Electron beam welding (EBW) is a specialist metal joining process specifically used for producing high-quality joints without causing any major distortion. In this process, a beam of high energy electrons is directed towards the joint that needs to be fused or welded.
These high energy electrons are produced by a filament or a cathode. Since heating is highly localized, most of the assembly continues to remain stable and cold, resulting in a narrow weld with a small heat affected zone (HAZ).
During the melting of the parent metal, there is no need for a filler metal. Since this is a line of sight approach, it is not possible to weld around corners or re-entrant.
Given that the heat input is highly localized, components that have been heat treated can be joined together. This presents a low-cost method for creating gear shafts, with a case hardened gear on a tempered and hardened shaft.
The Electron Beam Welding technique offers the following benefits:
• High Welding Speed.
• Minimal Distortion.
• Low heat input for joined parts.
• Narrow and small HAZ and Melt Zone (MZ).
• Deep weld penetration from 0.05 to 13mm in a single pass.
• Vacuum process results in clean, reproducible environment.
• All metals can be welded, even those with high thermal conductivities.
• Metals can be welded, even those with high thermal conductivities.
• Metals can be welded with dissimilar melting points.
• Natural welding process for niobium, titanium, zirconium and other materials requiring oxygen.
• Low-cost welding process for large-scale production in automatic mode.
• Machine process ensured for consistency and reproducibility of the operating conditions.
• Components can often be utilised in the as welded condition without the need for sub-machining.
As the Electron Beam Welding process takes place in the vacuum, the welds are clean and free of oxides and nitrides. Narrow, deeper penetration from .001 to 2 inches, with high depth to width ration eliminates multiple pass welds completely.
Narrow/Deep – High depth to width ratio eliminates multiple pass welds. Penetration from 001” to ½”.
Low Heat – Minimises shrinkage and distortion and allows welds in close proximity to heat sensitive components.
Strength – Welds up to 95% of the strength of the base material.
Versatility – Precise control and repeatability.
High Purity – Vacuum environment eliminates impurities such as oxides and nitrides.
Unique – Permits welding of refractory and dissimilar metals not weld able with conventional welding process.
Electron Beam Welding is used in the following applications:
• Power generation
• Vacuum systems
• Aerospace – sensors. jet engine components, transmission components, parts of structures
• Space – sensors, titanium tanks
• Automotive – gears, transmission part, parts of turbocharger
• Electrical/electronic industries – parts in copper material
• Nuclear – instrumentations, valves, fuel housing, parts of structure
• Research centers – superconductivity material components, copper parts
• All metals even with high thermal conductivity – steel and stainless steel, copper and alloys, titanium and alloys, nickel alloys, aluminum and alloys, refractory metals, Mo, Zr, Ta, W, Nb, Hf, and so on
• Welding of metals with dissimilar melting points – steel to nickel alloys, copper to nickel alloys, copper to steel, tantalum to tungsten
ELECTRON BEAM WELDING is the bombardment of a metallic surface by a tightly focussed stream of electrons. This results in a very concentrated (approx. 0.1mm dia.) and intense heat source that melts the metal. By aiming the beam at a joint and then moving the joint under the beam a fully homogeneous fusion of the mating surfaces can be achieved. This activity is carried out within a vacuum chamber thus preventing the electron beam from being defused by air molecules and also providing a virtually inert atmosphere.
When the beam hits the joint it creates a ‘keyhole’ in the material that is surrounded by a molten sleeve of parent metal. As the work traverses under the beam this molten sleeve solidifies and creates the joint. The resultant welded joint is in affect a vacuum re-melted area of parent material.
The use of ELECTRON BEAM WELDING can be found in virtually every market, aerospace, medical, automotive, nuclear, defence, oil and gas, civil engineering and even art.
Assemblies can be welded using finished or part finished details using a vast range of materials. The most common are titanium, stainless steel, Inconel, aluminium, copper, low carbon steel, bronze, super duplex, Hastelloy and magnesium.
ELECTRON BEAM WELDING is particularly effective when fusing delicate assemblies where excessive heat could be detrimental to the product. It can also be an economic alternative to conventional welding techniques when joining deep sections, as a single pass with an ELECTRON BEAM WELD can replace multiple runs using TIG, MIG or Arc methods.
Further advantages are; minimal distortion, a very narrow HAZ (heat affected zone) and as the welding normally takes place within a vacuum environment the risk of hydrogen contamination of the weld is minimised. This is a great advantage when fusing titanium and its alloys.
Following is a range of different joint designs that are acceptable for ELECTRON BEAM WELDING. A fully penetrating weld as shown in figure 1 is often used when the assembly requires no post weld machining. Figures 2 & 4 show joint designs that provide location for the mating parts which makes assembly simpler. This type of configuration can also lend itself to finish machined details though the additional material used to locate the joint is sometimes removed after welding. Figure 3 is a joint that although fully penetrating will probably require the top joint feature to be removed after ELECTRON BEAM WELDING. This is will prevent crack propagation from the unfused section of the joint.
Most standard NDT techniques can be used to check the integrity of electron beam welds; x-ray, PFD, ultrasonic and MFD.
Are the selected materials suitable for electron beam welding?
Can the joint be accessed by a beam of electrons?
Ensure nothing can eclipse the path of the beam.
Can the joint be designed as self-locating or will a fixture be required?
The joint tolerances must provide a maximum gap of 0,1mm. It some cases this may need to be even tighter. Consider the proximity of components that might be affected by temperature.
Will the design incorporate finish sized details or parts that require post weld machining?
If finished parts are to be welded the amount of weld shrinkage will need to be considered. Most materials will lose some of their mechanical properties after welding so an assessment of strength requirements will need to be made.
ELECTRON BEAM VS LASER WELDING EXPLAINED
ELECTRON BEAM WELDING (EBW) and laser beam welding (LBW) fall under the same category of power beam welding. Despite this, there are some fundamental variations between each welding process and its applications. This article, ELECTRON BEAM vs laser welding, will explore the similarities and differences between electron beam welding in a vacuum and laser welding with a shielding gas – helping you decide which welding machine is most suitable for your application.
WHAT IS THE DIFFERENCE BETWEEN ELECTRON BEAM AND LASER WELDING?
ELECTRON BEAM WELDING uses a finely focused stream or beam of electrons, whereas laser welding uses monochromatic coherent light (photons). In both cases, the kinetic energy of the electrons or photons is turned into heat energy when they hit the surface of the metal.
ELECTRON BEAM WELDING is lesser known than laser welding out of the two techniques. And this is not because it is inferior to laser but mostly because of people’s perceptions.
ELECTRON BEAM WELDING takes place in a vacuum chamber. This aids the weld quality, as it tends to pull contamination away from the weld pool. Welding in a vacuum also results in the operator not becoming exposed to the hazardous welding environment.
Conventional laser welding takes place at atmospheric pressure, with additional shielding gas. However, you can laser weld in a vacuum, which significantly increases the depth of the weld.
Shielding gas is not required for ELECTRON BEAM WELDING as the process takes place in either a low or high vacuum.
Laser welding at atmospheric pressure requires a shielding gas; it is an expensive but essential consumable. Fume extraction may also be an issue.
The vacuum chamber on an ELECTRON BEAM WELDER restricts the component size, as parts must fit within it. Chamber volumes are kept to a minimum to reduce evacuation times.
Laser welding with a shielding gas can accommodate any component size, as there is no vacuum chamber. Furthermore, you can use fibre optic delivery systems. This allows the welding head to be remote from the power source.
ELECTRON BEAM WELDING can achieve deep penetration welds over a wide range of speeds, whereas laser welding with a shielding gas always requires high welding speeds due to the plume of metal vapour that forms.
ELECTRON BEAM WELDING produces high-quality weld joints in a wide variety due to the inert atmosphere, which creates a very stable and repeatable environment. Joint finding and imaging using backscattered electrons are advanced options that can further increase the weld quality.
Laser welding needs a shielding gas, typically nitrogen or argon, to prevent oxidisation of the weld area and ensure the stability of the weld pools. Real-time monitoring of weld depth and quality are expensive options, but they can improve weld quality.