In-situ monitoring laser powder bed melting forming device and method

Abstract

The invention discloses an in-situ monitoring laser powder bed fusion forming device and method, the device comprises a fusion chamber and a computer, a laser, a focusing lens, a galvanometer and an alloy sample are arranged in the fusion chamber, and light emitted by the laser sequentially passes through the focusing lens and the galvanometer and is finally emitted to the surface of the alloy sample; the computer is respectively connected with the laser and the data collecting and processing device, the data collecting and processing device is connected with the laser transmitting and receiving device, and a scanning lens for focusing laser is fixed on the laser transmitting and receiving device; and the computer can regulate and control laser forming process parameters when detecting that metallurgical defects exist on the surface of the alloy sample. In the laser additive manufacturing process of the tungsten alloy, generation of unmelted pores and spheroidization in the laser additive manufacturing process of the tungsten alloy can be monitored through laser signal processing of the reflected laser, and laser forming process parameters are adjusted in real time, so that metallurgical defects are eliminated, and the laser additive manufacturing requirement of high-forming-quality alloy materials is met.

Description

Technical Field

[0001] The present invention relates to an additive manufacturing device and method, and specifically to an in-situ monitoring laser powder bed melting forming device and method. Background Art

[0002] Metal laser additive manufacturing technology integrates complex components by melting and depositing metal materials layer by layer. It has the forming characteristics that are not constrained by complex structures, has higher material utilization, short production cycle and can realize complex internal features. Among them, based on the layer-by-layer spreading of the powder bed and the selective melting of the loose metal powder thin layer by high-energy laser, the high-density components of arbitrary complex shapes are formed. This is one of the metal laser additive manufacturing technologies, which has broad application prospects in the fields of aerospace and biomedicine. Metal additive manufacturing involves the rapid interaction between metal materials and high-energy excitation heat sources. In this process, the metal material is instantly melted by the high-energy beam heat source and rapidly solidified in a very short time. It undergoes a complex non-equilibrium metallurgical process, which makes the additive manufacturing of metal materials the most challenging.

[0003] At present, there is a problem of limited strengthening and toughening performance in tungsten alloy components formed by selective laser melting. There are many defects, including unmelted pores, spheroidization, residual stress and cracks, which affect the structural integrity and mechanical properties of metal components. On the one hand, the inherent properties of tungsten, such as high melting point, high thermal conductivity and high toughness-brittle transition temperature, have always been the difficulty and challenge of selective laser melting. On the other hand, the atomic bonding force of W is very large, and the viscosity of the melt is very large at high temperature, resulting in poor melt fluidity and poor melt wetting and spreading ability. The spheroidization effect is obvious during the forming process, resulting in low density of the formed components. At present, there is a lack of effective processing methods and strengthening mechanisms to coordinate the contradictory relationship between strength and plasticity / toughness. Internal defects or morphological defects such as abnormal accumulation lead to low yield. Therefore, it is necessary to quickly diagnose the forming quality and perform corresponding control when additively manufacturing parts to ensure defect-free manufacturing of parts. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies of the prior art, an object of the present invention is to provide an apparatus for in-situ monitoring of laser powder bed fusion forming. Another object of the present invention is to provide a method for in-situ monitoring of laser powder bed fusion forming.

[0005] Technical solution: The in-situ monitoring laser powder bed melting forming device described in the present invention includes a melting chamber and a computer. A laser, a focusing lens, a galvanometer, and an alloy sample are arranged in the melting chamber. The laser emitted by the laser passes through the focusing lens and the galvanometer in sequence and is finally emitted to the surface of the alloy sample. The computer is respectively connected to the laser and the data collection and processing device, and the data collection and processing device is connected to the laser transmitter and receiver. The laser transmitter and receiver is fixed with a scanning lens for focusing the laser. The computer can adjust the laser forming process parameters when metallurgical defects are detected on the surface of the alloy sample.

[0006] Furthermore, the alloy sample is disposed on the surface of the substrate.

[0007] Furthermore, the laser transmitter and receiver scan the selected area according to the shape of the shaping layer set by the computer.

[0008] Furthermore, metallurgical defects include surface spheroidization and unmelted pores. The laser emission signal generated by the unmelted pores has a long duration and a large distance, while the laser emission signal generated by the surface spheroidization has a short duration and a small distance.

[0009] The in-situ monitoring method of laser powder bed fusion forming according to the present invention comprises the following steps:

[0010] Step 1: Use 3D modeling software to establish a 3D solid geometric model of the tungsten alloy sample to be printed;

[0011] Step 2: Based on the 3D solid geometric model in step 1, software is used to perform layered slicing and plan the laser scanning path, and the 3D geometric model is discretized into a series of 2D data, which are then imported into a computer;

[0012] Step three, use a laser for 3D printing, monitor the surface of the forming layer of the alloy sample through the laser transmitter and receiver, and based on the reflected laser signal data, if metallurgical defects are detected, adjust the forming process parameters of the laser in real time through the computer to perform in-situ laser treatment on the sample surface to eliminate metallurgical defects and finally obtain a dense alloy sample.

[0013] Furthermore, the reflected laser signal data includes intensity data, distance data, and time delay data.

[0014] Furthermore, the distance data forms a three-dimensional surface morphology point cloud, and the corresponding defect type is obtained by analyzing the three-dimensional surface morphology point cloud.

[0015] Furthermore, the distance d is the distance between a point in the alloy sample area unit and the scanning lens, which is determined by calculating the time delay from the laser beam being emitted to being reflected back to the laser transmitter receiver. The calculation formula for the distance d is:

[0016]

[0017] Where c is the propagation speed of the laser beam, and t is the propagation time of the laser beam from emission to reflection back to the laser transmitter and receiver.

[0018] Furthermore, the time delay data is obtained by real-time measurement using a data collection and processing device.

[0019] Furthermore, the forming process parameters of the laser include laser power and laser scanning speed. Increasing the laser power can increase the heat input and the molten pool temperature, reduce the melt viscosity, and facilitate the complete melting and wetting and spreading of the powder, thereby reducing the formation of unmelted pores and spheroidization. Reducing the laser scanning speed can prolong the solidification time of the molten pool, facilitate the overflow of gas in the molten pool, reduce the formation of pores in the molten pool, and thus reduce the porosity.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0021] 1. In the process of laser additive manufacturing of tungsten alloy, the generation of unmelted pores and spheroidization in the process of laser additive manufacturing of tungsten alloy can be monitored by processing the laser signal of the reflected laser, and the laser forming process parameters can be adjusted in real time to eliminate metallurgical defects such as unmelted pores and spheroidization, meeting the requirements of laser additive manufacturing of high forming quality alloy materials;

[0022] 2. Without destroying its original structure and function, the existing laser additive manufacturing equipment is modified. Compared with the detection and analysis of alloy samples after laser forming, real-time laser monitoring can be used to adjust the laser forming process in real time according to defects such as unmelted porosity and spheroidization generated during the laser additive manufacturing process, thereby ensuring the forming quality and performance of the alloy samples, saving component processing time, improving processing efficiency, improving the performance of the metal layer formed by laser powder bed melting, and greatly improving the one-time forming quality of metal laser powder bed melting. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the present invention;

[0024] Figure 2 It is a schematic diagram of the coordinates of the regional unit;

[0025] Figure 3 is a schematic diagram of the structure of alloy sample 6 without in-situ laser improvement;

[0026] Figure 4 is a schematic diagram of the structure of alloy sample 6 obtained in the present invention;

[0027] Figure 5 is a schematic diagram of the surface roughness of alloy sample 6 obtained in Example 1 of the present invention;

[0028] Figure 6 is a microstructure diagram of the surface of alloy sample 6 obtained in Example 1 of the present invention;

[0029] Figure 7 is a graph of the ultimate compressive strength of alloy sample 6 obtained in Example 1 of the present invention;

[0030] Figure 8 is a schematic diagram of the surface roughness of alloy sample 6 obtained in comparative example 1 of the present invention;

[0031] Fig. 9 is a microstructure diagram of the surface of alloy sample 6 obtained in comparative example 1 of the present invention;

[0032] Fig.10 is a graph of the ultimate compressive strength of alloy sample 6 obtained in comparative example 1 of the present invention;

[0033] Fig.11 It is a bar graph of the ultimate compressive strength and elongation of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0034] like Figure 1 The in-situ monitoring laser powder bed melting forming device includes a laser powder bed melting forming device and an additional laser monitoring system. The laser powder bed melting forming device includes a melting chamber 1, a laser 3, a substrate 10 and a computer 2. The melting chamber 1 is a sealed structure, and a high concentration of inert gas such as argon and nitrogen is introduced into the interior to ensure that the oxygen content is less than 50ppm during the processing. The computer 2 is used to control the various components of the device according to the processing plan. The laser 3 is used to provide the energy required for the laser powder bed melting process, and the laser monitoring system is used to monitor the defects of the surface layer of the alloy sample 6 in real time during the processing. The light emitted by the laser 3 passes through the focusing lens 4 and the galvanometer 5 in sequence, and is finally emitted to the surface of the alloy sample 6. The laser monitoring system includes a laser transmitter and receiver 8, a scanning lens 9 and a data collection and processing device 7, all of which are installed in the melting chamber 1. The laser transmitter and receiver 8 is installed above the side of the substrate 10, and can scan the selected area according to the shape of the forming layer set by the computer 2. The alloy sample 6 planned to be formed is placed above the substrate 10. The laser transmitter and receiver 8 are respectively connected to the scanning lens 9 and the data collection and processing device 7. The laser transmitter and receiver 8 is used to receive the reflected laser signal and send the reflected laser signal to the data collection and processing device 7. The data collection and processing device 7 is connected to the computer 2 for processing the overall reflected laser signal. If metallurgical defects are detected, the computer 2 adjusts the laser forming process parameters in real time to eliminate the metallurgical defects on the surface of the formed sample. The laser powder bed fusion forming equipment also includes an automatic powder spreading system, a protective atmosphere device, and a cooling circulation system, which are all prior art.

[0035] Alloy sample 6 is made of printed tungsten alloy, and its chemical composition includes: Ni: 4.8-5.0wt.%, Fe: 2.0-2.2wt.%, and the rest is tungsten. To ensure that the powder has good fluidity, the particle size range is 5-45μm.

[0036] The forming method of the in-situ monitoring laser powder bed fusion forming device of this embodiment includes the following steps:

[0037] (1) The laser monitoring system (data collection and processing device 7, laser transmitter and receiver 8, scanning lens 9) is installed in the laser additive manufacturing system (computer 2, laser 3, focusing lens 4, galvanometer 5). The data collection and processing device 7 is connected to the computer 2. The laser powder bed fusion forming equipment can be subsequently controlled by the computer 2 to change the laser forming process parameters. When the unmelted pores and spheroidization generation are monitored, the forming process parameters can be adjusted in real time.

[0038] (2) The 3D solid geometric model of the target part was established using computer-aided design software and exported as an STL file. The geometric model was then sliced ​​and layered using Materialise Magics software, and the laser scanning path and laser process parameters were set to discretize the set 3D solid into a series of 2D data. The 3D printing process parameters were set as follows: laser power 200W, scanning speed 300mm / s, scanning spacing 50μm, powder layer thickness 20μm, and the laser scanning path was set as a partitioned island scanning strategy.

[0039] (3) Import the slice file obtained in step (2) into computer 2, place the tungsten alloy powder in the melting chamber, and use it to 3D print the alloy sample 6. During the forming process, each time a metal layer is formed, the laser transmitter and receiver 8 will emit a laser signal to any area unit 011 on the surface of the alloy sample 6, and receive the laser signal reflected from the surface of the alloy sample 6 in real time, and process the area unit laser signal in the data collection and processing device 7. The three-dimensional point cloud of the surface morphology of the area unit is obtained based on the reflected laser signal data. By analyzing the three-dimensional point cloud of the surface morphology, it is determined whether there are metallurgical defects. If the analysis shows that there are metallurgical defects, the forming process parameters of the laser 3 are adjusted in real time by computer 2 to perform in-situ laser treatment on the sample surface to eliminate the metallurgical defects, and finally obtain a dense alloy sample 6. The reflected laser signal data includes intensity data, distance data, and time delay data. The spatial coordinates of any point in the area unit are (x, y, d), such as Figure 2 As shown, a three-dimensional point cloud is formed by spatial coordinate data, and the corresponding defect type is obtained by analyzing it. The distance d is the distance between the point in the alloy sample area unit and the scanning lens 9. The calculation formula for determining the distance is determined by calculating the time delay from the laser beam being emitted to being reflected back to the laser transmitter and receiver 8:

[0040]

[0041] Wherein, c is the propagation speed of the laser beam, and t is the time from the laser beam being emitted to the laser beam being reflected back to the laser transmitting and receiving device 8.

[0042] The time delay data is measured and obtained in real time by the data collection and processing device 7. After the data collection and processing device 7 analyzes and identifies the unmelted pores and spheroidization generated during the forming process, it adjusts the laser forming process parameters, including laser power and laser scanning speed, in real time through the computer 2 to eliminate the following problems: Figure 3 The defects such as unmelted pores and spheroidization on the surface of the formed sample 6 shown in the figure are eliminated to ensure the forming quality of each layer of the tungsten alloy sample, and finally obtain a uniform and dense alloy sample 6 without unmelted pores. Figure 4 As shown. Increasing the laser power can increase the heat input and the molten pool temperature, reduce the melt viscosity, and facilitate complete melting and wetting and spreading of the powder, thereby reducing the formation of unmelted pores and spheroidization. Reducing the laser scanning speed can prolong the solidification time of the molten pool, facilitate the overflow of gas in the molten pool, reduce the formation of pores in the molten pool, and thus reduce the porosity.

[0043] like Figures 5 to 7 The surface roughness of the alloy sample 6 obtained in this embodiment is Sa=5.854, the final density can reach 99.51%, the ultimate compressive strength is 2980.45Mpa, and the elongation is 43.07%.

[0044] Comparative Example

[0045] The remaining steps of this comparative example are the same as those of Example 1, except that the laser transmitter and receiver 8, the scanning lens 9, and the data collection and processing device 7 are omitted. It is found that the spheroidization and unmelted pores generated during the laser additive manufacturing process cannot be monitored in real time, making it difficult to adjust the laser forming process parameters in real time. Figures 8 to 10 After the formed tungsten alloy sample is polished with coarse sandpaper, diamond polished, and corrosive, an optical microscope can be used to observe the presence of a large number of unmelted pores and powder accumulation in the longitudinal microstructure of the sample. This is because the surface spheroidization effect of the forming layer is serious, resulting in an uneven surface. When the next layer of powder is printed, the uneven surface of the sample will cause the thickness of the powder layer to be different at different positions. Under a fixed laser power, the relatively thick powder layer cannot be completely melted, and due to the high melt viscosity, the spheroidization effect is obvious, resulting in a large number of unmelted voids, which will lead to a large number of defects in the forming layer. The defects superimposed layer by layer eventually lead to the surface roughness of the sample Sa = 19.721, and the overall forming quality is poor, with a density of only 88.49%, an ultimate compressive strength of 1864.72Mpa, and an elongation of 18.53%. Fig.11, which is a comparison chart of the ultimate compressive strength and elongation data of the embodiment and the comparative example, the ultimate compressive strength of the sample monitored in situ is improved by 159.8% and the elongation is improved by 234.4% in terms of mechanical properties compared with the sample not monitored.

Claims

1. An in-situ monitoring laser powder bed fusion forming device, comprising a fusion chamber (1) and a computer (2), characterized in that: A laser (3), a focusing lens (4), a galvanometer (5), and an alloy sample (6) are arranged in the melting chamber (1); the light emitted by the laser (3) passes through the focusing lens (4) and the galvanometer (5) in sequence, and is finally emitted to the surface of the alloy sample (6); the computer (2) is connected to the laser (3) and the data collection and processing device (7) respectively; the data collection and processing device (7) is connected to the laser transmitter and receiver (8); a scanning lens (9) for focusing the laser is fixed on the laser transmitter and receiver (8); the computer (2) can adjust the laser forming process parameters when metallurgical defects are detected on the surface of the alloy sample (6).

2. The in-situ monitoring laser powder bed fusion forming device according to claim 1 is characterized in that: The alloy sample (6) is arranged on the surface of a substrate (10).

3. The in-situ monitoring laser powder bed fusion forming device according to claim 1 is characterized in that: The laser transmitter and receiver (8) scans the selected area according to the shape of the shaping layer set by the computer (2).

4. The in-situ monitoring laser powder bed fusion forming device according to claim 1 is characterized in that: The metallurgical defects include surface spheroidization and unmelted porosity.

5. A method for in-situ monitoring of laser powder bed fusion forming, characterized in that: The following steps are involved: Step 1: Use 3D modeling software to establish a 3D solid geometric model of the tungsten alloy sample to be printed; Step 2: Based on the three-dimensional solid geometric model in step 1, software is used to perform layered slicing and plan the laser scanning path, and the three-dimensional geometric model is discretized into a series of two-dimensional data, which are then imported into a computer (2); Step three, 3D printing is performed using a laser (3), and the surface of the formed layer of the alloy sample (6) is monitored by a laser transmitter and receiver (8). If metallurgical defects are detected based on the reflected laser signal data, the forming process parameters of the laser (3) are adjusted in real time by a computer (2) to perform in-situ laser treatment on the sample surface to eliminate the metallurgical defects, thereby finally obtaining a dense alloy sample (6).

6. The in-situ monitoring laser powder bed fusion forming method according to claim 5, characterized in that: The reflected laser signal data includes intensity data, distance data, and time delay data.

7. The in-situ monitoring laser powder bed fusion forming method according to claim 6, characterized in that: The distance data within the area unit forms a three-dimensional point cloud, and the corresponding defect type is obtained by analyzing the three-dimensional point cloud of the surface morphology.

8. The in-situ monitoring laser powder bed fusion forming method according to claim 6, characterized in that: The distance is the distance between a point in the area unit of the alloy sample (6) and the scanning lens (9), and is determined by calculating the time delay of the laser beam from emission to reflection back to the laser emission receiver (8). The calculation formula of the distance d is: Wherein, c is the propagation speed of the laser beam, and t is the propagation time of the laser beam from emission to reflection back to the laser emission receiver (8).

9. The in-situ monitoring laser powder bed fusion forming method according to claim 6, characterized in that: The time delay data is obtained by real-time measurement through a data collection and processing device (7).

10. The in-situ monitoring laser powder bed fusion forming method according to claim 5, characterized in that: The forming process parameters of the laser (3) include laser power and laser scanning speed.

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