In-situ measuring method and measuring device for residual stress of laser additive manufacturing part

Abstract

The invention discloses a laser additive manufacturing part residual stress in-situ measurement method and device, and the method comprises the steps: preprocessing, synchronous monitoring, data correction, and whole-process output, and comprises the steps: synchronously collecting lattice strain data and temperature data of a same monitoring point, and carrying out the in-situ measurement of the residual stress of a laser additive manufacturing part; and a thermal-mechanical coupling correction model is combined to eliminate temperature errors, and full-flow accurate measurement of dynamic stress in the forming process and static stress after forming is achieved. The matching device comprises a core measuring unit and a data processing unit, and has the advantages of in-situ synchronization, nondestructive testing, interference resistance, low cost and the like. According to the measuring method and the measuring device, full-process accurate capturing of residual stress in the forming process and after forming can be achieved, real-time and reliable data support is provided for optimization of the laser additive manufacturing process, and the component forming quality and the service reliability are improved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing, and specifically provides a method and device for in-situ measurement of residual stress in laser additive manufactured parts. Background Technology

[0002] Laser additive manufacturing technology uses a laser as a heat source to melt and deposit materials layer by layer. Its advantages, such as high degree of freedom in forming, high material utilization, and the ability to manufacture complex structural components, have led to its widespread application in aerospace, high-end equipment, and other fields. However, the rapid heating and cooling process creates a dramatic temperature gradient, resulting in uneven residual stress within the component. These residual stresses can easily cause defects such as cracking, deformation, and performance degradation, directly determining the component's reliability and service life. This is one of the key bottlenecks restricting the large-scale application of laser additive manufacturing technology.

[0003] Existing methods for measuring residual stress have many significant shortcomings, making it difficult to meet the process control and quality inspection requirements of laser additive manufacturing:

[0004] 1) Offline measurement methods (such as drilling method and X-ray diffraction method): Measurements need to be taken after the component is formed. They cannot capture the dynamic evolution of residual stress during the forming process. The measurement results lag behind the process control requirements and it is difficult to achieve real-time process optimization.

[0005] 2) Existing in-situ measurement methods: Most of them only monitor stress or temperature parameters, ignoring the important influence of thermo-mechanical coupling effect on residual stress, resulting in low measurement accuracy and failure to accurately reflect the true stress state of the component;

[0006] 3) High-precision measurement methods (such as neutron diffraction): rely on large-scale special equipment, the purchase and operation costs of the equipment are high, and the portability is extremely poor, which cannot meet the rapid detection needs of industrial sites.

[0007] 4) Measurement stability issues: The laser additive manufacturing process involves harsh conditions such as high temperature, metal splash, and dust. Existing measurement probes are susceptible to high temperature corrosion and splash contamination, resulting in insufficient measurement stability and affecting the continuity and reliability of data.

[0008] In summary, there is an urgent need for a residual stress measurement solution that is adaptable to the harsh working conditions of laser additive manufacturing, can simultaneously capture key thermo-mechanical parameters, and is in-situ non-destructive and accurate, in order to solve many of the pain points of existing technologies. Summary of the Invention

[0009] Therefore, the purpose of this invention is to provide an in-situ measurement method and device for residual stress in laser additive manufacturing parts, so as to solve the problems of lag, low precision, poor adaptability and insufficient stability in the prior art.

[0010] This invention provides a method for in-situ measurement of residual stress in laser additive manufacturing parts, comprising:

[0011] Preprocessing: Calibrate the laser additive manufacturing platform and measuring device, wherein the measuring device includes a micro-area X-ray diffraction module and a fiber optic temperature measurement module; preset one-to-one stress monitoring points and temperature monitoring points in the area to be formed; and perform high-temperature resistant and anti-spatter coating treatment on the measuring probe.

[0012] Synchronous monitoring: During laser additive manufacturing, the micro-area X-ray diffraction module is used to collect lattice strain data at each monitoring point in real time and convert it into instantaneous stress; the fiber optic temperature measurement module is used to synchronously collect temperature data at the corresponding monitoring points.

[0013] Data Correction: Based on synchronously acquired raw stress and temperature data, a pre-built thermo-mechanical coupling correction model is used to correct lattice distortion errors caused by temperature gradients, thereby obtaining accurate residual stress values. The formula for the thermo-mechanical coupling correction model is as follows: In the formula: The diffraction stress constant is... The lattice strain is acquired by the micro-area X-ray diffraction module, α is the coefficient of thermal expansion of the material under test, and E is the elastic modulus of the material under test. The real-time temperature difference is calculated from the temperature data collected by the fiber optic temperature measurement module and the reference temperature.

[0014] Full-process output: During the component forming process, the dynamic residual stress curve is output in real time. After the component is formed, the entire component is scanned and re-measured to output the global residual stress distribution map.

[0015] Preferably, the distance between the corresponding stress monitoring point and the temperature monitoring point is ≤0.5mm.

[0016] Further preferably, the sampling frequency of the micro-area X-ray diffraction module and the fiber optic temperature measurement module is the same as the additive manufacturing frequency.

[0017] The present invention also provides an in-situ measurement device for residual stress in laser additive manufacturing parts that implements the above method, comprising: a core measurement unit and a data processing unit;

[0018] The core measurement unit includes a micro-area X-ray diffraction probe and a fiber optic temperature probe. The micro-area X-ray diffraction probe is used to collect lattice strain data at each monitoring point in real time and convert it into instantaneous stress; the fiber optic temperature probe is used to collect temperature data at the corresponding monitoring point synchronously.

[0019] The data processing unit has a built-in thermo-mechanical coupling correction model algorithm, which is used to receive the raw stress data and temperature data collected by the core measurement unit in real time, and use the algorithm to quickly complete error correction, data storage and dynamic stress curve plotting.

[0020] Preferably, the micro-area X-ray diffraction probe and the fiber optic temperature probe are integrated on the same adjustment bracket.

[0021] Further preferably, the focal length adjustment range of the micro-area X-ray diffraction probe is 5~20mm, and the temperature measurement range of the fiber optic temperature probe is 20~1200℃.

[0022] Further preferably, the in-situ measurement device for residual stress of laser additive manufacturing parts also includes an anti-interference protection unit, wherein the anti-interference protection unit includes a double-layer protection structure and an airflow purging assembly; the double-layer protection structure is disposed at the front end of the probe, the inner layer is made of high-temperature resistant quartz glass with a temperature resistance of ≥1500℃, and the outer layer is a detachable anti-splash metal filter; the airflow purging assembly is used to continuously output dry inert gas to form an air curtain at the front end of the probe to isolate metal splashes and smoke pollution.

[0023] In a further preferred embodiment, the in-situ residual stress measurement device for laser additive manufacturing parts further includes a linkage control unit, wherein the linkage control unit is communicatively connected to the laser additive manufacturing equipment, and is used to receive additive process parameters in real time, and synchronously trigger the measurement device to start or adjust the measurement parameters according to changes in process parameters.

[0024] Further preferably, the linkage control unit also includes an alarm unit, used to issue a warning signal when the measured residual stress exceeds a preset threshold.

[0025] The in-situ measurement method and device for residual stress in laser additive manufacturing parts provided by this invention can accurately capture residual stress throughout the entire process of forming and after forming, providing real-time and reliable data support for the optimization of laser additive manufacturing process, and improving the forming quality and service reliability of components. Detailed Implementation

[0026] The present invention will be further explained below with reference to specific implementation schemes, but this explanation does not limit the scope of the invention.

[0027] This invention provides a method for in-situ measurement of residual stress in laser additive manufacturing parts, comprising four steps: preprocessing, synchronous monitoring, data correction, and full-process output, as detailed below:

[0028] S1: Pre-processing: First, the laser additive manufacturing platform and measuring device are precisely calibrated to ensure that the measurement benchmark is consistent; several stress monitoring points and temperature monitoring points are preset in the area to be formed according to the component structure and testing requirements. Each stress monitoring point corresponds to one temperature monitoring point, and the distance between the two points is ≤0.5mm to ensure the synchronous matching and correspondence of thermal and mechanical data; at the same time, the measuring probe is treated with high temperature resistant and anti-splash coating to enhance the probe's protection capability under harsh working conditions;

[0029] S2: Synchronous Monitoring: When the laser additive manufacturing equipment is started to form components, the measuring device is started simultaneously; the lattice strain data of each monitoring point is collected in real time through the micro-area X-ray diffraction module, and the instantaneous stress data is calculated according to the X-ray diffraction stress measurement principle; the temperature data of the corresponding monitoring point is collected synchronously through the fiber optic temperature measurement module, and the sampling frequency is consistent with the additive manufacturing frequency, with a range of 10~100Hz, to ensure the synchronous linkage acquisition of thermo-mechanical parameters and avoid errors caused by data time difference;

[0030] S3: Data Correction: Based on the synchronously acquired raw stress and temperature data, a pre-constructed thermo-mechanical coupling correction model is used to correct the lattice distortion error caused by the temperature gradient, obtaining an accurate residual stress value. The formula for the thermo-mechanical coupling correction model is as follows: In the formula: K is the diffraction stress constant (related to material type, X-ray wavelength and diffraction crystal plane). Lattice strain acquired by the micro-area X-ray diffraction module. ΔT is the coefficient of thermal expansion of the material of the component under test, E is the elastic modulus of the material of the component under test, and ΔT is the real-time temperature difference (calculated from the temperature data collected by the fiber optic temperature measurement module and the reference temperature).

[0031] S4: Full-process output: During the component forming process, the dynamic residual stress curves of each monitoring point are output in real time, which intuitively reflects the change law of stress with the forming process; after the component is formed, the control and measurement device performs a scanning retest of the entire component, comprehensively collects the stress data of each area of ​​the component, outputs the global residual stress distribution map, and completes the full-process residual stress measurement from the forming process to the post-forming process.

[0032] This invention also provides an in-situ measurement device for residual stress in laser additive manufacturing parts, comprising: a core measurement unit, an anti-interference protection unit, a data processing unit, and a linkage control unit. These four units are integrated into a portable frame, resulting in a compact overall structure suitable for online use with laser additive manufacturing equipment. The specific structure and function of each unit are as follows:

[0033] The core measurement unit, as the core component of the measurement device, includes a micro-area X-ray diffraction probe and a fiber optic temperature probe. The two probes are integrated on the same adjustment bracket and achieve precise positioning at the 0.01mm level through a precision drive mechanism. It can flexibly switch between multiple measurement points according to the distribution of monitoring points. Among them, the focal length of the micro-area X-ray diffraction probe is adjustable, with an adjustment range of 5~20mm, which can adapt to laser additive manufacturing parts of different thicknesses. The fiber optic temperature probe adopts a high-temperature resistant fiber design, with a temperature measurement range of 20~1200℃, which can stably adapt to the high-temperature working conditions of laser additive manufacturing.

[0034] The anti-interference protection unit is designed for the harsh working conditions of laser additive manufacturing. It includes a double-layer protection structure and an airflow purging assembly. The double-layer protection structure is located at the front end of the probe. The inner layer is made of high-temperature resistant quartz glass with a temperature resistance of ≥1500℃, which can effectively block the corrosion of the core components of the probe by high-temperature radiation. The outer layer is a detachable anti-splash metal filter, which can intercept most metal splashes. The airflow purging assembly continuously outputs dry inert gas (such as argon) to form an air curtain at the front end of the probe, isolating metal splashes and dust pollution, and significantly improving the stability of the probe under complex working conditions.

[0035] The data processing unit has a built-in thermo-mechanical coupling correction model algorithm. It receives the raw stress and temperature data collected by the core measurement unit in real time through the data transmission module. The algorithm is used to quickly complete error correction, data storage and dynamic stress curve plotting. It also supports data export function, which can export the measurement data and analysis results to a general format for easy subsequent process analysis and data archiving.

[0036] The linkage control unit communicates with the laser additive manufacturing equipment via a standardized interface. It can receive additive manufacturing process parameters such as laser power and scanning speed in real time, and synchronously trigger the measurement device to start or adjust the measurement parameters according to changes in process parameters. A preset threshold for residual stress is set. When the measured residual stress exceeds the threshold, the linkage control unit automatically issues an early warning signal to remind the operator to adjust the process parameters in time, thereby achieving closed-loop control of the process.

[0037] The in-situ measurement method and device for residual stress in laser additive manufacturing parts have the following advantages:

[0038] 1) High measurement accuracy: By adopting a combination of synchronous monitoring and coupling correction of thermo-mechanical parameters, the lattice distortion error caused by temperature gradient is effectively eliminated. The measurement accuracy error is ≤ ±5MPa, which is far more accurate than the traditional single-parameter measurement method and can accurately reflect the true residual stress state of the component.

[0039] 2) Full-process monitoring: It breaks through the lag limitation of offline measurement and realizes the full-process measurement of dynamic residual stress during laser additive manufacturing and static residual stress after forming. It can output dynamic stress curves and full-domain stress distribution maps in real time, providing real-time and comprehensive data support for closed-loop process control.

[0040] 3) Strong adaptability to working conditions: The double-layer protection structure and airflow purging components of the anti-interference protection unit can effectively resist the effects of harsh working conditions such as high temperature, metal splash, and dust, improving the stability of the probe by 80%; the device adopts a portable rack integrated design, which does not rely on large equipment, reduces costs by 60%, and can be flexibly adapted to online use with laser additive equipment in industrial sites.

[0041] 4) Non-destructive testing: Micro-area X-ray diffraction and fiber optic temperature measurement are both non-destructive testing methods. They will not cause damage to the component body during the measurement process, making them particularly suitable for the quality inspection needs of high-precision, high-value laser additive manufacturing parts.

[0042] Example 1

[0043] Residual stress measurement of titanium alloy laser selective melting components

[0044] S1: Pre-treatment stage: TC4 titanium alloy powder is selected as the forming material, and the laser additive forming platform is preheated to 150℃; 5 monitoring points are evenly selected in the area to be formed, with a spacing of 10mm between adjacent monitoring points. Each monitoring point is set with one stress monitoring point and one temperature monitoring point, and the spacing between the two points is controlled to be 0.3mm; after the micro-area X-ray diffraction probe and fiber optic temperature probe are treated with high temperature resistance and anti-spatter coating, they are installed on the adjustment bracket, the probe positioning accuracy is calibrated to 0.01mm level, the double-layer protective structure of the anti-interference protection unit and the airflow purging assembly are installed, and the airflow purging assembly is turned on to output dry argon gas;

[0045] S2: Synchronous monitoring stage: Set the laser additive manufacturing process parameters, laser power 200W, scanning speed 800mm / s, and start laser selective melting and forming; after receiving the process parameters, the linkage control unit synchronously triggers the measuring device, sets the sampling frequency to 50Hz, collects the lattice strain data of each monitoring point in real time through the micro-area X-ray diffraction probe and calculates the instantaneous stress, and synchronously collects the temperature data of the corresponding monitoring point through the fiber optic temperature probe. During the measurement process, the temperature peak reaches 1150℃;

[0046] S3: Data Correction Stage: The data processing unit receives the synchronously acquired raw stress and temperature data and substitutes them into the thermo-mechanical coupling correction model. Error correction is performed (wherein, the diffraction stress constant of TC4 titanium alloy is...). coefficient of thermal expansion (The elastic modulus E = 110 GPa, and ΔT is the difference between the real-time measured temperature and the reference temperature of 150℃), thus obtaining the accurate residual stress value at each monitoring point;

[0047] S4: Full-Process Output Stage: During the molding process, the data processing unit outputs the dynamic residual stress curves of each monitoring point in real time. After molding, the control and measurement device performs a full-area residual stress distribution map by scanning the entire component. The measurement results show that the maximum instantaneous stress during molding is 280 MPa, and the static residual stress after molding is 120 MPa. Moreover, the stress value at the edge monitoring points is higher than that in the central area. This result provides clear data basis for optimizing the laser scanning path and reducing residual stress. The component is undamaged during the entire measurement process, and the probe is free of metal splashes and dust pollution, demonstrating excellent stability.

[0048] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for in-situ measurement of residual stress in laser additive manufacturing parts, characterized in that, include: Preprocessing: Calibrate the laser additive manufacturing platform and measuring device, wherein the measuring device includes a micro-area X-ray diffraction module and a fiber optic temperature measurement module; preset one-to-one stress monitoring points and temperature monitoring points in the area to be formed; and perform high-temperature resistant and anti-spatter coating treatment on the measuring probe. Synchronous monitoring: During laser additive manufacturing, the micro-area X-ray diffraction module is used to collect lattice strain data at each monitoring point in real time and calculate the instantaneous stress; the fiber optic temperature measurement module is used to synchronously collect temperature data at the corresponding monitoring points. Data Correction: Based on synchronously acquired raw stress and temperature data, a pre-built thermo-mechanical coupling correction model is used to correct lattice distortion errors caused by temperature gradients, thereby obtaining accurate residual stress values. The formula for the thermo-mechanical coupling correction model is as follows: In the formula: The diffraction stress constant is... The lattice strain is acquired by the micro-area X-ray diffraction module, α is the coefficient of thermal expansion of the material under test, and E is the elastic modulus of the material under test. The real-time temperature difference is calculated from the temperature data collected by the fiber optic temperature measurement module and the reference temperature. Full-process output: During the component forming process, the dynamic residual stress curve is output in real time. After the component is formed, the entire component is scanned and re-measured to output the global residual stress distribution map.

2. The method for in-situ measurement of residual stress in laser additive manufacturing parts according to claim 1, characterized in that: The distance between the corresponding stress monitoring point and temperature monitoring point is ≤0.5mm.

3. The method for in-situ measurement of residual stress in laser additive manufacturing parts according to claim 1, characterized in that: The sampling frequency of the micro-area X-ray diffraction module and the fiber optic temperature measurement module is the same as the additive manufacturing frequency.

4. A device for in-situ measurement of residual stress in laser additive manufacturing parts, implementing the method of any one of claims 1 to 3, characterized in that, include: Core measurement unit and data processing unit; The core measurement unit includes a micro-area X-ray diffraction probe and an optical fiber temperature measurement probe. The micro-area X-ray diffraction probe is used to collect lattice strain data at each monitoring point in real time and convert it into instantaneous stress. The fiber optic temperature probe is used to synchronously collect temperature data at the corresponding monitoring points. The data processing unit has a built-in thermo-mechanical coupling correction model algorithm, which is used to receive the raw stress data and temperature data collected by the core measurement unit in real time, and use the algorithm to quickly complete error correction, data storage and dynamic stress curve plotting.

5. The in-situ measurement device for residual stress in laser additive manufacturing parts according to claim 4, characterized in that: The micro-area X-ray diffraction probe and the fiber optic temperature measurement probe are integrated on the same adjustment bracket.

6. The in-situ residual stress measurement device for laser additive manufacturing parts according to claim 4, characterized in that: The focal length adjustment range of the micro-area X-ray diffraction probe is 5~20mm, and the temperature measurement range of the fiber optic temperature probe is 20~1200℃.

7. The in-situ measurement device for residual stress in laser additive manufacturing parts according to claim 4, characterized in that: It also includes an anti-interference protection unit, wherein the anti-interference protection unit includes a double-layer protection structure and an airflow purging assembly; the double-layer protection structure is set at the front end of the probe, the inner layer is made of high-temperature resistant quartz glass with a temperature resistance of ≥1500℃, and the outer layer is a detachable anti-splash metal filter; the airflow purging assembly is used to continuously output dry inert gas to form an air curtain at the front end of the probe to isolate metal splashes and smoke pollution.

8. The in-situ measurement device for residual stress in laser additive manufacturing parts according to claim 4, characterized in that: It also includes a linkage control unit, which is communicatively connected to the laser additive manufacturing equipment to receive additive manufacturing process parameters in real time and synchronously trigger the measuring device to start or adjust the measuring parameters according to changes in the process parameters.

9. The in-situ measurement device for residual stress in laser additive manufacturing parts according to claim 8, characterized in that: The linkage control unit also includes an alarm unit, which is used to issue a warning signal when the measured residual stress exceeds a preset threshold.