Ultrasonic assisted high differential melt gradient material laser additive manufacturing system and method

Abstract

An ultrasonic-assisted laser additive manufacturing system and method for high melting point gradient materials includes a nozzle, a molten pool, a substrate, a temperature control device, an ultrasonic generator, high-purity argon gas, a powder feeder, an industrial computer, a laser, a chiller, and an ultrasonic tool head. First, high melting point powders of different proportions are placed into the two cylinders of the powder feeder, and the top of the ultrasonic tool head is brought into contact with the substrate. Second, high melting point powder material is deposited on the substrate. The ultrasonic generator controls the ultrasonic tool head to output ultrasound to act on the substrate, and the distribution of high melting point powder on the substrate is observed. Functionally graded materials are deposited at antinodes. Third, the high melting point powder on the substrate is cleaned, the laser additive manufacturing system is turned on, and the high melting point powder is conveyed to the nozzle through the powder feeder. The laser melts the high melting point powder, forming a molten pool on the substrate under ultrasonic action. After cooling, a sample is obtained. This invention achieves a gradient transition from low-melting-point metals to high-melting-point metals by switching powder feeding cylinders containing different proportions of high-melting-point powders and applying ultrasound during the process of laser-induced powder formation of a molten pool. The ultrasound is transmitted through the substrate to the sample and finally acts on the molten pool. By interfering with the solidification behavior of the molten pool, this invention solves the technical problems in the manufacturing of traditional high-melting-point functional graded materials.

Description

Technical Field

[0001] This invention belongs to the field of laser manufacturing and relates to an ultrasonic-assisted laser additive manufacturing system and method for high melting gradient materials. Background Technology

[0002] With the increasingly urgent need for reliable and stable flight of hypersonic vehicles in my country's aerospace industry, traditional materials such as titanium alloys and stainless steel have reached their high-temperature resistance limits and are insufficient to meet the high-temperature requirements of components. Nickel-based superalloys have high service temperatures but high densities, leading to a significant increase in component weight. Therefore, single materials are insufficient to meet the requirements, and there is an urgent need to develop functionally graded materials (FJTs) with multifunctional coupling and synergistic performance to improve the performance of key components. High melting point FJTs simultaneously meet the requirements of high temperature resistance, high strength, and lightweight, possessing advantages unmatched by other material systems, and have shown great application potential in the fabrication of high-temperature resistant components for hypersonic vehicles.

[0003] Currently used mechanical joining methods suffer from severe heat accumulation and structural deformation, affecting overall performance. Traditional spraying / welding processes generally suffer from low density and poor bonding when preparing materials with large melting point differences. Laser additive manufacturing (LAM) technology, compared with traditional subtractive manufacturing processes, employs a layer-by-layer method to build parts. This process begins with the design of a three-dimensional digital model, created using computer-aided design (CAD) software, which is then sliced ​​to generate two-dimensional contour data. This data is transmitted to a laser additive manufacturing device, where a laser beam, guided by the cross-sectional geometry, melts and deposits material along a predetermined path, thereby achieving layer-by-layer manufacturing of the part. This technology avoids traditional steps such as casting, forging, and mold making, significantly shortening the manufacturing cycle. Meanwhile, laser additive manufacturing technology has the advantages of high energy density and integrated control of gradient interface structure and properties, making it one of the effective means to prepare gradient material components. However, for high melting point functional gradient material systems, defects such as pores and cracks may occur during the additive manufacturing process due to the large difference in melting points. The compatibility between the two material interfaces is poor, and the gradient interface bonding strength is low, which leads to a decrease in the mechanical properties of gradient material components and affects the stability of subsequent heat treatment, machining and other processes.

[0004] To meet the fabrication needs of hypersonic vehicle components, and addressing issues such as porosity, cracks, and poor interfacial bonding in high-melting-difference functionally graded materials, an ultrasound-assisted laser additive manufacturing method for high-melting-difference gradient materials is proposed. By intervening in the molten pool solidification behavior during the additive manufacturing process with an energy field, the microstructure and stress can be controlled, improving the gradient interface bonding and enhancing the overall mechanical properties of the gradient components.

[0005] The principles and methods of ultrasound-assisted laser additive manufacturing can not only provide a way to directly manufacture high-melting-point functionally graded components, but also have the potential to solve problems such as component segregation, poor microstructure uniformity and easy cracking in the additive manufacturing process. This will enable high-quality manufacturing of graded material components with large differences in physicochemical properties, and has great theoretical significance and practical value for improving the manufacturing system of graded components and developing innovative additive manufacturing technologies.

[0006] Some scholars have conducted in-depth research on ultrasound-assisted laser additive manufacturing of functionally graded materials:

[0007] Patent CN108356266A discloses a method for ultrasonic-assisted laser near-net-shape forming of titanium-nickel alloy gradient materials. The method utilizes an ultrasonic-assisted laser near-net-shape forming system to additively manufacture titanium-nickel-based alloy gradient materials. Key steps include: mounting an ultrasonic generator and a preheating device on a machine tool table, and fixing a substrate on this device. During the manufacturing process, the gradient transition of material properties is achieved by gradually changing the volume ratio of titanium alloy and nickel-based alloy powders. The combined effect of ultrasonic assistance and preheating technology reduces internal defects such as porosity and shrinkage cavities, optimizes the distribution of brittle phases, and improves the material's hardness and wear resistance. Furthermore, preheating reduces the temperature gradient during forming, lowering the risk of crack formation. However, this method is only applicable to titanium and nickel-based alloys, two materials with relatively small differences in thermophysical parameters, and does not provide a method for manufacturing high melting point materials.

[0008] Patent CN104086184A proposes a method for ultrasonic-assisted laser near-net-shape forming of ceramic parts. This method involves introducing a preheated and slowly cooled substrate into the ultrasonic-assisted laser near-net-shape forming process. Cladding is performed under the continuous action of substrate heating and ultrasonic vibration. The coupling effect of preheating / slow cooling and ultrasonic vibration can reduce defects in the three-dimensional ceramic parts. However, as the ultrasonic wave is applied from the substrate and propagates with increasing forming height, its intensity significantly attenuates, causing the equivalent ultrasonic assistance effect at higher positions to gradually weaken. This energy attenuation during ultrasonic wave transmission affects its efficiency in material processing, posing specific limitations for the fabrication of large components.

[0009] Patent CN115927892A proposes a vacuum induction melting method for a multi-element alloy containing high-melting-point elements. First, low-melting-point and high-melting-point metals are identified in the binary alloy AB. The low-melting-point metal is added to a vacuum induction furnace, and after it melts completely, the temperature is raised. Then, the high-melting-point metal is added to the furnace. By controlling the furnace chamber pressure and melting the low-melting-point and high-melting-point pure metals separately at different temperatures, the binary alloy containing high-melting-point metal elements is melted using a dissolution method. However, through single and double metal additions, the dissolution and diffusion between the low-melting-point and high-melting-point elements often exhibit inhomogeneity, affecting the microstructure and distribution, resulting in poor mechanical properties of the component. This method cannot precisely control the composition of high-melting-point material regions, making it difficult to prepare high-melting-point functionally graded components.

[0010] Therefore, there is an urgent need for a method specifically designed for the manufacturing process of functionally graded materials (FGMs) with high melting point differences, in order to address the challenges faced in existing technologies and optimize the production efficiency and quality of such materials. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention proposes an ultrasound-assisted laser additive manufacturing method for high functional gradient materials. By introducing an ultrasonic energy field, this invention solves problems such as porosity, cracks, and poor interfacial bonding in high functional gradient materials; simultaneously, it improves the hardness and wear resistance of the samples, meeting the requirements for high strength and lightweight materials, thereby enabling the manufacturing of complex functional gradient parts.

[0012] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0013] An ultrasonic-assisted laser additive manufacturing system for high melting gradient materials is disclosed. The system includes a nozzle 1, a molten pool 2, a sample 3, a substrate 4, a temperature control device 5, an ultrasonic generator 6, high-purity argon gas 7, a powder feeder 8, an industrial computer 9, a laser 10, a chiller 11, and an ultrasonic tool head 12. The ultrasonic generator 6 is connected to the ultrasonic tool head 12, which is fixed to the substrate 4 by a clamp. The temperature control device 5 is mounted on a worktable, the substrate 4 is placed on the temperature control device 5, and the sample 3 is located on the substrate 4. The laser output from the nozzle 1 forms a molten pool 2 on the sample 3. The CNC machine tool controls the worktable to descend, i.e., increases the Z-axis lift, to ensure that the relative distance between the top of the sample 3 and the plane at the nozzle 1 outlet remains constant in the Z direction. The temperature control device 5 ensures good bonding between the substrate 4 and the sample 3 before forming and reduces the temperature gradient. The powder feeder 8 is connected to the nozzle 1 via a pipeline, and the high-purity argon gas 7 is connected to both the powder feeder 8 and the nozzle 1. The nozzle 1 is connected to the laser 10, and the laser 10 is connected to the industrial control computer 9 and the chiller 11.

[0014] An ultrasonic-assisted laser additive manufacturing method for high melting gradient materials is implemented based on the aforementioned manufacturing system. First, the mixed powder is dried in a drying oven. Different proportions of high melting gradient powder are then placed into the cylinders of a powder feeder 8. Simultaneously, an ultrasonic tool head 12 is fixed to the CNC machine tool table using a fixture, and the top of the ultrasonic tool head contacts the substrate 4. The angle between the axis of the ultrasonic tool head 12 and the substrate 4 can be controlled from 0° to 90° by adjusting the fixture. Then, high melting gradient powder material is deposited on the substrate 4. An ultrasonic generator 6 controls the ultrasonic tool head 12 to output ultrasonic waves that act on the substrate 4. The distribution of the high melting gradient powder on the substrate 4 is then observed, clearly showing the powder aggregation and dispersion points, i.e., antinodes and nodes. Functional gradient materials are deposited and formed in areas with stronger ultrasonic effects, such as antinodes. The high melting point powder on substrate 4 is cleaned, and the laser additive manufacturing system is turned on. The high melting point powder is transported to nozzle 1 through a pipeline via powder feeder 8. High-purity argon gas 7 serves as both the power source for transporting the high melting point powder and a protective atmosphere. The laser output from laser 10 to nozzle 1 melts the high melting point powder, forming a molten pool 2 on substrate 4 under ultrasonic treatment. After cooling, a sample 3 is formed. By switching powder feeders containing different proportions of high melting point powder, a gradient transition from low-melting-point metals to high-melting-point metals is achieved, i.e., the preparation of high melting point gradient materials with a mass fraction / volume fraction of 0%-100%. Before forming, substrate 4 is heated to 200℃-400℃ using temperature control device 5. During forming, the opening and closing of different powder feeders are controlled to prepare high melting point gradient materials. After forming, substrate 4 is cooled at a rate of 10-20℃ / min using temperature control device 5. The manufacturing method includes the following steps:

[0015] A. Select substrate 4 material and high melting point powder in powder feeder 8.

[0016] The substrate 4 is made of a material with similar thermal properties to the powder material. Before use, it is polished, cleaned and dried.

[0017] High-melting-point tungsten, tantalum, niobium, molybdenum, titanium carbide and rhenium powders (melting point > 1800℃) and low-melting-point titanium and titanium alloys, iron-based alloys, aluminum alloys and other powders (melting point < 1800℃) are selected to prepare a high melting difference (melting point difference > 1000℃) mixed powder by combining high-melting-point powder and low-melting-point powder. The powders are put into a ball mill in batches and stirred evenly. The mixed powders are then placed in a drying oven for drying. Powders with different proportions of high melting difference are placed into the cylinder of powder feeder 8.

[0018] Furthermore, in step A, the drying temperature of the vacuum drying oven is 100-120℃, and the drying time is 4-6 hours.

[0019] B. Calculate the amplitude ratio of the reflected wave to the incident wave, and then determine the ultrasonic incident angle.

[0020] The formula for calculating the amplitude ratio is as follows: and Among them: A L A represents the amplitude of the reflected longitudinal wave. S To transmit transverse wave amplitude; A O θ represents the amplitude of the incident ultrasonic longitudinal wave. O The angle between the axis of the ultrasonic tool head 12 and the substrate 4 is the ultrasonic incident angle; θ S θ is the transverse wave reflection angle. O With θ S Satisfies the relation: ksinθ S =sinθ O k is a material constant. v represents Poisson's ratio.

[0021] Based on the material properties, determine the specific value of the material's Poisson's ratio v, and then determine the material constant k;

[0022] By arbitrarily selecting multiple sets of ultrasonic incident angles θ from the range of 0°-90° O Calculate the amplitude ratio of the reflected wave to the incident wave; then compare the amplitude ratio A of the reflected wave and the incident wave. L / A O A S / A O The absolute value of the amplitude ratio is selected to determine the ultrasonic incident angle θ when both the absolute values ​​of the amplitude ratio of the reflected wave and the incident wave are relatively large. O .

[0023] C. Determine the ultrasonic process parameters based on the ultrasonic energy formula.

[0024] The calculation formulas for each ultrasonic process parameter are as follows: Where E(h,r) is the ultrasonic energy at the height h and radial distance r from the ultrasonic action point of the sample (3), E0 is a reference energy value, P is the ultrasonic power, f is the ultrasonic frequency, and A is the amplitude of the ultrasonic generator 6. The fitting parameter values ​​in the empirical formula are determined according to the material density, elastic modulus and damping characteristics, as well as the dimensions of the substrate and the formed sample. x1 is the power coefficient with a value of 1, x2 is the frequency coefficient with a value of -1 to +1, x3 is the amplitude coefficient with a value of 0 to 1, the depth attenuation coefficient a is 0.001 to 0.01, and the radial attenuation coefficient b is 0.001 to 0.01.

[0025] D. First, fix the ultrasonic tool head 12 onto the CNC machine tool table using a fixture, and use the fixture to make the top of the ultrasonic tool head contact the substrate 4. Adjust the fixture to control the angle between the axis of the ultrasonic tool head 12 and the substrate 4 to achieve the ultrasonic incident angle θ confirmed in step B.O The deposition location was then located and marked with a marker. High-melting-point powder was cleaned from substrate 4 using a vacuum cleaner. Temperature control device 5 was activated, and once the temperature stabilized at 200℃-400℃, the CNC machine tool, laser 10, chiller 11, and industrial computer 9 were turned on. The high-purity argon outlet pressure was set to 0.35-0.40 MPa, and the powder feeding gas pressure and protective gas pressure were adjusted to 0.1-0.2 MPa, with flow rates of 6.5 L / min and 7.5 L / min respectively. The flow rate at powder feeder 8 was set to 5-8 L / min. The laser head nozzle 1 output port was moved 9 mm above the deposition location using the CNC machine tool. The ultrasonic generator 6, high-purity argon gas 7, and powder feeder 8 were activated. The laser was simultaneously activated via the CNC machine tool and industrial computer 9. Finally, a molten pool 2 was formed on the surface of substrate 4 for sample 3 deposition.

[0026] Furthermore, in step D, the deposition location is an antinode within a range of 0.02m-0.06m from the ultrasonic tool head 12. The antinodes are determined as follows: a. High-melting-point powder material is uniformly spread on the substrate 4 using a scraper. The ultrasonic generator 6 controls the ultrasonic tool head 12 to output ultrasound to the substrate 4. The distribution of the high-melting-point powder on the substrate 4 is then observed, clearly showing the locations of powder aggregation and dispersion, i.e., antinodes and nodes; b. On the one hand, the attenuation of ultrasonic energy from the point of action of the ultrasonic tool head to the deposition location is calculated using the ultrasonic energy formula (<6%) to reduce the influence of ultrasonic attenuation. On the other hand, the safe operating range of the laser head and the ultrasonic tool head 12 is ensured.

[0027] E. As the height of sample 3 continues to deposit, the ultrasonic power is changed to ensure that the ultrasonic energy received by sample 3 at this height is constant. According to the ultrasonic energy formula determined in step C, each process parameter is selected. Through the CNC system, the above process parameters are used to gradually realize the transition from low melting point to high melting point material for the deposition layers of different material compositions, forming a high melting gradient component.

[0028] Furthermore, in step E, the ranges of each process parameter are as follows: the ultrasonic power of the ultrasonic generator 6 is 1000W-2000W, the ultrasonic frequency is 10-35kHz, and the ultrasonic amplitude is 10-50μm; the powder feeding rate is set to 0.2-3.0g / min; the laser power is 600-3000W, and the scanning speed is 60-1000mm / min; the Z-axis lifting amount is adjusted at any time. Here, the Z-axis lifting amount refers to the amount of descent of the worktable controlled by the CNC machine tool, mainly to ensure that the relative distance between the top of the formed sample 3 and the plane at the outlet of the nozzle 1 in the Z direction remains unchanged at 9mm.

[0029] F. After the forming is completed, the laser 10, powder feeder 8, high-purity argon gas 7, chiller 11 and ultrasonic generator 6 are turned off in sequence, and the substrate 4 is slowly cooled to room temperature by the temperature control device 5.

[0030] Furthermore, in step F, the cooling rate is 10-20℃ / min.

[0031] Compared with the prior art, the main beneficial effects of the above-conceptual technical solution of this invention are as follows:

[0032] (1) This invention addresses the compatibility issues between low-melting-point and high-melting-point heterogeneous materials, such as interfacial melting point mismatch, differences in thermal expansion coefficients, and poor wettability, as well as the structural defects easily generated in the transition gradient region under complex non-equilibrium conditions. It proposes an ultrasound-assisted method for manufacturing high-melting-point functionally graded materials. This method effectively couples the acoustic flow, cavitation, and thermal effects of ultrasound with preheating and slow cooling processes to promote uniform dissolution and diffusion between high-melting-point materials, reduce component segregation, and thus significantly reduce defect formation during manufacturing. Furthermore, this method can improve the microstructure of the material, thereby enhancing the mechanical properties of the final component. Through this innovative method, this invention solves key technical challenges in the traditional manufacturing of high-melting-point functionally graded materials.

[0033] (2) The ultrasonic tool head design of this invention adopts an easy-to-operate clamp installation method, making the tool head extremely convenient to install and disassemble, and providing the possibility for rapid on-site replacement. In addition, this design simplifies the maintenance of the tool head. When the tool head is damaged, it can be quickly replaced or repaired, greatly improving production efficiency and equipment lifespan. The incident angle between the tool head and the substrate can be finely adjusted by the clamp. This feature allows the operator to adjust the amplitude ratio of the reflected wave to the incident wave as needed, thereby optimizing the treatment effect of the molten pool. Experimental data shows that the molten pool effect is best when the angle between the ultrasonic wave and the substrate is 30°. This angle setting provides a reliable basis for precise control in the manufacturing process. Through precise control of ultrasonic waves, this invention can clearly identify areas with strong ultrasonic effects based on the pre-laid powder on the substrate. For substrates of a specific size (length and width 120mm), based on the empirical formula for ultrasonic energy and considering experimental safety, it is concluded that the deposition effect is most ideal at the antinodes within a range of 0.02m to 0.06m from the ultrasonic tool head. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the ultrasonic-assisted high melting gradient material laser additive manufacturing system of the present invention.

[0035] In the figure: 1 Nozzle; 2 Molten pool; 3 Sample; 4 Substrate; 5 Temperature control device; 6 Ultrasonic generator; 7 High-purity argon gas; 8 Powder feeder; 9 Industrial control computer; 10 Laser; 11 Chiller; 12 Ultrasonic tool head. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings. Taking the ultrasound-assisted laser additive manufacturing method of W / TC4 gradient materials as an example, a specific implementation method is given:

[0037] An ultrasonic-assisted laser additive manufacturing system for high melting gradient materials is disclosed. The system includes a nozzle 1, a molten pool 2, a sample 3, a substrate 4, a temperature control device 5, an ultrasonic generator 6, high-purity argon gas 7, a powder feeder 8, an industrial computer 9, a laser 10, a chiller 11, and an ultrasonic tool head 12. The ultrasonic generator 6 is connected to the ultrasonic tool head 12, which is fixed to the substrate 4 by a clamp. The temperature control device 5 is mounted on a worktable, the substrate 4 is placed on the temperature control device 5, and the sample 3 is located on the substrate 4. The laser output from the nozzle 1 forms a molten pool 2 on the sample 3. The CNC machine tool controls the worktable to descend, ensuring that the relative distance between the top of the sample 3 and the plane of the nozzle outlet in the Z direction remains constant at 9 mm. The temperature control device 5 ensures good bonding between the substrate 4 and the sample 3 before forming and reduces the temperature gradient. The powder feeder 8 is connected to the nozzle 1 via a pipeline, and the high-purity argon gas 7 is connected to both the powder feeder 8 and the nozzle 1. The nozzle 1 is connected to the laser 10, which is connected to the industrial control computer 9 and the chiller 11. An ultrasonic-assisted laser additive manufacturing method for high melting point gradient materials is implemented based on the above manufacturing system. First, the mixed powder is placed in a drying oven for drying. Different proportions of high melting point gradient powder are placed into the cylinder of the powder feeder 8. Simultaneously, the ultrasonic tool head 12 is fixed to the CNC machine tool table using a clamp, and the top of the ultrasonic tool head contacts the substrate 4 using the clamp. By adjusting the clamp, the angle between the axis of the ultrasonic tool head 12 and the substrate 4 can be controlled from 0° to 90°. Then, high melting point gradient powder material is laid on the substrate 4. The ultrasonic generator 6 controls the ultrasonic tool head 12 to output ultrasound that acts on the substrate 4. The distribution of the high melting point gradient powder on the substrate 4 is then observed. The locations of powder aggregation and dispersion, i.e., antinodes and nodes, can be clearly seen. Functional graded materials are deposited and formed in areas where the ultrasonic effect is stronger at the antinodes. The high melting point powder on substrate 4 is cleaned, and the laser additive manufacturing system is turned on. The high melting point powder is transported to nozzle 1 through a pipeline via powder feeder 8. High-purity argon gas 7 serves as both the power source for transporting the high melting point powder and a protective atmosphere. The laser output from laser 10 to nozzle 1 melts the high melting point powder, forming a molten pool 2 on substrate 4 under ultrasonic treatment. After cooling, a sample 3 is formed. By switching powder feeders containing different proportions of high melting point powder, a gradient transition from low-melting-point metal to high-melting-point metal is achieved, i.e., the preparation of a high melting point gradient material of 20wt.%W / 80wt.%TC4-80wt.%W / 20wt.%TC4 is realized. Before forming, substrate 4 is heated to 200°C using temperature control device 5. During forming, the opening and closing of different powder feeders 13 are controlled to achieve the preparation of functionally graded materials. After forming, substrate 4 is cooled at a rate of 10°C / min using temperature control device 5. The manufacturing method includes the following steps:

[0038] A. Experimental substrate 4 is made of TC4 material. Before use, it is polished and then cleaned and dried with anhydrous ethanol and deionized water. Commercial 15-53μm W spherical powder and 45-90μm TC4 spherical powder are selected. Using an electronic balance, 20wt.%W / 80wt.%TC4, 40wt.%W / 60wt.%TC4, 60wt.%W / 40wt.%TC4 and 80wt.%W / 20wt.%TC4 mixed powders are weighed and mixed in batches in a ball mill for 10 hours to ensure thorough and uniform mixing. The mixed powder is then placed in an electric heating vacuum drying oven and dried at 120℃ for 5 hours. The high melting point powders of different proportions are placed into the four cylinders of the powder feeder 8.

[0039] B. Determine the ultrasound incident angle by calculating the amplitude ratio of the reflected wave to the incident wave using the formula: and Where ksinθ S =sinθ O and In the formula, A L To reflect longitudinal waves, A S To emit a transverse wave, A O For the incident wave, θ O For the angle between the substrate 4 and the substrate 4, θ S The angle between the reflected image and the substrate is 4, k is a material constant, and v is Poisson's ratio. Specifically:

[0040] Based on the material's behavior at different temperatures, Poisson's ratio was set to 0.35. Calculations showed that when the angle was 30°, A... L / A O A is -0.79. S / A O The effective amplitude is 0.84, which is relatively large. Therefore, a 30° angle between the ultrasonic tool head 12 and the substrate 4 is selected, which has a better effect on the molten pool 2. The output frequency of the ultrasonic generator 6 is set to 20-35kHz and the output power to 1000W-2000W. High melting point powder material is pre-laid on the substrate 4. The ultrasonic generator 6 controls the ultrasonic tool head 12 to output ultrasound to act on the substrate 4. Then, the distribution position of the high melting point powder on the substrate 4 is observed. The locations of powder aggregation and dispersion, namely antinodes and nodes, can be clearly seen. The antinodes are selected as the deposition area.

[0041] By making assumptions about ultrasonic propagation, the formula for the ultrasonic energy propagating to sample 3 is derived: Where E(h,r) is the ultrasonic energy at the height h and radial distance r from the ultrasonic action point of the sample (3), E0 is a reference energy value, P is the ultrasonic power, which ranges from 1000W to 2000W, f is the ultrasonic frequency, which ranges from 20kHz to 35kHz, A is the ultrasonic amplitude, which ranges from 10m to 50μm, x1 is the power coefficient, which has a value of 1, x2 is the frequency coefficient, which has a value of -1 to +1, x3 is the amplitude coefficient, which has a value of 0 to 1, the depth attenuation coefficient a is 0.001 to 0.01, and the radial attenuation coefficient b is 0.001 to 0.01.

[0042] Because ultrasound attenuates less in solids, the deposition location is at an antinode 0.04m away from the point of action of the ultrasonic tool head 12. The method for determining the antinode is as follows: a. High melting point powder material is uniformly spread on the substrate 4 beforehand using a scraper. The ultrasonic generator 6 controls the ultrasonic tool head 12 to output ultrasound to act on the substrate 4. Then, the distribution of high melting point powder on the substrate 4 is observed, and the locations of powder aggregation and dispersion, i.e., antinodes and nodes, can be clearly seen; b. On the one hand, the attenuation of ultrasonic energy from the point of action of the ultrasonic tool head to the deposition location is calculated using the ultrasonic energy formula (<6%) to reduce the influence of ultrasonic attenuation. On the other hand, the safe operating range of the laser head and the ultrasonic tool head 12 is ensured.

[0043] First, the ultrasonic tool head 12 is fixed on the CNC machine tool workbench using a clamp, and the top of the ultrasonic tool head is brought into contact with the substrate 4 using the clamp. The angle between the axis of the ultrasonic tool head 12 and the substrate 4 can be controlled to 30° by adjusting the clamp. Then, the deposition position is found and marked with a marker. The high melting point powder on the substrate 4 is cleaned with a vacuum cleaner. The temperature control device 5 is turned on. After the temperature stabilizes at 200℃, the CNC machine tool, laser 10, chiller 11 and industrial control computer 9 are turned on. The high-purity argon outlet pressure is set to 0.35-0.40MPa. The powder feeding gas pressure and protective gas pressure are adjusted to 0.1-0.2MPa, and the flow rates are 6.5L / min and 7.5L / min, respectively. The flow rate at the powder feeder 8 is set to 5-8L / min. The laser head nozzle 1 output port is moved to a position 9mm above the deposition position using the CNC machine tool. The ultrasonic generator 6, high-purity argon gas 7 and powder feeder 8 are turned on. The laser is turned on simultaneously using the CNC machine tool and industrial control computer 9. Finally, a molten pool 2 is formed on the surface of the substrate 4 for the deposition of the sample 3.

[0044] As the sample 3 was deposited at its height, the ultrasonic power was adjusted to ensure a constant ultrasonic energy level at that height. The ultrasonic power was set to 1000W-2000W, the powder feed rate to 2g / min, the laser power to 600-800W, the scanning speed to 60-100mm / min, and the Z-axis lift to be adjusted as needed. A total of 16 layers were deposited in a single pass. The control system used the above process parameters to create a gradient transition from 20% to 80% W by mass fraction. By mixing powders with different mass fractions, the laser energy density could be increased to achieve a gradient transition from TC4 to W.

[0045] C. After the forming is completed, the laser 10, powder feeder 8, high-purity argon gas 7, chiller 11 and ultrasonic generator 6 are turned off in sequence, and the mixture is slowly cooled to room temperature at a cooling rate of 10℃ / min through the temperature control device 5.

[0046] This invention enables the preparation of high melting gradient materials through the coupling of ultrasonic assistance and preheating and slow cooling equipment, thereby achieving the manufacturing of multi-performance and multi-functional components with high temperature resistance and high strength. Compared with traditional manufacturing methods, this method can effectively improve the quality of parts and reduce defects. At the same time, compared with the method of applying ultrasound to the bottom substrate, it has a higher degree of freedom and can also couple the ultrasonic tool head and the laser head for collaborative additive manufacturing through fixture design. This manufacturing method can control the transition interface region of high melting gradient materials to prepare high-quality high melting gradient functional gradient components.

[0047] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for ultrasonic-assisted laser additive manufacturing of high melting gradient materials, characterized in that, This is achieved using an ultrasonic-assisted high melting gradient material laser additive manufacturing system. The manufacturing system includes a nozzle (1), a molten pool (2), a substrate (4), a temperature control device (5), an ultrasonic generator (6), high-purity argon gas (7), a powder feeder (8), an industrial computer (9), a laser (10), a chiller (11), and an ultrasonic tool head (12). The ultrasonic generator (6) is connected to the ultrasonic tool head (12), and the ultrasonic tool head (12) is fixed to the substrate (4) by a clamp. The temperature control device (5) is mounted on the worktable, the substrate (4) is arranged on the temperature control device (5), and the sample (3) is located on the substrate (4). (1) The output laser can form a molten pool (2) on the sample (3). The CNC machine tool controls the table to descend, i.e., increases the Z-axis lifting amount to ensure that the relative distance between the top of the sample (3) and the plane at the nozzle (1) outlet remains unchanged in the Z direction. The temperature control device (5) is used to ensure that the substrate (4) and the sample (3) have a good bond before forming and to reduce the temperature gradient. The powder feeder (8) and the nozzle (1) are connected through a pipeline. High-purity argon gas (7) is connected to the powder feeder (8) and the nozzle (1). The nozzle (1) is connected to the laser (10). The laser (10) is connected to the industrial control computer (9) and the chiller (11) respectively. The manufacturing method includes the following steps: First, high-melting-point powders of different proportions are placed into the two powder feeding cylinders of the powder feeder (8); at the same time, the top of the ultrasonic tool head (12) is brought into contact with the substrate (4) through the clamp, and the angle between the axis of the ultrasonic tool head (12) and the substrate (4) is controlled by adjusting the clamp; second, high-melting-point powder material is laid on the substrate (4), and the ultrasonic tool head (12) is controlled by the ultrasonic generator (6) to output ultrasound to act on the substrate (4), the distribution position of high-melting-point powder on the substrate (4) is observed, the powder aggregation and dispersion points, i.e., antinodes and nodes, are determined, and the antinode areas are selected and recorded for functional analysis. Gradient material deposition and forming; next, the high melting point powder on the surface of the substrate (4) is cleaned, the laser additive manufacturing system is turned on, and the high melting point powder is transported to the nozzle (1) through the powder feeder (8) by high-purity argon gas (7). The high-purity argon gas (7) also serves as the power source and protective atmosphere for transporting the high melting point powder. The laser output from the laser (10) to the nozzle (1) melts the high melting point powder and forms a molten pool (2) on the substrate (4) under ultrasonic action. After cooling, a sample (3) is formed; by switching the powder feeder containing different proportions of high melting point powder, the gradient transition from low melting point metal to high melting point metal is achieved, specifically: A. Select the substrate (4) material and the high melting point powder in the powder feeder (8); The substrate (4) is made of a material with similar thermal properties to the powder material. It is polished, cleaned and dried before use. A high melting point mixed powder is obtained by combining a high melting point powder with a melting point >1800℃ and a low melting point powder with a melting point <1800℃, wherein the melting point difference between the high melting point powder and the low melting point powder is >1000℃; and high melting point powders of different proportions are placed into the cylinder of the powder feeder (8). B. Calculate the amplitude ratio of the reflected wave to the incident wave, and then determine the ultrasonic incident angle; The formula for calculating the amplitude ratio is as follows: and ,in: This represents the amplitude of the reflected longitudinal wave. To transmit transverse wave amplitude; The amplitude of the incident ultrasonic longitudinal wave; The angle between the axis of the ultrasonic tool head (12) and the substrate (4) is the ultrasonic incident angle; The angle of reflection of the transverse wave; and Satisfying the relation: ; For material constants, , Poisson's ratio; Determine the Poisson's ratio of the material based on its properties. Specific values ​​are then used to determine material constants. ; By arbitrarily selecting multiple sets of ultrasonic incident angles within the range of 0°-90° Calculate the amplitude ratio of the reflected wave to the incident wave; then compare the amplitude ratios of the reflected wave and the incident wave. , The absolute value of the amplitude ratio is selected to determine the ultrasonic incident angle when both the absolute values ​​of the amplitude ratio of the reflected wave and the incident wave are relatively large. ; C. Determine the ultrasonic process parameters based on the ultrasonic energy formula; The calculation formulas for each ultrasonic process parameter are as follows: ,in The ultrasonic energy is located at the height h of the sample (3) and the radial distance r from the ultrasonic action point. It is a baseline energy value. It is ultrasonic power. It is an ultrasonic frequency. It is the amplitude of the ultrasonic generator (6); the fitting parameter values ​​in the empirical formula are determined based on the material's density, elastic modulus, damping characteristics, and the dimensions of the substrate and the formed sample. The power factor is 1, where This is the frequency coefficient, with a value ranging from -1 to +1. The amplitude coefficient has a value of 0-1, and the depth attenuation coefficient is... The radial attenuation coefficient is 0.001-0.

01. It is 0.001-0.01; D. Deposit sample (3) on the surface of substrate (4); The ultrasonic tool head (12) is brought into contact with the substrate (4) by the clamp. The angle between the axis of the ultrasonic tool head (12) and the substrate (4) is controlled by adjusting the clamp to achieve the ultrasonic incident angle confirmed in step B. Clean the high melting point powder on the surface of the substrate (4), turn on the laser additive manufacturing system, and deposit at the deposition location; In step D, the deposition location is an antinode within a range of 0.02 m to 0.06 m from the ultrasonic tool head (12). The antinode is determined as follows: a high melting point powder material is laid on the substrate (4), and the ultrasonic tool head (12) is controlled by the ultrasonic generator (6) to output ultrasonic waves to act on the substrate (4). The distribution location of the high melting point powder on the substrate (4) is observed, and the locations of powder aggregation and dispersion, i.e., antinodes and nodes, are determined. The antinode area is recorded and selected as the deposition location for gradient material deposition. E. As the height of the sample (3) continues to accumulate, the ultrasonic power is changed to ensure that the ultrasonic energy received by the sample (3) at this height is constant. According to the ultrasonic energy formula determined in step C, each process parameter is selected. The above process parameters are used to gradually realize the transition from low melting point to high melting point material for different components through the CNC system, forming a high melting gradient component. F. After the forming is completed, the laser (10), powder feeder (8), high-purity argon gas (7), chiller (11) and ultrasonic generator (6) are turned off in sequence, and the substrate (4) is slowly cooled to room temperature by temperature control device (5).

2. The method for ultrasonic-assisted laser additive manufacturing of high melting gradient materials according to claim 1, characterized in that, In step A, the high-melting-point powder includes tungsten, tantalum, niobium, molybdenum, titanium carbide, and rhenium; the low-melting-point powder includes titanium and titanium alloys, iron-based alloys, and aluminum alloys.

3. The method for ultrasonic-assisted laser additive manufacturing of high melting gradient materials according to claim 1, characterized in that, In step D, starting the laser additive manufacturing system involves: turning on the temperature control device (5), and after the temperature stabilizes at 200℃-400℃, turning on the CNC machine tool, laser (10), chiller (11), and industrial control computer (9), setting the high-purity argon outlet pressure to 0.35-0.40MPa, adjusting the powder feeding gas pressure and protective gas pressure to 0.1-0.2MPa, with flow rates of 6.5L / min and 7.5L / min respectively, and setting the flow rate at the powder feeder (8) to 5-8L / min. Using the CNC machine tool, the output port of the laser head nozzle (1) is moved to a suitable position above the deposition position. The ultrasonic generator (6), high-purity argon (7), and powder feeder (8) are turned on. The laser is turned on simultaneously by the CNC machine tool and the industrial control computer (9) to form a molten pool (2) on the surface of the substrate (4) for the deposition of the sample (3).

4. The method for ultrasonic-assisted laser additive manufacturing of high melting gradient materials according to claim 1, characterized in that, In step E, the range of each process parameter is as follows: the ultrasonic power of the ultrasonic generator (6) is 1000W-2000W, the ultrasonic frequency of the ultrasonic generator (6) is 10-35kHz, and the ultrasonic amplitude is 10-50μm; the powder feeding amount is set to 0.2-3.0g / min; the laser power is 600-3000W, and the scanning speed is 60-1000mm / min; the Z-axis lifting amount is adjusted at any time; the Z-axis lifting amount here refers to the amount of descent of the control table of the CNC machine tool, which is used to ensure that the relative distance between the top of the sample (3) and the plane at the outlet of the nozzle (1) in the Z direction remains unchanged.

5. The method for ultrasonic-assisted laser additive manufacturing of high melting gradient materials according to claim 1, characterized in that, Furthermore, in step F, the cooling rate is 10-20℃ / min.

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