Apparatus and method for controlling residual stress in a laser additive manufacturing process

Abstract

The present application relates to the field of metal component additive manufacturing, and particularly relates to a residual stress control device and method in a laser additive manufacturing process.The device comprises a laser, a powder feeder, a laser head module and a water-cooled copper plate, the laser head module is communicated with the powder feeder through a powder feeding pipe, the lower end of the laser head module is installed with a laser head, the laser head module is communicated with the laser head through the powder feeding pipe, the laser generated by the laser passes through the laser head module and the laser head vertically, and the water-cooled copper plate is located below the laser head.The alloy sample is manufactured by using different laser powers in different areas, the relationship between the internal residual stress of the alloy sample and the laser power is analyzed, the alloy finished product is produced in a manner that the laser power gradually decreases from the bottom to the top of the alloy according to the obtained relationship, the material below the deposited layer in the printing process will not produce obvious temperature gradient due to repeated heating and cooling, the residual stress in the final bulk alloy is obviously reduced, and the use performance of the material is improved.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing of metal components, and more specifically to a device and method for controlling residual stress during laser additive manufacturing. Background Technology

[0002] Laser additive manufacturing technology, as an emerging material preparation technology, has been widely used in manufacturing industries such as aerospace, automobile manufacturing, and medical devices. Its principle involves first using a computer to slice and process a three-dimensional workpiece model into digital information, then combining this with a suitable printing process and using a laser additive manufacturing printer to fabricate point by point, line by line, and layer by layer, ultimately obtaining large-sized, complex-shaped three-dimensional solid workpieces.

[0003] Due to the unique layer-by-layer manufacturing process of laser additive manufacturing, the workpiece undergoes repeated and rapid heating and cooling during processing, generating a large thermal gradient and leading to the accumulation of substantial residual stress within the workpiece. Significant residual stress can affect the workpiece's corrosion resistance and fatigue performance, and may even cause defects such as cracks and deformation, ultimately reducing workpiece quality and safety. During the printing process, different printing parameters and scanning paths can all influence the residual stress in the workpiece. Summary of the Invention

[0004] In order to overcome the technical problem in the prior art that the huge thermal gradient caused by repeated and rapid heating and cooling leads to the accumulation of a large amount of residual stress inside the workpiece, the present invention provides a device and method for controlling residual stress in the laser additive manufacturing process.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A device for controlling residual stress in laser additive manufacturing includes a laser 8, a powder feeder 7, a laser head module 6, and a water-cooled copper plate 1. The laser head module 6 is connected to the powder feeder 7 via a powder feeding pipe 5. A laser head 4 is installed at the lower end of the laser head module 6 and is connected to the laser head 4 via the powder feeding pipe 5. The laser emitted by the laser 8 passes vertically through the laser head module 6 and the laser head 4. The water-cooled copper plate 1 is located below the laser head 4 and has a substrate 2 on it.

[0007] The thickness of the substrate 2 is 30 mm.

[0008] A method for controlling residual stress during laser additive manufacturing, comprising the following steps using the aforementioned device for controlling residual stress during laser additive manufacturing:

[0009] S1. Using a residual stress control device during laser additive manufacturing, alloy samples are produced by using different laser powers on different printing layers;

[0010] S2. Perform residual stress analysis on the alloy sample to obtain the relationship between residual stress and corresponding laser power;

[0011] S3. Based on the relationship between the obtained residual stress and the laser power, the residual stress control device in the laser additive manufacturing process is re-set so that the laser power used by the residual stress control device in the production of the alloy changes regularly.

[0012] The number of printing layers in step S3 is 20, and each of the four adjacent layers uses the same laser power. The laser power distribution from bottom to top is 2300w, 2000w, 1700w, 1400w, and 1100w.

[0013] In the production process of the alloy sample in step S1, the laser beam diameter is 3mm, the scanning rate is 600mm / min, the powder feeding rate is 10 g / min, the layer height is 0.5mm, the overlap rate is 30%, and the oxygen content is less than 10 ppm.

[0014] Step S2, which involves residual stress analysis of the alloy sample, includes the following steps:

[0015] S2-1. Obtain X-ray diffraction data of the alloy sample using X-ray stress analyzer and X-ray diffraction technology;

[0016] S2-2. The residual stress inside the alloy sample is calculated using the sin2ψ method based on the obtained diffraction data. The calculation formula is as follows:

[0017]

[0018] In the formula, E is Young's modulus, υ is Poisson's ratio, ψ is the off-axis angle, and d ψ d is the lattice spacing of the diffraction plane under stress, and d0 is the lattice spacing of the diffraction plane under stress-free conditions.

[0019] S2-3. Convert the residual stress calculation results into a two-dimensional contour map.

[0020] In step S2-1, the X-ray stress analyzer operates at a voltage of 20 kV and a current of 40 mA. In step S2-2, E is 189 GPa and υ is 0.30.

[0021] Step S1 involves manufacturing alloy samples using CrMnFeCoNi alloy spherical powder, with a particle size of 45-105 μm.

[0022] The advantages of this invention compared to the prior art are:

[0023] By manufacturing alloy samples using varying laser powers in different regions, the relationship between residual stress within the alloy and laser power was analyzed. Based on this relationship, finished alloy products were produced. During the production process, the laser power used gradually decreased from the bottom to the top of the alloy. This prevented significant temperature gradients in the material below the deposition layer due to repeated heating and cooling during printing. The deposition layer did not generate substantial residual stress during cooling, resulting in a significant reduction in residual stress within the bulk alloy and improved material performance. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a residual stress control device in the laser additive manufacturing process according to the present invention.

[0025] Figure 2 This is a two-dimensional contour map obtained by the present invention based on the calculation results of residual stress.

[0026] In the diagram: 1. Water-cooled copper plate; 2. Substrate; 3. Workpiece; 4. Laser head; 5. Powder feeding tube; 6. Laser head module; 7. Powder feeder; 8. Laser. Detailed Implementation

[0027] like Figure 1 As shown, the present invention provides a residual stress control device in the laser additive manufacturing process, including a laser 8, a powder feeder 7, a laser head module 6, and a water-cooled copper plate 1. The laser head module 6 is connected to the powder feeder 7 through a powder feeding pipe 5. A laser head 4 is installed at the lower end of the laser head module 6, and the laser head module 6 is connected to the laser head 4 through the powder feeding pipe 5. The laser emitted by the laser 8 passes vertically through the laser head module 6 and the laser head 4. The water-cooled copper plate 1 is located below the laser head 4. A thick substrate 2 is provided on the water-cooled copper plate 1. The substrate 2 has a thickness of 30mm to prevent the substrate 2 from deforming and releasing stress, so as to retain residual stress to the maximum extent and ensure measurement results. The substrate 2 is made of 45 steel (AISI 1045) and has a size of 60*60*30mm. Before the experiment, it is polished with sandpaper of different grits to remove the surface oxide layer and cutting marks, so that its surface is smooth and flat. Laser head module 6 is used to adjust the laser focal length and laser spot diameter. Its size is 25*25*25 or 50*50*50mm. Laser head module 6 is a commonly used device in reality.

[0028] A method for controlling residual stress during laser additive manufacturing, comprising the following steps using the aforementioned device for controlling residual stress during laser additive manufacturing:

[0029] S1. Spherical CrMnFeCoNi alloy powder with a particle size of 45-105μm is loaded into the powder feeder 7. Using a residual stress control device, alloy sample workpiece 3 is produced by applying different laser powers to different printing layers. During the group experiments for producing alloy sample workpiece 3, all printing parameters except laser power are kept consistent: laser beam diameter 3mm, scanning rate 600mm / min, powder feed rate 10 g / min, layer height 0.5mm, overlap rate 30%, oxygen content less than 10 ppm, and scanning path: serpentine path layer-by-layer scanning. The dimensions of printed workpiece 3 are 40*40*10mm.

[0030] S2. Perform residual stress analysis on alloy sample workpiece 3 to obtain the relationship between residual stress and corresponding laser power; the residual stress analysis of the alloy sample includes the following steps:

[0031] S2-1. X-ray diffraction data of the alloy sample were obtained using X-ray stress analyzer (iXRD, Proto, Canada) with X-ray diffraction technology; the operating voltage of the X-ray stress analyzer was 20 kV and the current was 40 mA during operation.

[0032] S2-2. The (311) diffraction peak (2θ≈152.8°) was detected using a Mn-Ka radiation source. The residual stress inside the alloy sample was calculated using the sin2ψ method based on the obtained diffraction data. The calculation formula is as follows:

[0033]

[0034] In the formula, E is Young's modulus of 189 GPa, υ is Poisson's ratio of 0.30, ψ is the off-axis angle (i.e., the tilt angle between the sample normal and the bisector of the incident X-ray diffraction beam), and d is the angle between the sample normal and the incident X-ray diffraction beam. ψ d0 is the lattice spacing of the diffraction plane under stress (additive manufacturing) conditions, while d0 is the lattice spacing of the diffraction plane under stress-free conditions.

[0035] The top and bottom of the workpiece have residual tensile stress and residual compressive stress, respectively, with the residual stress being the largest at 1400W. Subsequently, the higher the laser power, the smaller and more uniform the residual stress becomes.

[0036] S2-3. Measure and record residual stress data on the BD×SD plane, and use Origin software to convert the residual stress calculation results into a two-dimensional contour map, such as... Figure 2 As shown.

[0037] S3. Based on the obtained relationship between residual stress and laser power, the residual stress control device in the laser additive manufacturing process is redesigned, and the alloy product is manufactured. During the alloy product manufacturing process, the laser power used for alloy production varies systematically. The optimal choice is 20 printing layers, with every four adjacent layers using the same laser power, distributed from bottom to top as 2300W, 2000W, 1700W, 1400W, and 1100W. Alternatively, other methods can be used, such as every five adjacent layers using the same laser power, distributed from bottom to top as 2300W, 1900W, 1500W, and 1100W. By changing the laser power, the residual stress of the bulk CrMnFeCoNi alloy is controlled; the laser power decreases systematically from bottom to top, preventing a significant temperature gradient in the material below the deposition layer due to repeated heating and cooling during the printing process. By controlling the laser power of each deposition layer, the temperature field gradient of the bulk alloy is reduced, thereby reducing the residual stress inside the bulk alloy. The deposition layer does not generate a large amount of residual stress during the cooling process, and the residual stress inside the bulk alloy is significantly reduced, thus improving the performance of the material.

[0038] The technical solution of this invention is highly practical, has no additional production cost, and is applicable not only to additive manufacturing of metal workpieces, but also to laser repair and remanufacturing of metal workpieces.

[0039] This invention has been described through embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this invention.

Claims

1. A method for controlling residual stress during laser additive manufacturing, characterized in that, The residual stress control device in the laser additive manufacturing process includes a laser (8), a powder feeder (7), a laser head module (6), and a water-cooled copper plate (1). The laser head module (6) is connected to the powder feeder (7) through a powder feeding pipe (5). A laser head (4) is installed at the lower end of the laser head module (6). The laser head module (6) is connected to the laser head (4) through the powder feeding pipe (5). The laser emitted by the laser (8) passes vertically through the laser head module (6) and the laser head (4). The water-cooled copper plate (1) is located below the laser head (4). A substrate (2) is provided on the water-cooled copper plate (1). The thickness of the substrate (2) is 30 mm; The following steps are performed using the aforementioned residual stress control device in laser additive manufacturing: S1. Using a residual stress control device during laser additive manufacturing, alloy samples are produced by using different laser powers on different printing layers; S2. Perform residual stress analysis on the alloy sample to obtain the relationship between residual stress and corresponding laser power; S3. Based on the obtained relationship between residual stress and laser power, the residual stress control device in the laser additive manufacturing process is re-set so that the laser power used by the residual stress control device in the laser additive manufacturing process changes regularly during the alloy production process. Step S2, which involves residual stress analysis of the alloy sample, includes the following steps: S2-1. Obtain X-ray diffraction data of the alloy sample using X-ray stress analyzer and X-ray diffraction technology; S2-2. Using sin 2 The ψ method calculates the residual stress inside the alloy sample based on the obtained diffraction data. The calculation formula is as follows: ； In the formula, E is Young's modulus, υ is Poisson's ratio, ψ is the off-axis angle, and d ψ d is the lattice spacing of the diffraction plane under stress, and d0 is the lattice spacing of the diffraction plane under stress-free conditions. S2-3. Convert the residual stress calculation results into a two-dimensional contour map; In step S2-1, the X-ray stress analyzer operates at a voltage of 20 kV and a current of 40 mA; in step S2-2, E is 189 GPa and υ is 0.

30. Step S1 uses CrMnFeCoNi alloy spherical powder to manufacture alloy samples, and the particle size of the CrMnFeCoNi alloy spherical powder is 45-105μm. The number of printing layers in step S3 is 20, and each of the four adjacent layers uses the same laser power. The laser power distribution from bottom to top is 2300w, 2000w, 1700w, 1400w, and 1100w.

2. The method for controlling residual stress in laser additive manufacturing according to claim 1, characterized in that, In the production process of the alloy sample in step S1, the laser beam diameter is 3mm, the scanning rate is 600mm / min, the powder feeding rate is 10 g / min, the layer height is 0.5mm, the overlap rate is 30%, and the oxygen content is less than 10 ppm.

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