A method for controlling the nanostructuring of interlayer structure based on additive manufacturing

Abstract

This invention provides a method for controlling interlayer nanostructural structure based on additive manufacturing, comprising the following steps: A) preheating the worktable; B) printing a single layer under ultrasonic assistance; C) using a surface nanostructuring device to nanostruct the surface of the printed single layer, while simultaneously using ultrasound to uniformly transfer vibration energy to the printed body to assist in interlayer nanostructuring; D) repeating steps B) and C) until printing is complete, obtaining the additive material. This invention uses ultrasonic-assisted molten pool forming and interlayer nanostructuring simultaneously, suppressing defects in real time and directly eliminating defects such as porosity, incomplete fusion, and internal tensile stress, without requiring additional post-processing. This invention uses high-frequency longitudinal wave ultrasound to induce dislocation slip and dynamic recrystallization, achieving surface nanostructuring of metals with poor plasticity; simultaneously, pre-setting compressive stress on the workpiece offsets the workpiece vulnerability caused by tensile stress in the molten pool.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and particularly relates to a method for controlling the nanostructuring of interlayer structures based on additive manufacturing. Background Technology

[0002] With the continuous development of manufacturing technology, additive manufacturing (3D printing) technology has been widely used in high-end manufacturing fields such as aerospace and automobiles. Its core advantages lie in the flexibility of manufacturing complex structures and the high material utilization rate. However, this technology still faces multiple technical bottlenecks in its industrialization process:

[0003] 1. Unstable dynamic forming quality

[0004] In additive manufacturing (3D printing), instantaneous energy fluctuations (±10% power deviation) in the laser / electron beam heat source can cause molten pool kinetic instability, leading to keyhole effects and defects such as pores in the components. Taking selective laser melting (SLM) of titanium alloy (Ti-6Al-4V) as an example, when the energy density exceeds the critical threshold (120 J / mm³), the vapor pressure inside the molten pool breaks through the surface tension limit, forming spherical pores with a diameter of 20-50 μm, reducing the fatigue life of the component by 40%-60%. Simultaneously, the layer-by-layer deposition characteristic results in interlayer bonding strength being only 70%-85% of that of the bulk material. Especially in arc-fused wire additive manufacturing of high-strength aluminum alloys (such as AlSi10Mg), the interlayer shear strength fluctuation reaches 15%, significantly affecting the reliability of load-bearing components.

[0005] 2. Stress-defect cross-scale coupling

[0006] The high cooling rate of 300-500℃ / ms during additive manufacturing can lead to severe thermal stress accumulation. For example, the residual tensile stress inside an Inconel 718 component formed by SLM can reach 350MPa. Although the tensile stress at a depth of 50μm on the surface can be reduced to below 50MPa by traditional hot isostatic pressing (HIP) post-processing, the core of the component still reaches 200MPa, becoming a source of fatigue crack initiation. More seriously, dendritic segregation during the solidification of the molten metal pool can form micron-level unfused defects. For example, CT scans of a certain type of aircraft bracket showed an internal porosity of 0.12vol%, which is more than 10 times worse than the forging standard (<0.01vol%).

[0007] 3. Severe lack of process synergy.

[0008] In the current technical approach, printing and post-processing are independent processes, that is, a serial process in which the component is printed and then processed. The main problems of this process are: (1) It is difficult to eliminate internal defects in the component after printing and post-processing, so there are many internal defects and large residual stress in the product; (2) Offline processing cannot intervene in the dynamics of the molten pool in real time, so the unfused defects at a depth of 50-200μm below the surface cannot be repaired. For example, the service life of a certain aerospace gearbox component is only 65% ​​of the design value due to internal defects; (3) It is inefficient and easy to introduce secondary defects.

[0009] 4. Lack of effective technologies to improve the performance of additively manufactured parts.

[0010] Currently, ultrasonic-assisted methods are mainly used to improve the performance of additively manufactured components, but this method has significant limitations. Taking ultrasonic-assisted rolling as an example, when ultrasonic waves are used as a power source to process metal materials with poor plasticity, the poor ductility of the material and the severe plastic deformation can easily cause micro-cracks or even macroscopic peeling (powdering) on ​​the surface, which cannot improve the core performance of the component. Existing ultrasonic-assisted technologies are unable to overcome the limitations of the intrinsic properties of materials.

[0011] Furthermore, the matching of additive manufacturing process parameters with post-processing parameters also relies heavily on experience based on trial and error. For example, to determine the optimal energy density window (80-100 J / mm³) for titanium alloy SLM forming, more than 200 sets of orthogonal experiments need to be conducted, with a single parameter verification cycle of up to 72 hours, resulting in long project development cycles and high costs. Summary of the Invention

[0012] The purpose of this invention is to provide a method for controlling the nanostructuring of interlayer structures based on additive manufacturing. The method in this invention has a precise control mode, high integration, and few internal defects.

[0013] This invention provides a method for controlling the nanostructuring of interlayer structures based on additive manufacturing, comprising the following steps:

[0014] A) Preheat the workbench;

[0015] B) Printing a single layer under ultrasound assistance;

[0016] C) A surface nano-sizing device is used to nano-size the printed single layer, and ultrasound is used to uniformly transfer vibration energy to the printed body to assist in interlayer nano-sizing.

[0017] D) Repeat steps B) and C) until printing is complete, resulting in additive manufacturing.

[0018] Preferably, in step B), during the printing of a single layer, the ultrasonic frequency f w Power P w and time t wCalculated according to equations I through III:

[0019] Formula I;

[0020] In formula I, P represents the surface tension of molten metal, expressed in N / m. cav The cavitation threshold pressure is expressed in Pa, and ρ represents the density of the molten metal in kg / m³. 3 c represents the speed of sound in the melt, in m / s, η energy Represents ultrasonic energy transfer efficiency, expressed in % %.

[0021] Formula II;

[0022] In Equation II, μ represents the dynamic viscosity of the melt, with units of Pa·s and v flow Represents the velocity of sound stream, measured in m / s, A. melt Represents the cross-sectional area of ​​the molten pool, in meters (m). 2 η mech P represents mechanical energy conversion efficiency, expressed as a percentage (%). laser This represents laser power, measured in W.

[0023] Formula III;

[0024] In Equation III, δ layer Represents the length of a single layer of printing, in meters (m). scan Represents printing speed in m / s, d melt Represents the depth of the molten pool, in meters (m), α thermal The thermal diffusivity m of the melt 2 / s.

[0025] Preferably, in step C), during the ultrasound-assisted interlayer nanostructuring process, the frequency f of the ultrasound is... s Power P s and time t s Calculated according to equations IV through VI:

[0026] Formula IV;

[0027] In Equation IV, Represents the critical strain rate, with units of s. -1 c is the speed of sound, in m / s, d initial Represents the initial grain size, in meters (m), σ y The value represents the yield strength in MPa, Q represents the activation energy in J, R represents the gas constant with a value of 8.314 J / (mol·K), T represents the treatment temperature in °C, and exp(Q / RT) is dimensionless.

[0028] Formula V;

[0029] In formula V, ρ represents the density of the solid metal, with units of kg / m³. 3 f represents the ultrasonic frequency, measured in Hz, and A. mp The vibration pair value is represented in meters (m), A represents the machining actuator dimension in meters (m), δ represents the preset nanolayer depth in meters (m), and η represents the energy conversion efficiency in percentage (%).

[0030] Formula VI;

[0031] In equation VI, δ layer Represents the total length of a single-layer print, in meters (m). smart This represents the surface treatment speed, measured in m / s.

[0032] Preferably, the preheating temperature of the workbench is 200~400℃;

[0033] An ultrasonic generator is installed below the workbench.

[0034] Preferably, the ultrasonic generator applies vibration to the molten pool via an amplitude transformer.

[0035] The ultrasonic generator transmits vibration energy evenly to the printed body through a transducer.

[0036] Preferably, during the single-layer printing process, the laser power is 0~2000W, the spot diameter is 0~5mm, the scanning speed is 0~500mm / s, and the scanning line distance is 0~2mm.

[0037] Preferably, during the single-layer printing process, the temperature field distribution of the molten pool is monitored by the molten pool monitoring module. When local overheating of the molten pool is detected, the ultrasonic power is reduced by 10-20%. When the temperature of the printed body drops to 10-20% of the melting point temperature, interlayer nano-sizing is performed.

[0038] Preferably, when the temperature is greater than 1.2 times the melting point of the additive material, it is judged as local overheating, and the ultrasonic power is reduced by 10-20%.

[0039] Preferably, the pressure for surface nanoforming is 200~500MPa, the moving speed is 100~5000 mm / min, and the spacing is 0~1mm.

[0040] Preferably, after step C), residual stress and grain size detection are also included. If the detection fails, the unqualified area is subjected to ultrasonic-assisted interlayer nano-sizing again.

[0041] This invention provides a method for controlling interlayer nanostructural structure based on additive manufacturing, comprising the following steps: A) preheating the worktable; B) printing a single layer under ultrasonic assistance; C) using a surface nanostructuring device to perform surface nanostructuring on the printed single layer, while simultaneously using ultrasound to uniformly transfer vibration energy to the printed body to assist in interlayer nanostructuring; D) repeating steps B) and C) until printing is completed to obtain additive manufacturing.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] (1) This invention establishes a composite process method that combines additive manufacturing and nano-control, and quantitatively correlates ultrasonic parameters with material physics, mechanics and process conditions, upgrading from "experience-driven" to a precise control mode of "theoretical guidance + data verification".

[0044] (2) The present invention uses ultrasonic-assisted molten pool forming and interlayer nanoforming to suppress defects in real time and directly eliminate defects such as porosity, lack of fusion, and internal tensile stress without additional post-processing.

[0045] (3) The present invention uses high-frequency longitudinal wave ultrasonic waves to induce dislocation slip and dynamic recrystallization, thereby realizing the surface nano-sizing of metals with poor plasticity; at the same time, the pre-set compressive stress of the workpiece offsets the workpiece damage caused by the tensile stress of the molten pool.

[0046] (4) After processing by the device and method of the present invention, the mechanical properties of the material, including surface hardness, wear resistance, corrosion resistance and fatigue resistance, are greatly improved, the material utilization rate is increased, and the overall cost is greatly reduced.

[0047] (5) This invention integrates additive manufacturing with nanotechnology, and improves efficiency by more than 50% through a cyclical pattern of layer-by-layer printing and layer-by-layer nanotechnology. At the same time, it eliminates the post-processing separation and connection losses of traditional multi-step processes (printing-stress relief-post-processing) and avoids secondary defects caused by workpiece handling. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the device structure used in the additive manufacturing-based interlayer nanostructural control method of the present invention.

[0050] Figure 1In the diagram, 1 is the molten pool monitoring module, 2 is the surface nano-sizing device, 3 is the residual stress and grain size detection device, 4 is the 3D printing device, 5 is the ultrasonic generator, and 6 is the worktable.

[0051] Figure 2 This is a flowchart illustrating the operation of the interlayer nanostructuring control method based on additive manufacturing according to the present invention. Detailed Implementation

[0052] This invention provides a method for controlling the nanostructuring of interlayer structures based on additive manufacturing, comprising the following steps:

[0053] A) Preheat the workbench;

[0054] B) Printing a single layer under ultrasound assistance;

[0055] C) A surface nano-sizing device is used to nano-size the printed single layer, and ultrasound is used to uniformly transfer vibration energy to the printed body to assist in interlayer nano-sizing.

[0056] D) Repeat steps B) and C) until printing is complete, resulting in additive manufacturing.

[0057] In this invention, the worktable is the core load-bearing and energy transfer platform of the metal forming device. Its main body is composed of a 20-30mm thick titanium alloy substrate and a 0.5-1mm thick zirconia ceramic heat-insulating coating, combining high rigidity and resistance to thermal deformation. A heating device is installed at its bottom to preheat the worktable before 3D printing, preventing a decrease in internal stress of the printed layer due to excessive temperature differences during the printing process.

[0058] In this invention, the preheating temperature of the workbench is preferably 200~400℃, more preferably 250~350℃, such as 200℃, 250℃, 300℃, 350℃, 400℃, and preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0059] After the worktable is preheated, the present invention performs layer-by-layer printing with the assistance of ultrasound to obtain additive material.

[0060] In this invention, an ultrasonic generator is installed below the worktable. The main function of the ultrasonic generator is to optimize the quality of the molten pool during 3D printing and assist in interlayer nanostructuring, while also increasing the plasticity of the metal. It is installed below the worktable and consists of an array of nine piezoelectric ceramic transducers. Phase synchronization control is used to ensure uniform transmission of vibration energy to the workpiece.

[0061] In this invention, the printing of each layer includes ultrasonic-assisted printing of a single layer and ultrasonic-assisted interlayer nano-sizing.

[0062] In this invention, the ultrasonic-assisted single-layer printing is performed using a 3D printing device located on one side of the worktable, such as at the 9 o'clock position. This 3D printing device is responsible for the layer-by-layer cladding of metal materials and consists of a robotic arm, a high-power fiber laser (1070nm wavelength, adjustable from 300 to 2000W), and a four-channel coaxial powder feeding system. The robotic arm is responsible for moving the laser and powder feeding device during the single-layer printing process, while the laser and coaxial powder feeding system are responsible for the printing itself.

[0063] In the ultrasound-assisted single-layer printing process, the laser power is preferably 0~2000W, more preferably 50~1000W, such as 10 W, 50 W, 100 W, 200 W, 300 W, 400 W, 500 W, 600 W, 700 W, 800 W, 900 W, 1000 W, preferably within the range of any of the above values ​​as the upper or lower limit; the spot diameter is preferably 0~5 mm, more preferably 1~5 mm, such as 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, preferably within the range of any of the above values ​​as the upper or lower limit; the scanning speed is preferably 0~500 mm / s, more preferably 50~400 mm / s, such as 10 mm / s, 50 mm / s, 100 mm / s, 150 mm / s, 200 mm / s, 250 mm / s, 300 mm / s, 350 mm / s, 400 mm / s, 450 mm / s, 500 mm / s, etc. mm / s, preferably a range of values ​​with any of the above values ​​as the upper or lower limit; the scan line distance is preferably 0~2mm, more preferably 0.5~2mm, such as 0.5 mm, 1 mm, 1.5 mm, 2 mm, preferably a range of values ​​with any of the above values ​​as the upper or lower limit.

[0064] During the ultrasonic-assisted printing of a single layer, the ultrasonic generator is turned on to apply vibration to the molten pool through the amplitude transformer. The cavitation effect and acoustic flow effect are used to promote the flow of molten metal, break up bubbles in the molten pool, eliminate incomplete fusion defects, and reduce porosity.

[0065] The frequency f of ultrasound w Power P w and time t w Calculated according to equations I through III:

[0066] Formula I;

[0067] In formula I, P represents the surface tension of molten metal, expressed in N / m. cav The cavitation threshold pressure is expressed in Pa, and ρ represents the density of the molten metal in kg / m³. 3 c represents the speed of sound in the melt, in m / s, η energyRepresents ultrasonic energy transfer efficiency, expressed in % %.

[0068] Formula II;

[0069] In Equation II, μ represents the dynamic viscosity of the melt, with units of Pa·s and v flow Represents the velocity of sound stream, measured in m / s, A. melt Represents the cross-sectional area of ​​the molten pool, in meters (m). 2 η mech Represents mechanical energy conversion efficiency, expressed in % (P). laser This represents laser power, measured in W.

[0070] Formula III;

[0071] In Equation III, δ layer v represents the length of a single layer of printing. scan Represents printing speed, d melt Represents the depth of the molten pool, α thermal This represents the thermal diffusivity of the melt.

[0072] The initial parameter frequency f is calculated and set according to equations I to III. w Power P w and time t w The waveform is a longitudinal wave. The additive manufacturing equipment is turned on, and the first layer is printed according to the product shape.

[0073] During the additive manufacturing process, the temperature field distribution is monitored by the molten pool monitoring module, which adjusts the ultrasonic power during the printing process and provides a basis for the start time of surface nano-sizing.

[0074] By dynamically adjusting the transducer below the worktable to compensate for energy distribution, if local overheating is detected (>1.2 times the material melting point), the ultrasonic power is reduced by 10%~20%. At the same time, when the temperature of the printed body drops to 15% of the melting point temperature, surface nano-sizing is performed.

[0075] After completing single-layer printing, a surface nano-sizing device is used to nano-scale the surface of the printed layer. At the same time, the parameters of the ultrasonic generator need to be switched to uniformly transmit the vibration energy of the ultrasonic to the printed body for interlayer nano-sizing. At this time, the function of the ultrasonic becomes to provide energy for activating dislocation sources and improve the plastic deformation capacity of the metal.

[0076] In this invention, the surface nanostructuring device is located on the other side of the worktable, such as at the 3 o'clock position. Its function is to nanostruct the metal surface. The surface nanostructuring method is not limited to surface mechanical grinding, surface mechanical rolling, surface mechanical pressing, ultrasonic rolling, and laser shock blasting. It achieves grain nanostructuring and pre-setting compressive stress. It consists of a robotic arm, a processing execution end, and a pressure generating device. The robotic arm is responsible for moving the surface nanostructuring device. The processing execution end processes the workpiece after additive manufacturing. The pressure generating device provides processing force to the processing execution end. As the robotic arm moves, the processing execution end processes the workpiece. During the surface nanostructuring process, the robotic arm drives the surface nanostructuring device to move along the printing path. The pressure generated by the pressure generating device provides pressure to the processing execution end, causing plastic deformation of the printed surface layer to form a gradient nanostructure. At the same time, the surface compressive stress is pre-set (the compressive stress is the residual surface compressive stress, ranging from 200 to 1500 MPa) to offset the tensile stress concentration caused by the thermal stress of 3D printing.

[0077] In this invention, during the interlayer nanostructuring process, the frequency f of the ultrasound is... s Power P s and time t s Calculated according to equations IV through VI:

[0078] Formula IV;

[0079] In Equation IV, Represents the critical strain rate, with units of s. -1 c is the speed of sound, in m / s, d initial Represents the initial grain size, in meters (m), σ y The value represents the yield strength in MPa, Q represents the activation energy in J, R represents the gas constant with a value of 8.314 J / (mol·K), T represents the treatment temperature in °C, and exp(Q / RT) is dimensionless.

[0080] Formula V;

[0081] In formula V, ρ represents the density of the solid metal, with units of kg / m³. 3 f represents the ultrasonic frequency, measured in Hz, and A. mp The vibration pair value is represented in meters (m), A represents the machining actuator dimension in meters (m), δ represents the preset nanolayer depth in meters (m), and η represents the energy conversion efficiency in percentage (%).

[0082] Formula VI;

[0083] In equation VI, δ layer Represents the total length of a single-layer print, in meters (m). smart This represents the surface treatment speed, measured in m / s.

[0084] In this invention, the pressure for surface nanoforming is preferably 200-500 MPa, more preferably 300-400 MPa, such as 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, and preferably a range where any of the above values ​​is the upper or lower limit; the moving speed is preferably 100-5000 mm / min, more preferably 500-4000 mm / min, such as 100 mm / min, 200 mm / min, 300 mm / min, 400 mm / min, 500 mm / min, 600 mm / min, 700 mm / min, 800 mm / min, 900 mm / min, 1000 mm / min, 1500 mm / min, 2000 mm / min, 2500 mm / min, 3000 mm / min, 3500 mm / min, 4000 mm / min, 4500 mm / min. The speed is 5000 mm / min, preferably within the range of any of the above values ​​as the upper or lower limit; the spacing is preferably 0~1 mm, more preferably 0.5~1 mm.

[0085] After surface nano-sizing is completed, the present invention preferably uses an X-ray residual stress and grain size detection module to detect the surface residual stress and grain size. The X-ray residual stress and grain size detection module detects the grain size and stress state and is located on the other side of the gradient nano-sizing arm. After gradient nano-sizing, the system switches to the residual stress and grain size module. If the compressive stress or grain size does not reach the threshold (grain size less than 500 nm, residual compressive stress exceeding 200 MPa), the printed surface is subjected to surface nano-sizing treatment again until the compressive stress and grain size reach the threshold.

[0086] Repeat the above process of ultrasonic-assisted printing of single layers, ultrasonic-assisted interlayer nano-sizing, and residual stress and grain size detection, and print layer by layer until the additive manufacturing is completed.

[0087] This invention provides a method for controlling interlayer nanostructural structure based on additive manufacturing, comprising the following steps: A) preheating the worktable; B) printing a single layer under ultrasonic assistance; C) using a surface nanostructuring device to perform surface nanostructuring on the printed single layer, while simultaneously using ultrasound to uniformly transfer vibration energy to the printed body to assist in interlayer nanostructuring; D) repeating steps B) and C) until printing is completed to obtain additive manufacturing.

[0088] Compared with the prior art, the present invention has the following advantages:

[0089] (1) This invention establishes a composite process method based on the interlayer nano-control of additive manufacturing, which quantitatively correlates ultrasonic parameters with material physics, mechanics and process conditions, upgrading from "experience-driven" to a precise control mode of "theoretical guidance + data verification".

[0090] (2) The present invention uses ultrasonic-assisted molten pool forming and interlayer nanoforming to suppress defects in real time and directly eliminate defects such as porosity, lack of fusion, and internal tensile stress without additional post-processing.

[0091] (3) The present invention uses high-frequency longitudinal wave ultrasonic waves to induce dislocation slip and dynamic recrystallization, thereby realizing the surface nano-sizing of metals with poor plasticity; compressive stress is generated in the workpiece, which offsets the workpiece's vulnerability caused by the tensile stress of the molten pool.

[0092] (4) After processing by the device and method of the present invention, the mechanical properties of the material, including surface hardness, wear resistance, corrosion resistance and fatigue resistance, are greatly improved, the material utilization rate is increased, and the overall cost is greatly reduced.

[0093] (5) This invention integrates additive manufacturing with nanotechnology, and improves efficiency by more than 50% through a cyclical pattern of layer-by-layer printing and layer-by-layer nanotechnology. At the same time, it eliminates the post-processing separation and connection losses of traditional multi-step processes (printing-stress relief-post-processing) and avoids secondary defects caused by workpiece handling.

[0094] To further illustrate the present invention, the following detailed description of an additive manufacturing-based method for controlling the nanostructure of interlayer structures is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0095] Example 1

[0096] According to the design, the total print length is 100mm, with a gauge length of 60mm and a width of 30mm (i.e., each layer consists of 30 print layers, each 1mm wide and 60mm long). layer A dumbbell-shaped Ti-6Al-4V sample (60mm × 30mm) with a thickness of 5mm was prepared, with clamping ends 10mm wide. A laser coaxial powder feeding device was used, and the printing powder was Ti-6Al-4V spherical powder (particle size 15~53μm, oxygen content ≤0.13%).

[0097] 1. Preheat the worktable to 300℃ and maintain the temperature for 15 minutes to reduce thermal stress; the scanning path adopts a checkerboard filling strategy to reduce anisotropy.

[0098] 2. Obtain the basic material parameters: density (ρ) = 4430 kg / m³, c = 4270 m / s, melting point (Tm) = 1660℃, solid velocity of sound (c_solid) = 6100 m / s, melt velocity of sound (c) = 0.7 × 6100 = 4270 m / s, surface tension (σ) = 1.6 N / m, dynamic viscosity (μ) = 4.2 c × 10 -3 Pa·s, thermal diffusivity (α_thermal) = 8.6 mm² / s, activation energy (Q) = 240 kJ / mol (typical value for titanium alloy), yield strength (σ_y) = 850 MPa; v flow =0.8 m / s, molten pool cross-sectional area A melt =0.5 ×10 -6 m 2 Mechanical energy conversion efficiency η mech =0.7, allowable temperature rise ΔT=25℃, specific heat capacity Cp=526. η energy =0.7, cross-sectional area of ​​the molten pool A melt =0.5 mm 2 The heat input Q generated by ultrasonic vibration heat =500J / s, molten pool depth d melt =250·10 -6 m, printing speed v scan =16mm / s

[0099] Calculate ultrasonic parameters and frequencies during the additive manufacturing stage. and power The frequencies were 21.5 kHz and 551.6 W, respectively, with durations of action of [missing information]. The printing time is 113 seconds per layer. Ultrasonic-assisted additive manufacturing printing parameters: laser power 1000W, spot diameter 0.5mm, layer-by-layer stacking (25 layers in total, total height 5mm);

[0100] P cav ≈3.2×10 6 Pa.

[0101]

[0102]

[0103]

[0104] 4. Melt pool monitoring module detection: The infrared thermal imager monitors the temperature in real time. When the local temperature exceeds 1660℃, the laser power is reduced to 800W; when the temperature drops to 300℃, the interlayer nano-processing begins.

[0105] 5. Ultrasonic generator switching parameters: frequency switched to 151kHz, power increased to 2059W, action time approximately 187.5 seconds / layer;

[0106] Initial grain size d grain =50 μm, critical strain rate =103 s -1 Material constant K=0.05, processing temperature T=300℃, Amp=15 μm, processing area A=1 mm 2 The preset nanolayer depth δ=300 μm, energy conversion efficiency η=0.5, and surface treatment speed v smart =25mm / s, processing width is 0.4mm / pass.

[0107]

[0108]

[0109]

[0110] 6. Interlayer surface nano-sizing: The processing end is gradient nano-sized along the sample length direction (pressure 400N, moving speed 1500mm / min, spacing 0.4mm).

[0111] 7. Residual stress and grain size detection: The surface grains are refined to 150nm, the compressive stress layer depth is 300μm, and the residual compressive stress is -280MPa, which exceeds the residual compressive stress threshold of 200MPa. The residual stress and grain size detection are qualified.

[0112] 8. Repeat steps 3-6 above until the workpiece is completed.

[0113] The test data of the treated titanium alloy tensile specimens are as follows:

[0114] Table 1. Test data of titanium alloy tensile specimens after treatment in Example 1

[0115]

[0116] Example 2

[0117] Printing of aluminum alloy AlSi10Mg structural parts (wall thickness 80mm, height 80mm, width 80mm) using a laser coaxial powder feeding device, with AlSi10Mg spherical powder as the printing powder.

[0118] 1. Preheat the workbench to 250℃ and maintain the temperature for 20 minutes to reduce thermal stress;

[0119] 2. Obtain basic material parameters and calculate ultrasonic parameters for the additive manufacturing stage:

[0120] The laser power was set to 800W, the powder density and acoustic velocity v_flow = 0.8 m / s, the molten pool cross-sectional area A_melt = 0.5 mm², and η_mech = 0.7.

[0121] Powder density (ρ) = 2.68 g / cm³;

[0122] Melting point (Tm) = 570℃;

[0123] The velocity of sound in solid state (c_solid) = 5100 m / s → the velocity of sound in melt (c_melt) = 0.7 × 5100 = 3570 m / s;

[0124] Dynamic viscosity (μ) = 3.5 mPa·s;

[0125] Thermal diffusivity (α_thermal) = 50 mm² / s;

[0126] Surface tension (σ) = 0.85 N / m;

[0127] Specific heat capacity Cp = 1230

[0128] ηenergy=0.6

[0129] Heat input Q generated by ultrasonic vibration heat =800J / s

[0130] Molten pool depth d melt =0.2mm

[0131] Printing speed v scan =16mm / s

[0132] P cav ≈2.4 MPa

[0133]

[0134]

[0135]

[0136] 3. Ultrasonic-assisted additive manufacturing: 800W laser power, 0.4mm spot diameter, layer-by-layer stacking;

[0137] 4. Melt pool monitoring module detection: Infrared thermal imager monitors the temperature in real time. When the temperature drops to 300℃, interlayer nano-processing begins.

[0138] 5. Ultrasonic generator switching parameters: frequency switched to 81kHz, power increased to 1800W, action time approximately 6.6 seconds / layer;

[0139] Initial grain size d_grain = 50 μm, critical strain rate ε̇_critical = 10³ s -1 σ_y=200 MPa, Q=140 kJ / mol, T=200℃, amplitude Amp=10 μm, actuator end size A=1 mm², preset layer depth δ=250 μm, η=0.5. Processing speed 1800 mm / min, processing width 0.4 mm / pass.

[0140]

[0141]

[0142]

[0143] 6. Interlayer surface nano-sizing: The processing end is gradient nano-sized along the sample length direction (pressure 400N, moving speed 1500mm / min, spacing 0.4mm).

[0144] 7. Residual stress and grain size detection: The surface grains are refined to 200nm, the compressive stress layer depth is 300μm, the residual compressive stress is -320MPa, and the residual stress and grain size detection are qualified.

[0145] 8. Repeat steps 3-6 above until the workpiece is completed.

[0146] Comparative Example 1: Traditional 3D Printing Post-Processing via Ultrasonic Rolling

[0147] According to the design, a dumbbell-shaped Ti-6Al-4V sample with a total length of 100mm, a gauge length of 60mm, a width of 30mm, and a thickness of 5mm was printed, with clamping ends of 10mm width at both ends. A laser coaxial powder feeding device was used, and the printing powder was Ti-6Al-4V spherical powder (particle size 15~53μm, oxygen content ≤0.13%, density ρ=4.43 g / cm³).

[0148] 1. Preheat the worktable to 300℃ and maintain the temperature for 15 minutes to reduce thermal stress; the scanning path adopts a checkerboard filling strategy to reduce anisotropy.

[0149] 2. Printing parameters: laser power 1000W, spot diameter 0.5mm, layer by layer stacking (25 layers in total, total height 5mm).

[0150] 3. Molten pool monitoring module detection: The infrared thermal imager monitors the temperature in real time. When the local temperature exceeds 1660℃, the laser power is reduced to 800W; when the temperature drops to 300℃, the surface nano-processing begins.

[0151] 4. Surface nano-sizing: The processing end is gradient nano-sized along the length of the sample (pressure 400N, moving speed 1500mm / min, spacing 0.4mm).

[0152] 5. Repeat steps 2 to 4 above until the workpiece is completed.

[0153] The difference between Comparative Example 1 and Example 1 is that there is no ultrasonic assistance during the workpiece printing process, and in the surface nano-sizing step, ultrasound is only used as a power source to drive the surface nano-sizing device.

[0154] result:

[0155] 1. Due to the elimination of ultrasonic assistance, a large amount of residual compressive stress and micropores remain after the laser printing process.

[0156] 2. A large number of pores collapsed during the rolling process;

[0157] 3. Without ultrasonic optimization of plasticity, cracks and powdering occur during the ultrasonic rolling process on the surface.

[0158] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the nanostructuring of interlayer microstructure based on additive manufacturing, comprising the following steps: A) Preheat the workbench; B) Printing a single layer under ultrasound assistance; During the single-layer printing process in step B), the frequency of ultrasound... f w ,power P w and time t w Calculated according to equations I through III: Formula I; In formula I, ρ represents the surface tension of the molten metal, in N / m; Pcav is the cavitation threshold pressure, in Pa; ρ represents the density of the molten metal, in kg / m³. 3 c represents the speed of sound in the melt, in m / s, η energy Represents ultrasonic energy transfer efficiency, expressed in % %. Formula II; In Equation II, μ represents the dynamic viscosity of the melt, with units of Pa·s, and v flow Represents the velocity of sound stream, measured in m / s, A. melt Represents the cross-sectional area of ​​the molten pool, in meters (m). 2 η mech Represents mechanical energy conversion efficiency, expressed in % (P). laser Represents laser power, measured in W; Formula III; In Equation III, δ layer This represents the length of a single layer of printing, in meters. v scan Represents printing speed in m / s. d melt Represents the depth of the molten pool, in meters (m). α thermal The thermal diffusivity m of the melt 2 / s; C) A surface nano-sizing device is used to nano-size the printed single layer, and ultrasound is used to uniformly transfer vibration energy to the printed body to assist in interlayer nano-sizing. D) Repeat steps B) and C) until printing is complete, resulting in additive manufacturing.

2. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 1, characterized in that, In step C), during the ultrasound-assisted interlayer nanostructuring process, the frequency of the ultrasound... f s ,power P s and time t s Calculated according to equations IV through VI: Formula IV; In Equation IV, denoted by σc, representing the critical strain rate in s-1; c represents the speed of sound in m / s; dinitial represents the initial grain size in m; σy represents the yield strength in MPa; Q represents the activation energy in J; R represents the gas constant, with a value of 8.314 J / (mol•K); T represents the processing temperature in °C; and exp(Q / RT) is dimensionless. Formula V; In formula V, ρ represents the density of the solid metal, with units of kg / m³. 3 f represents the ultrasonic frequency, measured in Hz, and A. mp The vibration pair value is represented in meters (m), A represents the machining actuator dimension in meters (m), δ represents the preset nanolayer depth in meters (m), and η represents the energy conversion efficiency in percentage (%). Formula VI; In Equation VI, δ layer This represents the total length of a single-layer print, in meters. v smart This represents the surface treatment speed, measured in m / s.

3. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 1, characterized in that, The preheating temperature of the workbench is 200~400℃; An ultrasonic generator is installed below the workbench.

4. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 3, characterized in that, The ultrasonic generator applies vibration to the molten pool via an amplitude transformer. The ultrasonic generator transmits vibration energy evenly to the printed body through a transducer.

5. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 1, characterized in that, During the single-layer printing process, the laser power is 0~2000W, the spot diameter is 0~5mm, the scanning speed is 0~500mm / s, and the scanning line distance is 0~2mm.

6. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 1, characterized in that, During the single-layer printing process, the temperature field distribution of the molten pool is monitored by the molten pool monitoring module. When local overheating of the molten pool is detected, the ultrasonic power is reduced by 10-20%. When the temperature of the printed body drops to 10-20% of the melting point temperature, interlayer nano-sizing is performed.

7. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 6, characterized in that, When the temperature exceeds 1.2 times the melting point of the additive material, it is judged as local overheating, and the ultrasonic power is reduced by 10-20%.

8. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 1, characterized in that, The pressure for surface nanoforming is 200~500MPa, the moving speed is 100~5000 mm / min, and the spacing is 0~1mm.

9. The method for controlling the nanostructuring of interlayer structure based on additive manufacturing according to claim 1, characterized in that, After step C), residual stress and grain size detection are also included. If the detection fails, ultrasonic-assisted interlayer nano-sizing is performed again on the unqualified area.

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