Advantages and Limitations of Laser Beam Welding Laser beam welding (LBW) produces coalescence with the heat from a laser beam impinging on the joint. While filler metal may be used, the process is primarily used autogenously. Laser is an acronym for light amplification by stimulated emission of radiation. A laser uses an optical resonating system incorporating a crystal or gas medium and reflective mirrors or focusing lenses to amplify and synchronize light waves into a coherent beam. The laser emits this concentrated beam as energy that can be focused on the weld joint or cutting site and applied as heat to make the weld or cut. While LBW has numerous advantages over other processes, it also has several limitations that should be considered when selecting the welding process for a particular application. Following are the major advantages and limitations of LBW. Advantages 1. Heat input is close to the minimum required to fuse the weld metal. Heat-induced distortion of the workpiece and metallurgical effects in the heat-affected zone (HAZ) are minimized. 2. Single-pass laser beam welding procedures have been qualified for metals up to 3.2 mm (1.25 in.) thick, although more typically joints up to 19 mm (0.75 in.) may be welded. This reduces the time needed to weld thick sections and reduces or eliminates the need for welding wire and elaborate joint preparation. 3. Electrodes are not required to conduct current to the workpiece, thereby eliminating electrode contamination, indentation, or damage from the high currents used in other welding processes. 4. Tool wear is essentially eliminated because LBW is a noncontact process. 5. Laser beams are readily focused, aligned, and directed by optical elements, permitting welding in areas not easily accessible by other processes and allowing the laser to be conveniently located relative to the workpiece or redirected around tooling and obstacles. 6. The process allows workpieces with internal volumes to be hermetically welded to leave a vacuum or a controlled atmosphere in the finished product. 7. The laser beam can be focused on a small area, permitting the joining of small, closely spaced components with extremely small welds. 8. A wide variety of materials and many combinations of different types of materials can be welded, including those with dissimilar physical properties, such as electrical resistance, and several that are electrically insulating. 9. The laser can be readily mechanized for automated, high-speed welding, including the use of computer numerical controls or computer-controlled welding. 10. Welds in thin metal and small-diameter wire are less susceptible to incomplete fusion than arc welds. 11. Laser welds are not influenced by the presence of magnetic fields, as are arc welds and electron beam welds. 12. No vacuum is required and no x-rays are generated. 13. Aspect ratios (depth-to-width ratios) on the order of 10:1 are attainable when a keyhole weld is made by forming a cavity in the metal. 14. The laser beam can be transmitted to more than one workstation using beam-switching optics, which allows beam timesharing. Limitations 1. Joints must be accurately positioned laterally under the laser beam and at a controlled position with respect to the laser beam focal spot. 2. When weld surfaces must be mechanically forced together, the clamping mechanism must ensure that the final joint position is accurately aligned with the laser beam impingement point. 3. The maximum joint thickness is somewhat limited, as weld penetrations greater than 19 mm (0.75 in.) generally are considered impractical for LBW production applications. 4. The high reflectivity and high thermal conductivity of some metals, such as aluminum and copper alloys, may adversely affect weldability with the laser. 5. When performing moderate-to-high-power laser beam welding, appropriate plasma and plume control devices must be employed to ensure that welds are reproducible. 6. Lasers tend to have low energy conversion efficiency. 7. As a consequence of the rapid solidification characteristic of laser beam welds, some weld porosity and brittleness can be expected in many common engineering alloys. 8. Laser equipment and fixturing costs may be high. Laser Beam Systems Fig. 1 — Parts of an Nd:YAG laser. Laser beam welding systems include solid-state lasers, direct-diode lasers, fiber lasers, and gas lasers. Solid-state Nd:YAG lasers and gas CO2 lasers are two of the most widely used in industry. Figure 1 shows the elements of an Nd:YAG laser. WELDING WORKBOOK 68 WELDING JOURNAL / MARCH 2016 WJ DATASHEET 363 Excerpted from the Welding Handbook, Ninth Edition, Volume 3, Welding Processes, Part 2.
Welding Journal | March 2016
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