Relationship Between Nugget Size And Characteristics Of Frequency Spectrum Of Welding Current In AC Spot Welding

Aiming at the localization of traditional quality detection method during resistance spot welding, a new method is set up to detect the nugget size in real time. On the basis of digital signal process and nondestructive testing, the effect of welding process on the frequency spectrum of the current signal in AC spot welding is analyzed. Through the analysis of Fast Fourier Transform (FFT), the amplitude frequency charts and phase frequency charts of current signal are constructed. The characteristic of the correlation between frequency spectrum and nugget size is studied, and the relationship is founded. In addition, the dynamic resistance in spot welding and its frequency spectrum are analyzed. The relationship between the dynamic resistance curve without type character and nugget size is founded.The results show that there is the exponential relationship between quasi-stable state resistance value and nugget size. It is tenable with shunt effect, different plate thickness and warp effect. The correlated information can be picked up in the frequency spectrum charts of dynamic resistance curves. The variation regularity of nugget diameter is shown in the frequency spectrum charts of the current signal. The experimentations show that there is corresponding relationship between nugget size and the amplitude frequency of first harmonics and third harmonics on the condition of shunt effect and different pressure. So it can be one of the methods to detect nugget size.The results are of important worth in theory and engineer application for the nondestructive testing of resistance spot welding quality.