Research On Precision Control Effect For Resistance Spot Welding Quality Using IDRC Method

Resistance spot welding is extensively used in the modern industry fields for its high productivity, high-mechanization and high-automation. It has been one of the most important mechanical processes in the automotive industry field. With the development of industrial technology, the request for the welding quality and reliability is increasing in many industry products. So that, in recent years many experts all over the world have constantly tried their best to study on the resistance spot welding quality supervise and control techniques.With the basis of the scientific research and development in recent years, we not only have put forward the IDRC cooperative control mode, but also have initially developed the new IDRC intelligent spot welding controller which has been used in teaching and research experiments. To the basis of the characteristics of resistance spot welding nucleation process, the IDRC cooperative control mode adopts the relay control strategy of separate step that is made of constant current control and DRC modeling control, finally it fundamentally canceled disadvantageous factor when constant current method or DRC method is individually adopted, embodies the merit of advantage mutual complement. However, as the current lag angel is adopted for quality control information on the DRC modeling control stage, the adjusting of the welding heat inevitably lead to the electrical noise in the quality control information in theory or practice, and lead the crisis to the accuracy of the resistance spot welding quality control. It is the crisis that the consistency of the welding quality and the welding time is very difficult to be ensured during the welding heat significant fluctuations or the serious triage.To achieve the precise control of the resistance spot welding quality, being based on the thermal linear control theory about single-phase alternating current welder, the paper sets up the twin-function to a given heat percentage of premise which can calculates the trigger control angelαn of main circuit transistors and the corresponding current lag angelψn. Then the paper designs the C language program by the dichotomy method, and establishes the twin-function table corresponding to the certain power factor angel ? and the different heat percentages mn . All of that provides the control means and the data base by the IDRC cooperative control strategy for scalping the electrical noise from adjusting the welding heat.To do the experiments effectively, the paper makes use of the ATmega168 microcontroller as the control core of the control system to design and modify the control software, which can modify the current lag angel incremental deviation and compensate the threshold. The control effect of the software has been showed by the further experiments.The results of the welding experiments show that the real-time control to the welding heat can not only lead the electrical noise, but also the relative changes of the dynamic resistance in the welding zone mental. Through the theory analysis, both of that can impact the current lag angelψn on the contrary. The difference in the numerical and the specific quantitative relationship still should be considered carefully. The better electrical noise-scalping ratio has been got by the welding contrast experiments with the different scalping ratio. Then the current lag angel incremental deviation-modifying subprogram and the threshold-compensating subprogram have been designed, so that the adaptability of the control system has been proved when the welding heat is adjusted significantly. Finally the accurate control results can be got in the nugget quality.