LASER BRAZING is a joining process for sheet metals where the filler material with low melting point is melted with laser beam while the base material with higher melting point does not melt. In laser brazing the working temperature is above 450 °C while another process is laser soldering, where the working temperature is below 450 °C. Laser soldering is used especially in electronics industry in soldering the circuit boards.
LASER BEAM diameter on the workpiece surface is typically about 1.5…3 mm. Laser beam heats up the joint surfaces but does not melt the material. The filler material, typically a wire with diameter of 1.0 mm, is fed to the process. Laser beam melts the wire and the melt penetrates into the gaps in the joint and wets the joint surfaces. Filler solidifies and forms a smooth joint. The filler wire can be pre-heated to increase the process speed.
JOINT GEOMETRY must be designed so that the laser beam can heat up the joint surfaces and the filler material can deploy on the joint surfaces. Most common joint types are fillet weld and lap weld.
MATERIALS for laser brazing are typically zinc coated steel sheet metals. In welding the process temperature increases well over the vaporization temperature of zinc (906 °C) and the vaporized zinc causes process instability and porosity. Additionally, the vaporized zinc coating leaves the base material exposed to corrosion. In laser brazing the process is more stable and due to the lower process temperature the zinc coating is vaporized only in a very narrow area next to the joint. The corrosion resistance of the filler material is usually very good and the intact zinc coating next to the joint can protect the area of reduced zinc from corrosion.
FILLER MATERIAL melting point must be lower than the base material melting point. For example in laser brazing of steels the filler materials are typically silicon bronzes (e.g. CuSi3, melting point of 910-1025 °C) or aluminum bronzes (CuAl8, melting point of 1030-1040 °C).
LASER BRAZING OF DISSIMILAR METALS is also possible. For example in laser brazing of carbon steel and aluminum the filler material is welded to the aluminum part and brazed to the steel part. Carbon steel and stainless steel can also be brazed easily together.
TYPICAL APPLICATIONS for laser brazing are sheet metal structures where low heat input, good corrosion resistance and reduced need for refinishing work are important. For example automotive industry uses laser brazing in long, visible seams in body and door structures.
BENEFITS OF LASER BRAZING:
- Excellent joint surface quality
- Excellent joint corrosion resistance
- High process speed (2-6 m/min)
- Reduced need for refinishing work
- The process is easy to control
- Joining of dissimilar metals
LIMITATIONS OF LASER BRAZING:
- Typically only for thin materials
- Relatively high investment cost
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