Laser composite additive manufacturing method for controlling molten pool flow based on pulse laser

Abstract

The invention relates to the technical field of laser additive manufacturing, and discloses a laser composite additive manufacturing method for controlling molten pool flow based on pulse laser, which comprises the steps of base material treatment, powder laying, additive manufacturing, remelting, forming and post-treatment. Parameters of pulse laser and ultrasonic vibration are adjusted according to different stages of the molten pool in the material adding stage, so that convection of the molten pool is sufficient, thermal stress in the solidification stage is remarkably relieved, and the flowing speed is more uniform. And meanwhile, a remelting step is also set, and an excessive molten pool is formed on the surface of the front layer, so that the thickness of an oxide layer on the surface of the front layer is reduced, and the bonding strength among the layers is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser additive manufacturing, in particular to a laser composite additive manufacturing method based on pulse laser control of molten pool flow. BACKGROUND

[0002] Laser additive manufacturing (such as selective laser melting SLM, laser metal deposition LMD) has been widely used in the preparation of complex components due to its high forming freedom, but the existing technology has the following key defects: 1. Molten pool flow out of control: the existing continuous laser or fixed parameter pulse laser cannot adapt to the flow requirements of the three stages of "formation-expansion-solidification" of the molten pool, which easily leads to pores (insufficient convection of the molten pool), cracks (concentration of thermal stress in the solidification stage), and composition segregation (uneven flow speed); 2. Weak interlayer bonding: when the layers are directly stacked, the surface oxidation layer and the excessive roughness of the previous layer lead to low interlayer bonding strength.

[0003] Therefore, it is of great practical significance to propose a laser composite additive manufacturing method based on pulse laser control of molten pool flow. SUMMARY

[0004] In view of this, the present application proposes a laser composite additive manufacturing method based on pulse laser control of molten pool flow, aiming to solve at least one of the background technologies.

[0005] The present application proposes a laser composite additive manufacturing method based on pulse laser control of molten pool flow, comprising the following steps: Substrate treatment: selecting a substrate corresponding to the target metal component and pretreating the substrate; Powder laying: fixing the pretreated substrate on the workbench of the additive manufacturing equipment, selecting metal powder of the same material as the substrate, and laying powder on the surface of the substrate using a powder laying device; Additive manufacturing: presetting a laser scanning path, performing pulse laser scanning treatment and ultrasonic vibration treatment on the metal powder to form a molten pool, during which the parameters of pulse laser scanning treatment and ultrasonic vibration treatment are adjusted according to different periods of the molten pool until single-layer additive manufacturing is completed; Remelting: remelting and cooling the single-layer additive using pulse laser; Forming: laying powder on the surface of the remelted layer using a powder laying device, repeating the additive manufacturing step and the remelting step to form a powder-laying-additive-remelting cycle until the target metal component is formed; Post-processing: post-processing the formed metal component.

[0006] Preferably, the pretreatment specifically comprises: The substrate is placed in anhydrous ethanol for ultrasonic cleaning, and after the end, the cleaned substrate surface is polished, and the substrate is vacuum preheated after polishing.

[0007] Preferably, the frequency of the ultrasonic cleaning is 40 kHz, and the cleaning time is 10-15 minutes; the vacuum degree of the vacuum preheating treatment is less than or equal to 5x10 -3 Pa, and the holding time is 30-60 min.

[0008] Preferably, the powder laying speed is 10 mm / s, and the powder thickness is 0.3 mm.

[0009] Preferably, the additive includes: The peak temperature of the molten pool, the diameter of the molten pool, and the flow speed of the molten pool are collected in real time; The pulsed laser is used to scan the metal powder at a pulse frequency of 50 kHz and an energy density of 400 J / cm 2 The pulsed laser is used to scan the metal powder at a pulse frequency of 50 kHz and an energy density of 400 J / cm When the diameter of the molten pool is equal to 0.5 times the diameter of the laser spot, and the peak temperature of the molten pool is 200℃ higher than the melting point of the metal powder, the laser frequency of the pulsed laser scanning treatment is increased to 150 kHz, and the energy density is reduced to 250 J / cm 2 , and the scanning speed is kept at 1500 mm / s; When the flow speed of the molten pool is between 8 mm / s and 12 mm / s, the diameter of the molten pool is between 1-1.5 times the diameter of the laser spot, and the peak temperature of the molten pool is between 50-200℃ higher than the melting point of the metal powder, the laser frequency of the pulsed laser scanning treatment is increased to 300 kHz, and the energy density is reduced to 100 J / cm 2 , and the scanning speed is kept at 1500 mm / s; When the preset scanning path is completed, and the peak temperature of the molten pool is 50℃ lower than the melting point of the metal powder, the flow speed of the molten pool is less than or equal to 1 mm / s, and the diameter of the molten pool is 0.3 mm, a single layer of additive is completed.

[0010] Preferably, the remelting specifically includes: presetting a laser scanning path, adjusting the frequency of the pulsed laser to 250 kHz, and adjusting the energy density to 120 J / cm 2 , and remelting the surface of the completed single layer.

[0011] Preferably, the preset laser scanning path during remelting intersects the preset laser scanning path during additive at 90℃, and the melting thickness is 5-10 μm, and after completion, it is cooled for 10 min.

[0012] Preferably, during the forming step, the average temperature of the detection surface is detected every 5 layers, if the temperature is less than 300 DEG C, the forming is continued; if the temperature is greater than or equal to 300 DEG C, the forming is continued after natural cooling to 150 DEG C. The difference between the actual height and the target height of the forming height is detected every 10 layers, wherein the target height = cycle number x 0.3 mm, and when the difference is greater than 0.05, the powder thickness of the lower layer is adjusted.

[0013] Preferably, the post-processing specifically comprises: taking out the target metal component after cooling to room temperature, performing low-temperature aging treatment, and then performing component separation and polishing treatment.

[0014] Preferably, Ar gas is continuously introduced at a flow rate of 15 L / min during the powder laying, adding, remelting and forming stages.

[0015] Compared with the prior art, the present application has the following beneficial effects: (1) The present application adjusts the parameters of the pulse laser and ultrasonic vibration for different stages of the molten pool, so that the convection of the molten pool is sufficient, the thermal stress in the solidification stage is significantly relieved, and the flow velocity is more uniform.

[0016] (2) The present application forms an excessive molten pool on the surface of the previous layer by remelting, reduces the thickness of the oxidation layer on the surface of the previous layer, and greatly improves the bonding strength between the layers. DETAILED DESCRIPTION

[0017] The various illustrative embodiments of the present application will now be described in detail in connection with the following figures. This description is not to be considered limiting in scope, but rather as being exemplary of the various aspects, features and implementations of the present application. It is expressly intended that all such variations, modifications and enhancements of the present application as set forth in the detailed description, drawings and claims be included within the scope of the present application.

[0018] In addition, for numerical ranges of the present application, it is intended that every intermediate value of the upper and lower limits of the range is specifically included. Each smaller range between any stated value or intervening value in the stated range and any other stated or intervening value in the stated range is also encompassed within the application. The upper and lower limits of these smaller ranges can independently be included or excluded in the range.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. Any and all such similar methods and materials that are suggested either inherently or by citation in this document are intended to be encompassed by the application.

[0020] Many modifications and variations to the illustrative embodiments described herein will be apparent to those skilled in the art from consideration of the specification and practice of the subject technology. Additional embodiments of the subject technology will be apparent to those skilled in the art from consideration of the specification and practice of the subject technology. The specification and examples given herein are by way of illustration only and are not intended to limit the subject technology in any way.

[0021] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" or the like are open-ended and do not exclude additional, unrecited elements or method steps.

[0022] The present application provides a laser composite additive manufacturing method based on pulse laser control of molten pool flow, comprising the following steps: Substrate treatment: selecting a substrate corresponding to the target metal component and pretreating the substrate; Powder laying: fixing the pretreated substrate on the workbench of the additive manufacturing device, selecting metal powder of the same material as the substrate, and laying powder on the surface of the substrate using a powder laying device; Additive manufacturing: presetting a laser scanning path, performing pulse laser scanning and ultrasonic vibration treatment on the metal powder to form a molten pool, and adjusting the parameters of pulse laser scanning and ultrasonic vibration treatment according to different periods of the molten pool until single-layer additive manufacturing is completed; Remelting: remelting and cooling the single-layer additive using pulse laser; Shaping: laying powder on the surface of the remelted layer using a powder laying device, repeating the additive manufacturing step and the remelting step to form a powder-additive-remelting cycle until the target metal component is shaped; Post-processing: post-processing the shaped metal component.

[0023] It can be understood that the present application adjusts the parameters of pulse laser and ultrasonic vibration according to different stages of the molten pool to make the molten pool convection sufficient, significantly relieve thermal stress in the solidification stage, and make the flow velocity more uniform.

[0024] It can be understood that the present application forms an excessive molten pool on the surface of the previous layer through remelting, reduces the thickness of the oxidation layer on the surface of the previous layer, and greatly improves the bonding strength between layers.

[0025] In the present application, the pretreatment specifically comprises: Placing the substrate in anhydrous ethanol for ultrasonic cleaning, taking out the cleaned substrate after completion, and polishing the surface of the cleaned substrate, then vacuum preheating the substrate after polishing.

[0026] The frequency of the ultrasonic cleaning is 40 kHz, and the cleaning time is 10-15 minutes; the vacuum degree of the vacuum preheating treatment is less than or equal to 5x10 -3Pa, the holding time is 30-60 min.

[0027] The ultrasonic cleaning step is preferably as follows: a single-tank ultrasonic cleaning machine is selected, anhydrous ethanol is injected into the tank, the injection amount is determined according to the liquid level height completely submerging the substrate; the substrate is placed in a 304 stainless steel cleaning basket, and then the cleaning basket is placed in the ultrasonic tank to ensure that the substrate does not directly contact the tank wall; the frequency and cleaning time are set, and after the end, the substrate is taken out, and nitrogen is used to blow along the surface of the substrate until there is no ethanol residue on the surface.

[0028] The polishing treatment step is preferably as follows: a handheld grinder is used to polish the cleaned substrate, and during polishing, 800 mesh sandpaper is used to polish the surface of the substrate for 3-5 times per square centimeter, and then 1200 mesh sandpaper is used for fine polishing, 5-8 times per square centimeter.

[0029] The vacuum preheating treatment step is preferably as follows: the polished substrate is placed in the tray of a ZK-2 type vacuum furnace, the furnace door is closed, the vacuum pump is started, and the vacuum degree is extracted to be less than or equal to 5*10 -3 Pa, and after reaching, the pressure is maintained for 5 min; the temperature of the substrate is increased at a rate of 5℃ / min (the specific temperature increase is determined according to the material quality of the substrate), and the temperature is maintained for 45 min; the heating is stopped, the vacuum state is maintained, and the temperature is naturally cooled to below 150℃, nitrogen is introduced to break the vacuum, and the substrate is taken out and cooled to room temperature in a desiccator containing silica gel desiccant.

[0030] The present application sequentially performs ultrasonic cleaning, polishing and vacuum preheating on the substrate, which can lay a stable foundation for subsequent additive manufacturing from three aspects of surface cleanliness, surface flatness, internal stress and temperature adaptability: among them, 40 kHz ultrasonic wave cooperates with anhydrous ethanol cleaning to completely remove impurities such as oil stains and dust on the surface of the substrate (avoiding impurities to form inclusions or cause local oxidation in the molten pool, reducing porosity defects); 800-1200 mesh sandpaper polishing reduces the surface roughness of the substrate to Ra≤1.6μm (ensuring the uniformity of subsequent powder spreading, preventing the molten pool flow velocity from being uneven due to the surface concave-convex, avoiding component segregation); and the vacuum preheating with a vacuum degree less than or equal to 5*10 -3 Pa not only can eliminate the internal residual stress of the substrate (avoiding thermal shock cracks caused by large temperature difference between the molten pool and the substrate during additive manufacturing), but also can remove the water vapor adsorbed on the surface of the substrate (preventing bubbles from being generated by water vapor entering the molten pool), and the three synergistic effects ensure the good combination of the substrate and the molten pool, and provide key protection for the stable operation of subsequent pulse laser-ultrasonic composite additive manufacturing and the final quality of the component (such as mechanical properties and dimensional accuracy).

[0031] In the present application, the powder laying speed of the powder laying is preferably 10 mm / s, and the powder laying thickness is preferably 0.3 mm.

[0032] The powder laying step is preferably as follows: The metal powder of the same material as the base material is selected, the metal powder is poured into a vacuum drying oven, dried at a temperature of 90 DEG C and a vacuum degree of 50 Pa for 3 hours, cooled to below 50 DEG C after the end of the vacuum state, and the vacuum is broken by introducing nitrogen, and the metal powder is taken out; The dried metal powder is poured into the powder distributor hopper by using a scraper type powder distributor (the material is tungsten carbide, the scraper thickness is 5 mm, and the blade flatness is less than or equal to 0.01 mm).

[0033] It can be understood that the powder spreading speed of 10 mm / s is in the medium speed range of industrial powder spreading, which can avoid uneven powder spreading (such as local accumulation or missing) caused by too high speed, and can avoid reducing the forming efficiency caused by too low speed, and can ensure that the density fluctuation range of the powder layer on the surface of the base material is small, thereby laying a foundation for uniform formation of the molten pool; the powder spreading thickness of 0.3 mm matches the laser spot diameter (0.3 mm), so that the pulse laser energy can completely penetrate the powder layer and fully melt the powder, and the bottom layer powder is not melted or the laser energy is excessively penetrated (burning the surface of the base material, affecting the bonding strength) caused by too thick thickness.

[0034] In the application, the additive includes: The peak temperature of the molten pool, the diameter of the molten pool and the flow speed of the molten pool are collected in real time; The pulse laser with an energy density of 400 J / cm 2 The metal powder is subjected to the pulse laser scanning treatment at a scanning speed of 1500 mm / s, and is subjected to ultrasonic vibration treatment at a frequency of 80 kHz; When the diameter of the molten pool is equal to 0.5 times the diameter of the laser spot, and the peak temperature of the molten pool is 200 DEG C or more than the melting point temperature of the metal powder, the laser frequency of the pulse laser scanning treatment is increased to 150 kHz, the energy density is reduced to 250 J / cm 2 , and the scanning speed is kept at 1500 mm / s; When the flow speed of the molten pool is between 8 mm / s and 12 mm / s, the diameter of the molten pool is between 1-1.5 times the diameter of the laser spot, and the peak temperature of the molten pool is between 50-200 DEG C higher than the melting point of the metal powder, the laser frequency of the pulse laser scanning treatment is increased to 300 kHz, the energy density is reduced to 100 J / cm 2 , and the scanning speed is kept at 1500 mm / s; When the preset scanning path is completed, the peak temperature of the molten pool is 50 DEG C or less than the melting point of the metal powder, the flow speed of the molten pool is less than or equal to 1 mm / s, and the diameter of the molten pool is 0.3 mm, a single layer of additive is completed.

[0035] The additive equipment is: Pulsed laser generator (IPG YLR-1000-P type, wavelength 1064nm, maximum output power 1000W). An ultrasonic vibration device (such as the JZ-200 model, with a maximum amplitude of 20μm) is fixed to the center of the bottom of the worktable (rigidly connected to the worktable). The protective atmosphere system is supplied with Ar gas (purity 99.999%) at a flow rate of 15 L / min (monitored in real time by a flow meter, with an error ≤ ±0.5 L / min). High-speed camera systems (such as the Phantom V2512, 1000fps) 4 fps, resolution 1280×800): Mounted on top of the work chamber, with the lens vertically aligned with the molten pool area, equipped with a 10x microscope lens (Navitar 12X), and the focus adjusted to clearly capture the molten pool in the range of 0.1-1mm; Infrared thermometer (such as Optris PI 450, temperature range 500-3000℃): installed next to the high-speed camera system, measuring distance 300mm.

[0036] Understandably, this invention accurately captures the molten pool state by real-time acquisition of peak molten pool temperature, diameter, and flow velocity, providing data support for dynamic parameter adjustment and avoiding defects caused by blind control. During the molten pool formation period, an initial pulse frequency of 50kHz and a flow rate of 400J / cm are used. 2 A pulsed laser with a high energy density (1500 mm / s scanning speed) combined with 80 kHz ultrasonic vibration can rapidly melt metal powder to form an initial molten pool. Simultaneously, high-frequency ultrasound breaks up initial bubbles in the molten pool, reducing the risk of porosity. When the molten pool diameter is 0.5 times the laser spot diameter and the peak temperature exceeds the metal's melting point by 200°C, the molten pool enters the expansion phase. At this point, the laser frequency is increased to 50 kHz and the energy density is reduced to 250 J / cm². 2 It can precisely control the expansion rhythm of the molten pool, avoiding excessive expansion that could cause splashing or uneven convection. When the molten pool flow velocity is 8-12 mm / s, the diameter is 1-1.5 times the laser spot diameter, and the peak temperature exceeds the melting point by 50-200℃, the molten pool enters the solidification period, further increasing the laser frequency to 300 kHz and reducing the energy density to 100 J / cm³. 2This process slows down the cooling rate of the molten pool, inhibits the growth of columnar crystals, alleviates solidification thermal stress, and reduces crack formation. The final standard for single-layer additive manufacturing is achieved by using a preset scanning path, a peak molten pool temperature below the melting point of 50°C (ensuring complete solidification), a flow rate ≤1mm / s (no liquid flow), and a diameter of 0.3mm (matching powder thickness). This ensures stable single-layer molding quality, avoids interlayer bonding defects caused by incomplete solidification, and guarantees single-layer dimensional accuracy. This lays a good foundation for subsequent multi-layer cycles and interlayer remelting, ultimately significantly reducing problems such as porosity, cracks, and component segregation in components, and improving the mechanical properties and dimensional accuracy of components.

[0037] In this invention, the remelting specifically involves: setting a preset laser scanning path, adjusting the frequency of the pulsed laser to 250 kHz, and adjusting the energy density to 120 J / cm². 2 The completed single-layer surface is then remelted.

[0038] The laser scanning path preset for remelting intersects the laser scanning path preset for additive manufacturing at a 90° angle, with a melting thickness of 5-10 μm, followed by cooling for 10 minutes after completion.

[0039] The remelting process is preferably performed as follows: after the single-layer additive manufacturing is completed and naturally cooled to below 150°C, a laser scanning path is preset. The laser scanning path preset for remelting intersects the laser scanning path preset during additive manufacturing at a 90° angle (if the additive manufacturing path is longitudinal, then the remelting path is transverse). The scanning range is consistent with the additive manufacturing range, and the path spacing is 0.15 mm (0.5 times the spot diameter to ensure no melt leakage area). The frequency of the pulsed laser generator was adjusted to 250kHz, and the energy density was 120J / cm². 2 (Below the additive manufacturing stage to avoid over-melting), scan at a speed of 1200 mm / s (0.8 times the additive manufacturing speed to ensure sufficient remelting), remelt a single layer surface with a melting thickness of 5-10 μm, and cool for 10 min after completion.

[0040] It is understood that the interlayer pulsed laser remelting performed in this invention does not require additional equipment; it directly utilizes the pulsed laser device used in additive manufacturing, employing a high frequency of 250kHz and a pulsed laser speed of 120J / cm². 2The low energy density and 1200mm / s scanning speed (with a scanning method that intersects the previous layer's additive path at a 90° angle) can efficiently solve the core defect of direct interlayer superposition in existing technologies: on the one hand, it can completely remove the 5-10nm thick oxide layer on the surface of the previous layer (reducing it to below 1-2nm), while reducing the surface roughness of the previous layer and eliminating the "barrier layer" for interlayer bonding; on the other hand, it can remelt the 5-10μm deep region on the surface of the previous layer to form a "transition molten pool". This molten pool can fully fuse with the molten pool of the newly laid powder of the next layer, avoiding interlayer interface separation and ultimately greatly improving the interlayer bonding strength. At the same time, the flat remelted surface also provides a guarantee for the uniform spreading of the next layer of powder, further reducing the problem of uneven molten pool flow in subsequent additive manufacturing, forming a virtuous cycle of "interlayer quality - subsequent molding".

[0041] In this invention, during the molding step, the average surface temperature is checked every 5 layers. If the temperature is less than 300°C, molding continues; if the temperature is greater than or equal to 300°C, it is allowed to cool naturally to 150°C before molding. Every 10 layers in a cycle, the difference between the actual height and the target height is measured, where the target height = number of cycles × 0.3 mm. When the difference is greater than 0.05, the thickness of the next layer of powder is adjusted.

[0042] The molding process is as follows: after remelting, the same parameters are used to perform a cycle of powder spreading-addition-remelting on the surface of the remelted layer until the target metal component is completely formed. During this process, the average surface temperature is checked every 5 layers. If the temperature is less than 300°C, molding continues; if the temperature is greater than or equal to 300°C, it is allowed to cool naturally to 150°C before molding. Every 10 layers in a cycle, the difference between the actual height and the target height is checked, where the target height = number of cycles × 0.3mm. When the actual height is less than 0.05mm less than the target height, the powder thickness of the lower layer is adjusted to 0.32mm; when the actual height is greater than 0.05mm more than the target height, the powder thickness of the lower layer is adjusted to 0.28mm.

[0043] Understandably, the average surface temperature is checked every 5 layers in a cycle. If the temperature is below 300℃, molding continues to avoid unnecessary cooling and maintain production efficiency. If the temperature is ≥300℃, it is allowed to cool naturally to 150℃ before molding, effectively alleviating the accumulated thermal stress during multi-layer additive manufacturing (preventing overheating of the molten pool leading to coarse grains, component deformation, or crack initiation), maintaining a stable thermal environment throughout the three stages of molten pool formation, expansion, and solidification. Every 10 layers in a cycle, the actual molding height is compared with the target height of "cycle number × 0.3mm." If the difference is >0.05mm, the powder thickness of the next layer is adjusted in time. This allows for real-time correction of minor dimensional deviations caused by single-layer powder application or molten pool shrinkage (avoiding cumulative deviations that could lead to excessive final component height), ensuring accurate overall component height after multi-layer molding. The synergistic effect of these two methods avoids quality defects caused by heat accumulation and prevents the gradual amplification of dimensional deviations, significantly improving the quality consistency and batch stability of multi-layer components, thus meeting the needs of large-scale manufacturing of complex, high-precision components.

[0044] In this invention, the post-processing specifically involves: cooling the target metal component to room temperature, removing it, performing a low-temperature aging treatment, and then separating and polishing the component.

[0045] The preferred post-processing is as follows: After molding, turn off the laser and ultrasonic devices, maintain a protective atmosphere (the Ar gas flow rate is gradually reduced from 15L / min to 5L / min to avoid airflow disturbance to the components), allow it to cool naturally to below 150°C, open the working chamber door, remove the components with high-temperature resistant gloves, and place them in a desiccator to cool to room temperature (25°C). Select the SX2-12-10 box-type resistance furnace, place the components in the furnace tray (the tray is lined with graphite paper to prevent sticking), and introduce Ar gas into the furnace (flow rate 5L / min to prevent oxidation). Heating is performed at a rate of 5℃ / min and then held at that temperature (the heating temperature and holding time are determined according to the material of the component; for example, the heating temperature of TC4 titanium alloy is 550℃ and the holding time is 3 hours, while the heating temperature of GH4169 alloy is 620℃ and the holding time is 4 hours).

[0046] After the heat preservation is completed, the component is cooled to below 50°C in the furnace. The component is then removed and separated from the substrate using a wire cutting machine. The surface of the component is first manually sanded with 1200-grit sandpaper (focusing on removing wire cutting marks), and then finely sanded with 2000-grit sandpaper until Ra≤1.6μm.

[0047] It is understood that the SX2-12-10 box-type resistance furnace is used in the post-processing of this invention, and graphite paper is laid on the tray to avoid surface damage caused by the component sticking to the tray, thus ensuring the integrity of the component molding; Ar gas is introduced into the furnace at a rate of 5L / min to form an inert protective atmosphere and prevent the component from oxidizing during the heating and holding process (avoiding the formation of an oxide layer on the surface that would affect the mechanical properties); at a rate of 5℃ / min The slow heating rate reduces the temperature gradient between the inside and outside of the component, preventing new residual stress caused by uneven thermal expansion and contraction. Customizing the heating temperature and heat preservation time according to the component material allows for targeted elimination of residual stress accumulated during additive manufacturing, optimizing the component's microstructure and improving mechanical performance stability. After heat preservation, the component is cooled to below 50°C in the furnace to avoid stress concentration caused by rapid cooling, further ensuring structural stability. Wire cutting separates the component from the substrate, precisely controlling the separation accuracy and avoiding damage to the component from mechanical separation. First, 1200-grit sandpaper is used to manually remove wire cutting marks, followed by 2000-grit sandpaper for fine polishing. The polishing rhythm is controlled every 10 minutes to ensure uniform polishing and prevent over-polishing leading to dimensional deviations. Ultimately, the surface roughness of the component is reduced to Ra≤1.6μm, meeting design accuracy requirements and providing good surface quality for subsequent assembly or application, comprehensively ensuring the final performance and usability of the component.

[0048] In this invention, Ar gas is continuously introduced at a flow rate of 15 L / min during the powder spreading, additive manufacturing, remelting, and molding stages.

[0049] Example 1 I. Target Metal Components Material: TC4 titanium alloy; Dimensions: 100mm×100mm×10mm II. Raw Materials Used Substrate: TC4 titanium alloy sheet (110mm×110mm). Metal powder: TC4 titanium alloy powder (particle size 15-45μm, loose packing density 4.8g / cm³) 3 (Compliant with GB / T 39265-2020) III. Additive Manufacturing Equipment Pulsed laser generator (IPG YLR-1000-P type, wavelength 1064nm, maximum output power 1000W): Ultrasonic vibration device (JZ-200 type, maximum amplitude 20μm): fixed in the center of the bottom of the worktable (rigidly connected to the worktable). Protective atmosphere system: Ar gas (99.999% purity) is introduced at a flow rate of 15 L / min; High-speed camera system (Phantom V2512, 10fps) 4(fps, resolution 1280×800), mounted on the top of the work chamber, with the lens vertically aligned with the molten pool area, equipped with a 10x microscope lens (Navitar 12X), and the focus adjusted to clearly capture the molten pool in the range of 0.1-1mm; Infrared thermometer (Optris PI 450, temperature range 500-3000℃): installed next to the high-speed camera system, measuring distance 300mm.

[0050] IV. Manufacturing Method S1. Select a single-tank ultrasonic cleaner (KQ-500VDE model, power 500W, tank size 500mm×300mm×300mm), inject anhydrous ethanol (analytical grade, purity ≥99.7%) into the tank, ensuring the liquid level completely submerges the substrate. Place the substrate in a cleaning basket (made of 304 stainless steel to avoid reaction with ethanol), then place the cleaning basket into the ultrasonic tank. Start the ultrasonic cleaner, set the frequency to 40kHz, power to 300W, and cleaning time to 12 minutes. After cleaning, remove the substrate with clean tweezers (made of 304 stainless steel), and use nitrogen gas to blow along the surface of the substrate at a uniform speed (5cm / s) until there is no ethanol residue on the surface (no visible wetness).

[0051] S2. Use a handheld sander to polish the cleaned substrate. First, use 800-grit sandpaper to polish the surface of the substrate 4 times per square centimeter. Then, use 1200-grit sandpaper for fine polishing, 6 times per square centimeter. Place the polished substrate into the tray in the ZK-2 vacuum furnace, close the furnace door, start the vacuum pump, and evacuate to a vacuum level of less than or equal to 5 × 10⁻⁶. - 3 After reaching the set pressure, maintain the pressure for 5 minutes; raise the substrate temperature to 250°C at a rate of 5°C / min and maintain the temperature for 45 minutes; stop heating, maintain the vacuum state and allow it to cool naturally to below 150°C, then introduce nitrogen to break the vacuum, remove the substrate, and cool it to room temperature in a desiccator containing silica gel desiccant for later use.

[0052] S3. Pour the metal powder into a vacuum drying oven and dry it at 90°C and 50Pa for 3 hours. After drying, keep it under vacuum and cool it to below 50°C. Then, introduce nitrogen to break the vacuum and remove the metal powder for later use.

[0053] S4. Fix the substrate in the worktable of the additive manufacturing equipment, select a scraper-type powder spreader (material is tungsten carbide, scraper thickness is 5mm, and blade flatness is ≤0.01mm), pour the dried metal powder into the hopper of the powder spreader, and spread the metal powder evenly on the surface of the substrate at a speed of 10mm / s.

[0054] S5. Activate the protective atmosphere system in sequence (first purge with Ar gas for 10 minutes to replace the air in the working chamber, and proceed to the next step after the oxygen content is ≤50ppm), ultrasonic vibration device, and high-speed camera and infrared temperature measurement system (shoot 10s blank video to confirm that the image is clear and the temperature measurement is stable). S6. Preset longitudinal laser scanning path, with a pulse frequency of 50kHz and a speed of 400J / cm. 2 The metal powder is subjected to pulsed laser scanning at an energy density of 1500 mm / s, while the metal powder is subjected to ultrasonic vibration at a frequency of 80 kHz. S7. When the diameter of the molten pool is equal to 0.5 times the diameter of the laser spot, and the peak temperature of the molten pool is above 200°C (the melting point temperature of the metal powder), the laser frequency of the pulsed laser scanning process is increased to 150kHz, and the energy density is reduced to 250J / cm². 2 The scanning speed is maintained at 1500 mm / s; when the molten pool flow velocity is between 8 mm / s and 12 mm / s, the molten pool diameter is between 1 and 1.5 times the laser spot diameter, and the peak temperature of the molten pool is between 50 and 200°C higher than the melting point of the metal powder, the laser frequency of the pulsed laser scanning process is increased to 300 kHz, and the energy density is reduced to 100 J / cm³. 2 The scanning speed is maintained at 1500 mm / s. When the preset scanning path is completed and the peak temperature of the molten pool is 50°C lower than the melting point of the metal powder, the flow velocity of the molten pool is less than or equal to 1 mm / s, and the diameter of the molten pool is 0.3 mm, the single-layer additive manufacturing is completed.

[0055] S8. After the single-layer additive manufacturing is completed and naturally cooled to below 150℃, a preset transverse laser scanning path is established, with the scanning range consistent with the additive manufacturing range and a path spacing of 0.15mm. The frequency of the pulsed laser generator is adjusted to 250kHz, and the energy density is 120J / cm². 2 The scanning speed was 1200 mm / s, and a single layer surface was remelted with a melting thickness of 8 μm. After completion, the surface was cooled for 10 min.

[0056] S9. After remelting, repeat the powder-additive-remelting cycle on the remelted layer surface with the same parameters until the target metal component is fully formed. During this process, check the average surface temperature every 5 layers. If the temperature is less than 300℃, continue forming; if the temperature is greater than or equal to 300℃, allow it to cool naturally to 150℃ before forming. Every 10 layers, check the difference between the actual forming height and the target height, where the target height = number of cycles × 0.3mm. When the actual height is less than the target height by 0.05mm, adjust the powder thickness of the lower layer to 0.32mm; when the actual height is greater than the target height by 0.05mm, adjust the powder thickness of the lower layer to 0.28mm.

[0057] S10. After the cyclic molding is completed, turn off the laser and ultrasonic devices, and gradually reduce the flow rate of the protective atmosphere Ar gas from 15L / min to 5L / min. Allow it to cool naturally to below 150℃, remove the component, and place it in a desiccator to cool to room temperature (25℃).

[0058] S11. Place the dried component into the inner tray of the SX2-12-10 type box-type resistance furnace. Introduce Ar gas into the furnace at a flow rate of 5L / min and heat it to 550℃ at a rate of 5℃ / min. Hold the temperature for 3 hours. After the holding period, cool the component with the furnace to below 150℃. Remove the component and separate it from the substrate using a wire cutting machine (DK7732 type). First, manually polish the surface of the component with 1200-grit sandpaper, and then finely polish it with 2000-grit sandpaper until Ra≤1.6μm to obtain the target metal component.

[0059] Example 2 I. Target Metal Components Material: GH4169 alloy; Dimensions: 100mm×100mm×10mm II. Raw Materials Used Substrate: GH4169 alloy sheet (110mm×110mm); Metal powder: GH4169 alloy powder (particle size 20-50μm, loose packing density 4.6g / cm³) 3 (Compliant with GJB 3807A-2021) III. Additive Manufacturing Equipment Pulsed laser generator (IPG YLR-1000-P type, wavelength 1064nm, maximum output power 1000W): Ultrasonic vibration device (JZ-200 type, maximum amplitude 20μm): fixed in the center of the bottom of the worktable (rigidly connected to the worktable). Protective atmosphere system: Ar gas (99.999% purity) is introduced at a flow rate of 15 L / min; High-speed camera system (Phantom V2512, 10fps) 4 (fps, resolution 1280×800), mounted on the top of the work chamber, with the lens vertically aligned with the molten pool area, equipped with a 10x microscope lens (Navitar 12X), and the focus adjusted to clearly capture the molten pool in the range of 0.1-1mm; Infrared thermometer (Optris PI 450, temperature range 500-3000℃): installed next to the high-speed camera system, measuring distance 300mm.

[0060] IV. Manufacturing Method S1. Select a single-tank ultrasonic cleaner (KQ-500VDE model, power 500W, tank size 500mm×300mm×300mm), inject anhydrous ethanol (analytical grade, purity ≥99.7%) into the tank, ensuring the liquid level completely submerges the substrate. Place the substrate in a cleaning basket (made of 304 stainless steel to avoid reaction with ethanol), then place the cleaning basket into the ultrasonic tank. Start the ultrasonic cleaner, set the frequency to 40kHz, power to 300W, and cleaning time to 12 minutes. After cleaning, remove the substrate with clean tweezers (made of 304 stainless steel), and use nitrogen gas to blow along the surface of the substrate at a uniform speed (5cm / s) until there is no ethanol residue on the surface (no visible wetness).

[0061] S2. Use a handheld sander to polish the cleaned substrate. First, use 800-grit sandpaper to polish the surface of the substrate 4 times per square centimeter. Then, use 1200-grit sandpaper for fine polishing, 6 times per square centimeter. Place the polished substrate into the tray in the ZK-2 vacuum furnace, close the furnace door, start the vacuum pump, and evacuate to a vacuum level of less than or equal to 5 × 10⁻⁶. - 3 After reaching the set pressure, maintain the pressure for 5 minutes; raise the substrate temperature to 200°C at a rate of 5°C / min and maintain the temperature for 45 minutes; stop heating, maintain the vacuum state and allow it to cool naturally to below 150°C, then introduce nitrogen to break the vacuum, remove the substrate, and cool it to room temperature in a desiccator containing silica gel desiccant for later use.

[0062] S3. Pour the metal powder into a vacuum drying oven and dry it at 90°C and 50Pa for 3 hours. After drying, keep it under vacuum and cool it to below 50°C. Then, introduce nitrogen to break the vacuum and remove the metal powder for later use.

[0063] S4. Fix the substrate in the worktable of the additive manufacturing equipment, select a scraper-type powder spreader (material is tungsten carbide, scraper thickness is 5mm, and blade flatness is ≤0.01mm), pour the dried metal powder into the hopper of the powder spreader, and spread the metal powder evenly on the surface of the substrate at a speed of 10mm / s.

[0064] S5. Activate the protective atmosphere system in sequence (first purge with Ar gas for 10 minutes to replace the air in the working chamber, and proceed to the next step after the oxygen content is ≤50ppm), ultrasonic vibration device, and high-speed camera and infrared temperature measurement system (shoot 10s blank video to confirm that the image is clear and the temperature measurement is stable). S6. Preset longitudinal laser scanning path, with a pulse frequency of 50kHz and a speed of 400J / cm. 2 The metal powder is subjected to pulsed laser scanning at an energy density of 1500 mm / s, while the metal powder is subjected to ultrasonic vibration at a frequency of 80 kHz. S7. When the diameter of the molten pool is equal to 0.5 times the diameter of the laser spot, and the peak temperature of the molten pool is above 200°C (the melting point temperature of the metal powder), the laser frequency of the pulsed laser scanning process is increased to 150kHz, and the energy density is reduced to 250J / cm². 2 The scanning speed is maintained at 1500 mm / s; when the molten pool flow velocity is between 8 mm / s and 12 mm / s, the molten pool diameter is between 1 and 1.5 times the laser spot diameter, and the peak temperature of the molten pool is between 50 and 200°C higher than the melting point of the metal powder, the laser frequency of the pulsed laser scanning process is increased to 300 kHz, and the energy density is reduced to 100 J / cm³. 2 The scanning speed is maintained at 1500 mm / s. When the preset scanning path is completed and the peak temperature of the molten pool is 50°C lower than the melting point of the metal powder, the flow velocity of the molten pool is less than or equal to 1 mm / s, and the diameter of the molten pool is 0.3 mm, the single-layer additive manufacturing is completed.

[0065] S8. After the single-layer additive manufacturing is completed and naturally cooled to below 150℃, a preset transverse laser scanning path is established, with the scanning range consistent with the additive manufacturing range and a path spacing of 0.15mm. The frequency of the pulsed laser generator is adjusted to 250kHz, and the energy density is 120J / cm². 2 The scanning speed was 1200 mm / s, and a single layer surface was remelted with a melting thickness of 8 μm. After completion, the surface was cooled for 10 min.

[0066] S9. After remelting, repeat the powder-additive-remelting cycle on the remelted layer surface with the same parameters until the target metal component is fully formed. During this process, check the average surface temperature every 5 layers. If the temperature is less than 300℃, continue forming; if the temperature is greater than or equal to 300℃, allow it to cool naturally to 150℃ before forming. Every 10 layers, check the difference between the actual forming height and the target height, where the target height = number of cycles × 0.3mm. When the actual height is less than the target height by 0.05mm, adjust the powder thickness of the lower layer to 0.32mm; when the actual height is greater than the target height by 0.05mm, adjust the powder thickness of the lower layer to 0.28mm.

[0067] S10. After the cyclic molding is completed, turn off the laser and ultrasonic devices, and gradually reduce the flow rate of the protective atmosphere Ar gas from 15L / min to 5L / min. Allow it to cool naturally to below 150℃, remove the component, and place it in a desiccator to cool to room temperature (25℃).

[0068] S11. Place the dried component into the inner tray of the SX2-12-10 type box-type resistance furnace. Introduce Ar gas into the furnace at a flow rate of 5L / min and heat it to 620℃ at a rate of 5℃ / min. Hold the temperature for 4 hours. After the holding period, cool the component with the furnace to below 150℃. Remove the component and separate it from the substrate using a wire cutting machine (DK7732 type). First, manually polish the surface of the component with 1200-grit sandpaper, and then finely polish it with 2000-grit sandpaper until Ra≤1.6μm to obtain the target metal component.

[0069] Example 3 The only difference from Example 1 is that the ultrasonic cleaning time in step S1 is 10 minutes, the heat preservation time in step S2 is 30 minutes, and the melting thickness in step S8 is 5 μm.

[0070] Example 4 The only difference from Example 1 is that the ultrasonic cleaning time in step S1 is 15 minutes, the heat preservation time in step S2 is 60 minutes, and the melting thickness in step S8 is 10 μm.

[0071] Effect test Test objects: TC4 titanium alloy (a typical material for aerospace load-bearing components) and GH4169 high-temperature alloy (a typical material for high-temperature components), commonly used in additive manufacturing, were selected as test materials. Both materials comply with industry standards (TC4 complies with GB / T 3620.1-2022, and GH4169 complies with GJB 2611-1996 "Specification for Cold-drawn Bars of High-Temperature Alloys for Aerospace").

[0072] Control group 1: Continuous laser group, laser power 300W, scanning speed 1500mm / s, no ultrasonic synergy, no interlayer remelting; Control group 2: Fixed parameter pulsed laser group, pulse frequency 50kHz, energy density 250J / cm², scanning speed 1500mm / s, no ultrasonic synergy, no interlayer remelting; The experimental group includes the TC4 titanium alloy prepared by the method in Example 1 and the GH4169 high-temperature alloy prepared in Example 2; Sample preparation: Defect detection sample: 10mm×10mm×5mm (for metallographic analysis and CT scanning); Mechanical property test specimens: tensile specimens (according to GB / T228.1-2021, gauge length 50mm×10mm×4mm), interlaminar tensile specimens (according to GB / T35465.2-2017, dimensions 20mm×10mm×8mm), impact specimens (according to GB / T 229-2020, U-notch, 10mm×10mm×55mm); Sample for compositional homogeneity: 20mm×20mm×3mm (for EDS surface scanning); Test Results 1. Performance testing related to runaway flow in the molten pool The porosity of the samples prepared by the above three methods was tested using CT scanning (according to GB / T 29062-2012), and the results are shown in Table 1: Table 1 Porosity test results

[0073] Metallographic analysis was performed (according to GB / T 13298-2015, observation area 10 mm²). 2 The crack rate of the samples prepared by the above three methods was tested, and the results are shown in Table 2: Table 2 Crack Rate Test Results

[0074] The fluctuations in the content of major elements in the samples prepared by the above three methods were analyzed by EDS surface scanning. The results are shown in Table 3. Table 3 Results of component homogeneity test

[0075] As shown in Table 1, the porosity of the TC4 titanium alloy prepared by the method in Example 1 (0.4%) is reduced by 81.8% compared to the existing continuous laser group (2.2%), and the porosity of the GH4169 alloy prepared by the method in Example 2 (0.5%) is reduced by 80% compared to the existing continuous laser group (2.5%). This demonstrates that the present invention can enhance molten pool convection and eliminate bubbles. As shown in Table 2, the crack rate of the TC4 titanium alloy prepared by the method in Example 1 (0.6%) is reduced by 78.6% compared to the existing continuous laser group (2.8%), demonstrating that the preparation method of the present invention can effectively alleviate thermal stress concentration. As shown in Table 3, the Ti element fluctuation in the TC4 titanium alloy prepared by the method in Example 1 is ±5.2%, while the Ti element fluctuation in the TC4 titanium alloy prepared by the method in Example 1 of the present invention is ±1.5%. This demonstrates that the present invention preferably avoids component segregation caused by uneven flow velocity and completely solves the problem of uncontrolled molten pool flow.

[0076] 2. Interlayer bonding performance test The thickness of the interlayer oxide layer in the samples prepared by the above three methods was tested using SEM cross-sectional observation (according to GB / T 6462-2005), and the results are shown in Table 4: Table 4. Test results of interlayer oxide layer thickness

[0077] The interlayer surface roughness of the samples prepared by the above three methods was tested using a stylus-type roughness tester (according to GB / T 3505-2009), and the results are shown in Table 5: Table 5. Results of interlayer surface roughness test

[0078] The interlaminar tensile strength and interlaminar shear strength of the samples prepared by the above three methods were tested (interlaminar tensile strength according to GB / T 35465.2-2017, interlaminar shear strength according to GB / T 35465.3-2017), and the results are shown in Table 6: Table 6. Test results of interlaminar tensile strength and interlaminar shear strength

[0079] As shown in Tables 4-6, compared with existing preparation methods, the thickness of the interlayer oxide layer in the preparation method of the present invention is reduced from 7-10 nm to 1.5-1.8 nm, and the roughness is reduced from 3.2-4.2 μm to 1.2-1.4 μm. It can be seen that the preparation method of the present invention can effectively remove the oxide layer and reduce the roughness. In terms of interlayer tensile strength, TC4 titanium alloy is increased from 920 MPa to 1120 MPa, and GH4169 alloy is increased from 880 MPa to 1080 MPa. The strength gap with forgings is reduced from 22%-32% to 8%-10%. This shows that the preparation method of the present invention strengthens the interlayer fusion, completely breaks through the bottleneck of weak interlayer bonding, and makes the mechanical properties of the component close to the level of forgings, meeting the stringent requirements of high-end equipment for interlayer performance. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow, characterized in that, Includes the following steps: Substrate preparation: Select a substrate corresponding to the target metal component and pre-treat the substrate; Powder spreading: The pretreated substrate is fixed on the worktable of the additive manufacturing equipment, and metal powder of the same material as the substrate is selected and spread on the surface of the substrate using a powder spreading device; Additive manufacturing: A preset laser scanning path is used to perform pulsed laser scanning and ultrasonic vibration processing on the metal powder to form a molten pool. During this process, the parameters of pulsed laser scanning and ultrasonic vibration processing are adjusted according to different stages of the molten pool until the single-layer additive manufacturing is completed. Remelting: The single-layer additive is remelted using a pulsed laser and then cooled; Forming: Powder is spread on the surface of the remelted layer using a powder spreading device. The additive manufacturing and remelting steps are repeated to form a powder spreading-additive manufacturing-remelting cycle until the target metal component is formed. Post-processing: The formed metal component undergoes post-processing.

2. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 1, characterized in that, The preprocessing specifically includes: The substrate is placed in anhydrous ethanol for ultrasonic cleaning. After cleaning, the substrate is removed and its surface is polished. After polishing, the substrate is subjected to vacuum preheating treatment.

3. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 2, characterized in that, The ultrasonic cleaning frequency is 40kHz, and the cleaning time is 10-15 minutes; the vacuum degree of the vacuum preheating treatment is less than or equal to 5×10⁻⁶. -3 Pa, heat preservation time is 30-60 minutes.

4. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 3, characterized in that, The powder spreading speed is 10 mm / s, and the powder spreading thickness is 0.3 mm.

5. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 4, characterized in that, The additive manufacturing includes: Real-time acquisition of peak molten pool temperature, molten pool diameter, and molten pool flow velocity; With a pulse frequency of 50kHz and a speed of 400J / cm 2 The metal powder is subjected to pulsed laser scanning at an energy density of 1500 mm / s, while the metal powder is subjected to ultrasonic vibration at a frequency of 80 kHz. When the diameter of the molten pool is equal to 0.5 times the diameter of the laser spot, and the peak temperature of the molten pool is above 200°C (the melting point of the metal powder), the laser frequency of the pulsed laser scanning process is increased to 150 kHz, and the energy density is reduced to 250 J / cm². 2 The scanning speed is maintained at 1500 mm / s; When the molten pool flow velocity is between 8 mm / s and 12 mm / s, the molten pool diameter is between 1 and 1.5 times the laser spot diameter, and the peak temperature of the molten pool is between 50 and 200°C higher than the melting point of the metal powder, the laser frequency of the pulsed laser scanning process is increased to 300 kHz, and the energy density is reduced to 100 J / cm³. 2 The scanning speed is maintained at 1500 mm / s; When the preset scanning path is completed and the peak temperature of the molten pool is 50°C lower than the melting point of the metal powder, the flow velocity of the molten pool is less than or equal to 1 mm / s, and the diameter of the molten pool is 0.3 mm, the single-layer additive manufacturing is completed.

6. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 5, characterized in that, The remelting process specifically involves: pre-setting a laser scanning path, adjusting the frequency of the pulsed laser to 250kHz, and adjusting the energy density to 120J / cm². 2 The completed single-layer surface is then remelted.

7. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 6, characterized in that, The laser scanning path preset during remelting intersects the laser scanning path preset during additive manufacturing at a 90° angle, with a melting thickness of 5-10 μm, followed by cooling for 10 minutes after completion.

8. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 7, characterized in that, During the molding process, the average surface temperature is checked every 5 layers. If the temperature is less than 300°C, molding continues; if the temperature is greater than or equal to 300°C, the surface is allowed to cool naturally to 150°C before molding. Every 10 layers in a cycle, the difference between the actual height and the target height is measured, where the target height = number of cycles × 0.3 mm. When the difference is greater than 0.05, the thickness of the next layer of powder is adjusted.

9. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 8, characterized in that, The post-processing specifically involves: cooling the target metal component to room temperature, removing it, performing low-temperature aging treatment, and then separating and polishing the component.

10. The laser composite additive manufacturing method based on pulsed laser-controlled molten pool flow according to claim 9, characterized in that, Ar gas is continuously introduced at a flow rate of 15 L / min during the powder spreading, additive manufacturing, remelting, and forming stages.

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