An in-situ stress measurement device and method for laser selective melting of multi-material interfaces

Abstract

The present invention discloses an in-situ stress measurement device and method for a multi-material interface by laser selective melting, which relates to the technical field of metal additive manufacturing. The in-situ stress measurement device for a multi-material interface by laser selective melting comprises a laser selective melting forming system, a stress and strain measuring device, an embedding system, and a positioning system. During the laser selective melting process, when material A is formed to the position where the stress and strain measuring device is to be embedded, the forming is suspended; the powder at the position to be embedded is first sucked out by a powder suction nozzle according to the coordinate information of the position to be embedded through the positioning system, and then the stress and strain measuring device is sucked out by an electromagnet and placed in the position to be embedded; the forming is continued to embed the stress and strain measuring device; then the multi-material structure can be formed, and in-situ stress and strain measurement of the multi-material interface can be achieved during the forming process of the multi-material structure.

Description

Technical Field

[0001] The present invention relates to the technical field of metal additive manufacturing, and in particular to an in-situ stress measurement method for a multi-material interface during laser selective melting. Background Art

[0002] Selective laser melting (SLM) is one of the mainstream technologies in the field of laser metal additive manufacturing. Based on the principle of discrete materials and layer-by-layer stacking, the technology first designs a three-dimensional model of the part. Then, the model is sliced ​​and layered according to the forming process. The resulting slice data is imported into the SLM forming equipment, and a specific scanning route is set. During the forming process, the metal powder evenly spread through the powder feeding device is melted layer by layer according to the set scanning route until the part is formed.

[0003] Multi-material parts are composed of multiple materials distributed inside the part, which can integrate the structures and functions of multiple materials to achieve specific properties (local wear resistance, high temperature resistance, high thermal conductivity, etc.) at specified locations on the part. In recent years, multi-material SLM technology has provided an innovative way to directly form complex multi-material parts. The overall mechanical properties of multi-material parts depend to a large extent on the quality of interface bonding. However, the mismatch in thermal expansion coefficients and stresses of different materials at the interface will produce residual stress, which will further cause interface cracking and component deformation, and even cause part warping and forming failure. In addition, it will also reduce the corrosion resistance of the material interface. Therefore, measuring and evaluating the residual stress at the interface of multi-material structures and exploring optimization processes are of great significance for the laser additive forming of multi-material structures.

[0004] At present, the stress of SLM-formed parts is usually characterized by offline measurement methods. However, this method can only obtain the overall stress value of the part after forming, and the stress of the part will be partially released after it is cut from the substrate. Therefore, it is impossible to accurately evaluate the stress evolution process of the part during the forming process. Recently, the in-situ stress measurement methods used in the SLM forming process include resistance strain gauge measurement method, displacement sensor detection method, etc. However, the resistance strain gauge measurement method requires pausing the forming process and opening the hatch to manually install the detection instrument, which is inefficient; the displacement sensor detection method can usually only measure the deformation in the direction perpendicular to the substrate, which cannot meet the needs of multi-material part interface stress measurement.

[0005] Therefore, there is an urgent need for an automated in-situ and precise measurement method for SLM multi-material interface stress. Summary of the Invention

[0006] The present invention aims to address, at least to some extent, one of the aforementioned technical problems in the prior art. To this end, an embodiment of the present invention provides an in-situ stress measurement device for a multi-material interface during selective laser melting, which enables in-situ monitoring of stress and strain at the interface of a multi-material structure during the forming process.

[0007] An embodiment of the present invention also provides an in-situ stress measurement method for a multi-material interface by laser selective melting.

[0008] According to an embodiment of the first aspect of the present invention, there is provided an in-situ stress measurement device for a laser selective melting multi-material interface, comprising a laser selective melting forming system, wherein the laser selective melting forming system comprises a forming cavity, an optical path component located above the forming cavity, a forming cylinder located below the forming cavity, a first powder cylinder for storing material A, a second powder silo for storing material B, and a powder spreading vehicle located between the first powder cylinder and the second powder silo, wherein the second powder silo is mounted on the powder spreading vehicle, the powder spreading vehicle is located above the first powder cylinder, and the powder spreading vehicle is provided with a powder cleaning device to spread the powders of the first powder cylinder and the second powder silo respectively onto the forming cylinder, thereby forming a multi-material structure; a stress and strain measuring device, wherein the stress and strain measuring device is embedded in the multi-material structure to form a temperature compensation measurement system, the stress and strain measuring device is connected to a computer via a demodulator, the computer is used to process the measurement data input by the stress and strain measuring device to display the stress and strain to be measured, and the stress and strain measuring device is connected to a temperature display display, and feeds back temperature data to the computer; an embedding system for embedding the stress and strain measuring device into the multi-material structure, the embedding system comprising a feed rack arranged in the forming cavity, a three-axis motion assembly arranged in the forming cavity, and a pick-and-place assembly installed on the three-axis motion assembly, the feed rack being provided with a clamping position for placing the stress and strain measuring device and being set with a corresponding number, the coordinate information of the corresponding clamping position in the x-direction and z-direction and the information of the stress and strain measuring device corresponding to the number being stored in the computer, the pick-and-place assembly being driven by the three-axis motion assembly to embed the stress and strain measuring device on the feed rack into the multi-material structure, the three-axis motion assembly being further connected to a powder suction nozzle to remove powder from the position to be embedded in the multi-material structure; and a positioning system, the positioning system comprising a control assembly and a plurality of magnetic induction switches, each of the magnetic induction switches being used to sense the position of the three-axis motion assembly and the feed rack, and the control assembly receiving the electrical signal of the magnetic induction switch to control the embedding system.

[0009] The above-mentioned in-situ stress measurement device for a multi-material interface during laser selective melting has at least the following beneficial effects: The above-mentioned technical solution breaks through the traditional method of manually inserting measurement components by stopping the machine. Instead, it combines a positioning system with an embedding system based on an xyz three-axis platform to achieve precise and automatic embedding of stress and strain measurement components during the forming process, improving efficiency and measurement accuracy. Therefore, the present invention achieves the integration of component structures while ensuring the transmission stability of measurement signals and the accuracy of measurement data, which has a significant impact on promoting the advancement of additive manufacturing technology. The stress and strain measurement device includes a fiber Bragg grating (FBG) and a thermocouple. The present invention first uses a single material to form a structure with a reserved position for embedding the fiber Bragg grating and thermocouple; then uses a positioning system to obtain the position information of the embedded fiber Bragg grating and thermocouple; then, based on the position information, a three-axis motion assembly grasps the fiber Bragg grating and thermocouple and places them in the embedding position. Next, the multi-material structure is formed, with the multi-material interface directly above the fiber Bragg grating. This allows in-situ monitoring of stress and strain at the interface of the multi-material structure during the forming process.

[0010] According to an embodiment of the first aspect of the present invention, the three-axis motion assembly includes an x-axis motion assembly arranged in the forming cavity, a y-axis motion assembly installed on the x-axis motion assembly, and a z-axis motion assembly installed on the y-axis motion assembly. The x-axis motion assembly, the y-axis motion assembly, and the z-axis motion assembly are respectively installed with the magnetic induction switch. The pick-and-place assembly includes a rotating frame installed on the z-axis motion assembly and a plurality of electromagnets arranged on the rotating frame. The powder suction nozzle is installed at the lower end of the z-axis motion assembly. The installation height of the rotating frame on the z-axis motion assembly is higher than the powder suction nozzle. The electromagnet grabs and embeds the stress and strain measuring device through a fixture assembly.

[0011] According to an embodiment of the first aspect of the present invention, the fixture assembly includes an upper fixture and a lower fixture that match each other, the stress and strain measuring device is bound to the upper fixture, the pick-and-place assembly magnetically connects the upper fixture through the electromagnet, and the lower fixture is formed in a multi-material structure. The electromagnet grabs the upper fixture and then matches it with the lower fixture, thereby burying the stress and strain measuring device in the multi-material structure.

[0012] According to an embodiment of the first aspect of the present invention, the electromagnet is provided with a protrusion, and the upper fixture is provided with a groove that cooperates with the protrusion.

[0013] According to an embodiment of the first aspect of the present invention, the upper fixture is provided with a mechanical locking structure, and the lower fixture is formed with an inverted cone structure to guide the insertion of the mechanical locking structure of the upper fixture.

[0014] According to an embodiment of the first aspect of the present invention, the stress and strain measurement device includes a fiber Bragg grating and a thermocouple.

[0015] According to an embodiment of the first aspect of the present invention, the fiber Bragg grating (FBG) comprises a core, a cladding, a coating, and a sheath, which are sequentially wrapped from the inside out. The sheath is made of thermally insulating material and is processed into a semicircular shape to facilitate safe, reliable, and low-profile embedding of the fiber Bragg grating into a multi-material structure. The stress and strain measurement results of the fiber Bragg grating are caused by both stress and temperature. Thermocouples are embedded in one side of the fiber Bragg grating and spaced apart to measure temperature and compensate for the temperature-induced measurement results of the fiber Bragg grating.

[0016] According to an embodiment of the first aspect of the present invention, the stress and strain measurement device satisfies:

[0017] Δλ B =λ B (1-Pe)Δε+λ B (α-ξ)ΔT, where

[0018] Δλ B is the change in reflected wavelength; Δε is the change in strain; ΔT is the change in temperature; Pe is the effective elastic-optical coefficient; α is the linear expansion coefficient of the optical fiber; ξ is the thermo-optical coefficient of the optical fiber material; Pe, α, and ξ are standard coefficients; Δλ B The measured value Δε is obtained by the fiber Bragg grating and is displayed on a computer after being processed by a demodulator; ΔT is measured by the thermocouple.

[0019] According to an embodiment of the first aspect of the present invention, the laser selective melting forming system further includes a powder recovery cylinder for recovering excess powder during the forming process, and the powder recovery cylinder and the first powder cylinder are respectively located on both sides of the forming cylinder.

[0020] According to an embodiment of the second aspect of the present invention, a method for in-situ stress measurement of a multi-material interface by selective laser melting is provided, using the in-situ stress measurement device for selective laser melting of a multi-material interface according to the embodiment of the first aspect of the present invention, comprising the following steps:

[0021] Step S1, preparation stage;

[0022] Preparation for the selective laser melting (SLM) system: Use 3D modeling software to create a model of the multi-material structure and the lower fixture. Reserve space consistent with the size of the stress and strain measurement device where it will be embedded. Slice the model data of the multi-material structure and the lower fixture and import it into the SLM equipment. Add powder material and the forming substrate to the SLM system. Level the forming substrate to complete the preparation of the SLM system.

[0023] Preparation for embedding system: After binding the stress and strain measuring device to the upper fixture, place it on the card position of the feeder rack. The control component numbers the different card positions of the feeder rack to determine the type of stress and strain measuring device placed on the card position. When the embedding system takes it, the rotating frame of the pick-and-place component is made perpendicular to the z-axis motion component to complete the embedding system preparation.

[0024] Prepare the positioning system by returning each axis of the three-axis motion assembly to zero, starting with the z-axis, then returning the z-axis motion assembly to a safe position, then returning the x- and y-axes to zero, and finally moving the three-axis motion assembly to a safe position to complete the positioning system preparation.

[0025] Prepare stress and strain measurement devices and connect the lines between stress and strain measurement devices;

[0026] Step S2, forming stage;

[0027] The laser selective melting forming system is working. The laser selective melting forming system uses material A to form a solid body of material A with a reserved position for embedding stress and strain measurement devices. The forming process is paused and the powder spreading vehicle returns to the side of the first powder tank.

[0028] The embedding system and the positioning system work. The embedding system first passes over the powder spreading car and reaches the forming cylinder area. Then, it reads the position information of the position to be embedded and the lower fixture from the computer, and transmits the relevant action instructions to the embedding system. The embedding system moves the powder suction nozzle to the corresponding position to remove the powder from the position to be embedded. Then, the coordinate information and number information of the stress and strain measuring device on the feeder are read from the computer system, and the relevant action instructions are transmitted to the embedding system, so that the pick-and-place component moves to the position where the stress and strain measuring device is stored. The electromagnet is energized to adsorb the upper fixture bound to the stress and strain measuring device. The embedding system absorbs the stress and strain measuring device and moves it to the position to be embedded. During the movement, the rotating frame rotates downward 90° to make the upper fixture and the lower fixture cooperate. The electromagnet is de-energized, and the adsorption with the upper fixture is cancelled. The stress and strain measuring device is then placed in the reserved embedding position.

[0029] The embedding system returns to a safe position, and the laser selective melting forming system continues to form using material A, so that the stress and strain measurement device is completely embedded;

[0030] Step S3, measurement phase;

[0031] The selective laser melting forming system forms a multi-material structure including a material A region and a material B region above the formed material A solid body, and the multi-material interface of the multi-material structure is located directly above the stress and strain measuring device;

[0032] During the forming process, the stress and strain of the multi-material interface can be displayed in real time on the computer.

[0033] The above-mentioned method for in-situ stress measurement of a multi-material interface by laser selective melting has at least the following beneficial effects: during the laser selective melting process, when material A is formed to the position where the stress and strain measuring device is to be embedded, the forming process is paused; through the positioning system, the powder suction nozzle is first used to remove the powder at the position to be embedded according to the coordinate information of the position to be embedded, and then the stress and strain measuring device is sucked by the electromagnet and placed in the position to be embedded; the forming process is continued to embed the stress and strain measuring device; then the multi-material structure can be formed, and in-situ stress and strain measurement of the multi-material interface can be achieved during the forming process of the multi-material structure. During the laser selective melting process of a multi-material part, the present invention uses a positioning system and an embedding system to embed a fiber Bragg grating that can measure stress and strain data and a thermocouple that can measure temperature as temperature compensation near the material interface, so that the fiber Bragg grating can collect stress and strain signals at the material interface, and finally achieves real-time, in-situ monitoring of the stress evolution behavior of the multi-material part interface during the forming process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments;

[0035] Figure 1 1. It is a schematic structural diagram of an in-situ stress measurement device for a multi-material interface by selective laser melting according to an embodiment of the present invention;

[0036] Figure 2 is a schematic structural diagram of an embedded system according to an embodiment of the present invention;

[0037] Figure 3 2. It is a schematic diagram of the structure of the powder suction nozzle in the embodiment of the present invention for sucking away the powder at the position to be buried;

[0038] Figure 4 2 is a schematic structural diagram of an embedding system according to an embodiment of the present invention placing a stress and strain measuring device in a position to be embedded;

[0039] Figure 5 2 is a schematic structural diagram of a multi-material structure after completing multi-material interface stress and strain measurement in an embodiment of the present invention;

[0040] Figure 6 2 is a schematic structural diagram of a fixture assembly according to an embodiment of the present invention;

[0041] Figure 7 It is a schematic flow chart of the in-situ stress and strain measurement method of the laser selective melting multi-material interface of the present invention.

[0042] Reference numerals: selective laser melting forming system 10, forming cavity 11, optical path component 12, second powder silo 13, first powder cylinder 14, powder spreading vehicle 15, powder cleaning device 16, forming cylinder 17, powder recovery cylinder 18;

[0043] Embedding system 20, feeding rack 21, three-axis motion assembly 22, x-axis motion assembly 221, y-axis motion assembly 222, z-axis motion assembly 223, pick-and-place assembly 23, rotating rack 231, electromagnet 232, powder suction nozzle 241, powder suction nozzle air pipe 242, fixture assembly 25, upper fixture 251, lower fixture 252, mechanical locking structure 253, inverted cone structure 254;

[0044] Multi-material structure 31, material A region 311, material B region 312, multi-material interface 313, reserved semicircular groove 314, reserved U-shaped groove 315, powder to be embedded 316, fiber Bragg grating 32, thermocouple 33, temperature display 34, demodulator 35, computer 36;

[0045] Magnetic induction switch 41. DETAILED DESCRIPTION

[0046] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it should not be understood as a limitation on the scope of protection of the present invention.

[0047] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0048] In the description of the present invention, "several" means one or more, "many" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0049] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0050] Reference Figures 1 to 6 , presents a stress in-situ measurement device for a multi-material interface formed by selective laser melting, including a selective laser melting forming system 10, a stress and strain measuring device, an embedding system 20, and a positioning system.

[0051] Specifically, such as Figure 1 As shown, the laser selective melting forming system 10 includes a forming chamber 11, an optical path component 12 located above the forming chamber 11, a forming cylinder 17 located below the forming chamber 11, a first powder cylinder 14 for storing material A, a second powder silo 13 for storing material B, and a powder spreading vehicle 15 located between the first powder cylinder 14 and the second powder silo 13. The second powder silo 13 is mounted on the powder spreading vehicle 15, which is located above the first powder cylinder 14. The powder spreading vehicle 15 is provided with a powder cleaning device 16 to spread the powders in the first powder cylinder 14 and the second powder silo 13 respectively onto the forming cylinder 17, thereby forming a multi-material structure 31. Both materials A and B are stored in the form of powder. Driven by a motor, the powder spreading vehicle 6 can spread the powders in the first powder cylinder 14 or the second powder silo 13 onto the forming cylinder 10.

[0052] Among them, the optical path component 12 includes a laser, a beam expander or a collimator, a scanning galvanometer and a focusing mirror (f-θ mirror). The specific structure of the optical path component 12 is known to those skilled in the art and will not be repeated here.

[0053] In addition, the selective laser melting forming system 10 further includes a powder recovery cylinder 18 for recovering excess powder during the forming process. The powder recovery cylinder 18 and the first powder cylinder 14 are respectively located on both sides of the forming cylinder 17 .

[0054] In this embodiment, the stress and strain measuring device is embedded in the multi-material structure 31 to form a temperature compensation measurement system. Figure 3 and Figure 4 The stress and strain measuring device includes a fiber Bragg grating 32 and a thermocouple 33. Furthermore, the fiber Bragg grating 32 includes a core, a cladding, a coating layer, and a sheath, which are wrapped in sequence from the inside to the outside. In order to adapt to the forming conditions of laser selective melting, the sheath is processed into a semicircular shape. The sheath is made of a heat-insulating material so that the fiber Bragg grating 32 can be safely and reliably embedded in the multi-material structure 31. At the position where the stress and strain measuring device needs to be embedded in the multi-material structure 31, a reserved semicircular groove 314 for embedding the fiber Bragg grating 32 and a reserved U-shaped groove 315 for embedding the thermocouple 33 are provided.

[0055] The stress and strain measurements of the fiber Bragg grating (FBG) 32 are caused by both stress and temperature. Thermocouples 33 are embedded in one side of the FBG 32 and spaced apart to measure temperature and compensate for temperature-induced measurements of the FBG 32. The stress and strain measurement device is connected to a computer 36 via a demodulator 35. Computer 36 processes the measurement data input by the stress and strain measurement device to display the measured stress and strain. The stress and strain measurement device is also connected to a temperature display 34, which provides feedback to computer 36.

[0056] Stress and strain measurement devices meet the following requirements: Δλ B =λ B (1-PeΔε+λ B (α-ξ)ΔT.

[0057] Δλ B =λ B (1-Pe)Δε+λ B (α-ξ)ΔT.

[0058] Where Pe is the effective elastic-optic coefficient, α is the linear expansion coefficient of the optical fiber, and ξ is the thermo-optic coefficient of the optical fiber material; Pe, α, and ξ are standard coefficients that can be obtained by referring to relevant standards. B is the change in reflected wavelength; Δε is the change in strain; ΔT is the change in temperature; Δλ B It is measured by fiber Bragg grating and displayed on a computer through demodulator processing; Δε is measured by thermocouple.

[0059] Combine Figures 2 to 5 The embedding system 20 is used to embed the stress and strain measuring device into the multi-material structure 31. The embedding system 20 includes a feed rack 21 arranged in the forming cavity 11, a three-axis motion component 22 arranged in the forming cavity 11, and a pick-and-place component 23 installed on the three-axis motion component 22. The feed rack 21 is provided with a clamping position for placing the stress and strain measuring device and is set with a corresponding number. The coordinate information of the corresponding clamping position in the x-direction and z-direction and the information of the stress and strain measuring device corresponding to the number are stored in the computer. The pick-and-place component 23 is driven by the three-axis motion component 22 to embed the stress and strain measuring device on the feed rack 21 into the multi-material structure 31. The three-axis motion component 22 is also connected to a powder suction nozzle 241 to remove the powder at the position to be embedded in the multi-material structure 31.

[0060] Reference Figure 2Specifically, the three-axis motion assembly 22 includes an x-axis motion assembly 221 disposed in the forming cavity 11, a y-axis motion assembly 222 mounted on the x-axis motion assembly 221, and a z-axis motion assembly 223 mounted on the y-axis motion assembly 222. In this embodiment, the x-axis motion assembly includes a single-axis driver and a linear motion guide rail, which are mounted on the front and rear side walls of the forming cavity 11; the y-axis motion assembly is a single-axis driver, which is mounted on the x-axis motion assembly; the z-axis motion assembly is an electric telescopic cylinder, which is mounted on the y-axis motion assembly; those skilled in the art can refer to the specific connection position relationship. Figure 2 Make a design.

[0061] The pick-and-place assembly 23 includes a rotating frame 231 mounted on the z-axis motion assembly 223 and multiple electromagnets 232 mounted on the rotating frame 231. The pick-and-place assembly 23 and a powder suction nozzle 241 are mounted at the lower end of the telescopic rod of the electric telescopic cylinder. The rotating frame 231 is mounted on the z-axis motion assembly 223 at a height higher than the powder suction nozzle 241, specifically 20 mm higher. The electromagnets 232 grasp and embed the stress and strain measurement device through the fixture assembly 25.

[0062] The fixture assembly 25 includes an upper fixture 251 and a lower fixture 252 that match each other. The stress and strain measuring device is bound to the upper fixture 251. The pick-and-place assembly 23 magnetically connects the upper fixture 251 through the electromagnet 232. The lower fixture 252 is formed in the multi-material structure 31. The electromagnet 232 grabs the upper fixture 251 and then cooperates with the lower fixture 252, thereby embedding the stress and strain measuring device into the multi-material structure 31.

[0063] The stress and strain measurement device is attached to an upper fixture 251 and placed on the feeder 21. A single upper fixture 251 is attached to each end of the fiber Bragg grating 32, with the distance between the two upper fixtures being the same as the distance between the two electromagnets 20 of the pick-and-place assembly 23. A single upper fixture is attached to one end of the thermocouple 33. After the stress and strain measurement device is positioned for embedding, each fixture assembly 25 secures the device, preventing it from shifting from its embedded position during subsequent SLM processes.

[0064] Specifically, the electromagnet 232 is provided with a protrusion, and the upper fixture 251 is provided with a groove that matches the protrusion. Figure 6 The upper fixture 251 is provided with a mechanical locking structure 253, and the lower fixture 252 is formed with an inverted cone structure 254 to guide the insertion of the mechanical locking structure of the upper fixture 251.

[0065] The positioning system includes a control component and multiple magnetic induction switches 41. Each magnetic induction switch 41 is used to sense the position of the three-axis motion assembly 22 and the feeder 21. The control component receives electrical signals from the magnetic induction switches 41 to control the embedding system 20. In this embodiment, five magnetic induction switches 41 are provided: one each for the x-axis motion assembly 221, the y-axis motion assembly 222, and the z-axis motion assembly 223, and two for the feeder 21.

[0066] The positioning system can make the projection center of the z-axis motion assembly 223 located at the center of the forming cylinder 17 when the embedding system is zeroed in the x and y directions; when the z-axis motion system is zeroed, the powder suction nozzle 241 is 0.2 mm away from the bottom surface of the forming cavity 17; one of the two magnetic induction switches 41 of the feeding rack 21 is located directly above the center of the upper fixture 251 to which the fiber Bragg grating 32 is bound, and the other is located directly above the center of the upper fixture to which the thermocouple 33 is bound. The two magnetic induction switches 41 of the feeding rack 21 are collinear in the vertical direction and are located on the side close to the operator.

[0067] In other embodiments, the multi-material embedded object, i.e., the stress and strain measurement device, is not limited to fiber Bragg gratings (FBGs) and thermocouples, but may also be other ferromagnetic devices or devices that can be bound to ferromagnetic materials without affecting their functionality. The embedding system can read the exact location information of the embedded position of the stress and strain measurement device, as well as the x- and z-direction coordinates of the positioning position on the feed rack 21 and the component type information from a computer, and perform a series of operations including removing powder from the location to be embedded in the stress and strain measurement device and embedding the stress and strain measurement device.

[0068] The embodiment of the present invention also provides a method for in-situ stress measurement of a multi-material interface by laser selective melting. Using the above-mentioned in-situ stress measurement device for laser selective melting of a multi-material interface, referring to Figure 7 , including the following steps:

[0069] Step S1, preparation stage.

[0070] S1.1. Prepare the laser selective melting system 10. Use 3D modeling software to create a model of the multi-material structure 31 and the lower fixture 252. Reserve space consistent with the size of the stress and strain measuring device at the location where the stress and strain measuring device needs to be embedded. A semicircular groove 314 needs to be reserved for the fiber Bragg grating 32, and a U-shaped groove 315 needs to be reserved for the thermocouple 33. At the same time, based on the accuracy of the SLM equipment, reasonable tolerances are set to facilitate the coordination of the stress and strain measuring device with the reserved position and the mechanical locking structure 253 between the lower fixture 252 and the upper fixture 251. Slice the model data and import it into the SLM equipment; add the powder material and the forming substrate to the laser selective melting system, level the substrate, and complete the preparation of the laser selective melting system.

[0071] S1.2, prepare the embedding system 20, bind the stress and strain measuring device to the upper fixture 251 and place it on the card position of the feed rack 21, and number the different card positions of the feed rack 21 through the control component to determine the type of stress and strain measuring device placed on the card position, and wait for the embedding system to use it, so that the rotating frame 231 of the pick-and-place component 23 is perpendicular to the z-axis motion component 223, and the embedding system preparation work is completed.

[0072] S1.3, positioning system preparation, reset each coordinate axis of the three-axis motion assembly 22 to zero, first reset the z-axis to zero, then return the telescopic cylinder of the z-axis motion assembly 223 to a safe position, then reset the x and y axes, and then move the three-axis motion assembly 22 to a safe position to complete the positioning system preparation.

[0073] S1.4, prepare stress and strain measurement devices and connect the lines between the stress and strain measurement devices.

[0074] Step S2, forming stage.

[0075] S2.1, the laser selective melting forming system 10 works, and the laser selective melting forming system 10 uses material A to form an A material entity with a reserved position for embedding a stress and strain measuring device. The forming is paused, and the powder spreading car 15 returns to the side of the first powder cylinder 14.

[0076] S2.2, the embedding system and the positioning system work. The embedding system first passes over the powder spreading car 15 and reaches the forming cylinder 17 area, then reads the position information of the position to be embedded and the lower fixture 252 from the computer, and transmits the relevant action instructions to the embedding system. The embedding system moves the powder suction nozzle 241 to the corresponding position. The powder suction nozzle 241 is connected to the powder suction nozzle air pipe 242, and the powder 316 at the position to be embedded is removed by suction through the powder suction nozzle air pipe 242. Subsequently, the coordinate information and number information of the fiber Bragg grating 32 on the feeding rack 21 are read from the computer system, and the relevant action instructions are transmitted to the embedding system 20, so that the pick-and-place component moves to the position where the fiber Bragg grating 32 is stored. The electromagnet 232 is energized to adsorb the upper fixture 251 bound to the fiber Bragg grating 32. The embedding system absorbs the fiber Bragg grating 32 and moves it to the position to be embedded. During the movement, the rotating rack 231 is rotated downward by 90° to cooperate with the upper fixture 251 and the lower fixture 252. The electromagnet 232 is de-energized, and the adsorption with the upper fixture 251 is cancelled. The fiber Bragg grating 32 is then placed in the reserved embedding position.

[0077] S2.3, then read the coordinate information and number information of the thermocouple 33 position on the feeding rack 21 from the computer system, and transmit the relevant action instructions to the embedding system 20, so that the pick-up and placement component moves to the position where the thermocouple 33 is stored, and the electromagnet 232 is energized to adsorb the upper fixture 251 bound to the thermocouple 33. The embedding system absorbs the thermocouple 33 and moves it to the position to be embedded. During the movement, the rotating rack 231 rotates downward 90°, so that the upper fixture 251 and the lower fixture 252 cooperate. The electromagnet 232 is powered off, and the adsorption with the upper fixture 251 is cancelled, and the thermocouple 33 is placed in the reserved embedding position.

[0078] S2.4, the embedding system 20 returns to a safe position, and the selective laser melting forming system 10 continues to form using material A, so that the stress and strain measuring device is completely embedded.

[0079] Step S3: measurement phase.

[0080] S3.1. Selective laser melting system 10 forms a multi-material structure 31 comprising a material A region 311 and a material B region 312 above the formed material A solid. Multi-material interface 313 of multi-material structure 31 is located directly above the stress and strain measurement device.

[0081] S3.2, during the forming process, the stress and strain of the multi-material interface 313 can be displayed in real time on the computer 36.

[0082] In this embodiment, refer to Figure 1 and Figure 2, showing an xyz coordinate system, where the origin is located at the center of the forming cylinder. Because the y-coordinate information for the corresponding latch is unknown, the embedding system 20 first moves to the negative y-axis limit. Then, based on the x- and z-coordinates of the corresponding latch stored in the computer, it moves to the corresponding x- and z-positions. Subsequently, the embedding system 20 moves in the positive y-axis direction. When it approaches the magnetic induction switch 41 on the corresponding latch, the embedding system 20 stops moving, at which point the center of the electromagnet 232 coincides with the center of the upper fixture 251.

[0083] It is understandable that in the present invention, when forming material A to the position to be embedded in the position during the laser selective melting process, the forming is suspended. Through the positioning system, the powder suction nozzle is first used to suck out the powder at the position to be embedded according to the coordinate information of the position to be embedded, and then the stress strain measuring device is sucked by the electromagnet and placed in the position to be embedded. The forming is continued to embed the stress strain measuring device. Then the multi-material structure can be formed, and in the process of forming the multi-material structure, the in-situ measurement of the stress and strain of the multi-material interface can be realized. In addition, the present invention breaks through the traditional method of stopping the machine and manually placing the measuring components, and instead adopts a combination of a positioning system and an embedding system based on an xyz three-axis platform to realize the accurate and automatic embedding of the stress strain measuring device during the forming process, thereby improving efficiency and measurement accuracy. Therefore, while ensuring the transmission stability of the measurement signal and the accuracy of the measurement data, the present invention realizes the integration of the part structure, which plays a significant role in promoting the progress of additive manufacturing technology.

[0084] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the technical field without departing from the scope of the present invention.

Claims

1. An in-situ stress measurement device for a multi-material interface subjected to selective laser melting, characterized by: include A selective laser melting forming system includes a forming chamber, an optical path assembly located above the forming chamber, a forming cylinder located below the forming chamber, a first powder cylinder for storing material A, a second powder silo for storing material B, and a powder spreading vehicle located between the first powder cylinder and the second powder silo. The second powder silo is mounted on the powder spreading vehicle, which is located above the first powder cylinder. The powder spreading vehicle is equipped with a powder cleaning device capable of spreading powder from the first and second powder silos, respectively, onto the forming cylinder, thereby forming a multi-material structure. a stress and strain measuring device embedded in the multi-material structure to form a temperature-compensated measurement system; the stress and strain measuring device is connected to a computer via a demodulator; the computer is used to process measurement data input by the stress and strain measuring device to display the stress and strain to be measured; the stress and strain measuring device is connected to a temperature display and feeds back temperature data to the computer; An embedding system for embedding the stress and strain measuring device into the multi-material structure, the embedding system comprising a feed rack disposed within the forming cavity, a three-axis motion assembly disposed within the forming cavity, and a pick-and-place assembly mounted on the three-axis motion assembly. The feed rack is provided with positions for placing the stress and strain measuring device and is assigned corresponding numbers. The coordinate information of the corresponding positions in the x- and z-directions and the information of the stress and strain measuring device corresponding to the numbers are stored in a computer. The pick-and-place assembly is driven by the three-axis motion assembly to embed the stress and strain measuring device on the feed rack into the multi-material structure. The three-axis motion assembly is also connected to a powder suction nozzle to remove powder from the position of the multi-material structure to be embedded. as well as The positioning system includes a control component and multiple magnetic induction switches, each of which is used to sense the position of the three-axis motion component and the feed rack. The control component receives the electrical signal of the magnetic induction switch to control the embedding system.

2. The in-situ stress measurement device for a multi-material interface by selective laser melting according to claim 1, characterized in that: The three-axis motion assembly includes an x-axis motion assembly arranged in the forming cavity, a y-axis motion assembly installed on the x-axis motion assembly, and a z-axis motion assembly installed on the y-axis motion assembly. The x-axis motion assembly, the y-axis motion assembly, and the z-axis motion assembly are respectively installed with the magnetic induction switch. The pick-and-place assembly includes a rotating frame installed on the z-axis motion assembly and a plurality of electromagnets arranged on the rotating frame. The powder suction nozzle is installed at the lower end of the z-axis motion assembly. The installation height of the rotating frame on the z-axis motion assembly is higher than the powder suction nozzle. The electromagnet grabs and embeds the stress and strain measuring device through a fixture assembly.

3. The in-situ stress measurement device for a multi-material interface subjected to selective laser melting according to claim 2, characterized in that: The fixture assembly includes an upper fixture and a lower fixture that match each other. The stress and strain measuring device is bound to the upper fixture. The pick-and-place assembly magnetically connects the upper fixture through the electromagnet. The lower fixture is formed in a multi-material structure. The electromagnet grabs the upper fixture and then matches it with the lower fixture, thereby embedding the stress and strain measuring device into the multi-material structure.

4. The in-situ stress measurement device for a multi-material interface subjected to selective laser melting according to claim 3, characterized in that: The electromagnet is provided with a protrusion, and the upper clamp is provided with a groove matched with the protrusion.

5. The in-situ stress measurement device for a multi-material interface subjected to selective laser melting according to claim 3, characterized in that: The upper fixture is provided with a mechanical locking structure, and the lower fixture is formed with an inverted cone structure to guide the mechanical locking structure of the upper fixture to be inserted.

6. The in-situ stress measurement device for a multi-material interface by selective laser melting according to any one of claims 3 to 5, characterized in that: The stress and strain measuring device includes a fiber Bragg grating and a thermocouple.

7. The in-situ stress measurement device for a multi-material interface subjected to selective laser melting according to claim 6, characterized in that: The fiber Bragg grating includes a core, a cladding, a coating, and a sheath, which are wrapped sequentially from the inside out. The sheath is made of a heat-insulating material and is processed into a semicircular shape to facilitate the safe, reliable, and low-profile embedding of the fiber Bragg grating into a multi-material structure. The stress and strain measurement results of the fiber Bragg grating are caused by both stress and temperature. The thermocouples are embedded in one side of the fiber Bragg grating and are distributed at intervals to measure temperature to compensate for the temperature-induced measurement results of the fiber Bragg grating.

8. The in-situ stress measurement device for a multi-material interface by selective laser melting according to any one of claims 3 to 5, characterized in that: The selective laser melting forming system further includes a powder recovery cylinder for recovering excess powder during the forming process. The powder recovery cylinder and the first powder cylinder are respectively located on both sides of the forming cylinder.

9. A method for in-situ measurement of stress at a multi-material interface by laser selective melting, characterized in that: The in-situ stress measurement device for a multi-material interface using laser selective melting according to any one of claims 3 to 8 comprises the following steps: Step S1, preparation stage; Prepare the selective laser melting system. Use 3D modeling software to build a model of the multi-material structure and the lower fixture. Reserve space consistent with the size of the stress and strain measurement device where it will be embedded. Slice the model data of the multi-material structure and the lower fixture and import it into the SLM equipment. Add powder material and the forming substrate to the selective laser melting system. Level the forming substrate to complete the preparation of the selective laser melting system. Preparation for embedding system: After binding the stress and strain measuring device to the upper fixture, place it on the card position of the feeder rack. The control component numbers the different card positions of the feeder rack to determine the type of stress and strain measuring device placed on the card position. When the embedding system takes it, the rotating frame of the pick-and-place component is made perpendicular to the z-axis motion component to complete the embedding system preparation. Prepare the positioning system by returning each axis of the three-axis motion assembly to zero, starting with the z-axis, then returning the z-axis motion assembly to a safe position, then returning the x- and y-axes to zero, and finally moving the three-axis motion assembly to a safe position to complete the positioning system preparation. Prepare stress and strain measurement devices and connect the lines between stress and strain measurement devices; Step S2, forming stage; The laser selective melting forming system is working. The laser selective melting forming system uses material A to form a solid body of material A with a reserved position for embedding stress and strain measurement devices. The forming process is paused and the powder spreading vehicle returns to the side of the first powder tank. The embedding system and the positioning system work. The embedding system first passes over the powder spreading car and reaches the forming cylinder area. Then, it reads the position information of the position to be embedded and the lower fixture from the computer, and transmits the relevant action instructions to the embedding system. The embedding system moves the powder suction nozzle to the corresponding position to remove the powder from the position to be embedded. Then, the coordinate information and number information of the stress and strain measuring device on the feeder are read from the computer system, and the relevant action instructions are transmitted to the embedding system, so that the pick-and-place component moves to the position where the stress and strain measuring device is stored. The electromagnet is energized to adsorb the upper fixture bound to the stress and strain measuring device. The embedding system absorbs the stress and strain measuring device and moves it to the position to be embedded. During the movement, the rotating frame rotates downward 90° to make the upper fixture and the lower fixture cooperate. The electromagnet is de-energized, and the adsorption with the upper fixture is cancelled. The stress and strain measuring device is then placed in the reserved embedding position. The embedding system returns to a safe position, and the laser selective melting forming system continues to form using material A, so that the stress and strain measurement device is completely embedded; Step S3, measurement phase; The selective laser melting forming system forms a multi-material structure including a material A region and a material B region above the formed material A solid body, and the multi-material interface of the multi-material structure is located directly above the stress and strain measuring device; During the forming process, the stress and strain of the multi-material interface can be displayed in real time on the computer.

Images