A selective laser melting forming method based on high repetition frequency pulse train femtosecond laser

Abstract

This invention discloses a selective laser melting and forming method based on a high-repetition-rate femtosecond laser pulse train, belonging to the field of metal additive manufacturing technology. The method uses a high-repetition-rate femtosecond laser to melt and form material powder layer by layer. The laser has higher heating efficiency for the processed material, thereby achieving a faster processing speed and higher processing accuracy at the same laser power. By optimizing parameters such as the modulation frequency and duty cycle of the laser pulse train, this method can achieve adaptive selective laser melting of materials with low absorptivity, high thermal conductivity, and high melting point.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology, and in particular to a selective laser melting and forming method based on a high repetition rate pulse train femtosecond laser. Background Technology

[0002] Selective laser melting (SLM) is a mainstream additive manufacturing technology that uses a focused laser beam to selectively melt powder materials layer by layer to achieve near-net-shape forming of complex structural parts. High-power continuous lasers with wavelengths around 1μm are widely used as light sources due to their maturity, low cost, and applicability to the effective melting of various metals (such as stainless steel, titanium alloys, and nickel-based high-temperature alloys).

[0003] When using selective laser melting (SLM) to process materials with low absorptivity and high thermal conductivity (such as copper and aluminum), a challenge arises: only a small portion of the laser energy is absorbed by the material, while the vast majority is lost through reflection, transmission, or conduction to surrounding areas. To avoid using high-power lasers, shorter wavelength lasers or pretreatments such as surface coating of the powder are typically employed to improve the material's laser absorption rate. However, for high-melting-point materials (such as tungsten and tantalum), SLM processing relies on significantly increasing the laser power to ensure complete melting. However, using excessively high laser power for SLM of these materials not only wastes energy, but power fluctuations at high power can also affect microstructure uniformity, reducing the resolution and accuracy of structural forming. Furthermore, the use of high-power lasers increases production costs and is detrimental to production safety.

[0004] Therefore, there is an urgent need for a new laser selective melting method that can achieve high material adaptability, high efficiency, high precision, and low energy consumption by matching parameters with the optical and thermophysical properties of materials. Summary of the Invention

[0005] The purpose of this invention is to provide a laser selective melting forming method using a high repetition rate femtosecond laser, belonging to the field of powder bed fusion additive manufacturing technology. The method utilizes a femtosecond laser with a repetition rate ≥1 GHz as the energy source. The laser pulse is modulated by a modulator and output in pulse train mode. By changing the duty cycle of the pulse, the energy of a single pulse can be adjusted accordingly while maintaining a constant average power. This method eliminates the need for lasers of different wavelengths (such as green lasers); it achieves adaptability to different materials simply by adjusting the power and modulated pulse, improving the energy efficiency of laser selective melting material processing. It also solves the problems of low energy utilization, poor forming quality, and complex pretreatment processes in existing laser selective melting technologies when processing materials with low absorptivity, high thermal conductivity, and high melting points.

[0006] At the same average power, femtosecond lasers with higher peak power can reduce heat diffusion losses and heat materials faster than continuous lasers. This characteristic can be used to shorten single-point exposure time, improve scanning speed, and increase the efficiency of selective laser melting (SLM). However, low-repetition-rate femtosecond lasers have large pulse intervals, resulting in weak heat accumulation and uneven effects, affecting the efficiency and quality of SLM. By increasing the laser pulse repetition frequency to the GHz level, the time interval between pulses is made smaller than the heat diffusion time, reducing the single-pulse energy required to reach the melting point and avoiding material ablation and energy waste caused by excessive single-pulse energy. Therefore, high-repetition-rate femtosecond lasers combine high heating rate and high energy utilization. Simultaneously, due to their higher pulse density, the laser effect is more uniform, optimizing the quality of SLM.

[0007] By modulating the pulse, the energy of a single pulse can be changed while keeping the average power constant, making the laser more effective at dealing with materials with different absorptivity, thermal conductivity, and melting point.

[0008] To achieve the above objectives, this invention proposes a laser selective melting method using a high-repetition-rate femtosecond laser. This invention uses a high-repetition-rate femtosecond laser pulse train instead of the continuous laser used in traditional laser selective melting as the light source. The high-repetition-rate femtosecond laser has a repetition frequency ≥ 1 GHz and a time interval between adjacent pulses ≤ 1 ns, which can more effectively achieve the heat accumulation effect and reduce losses caused by heat conduction. The pulse train is obtained by electro-optic or acousto-optic modulation of the pulses, concentrating energy into the pulses within the pulse train, and adjusting the energy of a single pulse while maintaining a constant average power.

[0009] To achieve the objective of this invention, the present invention provides a selective laser melting and forming method based on a high repetition rate pulse train femtosecond laser, comprising the following steps: S1. Import the 3D digital model of the printed part; S2. Slice the 3D digital model to generate the scan path for each layer; S3. Based on the optical and thermophysical properties of the material to be processed, set the laser parameters, including average power, modulation frequency, and duty cycle; S4. Replace the molding chamber with inert gas; S5. Spread a layer of powder on the molding platform; S6. Control the high repetition rate pulse train femtosecond laser to selectively melt the powder layer according to the preset scanning path; S7. The forming platform moves down by a preset height; S8. Repeat steps S5–S7 layer by layer until the path scan of all slices is completed.

[0010] Furthermore, printing strategies include the slice thickness of the digital model, the scanning path, and the scanning speed.

[0011] Furthermore, the gas replacement involves introducing gases such as nitrogen or argon into the molding chamber to replace the air, maintain a low oxygen and water vapor concentration in the molding chamber, prevent material oxidation, remove fumes generated during processing, and ensure the quality of the molded parts.

[0012] Furthermore, the powder spreading involves evenly spreading a layer of powder material on the forming platform using a scraper or roller; Furthermore, the high repetition rate femtosecond laser has a wavelength range of 1000-1100nm, a pulse width of ≤500fs, a repetition rate of ≥1GHz, a modulation frequency adjustment range of 1kHz-100MHz, and a duty cycle adjustment range of 0.01%-100%.

[0013] Furthermore, the generation process of high repetition rate femtosecond laser is as follows: the control system controls the seed laser to start and output a high repetition rate femtosecond seed laser. The seed laser first passes through a stretcher to broaden the pulse width of the pulse laser in the time domain, and then passes through a modulator and an amplifier to modulate and amplify the power of the pulse laser respectively. Finally, the compressor recompresses the pulse width of the pulse laser, thereby outputting a high repetition rate pulse train femtosecond laser.

[0014] Furthermore, the generation process of high repetition frequency pulse train femtosecond laser is as follows: the control system controls the signal generator to generate a waveform signal, which is loaded onto the modulator. The laser pulse is adjusted through the physical effect inside the modulator, and finally the laser pulse is modulated into a pulse train with a specific envelope and modulation frequency for output.

[0015] Furthermore, the average power, modulation frequency, and duty cycle are adjusted according to the material type.

[0016] Furthermore, a single modulation period of the pulse train contains several femtosecond pulses, and the energy of the single pulse is adjusted accordingly by changing the duty cycle.

[0017] Furthermore, the pulse is modulated by adjusting the modulation frequency and duty cycle.

[0018] Traditional laser selective melting systems generally employ continuous laser processing. Continuous laser energy input offers the advantages of sustained and stable thermal effects but a slow cooling rate. This leads to drawbacks such as a large heat-affected zone, severe molten pool fluctuations, increased spatter, and high residual stress. This invention utilizes a pulsed modulated femtosecond laser with a repetition rate in the GHz range. Compared to existing technologies, the advantages of this invention are: (1) Compared with continuous laser, high repetition frequency femtosecond laser has a higher peak power at the same average power, and its extremely short pulse spacing can effectively reduce heat diffusion, resulting in higher heating efficiency, allowing materials to reach the melting point in a shorter time, greatly shortening the single-point laser action time, and thus achieving a higher scanning speed. (2) Compared with low repetition frequency lasers, high repetition frequency lasers have lower single-pulse energy at the same average power, which can avoid the adverse effects of single-pulse direct heating of materials above the boiling point, causing ablation and other energy waste and surface quality deterioration. The short pulse interval of high repetition frequency lasers makes the material heating process more continuous and uniform, which also helps to improve the surface quality and internal structure consistency of the molded parts; (3) After the laser is output in pulse train mode by adjusting the modulation frequency and duty cycle, the single pulse energy can be changed while maintaining the average power. This allows the same system to adapt to a variety of materials with different reflectivities, thermal conductivity and melting points without changing the laser wavelength or modifying the surface of the powder, thus expanding the application range of laser selective melting technology.

[0019] (4) The method of the present invention can be used not only for conventional laser selective melting of materials, but also for laser selective melting of materials with low absorption rate, high thermal conductivity or high melting point that are difficult to handle by traditional continuous lasers, thereby achieving laser selective melting manufacturing with high material adaptability, high efficiency, high precision and low energy consumption. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the 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 some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic diagram of a laser selective melting system based on a high repetition rate pulse train femtosecond fiber laser according to an embodiment of the present invention. Figure 2 This is a schematic diagram illustrating the principle of high repetition rate pulse train femtosecond fiber laser modulation according to an embodiment of the present invention. Figure 3 This is a flowchart of a selective laser melting and forming method based on a high repetition rate pulse train femtosecond laser according to an embodiment of the present invention; Figure 4 This is a schematic diagram of temperature-time simulation at the focal point corresponding to Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the temperature-time simulation at the focal point corresponding to Embodiment 2 of the present invention; Figure 6This is a schematic diagram of temperature-time simulation at the focal point corresponding to Embodiment 3 of the present invention.

[0021] In the diagram: 101, Control system; 102, Signal generator; 103, Seed laser; 104, Stretcher; 105, Modulator; 106, Amplifier; 107, Compressor. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the invention will be further described below with reference to the accompanying drawings and specific embodiments. Obviously, the embodiments described below are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 This embodiment provides a selective laser melting and forming method for WRe alloy materials based on high repetition rate femtosecond lasers, such as... Figure 3 As shown.

[0024] The WRe alloy material exhibits a laser wavelength reflectivity of <20%, a thermal conductivity of <200 W / m·K, and a melting point >3300°C. This high melting point allows for rapid temperature accumulation in the focal region when using a high-repetition-rate femtosecond laser. Figure 4 As shown.

[0025] The selective laser melting forming method is implemented through a selective laser melting forming system, which includes a control system 101, a signal generator 102, a seed laser 103, a stretcher 104, a modulator 105, an amplifier 106, and a compressor 107. The seed laser 103, stretcher 104, modulator 105, amplifier 106, and compressor 107 are connected sequentially. The control system 101 is connected to the modulator 105 through the signal generator 102, and is directly connected to the seed laser 103 and amplifier 106.

[0026] Please see Figure 3 A selective laser melting and forming method based on high repetition rate pulse train femtosecond laser includes the following steps: S1. Input the three-dimensional digital model of the printed part into the control system 101.

[0027] S2. Slice the 3D digital model to generate the scanning path for each layer.

[0028] S3. Set the laser parameters according to the optical and thermophysical properties of the material to be processed. The laser parameters include average power, modulation frequency, and duty cycle.

[0029] The seed laser 103 is activated using the control system 101, and outputs a seed laser with a pulse repetition frequency of 1 GHz. The amplifier 106 is adjusted to boost the laser and change its average power. The signal generator 102 is adjusted to input a square wave signal with a modulation frequency of 20 MHz and a duty cycle of 7% into the modulator 105, concentrating energy into a few pulses and reducing the average power required for melting. By adjusting the modulation frequency and duty cycle, the energy of a single pulse can be adjusted without changing the average power.

[0030] Under the above parameters, the seed laser is stretched in the time domain by the stretcher 104, and then the pulse laser is modulated and amplified by the modulator 105 and the amplifier 106 respectively. Finally, the pulse laser is recompressed by the compressor 107 and then output to the molding chamber.

[0031] S4. Replace the molding chamber with inert gas.

[0032] The atmosphere inside the molding chamber is replaced with argon gas using the control system 101.

[0033] S5. Spread a layer of powder on the molding platform.

[0034] S6. Control the high repetition frequency pulse train femtosecond laser to selectively melt the powder layer according to the preset scanning path.

[0035] During the molding process, the control system 101 controls the laser spot to scan the WRe alloy powder along a predetermined path according to a preset program, so that the WRe alloy powder is selectively melted.

[0036] S7. The molding platform is lowered by a preset height.

[0037] In this embodiment, after each layer of powder is scanned, the control system 101 first controls the forming platform to descend, then controls the scraper to complete the powder spreading, and finally controls the laser spot to scan a new layer.

[0038] S8. Repeat steps S5–S7 layer by layer until the path scan of all slices is completed. After each layer of powder is scanned, the control system 101 first controls the forming platform to descend, then controls the scraper to complete the powder spreading, and finally controls the laser spot to scan the new layer. This cycle continues until the entire WRe alloy part is completely formed.

[0039] Example 2 A laser selective melting and forming method for AlSiMg alloy materials based on high repetition rate femtosecond laser, such as... Figure 3 As shown.

[0040] The AlSiMg alloy material has a laser wavelength reflectivity >60%, a thermal conductivity >200 W / m·K, and a melting point <600°C. This type of material has a relatively low laser energy deposition efficiency, and the deposited energy conducts rapidly within the material. However, due to its low melting point, a higher duty cycle can be used while maintaining a certain pulse energy.

[0041] The 3D digital model of the printed part is input into the control system 101 and processed. The seed laser 103 is activated using the control system 101, outputting a seed laser with a pulse repetition frequency of 1 GHz. The amplifier is adjusted to boost the laser and change its average power. The signal generator 102 is adjusted to input a square wave signal with a modulation frequency of 5 MHz and a duty cycle of 30% into the modulator, using a long pulse train to maintain melting for a longer period of time, such as... Figure 5 As shown.

[0042] The atmosphere inside the molding chamber is replaced with argon gas using the control system 101.

[0043] During the molding process, the control system 101 controls the laser spot to scan the AlSiMg alloy powder along a predetermined path according to the set program, so that the powder is selectively melted.

[0044] After each layer of powder is scanned, the control system 101 first controls the forming platform to descend, then controls the scraper to complete the powder spreading, and finally controls the laser spot to scan the new layer. This cycle continues until the entire AlSiMg alloy part is completely formed.

[0045] Example 3 This embodiment provides a laser selective melting and forming method for CuCr alloy materials based on a high repetition rate femtosecond laser, such as... Figure 3 As shown.

[0046] The CuCr alloy material exhibits a laser wavelength reflectivity >90%, thermal conductivity >400 W / m·K, and melting point >1100°C. This type of material has extremely low laser energy deposition efficiency, and the deposited energy diffuses outwards very rapidly, posing a significant challenge in laser selective melting processes.

[0047] The 3D digital model of the printed part is input into the control system 101 and processed. The amplifier is adjusted to boost the laser and change its average power. The seed laser 103 is activated using the control system 101, outputting a seed laser with a pulse repetition frequency of 1 GHz. The signal generator 102 is adjusted to input a square wave signal with a modulation frequency of 80 MHz and a duty cycle of 0.1% into the modulator, which concentrates the energy of one modulation cycle into a single pulse, thereby heating the material to its melting point with that single pulse. Figure 6 As shown.

[0048] The inert gas inside the molding chamber is replaced using the control system 101.

[0049] During the forming process, the control system 101 controls the laser spot to scan the CuCr alloy powder along a predetermined path according to the set program, so that the powder is selectively melted.

[0050] After each layer of powder is scanned, the control system 101 first controls the forming platform to descend, then controls the scraper to complete the powder spreading, and finally controls the laser spot to scan the new layer. This cycle continues until the entire CuCr alloy part is completely formed.

[0051] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily obtained by those skilled in the art within the scope of the present invention and by conceiving the solution according to the present invention should be included within the scope of protection of the present invention.

Claims

1. A selective laser melting and forming method based on high repetition rate femtosecond laser pulse trains, characterized in that, Includes the following steps: S1. Import the 3D digital model of the printed part; S2. Slice the 3D digital model to generate the scan path for each layer; S3. Based on the optical and thermophysical properties of the material to be processed, set the laser parameters, including average power, modulation frequency, and duty cycle; S4. Replace the molding chamber with inert gas; S5. Spread a layer of powder on the molding platform; S6. Control the high repetition rate pulse train femtosecond laser to selectively melt the powder layer according to the preset scanning path; S7. The forming platform moves down by a preset height; S8. Repeat steps S5–S7 layer by layer until the path scan of all slices is completed.

2. The selective laser melting and forming method according to claim 1, characterized in that, The high repetition rate femtosecond laser pulse repetition frequency is ≥1 GHz.

3. The selective laser melting forming method according to claim 1, characterized in that, The process of generating high repetition rate femtosecond laser is as follows: the control system controls the seed laser to start and output a high repetition rate femtosecond seed laser. The seed laser first passes through a stretcher to broaden the pulse width of the pulse laser in the time domain. Then, the pulse laser is modulated and amplified by a modulator and an amplifier, respectively. Finally, the pulse width of the pulse laser is recompressed by a compressor, thereby outputting a high repetition rate pulse train femtosecond laser.

4. The selective laser melting forming method according to claim 1, characterized in that, The process of generating a high repetition rate pulse train femtosecond laser is as follows: the control system controls the signal generator to generate a waveform signal, which is loaded onto the modulator. The laser pulse is adjusted through the physical effects inside the modulator, and finally the laser pulse is modulated into a pulse train with a specific envelope and modulation frequency for output.

5. The method of claim 1, wherein, Adjust the average power, modulation frequency, and duty cycle according to the material type.

6. The selective laser melting forming method according to claim 1, characterized in that, A single modulation period of a pulse train contains several femtosecond pulses, and the energy of a single pulse is adjusted accordingly by changing the duty cycle.

7. The method of claim 1, wherein, The pulse is modulated by adjusting the modulation frequency and duty cycle.

8. The method of claim 1, wherein, The high repetition rate femtosecond laser has a wavelength range of 1000-1100nm and a pulse width of ≤500fs.

9. The method of claim 1, wherein, The modulation frequency adjustment range is 1kHz-100MHz.

10. The selective laser melting forming method according to any one of claims 1-9, characterized in that, The duty cycle adjustment range is 0.01%-100%.

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