Active acoustic emission signal monitoring device for laser directional energy deposition

Abstract

The utility model discloses an active acoustic emission signal monitoring device for laser directional energy deposition, which comprises an acoustic signal generating device arranged on a first substrate and used for generating acoustic vibration signals propagating in the substrate in the form of longitudinal waves; the piezoelectric vibration sensor is arranged on the second substrate and is used for receiving the acoustic vibration signal; wherein the first substrate is opposite to the second substrate. High-frequency acoustic signals are provided through the acoustic signal generating device arranged on the side face of the substrate, applied high-frequency longitudinal waves are received by the piezoelectric vibration sensor after passing through the substrate and the molten pool, and high-dimensional information used for describing the dynamic process of the molten pool can be provided. The device can be widely applied to the field of metal additive manufacturing.

Description

Technical Field

[0001] The utility model relates to the field of metal additive manufacturing, in particular to a laser directional energy deposition active acoustic emission signal monitoring device. Background Art

[0002] In order to obtain the molten pool information in the metal additive manufacturing process to evaluate the quality of printing, it is necessary to use multi-source sensors to collect the molten pool process information. Coaxial / paraxial optical signal acquisition can usually only capture the characteristics of the upper surface and nearby areas of the molten pool, and the information dimension is low. The acoustic signals and features collected based on microphones can contain information inside the molten pool, so they have been widely used in laser selective melting and directed energy deposition processes. However, when the acoustic signal is collected by a microphone, the background noise exists in the collected acoustic signal due to the vibration of the equipment. Therefore, it is necessary to use spectrum analysis and designed specific filters to filter out the background noise with a high energy ratio, and then extract effective molten pool features from the preprocessed acoustic signal. This preprocessing process is complex and has poor generalization ability. When the laser power increases significantly, the working mode and vibration noise of the equipment are unstable. It is necessary to dynamically correct the parameters in the filtering algorithm to improve the scope of application of the model. Utility Model Content

[0003] In order to solve the above technical problems, the purpose of the utility model is to provide a laser directional energy deposition active acoustic emission signal monitoring device.

[0004] The technical solution adopted by the utility model is:

[0005] A laser directional energy deposition active acoustic emission signal monitoring device, comprising:

[0006] An acoustic signal generating device, disposed on the first substrate, for generating an acoustic vibration signal, wherein the acoustic vibration signal propagates in the substrate in the form of a longitudinal wave;

[0007] A piezoelectric vibration sensor, disposed on the second substrate, for receiving the acoustic vibration signal;

[0008] Wherein, the first substrate and the second substrate are opposite to each other.

[0009] Furthermore, the position of the acoustic signal generating device matches the position of the piezoelectric vibration sensor.

[0010] Furthermore, a connection line between the acoustic signal generating device and the piezoelectric vibration sensor passes through a printing area.

[0011] Furthermore, the acoustic signal generating device outputs a signal at a preset frequency.

[0012] Furthermore, the piezoelectric vibration sensor samples the received acoustic vibration signal at a preset sampling frequency.

[0013] Furthermore, it is applied to a laser selective melting system, wherein the laser selective melting system comprises a mechanical arm; a molding cavity, a laser head and a powder spreading device;

[0014] The laser head is arranged at the end of the mechanical arm, and the first substrate and the second substrate are arranged at the periphery of the molding cavity.

[0015] Furthermore, the powder spreading device comprises an annular nozzle, which is arranged at the end of the robot arm and is used to spread metal powder to the printing area.

[0016] The beneficial effect of the utility model is that the utility model provides a high-frequency sound signal through the sound signal generating device arranged on the side of the substrate. The applied high-frequency longitudinal wave passes through the substrate and the molten pool and is received by the piezoelectric vibration sensor, which can provide high-dimensional information for describing the dynamic process of the molten pool. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0018] Figure 1 It is a schematic diagram of a laser selective melting system in an embodiment of the utility model;

[0019] Figure 2 It is a schematic diagram of signals collected by the piezoelectric vibration sensor in the embodiment of the utility model.

[0020] Figure 1 Figure numerals: 1-forming cavity; 2-molten pool; 3-laser; 4-powder; 5-annular nozzle; 6-mechanical arm; 7-acoustic signal generating device; 8-piezoelectric vibration sensor. DETAILED DESCRIPTION

[0021] This section will describe in detail the specific embodiments of the utility model. The preferred embodiments of the utility model are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the utility model, but it cannot be understood as a limitation on the protection scope of the utility model.

[0022] In the description of the present invention, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0023] In the description of the present utility model, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0024] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0025] like Figure 1 As shown, this embodiment provides a laser selective melting system, including a laser directional energy deposition active acoustic emission signal monitoring device, a molding cavity 1 and a robot 6, wherein the laser directional energy deposition active acoustic emission signal monitoring device includes an acoustic signal generating device and a piezoelectric vibration sensor. The molten pool 2 is arranged in the molding cavity 1, and the molding cavity 1 is surrounded by a first substrate, a second substrate, a third substrate and a fourth substrate, wherein the first substrate and the second substrate are opposite, an acoustic signal generating device 7 is arranged on the first substrate, and a piezoelectric vibration sensor 8 is arranged on the second substrate. A laser head and an annular nozzle are arranged at the end of the robot 6, and the annular nozzle is used for spreading powder. Under the control of the robot, the metal powder can be spread to a specified position, and the laser head is used to generate laser light, which is irradiated on the metal powder to generate a molten pool.

[0026] Laser directed energy deposition adopts the forming principle of "discrete-accumulation" and is capable of forming complex large-scale structural parts. The laser directed energy deposition active acoustic emission signal monitoring device proposed in the utility model avoids the interference of background noise such as equipment vibration by emitting a vibration signal of a fixed frequency into the substrate and receiving the acoustic signal modulated by the dynamic behavior of the molten pool on the other side. It is not limited by the process range and has enhanced applicability and generalization. When performing batch rapid forming, the molten pool process can be monitored and the printing quality can be evaluated by the emission and collection of acoustic signals. The laser directed energy deposition active acoustic emission signal monitoring device mainly includes a sound generating device (which applies longitudinal waves to the side of the substrate, and the frequency can be adjusted from 200Hz to 5000Hz) and a piezoelectric acoustic signal receiving sensor for collecting modulated longitudinal vibration waves. The layout of the device is shown in the schematic diagram Figure 1 As shown. Specifically, the acoustic signal generating device and the piezoelectric vibration sensor are symmetrically arranged on both sides of the substrate, and the center line passes through the printing area as much as possible. The horizontally propagating acoustic vibration signal propagates in the substrate in the form of longitudinal waves. The piezoelectric sensor collects acoustic signals within a large bandwidth range, and since the input spectrum of the external acoustic signal is known. Therefore, it is very easy to extract the target signal from the collected signal.

[0027] The working principle of the active acoustic emission signal monitoring device for laser directed energy deposition is as follows: a suitable output frequency (e.g. 2kHz) is selected, and the acoustic signal generator 7 outputs a longitudinal wave with a fixed frequency, and the sampling frequency of the piezoelectric vibration sensor 8 is 20kHz. First, the input acoustic signal is tested when it is not printed, and its waveform and amplitude distribution are obtained on the other side of the substrate, such as Figure 2 As shown in (a) in the figure, the acoustic signal during the printing process is then collected. Since the frequency of the input acoustic signal is known a priori, the signal obtained from the test can be filtered through a filter to retain the signal with a spectrum distribution of 2kHz±100Hz, as shown in Figure 2 As shown in (b). In this process, the input acoustic signal longitudinal wave is received by the piezoelectric vibration sensor 8 through the medium of the printed substrate. When the molten pool exists, part of the longitudinal wave passes through the molten metal of the molten pool scale and continues to propagate toward the sensor side. The signal component on this path is affected by the dynamic behavior of the molten pool and modulated, resulting in changes in the amplitude and instantaneous phase of the signal component. Therefore, the waveform and amplitude of the sampled acoustic signal change, and the modulated component is usually superimposed on the unprinted steady acoustic signal in the form of a riding wave. By subtracting Figure 2 The waveform in (a) above obtains the modulation signal component that is only affected by the movement of the molten pool, such as Figure 2 As shown in (c).

[0028] In some embodiments, the piezoelectric vibration sensor 8 may be connected to an oscilloscope, and the waveform may be processed by the oscilloscope to obtain a high-frequency signal.

[0029] As an optional implementation, the modulation component in the signal is solely affected by the behavior of the molten pool, and can provide high-dimensional non-explicit features of the forming process. Therefore, the obtained modulation component can be further reconstructed into a sample for training the neural network model, such as a matrix with a size of N×N and a channel number of 1 or a sequence with a length of N. It is then placed in the network model for training, and then the printing anomalies in the forming process, such as over-melting and under-melting, are identified. The power of the acoustic signal generator is much lower than the high-energy beam acting on the molten pool, and the frequency is much lower than the frequency required for the cavitation effect to occur. Therefore, the influence of the mechanical vibration caused by the acoustic signal on the directed energy deposition process cannot be considered. At the same time, the frequency and amplitude of the acoustic signal input excitation can be adjusted according to the actual printing process to obtain a more significant modulation signal as much as possible and strengthen the implicit features it contains.

[0030] In summary, the utility model adopts an active acoustic signal emission strategy, which provides a high-frequency acoustic signal through a vibration generating device arranged on the side of the substrate. The applied high-frequency longitudinal wave passes through the substrate and the molten pool and is received by the receiver. Among them, the molten pool acts as a dynamically changing complex high-order damping system, which modulates some components of the acoustic signal and transforms them into modulated signals. When the signal is collected from the opposite side of the vibration generator, a modulated acoustic signal affected by the molten pool is obtained. The difference between the external acoustic signal collected during the non-printing process and the acoustic signal collected under the influence of the molten pool during printing is the modulation component, which is completely caused by the dynamic behavior of the molten pool. The difference between the two sets of signals - the modulation component can provide high-dimensional information for describing the dynamic process of the molten pool, and further, it can be used to evaluate the forming quality through a neural network model.

[0031] Compared with the prior art, the device proposed by the utility model has at least the following advantages and beneficial effects:

[0032] (1) Different from traditional acoustic signal monitoring. The traditional acoustic signal monitoring scheme mainly monitors the molten pool as the acoustic signal emission source, and a large amount of high-amplitude background noise will be obtained synchronously during the acquisition process. Noise will potentially interfere with the model's extraction of key feature information in the signal, affecting the process identification and expression capabilities, and the background noise varies greatly with changes in the process environment. Based on the device proposed in the utility model, a horizontal acoustic signal excitation is first applied to the substrate printed by directed energy deposition, and then the excitation is collected on the other side. During the printing process, the presence of the molten pool will cause the passing acoustic signal (longitudinal wave) to be modulated, and the modulation component of this narrowband frequency band is only affected by the dynamic behavior of the molten pool, and is not affected by background noise such as equipment operation. Therefore, the applicable process window is increased and the generalization is enhanced.

[0033] (2) When training the model and identifying the printing process, the modulation signals under various states (normal, over-melted and under-melted) are first collected and used for training the neural network model. Subsequently, the model is applied to actual printing production to identify the abnormal printing state, which can efficiently obtain the printing state and evaluate the forming quality.

[0034] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention, and these equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A laser directed energy deposition active acoustic emission signal monitoring device, characterized in that: include: An acoustic signal generating device, disposed on the first substrate, for generating an acoustic vibration signal, wherein the acoustic vibration signal propagates in the substrate in the form of a longitudinal wave; A piezoelectric vibration sensor, disposed on the second substrate, for receiving the acoustic vibration signal; Wherein, the first substrate and the second substrate are opposite to each other.

2. The laser directed energy deposition active acoustic emission signal monitoring device according to claim 1, characterized in that: The position of the acoustic signal generating device matches the position of the piezoelectric vibration sensor.

3. The laser directed energy deposition active acoustic emission signal monitoring device according to claim 2, characterized in that: The connection line between the acoustic signal generating device and the piezoelectric vibration sensor passes through the printing area.

4. The laser directed energy deposition active acoustic emission signal monitoring device according to claim 1, characterized in that: The acoustic signal generating device outputs a signal at a preset frequency.

5. The laser directed energy deposition active acoustic emission signal monitoring device according to claim 1, characterized in that: The piezoelectric vibration sensor samples the received acoustic vibration signal at a preset sampling frequency.

6. The laser directed energy deposition active acoustic emission signal monitoring device according to claim 1, characterized in that: Applied to a laser selective melting system, the laser selective melting system comprises a mechanical arm; a molding cavity, a laser head and a powder spreading device; The laser head is arranged at the end of the mechanical arm, and the first substrate and the second substrate are arranged at the periphery of the molding cavity.

7. The laser directed energy deposition active acoustic emission signal monitoring device according to claim 6, characterized in that: The powder spreading device comprises an annular nozzle, which is arranged at the end of the robot arm and is used to spread metal powder to the printing area.

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