A laser additive manufacturing device with internal coaxially-fed wire

Abstract

A laser additive manufacturing device with in-light coaxial wire feeding: It mainly consists of a cylinder body, a holographic optical element I, a holographic optical element II with a central through-hole, a wire feeding tube, a cooling system, a positioning and supporting element installed above the cylinder body, and a coaxial laser head part. It is characterized in that: the incident laser beam forms two beams separated from each other in space after being diffracted by the holographic optical element I and is diffracted onto the surface of the holographic optical element II. After being diffracted by the holographic optical element II again, a conical beam with a hollow lightless area is formed. The wire feeding tube is inserted into this lightless area from the through-hole of the holographic optical element II, so as to achieve the complete coaxiality of the beam, the wire material and the shielding gas and perpendicularity to the additive manufacturing surface. The present invention utilizes the diffraction effect of two holographic optical elements on the laser beam, realizes in-light coaxial wire feeding, improves the forming quality and efficiency, reduces the structural complexity, ensures the isotropy of laser wire feeding forming, and the overall system is easy to control, thus improving the energy utilization rate.

Description

Technical Field:

[0001] The present invention belongs to the field of laser processing, and particularly relates to a laser additive manufacturing technology and a laser additive manufacturing device with internal coaxially-fed wire. Background Art:

[0002] In the process of laser additive forming of metal materials, the laser and the molten material are synchronously transmitted to the forming surface, and the metal material is continuously, accurately and uniformly put into the focused light spot that moves along a predetermined trajectory on the processing surface, so as to realize the synchronous action of light and material. The material undergoes the conversion of light and heat in the light beam, forms a molten pool, and completes the rapid melting and solidification metallurgical process. The main feeding methods in the laser additive process of metal materials can be divided into external powder feeding, internal powder feeding, external wire feeding, and internal wire feeding.

[0003] The external powder feeding method is as Figure 1 shown, and its disadvantages are as follows:

[0004] 1. The powder is ejected from the inclined powder feeding nozzle 13. The movement direction of the powder particles after leaving the nozzle is affected by their own inertia, air-borne pressure, gravity, etc., and will be affected by the protective gas and light pressure during the movement. Therefore, the powder particles fall in a parabolic shape, resulting in inconsistent air trajectories and landing points of the powder particles, and further increasing the powder falling area.

[0005] 2. Most of the powder 10 ejected from multiple powder tubes is shot into the light beam in a parabolic shape from outside the light beam, and then falls into the light spot to form a molten pool. Since the powder enters the light beam from outside the light beam, the powder interferes with the light beam before falling into the light spot, resulting in a decrease in the light intensity of the light spot, causing energy loss, poor boundary fusion, and an increase in internal defects.

[0006] The current internal powder feeding method mainly obtains a hollow focused light beam through optical path transformation, places the powder feeding tube in the hollow part of the focused light beam and coaxial with the light beam. During processing, the powder beam and the focused light beam are coaxially fed into the center of the light spot, and the powder is uniformly and symmetrically surrounded by the annular light beam all the time. For example, Chinese invention patent ZL200610116413.1 discloses a domestic powder feeding process and its nozzle for laser processing and forming. The specific structure is shown in the appendix Figure 2 . Through optical path transformation, the circular cross-section light beam is transformed into a circular annular cross-section light beam, and then the annular light beam is expanded and focused to form a conical focused light beam, forming a circular annular focused light spot on the forming surface. A conical lightless area is generated in the conical focused light beam, and then the powder feeding tube extends into this lightless area outside the light beam to be coaxial with the focused light beam, and then the powder is sprayed to the light spot for processing.

[0007] Although this solution realizes the coaxial action of the powder and the light beam, there are still the following deficiencies:

[0008] 1. The powder feeding tube extends from outside the light beam into the inside of the focused light beam. Although its surface is coated with light-absorbing material, it still passes through the light beam, causing energy loss.

[0009] 2. The powder feeding tube has a corner bend near the nozzle. Since the energy is relatively high near the nozzle, it is easy to cause powder blockage, which is not conducive to processing.

[0010] The external light wire feeding structure is as Figure 3 shown. It uses single-sided wire feeding. The laser beam 11 emitted by the laser is focused by the focusing mirror 110 into a conical light beam 12. However, since the wire feeding tube and the wire nozzle 13 can only be installed at an angle relative to the conical light beam 12, the wire 14 sent out by the wire nozzle can only be obliquely fed into the laser beam. Therefore, generally, it is necessary to adjust the wire before processing so that it intersects with the light beam at the spot position. The main disadvantage brought by external light wire feeding is that the wire enters the molten pool obliquely, and the thermal effects of the light beam irradiation, molten pool heat conduction and radiation are asymmetric and uneven. Especially during the additive manufacturing process, there will inevitably be directional changes. That is, when the laser beam makes scanning movements in different directions relative to the processing surface during processing, the relative movement directions of the light beam and the wire will have different orientations and postures, and the melting and molten pool action processes of the wire will change, resulting in large changes in the size, morphology, surface roughness, etc. of the solidified weld bead, and even causing intermittent melting processes.

[0011] Internal light wire feeding mainly obtains a hollow annular focused light beam through optical path transformation, so that the wire feeding tube is placed in the hollow part of the focused light beam and is coaxial with the light beam. During processing, the wire is coaxial with the focused light beam and is evenly and symmetrically surrounded by the annular light beam. For example, Chinese Patent Application for Invention ZL200710046020.2 discloses a laser internal light wire feeding device. The laser beam emitted by the laser enters the cylinder from the light inlet and is incident on the mirror surface of the central conical mirror in the cylinder. The conical mirror surface cuts and reflects the light beam, transforming it into an annular light beam. Then, the incident annular light beam is reflected and focused again by the annular reflection focusing mirror, forming an annular conical light beam. A conical hollow lightless area is formed in the middle of this annular conical light beam. A single wire feeding tube can enter this lightless area from the upper part or the side of the middle part of the cylinder, realizing wire feeding from inside the laser beam, that is, the so-called "internal light wire feeding". The specific structure is as attached Figure 4As shown, the light beam 2 enters from the light input port 27 and is incident on the mirror surface of the central conical mirror 46. It is cut and reflected into an annular light beam 39 by the central conical mirror 46. The annular light beam is incident on the annular reflective focusing mirror 47 and is reflected and focused again to form a conical light beam 40. A hollow lightless area 41 is formed in the middle of this conical light beam 40. A single wire feeding tube 42 is inserted from outside the cylinder, passes through the gap between the conical mirror 46 and the annular reflective focusing mirror 47, and turns to be coaxial with the conical light beam 40 after reaching the back of the conical mirror 46, so that the nozzle 43 at the end of the wire feeding tube 42 is placed inside the conical hollow lightless area 41 of the conical light beam 40 and is coaxial with the conical light beam 40. The outlet position of the nozzle 43 is close to the focus 44 of the conical light beam 40. The wire material 5 is fed into the wire feeding tube 42 and is output through the nozzle 43 at the lower end of the wire feeding tube 42. It is surrounded and irradiated by the lower part of the conical light beam 40 near the focus 44, and then is heated and continuously melted under the combined action of heat conduction, heat radiation, etc. of the light irradiation and the molten pool on the surface of the base material 45, and vertically enters the molten pool. The surface of the base material to be clad is adjusted to near the focus 44, and the wire material melted into the molten pool and the surface material of the partially melted base material jointly form a molten pool. The melt in the molten pool continuously solidifies to form a weld bead as the light beam and the base material move relatively.

[0012] The above technical solution has the following deficiencies:

[0013] 1. Using a conical light beam to achieve in-light wire feeding, the conical light beam will cross the support frame during the process of projecting onto the workpiece surface, resulting in relatively large laser energy loss and affecting the effective output power of the laser.

[0014] 2. True in-light coaxial wire feeding has not been achieved, and the interference between the wire feeding tube and the light beam has not been completely avoided. The wire feeding tube still passes through the focused light beam from one side. Although it is coated with light-absorbing material, energy loss will still occur.

[0015] Since the existing in-light powder feeding and in-light wire feeding schemes still have deficiencies, it is of great significance to further research and develop an in-light coaxial wire feeding additive manufacturing device. Therefore, the present invention introduces a holographic optical element to improve the in-light coaxial wire feeding additive manufacturing device.

[0016] Holography records an image by recording the intensity and phase of the light reflected from the irradiated object, and is used to create a diffraction pattern and form a 3D image of the irradiated object. Due to its characteristics such as three-dimensionality, divisibility, and strong information storage ability, holography has been gradually applied to fields such as imaging, microscopy, interferometry, and information storage. A holographic diffracted light beam is a light beam that records the intensity and phase of the light reflected from the irradiation point through a holographic optical element and forms a light beam with an arbitrarily specified energy density distribution that cannot be obtained by traditional lenses and mirrors, as Figure 5 shown. The present invention utilizes the diffraction characteristics of the holographic optical element to achieve in-light coaxial wire feeding laser additive manufacturing. Summary of the Invention:

[0017] The object of the present invention is to provide an in-light coaxial wire feeding device for laser additive manufacturing, which can reduce energy loss, simplify the device structure, ensure the isotropy of laser wire feeding forming, and improve the forming quality and efficiency.

[0018] To achieve the above object, the present invention provides the following technical solution: An in-light coaxial wire feeding laser additive manufacturing device, which receives an incident laser beam and diffracts the incident laser beam into two spatially separated beams through a holographic optical element I, and transmits the two beams to the surface of a holographic optical element II for re-diffraction to form a hollow annular conical beam, and finally forms a focus on the forming surface. The laser additive manufacturing device includes a cylinder, a holographic optical element I, a holographic optical element II with a central through hole, a wire feeding tube, a cooling system, a positioning and supporting element installed above the cylinder, and a coaxial laser head part. The holographic optical element I can diffract the incident laser beam into two spatially separated beams, and transmit the two beams to the surface of the holographic optical element II for re-diffraction to form an annular conical beam with a hollow lightless area, and the wire feeding tube extends into this lightless area through the through hole of the holographic optical element II.

[0019] Furthermore: The optical path conversion device includes a holographic optical element I and a holographic optical element II, and the holographic optical element II is located in the diffraction light direction of the holographic optical element I.

[0020] Furthermore: Cooling cavities are provided in both the holographic optical element I and the holographic optical element II.

[0021] Furthermore: A wire feeding tube is installed in the through hole of the holographic optical element II, and the wire feeding tube passes through the annular conical lightless area through the through hole.

[0022] Furthermore: A positioning and supporting element for ensuring the perpendicularity of the wire feeding tube and playing a fixing and supporting role is provided in a small hole on the cylinder, and the outer diameter of the wire feeding tube matches the inner diameter of the positioning and supporting element.

[0023] Furthermore: A semi-annular cooling system is installed inside the wire feeding tube.

[0024] The present invention has the following advantages: By diffracting the solid laser beam through the holographic optical element I into two spatially separated beams, and then diffracting through the holographic optical element II to form an annular conical beam with a hollow lightless area, the wire feeding tube and the nozzle are placed in the hollow part of the annular conical beam and are coaxial with the laser beam. During the processing, the wire material and the shielding gas are ejected parallel and coaxially from the lower end of the nozzle and sent to the center of the light spot, realizing complete in-light coaxial wire feeding, reducing energy loss, improving the forming quality and efficiency, simplifying the device structure, and ensuring the isotropy of laser wire feeding forming. Description of the drawings:

[0025] Figure 1Schematic diagram of the optical powder feeding method of the existing laser additive manufacturing technology;

[0026] Figure 2 Schematic diagram of the optical powder feeding method of the existing laser additive manufacturing technology;

[0027] Figure 3 Schematic diagram of the optical wire feeding method of the existing laser additive manufacturing technology;

[0028] Figure 4 Schematic diagram of the optical wire feeding method of the existing laser additive manufacturing technology;

[0029] Figure 5 Schematic diagram of the profiles of Gaussian beam and two holographic diffraction beams;

[0030] Figure 6 Schematic diagram of the internal structure of the coaxial wire feeding laser additive manufacturing equipment of the present invention;

[0031] Figure 7 Schematic diagram of the optical path direction and its cross-section in the present invention;

[0032] In the figure: 19, cooling cavity of holographic optical element II; 20, positioning and supporting element; 21, cylinder; 22, light inlet; 23, cooling cavity of holographic optical element I; 24, holographic optical element I; 25, light outlet; 26, focus; 27, wire; 28, air inlet of coaxial laser head; 29, hollow lightless area; 30, part of coaxial laser head; 31, holographic optical element II; 32, wire feeding tube. Specific embodiments:

[0033] Refer to Figure 6 、 Figure 7 , the holographic optical element I 24, the holographic optical element II 31, and the wire feeding tube 32 are sequentially installed inside the cylinder 21, and the laser beam is from Figure 7The light inlet 22 is incident on the holographic optical element I 24, and is diffracted by the holographic optical element I 24 to form two light beams separated in space to the surface of the holographic optical element II 31. The light beam is diffracted again by the holographic optical element II 31 to form a hollow annular cone-shaped light beam. The annular cone-shaped light beam is focused below the light outlet 25 to form a focus 26 on the forming surface. A through hole is opened in the center of the holographic optical element II 31 along the direction of its focus 26. A positioning support element 20 is installed in the through hole to support the wire feeding tube 32 and ensure its verticality. The upper part of the wire feeding tube 32 is aligned with the upper part of the tube. The wire feeder is connected to the top of the body 21, inserted into the cylinder 21 through the positioning support element 20, and extends from the through hole of the holographic optical element II 31 toward the lower part of the cylinder 21 into the hollow lightless area 29. The metal wire 27 in the wire feeding tube 32 and the protective gas in the cone sleeve of the coaxial laser head 28 are ejected together at the lower end, surrounded and irradiated by the lower part of the annular cone-shaped light beam near the focus 26, continuously melted and vertically entered into the molten pool. At the same time, the coolant circulates in the cooling cavity of the holographic optical element I 24, the cooling cavity of the holographic optical element II 31, and the cooling tube of the wire feeding tube 32 respectively.

[0034] Therefore, in this example, by setting holographic optical element I and holographic optical element II, the laser beam is changed from a solid to a hollow, lightless annular conical beam, and the wire feeding tube and the beam are completely staggered, thereby realizing true intra-optical coaxial wire feeding laser additive forming, avoiding beam interference, reducing energy loss, improving forming quality and efficiency, reducing the complexity of the device structure, and ensuring the isotropy of laser wire feeding forming.

Claims

1. A laser additive device with coaxial wire feeding in the optical system: mainly composed of a cylinder, a holographic optical element I, a holographic optical element II with a central through hole, a wire feeding tube, a cooling system, a positioning support element installed above the cylinder, and a coaxial laser head, characterized by: The holographic optical element I is inside the cylinder, and the holographic optical element II is installed along the diffracted light direction of the holographic optical element I. A through hole is opened on the mirror body of the holographic optical element II along the axis direction of the diffraction ring cone light beam, and a small hole coaxial with the through hole is opened on the wall of the cylinder. The wire feeding tube is a straight tube structure, inserted into the cylinder through the small hole, and extends toward the lower part of the cylinder through the through hole in the center of the holographic optical element II. The wire feeding tube is parallel to the direction of the incident light beam and perpendicular to the forming surface. The holographic optical element I can receive the incident laser beam and diffract it into two spatially separated beams to avoid interference with the wire feeding tube; A cooling cavity is provided in the holographic optical element I; The holographic optical element II can receive two separated light beams and diffract them into an annular cone-shaped light beam with a hollow lightless area. A cooling cavity is provided in the holographic optical element II.

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