WO2018216845A1

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

Info

Publication number: WO2018216845A1
Application number: PCT/KR2017/006945
Authority: WO
Inventors: 강래형; 한대현
Original assignee: 전북대학교산학협력단
Priority date: 2017-05-26
Filing date: 2017-06-30
Publication date: 2018-11-29
Also published as: KR101974722B1; KR20180129280A

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

Real-time machining status inspection and correction device for three-dimensional additive manufacturing and its method

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. 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.

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.

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.

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. .

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.

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.

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.

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.

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.

The computing device may estimate the size of the melt pool based on the calculated resonance frequency and the damping coefficient.

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.

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.

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.

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.

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.

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.

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,

2 is a conceptual diagram of an experimental setup for monitoring the Melt pool state to develop the system of 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.

4 is a graph that defines a Q-factor used to predict the resonance frequency and damping coefficient using the LDV of 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.

6 is a graph summarizing the results obtained by calculating the resonance frequency with the results obtained in FIG. 5;

7 is a graph summarizing the results of calculating the damping coefficients with the results obtained in FIG. 5, and

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.

Hereinafter, with reference to the drawings will be described the present invention in more detail.

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. .

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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. Using the electrical signal collected by the DAQ device, the PC 206 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. 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.

FIG. 7 is a graph summarizing the results of calculating the damping coefficients with the results obtained in FIG. 5.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

A sensor for measuring a 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 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.
The method according to claim 1,

The sensor,

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.
The method according to claim 1,

Actuator,

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.
The method according to claim 1,

Computing device,

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.
The method according to claim 1,

Computing device,

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.
The method according to claim 1,

Computing device,

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.
The method according to claim 6,

Computing device,

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.
The method according to claim 1,

The heat source is

Real-time processing state inspection apparatus for three-dimensional additive lamination, characterized in that the laser beam or electron beam.
A sensor for measuring a 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 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.