TW201822935A - Method for detecting abnormal event for laser welding process and detecting system using the same employing detection of vibration wave to determine existence of abnormal event during laser welding and issuing warning in real-time - Google Patents

Abstract

The present invention discloses a method for detecting abnormal event of laser welding process, which includes: using a detection unit to detect vibration wave generated by at least one set of welding objects while performing laser welding and obtain a measurement signal having at least one effective signal; converting each of effective signals as a frequency domain signal; and, determining whether there exists an abnormal event according to each frequency domain signal and at least one strength condition. In which, when no frequency domain signal meets the strength condition, it is determined that there exists an abnormal event during laser welding process for the set of welding objects; otherwise, when the frequency domain signal meets at least one strength condition, it is determined that there exists no abnormal event during laser welding process for the set of welding objects; wherein, an effective signal represents the execution of laser welding process for one set of welding objects.

Description

   Method and system for detecting laser welding abnormal events   

The invention relates to a laser welding technology, in particular to a method and a system for detecting abnormal events of laser welding.

With the development of industrial technology, laser welding technology is a new welding technology, and has been widely used in various industries such as information technology (IT), medical, electronics, automotive, machinery and aviation. Laser welding technology has incomparable advantages over other fusion welding technologies in terms of weld width, quality, welding speed, deformation, efficiency, welding control, and positioning accuracy.

Laser welding technology uses the principle of atomic stimulated radiation to stimulate the laser material to produce a laser beam with good monochromaticity, strong directivity and high intensity, and focuses the generated laser beam on the welding to be welded. As a result, the laser beam is absorbed by the welding object within a few thousandths of a second or even less, and then converted into thermal energy to melt the welding object. Finally, the molten welding object is cooled and crystallized to achieve the connection of the welding object.

On the laser welding automatic production line, although the laser welding machine is equipped with welding inspection equipment, this welding inspection equipment is only used to remind the operator of the number of welding operations performed and cannot be used to know whether the laser welding machine is correct. Welding of the welding object is performed in the ground. After the welding of a large number of welding objects is completed, the operator needs to visually inspect the welding points of each welding object one by one to determine whether there are bad welding points (unsuccessful joining). When there are bad solder joints on the welding object, the welding object is re-soldered by the laser welding machine. However, the re-soldering operation is quite troublesome, and the re-soldering part is not smooth and easily damaged.

Due to the strong light generated during the laser welding process, such as flashing light, plasma, etc., the operator cannot detect the welding state during the welding process. The operator can only perform the inspection after the welding process of each unit is completed. In addition, before the entire welding process is completed, welding operations and inspection operations must be repeatedly performed in batches, thereby reducing the advantages of laser welding that can achieve non-contact high-speed welding.

Furthermore, for the detection of welding strength, the welding of the welded material used as a test sample is generally destructively tested to determine whether the joint strength of the solder joints of each test sample is sufficient, and then it is determined that the test samples are formed. Weld quality of all welds formed in consecutive periods. In other words, each soldered object on the electronic product can only confirm whether the bonding is successful, and the soldering quality (eg, bonding strength) of the soldered object is only speculatively good and cannot be actually tested. However, the reliability and durability of electronic products are closely related to the welding quality of each solder.

In one embodiment, a method for detecting an abnormal event of laser welding includes: using a sensing unit to sense vibration waves generated during laser welding of at least one group of welding objects to obtain at least one valid signal. Measuring a measurement signal, converting each valid signal into a frequency domain signal, and determining whether there is an abnormal event according to each frequency domain signal and at least one intensity condition. Among them, when each frequency-domain signal does not satisfy any of the strength conditions, it is determined that there is an abnormal event during laser welding of this group of welding objects. Conversely, when each frequency-domain signal satisfies at least one strength condition, it is determined that there is no abnormal event during laser welding of this group of welding objects. Here, each valid signal represents the performance of laser welding of a group of welds.

In one embodiment, a laser welding abnormal event detection system includes a sensing unit, a signal generating circuit, and a processing unit. The signal generating circuit is coupled to the sensing unit, and the processing unit is coupled to the signal generating circuit. The signal generating circuit senses at least one group of welding objects to perform vibration welding by a sensing unit to obtain a measurement signal having at least one valid signal. The processing unit receives the measurement signal, converts each valid signal into a frequency domain signal, and determines whether there is an abnormal event according to each frequency domain signal and at least one strength condition. Wherein, when each frequency-domain signal does not meet any of the strength conditions, the processing unit determines that there is an abnormal event when the group of welding objects performs laser welding; and when each frequency-domain signal meets at least one strength condition, the processing unit determines this group of welding There are no abnormal events when objects are laser welded. Here, each valid signal represents the performance of laser welding of a group of welds.

In summary, according to the method and system for detecting abnormal events of laser welding according to the present invention, a vibration wave sensing unit is used to sense the vibration waves generated by each group of welding objects during laser welding and analyze the vibrations. The frequency-domain signal of the wave measurement signal is used to determine whether there are abnormal events in the laser welding process, so as to immediately warn about abnormal events that occur during welding (such as out-of-focus, abnormal laser power, excessive material clearance, etc.) , And can be further corrected immediately (for example, desoldering solders with unqualified solder joints and re-soldering solders after desoldering according to the test results), thereby improving the reliability and durability of electronic products.

10‧‧‧ Detection System

110‧‧‧Sound / Vibration Measurement Module

112‧‧‧Sensing unit

114‧‧‧Signal generating circuit

150‧‧‧ processing unit

170‧‧‧Storage unit

20‧‧‧laser welding machine

210‧‧‧welding stage

230‧‧‧laser welding head

250‧‧‧machine control components

30‧‧‧weld

330‧‧‧Soldering

SS‧‧‧Measurement signal

S1‧‧‧ effective signal

S40 ~ S80‧‧‧step

FIG. 1 is a functional block diagram of an abnormal event detection system for laser welding according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a laser welding machine using the detection system of FIG. 1.

3 is a flowchart of a method for detecting an abnormal event of laser welding according to an embodiment of the present invention.

FIG. 4 is a waveform diagram of an exemplary measurement signal.

FIG. 5 is a waveform diagram of a first exemplary example of a frequency domain signal.

FIG. 6 is a waveform diagram of a second exemplary example of a frequency domain signal.

FIG. 7 is a waveform diagram of a third exemplary example of a frequency domain signal.

FIG. 8 is a waveform diagram of a fourth exemplary example of a frequency domain signal.

FIG. 9 is a waveform diagram of a fifth exemplary example of a frequency domain signal.

FIG. 1 is a functional block diagram of an abnormal event detection system for laser welding according to an embodiment of the present invention. Referring to FIG. 1, an abnormal event detection system for laser welding (hereinafter referred to as “detection system 10”) includes a sound / vibration measurement module 110 and a processing unit 150. The sound / vibration measurement module 110 includes a sensing unit 112 and a signal generating circuit 114. The signal generating circuit 114 is coupled to the sensing unit 112, and the processing unit 150 is coupled to the signal generating circuit 114.

FIG. 2 is a schematic diagram of a laser welding machine using the detection system 10 of FIG. 1. 2, the laser welding machine 20 includes a welding stage 210, a laser welding head 230, and a machine control assembly 250. The laser welding head 230 corresponds to the welding stage 210 and is disposed on the machine control assembly 250. An electronic product or a component thereof (hereinafter referred to as “solder 30”) to be soldered is set on the soldering stage 210. The machine control assembly 250 can move the welding head 230 to a position to be welded and drive the welding head 230 to weld a group of welding objects 30 (for example, two sheet parts) together by laser welding. Here, a welding seam is formed at the joint of the group of welding objects 30, that is, the welding point 330. The sensing unit 112 is configured to sense vibration waves generated when laser welding is performed on each group of welding objects 30.

In some embodiments, the sensing unit 112 may be fixedly disposed on the welding stage 210 or fixedly disposed near the welding stage 210 and capable of receiving vibrations generated by the laser welding machine 20 during laser welding of the welding object 30. Arbitrary position of wave.

In some embodiments, the machine control assembly 250 has a moving assembly, a driving assembly, and a processing unit (not shown). The processing unit is coupled to the moving component and the driving component. The laser welding head 230 is mounted on the moving component and is coupled to the driving component. The processing unit controls the moving component to move the laser welding head 230 to a position to be welded, and then the processing unit controls the driving component to drive the laser welding head 230 to emit a laser beam for welding. In an embodiment, the laser welding machine 20 and the detection system 10 may be provided with independent processing units to perform respective operation control. In another embodiment, the laser welding machine 20 and the detection system 10 can also share the processing unit 150 for operation control. The following describes the detection operation using the common processing unit 150 as an example.

3 is a flowchart of a method for detecting an abnormal event of laser welding according to an embodiment of the present invention. Referring to FIGS. 1 to 3, the processing unit 150 activates the signal generating circuit 114 when or before the processing unit 150 starts to control the operation of the weldment. During the laser welding implementation process, the signal generating circuit 114 senses at least one group of welding objects 30 during the laser welding by the sensing unit 112 to obtain a measurement signal (step S40). In some embodiments, the measurement signal may be an original analog signal corresponding to the vibration wave sensed by the sensing unit 112, or an enhanced analog signal obtained by the signal generation circuit 114 for strengthening the original analog signal. . The enhancement processing may be a signal processing program that does not change the essence of the signal, such as filtering, amplification, or a combination thereof.

In one embodiment, the sensing unit 112 may be a microphone, and the signal generating circuit 114 may be an audio input circuit. In other words, the audio input circuit receives a sound (sound wave) generated by the welding object 30 during laser welding through a microphone to obtain a sound signal. In another embodiment, the sensing unit 112 may be an acceleration gauge. In other words, the signal generating circuit 114 senses the vibration (vibration wave) generated when the welding object 30 performs laser welding with an accelerometer to obtain a measurement signal.

Here, as shown in FIG. 4, the obtained measurement signal SS has at least one valid signal S1, and each valid signal S1 represents the execution of laser welding of a group of welding objects 30. In one embodiment, the processing unit 150 receives the measurement signals SS and finds each valid signal S1 in the received measurement signals SS. In some embodiments, the processing unit 150 finds each valued signal segment of the measurement signal SS according to the occurrence time and defines it as a valid signal S1. In other words, there is a blank time interval between any two valuable signal sections (any two valid signals S1). Here, the valued signal segment refers to a signal segment of continuous time in the measurement signal SS, and this signal segment has at least one signal peak that is not zero or greater than the strength threshold. The strength threshold is a preset positive value.

The processing unit 150 converts each valid signal S1 into a frequency domain signal (step S50). In addition, the processing unit 150 determines whether there is an abnormal event according to each frequency domain signal and at least one intensity condition (step S60), that is, confirms whether each frequency domain signal satisfies at least one intensity condition. Wherein, when each frequency-domain signal satisfies all the intensity conditions, the processing unit 150 determines that there is no abnormal event when the group of welding objects performs laser welding (step S70). Conversely, when each frequency-domain signal does not satisfy any of the intensity conditions, the processing unit 150 determines that there is an abnormal event when the group of welding objects performs laser welding (step S80). In some embodiments, the abnormal event may be abnormal process parameters such as defocus, abnormal laser power, excessive material clearance, and the like.

In some embodiments, the at least one intensity condition may include a first value corresponding to a first frequency band and a second value corresponding to a second frequency band. In other words, for each frequency domain signal, the processing unit 150 compares the sound intensity of the frequency domain signal at multiple time points in the first frequency band with a first value to confirm whether the sound intensity at multiple time points in the first frequency band is Both are smaller than the first value; and the processing unit 150 compares the sound intensity of the frequency domain signal at multiple time points in the second frequency band with a second value to confirm whether the sound intensity at multiple time points in the second frequency band is Both are smaller than the second value.

When the sound intensity of this frequency domain signal at multiple time points in the first frequency band is less than the first value and the sound intensity of multiple time points in the second frequency band is less than the second value (that is, this frequency domain signal meets all intensity conditions ), The processing unit 150 determines that there is no abnormal event during the laser welding of the group of welding objects (step S70).

Conversely, when the sound intensity of this frequency domain signal at any time point in the first frequency band is greater than or equal to the first value or the sound intensity at any time point in the second frequency band is greater than or equal to the second value (that is, this frequency domain signal When any strength condition is not satisfied), the processing unit 150 determines that there is an abnormal event when the group of welding objects performs laser welding (step S80).

The first frequency band is between 3000 Hz and 5000 Hz, preferably 4000 Hz. The second frequency band is between 7000 Hz and 9000 Hz, preferably 8000 Hz. The first value is 1.9Pa. The second value is 1 Pa. In some embodiments, the first value and the second value may be determined according to a process parameter actually used.

In other embodiments, the at least one intensity condition includes a first value range corresponding to a first frequency band and a second value range corresponding to a second frequency band. In other words, for each frequency domain signal, the processing unit 150 compares the sound intensity of the frequency domain signal at multiple time points in the first frequency band with a first numerical range to confirm the sound intensity at multiple time points in the first frequency band. Whether they all fall into the first numerical range; and the processing unit 150 compares the sound intensity of the frequency domain signal at multiple time points in the second frequency band with the second numerical range to confirm the multiple time points in the second frequency band Whether or not the sound intensity falls within the second numerical range. In some embodiments, the numerical range may be a numerical range composed of an upper limit value and a lower limit value. Here, falling within the numerical range (the first numerical range or the second numerical range) means that it is less than the upper limit value and greater than the lower limit value. Not falling within the value range means greater than or equal to the upper limit or less than or equal to the lower limit.

When the sound intensity of the frequency domain signal at multiple time points in the first frequency band falls within the first numerical range and the sound intensity of multiple time points in the second frequency band falls within the second numerical range (i.e. When all the strength conditions are satisfied), the processing unit 150 determines that there is no abnormal event during the laser welding of the group of welding objects (step S70).

Conversely, when the sound intensity of this frequency domain signal at any time point in the first frequency band does not fall within the first numerical range or the sound intensity at any time point in the second frequency band does not fall within the second numerical range (that is, this frequency When the domain signal does not satisfy any of the strength conditions), the processing unit 150 determines that there is an abnormal event when the group of welding objects performs laser welding (step S80).

The first frequency band is between 3000 Hz and 5000 Hz, preferably 4000 Hz. The second frequency band is between 7000 Hz and 9000 Hz, preferably 8000 Hz. The first value range is 0.8Pa ~ 1.9Pa. The second value range is 0.2Pa ~ 1Pa. In some embodiments, the first numerical range and the second numerical range may be determined according to a process parameter actually used.

In some embodiments, the intensity conditions used for different process parameters can be achieved by performing laser welding, radio, and signal analysis on the array welding 30 with accurate process parameters in advance (the signal analysis steps are the same as those applied to subsequent laser welding processes). The signal analysis steps used in the laser welding abnormality detection method) and one by one visual inspection and destructive detection are established.

In some embodiments, referring to FIG. 1, the detection system 10 may further include a storage unit 170. The storage unit 170 is coupled to the processing unit 150 and stores the aforementioned intensity conditions (a first numerical range and a second numerical range, or a first numerical range and a second numerical value). Among them, the storage unit 170 may also be used to store software / firmware programs, data, signals, and combinations thereof used to implement a method for detecting abnormal events of laser welding or related operations.

Take standard laser welding parameters for laser welding of 1mm and 2mm aluminum alloy sheet metal parts as an example. In the standard laser welding parameters, the laser focus position falls on the upper surface of the upper sheet metal part, and the gap between the two sheet metal parts is ideally 0 mm. Here, high-power laser is used to heat / weld two aluminum alloy sheets (the thickness of the upper sheet is 1mm and the thickness of the lower sheet is 2mm), and perform laser welding During the process, the microphone is used for radio (recording) to analyze the recorded sound signal.

Referring to FIG. 5, when the laser welding parameters are normal, the sound intensity of the frequency-domain signal after the sound signal conversion is 1.15 Pa at 4000 Hz and 0.6 Pa at 8000 Hz; it can be seen that the sound intensity at the two frequency points falls into In the corresponding numerical range (the first numerical range and the second numerical range).

Referring to FIG. 6, when the laser focus position of the laser welding parameter is shifted to a position about 2 mm (absolute distance) above the upper surface of the upper sheet metal (the remaining parameters remain normal), the frequency-domain signal after the sound signal conversion is at 4000 Hz. The sound intensity is 1.9Pa and the sound intensity at 8000Hz is 1Pa. It can be seen that compared with the normal laser welding parameters, the sound intensity at the two frequency points has increased significantly and does not fall into their respective numerical ranges.

Referring to FIG. 7, when the laser focus position of the laser welding parameter is shifted to a position about 3 mm (absolute distance) above the upper surface of the upper sheet metal (the remaining parameters remain normal), the frequency domain signal after the sound signal conversion is at 4000 Hz. The sound intensity is 1.9 Pa and the sound intensity is 1.1 Pa at 8000 Hz. It can be seen that compared to the normal laser welding parameters, the sound intensity at the two frequency points has increased significantly.

Referring to FIG. 8, when the laser power in the laser welding parameters is reduced by about 30% (the remaining parameters remain normal), the frequency-domain signal after the sound signal conversion has a sound intensity of 1.9 Pa at 4000 Hz and 1.35 Pa at 8000 Hz. ; It can be seen that compared with the normal laser welding parameters, the sound intensity at the two frequency points significantly increases and does not fall into the corresponding numerical range.

Referring to FIG. 9, when the gap between two sheet metal parts in the laser welding parameters is increased by 0.4 mm (the remaining parameters remain normal), the sound intensity of the converted frequency-domain signal at the frequency of 4000 Hz is 0.8 Pa and the sound at 8000 Hz The intensity is 0.2Pa; it can be seen that compared with the normal laser welding parameters, the sound intensity at the two frequency points is significantly reduced and does not fall into the corresponding numerical range.

In some embodiments, the aforementioned processing unit may be implemented by one or more processing elements. Here, each processing element may be, for example, a microprocessor, a microcontroller, a digital signal processor, a microcomputer, a central processing unit, a field programmable gate array, a programmable logic device, a state device, a logic circuit, an analog circuit, or a digital circuit. And / or any device that operates on signals (analogs and / or digits) based on operating instructions.

In some embodiments, the aforementioned storage unit may be implemented by one or more storage elements. Here, each storage element may be, for example, a memory or a register, but it is not limited thereto.

In some embodiments, the foregoing soldering object 30 may be a battery electrode of an electric vehicle, or a fixing structure of a circuit board, but it is not limited thereto.

It should be noted that although the foregoing steps are described in sequence, this order is not a limitation of the present invention. Those skilled in the art should understand that under reasonable circumstances, the execution order of some steps can be performed simultaneously or reversed.

In summary, according to the method and system for detecting abnormal events of laser welding according to the present invention, a vibration wave sensing unit is used to sense the vibration waves generated by each group of welding objects during laser welding and analyze the vibrations. The frequency-domain signal of the wave measurement signal is used to determine whether there are abnormal events in the laser welding process, so as to immediately warn about abnormal events that occur during welding (such as out-of-focus, abnormal laser power, excessive material clearance, etc.) , And can be further corrected immediately (for example, desoldering solders with unqualified solder joints and re-soldering solders after desoldering according to the test results), thereby improving the reliability and durability of electronic products.

Claims (9)

    A method for detecting an abnormal event of laser welding includes: using a sensing unit to sense vibration waves generated during laser welding of at least one group of welding objects to obtain a measurement signal, wherein the measurement signal has at least one A valid signal, and the at least one valid signal respectively represents the execution of the laser welding of the at least one group of welding objects; converting each of the valid signals into a frequency domain signal; judging whether or not there is based on each of the frequency domain signals and at least one strength condition An abnormal event; when each of the frequency-domain signals does not satisfy any of the intensity conditions, it is determined that the group of welding objects has the abnormal event when performing the laser welding; and when each of the frequency-domain signals satisfies the at least one intensity condition, it is determined There was no such abnormal event when the laser welding of the group of welding objects.         The method for detecting an abnormal event of laser welding according to claim 1, wherein the at least one intensity condition includes a first value range corresponding to a first frequency band and a second value range corresponding to a second frequency band, and The step of determining whether the abnormal event exists according to each of the frequency domain signals and the at least one intensity condition includes: comparing the sound intensity of the frequency domain signal at a plurality of time points in the first frequency band with the first numerical range ratio to confirm that Whether the sound intensities at the time points in the first frequency band all fall within the first numerical range; and comparing the sound intensities of the frequency domain signals at the plural time points in the second frequency band with the second numerical range, It is determined whether the sound intensities at the time points in the second frequency band fall into the second numerical range.         The method for detecting an abnormal event of laser welding according to claim 2, wherein the confirmation result that the frequency domain signal satisfies the at least one intensity condition is that the sound intensities at the time points in the first frequency band all fall within Both the first numerical range and the sound intensities at the time points in the second frequency band fall into the second numerical range.         The method for detecting an abnormal event of laser welding according to claim 2, wherein the confirmation result that the frequency domain signal does not satisfy any of the intensity conditions is that the sound intensity does not fall at any of the time points in the first frequency band The sound intensity that falls into the first numerical range or the second frequency band at that point in time does not fall into the second numerical range.         The method for detecting an abnormal event of laser welding according to claim 1, wherein the at least one intensity condition includes a first value corresponding to a first frequency band and a second value corresponding to a second frequency band, and according to each The step of determining whether there is an abnormal event by the signal intensity of the frequency domain signal and the at least one intensity condition includes: comparing the sound intensity of the frequency domain signal at a plurality of time points in the first frequency band with the first value to confirm Whether the sound intensities at the time points in the first frequency band are less than the first value; and the second value ratio is used to compare the sound intensity of the frequency domain signal at a plurality of time points in the second frequency band to confirm Whether the sound intensities at the time point in the second frequency band are less than the second value.         The method for detecting an abnormal event of laser welding according to claim 5, wherein the confirmation result that the signal strength of the frequency-domain signal satisfies the at least one strength condition is the sound intensities at the time points in the first frequency band Both are less than the first value and the sound intensities at the time points in the second frequency band are less than the second value.         The method for detecting an abnormal event of laser welding according to claim 5, wherein the confirmation result that the frequency-domain signal does not satisfy any of the intensity conditions is that the sound intensity at any time point in the first frequency band is greater than or The sound intensity equal to the first value or the second frequency band at any time point is greater than or equal to the second value.         The method for detecting an abnormal event of laser welding according to claim 1, wherein the sensing unit is a microphone or an acceleration gauge.         A detection system for an abnormal event of laser welding includes: a sensing unit; a signal generating circuit coupled to the sensing unit; and the sensing unit generates at least one group of welding objects for laser welding. A vibration wave to obtain a measurement signal, wherein the measurement signal has at least one valid signal, and the at least one valid signal respectively represents the execution of the laser welding of the at least one group of welds; and a processing unit, coupled The signal generating circuit receives the measurement signal, converts each valid signal into a frequency domain signal, and determines whether there is an abnormal event according to each of the frequency domain signal and at least one strength condition; wherein, when each of the frequency domain signals does not meet any When the strength condition is met, the processing unit determines that the group of welding objects has the abnormal event when performing the laser welding; and when each of the frequency-domain signals satisfies the at least one strength condition, the processing unit determines that the group of welding objects performs the This abnormal event does not exist during laser welding.