WO2018216845A1 - Device for real-time checking and correcting process state of three-dimensional lamination process, and method to which same is applied - Google Patents

Device for real-time checking and correcting process state of three-dimensional lamination process, and method to which same is applied Download PDF

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Publication number
WO2018216845A1
WO2018216845A1 PCT/KR2017/006945 KR2017006945W WO2018216845A1 WO 2018216845 A1 WO2018216845 A1 WO 2018216845A1 KR 2017006945 W KR2017006945 W KR 2017006945W WO 2018216845 A1 WO2018216845 A1 WO 2018216845A1
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Prior art keywords
resonance frequency
damping coefficient
melt pool
real
sensor
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PCT/KR2017/006945
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French (fr)
Korean (ko)
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강래형
한대현
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전북대학교산학협력단
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/20—Direct sintering or melting
    • B22F10/25—Direct deposition of metal particles, e.g. direct metal deposition [DMD] or laser engineered net shaping [LENS]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/31—Calibration of process steps or apparatus settings, e.g. before or during manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/38—Process control to achieve specific product aspects, e.g. surface smoothness, density, porosity or hollow structures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/90—Means for process control, e.g. cameras or sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y50/00—Data acquisition or data processing for additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/80—Data acquisition or data processing
    • B22F10/85—Data acquisition or data processing for controlling or regulating additive manufacturing processes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present invention relates to a three-dimensional printing-related technology, and more specifically, to predict the depth of the melt pool, to check whether the structure is being manufactured normally when manufacturing the structure using a three-dimensional additive manufacturing process and if a problem occurs normal It is about how to control to become a state.
  • Three-dimensional additive manufacturing is a method of manufacturing a structure by laminating the structure further, which is known to us recently as a 3D printing technique.
  • the first three-dimensional additive manufacturing was developed in 1981 with the success of three-dimensional structural lamination using polymers.
  • Three-dimensional additive manufacturing is excellent in quality, easy to manufacture complex shapes, and the structure can be manufactured for the user's purpose, the technology is growing rapidly in the short term.
  • various materials such as metals, nonmetals, and composites can be used, which are widely used in various fields such as aviation, aerospace, automotive, medicine, and biotechnology, and the market size is growing rapidly each year.
  • the fabrication speed of the structure is controlled by the laser intensity and rotation speed of melting the metal, but the laser intensity is greater than the reference value or the rotation speed is slow, and the size of the laminated structure As a result, the heat capacity changes, which may change the state of the melt pool and cause defects.
  • the defects of three-dimensional additive manufacturing can be divided into defects in the equipment itself and defects caused in the process.
  • an object of the present invention is to determine the quality of the structure through feedback control by determining whether the three-dimensional additive processing using metal as a material in real-time when manufacturing the structure
  • An object of the present invention is to provide a real-time processing state inspection and correction apparatus and method for three-dimensional additive manufacturing that can be manufactured without enhancement and additional defect inspection.
  • a method of predicting the depth of the melt pool in real time and determining the abnormality of the process during the fabrication of the structure is integrated with the additive manufacturing machine to improve the structure quality, build a database of manufacturing conditions, It provides a real-time machining status inspection and correction method for three-dimensional additive manufacturing without the need for additional defect inspection methods.
  • a real-time processing state inspection apparatus of the three-dimensional additive manufacturing the sensor for measuring the signal of the Melt pool;
  • An actuator having the structure at a reference resonance frequency and a damping coefficient;
  • Heat sources for melting metal materials An apparatus for supplying a material required for lamination;
  • a stacking head that collects sensor signals, heat sources, and materials in one place;
  • Equipment for acquiring data collected by the sensor and driving the actuator;
  • a computing device that calculates a resonance frequency and a damping coefficient from the acquired sensor data and controls the intensity of the heat source based on the calculated resonance frequency and the damping coefficient.
  • the sensor may include at least one LDV measuring the surface signal of the melt pool and the surface signal of the structure according to the laser light irradiation.
  • the actuator may be an impact hammer or piezoelectric actuator having the structure at a reference resonance frequency and a damping coefficient suitable for the stage of the structure to be manufactured.
  • the computing device may estimate the size of the melt pool based on the calculated resonance frequency and the damping coefficient.
  • the computing device may calculate the reference resonance frequency and the damping coefficient for each structure fabrication step through a numerical analysis method.
  • the computing device may adjust the intensity of the heat source through feedback control by comparing the reference resonance frequency and the damping coefficient with the calculated resonance frequency and the damping coefficient.
  • the computing device may generate a control signal to adjust the intensity of the heat source when an error greater than the value set as a result of the comparison occurs.
  • the heat source may be a laser beam or an electron beam.
  • the real-time processing state inspection apparatus of the three-dimensional additive manufacturing the sensor for measuring the signal of the Melt pool; An actuator having the structure at a reference resonance frequency and a damping coefficient; Equipment for acquiring data collected by the sensor and driving the actuator; And a computing device that calculates a resonance frequency and a damping coefficient from the acquired sensor data and controls the intensity of the heat source based on the calculated resonance frequency and the damping coefficient.
  • the three-dimensional additive manufacturing equipment using a metal as a material to determine the abnormality in real time when manufacturing the structure to improve the quality of the structure through the feedback control and manufacture without additional defect inspection It becomes possible.
  • the reference data is the resonant frequency and damping coefficient of the structure for each fabrication step by using a numerical analysis program to secure the resonant frequency and damping coefficient for each step and measured the resonance frequency and damping through the actual LDV
  • a numerical analysis program to secure the resonant frequency and damping coefficient for each step and measured the resonance frequency and damping through the actual LDV
  • 1 is a conceptual diagram showing the configuration of the Direct Energy Deposition equipment for real-time processing state monitoring and correction function of the three-dimensional additive lamination according to an embodiment of the present invention
  • FIG. 2 is a conceptual diagram of an experimental setup for monitoring the Melt pool state to develop the system of FIG.
  • FIG. 3 is an actual experimental scene for the development and verification of the original technology Melt pool monitoring and correction technique based on the experimental setup conceptual diagram of FIG.
  • FIG. 4 is a graph that defines a Q-factor used to predict the resonance frequency and damping coefficient using the LDV of FIG.
  • FIG. 5 is a graph obtained when the depth of the melt pool increases from 1 mm to 3 mm as a result obtained through the experimental setup shown in FIG.
  • FIG. 6 is a graph summarizing the results obtained by calculating the resonance frequency with the results obtained in FIG. 5;
  • FIG. 8 is based on the result obtained in FIG. 5 to predict the depth of the melt pool to determine whether there is an abnormality in real time when the 3D additive manufacturing equipment is a structure fabrication can be produced without improving the quality of the structure and additional defect inspection through feedback control Algorithm is a conceptual diagram.
  • the present invention provides a device and method that can be manufactured without improving the quality of the structure and additional defect inspection through feedback control by determining whether there is an abnormality in real time when the structure is manufactured by using the metal as a material. .
  • the function of measuring the signal of the Melt pool to determine whether there is an abnormality the function of having the resonant frequency of the product of each step, the function of calculating the resonant frequency of each step product through the finite element analysis, the collection
  • the function of calculating the resonant frequency and damping coefficient by analyzing the measured signal, the function of comparing and analyzing the reference data and the measured data, and the function of storing the data for each step are presented.
  • 1 is a conceptual diagram showing the configuration of a Direct Energy Deposition equipment for real-time processing state monitoring and correction function of three-dimensional additive manufacturing.
  • the real-time processing state inspection and correction apparatus 100 for three-dimensional lamination processing includes a laser doppler vibrometer (LDV) sensor 101, a piezoelectric actuator 102, a heat source 103, and a material supply device. 104, stacking head 105, DAQ equipment 106, and PC 107.
  • LDV laser doppler vibrometer
  • the LDV sensor 101 measures the surface signal of the structure and the melt pool according to the laser light irradiation at each stage to measure the state of the melt pool at each stage, and the piezoelectric actuator 102 has an impulse signal at the structure.
  • the heat source 103 melts the metal, and the material supply device 104 supplies the metal material necessary for lamination. When using a metallic material in powder form, this material is moved by the gas.
  • a laser beam or an electron beam may be used as the heat source 103.
  • a focusing lens (lens) located on the upper portion of the stacking head (105) melts the metal supplied by focusing the heat source (103), and also focuses the LDV signal to measure the state of the melt pool.
  • the lamination head 105 gathers the energy of the heat source, LDV signals, and materials into one place to enable lamination processing.
  • the stacking head 105 is installed in a multi-axis joint and can rotate in various directions.
  • the DAQ device 106 acquires the data collected from the sensor and drives the piezo actuator, and the PC 107 calculates the acquired sensor data processing and the resonant frequency step by step of the structure.
  • the real-time processing state inspection and correction device 100 of the three-dimensional additive manufacturing process can calculate the resonance frequency and the damping coefficient value that depends on the size of the melt pool when manufacturing the structure using a metal material, it is possible to predict the depth of the melt pool, This enables real-time machining condition monitoring and correction algorithms for three-dimensional additive manufacturing.
  • the real-time processing state inspection and correction apparatus 100 of the three-dimensional additive manufacturing process measures the Melt pool surface signal using the LDV 101 sensor to monitor the manufacturing state and obtains the sensor signal through the DAQ device 106.
  • the PC 107 may calculate a resonance frequency and a damping coefficient by performing signal processing, and a difference between the resonance frequency calculated according to the depth of the melt pool and the resonance frequency obtained through numerical analysis occurs.
  • a heat source 103 capable of supplying a metal material and melting the material in a solid state is required.
  • the heat source 103 may use an electron beam or a laser beam.
  • the metal material required for fabricating the structure is supplied through the material supply device 104, and may be composed of a powder supply method and a wire supply method according to the supply method.
  • the stacking head 105 which collects the heat source 103, the LDV 101 signal, and the material into one place, is attached to the multi-axis rotating body to move the stacking head 105 at various angles, thereby making it possible to manufacture a complicated shape.
  • the installation position of the LDV 101 can be freely installed according to the shape of the 3D stacking equipment, but it is necessary to align the laser beam so that the laser beam is located at the center of the stacking head 105 using a beam guidance system.
  • the piezoelectric actuator 102 is generally installed on a lathe of a three-dimensional laminating machine in order to excite the structure to be manufactured at a resonant frequency, and the piezoelectric actuator 102 has no limitation in the number of the piezoelectric actuators 102 since the piezoelectric actuator 102 has the same frequency.
  • FIG. 2 is an experimental setup conceptual diagram for observing Melt pool status to develop the system of FIG. 1.
  • the specimen 201 in which the melt pool is simulated has a diameter of 2 mm and a depth of 1 mm, 2 mm, and 3 mm, respectively, so that the difference between the excitation frequency and the measured resonance frequency can be confirmed according to the depth of the melt pool.
  • Two LDVs can be used, one of which measures the surface signal of the Melt pool, one of which measures the surface of the structure, and the other one of the 203 measures the surface of the structure. Analyze the difference in frequency change.
  • the specimen excitation method can use the impact hammer 205 to give an impulse signal and give the same force at the same location.
  • Two LDVs and impact hammers are connected to the DAQ device to calculate the melt pool for the impulse signal and the response function of the structure.
  • the PC 206 uses the electrical signal collected by the DAQ device, calculates a frequency response function.
  • FIG. 3 is an actual experimental photograph for developing and verifying a Melt pool monitoring and correction technique source technology based on the experimental setup conceptual diagram of FIG. 2.
  • FIG. 4 is a graph that defines the Q-factor used to predict the resonant frequency and damping coefficient using the LDV of FIG. 3.
  • the damping factor can be calculated using the Q factor.
  • Q factor is the resonance frequency divided by the frequency difference at the point where Magnitude drops 3dB from the resonance frequency in the FRF graph. Using this value, the damping coefficient can be found by dividing 1 by 2 times the Q factor.
  • FIG. 5 shows a result of the resonance frequency lowered and the graph waveform of the resonance frequency softened when the depth of the melt pool increases from 1 mm to 3 mm as a result of the FRF obtained through the experimental setup shown in FIG. 2.
  • FIG. 6 is a graph summarizing the results obtained by calculating the resonance frequency with the results obtained in FIG. 5.
  • Analytically obtained aluminum beams have a primary resonant frequency of 298.61 Hz and the structure's primary resonant frequency obtained from the experimental setup of FIG. 2 is about 287.49 Hz. The difference in this value shows an error of about 3.8%, but this can be seen as the error level of the experiment and analysis.
  • the aluminum beam's response to the impact signal shows a constant value regardless of the depth of the melt pool.
  • the Melt pool's response to the shock signal shows that as the depth of the Melt pool increases from 1mm to 3mm, the first resonant frequency is 4.93Hz lowered from 287.22Hz to 282.29Hz.
  • FIG. 7 is a graph summarizing the results of calculating the damping coefficients with the results obtained in FIG. 5.
  • the average level is approximately 0.0021 depending on the depth of the melt pool, but the melt pool increases from 0.0037 to 0.0067 as the depth increases from 1mm to 3mm.
  • Figure 8 is based on the results obtained in Figures 5, 6 and 7 predicts the Melt pool depth to determine the abnormality in real time when the three-dimensional additive manufacturing equipment in the fabrication structure after the quality control and improvement of the structure through feedback control This is a possible algorithm conceptual diagram.
  • the first-order resonant frequency and damping coefficient of the fabrication stage which are reference data using a PC, are obtained by numerical analysis.
  • the first resonant frequency and the damping coefficient obtained are then sent to the piezoelectric actuator to have the structure.
  • the LDV acquires a signal from the surface of the melt pool, and the first resonant frequency and the damping coefficient are obtained, and the error calculated by comparing the calculated data with the measured data and the actual measured signal has a larger error than the set value.
  • control signals can be generated to control the heating source or fabrication speed to ensure the quality of the structure in real time.
  • the first resonant frequency and the damping coefficient value measured are changed, thereby ensuring the quality of the fabricated structure in real time, so it is manufactured in the rapidly increasing three-dimensional lamination industry.
  • 3D additive manufacturing equipment using metal as a material is judged in real time during the construction of the structure, and it can be manufactured without improving the quality of the structure and additional defect inspection through feedback control.
  • the melt pool depth in real time by applying a laser Doppler Vibrometer (LDV), a piezo actuator, and a signal processing technique to predict the melt pool depth.
  • LDV laser Doppler Vibrometer
  • the laser intensity can be controlled automatically and the entire manufacturing process data can be saved, so that the position where the problem occurred can be checked without additional inspection after the final structure fabrication is completed.
  • the LDV is installed in the 3D additive manufacturing equipment to detect the Melt pool condition, and the piezoelectric actuator is attached to the structure to collect the specific frequency. Can be controlled and the Point by Point data can be stored to find the part where the problem occurred without additional defect inspection later.
  • LDV and piezoelectric actuators are added to the existing 3D additive manufacturing equipment to minimize the increase in equipment cost, and the optimized state can be controlled by monitoring the Melt pool status in real time. This makes it easy to find the location in case of a defect, improving production efficiency and quality.
  • the technical idea of the present invention can be applied to a computer-readable recording medium containing a computer program for performing the functions of the apparatus and method according to the present embodiment.
  • the technical idea according to various embodiments of the present disclosure may be implemented in the form of computer readable codes recorded on a computer readable recording medium.
  • the computer-readable recording medium can be any data storage device that can be read by a computer and can store data.
  • the computer-readable recording medium may be a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical disk, a hard disk drive, or the like.
  • the computer-readable code or program stored in the computer-readable recording medium may be transmitted through a network connected between the computers.

Abstract

Proposed is a device for three-dimensional lamination process using metal as a raw material, wherein the device determines in real time whether a structure being manufactured by the device has abnormality, and performs a feedback control, so that the device can improve the quality of the structure and can manufacture the structure without additional defect checking. The present invention provides a device equipped with a function of real-time monitoring and correcting a process state of a three-dimensional lamination process, and a method therefor, the device having the functions of: measuring a melt pool signal to determine whether there is abnormality; vibrating a product of each stage at a resonance frequency of the product; calculating a resonance frequency of a product of each stage via finite element analysis; analyzing a collected signal and calculating a resonance frequency and a damping coefficient; comparing and analyzing reference data and measured data; and storing data of each stage. Therefore, the device can improve the quality of a three-dimensional lamination structure, establish a forming condition database, and improve productivity.

Description

3차원 적층 가공의 실시간 가공 상태 검사와 보정 장치 및 이를 적용한 방법Real-time machining status inspection and correction device for three-dimensional additive manufacturing and its method
본 발명은 3차원 프린팅 관련 기술에 관한 것으로, 더욱 상세하게는 Melt pool의 깊이를 예측하여, 3차원 적층 가공 공정을 이용하여 구조물을 제작할 때 구조물이 정상적으로 제작되고 있는지를 검사하고 문제가 발생할 경우 정상 상태가 될 수 있도록 제어하는 방법에 관한 것이다.The present invention relates to a three-dimensional printing-related technology, and more specifically, to predict the depth of the melt pool, to check whether the structure is being manufactured normally when manufacturing the structure using a three-dimensional additive manufacturing process and if a problem occurs normal It is about how to control to become a state.
3차원 적층가공이란 구조물을 한층 한층 적층해서 제작하는 공법으로 최근 3D 프린팅 기법으로 우리에게 잘 알려져 있다. 최초의 3차원 적층가공은 1981년 폴리머를 이용해 3차원 구조물 적층을 성공하면서 개발되었다. 3차원 적층 가공은 품질이 우수하고 복잡한 형상 제작이 용이하며 사용자 목적에 맞는 구조물 제작이 가능해 단기간에 그 기술이 급속도로 성장하고 있다. 또한 사용할 수 있는 재료의 제약이 작아 금속, 비금속, 복합재료 등 다양한 재료를 사용 가능해서 항공, 우주, 자동차, 의학, 생명공학 등 다양한 분야에서 널리 사용되고 있고 시장 규모는 해마다 급속도로 성장하고 있다.Three-dimensional additive manufacturing is a method of manufacturing a structure by laminating the structure further, which is known to us recently as a 3D printing technique. The first three-dimensional additive manufacturing was developed in 1981 with the success of three-dimensional structural lamination using polymers. Three-dimensional additive manufacturing is excellent in quality, easy to manufacture complex shapes, and the structure can be manufactured for the user's purpose, the technology is growing rapidly in the short term. In addition, due to the limited material available, various materials such as metals, nonmetals, and composites can be used, which are widely used in various fields such as aviation, aerospace, automotive, medicine, and biotechnology, and the market size is growing rapidly each year.
3차원 적층 가공이 다양한 분야에서 널리 사용되는 만큼 중요시되는 것은 제작된 구조물의 품질 확보이다. 금속을 이용한 3차원 적층 가공 구조물의 경우 구조물의 제작 속도는 금속을 용융시키는 레이저 세기와 회전 속도에 의해 조절되는데 레이저 세기가 기준 값 보다 크거나 회전 속도가 느려지는 경우, 그리고 적층된 구조물의 크기에 따라 열용량이 변하게 되는데 이로 인하여 melt pool의 상태가 변경되어 결함이 발생할 수 있다. 이처럼 3차원 적층 가공의 결함은 장비 자체의 결함과 공정 중 야기되는 결함으로 구분할 수 있다.As 3D additive manufacturing is widely used in various fields, it is important to secure the quality of fabricated structures. In the case of a three-dimensional laminated processing structure using metal, the fabrication speed of the structure is controlled by the laser intensity and rotation speed of melting the metal, but the laser intensity is greater than the reference value or the rotation speed is slow, and the size of the laminated structure As a result, the heat capacity changes, which may change the state of the melt pool and cause defects. As such, the defects of three-dimensional additive manufacturing can be divided into defects in the equipment itself and defects caused in the process.
기존의 3차원 적층가공 구조물의 검사 방법은 X-Ray, CT, MT, VT 등과 같은 일반적인 비파괴 검사 방법이 있으나, 제작이 완료된 이후에 검사가 진행되어 구조물 내부에 결함이 발견될 경우 폐기 또는 수리가 요구되어 제작에 소요되는 시간적, 비용적인 손실이 발생하고, 모든 제품에 대해 비파괴 검사가 현실적으로 불가능 하여 결과적으로 양품 생산 및 품질관리에 적합하지 않은 경우가 많다. Existing non-destructive inspection methods such as X-ray, CT, MT, VT, etc. are available for inspection of existing 3D laminate structures, but if the inspection is performed after fabrication is completed and defects are found inside the structure, disposal or repair is not possible. There is a time and cost loss required for manufacturing, and non-destructive inspection of all products is practically impossible, and as a result, they are often not suitable for production and quality control.
위와 같은 문제를 해결하기 위해 실시간으로 3차원 적층 가공을 감시하기 위한 기술 개발이 진행되고 있다. 대표적으로 레이저 초음파 기술을 이용하여 액체 상태의 Melt pool이 형성된 후 다음 단계로 넘어갈 때 냉각 효과에 의해 고체 상태로 변경하는 위치에서 레이저를 이용해 특정 주파수로 가진 하고 LDV를 사용해서 신호를 계측 하는 기술, 광학적 발광 분광법(Optical Emission Spectroscopy)을 이용해 Melt pool 상태를 예측하는 기술 등이 개발되어 있다. 하지만 Melt pool의 깊이 정보를 직접 예측하는 기술에 대해서는 별도로 개시하고 있지 않다는 한계가 있어 실시간으로 Melt pool 깊이를 예측하여 최적 상태의 Melt pool을 유지하여 추가적인 결함 검사 없이 품질 확보가 가능한 기법 개발이 요구된다.In order to solve the above problems, technology development for monitoring 3D additive manufacturing in real time is underway. Representatively, the laser ultrasonic technology is used to create a melt pool of liquid state and then move to the next stage after the liquid phase is formed. Techniques for predicting the melt pool state using optical emission spectroscopy have been developed. However, there is a limitation that the technology for directly predicting the depth information of the melt pool is not disclosed separately. Therefore, it is required to develop a technique that can secure the quality without additional defect inspection by predicting the melt pool depth in real time and maintaining the optimal melt pool. .
본 발명은 상기와 같은 문제점을 해결하기 위하여 안출된 것으로서, 본 발명의 목적은, 금속을 재료로 사용하는 3차원 적층가공 장비가 구조물 제작 시 실시간으로 이상 유무를 판단하여 피드백 제어를 통해 구조물의 품질 향상 및 추가적인 결함 검사 없이 제작이 가능한 3차원 적층 가공의 실시간 가공 상태 검사와 보정 장치 및 방법을 제공함에 있다.The present invention has been made to solve the above problems, an object of the present invention is to determine the quality of the structure through feedback control by determining whether the three-dimensional additive processing using metal as a material in real-time when manufacturing the structure An object of the present invention is to provide a real-time processing state inspection and correction apparatus and method for three-dimensional additive manufacturing that can be manufactured without enhancement and additional defect inspection.
특히, 금속 재료를 사용하는 3차원 적층 가공 방법을 사용해 구조물 제작 시 실시간으로 Melt pool의 깊이를 예측하고 공정의 이상 유무를 판단하는 방법을 적층 가공 기계에 융합하여 구조물 품질 향상, 제작 조건 데이터베이스 구축, 추가적인 결함 검사 방법이 필요 없는 3차원 적층 가공의 실시간 가공 상태 검사 및 보정 방법을 제공한다.In particular, by using a three-dimensional additive manufacturing method using metal materials, a method of predicting the depth of the melt pool in real time and determining the abnormality of the process during the fabrication of the structure is integrated with the additive manufacturing machine to improve the structure quality, build a database of manufacturing conditions, It provides a real-time machining status inspection and correction method for three-dimensional additive manufacturing without the need for additional defect inspection methods.
상기 목적을 달성하기 위한 본 발명의 일 실시예에 따른, 3차원 적층 가공의 실시간 가공 상태 검사 장치는, Melt pool의 신호를 측정하는 센서; 기준 공진 주파수와 댐핑 계수로 구조물을 가진하는 작동기; 금속 재료를 녹여주는 열원; 적층에 필요한 재료를 공급하는 장치; 센서 신호, 열원, 재료를 한 곳으로 모아주는 적층 헤드; 센서에서 수집되는 데이터를 취득하고 작동기를 구동하는 장비; 및 취득한 센서 데이터로부터 공진 주파수와 댐핑 계수를 계산하고, 계산된 공진 주파수와 댐핑 계수를 기초로 열원의 세기를 제어하는 컴퓨팅 장치;를 포함한다.According to an embodiment of the present invention for achieving the above object, a real-time processing state inspection apparatus of the three-dimensional additive manufacturing, the sensor for measuring the signal of the Melt pool; An actuator having the structure at a reference resonance frequency and a damping coefficient; Heat sources for melting metal materials; An apparatus for supplying a material required for lamination; A stacking head that collects sensor signals, heat sources, and materials in one place; Equipment for acquiring data collected by the sensor and driving the actuator; And a computing device that calculates a resonance frequency and a damping coefficient from the acquired sensor data and controls the intensity of the heat source based on the calculated resonance frequency and the damping coefficient.
그리고, 센서는, 레이저광 조사에 따른 Melt pool의 표면 신호와 구조물의 표면 신호를 측정하는 적어도 하나의 LDV;를 포함할 수 있다.The sensor may include at least one LDV measuring the surface signal of the melt pool and the surface signal of the structure according to the laser light irradiation.
또한, 작동기는, 제작되는 구조물의 단계에 맞는 기준 공진 주파수와 댐핑 계수로 구조물을 가진하는 임팩트 해머 또는 압전 작동기일 수 있다.In addition, the actuator may be an impact hammer or piezoelectric actuator having the structure at a reference resonance frequency and a damping coefficient suitable for the stage of the structure to be manufactured.
그리고, 컴퓨팅 장치는, 계산된 공진 주파수와 댐핑 계수를 기초로 Melt pool의 크기를 예측할 수 있다.The computing device may estimate the size of the melt pool based on the calculated resonance frequency and the damping coefficient.
또한, 컴퓨팅 장치는, 수치 해석 방법을 통해 구조물 제작 단계별 기준 공진 주파수와 댐핑 계수를 계산할 수 있다.In addition, the computing device may calculate the reference resonance frequency and the damping coefficient for each structure fabrication step through a numerical analysis method.
그리고, 컴퓨팅 장치는, 기준 공진 주파수와 댐핑 계수를 계산된 공진 주파수와 댐핑 계수와 비교하여, 피드백 제어를 통해 열원의 세기를 조절할 수 있다.The computing device may adjust the intensity of the heat source through feedback control by comparing the reference resonance frequency and the damping coefficient with the calculated resonance frequency and the damping coefficient.
또한, 컴퓨팅 장치는, 비교 결과 설정한 값보다 큰 오차가 발생하면, 제어 신호를 발생시켜 열원의 세기를 조절할 수 있다.The computing device may generate a control signal to adjust the intensity of the heat source when an error greater than the value set as a result of the comparison occurs.
그리고, 열원은, 레이저 빔 또는 전자 빔일 수 있다.The heat source may be a laser beam or an electron beam.
한편, 본 발명의 다른 실시예에 따른, 3차원 적층 가공의 실시간 가공 상태 검사 장치는, Melt pool의 신호를 측정하는 센서; 기준 공진 주파수와 댐핑 계수로 구조물을 가진하는 작동기; 센서에서 수집되는 데이터를 취득하고 작동기를 구동하는 장비; 및 취득한 센서 데이터로부터 공진 주파수와 댐핑 계수를 계산하고, 계산된 공진 주파수와 댐핑 계수를 기초로 열원의 세기를 제어하는 컴퓨팅 장치;를 포함한다.On the other hand, according to another embodiment of the present invention, the real-time processing state inspection apparatus of the three-dimensional additive manufacturing, the sensor for measuring the signal of the Melt pool; An actuator having the structure at a reference resonance frequency and a damping coefficient; Equipment for acquiring data collected by the sensor and driving the actuator; And a computing device that calculates a resonance frequency and a damping coefficient from the acquired sensor data and controls the intensity of the heat source based on the calculated resonance frequency and the damping coefficient.
이상 설명한 바와 같이, 본 발명의 실시예들에 따르면, 금속을 재료로 사용하는 3차원 적층가공 장비가 구조물 제작 시 실시간으로 이상 유무를 판단하여 피드백 제어를 통해 구조물의 품질 향상 및 추가적인 결함 검사 없이 제작 가능해진다.As described above, according to the embodiments of the present invention, the three-dimensional additive manufacturing equipment using a metal as a material to determine the abnormality in real time when manufacturing the structure to improve the quality of the structure through the feedback control and manufacture without additional defect inspection It becomes possible.
특히, 본 발명의 실시예들에 따르면, Melt pool의 깊이 정보를 예측하고 Reference 데이터와 비교 분석하는 알고리즘을 적용함으로써 최적의 Melt pool의 상태를 유지하여 추가적인 결함 검사가 필요 없는 높은 품질의 구조물을 제작할 수 있다.In particular, according to embodiments of the present invention, by applying an algorithm that predicts the depth information of the melt pool and compares and analyzes it with the reference data, it is possible to maintain a state of the optimal melt pool to fabricate a high quality structure without additional defect inspection. Can be.
또한, 본 발명의 실시예들에 따르면, Reference 데이터는 각 제작 단계별 구조물의 공진 주파수와 댐핑 계수로 수치해석 프로그램을 이용하여 단계별 공진 주파수와 댐핑 계수를 확보 하고 실제 LDV를 통해 측정된 공진 주파수와 댐핑 계수를 비교 분석하여 제작 시 발생하는 문제에 대해 피드백 제어를 통해 능동형 3차원 적층가공이 가능해진다.In addition, according to the embodiments of the present invention, the reference data is the resonant frequency and damping coefficient of the structure for each fabrication step by using a numerical analysis program to secure the resonant frequency and damping coefficient for each step and measured the resonance frequency and damping through the actual LDV By comparing and analyzing the coefficients, active three-dimensional additive manufacturing is possible through feedback control on the manufacturing problems.
도 1은 본 발명의 일 실시예에 따른, 3차원 적층 가공의 실시간 가공 상태 감시 및 보정 기능을 하는 Direct Energy Deposition 장비의 구성을 보인 개념도,1 is a conceptual diagram showing the configuration of the Direct Energy Deposition equipment for real-time processing state monitoring and correction function of the three-dimensional additive lamination according to an embodiment of the present invention,
도 2는, 도 1의 시스템을 개발하기 위해 Melt pool 상태를 감시를 위한 실험 셋업 개념도,2 is a conceptual diagram of an experimental setup for monitoring the Melt pool state to develop the system of FIG.
도 3은, 도 2의 실험 셋업 개념도를 기반으로 한 Melt pool 감시 및 보정 기법 원천 기술 개발 및 검증을 위한 실제 실험 장면,3 is an actual experimental scene for the development and verification of the original technology Melt pool monitoring and correction technique based on the experimental setup conceptual diagram of FIG.
도 4는, 도 3의 LDV를 이용해 공진 주파수와 댐핑 계수를 예측하기 위해 사용된 Q-factor를 정의하는 그래프,4 is a graph that defines a Q-factor used to predict the resonance frequency and damping coefficient using the LDV of FIG.
도 5는, 도 2에 나타낸 실험 셋업을 통해 얻어진 결과로서 Melt pool의 깊이가 1mm에서 3mm로 증가할 경우 공진 주파수와 댐핑 계수가 낮아지는 결과를 얻은 그래프,5 is a graph obtained when the depth of the melt pool increases from 1 mm to 3 mm as a result obtained through the experimental setup shown in FIG.
도 6은, 도 5에서 얻어진 결과를 가지고 공진 주파수를 계산한 결과를 정리한 그래프,6 is a graph summarizing the results obtained by calculating the resonance frequency with the results obtained in FIG. 5;
도 7은, 도 5에서 얻어진 결과를 가지고 댐핑 계수를 계산한 결과를 정리한 그래프, 그리고,7 is a graph summarizing the results of calculating the damping coefficients with the results obtained in FIG. 5, and
도 8은, 도 5에서 얻어진 결과를 바탕으로 Melt pool 깊이를 예측하여 3차원 적층가공 장비가 구조물 제작 시 실시간으로 이상 유무를 판단하여 피드백 제어를 통해 구조물의 품질 향상 및 추가적인 결함 검사 없이 제작이 가능한 알고리즘 개념도 이다.FIG. 8 is based on the result obtained in FIG. 5 to predict the depth of the melt pool to determine whether there is an abnormality in real time when the 3D additive manufacturing equipment is a structure fabrication can be produced without improving the quality of the structure and additional defect inspection through feedback control Algorithm is a conceptual diagram.
이하에서는 도면을 참조하여 본 발명을 보다 상세하게 설명한다.Hereinafter, with reference to the drawings will be described the present invention in more detail.
본 발명의 실시예에서는, 금속을 재료로 사용하는 3차원 적층가공 장비가 구조물 제작 시 실시간으로 이상 유무를 판단하여 피드백 제어를 통해 구조물의 품질 향상 및 추가적인 결함 검사 없이 제작 가능한 장치 및 방법을 제시한다.In an embodiment of the present invention, the present invention provides a device and method that can be manufactured without improving the quality of the structure and additional defect inspection through feedback control by determining whether there is an abnormality in real time when the structure is manufactured by using the metal as a material. .
본 발명의 실시예에서는, 이상 유무를 판단하기 위해 Melt pool의 신호를 측정하는 기능, 각 단계별 제작물의 공진 주파수로 가진 하는 기능, 유한요소 해석을 통해 각 단계별 제작물의 공진 주파수를 계산하는 기능, 수집된 신호를 분석하여 공진 주파수와 댐핑 계수를 계산하는 기능, 기준 데이터와 측정된 데이터를 비교 분석하는 기능, 각 단계별 데이터를 저장하는 기능이 제시된다.In the embodiment of the present invention, the function of measuring the signal of the Melt pool to determine whether there is an abnormality, the function of having the resonant frequency of the product of each step, the function of calculating the resonant frequency of each step product through the finite element analysis, the collection The function of calculating the resonant frequency and damping coefficient by analyzing the measured signal, the function of comparing and analyzing the reference data and the measured data, and the function of storing the data for each step are presented.
도 1은 3차원 적층 가공의 실시간 가공 상태 감시 및 보정 기능을 하는 Direct Energy Deposition 장비의 구성을 보인 개념도이다.1 is a conceptual diagram showing the configuration of a Direct Energy Deposition equipment for real-time processing state monitoring and correction function of three-dimensional additive manufacturing.
도 1에 도시된 바와 같이, 3차원 적층 가공의 실시간 가공 상태 검사 및 보정 장치(100)는, LDV(Laser Doppler Vibrometer) 센서(101), 압전 작동기(102), 열원(103), 재료 공급장치(104), 적층 헤드(105), DAQ 장비(106) 및 PC(107)를 포함한다. As shown in FIG. 1, the real-time processing state inspection and correction apparatus 100 for three-dimensional lamination processing includes a laser doppler vibrometer (LDV) sensor 101, a piezoelectric actuator 102, a heat source 103, and a material supply device. 104, stacking head 105, DAQ equipment 106, and PC 107.
LDV 센서(101)는 각 단계별로 레이저광 조사에 따른 구조물과 Melt pool의 표면 신호를 측정하여 Melt pool의 상태를 각 단계별로 측정하고, 압전 작동기(102)는 구조물에 임펄스 신호를 가진 한다. 열원(103)은 금속을 녹이고, 재료 공급장치(104)는 적층에 필요한 금속 재료를 공급한다. 분말 형태의 금속 재료를 이용하는 경우, 이 재료는 가스에 의해 이동된다.The LDV sensor 101 measures the surface signal of the structure and the melt pool according to the laser light irradiation at each stage to measure the state of the melt pool at each stage, and the piezoelectric actuator 102 has an impulse signal at the structure. The heat source 103 melts the metal, and the material supply device 104 supplies the metal material necessary for lamination. When using a metallic material in powder form, this material is moved by the gas.
열원(103)으로 레이저 빔(laser beam) 또는 전자 빔(electron beam)을 이용할 수 있다. 적층 헤드(105)의 상부에 위치하는 집속 렌즈(lens)는 열원(103)을 집속하여 공급되는 금속을 용융시키고, LDV 신호 역시 집속시켜 Melt pool의 상태를 측정할 수 있게 한다.As the heat source 103, a laser beam or an electron beam may be used. A focusing lens (lens) located on the upper portion of the stacking head (105) melts the metal supplied by focusing the heat source (103), and also focuses the LDV signal to measure the state of the melt pool.
적층 헤드(105)는 열원의 에너지, LDV 신호, 그리고 재료를 한곳으로 모아모아 적층 가공을 가능하게 한다. 적층 헤드(105)는 다축(multi-axis) 관절에 설치되어 다양한 방향으로 회전이 가능하다.The lamination head 105 gathers the energy of the heat source, LDV signals, and materials into one place to enable lamination processing. The stacking head 105 is installed in a multi-axis joint and can rotate in various directions.
DAQ 장비(106)는 센서에서 수집되는 데이터를 취득 및 압전 작동기를 구동하며, PC(107)는 취득된 센서 데이터 처리와 구조물의 단계별 공진 주파수를 계산한다.The DAQ device 106 acquires the data collected from the sensor and drives the piezo actuator, and the PC 107 calculates the acquired sensor data processing and the resonant frequency step by step of the structure.
3차원 적층 가공의 실시간 가공 상태 검사 및 보정 장치(100)는 금속 재료를 이용하여 구조물을 제작할 때 Melt pool의 크기에 따라 달라지는 공진 주파수와 댐핑 계수 값을 계산하여 Melt pool의 깊이 예측이 가능하고, 이를 통해 3차원 적층 가공의 실시간 가공 상태 감시 및 보정 알고리즘이 실현될 수 있다.The real-time processing state inspection and correction device 100 of the three-dimensional additive manufacturing process can calculate the resonance frequency and the damping coefficient value that depends on the size of the melt pool when manufacturing the structure using a metal material, it is possible to predict the depth of the melt pool, This enables real-time machining condition monitoring and correction algorithms for three-dimensional additive manufacturing.
도 1에 도시된 장치(100)에 의한 3차원 적층 가공의 실시간 가공 상태 검사 및 보정 과정을 보다 상세히 설명하면 다음과 같다.The process of inspection and correction in real time of the three-dimensional additive manufacturing by the apparatus 100 shown in FIG. 1 will be described in more detail as follows.
3차원 적층 가공의 실시간 가공 상태 검사 및 보정 장치(100)는 제작 상태를 감시하기 위해 LDV(101) 센서를 사용하여 Melt pool 표면 신호를 측정하고 DAQ 장비(106)를 통해 센서 신호를 획득한다.The real-time processing state inspection and correction apparatus 100 of the three-dimensional additive manufacturing process measures the Melt pool surface signal using the LDV 101 sensor to monitor the manufacturing state and obtains the sensor signal through the DAQ device 106.
이후 PC(107)에서 신호처리를 하여 공진 주파수와 댐핑 계수를 계산할 수 있는데, Melt pool의 깊이에 따라 계산된 공진 주파수와 수치해석을 통해 구해진 공진 주파수의 차이가 발생한다.Thereafter, the PC 107 may calculate a resonance frequency and a damping coefficient by performing signal processing, and a difference between the resonance frequency calculated according to the depth of the melt pool and the resonance frequency obtained through numerical analysis occurs.
여기서는, PC(107)에서 수치해석을 통해 제작 단계별 구조물의 공진 주파수를 계산할 수 있고, 제작 단계별 공진 주파수를 압전 작동기(102)에 보내어 구조물을 가진시킬 수 있다.Here, it is possible to calculate the resonant frequency of the fabrication step by step through the numerical analysis in the PC 107, and send the resonant frequency of the step by step to the piezoelectric actuator 102 to excite the structure.
3차원 적층을 위해 금속 재료의 공급과 고체 상태의 재료를 녹일 수 있는 열원(103)이 필요하다. 열원(103)은 전자광선 또는 레이저 광선을 사용할 수 있다. 구조물 제작에 필요한 금속 재료는 재료 공급 장치(104)를 통해 공급되는데 공급 방법에 따라 분말 공급 방법 와이어 공급 방법으로 구성될 수 있다.For the three-dimensional lamination, a heat source 103 capable of supplying a metal material and melting the material in a solid state is required. The heat source 103 may use an electron beam or a laser beam. The metal material required for fabricating the structure is supplied through the material supply device 104, and may be composed of a powder supply method and a wire supply method according to the supply method.
열원(103), LDV(101) 신호, 그리고 재료를 한곳으로 모아주는 적층 헤드(105)는 다축 회전체에 부착되어 다양한 각도로 적층 헤드(105)를 이동시켜 복잡한 형상 제작이 가능하게 한다. The stacking head 105, which collects the heat source 103, the LDV 101 signal, and the material into one place, is attached to the multi-axis rotating body to move the stacking head 105 at various angles, thereby making it possible to manufacture a complicated shape.
LDV(101)의 설치 위치는 3차원 적층 장비 형상에 따라 자유롭게 설치 가능 하지만, Beam guidance system을 사용하여 레이저 빔이 적층 헤드(105)의 정 중앙에 위치하도록 정렬이 필요하다. The installation position of the LDV 101 can be freely installed according to the shape of the 3D stacking equipment, but it is necessary to align the laser beam so that the laser beam is located at the center of the stacking head 105 using a beam guidance system.
압전 작동기(102)는 제작되는 구조물에 공진 주파수로 가진하기 위해 3차원 적층 기계의 적층 선반 위에 설치하는 것이 일반적이며 동일한 주파수로 가진하기 때문에 압전 작동기(102) 수에는 제약이 없다.The piezoelectric actuator 102 is generally installed on a lathe of a three-dimensional laminating machine in order to excite the structure to be manufactured at a resonant frequency, and the piezoelectric actuator 102 has no limitation in the number of the piezoelectric actuators 102 since the piezoelectric actuator 102 has the same frequency.
도 2는, 도 1의 시스템을 개발하기 위해 Melt pool 상태를 관찰하기 위한 실험 셋업 개념도이다. FIG. 2 is an experimental setup conceptual diagram for observing Melt pool status to develop the system of FIG. 1.
Melt pool이 모사된 시편(201)은 직경 2mm, 깊이는 각각 1mm, 2mm, 그리고 3mm로 달리하여 Melt pool의 깊이에 따라 가진되는 주파수와 측정되는 공진 주파수의 차이를 확인할 수 있다.The specimen 201 in which the melt pool is simulated has a diameter of 2 mm and a depth of 1 mm, 2 mm, and 3 mm, respectively, so that the difference between the excitation frequency and the measured resonance frequency can be confirmed according to the depth of the melt pool.
2대의 LDV가 사용될 수 있는데 1대(202)는 Melt pool의 표면 신호를 측정하고, 나머지 1대(203)는 구조물 표면을 측정하여 DAQ 장비(204)를 통해 수집된 데이터가 PC에서 신호처리 후 주파수 변화의 차이를 분석한다.Two LDVs can be used, one of which measures the surface signal of the Melt pool, one of which measures the surface of the structure, and the other one of the 203 measures the surface of the structure. Analyze the difference in frequency change.
시편 가진 방법은 Impulse 신호를 주기 위해 충격 망치(205)를 사용할 수 있고 동일한 위치에 동일한 힘을 준다. Impulse 신호에 대한 Melt pool와 구조물의 응답 함수를 계산하기 위해 DAQ 장비에는 2대의 LDV와 충격 망치가 연결되어 있다. DAQ 장비를 통해 수집된 전기 신호를 이용하여 PC(206)는 주파수 응답 함수를 계산하게 된다.The specimen excitation method can use the impact hammer 205 to give an impulse signal and give the same force at the same location. Two LDVs and impact hammers are connected to the DAQ device to calculate the melt pool for the impulse signal and the response function of the structure. Using the electrical signal collected by the DAQ device, the PC 206 calculates a frequency response function.
도 3은, 도 2의 실험 셋업 개념도를 기반으로 한 Melt pool 감시 및 보정 기법 원천 기술 개발 및 검증을 위한 실제 실험 사진이다.FIG. 3 is an actual experimental photograph for developing and verifying a Melt pool monitoring and correction technique source technology based on the experimental setup conceptual diagram of FIG. 2.
도 4는, 도 3의 LDV를 이용해 공진 주파수와 댐핑 계수를 예측하기 위해 사용된 Q-factor를 정의하는 그래프이다.FIG. 4 is a graph that defines the Q-factor used to predict the resonant frequency and damping coefficient using the LDV of FIG. 3.
댐핑 계수는 품질 계수(Q factor)를 사용하여 계산할 수 있다. Q factor는 FRF 그래프에서 공진 주파수를 기준으로 Magnitude가 3dB 떨어지는 지점의 주파수 차이로 공진 주파수를 나눈 값이다. 이 값을 이용해 댐핑 계수는 1을 2배의 Q factor로 나누어 구할 수 있다.The damping factor can be calculated using the Q factor. Q factor is the resonance frequency divided by the frequency difference at the point where Magnitude drops 3dB from the resonance frequency in the FRF graph. Using this value, the damping coefficient can be found by dividing 1 by 2 times the Q factor.
도 5는, 도 2에 나타낸 실험 셋업을 통해 얻어진 FRF 결과로 Melt pool의 깊이가 1mm에서 3mm로 증가할 경우 공진 주파수는 낮아지고 공진 주파수의 그래프 파형이 부드러워진 결과를 보여준다. FIG. 5 shows a result of the resonance frequency lowered and the graph waveform of the resonance frequency softened when the depth of the melt pool increases from 1 mm to 3 mm as a result of the FRF obtained through the experimental setup shown in FIG. 2.
도 6은, 도 5에서 얻어진 결과를 가지고 공진 주파수를 계산한 결과를 정리한 그래프이다.FIG. 6 is a graph summarizing the results obtained by calculating the resonance frequency with the results obtained in FIG. 5.
해석적으로 구한 알루미늄 보의 1차 공진 주파수는 298.61Hz이고 도 2의 실험 셋업을 통해 구한 구조물의 1차 공진 주파수는 약 287.49Hz이다. 이 값의 차이는 약 3.8%의 오차를 보이지만 이는 실험과 해석의 오차 수준으로 볼 수 있다. 충격 신호에 대한 알루미늄 보의 응답을 보면 Melt pool의 깊이에 관계없이 일정한 값을 보이고 있다. 그 다음 충격 신호에 대한 Melt pool의 응답을 보면 Melt pool의 깊이가 1mm에서 3mm로 증가할수록 1차 공진 주파수는 287.22Hz에서 282.29Hz로 4.93Hz 낮아진 결과를 보여주고 있다. Analytically obtained aluminum beams have a primary resonant frequency of 298.61 Hz and the structure's primary resonant frequency obtained from the experimental setup of FIG. 2 is about 287.49 Hz. The difference in this value shows an error of about 3.8%, but this can be seen as the error level of the experiment and analysis. The aluminum beam's response to the impact signal shows a constant value regardless of the depth of the melt pool. Next, the Melt pool's response to the shock signal shows that as the depth of the Melt pool increases from 1mm to 3mm, the first resonant frequency is 4.93Hz lowered from 287.22Hz to 282.29Hz.
도 7은, 도 5에서 얻어진 결과를 가지고 댐핑 계수를 계산한 결과를 정리한 그래프이다.FIG. 7 is a graph summarizing the results of calculating the damping coefficients with the results obtained in FIG. 5.
알루미늄 보의 경우 Melt pool의 깊이에 따라 평균적으로 약 0.0021로 거의 동일한 수준을 유지하지만, Melt pool의 경우 깊이가 1mm에서 3mm로 증가할수록 0.0037부터 0.0067로 증가하는 결과를 보여주고 있다. In the case of aluminum beams, the average level is approximately 0.0021 depending on the depth of the melt pool, but the melt pool increases from 0.0037 to 0.0067 as the depth increases from 1mm to 3mm.
도 8은, 도 5, 도 6 및 도 7에서 얻어진 결과를 바탕으로 Melt pool 깊이를 예측하여 3차원 적층가공 장비가 구조물 제작 시 실시간으로 이상 유무를 판단 후 피드백 제어를 통해 구조물의 품질 보증 및 향상이 가능한 알고리즘 개념도 이다.Figure 8 is based on the results obtained in Figures 5, 6 and 7 predicts the Melt pool depth to determine the abnormality in real time when the three-dimensional additive manufacturing equipment in the fabrication structure after the quality control and improvement of the structure through feedback control This is a possible algorithm conceptual diagram.
이 알고리즘에서는, PC를 사용하여 참고 데이터인 제작 단계별 구조물의 1차 공진 주파수와 댐핑 계수가 수치해석 방법을 통해 구해진다. 이후 구해진 1차 공진 주파수와 댐핑 계수를 압전 작동기로 보내 구조물을 가진하게 된다.In this algorithm, the first-order resonant frequency and damping coefficient of the fabrication stage, which are reference data using a PC, are obtained by numerical analysis. The first resonant frequency and the damping coefficient obtained are then sent to the piezoelectric actuator to have the structure.
다음, LDV는 Melt pool 표면에서 신호를 취득하여, 1차 공진 주파수와 댐핑 계수가 구해지고 수치해석을 통해 구한 데이터와 실제 측정된 신호를 가지고 계산된 데이터를 비교 분석하여 설정한 값보다 큰 오차가 발생하면 제어 신호를 발생시켜 Heating source 또는 제작 속도를 제어하여 실시간으로 구조물의 품질을 확보할 수 있다.Next, the LDV acquires a signal from the surface of the melt pool, and the first resonant frequency and the damping coefficient are obtained, and the error calculated by comparing the calculated data with the measured data and the actual measured signal has a larger error than the set value. When generated, control signals can be generated to control the heating source or fabrication speed to ensure the quality of the structure in real time.
상기와 같이 Melt pool의 크기가 변화함에 따라 측정되는 1차 공진 주파수와 댐핑 계수 값이 변화되는 결과를 얻어 실시간으로 제작되는 구조물의 품질을 확보가 가능하므로 급속하게 증가하고 있는 3차원 적층 산업에서 제작되어 지는 구조물의 신뢰성 확보를 위해 금속을 재료로 사용하는 3차원 적층가공 장비가 구조물 제작 시 실시간으로 이상 유무를 판단하여 피드백 제어를 통해 구조물의 품질 향상 및 추가적인 결함 검사 없이 제작 가능해진다.As the size of the melt pool is changed as described above, the first resonant frequency and the damping coefficient value measured are changed, thereby ensuring the quality of the fabricated structure in real time, so it is manufactured in the rapidly increasing three-dimensional lamination industry. In order to secure the reliability of the structure, 3D additive manufacturing equipment using metal as a material is judged in real time during the construction of the structure, and it can be manufactured without improving the quality of the structure and additional defect inspection through feedback control.
지금까지, Melt pool의 깊이를 예측하여, 3차원 적층 가공 공정을 이용하여 구조물을 제작할 때 구조물이 정상적으로 제작되고 있는지를 검사하고 문제가 발생할 경우 피드백 신호를 발생시켜 정상 상태가 될 수 있도록 제어하는 방법에 대해 바람직한 실시예를 들어 상세히 설명하였다.Up to now, the method of predicting the depth of the melt pool, checking whether the structure is being manufactured normally when manufacturing the structure using the 3D additive manufacturing process, and generating a feedback signal in case of a problem, controlling the normal state It described in detail for the preferred embodiment for.
위 실시예에서는, Melt pool 깊이를 예측하기 위해 Laser Doppler Vibrometer (LDV), 압전작동기, 그리고 신호처리 기법을 적용하여 실시간 melt pool 깊이를 예측 할 수 있어 적정 수준의 Melt pool 크기 제어가 가능하며, 문제 발생 시 레이저 세기를 자동으로 제어하고 제작 공정 전체 데이터의 저장이 가능하여, 최종적으로 구조물 제작이 완료 된 이후 추가적인 검사 없이 문제가 발생한 위치를 확인할 수 있다.In the above embodiment, it is possible to predict the melt pool depth in real time by applying a laser Doppler Vibrometer (LDV), a piezo actuator, and a signal processing technique to predict the melt pool depth. When generated, the laser intensity can be controlled automatically and the entire manufacturing process data can be saved, so that the position where the problem occurred can be checked without additional inspection after the final structure fabrication is completed.
특히, 3차원 적층가공 장비에 Melt pool 상태를 감지하는 LDV를 설치하고 구조물에 특정 주파수로 가진하기 위해 압전 작동기를 부착하여 가진된 신호의 응답 신호를 수집 후 데이터를 분석하여 장비 스스로 Melt pool의 크기를 제어하고, Point by Point 데이터를 저장하여 추후 별도의 결함 검사 없이 문제가 발생한 부분을 찾을 수 있다.In particular, the LDV is installed in the 3D additive manufacturing equipment to detect the Melt pool condition, and the piezoelectric actuator is attached to the structure to collect the specific frequency. Can be controlled and the Point by Point data can be stored to find the part where the problem occurred without additional defect inspection later.
또한, 기존의 3차원 적층 가공 장비에 LDV와 압전 작동기를 추가하여 장비 단가 상승을 최소화 하였고, Melt pool 상태를 실시간으로 감시하여 최적화된 상태를 스스로 제어할 수 있으며, 제작 단계별 데이터를 수집 후 맵핑 알고리즘을 통해 결함이 발생 했을 경우 손쉽게 해당 위치를 찾을 수 있어 제작 효율 및 품질을 향상시킬 수 있다.In addition, LDV and piezoelectric actuators are added to the existing 3D additive manufacturing equipment to minimize the increase in equipment cost, and the optimized state can be controlled by monitoring the Melt pool status in real time. This makes it easy to find the location in case of a defect, improving production efficiency and quality.
한편, 본 실시예에 따른 장치와 방법의 기능을 수행하게 하는 컴퓨터 프로그램을 수록한 컴퓨터로 읽을 수 있는 기록매체에도 본 발명의 기술적 사상이 적용될 수 있음은 물론이다. 또한, 본 발명의 다양한 실시예에 따른 기술적 사상은 컴퓨터로 읽을 수 있는 기록매체에 기록된 컴퓨터로 읽을 수 있는 코드 형태로 구현될 수도 있다. 컴퓨터로 읽을 수 있는 기록매체는 컴퓨터에 의해 읽을 수 있고 데이터를 저장할 수 있는 어떤 데이터 저장 장치이더라도 가능하다. 예를 들어, 컴퓨터로 읽을 수 있는 기록매체는 ROM, RAM, CD-ROM, 자기 테이프, 플로피 디스크, 광디스크, 하드 디스크 드라이브, 등이 될 수 있음은 물론이다. 또한, 컴퓨터로 읽을 수 있는 기록매체에 저장된 컴퓨터로 읽을 수 있는 코드 또는 프로그램은 컴퓨터간에 연결된 네트워크를 통해 전송될 수도 있다.On the other hand, the technical idea of the present invention can be applied to a computer-readable recording medium containing a computer program for performing the functions of the apparatus and method according to the present embodiment. In addition, the technical idea according to various embodiments of the present disclosure may be implemented in the form of computer readable codes recorded on a computer readable recording medium. The computer-readable recording medium can be any data storage device that can be read by a computer and can store data. For example, the computer-readable recording medium may be a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical disk, a hard disk drive, or the like. In addition, the computer-readable code or program stored in the computer-readable recording medium may be transmitted through a network connected between the computers.
또한, 이상에서는 본 발명의 바람직한 실시예에 대하여 도시하고 설명하였지만, 본 발명은 상술한 특정의 실시예에 한정되지 아니하며, 청구범위에서 청구하는 본 발명의 요지를 벗어남이 없이 당해 발명이 속하는 기술분야에서 통상의 지식을 가진자에 의해 다양한 변형실시가 가능한 것은 물론이고, 이러한 변형실시들은 본 발명의 기술적 사상이나 전망으로부터 개별적으로 이해되어져서는 안될 것이다.In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Claims (9)

  1. Melt pool의 신호를 측정하는 센서;A sensor for measuring a signal of the melt pool;
    기준 공진 주파수와 댐핑 계수로 구조물을 가진하는 작동기;An actuator having the structure at a reference resonance frequency and a damping coefficient;
    금속 재료를 녹여주는 열원;Heat sources for melting metal materials;
    적층에 필요한 재료를 공급하는 장치;An apparatus for supplying a material required for lamination;
    센서 신호, 열원, 재료를 한 곳으로 모아주는 적층 헤드;A stacking head that collects sensor signals, heat sources, and materials in one place;
    센서에서 수집되는 데이터를 취득하고 작동기를 구동하는 장비;Equipment for acquiring data collected by the sensor and driving the actuator;
    취득한 센서 데이터로부터 공진 주파수와 댐핑 계수를 계산하고, 계산된 공진 주파수와 댐핑 계수를 기초로 열원의 세기를 제어하는 컴퓨팅 장치;를 포함하는 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.And a computing device for calculating the resonance frequency and the damping coefficient from the acquired sensor data and controlling the intensity of the heat source based on the calculated resonance frequency and the damping coefficient.
  2. 청구항 1에 있어서,The method according to claim 1,
    센서는,The sensor,
    레이저광 조사에 따른 Melt pool의 표면 신호와 구조물의 표면 신호를 측정하는 적어도 하나의 LDV;를 포함하는 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.And at least one LDV measuring the surface signal of the melt pool and the surface signal of the structure according to the laser light irradiation.
  3. 청구항 1에 있어서,The method according to claim 1,
    작동기는,Actuator,
    제작되는 구조물의 단계에 맞는 기준 공진 주파수와 댐핑 계수로 구조물을 가진하는 임팩트 해머 또는 압전 작동기인 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.Real-time machining state inspection apparatus of the three-dimensional additive manufacturing, characterized in that the impact hammer or piezo actuator having a structure with a reference resonance frequency and a damping coefficient for the stage of the structure to be manufactured.
  4. 청구항 1에 있어서,The method according to claim 1,
    컴퓨팅 장치는,Computing device,
    계산된 공진 주파수와 댐핑 계수를 기초로 Melt pool의 크기를 예측하는 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.A real-time processing state inspection apparatus for three-dimensional additive manufacturing, characterized in that the size of the melt pool is estimated based on the calculated resonance frequency and the damping coefficient.
  5. 청구항 1에 있어서,The method according to claim 1,
    컴퓨팅 장치는,Computing device,
    수치 해석 방법을 통해 구조물 제작 단계별 기준 공진 주파수와 댐핑 계수를 계산하는 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.A real-time machining state inspection apparatus for three-dimensional additive manufacturing, characterized by calculating the reference resonant frequency and the damping coefficient for each structure fabrication step through a numerical analysis method.
  6. 청구항 1에 있어서,The method according to claim 1,
    컴퓨팅 장치는,Computing device,
    기준 공진 주파수와 댐핑 계수를 계산된 공진 주파수와 댐핑 계수와 비교하여, 피드백 제어를 통해 열원의 세기를 조절하는 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.And comparing the reference resonance frequency and the damping coefficient with the calculated resonance frequency and the damping coefficient, and adjusting the intensity of the heat source through feedback control.
  7. 청구항 6에 있어서,The method according to claim 6,
    컴퓨팅 장치는,Computing device,
    비교 결과 설정한 값보다 큰 오차가 발생하면, 제어 신호를 발생시켜 열원의 세기를 조절하는 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.And a control signal is generated when an error larger than the set value is generated as a result of the comparison, thereby adjusting the intensity of the heat source.
  8. 청구항 1에 있어서,The method according to claim 1,
    열원은,The heat source is
    레이저 빔 또는 전자 빔인 것을 특징으로 하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.Real-time processing state inspection apparatus for three-dimensional additive lamination, characterized in that the laser beam or electron beam.
  9. Melt pool의 신호를 측정하는 센서;A sensor for measuring a signal of the melt pool;
    기준 공진 주파수와 댐핑 계수로 구조물을 가진하는 작동기;An actuator having the structure at a reference resonance frequency and a damping coefficient;
    센서에서 수집되는 데이터를 취득하고 작동기를 구동하는 장비;Equipment for acquiring data collected by the sensor and driving the actuator;
    취득한 센서 데이터로부터 공진 주파수와 댐핑 계수를 계산하고, 계산된 공진 주파수와 댐핑 계수를 기초로 열원의 세기를 제어하는 컴퓨팅 장치;를 포함하는 3차원 적층 가공의 실시간 가공 상태 검사 장치.And a computing device for calculating the resonance frequency and the damping coefficient from the acquired sensor data and controlling the intensity of the heat source based on the calculated resonance frequency and the damping coefficient.
PCT/KR2017/006945 2017-05-26 2017-06-30 Device for real-time checking and correcting process state of three-dimensional lamination process, and method to which same is applied WO2018216845A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11507072B2 (en) 2020-07-28 2022-11-22 General Electric Company Systems, and methods for diagnosing an additive manufacturing device using a physics assisted machine learning model

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11430118B2 (en) * 2019-07-12 2022-08-30 Bruker Nano, Inc. Methods and systems for process control based on X-ray inspection

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020144984A1 (en) * 2001-02-23 2002-10-10 Nissan Motor Co., Ltd. Laser weld quality monitoring method and system
KR20040012550A (en) * 2002-07-31 2004-02-11 미야치 테크노스 가부시키가이샤 Laser weld monitor
KR20140057706A (en) * 2012-10-30 2014-05-14 조선대학교산학협력단 Monitoring system and method for laser welding
KR20160129871A (en) * 2014-03-31 2016-11-09 미츠비시 쥬고교 가부시키가이샤 Three-dimensional lamination device and three-dimensional lamination method
WO2016198885A1 (en) * 2015-06-11 2016-12-15 Renishaw Plc Additive manufacturing apparatus and method

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100596713B1 (en) * 2004-05-17 2006-07-07 전자부품연구원 An overshoot reduction system and method for the precision robot actuated with piezoeletric device
KR101673062B1 (en) * 2014-12-08 2016-11-04 김화중 Method for measuring height of melt pool generated in laser cladding

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020144984A1 (en) * 2001-02-23 2002-10-10 Nissan Motor Co., Ltd. Laser weld quality monitoring method and system
KR20040012550A (en) * 2002-07-31 2004-02-11 미야치 테크노스 가부시키가이샤 Laser weld monitor
KR20140057706A (en) * 2012-10-30 2014-05-14 조선대학교산학협력단 Monitoring system and method for laser welding
KR20160129871A (en) * 2014-03-31 2016-11-09 미츠비시 쥬고교 가부시키가이샤 Three-dimensional lamination device and three-dimensional lamination method
WO2016198885A1 (en) * 2015-06-11 2016-12-15 Renishaw Plc Additive manufacturing apparatus and method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11507072B2 (en) 2020-07-28 2022-11-22 General Electric Company Systems, and methods for diagnosing an additive manufacturing device using a physics assisted machine learning model
US11906955B2 (en) 2020-07-28 2024-02-20 General Electric Company Systems, and methods for diagnosing an additive manufacturing device using a physics assisted machine learning model

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