light spots and toner spots can improve production efficiency. However, large-size workpieces also have areas with fine structures, so small-size light spots must be used for processing, and corresponding small-size toner spots are also required to ensure powder utilization. Currently, the switching between large and small toner spots is generally achieved by disassembling the toner inlet pipe and the toner nozzle. When the precision parts and large-size parts of the printed structural parts are frequently switched during the printing process, the above-mentioned disassembly and replacement will seriously affect production efficiency and cannot meet actual production needs.

[0039] Therefore, the present invention aims to provide a powder feeding structure capable of switching the size of the powder spot, especially to achieve the switching between large and small powder spots without disassembling the powder feeding pipe and nozzle. This application sets the powder feeding head to include two powder feeding channels, one of which can form a large powder spot and the other can form a small powder spot. The two powder feeding channels are independent of each other, and the powder feeding pipe and the air supply pipe are respectively connected to the two powder feeding channels. The switching between large and small powder spots is achieved by changing the connection state of the powder feeding pipe and the air supply pipe with the two powder feeding channels. At the same time, the other powder feeding channel is used to deliver protective gas. While protecting the molten pool, it can prevent impurities such as splashes or smoke from entering the powder feeding channel that is not in the powder feeding channel.

[0040] [Coaxial powder delivery structure with variable powder spots]

[0041] Combination Figure 1-2 As shown, the first aspect of the present invention proposes a coaxial powder feeding structure with variable powder spots, including a first nozzle 1, a second nozzle 2, a third nozzle 3, and a powder feeding component 5. The three nozzles are nested together to form a powder feeding head, forming two independent powder feeding channels. The powder spots formed when powder is fed through the two independent channels are of different sizes. The powder feeding component 5 is connected to the two independent powder feeding channels, and the powder feeding component 5 can switch the connection state with the two powder feeding channels to determine whether to supply air or powder to one of the powder feeding channels.

[0042] Combination Figure 4 As shown, the first nozzle 1 has a first cavity inside and a first powder feeding channel 11 inside; the second nozzle 2 is connected to the first cavity and has a second cavity inside; the third nozzle 3 is connected to the second cavity and forms a second powder feeding channel between the inner wall of the second nozzle 2 and the outer wall of the third nozzle 3, and has a channel 301 for laser to pass through inside.

[0043] Understandably, both the first powder feeding channel 101 and the second powder feeding channel can transport powder or gas. In order to achieve the formation of powder spots of two different sizes, the flow rates of the first powder feeding channel 101 and the second powder feeding channel are set to be large and small, respectively. For example, if the flow rate of the first powder feeding channel 101 is large, the powder spot size formed after the powder is transported from the first powder feeding channel 101 will be large. Thus, when switching between the first powder feeding channel 101 and the second powder feeding channel to transport powder, large-sized powder spots or small-sized powder spots will be formed. Combined with the large-sized or small-sized laser spot output from the channel 301, small-sized fine processing or large-sized processing can be performed.

[0044] In the following embodiments, the powder spot formed by the first powder feeding channel 11 is defined to be larger than the powder spot formed by the second powder feeding channel.

[0045] Furthermore, in combination Figure 3and 5 As shown, the powder feeding component 5 includes a powder feeding pipe 51 and an air feeding pipe 52; wherein, the first nozzle 1 is also provided with a connecting channel 101, the first end of the connecting channel 101 is connected to the powder feeding pipe 51 or the air feeding pipe 52, and the second end is connected to the powder feeding end of the second powder feeding channel.

[0046] Thus, through the connecting function of the connecting channel 101, the powder inlet end of the second powder feeding channel and the powder inlet end of the first powder feeding channel are positioned in a way that allows the powder inlet pipe 51 and the air inlet pipe 52 of the powder feeding component 5 to switch between each other.

[0047] Furthermore, the powder feeding component 5 is configured to switch between a first position and a second position, and when the powder feeding component 5 switches between the first position and the second position, the positions of the powder inlet pipe 51 and the air inlet pipe 52 are interchanged, so that the connection state of the first powder feeding channel 11, the second powder feeding channel and the corresponding powder inlet pipe 51 or air inlet pipe 52 is switched.

[0048] In an optional embodiment, the first nozzle 1, the second nozzle 2, or the third nozzle 3 is provided with positioning holes, and the powder feeding component 5 is equipped with ball-head set screws, which can cooperate with the positioning holes to position the powder when switching powder feeding methods, so that the powder reaches a suitable angle position.

[0049] Thus, when large-size processing is required, the powder feeding component 5 is adjusted to the first position. At this time, the powder inlet pipe 51 is connected to the first powder feeding channel, and the air inlet pipe 52 is connected to the second powder feeding channel. After the first powder feeding channel feeds powder, it forms a large-size powder spot, which, together with the large-size light spot, forms a large-size processing. The second powder feeding channel is supplied with air by the air inlet pipe 52, forming a protective gas around the molten pool, while also preventing splashes and dust from entering and adhering to the inner wall of the second powder feeding channel.

[0050] It is understandable that if splashes and dust enter the inner wall of the powder feeding channel, it will change the powder feeding path and the powder convergence point, and may even cause changes in the powder feeding flow or blockage. Therefore, it is essential to supply protective gas to the powder feeding channel that is not in the powder feeding state in the first powder feeding channel 11 and the second powder feeding channel.

[0051] In an optional embodiment, combined with Figure 1-2 As shown, the size of the first cavity at the first end of the first nozzle 1 is larger than the size of the second end. The second nozzle 2 is assembled into the first cavity from the first end of the first nozzle 1. The size of the second cavity at the first end of the second nozzle 1 is larger than the size of the second end. The third nozzle 3 is assembled into the second cavity from the first end of the second nozzle 2 and connected to the first nozzle 1. The third nozzle 3 has a portion that protrudes above the end face of the first end of the first nozzle 1.

[0052] In this way, the main body of the powder feeding head can be assembled by sequentially nesting the three parts: the first nozzle 1, the second nozzle 2, and the third nozzle 3. The assembly is simple and reliable.

[0053] Optionally, the first nozzle 1, the second nozzle 2, and the third nozzle 3 may be made of copper or chromium zirconium copper.

[0054] Specifically, such as Figure 4 As shown, the first nozzle 1 is constructed with an upper cylindrical shape and a lower conical shape on its outer contour. The inner and outer contours are approximately contour-like structures. In particular, the bottom of the inner contour of the first nozzle 1 is provided with a stepped structure. The second nozzle 2 is constructed with a thin-walled structure, with an upper cylindrical shape and a lower conical shape. The bottom of the second nozzle 2 is provided with a first step 21. When the second nozzle 2 is assembled into the first cavity of the first nozzle 1 from top to bottom, the step structure can lock the first step 21, which can restrict the second nozzle 2 from moving continuously toward the second end of the first nozzle 1, thus axially limiting one end of the second nozzle 2.

[0055] Furthermore, the third nozzle 3 is provided with a second step 31, which abuts against the upper end face of the second nozzle 2, restricting the second nozzle from moving toward the first end of the first nozzle 1. In this way, a limit is formed on the other end of the second nozzle 2. The third nozzle 3 and the first nozzle 1 are connected by bolts. When the bolts are tightened, the first nozzle 1, the second nozzle 2 and the third nozzle 3 form an integral structure.

[0056] Furthermore, below the second step 13, the third nozzle 3 is configured to have a recess 33. Below the recess 33, the third nozzle 3 is configured to have a gradually narrowing conical shape. Above the second step 13, the third nozzle 3 is configured to be approximately cylindrical.

[0057] Preferably, sealing rings are added at the connection between the second nozzle 2 and the first nozzle 1 below and above the second nozzle and the first nozzle 1 above, forming a sealed water-cooling cavity 102 between the second nozzle 2 and the first nozzle 1. The outer wall of the first nozzle 1 is provided with a water inlet hole 12 and a water outlet hole, which are connected to the water-cooling cavity 102.

[0058] Thus, by connecting to the water circulation system through the inlet and outlet holes, the nozzle can be cooled.

[0059] In an optional embodiment, the first powder feeding channel 11 extends from the first end face of the first nozzle 1 to the second end face, and the first powder feeding channel 11 is configured to include a plurality of independent tubular channels distributed axially symmetrically. In this way, the powder fed from the powder feeding pipe 51 can directly enter the tubular channels and be transported downward along the axial direction of the tubular channels, and finally converge into powder spots.

[0060] Preferably, a powder feeding pipe is provided inside the tubular channel, and a stepped groove is provided at the bottom of the tubular channel, with the outer diameter of the stepped groove being equal to the outer diameter of the powder feeding pipe. In this way, the powder feeding pipe can be installed inside the tubular channel, and powder feeding pipes with different inner diameters can be replaced according to processing requirements to change the conveying capacity of the powder feeding pipe and thus change the size of the powder spot.

[0061] Furthermore, the inner wall surface of the second nozzle 2 includes a first conical surface with a gradually decreasing inner diameter, and the outer wall surface of the third nozzle 3 includes a second conical surface with a gradually decreasing inner diameter. That is, the outer wall surface of the third nozzle 3 with a conical shape formed below the recess 33 forms an annular channel 202 with a diameter that gradually decreases from the first end to the second end between the first conical surface and the second conical surface. An annular cavity 201 is provided above the annular channel 202, and the annular cavity 201 is connected to the connecting channel 101.

[0062] In this way, the powder can enter the annular cavity 201 from the connecting channel 101, and be conveyed downward from the annular channel 202, and converge into small powder spots along the extension direction of the annular channel.

[0063] The first and second powder feeding channels thus formed have good powder aggregation and water-cooling structure, which can ensure the stable use of the nozzle for a long time.

[0064] Combination Figure 2 As shown, the powder feeding component 5 is constructed in an annular shape and is connected to the outer wall of the third nozzle 3. It can be driven relative to the third nozzle 3 along its axis. When the powder feeding component 5 is driven around the axis of the third nozzle 3 by a predetermined angle, the first position and the second position can be switched.

[0065] Understandably, when the powder inlet end of the first powder feeding channel 11 and the powder feeding end of the connecting channel 101 are in a centrally symmetrically distributed position, the powder feeding component 5 only needs to drive a predetermined angle to switch the connection state of all powder feeding pipes 51, air inlet pipes 52, and the first powder feeding channel 11 and the second powder feeding channel.

[0066] Optionally, the first end of the connecting channel 101 is connected to the upper end face of the first nozzle 1, the first end of the first powder feeding channel 11 is connected to the upper end face of the first nozzle 1, a gasket 4 is provided between the powder feeding component 5 and the first nozzle 1, and a plurality of through holes are provided on the gasket 4. The through holes are distributed corresponding to the connecting channel 101 and the first powder feeding channel 11, and the through holes corresponding to the connecting channel 101 and the through holes corresponding to the first powder feeding channel 11 are distributed at equal intervals.

[0067] Optionally, the gasket 4 is made of polytetrafluoroethylene, and the gasket 4 is positioned with the first nozzle 1 by a locating pin.

[0068] In other embodiments, the first end of the connecting channel 101 and the first end of the first powder feeding channel 11 can also be connected to the side of the first nozzle 1, and the powder feeding pipe 51 and the air inlet pipe 52 of the powder feeding component 5 can be correspondingly arranged on the side of the first nozzle 1, and the powder feeding state can be switched after the powder feeding component 5 completes the relative angle rotation.

[0069] Specifically, eight holes are formed on the upper surface of the first nozzle 1, four of which are powder inlets of the first powder feeding channel 11 and the other four are powder inlets of the connecting channel 101. The eight holes are distributed at 45° intervals, and the powder inlets of the first powder feeding channel 11 and the powder inlets of the connecting channel 101 are distributed alternately. The powder feeding component 5 includes four powder feeding pipes 51 and four air inlet pipes 52, and the air inlet pipes 52 and the powder feeding pipes 51 are distributed alternately.

[0070] Thus, when the powder feeding component 5 rotates 45°, the powder feeding pipe 51 originally connected to the first powder feeding channel 11 becomes the powder feeding port connected to the connecting channel 101, and the air inlet pipe 52 originally connected to the powder feeding port of the connecting channel 101 becomes the powder feeding port connected to the first powder feeding channel 11, thereby realizing the switching of powder / air feeding between the first powder feeding channel 11 and the second powder feeding channel.

[0071] The transmission state of the powder feeding component 5, which controls the switching between the first and second positions, can be adjusted manually or by using other automated equipment.

[0072] Furthermore, such as Figure 4-5 As shown, the outer wall of the third nozzle 3 is provided with a threaded connection structure 32, and a pressure plate 6 is provided on the threaded connection structure 32. When the pressure plate 6 is tightened on the threaded connection structure 32, it can press the powder feeding component 5, so that the powder feeding component 5 is kept in the first position or the second position.

[0073] Thus, when it is necessary to switch the toner spot size, the laser, air supply, and toner supply will be paused. After loosening the pressure plate 6, the toner feeding component 5 will be rotated 45 degrees, and then the pressure plate 6 will be tightened again to achieve the switching of toner / air supply between the first toner supply channel 11 and the second toner supply channel. The paused laser, air supply, and toner supply will be turned on and switched to the light spot of the predetermined size, so that the switching between large-size printing and fine printing can be achieved.

[0074] The loosening of the pressure plate 6 and the transmission powder feeding component 5 can be adjusted manually or by using other automated equipment.

[0075] In the above embodiment, the plane where the lower end face of the first nozzle 1 is located is defined as the powder outlet end face. The outlet of the first powder feeding channel 11 is located on the powder outlet end face, and the outlet of the second powder feeding channel is also located on the powder outlet end face. In this way, the powder can converge downward from the plane where the lower end face of the first nozzle 1 is located at a predetermined angle into a powder spot of predetermined size and shape, and the outlets of the two channels are on the same plane, avoiding axial displacement difference between the outlets of the two powder feeding channels, and especially avoiding excessive difference in powder convergence points or the adhesion of particles due to one of the outlets being too close to the molten pool.

[0076] Powder feeding methods for laser additive manufacturing

[0077] A second aspect of this invention provides a technical solution: a powder feeding method for laser additive manufacturing, using the aforementioned coaxial powder feeding structure with variable powder spots, comprising the following steps:

[0078] Step 1: Based on the dimensions of the part to be additively manufactured, select either the first or second laser spot for additive manufacturing;

[0079] Step 2: According to the selected light spot type, switch the size of the powder spot, with the first powder spot corresponding to the first light spot and the second powder spot corresponding to the second light spot;

[0080] The steps for switching the size of the powder spot include:

[0081] Step a: Pause powder delivery and air delivery;

[0082] Step b: Rotate the powder feeding component 5 to switch between the first position and the second position. After switching, turn on the powder feeding and air supply to change the powder feeding status of the first powder feeding channel 11 and the second powder feeding channel.

[0083] like Figure 6 As shown, at this time, the path indicated by the solid arrow in part A is the air delivery path along the second powder delivery channel, and the path indicated by the hollow arrow in part B is the powder delivery path along the first powder delivery channel. It can be seen that while the first powder delivery channel is delivering powder, the second powder delivery channel is delivering air. When the powder delivery component 5 switches positions, the powder delivery and air delivery states of the first and second powder delivery channels change. That is, the path indicated by the solid arrow in part A is the powder delivery path along the second powder delivery channel, and the path indicated by the hollow arrow in part B is the air delivery path along the first powder delivery channel.

[0084] In conjunction with the above embodiments, this application assembles a nozzle by nesting three nozzles together, resulting in a compact structure that can be applied to smaller working holes. The nozzle forms two independent powder feeding channels, with the powder feeding pipe and air feeding pipe in the powder feeding component connected to one of the two powder feeding channels respectively, i.e., one for powder feeding and one for air feeding. By changing the position of the powder feeding component, the medium conveyed by the two powder feeding channels can be switched between each other, realizing the switching between large and small powder spots. There is no need to disassemble the powder feeding pipe and nozzle, ensuring the continuity of processing.

[0085] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A coaxial powder feeding structure with variable powder spots, characterized in that, include: The first nozzle (1) has a first cavity on its inner side and a first powder feeding channel (11) inside its interior. The second nozzle (2) is connected to the first cavity, and the second nozzle (2) has a second cavity on its inner side; The third nozzle (3) is connected to the second cavity and forms a second powder feeding channel between the inner wall of the second nozzle (2) and the outer wall of the third nozzle (3). The inner side of the third nozzle (3) is provided with a channel (301) for the laser to pass through. The powder feeding component (5) includes a powder feeding pipe (51) and an air feeding pipe (52); The first nozzle (1) is also provided with a connecting channel (101), the first end of the connecting channel (101) is connected to the powder inlet pipe (51) or the air inlet pipe (52), and the second end is connected to the powder inlet end of the second powder feeding channel; The powder feeding component (5) is configured to switch between a first position and a second position. When the powder feeding component (5) switches between the first position and the second position, the positions of the powder feeding pipe (51) and the air inlet pipe (52) are interchanged, so that the connection state of the first powder feeding channel (11), the second powder feeding channel and the corresponding powder feeding pipe (51) or air inlet pipe (52) is switched. The powder spot formed by the first powder feeding channel (11) is larger than the powder spot formed by the second powder feeding channel; The powder feeding component (5) is constructed in an annular shape and connected to the outer wall of the third nozzle (3), and can be driven relative to the third nozzle (3) along its axis. When the powder feeding component (5) is driven around the axis of the third nozzle (3) by a predetermined angle, the first position and the second position can be switched. The outer wall of the third nozzle (3) is provided with a threaded connection structure (32), and a pressure plate (6) is provided on the threaded connection structure (32). When the pressure plate (6) is tightened on the threaded connection structure (32), it can press the powder feeding component (5) so that the powder feeding component (5) is kept in the first position or the second position. The first end of the connecting channel (101) is connected to the upper end face of the first nozzle (1), and the first end of the first powder feeding channel (11) is connected to the upper end face of the first nozzle (1). A gasket (4) is provided between the powder feeding component (5) and the first nozzle (1). The gasket (4) is provided with a plurality of through holes, which are distributed corresponding to the connecting channel (101) and the first powder feeding channel (11). The through holes corresponding to the connecting channel (101) and the through holes corresponding to the first powder feeding channel (11) are distributed at equal intervals. The inner wall surface of the second nozzle (2) includes a first conical surface with a gradually decreasing inner diameter, and the outer wall surface of the third nozzle (3) includes a second conical surface with a gradually decreasing inner diameter. An annular channel (202) with a diameter gradually decreasing from the first end to the second end is formed between the first conical surface and the second conical surface. An annular cavity (201) is provided above the annular channel (202), and the annular cavity (201) is connected to the connecting channel (101).

2. The coaxial powder feeding structure with variable powder spots according to claim 1, characterized in that, The first cavity is larger at the first end of the first nozzle (1) than at the second end. The second nozzle (2) is assembled into the first cavity from the first end of the first nozzle (1). The second cavity is larger at the first end of the second nozzle than at the second end. The third nozzle (3) is assembled into the second cavity from the first end of the second nozzle (2) and connected to the first nozzle (1). The third nozzle (3) has a portion that protrudes above the end face of the first nozzle (1).

3. The coaxial powder feeding structure with variable powder spots according to claim 1, characterized in that, The plane where the lower end face of the first nozzle (1) is located is defined as the powder outflow end face. The outlet of the first powder feeding channel (11) is located on the powder outflow end face, and the outlet of the second powder feeding channel is located on the powder outflow end face.

4. The coaxial powder feeding structure with variable powder spots according to claim 1, characterized in that, The first powder feeding channel (11) extends from the first end face of the first nozzle (1) to the second end face. The first powder feeding channel (11) is configured to include a plurality of independent tubular channels that are symmetrically distributed.

5. The coaxial powder feeding structure with variable powder spots according to claim 4, characterized in that, The tubular channel is equipped with a powder feeding pipe, and the bottom of the tubular channel is equipped with a stepped groove, the outer diameter of which is equal to the outer diameter of the powder feeding pipe.

6. The coaxial powder feeding structure with variable powder spots according to claim 2, characterized in that, The second nozzle (2) has a first step (21) at its second end. The first step (21) is connected to the inner wall of the first nozzle (1) and restricts the second nozzle (2) from moving continuously toward the second end of the first nozzle (1). The third nozzle (3) has a second step (31) at its second end. The second step abuts against the first end face of the second nozzle (2) and restricts the second nozzle from moving toward the first end of the first nozzle (1). The third nozzle (3) and the first nozzle (1) are connected by bolts.

7. The coaxial powder feeding structure with variable powder spots according to claim 2, characterized in that, A water-cooling chamber (102) is provided between the second nozzle (2) and the first nozzle (1). The outer wall of the first nozzle (1) is provided with a water inlet and a water outlet, which are connected to the water-cooling chamber (102).

8. A method for feeding powder in laser additive manufacturing, characterized in that, Using the coaxial powder feeding structure with variable powder spots according to any one of claims 1-7 includes the following steps: Step 1: Based on the dimensions of the part to be additively manufactured, select either the first or second laser spot for additive manufacturing; Step 2: According to the selected light spot type, switch the size of the powder spot, with the first powder spot corresponding to the first light spot and the second powder spot corresponding to the second light spot; The steps for switching the size of the powder spot include: Step a: Pause powder delivery and air delivery; Step b: Rotate the powder feeding component (5) to switch between the first position and the second position. After switching, turn on the powder feeding and air supply to change the powder feeding status of the first powder feeding channel (11) and the second powder feeding channel.

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