Research And Implementation Of The Real-Time Monitoring System For The Solder Joint Quality Of Car Body In White

Resistance spot welding is an important welding method in the automobile manufacturing process,and it is the main method for welding automobile body structures,the quality of its solder joints directly affects the body structure,safety and service life of the car,therefore,the inspection of solder joint quality becomes particularly important.At present,most automobile manufacturers mainly use the sampling method to perform destructive and non-destructive tests on the quality of automobile solder joints,the detection efficiency is low and the quality of automobile solder joints cannot be fully understood.Therefore,the development of a real-time monitoring system for the quality of automobile solder joints is extremely important for automobile production,which can not only ensure automobile quality,but also improve production efficiency.Aiming at the shortcomings of traditional resistance spot welding,such as the single welding point quality detection method,poor real-time performance,and no remote monitoring,a real-time detection method based on the fusion of the total heat value detection of the welding point and the power waveform quality detection of the welding point is proposed,this method realizes the quality inspection of automobile body-in-white solder joints.The system first uses Rogowski coils and direct measurement methods to sample the welding current and voltage through high-speed A/D during the welding process,the sampled data is sent to the FPGA for preprocessing,and the processed data is sent to the DSP through the data bus.The DSP calculates the real-time power of the solder joint based on the current and voltage values sampled in real time,and integrates the power to calculate the total heat value of the solder joint.At the same time,the leastsquares fitting algorithm is used to calculate the distortion value of the real-time power waveform relative to the standard solder joint power waveform.Finally,through comprehensive analysis of the data obtained by the two inspection methods,the quality of the solder joints is judged.At the same time,the DSP uploads the current,voltage,power,distortion value,total heat value,and judgment results of the solder joints to the computer through a wireless serial port for storage and display.First,resistance spot welding is a process in which the parts are melted by applying pressure to the electrodes to conduct welding currents,after cooling,forming solder joints is a process of heat accumulation and then cooling.Therefore,collecting the electrification parameters of resistance spot welding in the welding process can obtain the power waveform curve of the real-time welding process.However,the total heat value cannot fully reflect the quality of the solder joint.We found that the power curve can well reflect the thermal energy accumulation process of the solder joint.Therefore,a standard library of qualified welding point power waveforms is established,and the distortion power value of the tested welding point power waveform relative to the qualified welding point power waveform in the standard library is established,and combined with the total heat value of the solder joints,the quality of solder joints can be judged more comprehensively.Analyze and study the welding point power waveform,and consider that the welding point power waveform is an arbitrary waveform and a non-periodic signal.Therefore,traditional distortion detection methods cannot be used directly.We have studied and analyzed the traditional distortion and the distortion of arbitrary waveforms,based on the comparative analysis of the FFT method,the inner product method and the least squares fitting method,a least squares fitting method was proposed to detect the quality of welding power waveforms,and simulations were performed based on MATLAB.Secondly,a hardware system based on FPGA and DSP is designed.The system mainly includes signal conditioning modules,high-speed A/D and FPGA interface modules,FPGA and DSP interface modules,and wireless transmission modules.The corresponding software part of the system mainly includes three parts: preprocessing program in FPGA,data transmission and processing program in DSP,and upper computer program.Finally,through the design and production of prototypes in laboratory tests and field tests,the test results are basically consistent with the simulation data.By collecting welding current and voltage,the system realizes the detection and judgment of the quality of the welding point,which is a fusion of the total heat value of the welding point and the quality of the power waveform.The electrification parameters and test results during the test are also remotely stored and displayed.