Combining Beam and Electron Beam Welding Offers the Best of Both Worlds

John Lucas roponents of laser beam welding (LBW) and electron beam welding (EBW) praise the ben- Joining Technologies Pefits of their favored technology, but in many cases, the best solution for a customer is to Inc. use the two welding methods together. This is especially true for fusing together complex East Granby, Conn. geometries and meeting the demands for superior weld . Using both laser and electron beam technologies in a single facility can streamline the manufacturing process when the design of a component design incorporates both EBW and LBW welds. Examples include sensors, med- Using laser ical devices, and products that require a sealed vacuum within the finished part. Usually, both beam welding technologies are needed either when the size of the final assembly is too large for an available EB together with welding chamber, some component in an assembly is incompatible with vacuum processing (such electron beam as a liquid), or when the weld is non critical and shallow, therefore not requiring a potentially more welding is expensive EB weld. ideal for Laser beam welding complex LBW uses either a (CW) or pulsed beam of photons. With CW systems, geometries power output is operated continuously over time. Pulsed systems are modulated to output a series and superior of pulses. Beam energy can be tailored to produce desired pulse profiles. Weld seams may be pro- duced by overlapping individual pulses, which tends to reduce heat input by the brief cooling cycle weld between pulses, an advantage for producing welds in heat sensitive materials. With both methods, metallurgy. the laser beam is optically focused on the workpiece surface to be welded. Salay Stannard, mate- rials engineer for Joining Technologies, an innovator in laser cladding and electron beam and laser welding applications, notes that CW can achieve penetrations up to and exceeding 0.5 in., while pulsed lasers typically achieve only 0.030 to 0.045 in. She says, “These results may vary be- tween laser systems and are largely dependent on process- ing parameter choice and joint design.” It is the higher energy den- sity of the laser that allows the surface of the material to be brought to its liquidus tem- perature rapidly, allowing for a short beam interaction. Energy is thus given less time to dissipate into the interior of the substrate. This results in a shallow heat-affected zone and less fatigue debit to the component. Stannard adds, “Since the heat source in this type of welding process is the energy of photons, the weld material’s reflectivity should be considered. For example, gold, silver, copper, and aluminum require more intense energy input than iron and nickel-base alloys. Figure 1 depicts the construction of a solid-state laser welding Fig. 1 — Solid-state laser welding system. system. Continued

ADVANCED MATERIALS & PROCESSES • JUNE 2011 29 As noted, the laser’s high power density results in small weld that is critical for metals such as and heat-affected zones and ensures that critical components nickel-base superalloys. are unharmed. This has particular advantage for surgical However, the main advantage for operating under vac- instruments, electronic components, sensor assemblies, uum is to control the electron beam precisely. Scattering and other precision devices. LBW does not generate any occurs when electrons interact with air molecules; by low- x-rays and is easily controlled using automation and robot- ering the ambient pressure under vacuum, electrons can ics. Generally, LBW has simpler tooling requirements, and be tightly controlled. Modern vacuum chambers are there are no physical constraints of an enclosure or vac- equipped with state-of-the-art seals, vacuum sensors, and uum chamber. Shorter cycle times translate to cost advan- high performance pumping systems, enabling rapid evac- tages without sacrificing quality. Advantages of continuous uation and increased processing time. This advantage wave and pulse laser beam welding include: makes it possible to focus the electron beam to diameters • Lower capital equipment costs (cost advantage over of 0.3 to 0.8 mm. EBW); no physical constraints of an enclosure or By incorporating the latest in microprocessor control vacuum chamber enables simplified setup, rapid (CNC) and systems monitoring for superior part manipu- cycling, and less complex single station tooling lation, parts of various size and mass can be joined without • Shorter cycle times translate to lower cost excessive melting of smaller components. The precise con- • Simpler tooling requirements trol of both the diameter of the electron beam and the • Small heat affected zone travel speed allows materials from 0.001 to several inches • Scalable (1 laser servicing several platforms) thick to be fused together. These features make EBW an • Many OEMs support the technology extremely reliable technology. • Low training costs The process also puts a small amount of total heat into • No x-rays generated the workpiece being welded, which produces the smallest amount of distortion and allows finish machined compo- Electron beam welding nents to be joined together without additional processing. Widely accepted across many industries, EBW per- The main advantages of electron beam welding include: mits the welding of refractory and dissimilar metals that • Welding in a vacuum ensures no contamination are unsuited for other methods. As shown in Fig. 2, the • Deeper penetration with high aspect ratios workpiece is bombarded with a focused stream of elec- • Energy absorption independent of material or surface trons travelling at high speed. The kinetic energy of the conditions electrons is converted to heat energy, which, in turn, is • Similar heat-affected zone to that of LBW the driving force for fusion. No added filler material is re- • Permits welding of refractory and dissimilar metals quired and distortion is minimal. Ultrahigh energy den- not weldable using conventional welding process sity enables deep penetrations and high aspect ratios, • Proven track record (widely accepted) while a vacuum environment ensures a contaminant-free • Included in many welding specifications According to John Rugh, marketing and general sales manager for Enfield, Connecticut-based PTR-Precision Technologies Inc., EBW is a process that will be in use for High-voltage a long time. “Since most EB welding is performed inside a cable vacuum chamber, it is an excellent fit for joining advanced Incandescent cathode materials used in such industries as aerospace, power gen- Prism Bias cup eration, medical and nuclear, which need to be produced in Telescope Primary anode a vacuum environment to protect them from oxygen and for found in an open air environment.” He adds, “The viewing Electron beam cleanliness of the welding environment is one variable that Focusing coil you just don’t have to worry about. In addition to provid- Deflection ing the ideal welding environment, new EB welding con- coil trols allow for fast electromagnetic deflection of the beam, Weld bead which allows the heat input of the weld and surrounding area to be customized for optimum material properties.” For example, this rapid deflection allows preheating, weld- ing, and post heating simultaneously just by rapidly mov- ing the beam location, focus, and power levels. This Workpiece provides the ability to weld difficult or “impossible to weld” alloys. Vacuum chamber Another area where use of EBW is growing is in man- ufacturing turbochargers for diesel engines, which are growing in popularity due to their potential to increase en- Fig. 2 — Electron beam welding. ergy efficiency. Turbochargers are required to pressurize

30 ADVANCED MATERIALS & PROCESSES • JUNE 2011 Laser beam welding a cylinder piston. the fuel-air mixture going into the diesel engine. Geoffrey Young, general manager of Massachusetts-based Cam- Parts being electron beam welded in a vacuum chamber. bridge Vacuum Engineering, commented, “We are seeing many modern passenger car and commercial vehicle en- gines that are being equipped with turbochargers. Manu- facturers of these units had conventionally used inertia techniques to join the investment cast In- conel wheel to the carbon-steel shaft. Although this join- ing method produced a joint of adequate strength, the post-weld , grinding, and heat treatment oper- ations were expensive and time consuming. An alternative welding process using EBW has been adopted by a number of leading turbocharger manufacturers.” “EBW parts require a minimal post-weld machining and heat treatment, and, unlike other processes, EBW requires no shielding gases.” He adds, “The weld quality is exceptional, the process is extremely efficient (typically 95%), all the process parameters are carefully controlled, and the process is fully automated.”

Combined EBW and LBW: streamlining the process While each technology has its benefits, in practical terms, many component designs incorporate both EB and laser welds. In these cases, performing both types of weld- ing at the same facility definitely streamlines the manufac- Operator at EB-welding chamber. turing process. According to John Rugh, LBW is commonly used for If components are of high value, made of a material welding steel sheet metal components and machined com- that would benefit from the vacuum environment, such as ponents under 0.3 to 0.5 in. thick. Laser welding is also use- titanium and nickel alloys, the welds are deeper than 0.3 ful for joining parts that are not suitable for processing to 0.5 in., or if the laser beam has difficulty “coupling” with inside a vacuum chamber. the material being welded (such as aluminum alloys) EB “Some parts and their associated welding fixtures may welding is often the process of choice over laser welding. be too large to fit into the EB welding chambers available,” Rugh gives the example of gas turbine components where said Rugh. “Aside from size, if the components being EB welds are used for the deeper welds and welds requir- welded contain liquids that would interfere with vacuum ing minimal distortion. The same assembly also had laser pumping, laser welding would be a good choice.” LBW welds called out for sheet metal cover details. might also be chosen if the weld is non critical and shal- low, therefore not requiring a higher quality, potentially For more information: John Lucas, Process Development more expensive EB weld. It takes minutes to evacuate an Technician, Joining Technologies Inc., 17 Connecticut South EB welding chamber, and that time may not be worth it for Dr., East Granby, CT 06026; tel: 860/653-0111; fax: 860/413- a noncritical weld. 9029; email: [email protected]; www.joiningtech.com.

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