1, core diameter does not meet the requirements.
The nugget diameter is the most important index to measure the strength of solder joints. Small diameter of core leads to insufficient solder joint strength, which is mainly caused by small welding current or insufficient electrifying time. If the nugget diameter exceeds the standard value too much, the deformation of solder joint will be great, and the fatigue strength of solder joint will be affected, mainly because the welding parameters are too large. It is suggested that the diameter of solder joint should be the standard value (0, +0.5mm).
Step 2 shrink
The stainless steel used for car body is a cold-worked hardened stainless steel plate, which has high surface hardness and great shrinkage. If the electrode pressure is insufficient, when the liquid metal in the welding core solidifies from the outside to the inside, it can not effectively squeeze the shrinkage cavity, thus forming shrinkage cavity, which can be solved by increasing the electrode pressure and increasing the holding time after welding.
3. The amount of splashing
Cause of splash:
1) The workpiece gap is too large. Stainless steel spot welding workpieces are generally thin plate bending and special-shaped parts. When the number of workpieces is large, priority should be given to ensuring the size of spot welding position and ensuring the close fit of workpieces. When welding workpieces with weak rigidity and many welding spots, a reasonable spot welding sequence should be adopted, such as spot welding from the center to the periphery, with several spot welding intervals.
2) The surface of the workpiece is not completely cleaned. When the workpiece is blanking, impurities such as oil stain and iron filings will remain on the surface of the workpiece, resulting in splashing. Before spot welding, it must be cleaned to ensure that the contact surfaces between workpieces and between workpieces and electrodes are clean. Observe the state of electrode contact surface in time during welding. If the electrode cap or the front end of the electrode has obvious wear or impurities, the electrode film should be replaced or ground in time.
3) Workpiece pressure is too small. For this kind of problem, the equipment should be verified by pressure gauge and galvanometer.
4) The margin between the solder joint and the workpiece is too small. For manual welding, the operating ability of operators should be improved. If there is a problem with the automatic spot welding equipment, the workpiece position, tooling and automatic welding procedure should be checked in time.
4. Incomplete penetration
Incomplete fusion is one of the serious defects that affect the strength of spot welded joints. Incomplete fusion is caused by insufficient heat input, which can be improved by increasing welding current, electrode pressure or welding time.
5, the permeability is not up to standard
Solutions related to materials, electrode pressure and welding time are as follows:
1) When designing products, try to meet the maximum thickness ratio of stainless steel workpieces. According to practical experience, the maximum thickness ratio of stainless steel is: the sum of plate thickness/outer plate thickness is less than or equal to 5.
2) Take certain technological measures, such as changing the shape of the front end of the electrode and changing the material of the electrode.
6. Overburning
Overburning is usually caused by too long welding time and too short cooling time after welding. Check whether the cooling water circulation and shielding gas flow of spot welding equipment are normal, or optimize welding parameters and try to use argon protection.
7, solder joint appearance is bad
There are mainly the following categories:
1). The main reason is that the contact surface between the electrode and the workpiece is worn, so the electrode cap should be replaced or the electrode should be ground in time.
2) Crescent-shaped protrusion. The main reason is that the electrode is not perpendicular to the workpiece or the two electrodes are different axes, so the welding angle of spot welder should be changed or the coaxiality of the two electrodes should be adjusted.
3) The indentation of solder joint is too deep. The main reasons are mismatch of welding parameters and excessive electrode pressure. For the stainless steel car body of urban rail without painting requirements, it is generally required that the electrode indentation of the material supplier should not penetrate into 10% of the thickness of the visible surface plate. (purple flame)
Guangzhou Miller official website has many similar materials.