Laser Beam vs. Electron Beam Welding Which process works best for what?
- Sunday, 01 May 2011
Proponents of laser beam welding (LBW) and electron beam (EBW) welding each pronounce the singular praises of their favored technology, but often the best solution for a customer is to use both technologies together. Both processes are well suited to joining components with complex geometries, and capable of meeting the most stringent demands for metallurgical characteristics of the final assembly.
Using both laser and electron beam technologies in a single facility can streamline the manufacturing process when a component’s design incorporates multiple weld joints separately tailored for one process or the other. Examples include sensors, medical devices, and products that require an inert gas or vacuum to be sealed within the finished part.
Laser processing is required either when the size of the final assembly is too large for an EB welding chamber, some component in an assembly is incompatible with vacuum processing (such as a liquid or gas), or when the weld is inaccessible to an electron beam source. Electron beam will be the primary choice when the completed assembly must be sealed with internal components under vacuum, when weld penetrations exceed 1⁄2", when the material is challenging to initiate laser coupling, or when the weld must not be exposed to atmospheric conditions until it has cooled to an acceptable temperature. Examples are aerospace welding of titanium and its alloys, and many refractory metals such as tungsten, niobium, rhenium, and tantalum.
LBW – Simpler Tooling and Shorter Cycle Times
Laser welding energy sources utilize either a continuous wave (CW) or pulsed output of photons. With CW systems, the laser beam is always on during the welding process. Pulsed systems are modulated to output a series of pulses with an off time between those pulses. With both methods, the laser beam is optically focused on the workpiece surface to be welded. These laser beams may be delivered directly to the part via classical hard-optics, or through a highly flexible fiber optic cable capable of delivering the laser energy to distant workstations.
It is the high energy density of the laser that allows the surface of the material to be brought to its liquidus temperature rapidly, allowing for a short beam interaction time compared to traditional welding methods such as GTAW (TIG welding) and similar processes. Energy is thus given less time to dissipate into the interior of the workpiece. This results in a narrow heat-affected zone and less fatigue debit to the component.
Beam energy output can be highly controlled and modulated to produce arbitrary pulse profiles. Weld seams may be produced by overlapping individual pulses, which reduces heat input by introducing a brief cooling cycle between pulses, an advantage for producing welds in heat sensitive materials.
Salay Stannard, a materials engineer for Joining Technologies, an East Granby, CT-based innovator in laser cladding, electron beam and laser welding applications, notes that CW lasers can achieve penetrations up to and exceeding 0.5 inches, while pulsed lasers typically achieve only 0.030-0.045 inches. She says, “These results may vary between laser systems and are largely dependent on processing parameter choice and joint design.” Figure 1 depicts the construction of a solid-state laser welding system.