Method for manufacturing titanium alloy through wire powder synergistic multi-mode laser coupling additive

Abstract

The invention belongs to the technical field of laser processing, and particularly relates to a method for manufacturing a titanium alloy through wire powder coordinated multi-mode laser coupling additive manufacturing, and the method comprises the steps of base material pretreatment, multi-mode coupling laser construction, additive manufacturing, surface strengthening and the like. According to the titanium alloy part manufacturing device and method, material conveying is conducted in the mode that wire feeding and powder feeding are combined, structures with large areas in parts are rapidly manufactured through wire feeding, fine structures are manufactured through powder, and the titanium alloy parts can be efficiently manufactured in a high-precision mode. In the additive manufacturing step, multi-mode coupling annular laser is adopted, annular flat-topped pulse laser can accelerate flowing of a liquid phase before solidification, so that dendritic crystal arms formed through solidification in advance are broken to form new crystal nucleuses, then an equiaxed crystal structure is formed, and the strength and plasticity of the titanium alloy are improved. The annular flat-topped pulse laser can accelerate stirring of the molten pool, the heat mass conveying rate in the molten pool is increased, the element segregation phenomenon is relieved, and finally a uniform and stable titanium alloy structure is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and in particular relates to a method for additive manufacturing titanium alloy using silk powder and multi-modal laser coupling. Background Art

[0002] With the development of my country in the field of aerospace, aerospace equipment needs to have the characteristics of high performance, long life, high reliability and low cost. Based on this development trend, metal components are required to have good mechanical properties and special functions such as heat protection, heat insulation, vibration reduction, and radiation resistance. Since the 1950s, titanium alloys have developed rapidly as an important structural metal. They are widely used in the field of aerospace because of their high strength, excellent corrosion resistance, strong heat resistance and other excellent properties. However, since the structure of titanium alloy components used in the aerospace field is often more complex, and titanium alloys themselves are difficult to process, it is difficult to use the traditional casting + machining method to efficiently and accurately prepare titanium alloy components that meet the design requirements.

[0003] Since its birth, additive manufacturing technology has attracted the attention of many scholars for its high efficiency and economic advantages. It is completely different from the traditional subtractive processing method of cutting and removing materials. The core concept of additive manufacturing is to gradually build the required three-dimensional parts by stacking or adding materials layer by layer. The core idea of ​​this process can be simplified as "addition rather than removal", which can be used to manufacture complex titanium alloy components. There are two commonly used feeding methods for additive manufacturing, namely wire feeding and powder feeding. The wire feeding method has a utilization rate of nearly 100% in the printing process, less material waste, and wire is usually more economical than powder; in addition, wire can be fed continuously and can achieve uninterrupted production. However, since the processing accuracy of wire is affected by the wire diameter, the extremely thin parts of some parts are difficult to process by wire feeding, while the processing accuracy of powder can be adjusted by the spot diameter of the laser. At the same time, metal powder has a high absorption rate of laser energy and good processing formability, so the additive manufacturing of extremely thin parts of parts can be achieved by powder feeding. In addition, the powder composition is highly flexible, which is convenient for adjusting the composition and content of the powder. The additive manufacturing equipment in the prior art can only adopt a single feeding method, which makes it difficult to efficiently and accurately process titanium alloy components with complex structures.

[0004] In addition to the material feeding method, there are different heating energy sources in additive manufacturing. Common energy sources are arc and laser. Compared with arc additive, laser additive has the advantages of small heat affected zone and high precision. Therefore, laser additive method has been widely studied and applied. Traditional laser additive manufacturing technology often uses single-mode Gaussian laser as the energy source. The molten pool formed after its interaction with the material also presents the morphological characteristics of "two sharp ends and drum in the middle", which will cause the previous solidified weld to be heated unevenly during the subsequent processing. Moreover, in the subsequent overlap process, this morphological feature will cause the weld to have an obvious arc overlap area. The microstructure morphology of the overlap area is different from that of the non-overlap area, which will lead to uneven performance of the final processed parts. In addition, due to the extremely fast solidification speed of the laser additive process, there is often a strong layer of residual tensile stress on the surface of the manufactured parts, which will cause the parts to crack, which is not conducive to improving the mechanical properties and fatigue resistance of the parts. Summary of the invention

[0005] In response to the technical problem that existing additive manufacturing technologies are difficult to efficiently and accurately process titanium alloy components with complex structures, the present invention proposes a method for additively manufacturing titanium alloys using silk powder and multimodal laser coupling, which can efficiently and accurately prepare titanium alloy components with complex structures that have uniform tissue and good performance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling, comprising the following steps:

[0008] (1) using a continuous laser generator to emit a single-mode continuous Gaussian laser, using a laser beam shaping system to shape the single-mode continuous Gaussian laser into a single-mode continuous flat-top laser, and then using an optical element to reconstruct the single-mode continuous flat-top laser into a single-mode continuous flat-top ring laser;

[0009] (2) using a pulse laser generator to emit a single-mode pulsed Gaussian laser, using a laser beam shaping system to shape the single-mode pulsed Gaussian laser into a single-mode pulsed flat-top laser, and then using an optical element to reconstruct the single-mode pulsed flat-top laser into a single-mode pulsed flat-top ring laser;

[0010] (3) allowing the single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser to enter the multi-mode coupled laser nozzle respectively, and the single-mode pulsed flat-top ring laser is located in the light ring of the single-mode continuous flat-top ring laser, so as to form a multi-mode coupled ring laser;

[0011] (4) A wire feeder and a powder feeder are provided at the same time, and the titanium alloy wire is conveyed to the multi-mode coupling laser nozzle through the wire feeder, and the titanium alloy powder is conveyed to the multi-mode coupling laser nozzle through the powder feeder;

[0012] (5) Structural division and path planning are performed according to the structural characteristics of the parts. The multi-mode coupled laser nozzle runs according to the predetermined trajectory. During the operation, the opening and closing of the conveying channels of the wire feeder and the powder feeder are switched by the controller. According to the different structural parts of the titanium alloy parts, the wire feeder or the powder feeder is selectively used for raw material delivery. When printing the larger area of ​​the parts, the wire feeder is used to transport the wire material to achieve efficient additive manufacturing. When printing the small and fine parts, the powder feeder is used to transport the powder material to achieve high-precision additive manufacturing. The additive manufacturing process of the titanium alloy parts is completed by continuous operation.

[0013] Preferably, the powder material and the wire material are both input from the hollow part of a single-mode pulse flat-top ring laser.

[0014] Preferably, in step (5), the power of the pulsed flat-top ring laser is 0.05-2 kW, and the power of the continuous flat-top ring laser is 2-10 kW.

[0015] Preferably, in step (5), a water cooling device is used to cool the multi-mode coupled laser nozzle, and a protective gas is introduced to prevent the flying powder from adhering to the laser nozzle and to prevent the molten pool from oxidizing.

[0016] Preferably, when conveying the powder in step (5), a powder conveying protective gas is introduced at the outlet of the powder feeder to ensure continuous and uniform conveying of the powder.

[0017] Preferably, the wire feeder comprises a collimator, through which the continuity and stability of wire feeding are ensured.

[0018] Preferably, the optical element comprises a toroidal mirror and a conical mirror.

[0019] Preferably, the method further includes a substrate pretreatment step, specifically, grinding the surface of the titanium alloy substrate to be flat and smooth, then performing shot peening to increase the roughness and thereby reduce the reflection loss of the laser, and finally using acetone cleaning to remove surface dirt.

[0020] Preferably, in step (5), the substrate is heated to 400° C. and kept at this temperature until the additive process is completed.

[0021] Preferably, step (5) includes a surface strengthening step, that is, when processing the final surface portion of the part, a powder feeder is used to deliver strengthening powder material, and the content of strengthening elements is added or increased in the strengthening powder material. Thereafter, the continuous flat-top ring laser is turned off, and the surface of the material is impact strengthened using a pulsed flat-top ring laser.

[0022] Compared with the prior art, the advantages and positive effects of the present invention are:

[0023] (1) The present invention adopts a combination of wire feeding and powder feeding to transport materials, which can combine the advantages of high efficiency and high utilization of wire feeding to quickly manufacture large-area structures in parts, and combine the advantages of high precision of powder feeding to perform high-precision manufacturing of relatively fine structures of parts.

[0024] (2) The annular flat-top pulse laser used in the present invention can accelerate the flow of the liquid phase at the solidification front when the titanium alloy solidifies, thereby breaking the dendrite arms formed by the previous solidification, thereby forming new crystal nuclei, which then grow into fine equiaxed crystal structures, ultimately improving the strength and plasticity of the titanium alloy.

[0025] (3) The annular flat-top pulse laser used in the present invention can accelerate the stirring of the molten pool, increase the rate of heat and mass transfer inside the molten pool, reduce the segregation of elements caused by rapid solidification, and ultimately obtain a uniform and stable titanium alloy structure.

[0026] (4) After the additive manufacturing process is completed, a circular flat-top pulse laser is used to impact strengthen the material surface, regulate the residual stress state of the material surface, and convert the residual tensile stress generated by rapid solidification into residual compressive stress to resist the formation of microcracks, thereby improving the material's fatigue resistance.

[0027] (5) The annular continuous laser and annular pulsed laser used in the present invention are both processed by a beam shaping process to form a flat-top laser light source. During the additive process, the molten pool is affected by the laser energy distribution and presents a rectangular morphology, avoiding the problem of uneven heating and uneven microstructure morphology caused by Gaussian morphology welds.

[0028] (6) The present invention can use additional strengthening elements added to the powder to achieve a gradient change in the composition of the component, and ultimately obtain a titanium alloy component that is "hard on the outside and tough on the inside". Since the concentration of the strengthening elements changes gradiently, there is no problem of a fragile interface due to a sudden change in performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The process flow chart of the method for laser-coupled additive manufacturing of titanium alloy of the present invention;

[0030] Figure 2 Schematic diagram of the structure of a titanium alloy impeller manufactured in an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of using a wire feeder to feed wire material to manufacture the main part of a titanium alloy impeller in an embodiment of the present invention;

[0032] Figure 4It is a schematic diagram of using a powder feeder to transport powder material to manufacture a titanium alloy impeller blade part in an embodiment of the present invention;

[0033] In the above figures: 1. impeller body; 2. impeller blades; 3. titanium alloy substrate; 4. continuous flat-top ring laser; 5. pulsed flat-top ring laser; 6. titanium alloy wire; 7. titanium alloy powder. DETAILED DESCRIPTION

[0034] In order to better understand the present invention, a detailed description is given below in conjunction with the accompanying drawings and embodiments.

[0035] Example: Figure 1 As shown, a method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling comprises the following steps:

[0036] 1. Program settings

[0037] According to Figure 2 The structural features of the titanium alloy impeller shown in the figure are used to divide the typical structure and plan the additive path, and the set program is input into the controller.

[0038] 2. Substrate pretreatment

[0039] The titanium alloy substrate used as the carrier of the additive titanium alloy impeller is subjected to surface treatment, specifically, the surface of the titanium alloy substrate 3 is polished to keep the surface of the titanium alloy substrate 3 flat and smooth, and then the surface of the titanium alloy substrate 3 is treated by shot peening to increase its surface roughness and maximize the absorption rate of the titanium alloy substrate 3 to the laser. After shot peening, the surface is cleaned with acetone to remove as much dirt as possible on the surface of the titanium alloy substrate 3. Then the titanium alloy substrate 3 is placed on a heating device and preheated to 400°C and kept warm until the whole process is completed.

[0040] 3. Constructing multi-mode coupled laser

[0041] The first laser generator is turned on to emit a single-mode continuous Gaussian laser. After beam shaping, the energy of the light source is reconstructed in the spatial scale to form a single-mode continuous flat-top laser. The single-mode continuous flat-top laser passes through the optical path system containing optical elements such as a ring mirror and a conical mirror to form a Figure 3 The continuous flat-top ring laser 4 is shown.

[0042] The second laser generator is turned on to emit a single-mode pulsed Gaussian laser. After beam shaping, the energy of the light source is reconstructed in the spatial scale to form a single-mode pulsed flat-top laser. The single-mode pulsed flat-top laser passes through the optical path system containing optical elements such as a ring mirror and a conical mirror to form a Figure 3 The pulsed flat-top ring laser 5 is shown.

[0043] The single-mode continuous flat-top ring laser 4 and the single-mode pulsed flat-top ring laser 5 simultaneously enter the multi-mode coupled laser nozzle to form a multi-mode coupled laser. The pulsed flat-top ring laser 5 is located inside the continuous flat-top ring laser 4. In this embodiment, the ring diameter of the continuous flat-top ring laser 4 is smaller than the ring diameter of the pulsed flat-top ring laser 5, and the two light rings are concentric.

[0044] 4. Additive Manufacturing

[0045] like Figure 2 As shown, the impeller body 1 is a relatively simple part, which is manufactured efficiently by wire feeding additive manufacturing. The multi-mode coupling laser nozzle moves at a certain speed according to the preset trajectory, and the wire feeder controls the titanium alloy wire 6 to be fed to the center of the multi-mode coupling laser nozzle at a certain speed, and is transported under the control of the controller. In this process, circulating cooling water is introduced into the multi-mode coupling laser nozzle through a water cooling device to cool the equipment, and protective gas is introduced to prevent the splashing powder from sticking to the laser head, and the protective gas can also prevent the molten pool from oxidizing.

[0046] Under the action of the continuous flat-top ring laser 4 and the single-mode pulsed flat-top ring laser 5, the titanium alloy wire 6 is completely melted and combined with the titanium alloy substrate 3 to form a molten pool. After the molten pool is formed, the pulsed flat-top ring laser 5 located in the inner circle will accelerate the flow of the molten pool to promote the diffusion of elements inside the molten pool. In addition, the pulsed flat-top ring laser 5 will have an impact effect on the dendrites formed at the solidification front, causing the crystal arms of the dendrites to break and form new crystal nuclei, thereby increasing the nucleation rate and improving the strength of the impeller body 1.

[0047] After the impeller body 1 is manufactured, the impeller body 1 is used as a new load-bearing additive matrix, and the impeller blades 2 are additively manufactured on its side, such as Figure 3 As shown. The impeller blade 2 is a part with a relatively complex structure, which is manufactured with high precision using a powder feeding additive manufacturing method. The multi-mode coupling laser nozzle moves at a certain speed according to a preset trajectory, and the powder feeder controls the titanium alloy powder 7 to be fed to the center of the multi-mode coupling laser nozzle at a certain speed and transported under the control of the controller. In this process, a protective powder feeding gas is introduced, and the protective powder feeding gas surrounds the output metal powder to ensure continuous and uniform transportation of the powder.

[0048] The titanium alloy powder 7 interacts with the continuous flat-top ring laser 4 and the single-mode pulsed flat-top ring laser 5 during the falling process to form molten droplets, which are combined with the impeller body 1 to form a molten pool. After the molten pool is formed, the pulsed flat-top ring laser 5 located in the inner circle will accelerate the flow of the molten pool to promote the diffusion of elements inside the molten pool. In addition, the pulsed flat-top ring laser 5 will have an impact effect on the dendrites formed at the solidification front, causing the crystal arms of the dendrites to break and form new crystal nuclei, thereby increasing the nucleation rate and improving the strength of the impeller blades 2.

[0049] 5. Surface strengthening

[0050] Since the surface of a part is often the most likely place for the source of cracks in the part, the titanium alloy composition used on the surface of the part is different from that inside. When the part is processed to the final surface, the content of strengthening elements in the titanium alloy powder fed into the multi-modal coupled laser nozzle is adjusted by the controller, and the powder material with gradually increasing strengthening elements is delivered until the surface of the part is processed. Due to the extremely fast cooling speed of the laser additive manufacturing process, residual tensile stress is easily formed on the surface of the part. Therefore, after the processing is completed, the continuous flat-top ring laser 4 is turned off, and the pulsed flat-top ring laser 5 is used to impact strengthen the surface of the material, converting the residual tensile stress into residual compressive stress that helps resist crack formation. Finally, the process is repeated to complete the strengthening of the entire part.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for additively manufacturing titanium alloy by silk powder and multi-modal laser coupling, characterized in that: The following steps are involved: (1) using a continuous laser generator to emit a single-mode continuous Gaussian laser, using a laser beam shaping system to shape the single-mode continuous Gaussian laser into a single-mode continuous flat-top laser, and then using an optical element to reconstruct the single-mode continuous flat-top laser into a single-mode continuous flat-top ring laser; (2) using a pulse laser generator to emit a single-mode pulsed Gaussian laser, using a laser beam shaping system to shape the single-mode pulsed Gaussian laser into a single-mode pulsed flat-top laser, and then using an optical element to reconstruct the single-mode pulsed flat-top laser into a single-mode pulsed flat-top ring laser; (3) allowing the single-mode continuous flat-top ring laser and the single-mode pulsed flat-top ring laser to enter the multi-mode coupled laser nozzle respectively, and the single-mode pulsed flat-top ring laser is located in the light ring of the single-mode continuous flat-top ring laser, so as to form a multi-mode coupled ring laser; (4) Setting a wire feeder and a powder feeder to deliver titanium alloy wire or powder to the multi-mode coupled laser nozzle; (5) The multi-mode coupled laser nozzle runs along a predetermined trajectory. During operation, the opening and closing of the conveying channels of the wire feeder and the powder feeder are controlled by switching the controller. When printing a larger area of ​​a component, the wire feeder is used to convey the wire material, and when printing a smaller area, the powder feeder is used to convey the powder material. The continuous operation completes the additive manufacturing process of the titanium alloy parts.

2. The method for additive manufacturing of titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: The powder material and the wire material are both input from the hollow part of a single-mode pulse flat-top ring laser.

3. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: In step (5), the power of the pulse flat-top ring laser is 0.05-2kW, and the power of the continuous flat-top ring laser is 2-10kW.

4. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: In step (5), a water cooling device is used to cool the multi-mode coupled laser nozzle, and a protective gas is introduced to prevent the flying powder from adhering to the laser head and to prevent the molten pool from oxidizing.

5. The method for additive manufacturing of titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: When conveying the powder in step (5), a powder conveying protective gas is introduced at the outlet of the powder feeder to ensure continuous and uniform conveying of the powder.

6. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: The wire feeder includes a collimator.

7. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: The optical elements include a toroidal mirror and a conical mirror.

8. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: The method also includes a substrate pretreatment step, specifically grinding the surface of the titanium alloy substrate to be flat and smooth, followed by shot peening to increase the roughness, and finally using acetone cleaning to remove surface dirt.

9. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: In step (5), the substrate is heated to 400° C. and kept at this temperature until the additive process is completed.

10. The method for additively manufacturing titanium alloy by silk powder coordinated multi-modal laser coupling according to claim 1, characterized in that: The step (5) includes a surface strengthening step, that is, when processing the final surface portion of the part, a powder feeder is used to deliver strengthening powder material, and the content of strengthening elements is added or increased in the strengthening powder material. Thereafter, the continuous flat-top ring laser is turned off, and the surface of the material is impact strengthened by using a pulsed flat-top ring laser.

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