The Application Of The IDRC Control Method In Stainless Steel

Resistance spot welding has been widely used in manufacturing industries, such as aviation, aerospace and automotive. It is an efficient method of welding with concentrated energy, small deformation, less auxiliary processes, no filling materials, easy operating and so on. However, there are kinds of random disturbances in the industrial Field, and these disturbances make the welding process unstable. By now, the quality-consistency of the spot welding joints is still difficult to ensure. At present, there are still many difficulties in controlling the quality of resistance spot welding, such as the size and the strength of the nugget could not be measured directly. Some monitor methods that utilize some single process parameter or information are limited in some conditions. Therefore, improving the accuracy of quality controlling will be an effective way to develop multi-information and multi-parameter monitoring integrated.The stainless steel has been used without any surface treatments, for its beautiful surface and excellent corrosion resistance. Nowadays, the stainless steel are not only used in the aircraft manufacturing, but also widely used in the railway vehicle manufacturing in the industrial production. Therefore, how to improve the quality of spot welding joints of the stainless steel and develop the process control methods become particularly important.In recent years, the DRC control method has been put forward based on the relationship between the dynamic resistance and the nugget. But this method is limited to the metal material which has a significant peak of the dynamic resistance by now, such as mild carbon steel. The dynamic resistance curve of the stainless steel is negative characteristic monotonously, that means it does not exist a significant peak on the curve of the dynamic resistance because of its specific conductance and thermal conductivity. So it makes certain difficulties to monitor it by DRC.In order to get rid of the traditional idea that the materials which can be weld using the monitor method of DRC must have a significant peak of the dynamic resistance, the resistance spot welding process has been divided into two courses simply, in-nucleation and nucleation, on the base of the point of the nugget starting time which is found by physical experiments. The characteristics of dynamic resistance of the prime nugget including nugget starting point and the threshold have been determined through scientific experiments. Then, by analyzing the physical connotation of the dynamic resistance of stainless steel deeply, the IDRC control method is used successfully, using fuzzy control to create mechanism of equivalent heating. Thereby, the control effect of the stainless steel can be as good as the mild carbon steel.In the paper, the current signal has been sampled in the secondary circuit. And after appropriate treatments, the signal has been used in detecting the welding current information and the point of the zero-crossing. The rogowski coil and the interface circuit have been designed as a real-time sample system of the welding current. The rogowski is a sensor that widely used in measuring the current. It has a large range of the measurement, high precision. Besides stability and reliability, it has a lot of merits such as small size, light weight, security, wide response frequency and so on. The current signal is sampled on the secondary side of the welding transformer by the rogowski coil. After scaling the signal for one time, the signal will not to be amended for a second-time while the power series of the welder changed.The synergistic control theory of IDRC and the fuzzy control have been quoted in the paper. By researching the fuzzy domain and the control rules that suit for the stainless steel, the splashing that caused by wide-range fluctuation of the welding heat has been avoided effectively.The results show that: Despite the dynamic information of the stainless steel is monotonous, the IDRC control method can also be used in the spot welding process for real-time monitoring, The domains of the constant current control and the DRC control have been divided by the starting point of the nugget which is found out through experiments. For the quality control of the stainless steel, the influences of many random disturbances have been compensated because of the constant current control in the early stage of the welding. And the starting point of the nugget has also been stabilized, farther more, the accuracy of the quality control has been increased in the middle and later periods of resistance spot welding process.