Since the first laser beam was invented by scientists in 1960, laser processing has been regarded as scientific productivity. In recent years, laser processing technology has been widely used in the industrial field due to its flexible processing and improving production efficiency. Laser welding is an efficient and precise welding method which uses high energy density laser beam as heat source. It forms the "troika" of laser processing technology together with laser cutting and laser marking.
However, compared with laser cutting and laser marking, the development time of laser tin welding is relatively short and the process is more difficult. Among them, the problems that affect the spot welding quality of laser soldering machine have become the problems that customers pay more attention to when choosing laser soldering equipment. Zichen laser thinks that the main factors are welding current and time, electrode pressure and shunt.
1. Welding current and power on time. According to the welding current and duration, spot welding can be divided into hard specification and soft specification. The specification with large current in a short time is called hard specification. It has the advantages of high productivity, long electrode life and small deformation of weldment. It is suitable for welding metals with good thermal conductivity. The specification with lower current for a long time is called soft specification, which has low productivity and is suitable for welding metals with hardening tendency.
2. Electrode pressure. During spot welding, the pressure exerted on the weldment through the electrode is called electrode pressure. The electrode pressure should be selected properly. When the pressure is high, the shrinkage porosity and shrinkage cavity may be eliminated during nugget solidification. However, the decrease of resistance and current density leads to insufficient heating of weldment, decrease of nugget diameter and decrease of solder joint strength.
The electrode pressure can be selected according to the following factors:
(1) Material of weldment. The higher the high temperature strength of the material, the greater the electrode pressure required. Therefore, when welding stainless steel and heat-resistant steel, the electrode pressure should be higher than that of welding low carbon steel.
(2) Welding parameters. The harder the welding specification is, the greater the electrode pressure is.
3. Shunt. During spot welding, the current flowing from outside the main welding circuit is called shunt. The current flowing through the welding area is reduced by the shunt, which leads to insufficient heating, which leads to a significant decrease in the strength of the solder joint and affects the welding quality.
The main factors affecting the degree of shunt are as follows:
(1) The thickness of the weldment and the distance between the solder joints. With the increase of solder joint spacing, shunt resistance increases and shunt degree decreases. The shunt current accounts for 25% ～ 40% of the total current when the conventional spot distance is 30-50 mm, and the shunt degree decreases with the decrease of the thickness of the weldment.
(2) Surface condition of weldment. When there are oxides or dirt on the surface of the weldment, the contact resistance between the two weldments increases, and the current through the welding area decreases, that is, the shunt degree increases. The workpiece can be pickled, sandblasted or polished.
