Additive manufacturing method based on small-scale temperature gradient adaptive adjustment

Abstract

The application provides an additive manufacturing method based on small-scale temperature gradient adaptive adjustment, comprising the following steps: controlling a melting laser to scan on a powder bed preheated to a basic temperature, and melting the powder bed to form a molten pool; monitoring the temperature distribution of the powder bed in real time, and dynamically dividing a melting area centered on the molten pool and a heat affected zone surrounding the melting area according to the monitored temperature; controlling a temperature compensation device to generate a temperature compensation spot synchronous with the scanning path of the melting laser, and performing follow-up heating on the heat affected zone; and dynamically adjusting the heating power of the temperature compensation device on each pixel point in the heat affected zone according to the real-time temperature of each pixel point, so that the heat conduction rate of each pixel point in the heat affected zone tends to a preset optimal value. The application can actively, accurately and dynamically control the temperature gradient of the heat affected zone, thereby improving the forming quality of the additive manufacturing parts.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more specifically, to an additive manufacturing method based on adaptive adjustment of small-scale temperature gradient. Background Technology

[0002] Selective laser melting (SLM) technology primarily utilizes a laser source to scan layers to form three-dimensional parts. When a micro-spot melts powder, the temperature of the molten pool rises rapidly, melting the metal powder, which then cools and solidifies quickly. Influenced by the scanning speed, the molten pool continuously melts new powder. This process involves continuous localized heating of the powder, causing the metal powder near the molten pool (heat-affected zone) to expand rapidly, while the surrounding powder expands more slowly. This temperature difference between the heat-affected zone and the unaffected powder creates a thermal gradient, resulting in a difference between expansion and contraction. The rapid heating and cooling within a very short time leads to stress deformation. Furthermore, as the forming height changes, the heat dissipation conditions within each processing plane constantly change, resulting in constantly fluctuating longitudinal and transverse temperature gradients in the processed part. These gradients become a major factor affecting part quality during additive manufacturing.

[0003] Currently, the main method used to improve stress deformation is substrate preheating. Preheating measures heat the substrate or powder to a suitable temperature before melting, thereby reducing the thermal gradient between the heat-affected zone and the surrounding materials. This helps reduce thermal stress and residual stress caused by rapid expansion and contraction. However, the temperature gradient between the preheating temperature and the molten pool is still large, and the heating and cooling time of the molten pool is not significantly reduced, making it impossible to achieve a smooth temperature transition from the high-temperature molten pool to the unmelted powder. Especially as the printing height increases, the effect of substrate preheating becomes less significant. In addition, both powder-based and substrate-based heating methods are based on overall heating, which can only relatively reduce the temperature gradient, and the effect is very limited. Summary of the Invention

[0004] (a) Technical problems to be solved The technical problem to be solved by the present invention is to overcome the problem that the existing additive manufacturing technology is prone to thermal stress deformation, internal defects and unstable forming quality of parts because the overall preheating method cannot effectively control the dynamic and severe local temperature gradient near the molten pool.

[0005] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides an additive manufacturing method based on adaptive adjustment of small-scale temperature gradients. Its core idea is to: sense the transient temperature field of the molten pool and its surrounding area in real time, dynamically identify the "molten zone" and the "heat-affected zone" surrounding it; and utilize a precisely spatially modulated heating energy source, synchronously following the melting laser, to specifically perform pixel-level power-adjustable dynamic heating on the "heat-affected zone," thereby stabilizing the heat conduction rate within this region near a preset optimal value. The additive manufacturing method includes the following steps: S1. Control the molten laser to scan on the powder bed preheated to the base temperature, and the molten powder bed forms a molten pool; the "base temperature" here is a relatively low and safe preheating temperature, which serves to provide a stable temperature base for the entire processing. Preheating helps to improve the molding quality.

[0006] S2. Monitor the temperature distribution of the powder bed in real time, and dynamically divide the melting zone centered on the molten pool and the heat-affected zone around the melting zone according to the monitored temperature; the melting zone is the area where the temperature reaches or exceeds the melting point of the material, and the metal is in a liquid state; the heat-affected zone is the area where the temperature is higher than the base temperature but lower than the melting point, and the metal is in a solid state but is affected by heat.

[0007] S3. Control the heating device to generate a heating spot synchronized with the molten laser scanning path, and follow the heating of the heat-affected zone; S4. Based on the real-time temperature of each pixel within the heat-affected zone, dynamically adjust the heating power of the heating device for the corresponding pixel to make the heat conduction rate of each pixel within the heat-affected zone approach a preset optimal value. Through feedback control, ensure that the heat transfer rate of each point within the heat-affected zone remains consistent and in an optimal state, thereby effectively smoothing out the temperature gradient in this area.

[0008] Preferably, step S2 specifically includes the following steps: S21. Real-time acquisition of powder bed temperature data in pixels; real-time acquisition of temperature data of the entire powder bed surface in pixels using high-resolution temperature measuring devices such as infrared thermometers.

[0009] S22. Dynamically label pixel areas with temperatures greater than or equal to the material's melting point as melting zones; S23. Dynamically label pixel areas with temperatures below the material's melting point but above the base temperature as heat-affected zones. For example, for AlSi10Mg material, areas with temperatures between 800°C and 1700°C can be labeled as melting zones, and areas between 300°C and 800°C can be labeled as heat-affected zones.

[0010] Preferably, in step S4, the dynamic adjustment is achieved in the following way: The heating device includes a light source, a projector, and an optically addressed light valve; The projector projects a target image containing grayscale distribution information onto the optically addressed light valve to modulate the light beam emitted by the light source and form the temperature-compensated light spot; Based on the real-time temperature distribution of the heat-affected zone, the grayscale value of the corresponding pixel in the target image is dynamically adjusted to change the heating power of the heat-compensating spot at the corresponding position.

[0011] Preferably, the grayscale value is adjusted from 0 to 255, and the grayscale value is negatively correlated with the heating power.

[0012] Preferably, in step S4, the heat conduction rate is calculated using the formula Q = -KA(dT / dx), where K is the heat conduction coefficient, A is the area of ​​a single pixel, and dT / dx is the temperature gradient.

[0013] Preferably, the preset optimal value is determined through the following steps: In the additive manufacturing process, the heat conduction rate of the heat-affected zone is adjusted and a sample is prepared; Metallographic examination was performed on the sample, and the thermal conductivity rate corresponding to the minimum number of pores and non-fusion defects was selected as the preset optimal value.

[0014] Preferably, for the unmelted powder area outside the melting zone, the heating device heats and maintains it at the base temperature. For the large unmelted powder area outside the melting zone that is not designated as a heat-affected zone, the heating device can heat and maintain it at the base temperature as a whole, thus providing auxiliary heat preservation.

[0015] Preferably, when multiple molten pools appear on the powder bed (such as when multiple melting lasers are used for simultaneous operation or skip scanning), the corresponding melting zone and heat-affected zone are independently divided with the highest temperature point of each molten pool as the center, and step S4 is executed independently for each heat-affected zone.

[0016] Preferably, in step S3, the scanning mirror of the heating device and the scanning mirror of the melting laser are deflected synchronously to achieve the overlap of the scanning paths of the heating spot and the melting laser spot.

[0017] Preferably, the projection area of ​​the heat-compensating spot always completely covers the spot area of ​​the melting laser.

[0018] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. This invention monitors and dynamically divides the "melting zone" and "heat-affected zone" in real time. The system can accurately identify the key areas that need to be controlled (i.e., the heat-affected zone), which changes the traditional blind and extensive way of overall preheating. It realizes active, precise and dynamic control of the temperature gradient, fundamentally suppressing thermal stress and deformation.

[0019] 2. This invention utilizes a heating compensation device to continuously heat the "heat-affected zone" and dynamically adjusts the heating power based on the temperature of various points within it. This is equivalent to applying a "smart iron" behind the molten pool, actively and in real-time "smoothing" the steep temperature distribution within the heat-affected zone. This closed-loop temperature regulation, targeting a small scale and moving synchronously with the molten pool, can most effectively slow down the cooling rate of this area, significantly reducing the temperature gradient from the molten pool to the substrate, thereby fundamentally reducing the thermal stress that causes warping and cracking of parts.

[0020] 3. This invention creates a more stable and controllable thermal environment for the solidification of the molten pool by regulating the heat conduction rate of the heat-affected zone to a "preset optimal value." A gentler temperature gradient and a more reasonable cooling rate are beneficial for: allowing sufficient gas escape from the molten pool and reducing porosity; improving the fluidity and wettability of the molten pool, promoting complete powder melting and interlayer bonding, and reducing incomplete fusion defects; obtaining a more uniform and fine solidification structure, thereby improving the overall density and mechanical properties of the parts; and significantly improving the molten pool solidification process, effectively reducing internal metallurgical defects, thus improving the consistency of forming quality.

[0021] 4. This invention uses real-time temperature feedback for dynamic power adjustment, thus automatically adapting to changes in heat dissipation conditions caused by complex part geometry, changes in scanning path, and increased forming height during processing. Regardless of the scanning location, the system automatically maintains the heat-affected zone in an optimal thermal state, ensuring temperature field stability throughout the entire construction process. This ensures consistent forming quality at different locations and heights, solving the problem that traditional static process parameters cannot adapt to dynamic processes.

[0022] 5. In this invention, the supplemental heating energy is only applied to the "heat-affected zone," and the light spot is synchronized with the laser scanning, ensuring a clear energy utilization target. The power can be precisely adjusted at the pixel level as needed, avoiding energy waste. Compared with traditional overall preheating (which requires continuously maintaining a high temperature throughout the entire cavity), this significantly reduces ineffective energy consumption, achieving "on-demand heating" and making it more energy-efficient and effective. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the additive manufacturing apparatus based on small-scale temperature gradient adaptive adjustment provided in an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram illustrating the relationship between the melting zone, the heat-affected zone, and the pixel unit provided in an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram illustrating the formation of multiple melting zones and heat-affected zones during the same additive manufacturing process, as provided in an embodiment of the present invention.

[0027] The labels for the attached figures are as follows: 1. Diode laser array homogenizing light unit; 2. Optically addressed light valve imaging unit; 3. Light source deflection imaging component; 4. Two-laser array; 5. Homogenizing module; 6. Projector; 7. Slice image to be projected; 8. Dichroic mirror; 9. Optically addressed light valve; 10. Polarizing prism; 11. Black box; 12. Image of the part outside the projected image in the surface light source; 13. 4F projection lens system; 14. Reflector; 15. X-axis adjustment lens; 16. Y-axis adjustment lens; 17. Field lens; 18. Forming platform; 19. Projected image of the heating area of ​​the powder bed transmitted by the heating device; 20. Infrared thermometer; 21. Melting laser head and galvanometer module; A. Melting zone; B. Heat-affected zone. Detailed Implementation

[0028] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0029] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0030] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: like Figure 1 As shown, this embodiment of the invention provides an additive manufacturing system for implementing the above method, which mainly includes a melting laser module, a temperature compensation device, an infrared thermometer 20, and a main control unit (not shown in the figure, usually a computer).

[0032] The melting laser module includes a melting laser head and a galvanometer module 21, which is used to emit a high-energy melting laser and scan it on the powder bed under the control of the galvanometer to melt the metal powder and form a molten pool.

[0033] An infrared thermometer 20 is installed above the forming cavity, and its field of view covers the entire forming platform 18. It can collect temperature data of the entire powder bed surface in real time with high spatial resolution (corresponding to the pixel grid of the powder bed surface) and frequency, and upload it to the main control unit.

[0034] The temperature compensation device is the core component of this invention for achieving adjustable spatial power heating. Its optical path constitutes a spatial light modulation system. The temperature compensation device includes a diode laser array homogenizing light unit 1, an optically addressed optical valve imaging unit 2, and a light source deflection imaging component 3. The working process of the temperature compensation device is as follows: The diode laser array homogenizing light unit 1 includes a diode laser array 4 (the laser wavelength is 1064nm, and a 6-bar array is selected, with 104 light spots arranged in each bar) and a homogenizing module 5 (the light source is a square homogenized light spot with a size of 15mm*15mm). The laser emitted by the diode laser array 4 is processed by the homogenizing module 5 to form a rectangular surface light source with uniform intensity.

[0035] The optically addressed optical valve imaging unit 2 includes a projector 6 (using a 472nm projection laser), a dichroic mirror 8, an optically addressed optical valve 9, a polarizing prism 10, and a black box 11. The projector 6 emits the target image 7 (i.e., a digital slice image containing grayscale distribution information) generated by the main control unit. After being reflected by the dichroic mirror 8 (which can transmit a light source with a wavelength of 1064nm and reflect a light source with a wavelength of 472nm. Therefore, the surface light source from the laser can pass through the dichroic mirror and enter the optically addressed optical valve 9, and the projection light source from the projector 6 enters the optically addressed optical valve 9 after being reflected by the dichroic mirror), it illuminates the surface of the optically addressed optical valve 9. The optically addressed light valve 9 is an electrically addressed spatial light modulator based on materials such as liquid crystal. The transmittance or polarization modulation characteristics of each pixel are controlled by the voltage applied to that pixel (determined by the grayscale value of the projected image 7). In this embodiment, the light valve aperture of the optically addressed light valve 9 is 15mm*15mm, and an adjustable AC voltage is applied across the two ends of the light valve, with an average voltage of approximately 4V. After a uniform surface light source is incident on the optically addressed light valve 9, the polarization state of its emitted beam is spatially modulated by the image 7. Specifically, under the photoelectric effect, the liquid crystal material molecules in the bright area of ​​the light valve dynamically adjust their orderly arrangement according to the distribution of the projected light, resulting in different refractive indices along the long axis of the molecules and perpendicular to the long axis. After the liquid crystal material molecules of the light valve are redistributed, the light from the diode laser surface light source passing through the bright area of ​​the light valve is adjusted to P-polarized light, while the light from the surface light source passing through the dark area of ​​the light valve is adjusted to S-polarized light. That is, after passing through the optically addressed light valve, all slices of the image that need to be projected are converted into P-polarized light, while the rest of the unprojected portions are converted into S-polarized light. The beam modulated by the optically addressed light valve 9 enters the polarizing prism 10. The polarizing prism 10 is designed so that one polarization state (e.g., P-light) is completely transmitted, while another orthogonally polarized state (e.g., S-light) is reflected. The light corresponding to the area in the target image 7 that requires high-power heating (dark pixels) is modulated into P-light and passes through the polarizing prism 10 into the subsequent optical path; while the light corresponding to the area that requires low power or no heating (bright pixels) is modulated into S-light and reflected by the polarizing prism 10 into the black box 11 where it is absorbed. In this way, the purpose of controlling whether the beam of each "pixel" can reach the processing surface is achieved by using the image grayscale.

[0036] The light source deflection imaging assembly 3 includes a 4F projection lens system 13, a reflector 14, an X-axis adjustment lens 15, and a Y-axis adjustment lens 16. The light beam carrying spatial power information transmitted by the optically addressed light valve imaging unit 2 passes sequentially through the 4F projection lens system 13, the reflector 14, the X-axis adjustment lens 15, the Y-axis adjustment lens 16, and the field lens 17, and is finally precisely projected onto the powder bed of the forming platform 18 to form a heat-compensating area projection pattern 19. By controlling the scanning galvanometer of the heat-compensating device, the heat-compensating pattern 19 can be moved synchronously with the melting laser spot.

[0037] The main control unit is the brain of the system. It receives temperature data from the infrared thermometer 20 and executes a temperature field analysis algorithm: it compares the temperature field data with the material melting point and the basic temperature threshold in real time, and dynamically divides the data into categories such as... Figure 2 The melting zone A and heat-affected zone B are shown. Then, based on the real-time temperature of each pixel in heat-affected zone B and the preset optimal heat conduction rate value, the required compensation heating power for each pixel is calculated, and the corresponding target image 7 (grayscale image) is generated and sent to the projector 6. At the same time, the main control unit also synchronously controls the scanning system of the melting laser head 21 and the temperature compensation device to ensure that the two work together.

[0038] The following section uses AlSi10Mg powder as the processing material as an example to introduce the specific working process of this method: After spreading the powder, preheat the entire powder bed to a low base temperature (e.g., 200°C).

[0039] The main control unit controls the melting laser head 21 to scan along a preset path to form a moving molten pool.

[0040] The infrared thermometer 20 operates continuously, sending real-time temperature field data to the main control unit. Based on the digital model, path planning is performed. The main control unit then synchronously controls the scanning mirrors of the heating compensation device and the melting laser to deflect synchronously, ensuring that the scanning paths of the heating compensation spot and the melting laser spot coincide. This guarantees that the projection area of ​​the heating compensation spot always completely covers the area of ​​the melting laser spot.

[0041] The main control unit processes the data and divides the current melting laser spot area into melting zone A and heat-affected zone B (e.g., Figure 2 As shown, each grid represents a temperature-sensing pixel. For example, taking AlSi10Mg material as an example, when the temperature reaches 800-1700℃, the corresponding pixel area is marked as melting region A; when the temperature is between 300-800℃, the corresponding pixel area is marked as heat-affected region B.

[0042] By adjusting the temperature of the heat-affected zone B and performing metallographic analysis on the sample, the optimal thermal conductivity was determined to be 268 W / (m·K). Based on the temperature of each pixel within the heat-affected zone B, the main control unit calculated the heating power distribution required to optimize the thermal conductivity of the region and generated the corresponding target image 7.

[0043] The target image 7 is written into the optically addressed light valve 9 via the projector 6, modulating the heat-compensating beam to form a heat-compensating spot 19 with a corresponding power distribution on the powder bed. This spot moves closely following the molten laser spot under the control of the scanning galvanometer, precisely compensating for the heat-affected zone B. For the molten region A, based on a thermal conductivity coefficient of 268 W / (m·K), to ensure the conductivity coefficient remains constant, the main control unit dynamically adjusts the heat-compensating temperature of the corresponding pixel in the heat-compensating device, converting it to the grayscale value of the corresponding pixel's projection area according to the correspondence between grayscale value and power, ensuring the thermal conductivity coefficient remains constant. In this embodiment, the surface light source power is 500 W, and the grayscale value range of each pixel in each projected image is [0-255]. The grayscale value has a linear relationship with the laser power. That is, when the grayscale value is 0, the power is 500 W; when the grayscale value is 255, the laser power is 0.

[0044] like Figure 3 As shown, when the scanning strategy generates multiple molten pools, the system can independently divide each molten pool into A / B regions and generate multiple corresponding temperature compensation control regions to achieve parallel processing.

[0045] Through the closed-loop control described above, the system can sense and dynamically adjust the temperature field of the heat-affected zone in real time, keeping its thermal gradient within the optimal range, thereby significantly improving the forming quality.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An additive manufacturing method based on adaptive adjustment of small-scale temperature gradient, characterized in that, Includes the following steps: S1. Control the molten laser to scan on the powder bed preheated to the base temperature, and the molten powder bed forms a molten pool; S2. Monitor the temperature distribution of the powder bed in real time, and dynamically divide the melting zone centered on the molten pool and the heat-affected zone surrounding the melting zone based on the monitored temperature; S3. Control the heating device to generate a heating spot synchronized with the molten laser scanning path, and follow the heating of the heat-affected zone; S4. Based on the real-time temperature of each pixel in the heat-affected zone, dynamically adjust the heating power of the heating device on the corresponding pixel so that the heat conduction rate of each pixel in the heat-affected zone approaches the preset optimal value.

2. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 1, characterized in that, Step S2 specifically includes the following steps: S21. Real-time acquisition of powder bed temperature data in pixels; S22. Dynamically label pixel areas with temperatures greater than or equal to the material's melting point as melting zones; S23. Dynamically label pixel areas with temperatures below the material's melting point but above the base temperature as heat-affected zones.

3. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 2, characterized in that, In step S4, the dynamic adjustment is achieved in the following way: The heating device includes a light source, a projector, and an optically addressed light valve; The projector projects a target image containing grayscale distribution information onto the optically addressed light valve to modulate the light beam emitted by the light source and form the temperature-compensated light spot; Based on the real-time temperature distribution of the heat-affected zone, the grayscale value of the corresponding pixel in the target image is dynamically adjusted to change the heating power of the heat-compensating spot at the corresponding position.

4. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 4, characterized in that, The grayscale value is adjusted from 0 to 255, and the grayscale value is negatively correlated with the heating power.

5. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 1, characterized in that, In step S4, the thermal conductivity rate is calculated using the formula Q = -KA(dT / dx), where K is the thermal conductivity coefficient, A is the area of ​​a single pixel, and dT / dx is the temperature gradient.

6. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 1, characterized in that, The preset optimal value is determined through the following steps: In the additive manufacturing process, the heat conduction rate of the heat-affected zone is adjusted and a sample is prepared; Metallographic examination was performed on the sample, and the thermal conductivity rate corresponding to the minimum number of pores and non-fusion defects was selected as the preset optimal value.

7. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 1, characterized in that, For the unmelted powder area outside the melting zone, the heating device heats it and maintains it at the base temperature.

8. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 1, characterized in that, When multiple molten pools appear on the powder bed, the corresponding melting zone and heat-affected zone are independently divided with the highest temperature point of each molten pool as the center, and step S4 is executed independently for each heat-affected zone.

9. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 1, characterized in that, In step S3, the scanning mirror of the heating device and the scanning mirror of the melting laser are deflected synchronously to achieve the overlap of the scanning paths of the heating spot and the melting laser spot.

10. The additive manufacturing method based on small-scale temperature gradient adaptive adjustment as described in claim 9, characterized in that, The projection area of ​​the heat-compensating spot always completely covers the spot area of ​​the melting laser.

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