An experimental system for laser additive manufacturing in-situ characterization of synchrotron radiation

Abstract

The application significantly improves the X-ray penetration flux during in-situ characterization by synchrotron radiation, improves the characterization effect, improves the data quality, and provides the possibility for in-situ characterization of laser additive manufacturing of heavier high-density materials (X-ray penetration ability is weak) by designing an ultrathin metal powder bed, a powder laying method and an improved matching system. The laser adjustment system simplifies the equipment construction, greatly saves the experimental space, the numerical control displacement system and the design of the sealed cavity make the cavity can be further miniaturized, which saves the experimental space, reduces the equipment cost, and greatly shortens the propagation path of X-ray in the cavity, further improves the data quality.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology, and in particular to an experimental system for synchrotron radiation in-situ characterization of laser additive manufacturing, as well as an ultrathin metal powder bed device and powder spreading method. Background Technology

[0002] Laser additive manufacturing (LAM) is a near-net-shape manufacturing technology that directly transforms a three-dimensional digital model into a solid part with a complex shape by melting a powdered sample layer by layer with a laser and rapidly solidifying and depositing the powder. Compared with traditional casting and forging, LAM has advantages such as small-batch, rapid, and personalized production. The produced parts also have superior overall mechanical properties and generally require no further processing. In addition, the laser heat source is very suitable for processing high-melting-point materials such as titanium alloys and high-temperature alloys. Therefore, LAM has been widely used in key areas related to national security and development, such as aerospace, shipbuilding, military, and medical fields, and has a very broad development prospect.

[0003] The LAM process involves extremely high temperature gradients and rapid cooling rates, making parts highly susceptible to defects such as porosity, cracks, residual stress, and spheroidization. These defects severely compromise the overall mechanical properties of the parts, shortening their lifespan and potentially leading to serious safety accidents due to sudden fracture failure. This significantly increases production costs and limits the application and promotion of laser additive manufacturing parts in safety-critical fields. Therefore, understanding and mastering the dynamic process of defect formation and clarifying the defect formation mechanism are crucial to reducing or eliminating defect occurrence.

[0004] However, the non-equilibrium physical metallurgy and thermal processes in laser additive manufacturing (LAM) are extremely complex, involving not only multiphase reactions of laser-matter interactions but also dynamic changes such as molten pool evolution, solidification structure transformation, and defect formation. LAM has significant spatiotemporal limitations: the laser-matter interaction time is only on the order of microseconds to milliseconds, and the interaction space is limited to the order of micrometers to millimeters. Furthermore, most molten pools are optically opaque, making it difficult to observe the melt flow within. Traditional non-in-situ characterization methods, such as metallographic characterization, not only cause destructive damage to the parts but also fail to observe the real-time solidification process of the molten pool, making it difficult to accurately characterize the size, shape, and volume of the molten pool, especially the melt flow within it. High-speed infrared imaging and high-speed photography can only capture surface information of the molten pool in situ, but due to the optical opacity of most molten pools, it is impossible to further observe the melt flow and defect formation processes within the molten pool.

[0005] The emergence of synchrotron radiation technology, with its significant advantages such as high energy, high throughput, and high collimation, has made in-situ characterization of the LAM process possible. Synchrotron radiation in-situ imaging characterization can achieve a temporal resolution of microseconds and a spatial resolution of micrometers, making it very suitable for in-situ characterization of the molten pool evolution dynamics during laser additive manufacturing.

[0006] The most critical issue in synchrotron radiation in-situ characterization is the limitation of sample thickness in the X-ray direction. X-rays have weak penetrating power; excessively thick samples prevent X-rays from penetrating, thus hindering the acquisition of information related to the laser additive manufacturing (LAM) process. Therefore, most current research focuses on easily penetrable, low-density materials. Existing laser additive manufacturing equipment presented numerous problems when directly used for synchrotron radiation in-situ characterization. Therefore, it is necessary to design an ultrathin metal powder bed device, a powder spreading method, and an improved supporting experimental system for synchrotron radiation in-situ characterization of laser additive manufacturing to address these technical challenges. Summary of the Invention

[0007] To address the mismatch between existing laser additive manufacturing equipment and synchrotron X-ray in-situ characterization, the inventors designed a specially made ultrathin metal powder bed, a powder spreading method, and an improved supporting system based on the requirements of synchrotron X-ray in-situ characterization. The ultrathin metal powder bed makes X-rays easier to penetrate, significantly improving the characterization effect, enhancing data quality, and significantly expanding the range of materials that can be used for in-situ characterization. This makes in-situ characterization of materials with high density and poor X-ray penetration possible. The improvements to the supporting experimental system also increase the flexibility of experimental equipment setup and reduce the limitations imposed by external conditions such as laser and experimental space on the experiment, thus completing this invention.

[0008] Therefore, the present invention provides an experimental system for in-situ synchrotron radiation characterization of laser additive manufacturing. The system includes a laser adjustment system module, an ultrathin metal powder bed device module, a vacuum-sealed cavity module, and a displacement system module. The laser adjustment system module is located above the vacuum-sealed cavity module, the ultrathin metal powder bed device module is connected to the bottom of the vacuum-sealed cavity, and the displacement system module is connected to the bottom of the vacuum-sealed cavity.

[0009] Furthermore, the laser adjustment system module includes a laser beam expander, a laser reflector, and a laser focusing lens, which are mounted sequentially via an optical device clamping device and a support rod.

[0010] Furthermore, the ultrathin metal powder bed device includes a powder bed, a powder bed fixing device, and a powder bed support platform. The powder bed has a sandwich structure of "boron nitride sheet-metal substrate-boron nitride sheet". The powder bed fixing device has a slot that matches the size of the powder bed and is used to stabilize the powder bed. The powder bed support platform has a slot that matches the size of the powder bed fixing device and is used to further stabilize the powder bed.

[0011] Furthermore, the vacuum-sealed cavity module includes a cavity, a vacuum device, a protective gas device, a cooling water device, and a real-time monitoring device for the metal powder bed. Several windows are symmetrically located on the top and sides of the cavity. The top window is a vertical laser incidence window, and the side windows are X-ray transmission windows and observation windows for the real-time monitoring device for the metal powder bed.

[0012] Furthermore, if a CO2 laser is used, zinc selenide glass is installed in the top window; if a fiber laser is used, quartz glass is installed in the top window.

[0013] Furthermore, two symmetrical windows on the sides for X-ray transmission are fitted with Compton film, while the remaining windows on the sides are fitted with quartz glass.

[0014] Furthermore, the displacement system module is connected to the bottom of the vacuum-sealed cavity module and includes a horizontal CNC displacement stage and a vertical CNC displacement stage that can move independently of each other.

[0015] In a second aspect, the present invention provides a method for ultrathin powder coating of metal powder, the method comprising:

[0016] Step 1: Use adhesive to fix a metal substrate of appropriate size to the wall of a boron nitride sheet;

[0017] Step 2: Attach the boron nitride sheet with the metal substrate to the slotted side wall of the powder bed fixing device;

[0018] Step 3: Place the entire fixing device horizontally on its side, ensuring the exposed boron nitride sheet fits tightly against the stop block, with the side without boron nitride installed facing vertically upwards.

[0019] Step 4: Feed the material vertically into the powder spreading area using an external feeding device, and finally insert the second boron nitride sheet completely from the side. Use a scraper to remove excess powder to complete the ultra-thin powder spreading.

[0020] Furthermore, in step 4, the powder bed is further secured by using additional clamping parts to hold it on top of the powder bed.

[0021] Furthermore, in step 4, if there is insufficient powder in some areas of the powder bed after cleaning the powder bed surface, a small amount of powder can be added to the powder bed surface and the powder bed surface can be leveled and filled using a scraper.

[0022] Furthermore, after laser heating is completed, the surface of the boron nitride sheet is cleaned with a small amount of alcohol to remove the carbonized adhesive and the boron nitride sheet can be reused; for impurities and dirt that are difficult to remove, they are polished with sandpaper.

[0023] Compared with the prior art, the positive effects of the present invention are as follows:

[0024] This invention enables the streamlined preparation of ultrathin metal powder beds, significantly improving the in-situ characterization effect of synchrotron radiation, enhancing the quality of characterization data, and expanding the range of materials that can be characterized. It also optimizes the supporting experimental system for in-situ synchrotron radiation characterization, improves the flexibility of laser parameter settings through the laser adjustment system, simplifies the equipment setup process due to the relatively simple equipment, and has lower requirements for experimental space, making it particularly suitable for equipment setup at synchrotron radiation sources. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the improved synchrotron radiation in-situ characterization experimental system for laser additive manufacturing according to the present invention;

[0026] Figure 2 This is a schematic diagram of the ultrathin metal powder bed laying method.

[0027] Figure 3 This is a simplified diagram illustrating the principle of ultrathin metal powder bed preparation.

[0028] Figure 4 This is a simplified diagram of an ultrathin metal powder bed device. Detailed Implementation

[0029] The structure and effects of the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] This invention provides an experimental system for in-situ characterization of laser additive manufacturing using synchrotron X-rays, such as... Figure 1 As shown, the system includes a laser adjustment system module, an ultrathin metal powder bed device module, a vacuum-sealed cavity module, and a displacement system module. The laser adjustment system module is located above the vacuum-sealed cavity module, the ultrathin metal powder bed device module is connected to the bottom of the vacuum-sealed cavity, and the displacement system module is connected to the bottom of the vacuum-sealed cavity.

[0031] Laser modulation system module

[0032] The laser adjustment system module includes a laser beam expander, a laser reflector, and a laser focusing lens, which are sequentially mounted via an optical component clamping device and a support rod. The laser beam expander amplifies the initial laser beam spot size to reduce the laser energy density, thereby minimizing damage to the laser focusing lens from high-energy laser light and providing protection. The laser reflector reflects the horizontally emitted laser light into a vertically incident laser. The laser focusing lens refocuses the diverging laser beam into a suitable spot size. By adjusting the position of the laser focusing lens and replacing it with different lenses, the focal length and spot size requirements of the laser under different experimental conditions can be easily met.

[0033] The emitted laser beam is expanded by a beam expander to reduce energy (reducing the load on the focusing lens, or the beam expander can be removed if necessary). Then, a reflector is used to adjust the optical path so that the laser beam changes from horizontal to vertical propagation. Finally, the focusing lens reduces the spot size and increases the laser energy density to meet the experimental requirements.

[0034] The laser adjustment system of this invention is small in size, modularly assembled, easy to build and maintain, easy to replace parts, and low in cost. It is very suitable for the small space and frequent unexpected situations in in-situ experiments of synchrotron radiation sources. Furthermore, the laser focal length and spot size can be easily adjusted to meet different experimental needs.

[0035] Ultrathin metal powder bed device module

[0036] The ultrathin metal powder bed device module includes a powder bed, a powder bed fixing device, and a powder bed support platform. The powder bed has a sandwich structure of "boron nitride sheet-metal substrate-boron nitride sheet". The powder bed fixing device has a slot that matches the size of the powder bed and is used to stabilize the powder bed. The powder bed support platform has a slot that matches the size of the powder bed fixing device and is used to further stabilize the powder bed.

[0037] Boron nitride not only has a high melting point and excellent X-ray penetration characteristics, but also does not wet molten metal, making it easy to clean and reuse. Therefore, boron nitride was chosen as the "walls" on both sides of the metal powder bed. The thickness of the boron nitride is in the sub-millimeter range to further reduce X-ray loss and improve characterization results. Therefore, in this invention, "boron nitride sheet" and "boron nitride wall" refer to the same substance in different scenarios. The height of the metal substrate is slightly lower than that of the boron nitride sheet. The height difference determines the thickness of the metal powder layer (thickness in the laser direction, i.e., the vertical direction), and the thickness of the metal substrate determines the thickness of the metal powder bed (thickness in the X-ray direction). Therefore, metal substrates of different heights and thicknesses can be selected according to experimental requirements.

[0038] The function of the powder bed fixing device is to stably clamp the ultra-thin metal powder bed and prevent the powder bed from shaking violently due to the recoil pressure during laser heating. The function of the powder bed support platform is to fix the position of the powder bed fixing device, ensuring that the powder bed is in the same position every time it is installed, and further stabilizing the powder bed. In addition, the support platform can prevent the heat of the powder bed from being directly conducted to the cavity itself during laser heating, thus playing a protective role and increasing the upper limit of the heating temperature that can be used in experiments.

[0039] After the powder is spread, the fixing device carrying the ultra-thin metal powder bed needs to be fixed on the powder bed support platform inside the additive manufacturing vacuum-sealed cavity, such as... Figure 1 As shown, it serves for positioning and fixation. The powder bed support platform can be raised and lowered to adjust the distance between the powder bed and the laser entrance at the top of the vacuum-sealed cavity.

[0040] The ultrathin metal powder bed device of this invention can adjust the thickness of the powder in both X-ray and laser directions. Most importantly, it enables the streamlined preparation of ultrathin metal powder beds. The powder spreading method is simple and can significantly improve imaging quality. It is especially suitable for materials with high density, providing a solution for in-situ characterization of high-density materials. Furthermore, the adjustable thickness allows us to adjust the cooling rate of the powder bed and explore the effect of the cooling rate on experimental results, which is an aspect that has not been addressed in many current studies.

[0041] Vacuum-sealed cavity module

[0042] The vacuum-sealed cavity module includes a cavity, a vacuum device, a protective gas device, a cooling water device, and a real-time monitoring device for the metal powder bed. Several windows are symmetrically located on the top and sides of the cavity. The top window is a vertical laser incident window, and the side windows are X-ray transmission windows and observation windows for the real-time monitoring device for the metal powder bed.

[0043] When using a CO2 laser, the top window is fitted with zinc selenide glass; when using a fiber laser, the top window is fitted with quartz glass. Two symmetrical side windows for X-ray transmission are fitted with Compton film, while the remaining side windows are fitted with quartz glass. Furthermore, the materials for the top and side windows can be changed according to subsequent requirements.

[0044] The cavity is equipped with a vacuum port, a protective gas filling port, and a protective gas exhaust port to ensure an inert gas atmosphere inside the cavity during laser additive manufacturing. A powder bed support platform is located at the bottom of the cavity to position, fix, and raise the ultra-thin metal powder bed device.

[0045] The vacuum device is used to create a high vacuum within the cavity to prevent oxidation. The protective gas device is used to backflush the protective gas after evacuation, adjust the pressure within the cavity according to experimental requirements, and create an inert gas atmosphere to further prevent oxidation. The cooling water device is used to cool the cavity, providing protection and increasing the upper limit of the usable heating temperature for the experiment, thus allowing laser heating of high-melting-point materials such as high-temperature alloys. The real-time monitoring device for the metal powder bed is used to observe the changes in the state of the metal powder bed in real time during the experiment, thereby allowing for timely adjustment of experimental parameters or methods.

[0046] Furthermore, the vacuum-sealed cavity module of the present invention is also equipped with a "cooling water system" (such as...). Figure 1 As shown, the cooling water system enables the equipment cavity to be cooled in a timely manner, thereby allowing for experiments with higher laser power, achieving higher heating temperatures, and improving the flexibility of the experiments.

[0047] Displacement system module

[0048] The displacement system module is connected to the bottom of the vacuum-sealed cavity module and includes a horizontal CNC displacement stage and a vertical CNC displacement stage that can move independently of each other.

[0049] The function of the displacement stage is to control the direction, speed and distance of movement of the cavity, i.e., the powder bed, and to adjust the distance between the vacuum-sealed cavity and the vertically incident laser. The displacement stage has a large range of speed and distance adjustment and a large adjustment accuracy, which can greatly simplify the alignment process of the synchrotron radiation optical path.

[0050] The displacement system module of this invention has the following characteristics: a large speed adjustment range and adjustment accuracy, a large displacement distance and displacement accuracy, and the ability to achieve linkage in both horizontal and vertical directions. In particular, the high-precision ultra-small distance movement greatly facilitates the optical path alignment process during experiments. Synchrotron radiation optical path alignment is an unavoidable and very important process, which requires high precision. Due to the special nature of synchrotron radiation in-situ experiments, this process is very cumbersome and time-consuming. Therefore, this displacement stage is of great significance in simplifying the optical path alignment process.

[0051] The present invention also provides a method for ultra-thin powder coating of metal powder, the method comprising:

[0052] Step 1: Use adhesive to fix a metal substrate of appropriate size to the wall of a boron nitride sheet;

[0053] Step 2: Attach the boron nitride sheet with the metal substrate to the slotted side wall of the powder bed fixing device;

[0054] Step 3: Place the entire fixing device horizontally on its side, ensuring the exposed boron nitride sheet is tightly fitted against the stop block, with the side without boron nitride installed vertically upward (actually, tightly fitted against the protruding boron nitride sheet, such as...). Figure 3 , Figure 4 (as shown);

[0055] Step 4: Feed the powder vertically into the powder spreading area using an external feeding device, and finally insert the second boron nitride sheet completely from the side. Use a scraper to clean up excess powder to complete the ultra-thin powder spreading. Additional clamping parts can be used to clamp the powder bed on top to further fix the powder bed.

[0056] In addition, if there is insufficient powder in some areas of the powder bed after cleaning the powder bed surface, a small amount of powder can be added to the powder bed surface and the surface can be leveled with a scraper to fill the gap.

[0057] In addition, after laser heating is completed, the surface of the boron nitride sheet is cleaned with a small amount of alcohol to remove the carbonized adhesive and the boron nitride sheet can be reused; for impurities and dirt that are difficult to remove, sandpaper is used to polish them.

[0058] In summary, this invention, through the design of an ultrathin metal powder bed, a powder spreading method, and an improved supporting system, significantly improves the X-ray penetration flux during synchrotron radiation in-situ characterization, enhances the characterization effect, and improves data quality. It also makes in-situ characterization of heavier, high-density materials (which have weaker X-ray penetration) possible using laser additive manufacturing. The laser adjustment system simplifies equipment setup and greatly saves experimental space. The design of the CNC displacement system and the sealed cavity allows for further miniaturization of the cavity, saving experimental space, reducing equipment costs, and significantly shortening the X-ray propagation path within the cavity, further improving data quality.

[0059] In summary, the above only covers the main core content of this invention and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An experimental system for in-situ synchrotron radiation characterization of laser additive manufacturing, the system comprising a laser adjustment system module, an ultrathin metal powder bed device module, a vacuum-sealed cavity module, and a displacement system module, wherein the laser adjustment system module is located above the vacuum-sealed cavity module, the ultrathin metal powder bed device module is connected to the bottom of the vacuum-sealed cavity, and the displacement system module is connected to the bottom of the vacuum-sealed cavity; the laser adjustment system module includes a laser beam expander, a laser reflector, and a laser focusing lens, which are sequentially mounted via an optical device clamping device and a support rod; the ultrathin metal powder bed device module includes a powder bed, a powder bed fixing device, and a powder bed support stage, wherein the powder bed... The final bed has a sandwich structure of "boron nitride sheet - metal substrate - boron nitride sheet", with the thickness of the boron nitride sheet in the sub-millimeter range. The powder bed fixing device has a slot that matches the size of the powder bed and is used to stabilize the powder bed. The powder bed support platform has a slot that matches the size of the powder bed fixing device and is used to further stabilize the powder bed. The vacuum sealed cavity module includes a cavity, a vacuum device, a protective gas device, a cooling water device, and a real-time monitoring device for the metal powder bed. Several windows are symmetrically located on the top and sides of the cavity. The top window is a vertical laser incidence window, and the side windows are X-ray transmission windows and observation windows for the real-time monitoring device for the metal powder bed. When applying ultra-thin metal powder, the following steps are used: Step 1: Use adhesive to fix a metal substrate of appropriate size to the wall of a boron nitride sheet; Step 2: Attach the boron nitride sheet with the metal substrate to the slotted side wall of the powder bed fixing device; Step 3: Place the entire fixing device horizontally on its side, ensuring the exposed boron nitride sheet fits tightly against the stop block, with the side without boron nitride installed facing vertically upwards. Step 4: Feed the powder vertically into the powder spreading area using an external feeding device. Finally, insert the second boron nitride sheet completely from the side. Use a scraper to clean up excess powder to complete the ultra-thin powder spreading. Use additional clamping parts to hold the powder bed on top to further fix the powder bed. If there is insufficient powder in some places after cleaning the powder bed surface, add a small amount of powder to the powder bed surface and use a scraper to level the powder bed surface to fill it.

2. The experimental system according to claim 1, wherein, If a CO2 laser is used, zinc selenide glass is installed in the top window; if a fiber laser is used, quartz glass is installed in the top window.

3. The experimental system according to claim 1, wherein, The two symmetrical windows on the side for X-ray transmission are fitted with Compton film, while the remaining windows on the side are fitted with quartz glass.

4. The experimental system according to claim 1, wherein, The displacement system module is connected to the bottom of the vacuum-sealed cavity module and includes a horizontal CNC displacement stage and a vertical CNC displacement stage that can move independently of each other.

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