Study On The System Of Current And Pressure Online Monitoring For Resistance Spot Welding

Resistance spot welding is a high efficient welding method and extensively applied in many fields such as aerospace and automobile, etc. Now guarantee every welding spot is crucial to the welding quality. In order to guarantee the welding automation production works effectively and achieve the products management objective of no defective and no defect, it is necessary to develop a kind of online judging system with nondestructive and low cost.There are many process parameters in spot welding such as current, welding time, voltage, pressure, dynamic resistance, etc. It is difficult to acquire the welding pressure signal online in the spot welding process. The pressure is adjusts by air brake or hydraulic valve, which is too slow to reflect the real-time change of the pressure. However, the pressure signal is deemed to provide much more information of the nugget forming than any other parameter, and only when the current and the pressure cooperate well, the electrical contact can be guaranteed, and the plastic deformation grows well, thereby avoiding the defects such as splash. Therefore, it is meaningful to research the pressure signal of the spot welding for the real production.The paper has analyzed the present situation of domestic and foreign research on spot welding parameters monitor, and researched resistance spot welding current and pressure online monitoring system, which real time monitor spot welding technology parameters, such as welding current and welding pressure, with the function of data acquisition, data disposal, data storage, data display and alarm for the unusual. The paper analyses the advantages and characteristics of the USB data acquisition card, and select the USB-6008 from NI Corporation based on system requirements. The paper analyses the principle of the highly sensitive quartzose sensor and the superiority when it is used for acquire pressure signal, and select the highly sensitive quartzose sensor come from KISTLER Corporation with necessary electric charge amplifier.This system takes Visual C++ 2003 as the software development circumstance to design the measurement software, realizing the aim of collecting multi welding parameters and data disposal, calculating the quality information including current effective value, press value, current waveform, pressure waveform and so on, storing the result in the database. For sustaining the measurement software, the paper takes Microsoft Access 2003 as the manage system of the database, makes the data.mdb document of database, designs two data tables with Testdata and Paramer reasonably, satisfies various storage and management needs of welding quality information. The paper uses the discreteness and control parts in Visual C++ 2003 environment offered by Measurement Studio, designs the measurement software based on the technology of virtual instrument, specializes this system in terms of display and analysis of the waveforms. Except of the calculation of the current effective value,press value, current time and pressure time, in order to analyze the welding quality deeply, the system also demonstrates the pressure waveforms and the current waveforms synchronous through the use of the resources offered by measurement studio, and judges the occurrence of splash objection automatically. It offers abundant quality analysis methods of resistance spot welding widely.In order to validate the accuracy of welding parameters monitoring, the pressure value, current effective value, current time, pressure time, current waveform and pressure waveform which have been measured by the system are compared with the current tester, pressure tester and the digital oscillograph. The results show that the system can monitor parameters and demonstrate waveforms online very well. The accuracy of the parameters value and the waveform is more than 95%, and it also has good stability. This system have many advantages such as high gathering speed, high gathering efficiency, big memory capacitance and good human-computer interaction interface. It can be used in practical production as an online monitor instrument combining with producing technology, and it has high useful value and development foreground.