Laser Welding Techniques
"The main advantages of contour welding is the flexibility that the process offers with virtually any welding path able to be programmed," explains Steven Kocheny, applications engineer for laser technology at Leister Technologies LLC (Schaumburg, IL). He says contour welding is the most common laser process.
Line welding refers to the use of a laser line for welding. Instead of focusing the light emitted from the diode module to a spot, the light is collimated and shaped into a line. Simultaneous welding utilizes one or more laser lines to produce a weld along a part’s contour.
"Each laser diode is turned on at precisely the same time to allow an entire contour to be welded simultaneously," explains Kocheny. "The main advantage of simultaneous welding lies in the short cycle time required for completing a weld."
While part geometries for simultaneous welding have traditionally been limited to square or rectangular shapes, Kocheny says it is now possible to produce circular lines by using special optic lenses.
Quasi simultaneous laser welding is a technique in which the laser beam is projected along the weld contour by means of scanner mirrors. It is done at a rate of 10 meters per second and because of this high scan rate, depending on part size, 40 to 50 passes per second over the weld contour is possible.
"This enables the entire surface to be heated up and melted simultaneously with the pinpoint accuracy of a laser beam," says Frank Buck, president of Bielomatik Inc. (New Hudson, MI). "With the addition of some joining pressure during this welding operation, tolerances can be compensated for."
Buck claims this welding method allows online process control. "The method of monitoring depth and time is similar to that of linear vibration welding," he points out.
"Laser controls allow the geometry of the welding contour to be loaded into the machine as a CAD file," explains Buck. "This means that change is extremely simple and a wide range of parts can be welded without lengthy set up concerns, one after another."
Mask welding uses the same transmission welding principles as the contour and simultaneous methods. It uses a laser line to produce a weld, but unlike simultaneous welding, it uses a mask to block the transmission of the laser line. The mask shape determines the pattern of weld produced, and its precision is significant in determining the accuracy of the final weld.
The mask acts to selectively block the laser light from entering into the part. Where the laser light is allowed to enter, welding is achieved.
"Using the mask welding process, it is possible to produce an area of weld instead of just a line of weld," says Kocheny. "The main advantage of this process is that it allows for very precise and very fine weld lines. Weld lines as narrow as 100μm have been successfully made with the mask welding process. In addition, this process allows the possibility of producing welds with elaborate structures or contours."