Method of resistance welding quality control

As the extensive use of resistance welding process, the importance and representative to ensure the welding quality has become a main objective of the study of resistance welding, spot welding quality control circles and scholars at home and abroad is always an important issue to study. For example: Japan Welding Society has set up a spot welding quality control and testing group [27], the United States to address the resistance spot welding in the automotive industry research project carried out 2mm [28]. At present, the welding process control engineers face a major problem is to explore a reliable,low-cost, non-destructive technique to distinguish the quality of solder joint strength of solder joints and real-time forecast.
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In recent years, resistance welding quality control of research has maintained an upward trend, and its increasingly sophisticated means and methods, mainly in the following areas 3.1 direct spot welding process variables in real-time monitoring
University of Michigan Cho, Y speed digital cameras with real-time monitoring of nugget formation process of the formation mechanism of resistance spot welding and its welding process parameters [29].
3.2 Indirect welding process real-time detection of electrical parameters
American scholars Matsuyama, K is presented based on energy balance in integral form of the new monitoring algorithms, the system through access to welding voltage, current and total thickness, calculate the average temperature during welding in order to predict solder joint diameter and splash conditions spot welding is a low-cost real-time monitoring method [30]; Jou, Min and other scholars to explore the output signal by changing the control parameters to ensure the solder joint strength and quality monitoring method [31], the research method is to create an solder joint quality of the process output and the relationship between process input variables and input parameter selection directly affect the solder joint size and intensity of the percentage of heat input and output selection electrode displacement, it can accurately reflect the growth and deformation of the nugget, which monitor method of spot welding in automotive steel sheet has been applied.
There are many scholars in recent years, the use of dynamic resistance of solder joint quality control methods, such as Fanuc Robotics Corporation U.S. scholars Garza, Frank and other projections through the dynamic resistance, analysis and classification, and application in practice show that  this method For the detection of bad solder joints is effective [32]; Chinese scholar Wang, SC, etc. In this study, the dynamic resistance of the temperature through the welding area to obtain the total [33], the workpiece temperature and resistance welding zone, the workpiece and the electrode, the workpiece and resistance among artifacts related to the measured dynamic resistance curve can be divided into four phases: 1) With the decrease in contact resistance and rapid decline; 2) depends on the size of the workpiece resistance increases, a corresponding increase in dynamic resistance; 3) The resistance of the workpiece size increases, but the contact resistance decreases, which also increased the dynamic resistance; 4) contact with the surface of the nugget due to the formation of dynamic resistance becomes smaller. It was found, welding nugget in the third and fourth stages of formation; the University of Michigan Cho, Y with the    primary circuit by measuring the instantaneous current and voltage [34], using regression analysis to determine the welding quality of these factors and the relationship between to overcome the traditional method of measuring the secondary circuit dynamic resistance monitoring in real-time problems.
3.3 indirect spot welding process parameters in real-time monitoring force