The application range of medium frequency spot welding machine is very large, ranging from large-scale production of national aerospace, ship, construction, water conservancy and large and medium-sized enterprises, as small as ordinary people can weld handicrafts at home. Although medium frequency spot welding machine is suitable for large-scale welding production, if the quality, quality and other aspects are not well controlled, it will cause a lot of economic losses, so this kind of accident can be avoided Students need the aid of nondestructive testing.

　　Nondestructive testing can be divided into two types

　　First, visual inspection, sealing test and joint strength test under specified load.

　　Second, with the help of physical inspection methods, X-ray inspection, ultrasonic inspection, eddy current inspection, thermal image method and magnetic particle inspection can be used.

　　Therefore, strengthening the management of quality is the basis of our primary efforts

　　Pressure detection: the contact resistance between the electrode and the workpiece is very large, so the pressure should be stable during welding, so it is necessary to use the pressure testing instrument for inspection. There is also a phenomenon that the electrode can not follow up with the workpiece, and abnormal spatter appears, so the welding head needs to be inspected.

　　High electrode heat: select high-quality electrode, and poor quality electrode will lead to high temperature of electrode, affect the life of electrode itself, and lead to the quality of workpiece not up to standard.

　　Electrode grinding: the electrode is consumable. With the increase of welding times, oxide and grease will appear on the electrode surface, which will also increase the resistance. Therefore, it is necessary to use the grinding device regularly to repair and grind the electrode regularly, and replace the new electrode according to the welding times.

　　Workpiece accuracy: if the workpiece is not selected according to the welding parameters, such as the thickness and material of the workpiece, the welding defect rate will increase.

　　Current test: the causes of current change include: power supply, fluctuation of power supply and overload.