Method for eliminating solidification thermal stress through metal laser melting additive manufacturing technology

Abstract

The invention belongs to the field of metal powder laser melting additive manufacturing, and discloses a method for eliminating solidification thermal stress through a metal laser melting additive manufacturing technology. The method is realized by adopting SLM equipment and comprises the following steps: step 1, melting laser forming; the SLM equipment comprises a galvanometer, a high-frequency pulse laser, a collimating and beam expanding lens, a melting laser and an infrared thermometer; step 2, starting an infrared thermometer, detecting temperature values of solidified powder at different interval durations by an infrared temperature measurement scanning system at the first layers of scanning forming of the part, and determining the scanning lag duration according to the principle that the temperature of the material is 50 DEG C higher than the recrystallization temperature of the material; and then high-frequency forging laser is started at the same time interval to perform forging treatment, so that the material is subjected to impact forging vibration at the temperature to realize a recrystallization process, and the stress completely disappears. According to the method, the problem that failure is often caused by stress deformation when a selective laser melting method is adopted for manufacturing large-size parts is solved.

Description

Technical Field

[0001] The invention relates to a method for eliminating solidification thermal stress by using a metal laser melting additive manufacturing technology, and belongs to the field of metal powder laser melting additive manufacturing. Background Art

[0002] 3D printing technology (known as incremental manufacturing technology in the industry) originated in the United States in the 1980s. The development of CAD (computer-aided design), CNC (digital control), automatic control, laser and other technologies is the cause of its development. It has been developed for less than 30 years. It is a manufacturing technology that integrates optics / mechanics / electrics, computers, numerical control and new materials in the field of advanced manufacturing in the world. The reason why it is called incremental manufacturing is that it is different from the traditional material "removal" manufacturing process such as cutting. This technology "naturally grows" into a three-dimensional entity by stacking discrete materials such as powder, liquid, and thin sheets layer by layer, so it is popularly called "3D printing" technology. This technology changes the overall formation of a three-dimensional entity into the superposition of several two-dimensional planes, greatly reducing the complexity of manufacturing. In theory, any structural model that can be designed on a computer can be used to quickly turn the design prototype into a physical object without the need for cutting tools, molds and complex process conditions. At present, this technology plays an important role in the fields of national defense, aerospace, automobiles, biomedicine, molds, casting, agriculture, home appliances, arts and crafts, animation, etc. The development level of the future manufacturing industry will still be one of the key indicators of a country's overall strength, and future manufacturing technology will inevitably move towards digitalization and intelligence driven by the development of related technologies such as CNC technology, computers, machinery, and materials. As a result, this technology will inevitably gradually penetrate into many fields such as national defense, aerospace, automobiles, and biomedicine, affecting the design theories and concepts in each of the above fields, and in conjunction with other traditional technologies, improve or even update some commonplace manufacturing solutions, making manufacturing more intelligent, simple, and green, and product performance closer to the ideal state.

[0003] In the 3D printing technology industry, 3D printing of metal parts is very important and is an important link in today's manufacturing industry. The Selective Laser Melting (SLM) technology is precisely the most important type of 3D printing manufacturing technology for metal parts, and is a laser direct forming technology for metal parts with great development potential in the future. This technology uses laser to instantly melt metal powder to form and manufacture metal structural parts. Thermal stress is inevitable during the forming process, especially for large and complex structure parts. The high and complex temperature gradient caused by rapid condensation often causes thermal stress accumulation and complex deformation of the entire part. Therefore, how to avoid or eliminate the thermal stress of condensed metal parts is crucial. It is the key to ensure the smooth progress of the printing process. Summary of the invention

[0004] The purpose of the present invention is to provide a new method for controlling auxiliary laser to perform forming and then heat treating a solidified workpiece after scanning by a main laser beam to eliminate stress of a rapidly condensed metal workpiece.

[0005] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0006] The method of eliminating solidification thermal stress by metal laser melting additive manufacturing technology is implemented by SLM equipment and includes the following steps:

[0007] Step 1, melting laser forming: Use SLM equipment to complete the structural layout of the entire forming system according to single laser beam or multiple laser beams; when odd laser layout, place the single laser beam at the geometric center of the printing cavity, the laser beam output from the fiber laser is collimated and expanded by the collimating beam expander, enters the galvanometer and focusing mirror for direction change and focusing, and places the focal spot at the original position at the center of the focal plane of the printing cavity; when multiple laser beams are arranged, the focal spot of each laser beam is controlled at the center of its responsible area, and the energy distribution of the laser focal spot is Gaussian distribution, which is basically circular;

[0008] The SLM equipment includes a galvanometer, a high-frequency pulse laser, a collimating beam expander, a melting laser, and an infrared thermometer;

[0009] The high-frequency pulse laser is connected to the right galvanometer through the right collimating beam expander;

[0010] The melting laser is connected to the left galvanometer through the left collimating beam expander;

[0011] The infrared thermometer is arranged on the inner side of the top wall of the printing cavity, and can follow the scanning track of the melting laser 4 to monitor the temperature of the processing area in real time;

[0012] The SLM device is connected to the computer through the controller;

[0013] Step 2, start the infrared thermometer, adopt the interval asynchronous measurement method, in the first few layers of the part scanning forming, the infrared thermometer detects the temperature value of the powder after solidification at different intervals, and determines the scanning lag time of the infrared thermometer based on the principle of 50°C above the recrystallization temperature of the material;

[0014] Step 3, the high-frequency forging laser is started at the same interval to perform forging processing; the single beam laser described in step 1 is used as a processing unit, and a high-frequency and high-peak power forging processing pulse laser beam is matched for each processing unit; the galvanometer is used to control the light spot to scan the cross-sectional figure on the focal plane, and the laser scanning and filling processing is performed. The single beam laser of each processing unit scans the slice cross-sectional figure.

[0015] Furthermore, the forging treatment laser beam in step 1 uses pulses generated by a high-frequency pulse laser, with a pulse wavelength of 1030nm-1070nm, a pulse frequency range of 100KHz-4000KHz, a peak power of 1KW-20KW, and an average power of 100W-2000W.

[0016] Furthermore, in step 2, the interval asynchronous measurement method is adopted, and the interval duration is 0.5S-10S.

[0017] Furthermore, the focal spot of the forging treatment pulse laser beam in step 3 has a fixed translation position distance from the focal spot of the single laser beam of each processing unit, and the horizontal translation position distance ΔX is 50mm~500mm, and the vertical translation position distance ΔY is 50mm~500mm.

[0018] Furthermore, the laser scanning described in step 3 has a scanning time difference of 0.01s to 10s, and the scanning speed of a single laser beam of each processing unit is 200mm / s to 3000mm / s; and the number of scans for a comprehensive scan by each high-frequency forging laser beam is 1 to 20 layers / time.

[0019] The present invention has the following beneficial effects:

[0020] The present invention overcomes the problem of failure due to stress deformation when using the laser selective melting method to manufacture large-volume parts. The present invention can reduce the generation of temperature stress and avoid deformation caused by excessive stress during the printing and forming process of large-volume metal complex structure parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 Schematic diagram of the SLM equipment forming system structure.

[0023] Reference numerals:

[0024] In the figure, 1-galvanometer, 2-high frequency pulse laser, 3-collimating beam expander, 4-melting laser, 5-infrared thermometer, 6-controller, 7-computer. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0026] Example:

[0027] Combined with Figure 1 In this embodiment, a method for eliminating solidification thermal stress by using a metal laser melting additive manufacturing technology is implemented using an SLM device and includes the following steps:

[0028] Step 1, melting laser forming: Use SLM equipment to complete the structural layout of the entire forming system according to a single laser beam or multiple laser beams; when the single laser beam is arranged, the single laser beam is placed at the geometric center of the printing cavity, and the laser beam output from the melting laser 4 is collimated and expanded by the collimating beam expander 3, enters the galvanometer 1 and the focusing mirror for direction change and focusing, and the focal spot at the original position is placed at the center of the focal plane of the printing cavity; when the multiple laser beams are arranged, the focal spot of each laser beam is controlled at the center of the area it is responsible for, and the energy distribution of the laser focal spot is Gaussian distribution, which is basically circular;

[0029] The SLM device includes a galvanometer 1, a high-frequency pulse laser 2, a collimating beam expander 3, a melting laser 4, and an infrared thermometer 5;

[0030] The high-frequency pulse laser 2 is connected to the right galvanometer 1 through the right collimating beam expander 3;

[0031] The melting laser 4 is connected to the left galvanometer 1 through the left collimating beam expander 3;

[0032] The infrared thermometer 5 is arranged on the inner side of the top wall of the printing cavity; it can follow the scanning track of the melting laser 4 to monitor the temperature of the processing area in real time;

[0033] The SLM device establishes a connection with the computer 7 via the controller 6;

[0034] Step 2, start the infrared thermometer 5, adopt the interval asynchronous measurement method, in the first few layers of the part scanning forming, the infrared thermometer 5 detects the temperature value of the powder after solidification at different intervals, and determines the scanning lag time of the infrared thermometer 5 according to the principle of 50°C above the recrystallization temperature of the material;

[0035] Step 3, high-frequency forging laser is started at the same interval to perform forging processing; the single laser beam described in step 1 is used as a processing unit, and a high-frequency and high-peak power forging processing pulse laser beam is matched for each processing unit; the galvanometer 1 is used to control the light spot to scan the cross-sectional figure on the focal plane, and the laser scanning filling process is performed. The single laser beam of each processing unit scans the slice cross-sectional figure.

[0036] Furthermore, the forging treatment laser beam in step 1 uses pulses generated by a high-frequency pulse laser 2, with a pulse wavelength of 1030nm-1070nm, a pulse frequency range of 100KHz-4000KHz, a peak power of 1KW-20KW, and an average power of 100W-2000W.

[0037] Furthermore, in step 2, the interval asynchronous measurement method is adopted, and the interval duration is 0.5S-10S.

[0038] Furthermore, the focal spot of the forging treatment pulse laser beam in step 3 has a fixed translation position distance from the focal spot of the single laser beam of each processing unit, and the horizontal translation position distance ΔX is 50mm~500mm, and the vertical translation position distance ΔY is 50mm~500mm.

[0039] Furthermore, the laser scanning described in step 3 has a scanning time difference of 0.01s to 10s, and the scanning speed of a single laser beam of each processing unit is 200mm / s to 3000mm / s; and the number of scans for a comprehensive scan by each high-frequency forging laser beam is 1 to 20 layers / time.

[0040] Working principle and process:

[0041] The high-frequency pulse laser 2, as an energy source, emits a high-energy laser beam. The propagation direction of the laser beam is quickly and accurately changed through the right galvanometer 1, so that the laser scans according to the set path and pattern. The collimating beam expander 3 is used to adjust the diameter and divergence angle of the laser beam, so that the laser beam can be better focused on the processing area, thereby improving the processing accuracy and efficiency.

[0042] The melting laser 4 provides enough energy to melt the material for additive manufacturing; the propagation direction of the laser beam is quickly and accurately changed by the left galvanometer 1, so that the laser scans according to the set path and pattern; the collimating beam expander 3 is used to adjust the diameter and divergence angle of the laser beam, so that the laser beam can be better focused on the processing area, thereby improving the processing accuracy and efficiency;

[0043] The SLM equipment is provided with an infrared thermometer 5, which can follow the scanning trajectory of the melting laser 4 to monitor the temperature of the processing area in real time. The infrared rays provided by the infrared thermometer 5 can be synchronized or set at intervals with the laser scanning time; it is convenient to control the processing parameters to ensure that the material is accurately melted, while preventing the material from overheating or inadequate processing; here, an interval asynchronous measurement method is adopted, so that the infrared measurement is made later than the melting laser, and the interval time is 0.5-10S. The specific time is determined according to the measurement result, ensuring that the temperature value range of the measurement result is 200-500℃, and maintained at about 50℃ above the recrystallization temperature of the melted forming material, depending on the recrystallization temperature value of different materials.

[0044] The two types of lasers, high-frequency pulse laser and melting laser, cooperate with each other in the following way: first, the melting laser is used for forming, and in the first few layers of the part scanning and forming, the infrared temperature measurement scanning system detects the temperature value of the powder after solidification at different intervals, and determines the scanning lag time based on the principle of 50°C above the recrystallization temperature of the material; then the high-frequency forging laser is started at the same interval to carry out forging treatment, so that the material is subjected to impact forging vibration at this temperature to realize the recrystallization process, causing the stress to completely disappear.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for eliminating solidification thermal stress by metal laser melting additive manufacturing technology, which is implemented by SLM equipment and is characterized in that: The following steps are involved: Step 1, melting laser forming: using SLM equipment to complete the structural layout of the entire forming system according to a single laser beam or multiple laser beams; when the single laser beam is arranged, the single laser beam is placed at the geometric center of the printing cavity, the laser beam output from the melting laser (4) is collimated and expanded by the collimating beam expander (3), enters the galvanometer (1) and the focusing mirror for direction change and focusing, and the focal spot at the original position is placed at the center of the focal plane of the printing cavity; when the multiple laser beams are arranged, the focal spot of each laser beam is controlled at the center of the area it is responsible for, and the energy distribution of the laser focal spot is Gaussian distribution, which is basically circular; The SLM device comprises a galvanometer (1), a high-frequency pulse laser (2), a collimating beam expander (3), a melting laser (4), and an infrared thermometer (5); The high-frequency pulse laser (2) is connected to the right galvanometer (1) via the right collimating beam expander (3); The melting laser (4) is connected to the left galvanometer (1) via the left collimating beam expander (3); The infrared thermometer (5) is arranged on the inner side of the top wall of the printing cavity; it can follow the scanning track of the melting laser (4) to monitor the temperature of the processing area in real time; The SLM device establishes a connection with a computer (7) via a controller (6); Step 2, start the infrared thermometer (5), adopt the interval asynchronous measurement method, in the first few layers of the part scanning forming, the infrared thermometer (5) detects the temperature value of the powder after solidification at different intervals, and determines the scanning lag time of the infrared thermometer (5) based on the principle of 50° C. above the recrystallization temperature of the material; Step 3, high-frequency forging laser is started at the same interval to perform forging processing; the single laser beam described in step 1 is used as a processing unit, and a high-frequency and high-peak power forging processing pulse laser beam is matched for each processing unit; the galvanometer (1) is used to control the light spot to scan the cross-sectional figure on the focal plane, and the laser scanning filling process is performed, and the single laser beam of each processing unit scans the slice cross-sectional figure.

2. The method for eliminating solidification thermal stress by metal laser melting additive manufacturing technology according to claim 1, characterized in that: The forging laser beam in step 1 uses a pulse generated by a high-frequency pulse laser (2), with a pulse wavelength of 1030nm-1070nm, a pulse frequency range of 100KHz-4000KHz, a peak power of 1KW-20KW, and an average power of 100W-2000W.

3. The method for eliminating solidification thermal stress by metal laser melting additive manufacturing technology according to claim 2, characterized in that: In step 2, an interval asynchronous measurement method is adopted, and the interval duration is 0.5S-10S.

4. The method for eliminating solidification thermal stress by metal laser melting additive manufacturing technology according to claim 3 is characterized in that: The focal spot of the forging treatment pulse laser beam in step 3 has a fixed translation position distance from the focal spot of the single laser beam of each processing unit, the horizontal translation position distance ΔX is 50mm~500mm, and the vertical translation position distance ΔY is 50mm~500mm.

5. The method for eliminating solidification thermal stress by metal laser melting additive manufacturing technology according to claim 3, characterized in that: The laser scanning described in step 3 has a scanning time difference of 0.01s to 10s, and the scanning speed of a single laser beam of each processing unit is 200mm / s to 3000mm / s; each high-frequency forging laser beam scans 1 to 20 layers / time for a comprehensive scan.

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