Differential backfill friction stir spot welding decision-making method and system based on current monitoring

Abstract

The present invention provides a differential backfill stir friction spot welding decision-making method and system based on current monitoring, which belongs to the technical field of differential backfill stir friction spot welding; the method is: collecting current signals; processing and storing current signals; analyzing the stored and displayed current signals to determine whether the current amplitude is normal; analyzing the stored current signals, selecting current characteristic parameters and performing calculations to make a weld quality analysis. The decision-making system includes a current monitoring component, an acquisition module and a host computer, and the current signal of the differential backfill stir friction spot welding obtained by the current monitoring component is transmitted to the host computer through the acquisition module; the host computer is provided with a current signal processing module, a data processing module, and an alarm module. The present invention solves the defect that it is difficult to backfill due to excessive material that undergoes severe plastic deformation caused by unstable welding pressure, torque and temperature during the welding process, and the problem that the quality of the weld cannot be identified because the differential spot welding process is completed in an invisible plastic ring.

Description

Technical Field

[0001] The present invention belongs to the technical field of differential backfill friction stir spot welding, and in particular relates to a differential backfill friction stir spot welding decision-making method and system based on current monitoring. Background Art

[0002] As a new solid-phase joining technology, the differential backfill friction stir spot welding process is mainly divided into four steps. Figure 1 Steps (a) to (d): (1) First, the clamping ring contacts the surface of the upper plate to fix the plate to be welded, and the sleeve and the stirring needle begin to rotate in the same or opposite directions, generating friction with the material to be welded, causing the material to enter a plastic state; (2) While maintaining the rotational motion, the sleeve moves downward and the stirring needle moves upward, at which time the plastic metal is squeezed into the cavity generated by the relative movement of the stirring needle and the sleeve; (3) When the downward pressure reaches a preset distance, the sleeve begins to move upward and the stirring needle moves downward, causing the material to flow into the cavity formed by the downward pressure of the sleeve; (4) When the sleeve and the stirring needle return to the upper surface of the specimen, in order to obtain a weld with a smooth and clean surface, the two still need to stay on the weld surface and rotate for a certain period of time.

[0003] Backfill spot welding technology fully backfills the weld without the exit holes produced by traditional friction stir spot welding processes, improving the mechanical properties of welded joints. Current research shows that backfill spot welding significantly outperforms resistance spot welding in joint strength. However, in existing differential backfill spot welding techniques, inappropriate process parameters can easily lead to internal defects such as holes and weak connections, as well as surface defects such as annular grooves and cracks. This can cause unstable weld quality, which manifests macroscopically as large fluctuations in weld shear resistance and varying fracture patterns in joints under the same parameters. To meet the safety and reliability requirements of structural components in fields such as aerospace, it is necessary to monitor the welding process and establish a decision-making system for evaluating weld quality. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a differential backfill stir friction spot welding decision-making method and system based on current monitoring. Based on the current value collection of the AC friction spot welding machine, the current amplitude is observed to achieve the purpose of abnormal warning of welding parameters and recording the number of welds and preventing leaking welds; through the calculation of current characteristic parameters (current average value, variance, standard deviation, coefficient of variation, current frequency, etc.), the weld quality analysis, monitoring and evaluation are further realized, which helps to improve the stability of the differential spot welding process and obtain good welding joint performance. The present invention solves the defect of excessive material undergoing severe plastic deformation and being difficult to backfill due to unstable welding pressure, torque and temperature during the welding process, and at the same time solves the problem of being unable to identify the quality of the welds because the differential spot welding process is completed in an invisible plastic ring.

[0005] The technical solution of the present invention is: a differential backfill stir friction spot welding decision method based on current monitoring, the specific steps are as follows:

[0006] Step 1. Arrange the current monitoring components and collect current signals;

[0007] The current monitoring component converts the monitored current information of the differential backfill friction stir spot welding into a current signal and transmits it to the host computer through the acquisition module;

[0008] Step 2. Processing and storing the current signal;

[0009] After filtering the current signal of the acquisition module, storing and displaying it;

[0010] Step 3. Analyze the stored and displayed current signal to determine whether the current amplitude is normal;

[0011] Step 4. Analyze the stored current signal, select current characteristic parameters and perform calculations to make solder joint quality analysis.

[0012] A further technical solution of the present invention is: in step 1, the current monitoring component is a current sensor installed on the welding machine, and the acquisition module is a data acquisition card installed on the welding machine, which collects current information during the welding process in real time.

[0013] A further technical solution of the present invention is: in step 2, the acquisition module obtains an ideal waveform through filter processing, which is then displayed on the screen of the host computer through the data display module and stored in the data storage unit at the same time.

[0014] A further technical solution of the present invention is: in step 3, the amplitude of the current signal waveform on the display screen is analyzed and compared with the normal current signal waveform to determine whether it is normal; the abnormal range includes two situations as follows:

[0015] When the displayed amplitude is smaller than the normal welding amplitude, it indicates that the weldment is prone to detachment at the weld point. When the displayed amplitude is larger than the normal welding amplitude, it indicates that the welding pressure, torque and temperature at the corresponding moment are too large. At the same time, the current is too large, which affects the bottom joint diameter of the weldment and affects the product quality.

[0016] A further technical solution of the present invention is: in step 3, an alarm unit is used to prompt abnormal situations, and a warning value alarm subroutine is set in the alarm unit. When the amplitude exceeds the warning value, it indicates that the welding does not meet the requirements and an alarm prompt is issued in time.

[0017] A further technical solution of the present invention is: in step 4, the current characteristic parameters include the average value, mean square value, standard deviation, coefficient of variation, and current frequency of the current peak value, and the calculation formula is as follows:

[0018] Average value of current peak value

[0019]

[0020] Where x i is the i-th number in the current peak data; n is the total number of current peak data;

[0021] The mean square error of the current peak value is X:

[0022]

[0023] Standard deviation s of current peak value:

[0024]

[0025] Coefficient of variation v of current peak value:

[0026]

[0027] Therefore, the average value of the current peak is used to compare the actual values ​​of welding pressure, torque, and temperature with the power setting value; the standard deviation of the current peak is used to indicate the distribution of the real-time pressure value, torque value, and temperature value of welding around the average value, thereby reflecting the stability of the welding process; the coefficient of variation is used to reflect the stability of the welding process.

[0028] A differential backfill stir friction spot welding decision system based on current monitoring includes a current monitoring component, an acquisition module and a host computer. The acquisition module transmits the current signal of the differential backfill stir friction spot welding obtained by the current monitoring component to the host computer.

[0029] The host computer is provided with a current signal processing module, a data processing module, and an alarm module; in the current signal processing module, the signal acquisition unit receives the current signal of the acquisition module, and after the signal is filtered by the signal filtering unit, it is displayed by the data display unit; in the data processing module, the data signal is judged, stored and searched respectively, and the alarm module issues an alarm prompt for abnormal data.

[0030] A further technical solution of the present invention is: the host computer is a control system of the welding machine, including a processor, a memory and an application, wherein the application is stored in the memory and is configured to be executed by the processor, and the application is configured to execute the differential backfill stir friction spot welding decision method based on current monitoring.

[0031] A further technical solution of the present invention is: the alarm module includes a welding point number alarm subroutine and a warning value alarm subroutine; the welding point number alarm subroutine contains a counter function, and the counter automatically increases by one after each welding operation of the friction spot welder. When all welding friction points of a workpiece are welded, the proximity switch on the pneumatic clamp used to fix the workpiece will give the system an end signal, which indicates that the welding work of a welded part is completed. After that, the program automatically determines whether the number of all welding points on it is greater than or equal to the preset number of welding points; the warning value alarm subroutine determines whether it is normal through the current amplitude after the welding is completed.

[0032] A further technical solution of the present invention is: the host computer adopts Huichuan MTC industrial computer, the acquisition module is Zhongtai Lianchuang EM9636 network data acquisition module, and the current monitoring component is a current sensor.

[0033] Beneficial effects

[0034] The beneficial effects of the present invention are:

[0035] (1) The decision-making system established by the present invention collects the current value of the backfill type stir friction spot welding machine, and judges whether it is within the normal range by observing the current amplitude. When the current amplitude is abnormal during welding, an alarm is issued through the alarm module to remind the operator that there may be welding problems at the current welding point, thereby simply eliminating welded products with quality problems and making a preliminary check on the welding quality. While improving production work efficiency, it also improves welding quality; achieving the purpose of warning abnormal welding parameters, recording the number of weld points, and preventing leaking welds;

[0036] (2) When welding, the current data will be saved in real time on the welding machine host, and then the current characteristic parameters will be calculated as the basis for the quality analysis of the weld. Taking the current frequency as an example, the real-time monitored signal is filtered and its waveform is transformed by FFT (Fast Fourier Transform) to obtain the frequency domain signal of the current waveform. Then the frequency corresponding to the peak value in the frequency domain signal is calculated. This frequency is the true frequency value of the signal. Figure 1 By putting it into the main interface of the program, you can observe the waveform of the signal in real time and the frequency value of the current at the same time. Comparing it with the known operating frequency of the welding machine of 50Hz can reflect whether it meets the frequency requirements. It can also be seen whether the filtering effect is ideal and whether there are other interference sources on site.

[0037] (3) The current average value, variance, standard deviation and coefficient of variation are used for calculation, which is simple to calculate and easy to process. The processed current characteristic parameter values ​​have certain physical meanings and can reflect some characteristics of welding pressure, torque and temperature. Since the spot welding head is not necessarily the parameter value initially set during welding, the average value of the amplitude can be used to compare the actual value of welding pressure, torque and temperature with the power setting value; the standard deviation can be used to indicate the distribution of the real-time pressure value, torque value and temperature value of welding around the average value, so the stability of the welding process can be reflected by the value of the standard deviation; the coefficient of variation can also reflect the stability of the welding process. When the coefficient of variation becomes smaller, the stability is better. Because this system is mainly used to monitor AC friction welding machines, the current data presents a waveform similar to a sine distortion waveform, and the peak point is more meaningful for reference. Therefore, the parameter calculation is performed on the peak point of the weld, and the data of the negative half cycle is taken as its absolute value. Through the calculation of current characteristic parameters (current average value, variance, standard deviation, coefficient of variation, current frequency, etc.), the quality analysis and monitoring of the weld is further realized. The stable operation of the differential spot welding process is achieved, and good welding joint performance is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the differential backfill friction stir spot welding connection process in the prior art;

[0039] Figure 2 This is a block diagram of a differential backfill friction stir spot welding decision system based on current monitoring according to the present invention;

[0040] Figure 3 This is a flow chart of a differential backfill friction stir spot welding decision system based on current monitoring of the present invention;

[0041] Figure 4 It is a block diagram for monitoring and analyzing spot welding current information in the present invention;

[0042] Figure 5 This is a block diagram of the measurement system established based on the EM9636 data acquisition module of the present invention;

[0043] Figure 6 This is a diagram showing the location and function of the signal terminal board of the ADAM-3968 terminal board of the present invention;

[0044] Figure 7 This is the application principle diagram of the voltage stabilizing chip LM2576 of the present invention;

[0045] Figure 8 This is a schematic diagram of an oscilloscope monitoring screen of a differential backfill friction stir spot welding decision system based on current monitoring of the present invention;

[0046] Figure 9This is a schematic diagram of the main interface of a differential backfill friction stir spot welding decision system based on current monitoring of the present invention;

[0047] Figure 10 This is a waveform diagram of a fitting curve of a differential backfill friction stir spot welding decision system based on current monitoring according to the present invention;

[0048] Figure 11 It is a waveform diagram displayed on the main interface of a differential backfill stir friction spot welding decision system based on current monitoring of the present invention;

[0049] Figure 12 The present invention is a differential backfill stir friction spot welding decision system based on current monitoring. Experiment 3 collects welding current waveform and spectrum;

[0050] Figure 13 The present invention is a differential backfill stir friction spot welding decision system based on current monitoring. Experiment 4 collects welding current waveform and spectrum. DETAILED DESCRIPTION

[0051] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0052] The decision-making system involved in the present invention collects current values ​​of AC friction spot welding machines and achieves the purpose of warning abnormal welding parameters, recording the number of welds, and preventing leaking welds by observing the current amplitude; and further realizes weld quality analysis and monitoring by calculating current characteristic parameters (current average value, variance, standard deviation, coefficient of variation, current frequency, etc.).

[0053] Reference Figure 2 As shown, this embodiment provides a differential backfill stir friction spot welding decision system based on current monitoring, including a current sensor, a data acquisition card and an industrial computer. The current signal of the differential backfill stir friction spot welding obtained by the current sensor is transmitted to the industrial computer through the data acquisition card; the decision system flow chart is shown in FIG. Figure 3 shown.

[0054] Reference Figure 4 As shown, the industrial computer is modularly designed and specifically divided into a current signal processing module, a data processing module, and an alarm module. In the current signal processing module, the signal acquisition unit receives the current signal from the acquisition module, which is filtered by the signal filtering unit and then displayed by the data display unit. The data processing module judges, stores, and searches the data signal, and the alarm module issues an alarm for abnormal data.

[0055] The decision-making system of this embodiment uses a current sensor, a Zhongtai Lianchuang EM9636 network data acquisition module, and monitoring and analysis software built on an Inovance MTC industrial computer using a C++ development environment.

[0056] (1) Data acquisition module

[0057] The EM9636 data acquisition card features advanced circuit design, enabling it to offer expanded functionality and high quality assurance. It includes five of the most commonly used detection and control functions: 16 single-ended or 8 differential analog inputs, a 12-bit A / D converter (with a sampling rate up to 100 kHz), two 12-bit analog outputs, 16 digital inputs, 16 digital outputs, and counter / timer functions.

[0058] Reference Figure 5 As shown in the figure, the measurement system block diagram is built based on the EM9636 data acquisition card. The data acquisition card works in conjunction with the terminal board. The terminal board model is ADAM-3968. The signal terminal positions and functions of the ADAM-3968 terminal board are as follows: Figure 6 shown.

[0059] (2) Digital acquisition power supply circuit

[0060] Taking into account interference issues in industrial environments, the power supply system is divided into two parts: the main power supply system and the sub-power supply system. The main power supply system mainly provides a unified power supply for communications and various sub-modules; the sub-power supply system mainly converts the power provided by the main power supply system into the power required by each sub-module.

[0061] The voltage regulator chip of the main power supply module uses LM2576HV-ADJ, with input voltage Vin=7V~60V and adjustable output voltage Vout=1.23V~57V. The output voltage drop is 2~3V. The output current can reach 3A. The operating temperature is -40℃~125℃. Its biggest feature is its high working efficiency, which can reach more than 80%. This solves the problem of heating of the chip without a heat sink when the input voltage is much higher than the output voltage and the output current is also large. Under the condition of outputting 3A, its typical output ripple is less than 50mV. The typical application circuit of LM2576 is as follows Figure 7 shown.

[0062] (3) Digital processing and communication networks

[0063] Industrial environments are subject to significant spatial interference. To avoid this interference, based on the transmission characteristics of analog and digital signals, the transmission distance of analog signals is minimized, while the transmission distance of digital signals can be appropriately extended. Therefore, in hardware design, analog signals are converted to digital signals on-site and then transmitted over a longer serial bus network to digital processing equipment. This increases the signal's resistance to interference during transmission. Simultaneously, implementing necessary anti-interference processing in software and developing appropriate transmission protocols can minimize the probability of transmission errors.

[0064] (4) The filtering unit is located in the current signal processing module, and uses the filter function calling method to call the Chebyshev digital filter provided in the software.

[0065] (5) Monitoring and analysis of welding process parameters of spot welding current information

[0066] Use Lab VIEW 2014 programming to establish the current information detection and analysis module, which is specifically divided into current signal processing module, data processing module, and alarm module. Figure 4 shown.

[0067] (a) The signal acquisition unit in the current signal processing module is used to obtain the circuit signal from the data acquisition card. LabVIEW 2014 software is connected to the data acquisition card through a dynamic link library. The acquisition card processes the ideal waveform through a filter and then displays it on the screen through the data display module.

[0068] Install the DAQNavi Driver for the data acquisition card, establish an acquisition channel, create a channel, and add it to the current task. Select the required I / O type and corresponding signal type for this system in the DAQNavi Create Channel polymorphic VI. As shown in the figure, select Analog Input-Voltage for analog voltage input with a value of + / -5V.

[0069] (b) The data processing module can record the collected current data in real time, and can also measure the characteristic parameters of the waveform through the program to determine whether the welding parameters meet the requirements; the report generation tool provided by C++ is selected as the storage module to save the collected current values. After saving, the data can be retrieved for subsequent processing and analysis.

[0070] (c) The alarm module is a response module to the data processing module, and can promptly issue an alarm prompt when welding does not meet the requirements. The alarm module includes a welding point count alarm subroutine and a warning value alarm subroutine. The welding point count alarm subroutine contains a counter function, which automatically increases by one after each welding operation of the friction spot welder. When all welding points of a workpiece are welded, the proximity switch on the pneumatic clamp used to fix the workpiece will send an end signal to the system, marking the completion of the welding work of the welded part. The program then automatically determines whether the total number of welding points on the welded part is greater than or equal to the preset number of welding points. The warning value alarm subroutine determines whether the welding is normal by measuring the current amplitude after the welding is completed.

[0071] As the welding process explains, differential backfill spot welding involves multiple nonlinear factors, making quality control challenging. Unstable welding pressure, torque, and temperature can lead to excessive material undergoing severe plastic deformation, making backfill difficult. Furthermore, because differential spot welding occurs within an invisible plastic ring, weld quality cannot be determined. This makes online monitoring of differential spot welding data extremely challenging.

[0072] Process parameters (rotational speed, pressing depth, etc.) are closely related to the quality of differential spot welding. Different process parameters lead to changes in welding pressure, torque and temperature. These changes will be reflected in the fluctuation of current. Therefore, the current data of the welding process is collected and analyzed to determine the quality of the current weld in real time.

[0073] In summary, the key to the decision-making system is to ensure the accuracy, efficiency and real-time nature of current data acquisition. Using an industrial computer as the platform, through rational system hardware design and material selection, high-speed and high-precision signal acquisition is achieved, constructing a hardware platform for process parameter detection throughout the system. Based on a C++ and acquisition dynamic link library software platform, a highly adaptable user interface with a database access window and waveform display is established. This allows for rapid, accurate, and simultaneous data optimization during data acquisition. The time and frequency of each acquired data set are also recorded simultaneously. Finally, all data is saved, and based on the characteristics of current parameters during differential spot welding and actual production conditions, an alarm and early warning module are designed to monitor weld status in real time and prevent leaks, cold welds, and abnormal welding parameters. By calculating current characteristic parameters, not only can the stability (coefficient of variation) and filtering effect (current frequency) of the welding process be monitored, but also, through quality analysis of corresponding batches of welds, a relationship can be established between welding process parameters—pressure, torque, and temperature—current characteristic parameters—and weld quality, serving as a reference indicator for optimizing welding process parameters.

[0074] Reference Figure 3As shown, the steps of a differential backfill stir friction spot welding decision-making method based on current monitoring in this embodiment are as follows:

[0075] Step 1: Arrange current monitoring components and collect current signals;

[0076] The current sensor is installed on the welding machine, and the current information of the differential backfill friction stir spot welding is converted into a current signal through the current sensor, and then transmitted to the industrial computer through the acquisition module;

[0077] Step 2: Process and store the current signal;

[0078] After filtering the current signal of the acquisition module, an ideal waveform is obtained, which is then displayed on the screen of the industrial computer through the data display module and stored in the data storage unit at the same time.

[0079] Step 3: Analyze the stored and displayed current signal to determine whether the current amplitude is normal;

[0080] During actual welding operations, the amplitude of the filtered current signal waveform will stabilize within a certain normal range. Figure 8 As shown. When it is not within the normal range, two situations will occur: when the amplitude is too low, the two welds appear to be welded together, but after loading too little external force, the two welds are prone to detachment at the weld point, seriously affecting the welding quality of the weld; when the amplitude suddenly exceeds the normal welding amplitude floating range, it indicates that the welding pressure, torque and temperature at the corresponding moment are too large. Excessive current has a direct impact on the size of the joint diameter at the bottom of the weld, and the quality of the joint at the bottom of the weld has a serious impact on product quality. Therefore, for these two abnormal current amplitude phenomena during welding, we should promptly discover and issue an alarm to remind the operator that there may be a welding problem at the current welding point, so as to simply exclude welded products with quality problems and conduct a preliminary investigation for welding quality, thereby improving production efficiency while also improving welding quality.

[0081] Step 4: Analyze the stored current signal, select the current characteristic parameters and calculate them to make a solder joint quality analysis.

[0082] When welding, the current data will be saved in real time on the welding machine host, and then the current characteristic parameters will be calculated as the basis for the quality analysis of the weld. Taking the current frequency as an example, the real-time monitored signal is filtered and its waveform is transformed by FFT (Fast Fourier Transform) to obtain the frequency domain signal of the current waveform. Then the frequency corresponding to the peak value in the frequency domain signal is calculated, and this frequency is the true frequency value of the signal. Figure 1By putting it into the main interface of the program, you can observe the waveform of the signal in real time and the frequency value of the current at the same time. Comparing it with the known operating frequency of the welding machine of 50Hz can reflect whether it meets the frequency requirements. It can also be seen whether the filtering effect is ideal and whether there are other interference sources on site.

[0083] Specifically, the current's mean, variance, standard deviation, and coefficient of variation can be used for calculations. These parameters can all be expressed in physical units, making calculations simple and processing convenient. The processed current characteristic parameter values ​​have certain physical meanings and can reflect some characteristics of welding pressure, torque, and temperature. Since the spot welding head does not necessarily use the initially set parameter values ​​during welding, the amplitude mean can be used to compare the actual values ​​of welding pressure, torque, and temperature with the power supply setting values. The standard deviation can be used to indicate how the real-time pressure, torque, and temperature values ​​of the weld are distributed around the mean value, so the stability of the welding process can be reflected by the standard deviation value. The coefficient of variation can also reflect the stability of the welding process; the smaller the coefficient of variation, the better the stability. Because this system is primarily used to monitor AC friction welding machines, the current data presents a waveform similar to a sine-distorted waveform, and the peak point is more meaningful for reference. Therefore, the following parameter calculations are performed on the peak point of the weld, and the data in the negative half cycle is taken as its absolute value.

[0084] (1) Average value

[0085] By integrating and averaging the peak points of the collected current data, we can see the central trend of the current amplitude change, which is expressed as follows:

[0086]

[0087] Where, is the average value of the current peak; x i is the i-th number in the current peak data; n is the total number of current peak data.

[0088] (2) Mean square value

[0089] The square of the peak value of the collected current data is integrated and averaged to reflect the average situation of the current peak change. The expression is as follows:

[0090]

[0091] Where, X is the mean square error of the current peak; x i is the i-th number in the current peak data; n is the total number of current peak data.

[0092] (3) Standard deviation

[0093] The mean square value of the collected current data is obtained by subtracting the mean from the peak value. It can reflect the degree of dispersion by comparing the current amplitude with the mean value. The expression is as follows:

[0094]

[0095] Where s is the standard deviation of the current peak; is the average value of the current peak; xi is the i-th number in the current peak data; n is the total number of current peak data.

[0096] (4) Coefficient of variation

[0097] It indicates the degree of dispersion of the current peak value compared to the average value of the current peak value. It is the ratio of the standard deviation of the current peak value to the average value of the current peak value. The expression is as follows:

[0098]

[0099] The calculations and processing of the above current peak parameters can serve as a basis for judging welding quality, identifying patterns, identifying deficiencies, and implementing improvement measures to improve welding quality. By definition, the coefficient of variation (CV) is the deviation of the current peak from its average value, minimizing the influence of the dimension on the deviation from the average value. Therefore, based on the calculations of the above current parameters, the CV has a strong practical application in judging welding quality.

[0100] In addition, the current frequency value can be monitored to see if the current condition is normal. Through previous observations, it is known that the waveform of the AC friction spot welder during welding is a distorted sine-like waveform signal. It is known that the spectrum components of the theoretical sine waveform are very pure. Taking advantage of this characteristic of the sine wave, a spectrum analysis subroutine is added to this process parameter detection and analysis system to monitor welding interference through frequency, thereby further achieving the goal of improving the welding quality of the spot welding head.

[0101] Example:

[0102] The decision-making system established in this embodiment collects current values ​​of the AC friction spot welder and achieves the purpose of warning abnormal welding parameters, recording the number of welds, and preventing leaked welds by observing the current amplitude; and further realizes weld quality analysis and monitoring by calculating current characteristic parameters (current average value, variance, standard deviation, coefficient of variation, current frequency, etc.).

[0103] Before starting welding, click the "Parameter Setting" button first, and the parameter setting window will appear. Fill in the necessary parameters, including operator number, product number, etc.

[0104] This system is used to monitor the current and conduct simple quality analysis on the friction spot welding machine, such as Figure 9The following figure shows the main interface for current monitoring. Below the main interface are some buttons for basic function settings and two function indicator lights. When entering the standby state, just click to start acquisition.

[0105] Above the main interface are two waveform display windows: the current waveform and the corresponding current waveform spectrum. During operation, both windows display only the current waveform for the current point, and the horizontal and vertical coordinates of the windows automatically adjust as the amplitude and time of the current waveform change. The current value of the next point will be displayed on the top after refreshing. This design has the advantage of providing one point-by-one data, making observation more intuitive.

[0106] When an alarm occurs, the corresponding green warning light will turn red to remind the operator that there is a welding problem. The alarm light will not turn back to the normal green status indicator until the operator clicks the corresponding "Clear" button below the indicator light, waiting for the next welding to begin.

[0107] When welding, the current data will be saved in real time on the industrial computer, and then the current characteristic parameters will be calculated as the basis for the quality analysis of the weld. Taking the current frequency as an example, it can reflect whether there is an interference source on site, and also whether the filtering effect is ideal; after the real-time monitored signal is filtered, its waveform is transformed by FFT (Fast Fourier Transform), and the frequency domain signal of the current waveform is obtained. Then the frequency corresponding to the peak value in the frequency domain signal is calculated, and this frequency is the true frequency value of the signal. Figure 1 By inserting it into the main interface of the program, you can observe the waveform of the signal in real time and also the frequency value of the current. Comparing it with the known working frequency of the welding machine of 50Hz can reflect whether it meets the frequency requirements, and also whether the filtering effect is ideal and whether there are other interference sources on site. Actual experimental operation test is carried out, and the results are as follows Figure 11 As shown, the corresponding signal peak is approximately 7000A on the y-axis, and the x-axis corresponding to 7000A is the frequency value of this signal. Experiments have proven that the current waveform spectrum displayed in the current monitoring and analysis system interface updates rapidly in real time, plays a significant role in monitoring welding quality, and promotes improved welding quality.

[0108] The real-time frequency is displayed on the main interface of the actual system operation, and the average amplitude can be used to compare the deviation between the actual value and the power setting value. The standard deviation and coefficient of variation can reflect the stability of the welding process. These characteristic parameters do not need to be monitored in real time. Generally, after welding a batch of products, the data is called from the pre-set storage location, and the data is searched, analyzed and the characteristic parameters are calculated through EXCEL on the industrial computer to study the welding quality and optimize the welding parameters.

[0109] The decision-making system and method of this embodiment were used to conduct actual experimental operation tests, and the collection experiment was as follows:

[0110] Experiment 1: Welding pressure, torque, and temperature correspond to a welding current of 7.5KA, an electrode pressure of 2.5KN, and a welding time of 13 cycles. The acquisition frequency of the data acquisition card is set to 1kHz, meaning the device scans once every 1 millisecond. The data from one welding point of the on-site current data is taken out separately, and approximately 260 data points are collected. The collected current data is processed using Excel software for curve fitting, and the following is obtained: Figure 10 The welding pressure, torque and temperature values ​​at this point are shown in the real-time waveform in the current waveform diagram on the main interface. Figure 11 shown.

[0111] Experiment 2: Welding pressure, torque, and temperature for a welding current of 7.5kA, an electrode pressure of 2.5kN, and a welding time of 13 cycles. The data acquisition card's acquisition frequency was set to 10kHz, meaning the device scanned once every 0.1 milliseconds, resulting in approximately 2600 scans, a rate 10 times faster than at 1kHz.

[0112] Experiment 3: Welding pressure, torque and temperature correspond to welding current of 7.5KA, electrode pressure of 2.5KN, welding time is set to 13 cycles. The acquisition frequency is set to 100KHz, and the data acquisition card scans about 26,000 times. Figure 12 The welding shown is the corresponding current waveform spectrum in the system main interface.

[0113] Experiment 4: Welding pressure, torque and temperature correspond to welding current of 7.5KA, electrode pressure of 2.5KN, welding time of 8 cycles, acquisition frequency of 100KHz, and data acquisition card scanning of about 16,000 times. Figure 13 The welding shown is the current waveform diagram of the experiment and the corresponding current waveform spectrum diagram.

[0114] From the above schemes, it can be seen that when the current acquisition frequency increases, the more dense the collected data, the more complete the waveform display, and the more it can show the true situation of welding pressure, torque and temperature. When the acquisition frequency of the data acquisition card is set to 100kHz, the zero area of ​​the welding current of the AC friction spot welder can be acquired, while the 1kHz and 10kHz acquisition frequencies cause the acquired current waveform to have varying degrees of defects; in the two groups of experiments with different welding frequencies, the welding current waveform diagrams are the same as the current waveform observed by the DF4320A oscilloscope; because the current waveform spectrum will change in real time with the welding pressure, torque and temperature, the experiment found that the higher the acquisition frequency of the data acquisition card, the closer the corresponding spectrum will be to the left of the horizontal axis, which means that the interference components analyzed during acquisition are more detailed and the horizontal axis occupied by the spectrum is narrower, that is, the current peak value after filtering is uniform and the current frequency value is around 50Hz.

[0115] Therefore, different current acquisition schemes can be selected for different monitoring purposes: For monitoring the number of welds, preventing leaks, and simply judging welding quality, as well as recording and storing approximate current data, a data acquisition card acquisition frequency of 1kHz is sufficient. For current monitoring, with analysis of current characteristic parameters as the primary purpose, and the ability to store large amounts of complete current data as the basis for characteristic parameter calculations, the data acquisition frequency should be set to at least 100kHz, or even higher. In this case, due to the large amount of data, it is necessary to frequently transfer and back up the saved data.

[0116] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A differential backfill stir friction spot welding decision method based on current monitoring, characterized in that The specific steps are as follows: Step 1: Arrange current monitoring components and collect current signals; The current monitoring component converts the monitored current information of the differential backfill friction stir spot welding into a current signal and transmits it to the host computer through the acquisition module; Step 2: Process and store the current signal; After filtering the current signal of the acquisition module, storing and displaying it; Step 3: Analyze the stored and displayed current signal to determine whether the current amplitude is normal; Step 4: Analyze the stored current signal, select the current characteristic parameters and calculate them to make solder joint quality analysis; In step 4, the current characteristic parameters include the average value, mean square value, standard deviation, coefficient of variation, and current frequency of the current peak value, and the calculation formula is as follows: Average value of current peak value : （1） Where, is the i-th number in the current peak data; n is the total number of current peak data; The mean square error of the current peak value is X: （2） Standard deviation s of current peak value: （3） Coefficient of variation v of current peak value: （4） Therefore, the average value of the current peak is used to compare the actual values ​​of welding pressure, torque, and temperature with the power setting value; the standard deviation of the current peak is used to indicate the distribution of the real-time pressure value, torque value, and temperature value of welding around the average value, thereby reflecting the stability of the welding process; the coefficient of variation is used to reflect the stability of the welding process.

2. The differential backfill friction stir spot welding decision-making method based on current monitoring according to claim 1, characterized in that: In step 1, the current monitoring component is a current sensor installed on the welding machine, and the acquisition module is a data acquisition card installed on the welding machine, which collects current information during the welding process in real time.

3. The differential backfill friction stir spot welding decision-making method based on current monitoring according to claim 1, characterized in that: In step 2, the acquisition module obtains the ideal waveform through filter processing, and then displays it on the screen of the host computer through the data display module and stores it in the data storage unit at the same time.

4. The differential backfill friction stir spot welding decision-making method based on current monitoring according to claim 1, characterized in that: In step 3, the amplitude of the displayed current signal waveform is analyzed and compared with the normal current signal waveform to determine whether it is normal; the abnormal range includes two situations as follows: When the displayed amplitude is smaller than the normal welding amplitude, it indicates that the weldment is prone to detachment at the weld point. When the displayed amplitude is larger than the normal welding amplitude, it indicates that the welding pressure, torque and temperature at the corresponding moment are too large. At the same time, the current is too large, which affects the bottom joint diameter of the weldment and affects the product quality.

5. The differential backfill friction stir spot welding decision-making method based on current monitoring according to claim 4, characterized in that: In step 3, an alarm unit is used to prompt abnormal situations, and a warning value alarm subroutine is set in the alarm unit. When the amplitude exceeds the warning value, it means that the welding does not meet the requirements and an alarm prompt is issued in time.

6. A system for implementing the current monitoring-based differential backfill friction stir spot welding decision-making method according to any one of claims 1 to 5, characterized in that: The system comprises a current monitoring component, an acquisition module and a host computer, wherein the current signal of the differential backfill stir friction spot welding obtained by the current monitoring component is transmitted to the host computer through the acquisition module; The host computer is provided with a current signal processing module, a data processing module, and an alarm module; in the current signal processing module, the signal acquisition unit receives the current signal of the acquisition module, and after the signal is filtered by the signal filtering unit, it is displayed by the data display unit; in the data processing module, the data signal is judged, stored and searched respectively, and the alarm module issues an alarm prompt for abnormal data.

7. The implementation system according to claim 6, characterized in that: The host computer is a control system of the welding machine, including a processor, a memory and an application, wherein the application is stored in the memory and is configured to be executed by the processor, and the application is configured to execute the differential backfill stir friction spot welding decision method based on current monitoring as described in any one of claims 1-5.

8. The implementation system according to claim 6, characterized in that: The alarm module includes a welding point count alarm subroutine and a warning value alarm subroutine; the welding point count alarm subroutine contains a counter function, and the counter automatically increases by one each time the friction spot welder operates a welding operation. When all welding friction points of a workpiece are welded, the proximity switch on the pneumatic clamp used to fix the workpiece will give the system an end signal, which indicates that the welding work of a welded part is completed. After that, the program automatically determines whether the number of all welding points on it is greater than or equal to the preset number of welding points; the warning value alarm subroutine determines whether it is normal through the current amplitude after the welding is completed.

9. The implementation system according to claim 6, characterized in that: The host computer uses Huichuan MTC industrial computer, the acquisition module is Zhongtai Lianchuang EM9636 network data acquisition module, and the current monitoring component is a current sensor.

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