Electron Beam Welding of Busbars for Electric Vehicles

Introduction

Busbars are an essential component of an electric vehicle.

Typically made of conductive alloys such as aluminium, bronze, or copper, they distribute power between individual cells, as well as the battery packs to the motors.

CVE, designers and manufacturers of electron beam and laser welding process solution systems, have collaborated with TWI, membership-based research and technology organisation, to explore the feasibility of using the electron beam welding process for interconnection of cells and for joining busbars to the powertrain.

Background

The structure of a typical electric vehicle battery pack starts as a cell. Designs vary across manufacturers, but the industry has settled on 21700 cells as standard.

Battery packs welded together with busbars, typically 60-100 cells, create a module, and multiple modules (6-40) make a pack.

The welded busbars are typically produced from copper with nickel plating.

This new design represents a challenge for OEMs. The components are rapidly developing and replacing traditional components that have been manufactured for hundreds of years.

The International Energy Agency predicts that there will be 230m electric vehicles worldwide by 2030, signalling an industry requirement for a high-quality, reliable, and quick welding process for battery pack production.

Wide Angle Deflection Electron Beam Welding

CVE and TWI ran a series of test welds using a method of wide-angle deflection electron beam welding.

Electron beam spot melting trials on a 450-micron steel sheet (bus bar battery tab) showed that the test welds achieved a consistent depth of up to 200 microns.

 

Figure 1. 60kV, 2mA, 2msec spots.

Solution

CVE and TWI successfully developed high-quality welds joining bus bars to battery cell samples.

The investigation also found electron beam welding to be a much quicker process in comparison to resistance and laser welding.

The typical time to manufacture one battery pack using resistance welding is 12,000 seconds and 1,260 seconds using laser welding. In comparison, electron beam welding has demonstrated a speed of just 189 seconds per battery pack, with anticipated developments expected to take this number closer to just 75 seconds per pack, representing a 99.38% time saving.

The weld time comparison across resistance, laser, and electron beam welding results are shown in the table below.

 

  Time to weld one cell (4 welds)  Time to manufacture one battery pack 
Typical for resistance welding  4 seconds  12,000 seconds 
Typical for laser welding  0.42 seconds  1,260 seconds 
Demonstrated speed for electron beam  0.063 seconds  189 seconds 
Anticipated electron beam development  0.025 seconds  75 seconds 

 

Applications and Further Developments

There are many other advantages of electron beam welding for this application, including:

  • The weld quality is highly consistent
  • Electron beam welding is at least 10x faster than laser
  • There is no requirement for gas
  • Potential to implement vacuum load-lock systems
  • The vacuum chamber contains the welding process. This results in less spatter, so the welds are greatly more consistent than when using laser welding
  • An electron beam is less sensitive to reflectivity, the beam being a finely focused stream of electrons, rather than monochromatic coherent light (photons) like a laser
  • The vacuum environment closes micro-gaps, resulting in a stronger weld

 

Electron beam welding is already a well-established process for high-volume automotive components, such as turbochargers.

Production possibilities include implementing a vacuum load lock system, which would allow for high-speed cycles between assemblies, therefore resulting in very fast cycle times being readily achievable.

Electron Beam Welding of Turbochargers

Introduction

With increasing legislation demanding cleaner engines and higher fuel efficiency, manufacturers equip modern passenger car and commercial vehicle engines with turbochargers.

 

Figure 1. Turbocharger drawing.

Inertia Friction Welding

Automotive manufacturers previously used inertia friction welding to join the investment cast, Inconel wheel to the low alloy carbon steel shaft.

Although this produced a joint of adequate strength, the post-weld machining, grinding, and heat treatment operations were expensive and time-consuming.

Many leading turbocharger manufacturers have adopted an alternative welding process using electron beam welding (EBW).

EB Solution and Process Advantages

The process uses an electron beam that joins parts with high precision, significantly reducing the post-weld machining operations.

Consequently, because fewer machines are needed to produce a welded part, the investment cost of the manufacturing cell is reduced.

The welding process can be fully automated, and weld parameters, such as accelerating voltage, beam current, beam focus and traverse speed, are controlled. The high heat intensity produces a narrow fusion zone with very little distortion, so it is possible to weld together machined components in the finished or semi-finished condition.

Automotive turbocharger component shaft and wheel collet

Figures 2 and 3. Turbocharger shaft and wheel.

Automotive turbocharger component shaft and wheel collet

Future Developments

In addition to electron beam welding shafts and wheels, you can also apply the process to other applications in turbocharger technology, including variable geometry turbos and wastegate valves.

CVE has supplied around 100 turbocharger welding systems throughout the world. And the adoption of electron beam technology seems set to continue.

Download CVE’s technical datasheet with information on our turbocharger electron beam welding machines.

Figure 4. Close-up of diesel engine turbocharger.

Figure 5. Turbocharger structure with cross-section.

An Introduction to Laser Welding

History of Laser

Laser (Light Amplification by Stimulated Emission of Radiation) is a technology that was first theorised by Einstein in 1917, with the first working device tested in 1960. A laser can produce a directional, coherent, and monochromatic beam of light.

Directionality, coherence (when all wave fronts of the light are aligned) and monochromaticity (when all light produced is of approximately one wavelength) allow the beam to be focussed and steered into a single, very small, spot; a few tenths of a millimetre across depending on the application.

Welding lasers reach the tens of kilowatts for output power, allowing for the very high power densities that high-penetration keyhole welding requires.

Conduction Welding

This brings us to the two primary categories of laser welding: conduction mode and keyhole mode welding.

Conduction welding involves melting a bead of metal at the joint’s surface and fusing the halves of the joint together as the material resolidifies. The defining feature of conduction mode welding is its low penetration (around 1mm), with only a small volume of material melted. This makes conduction mode welding ideal for low heat input fusing of thin-walled or very small components; it is used for a variety of applications, from car body panels to electronics.

Figure 1. A conduction weld. Credit: Cranfield University.

Figure 2. A keyhole weld. Credit: Cranfield University.

Keyhole Welding

Keyhole mode welding is the high-power method used to join thicker components with close-to-parent-material strength.

In the keyhole mode, the power density becomes high enough to not only melt, but also vaporise material. As the metal vaporises and the vapour is propelled away from the melt pool, the vapour exerts a ‘recoil pressure’ on the melt pool opposite to its direction of travel, i.e., into the melt pool. This has the effect of ‘drilling’ a hole into the material coaxial with the laser beam. This column of metal vapour surrounded by molten metal is known as a keyhole.

The recoil pressure of vaporising metal eventually reaches an equilibrium with the hydrostatic pressure of the molten metal column surrounding it, this determines the depth of the final weld. The recoil pressure is proportional, among other things, to the energy applied to the material per unit time, making it a function of the laser beam’s power and the weld speed.

The uses of both conduction and keyhole mode welding are very broad, with modern lasers providing the power, positional accuracy and long-term reliability to produce high-quality welds for both high- and low-volume production.

What are the Limitations of Laser Welding?

A range of factors can impede and frustrate the laser welding process, making it either difficult and expensive, or simply impossible to implement.

Some material groups are excluded entirely from laser (or electron beam) welding, namely those that char instead of melting. Suitable materials, mainly metals, are further restricted by issues of reflectivity, thermal characteristics, and gas affinity.

Reflectivity is a physical property of a material and varies with wavelength. It determines how much of an incoming light beam’s thermal energy will be absorbed vs. reflected. High reflectivity naturally leads to a lower proportion of the laser beam’s energy being absorbed into the material and used to form the weld. Any reflected laser light is hazardous to both the operator and surrounding machinery and structures. Protective structures around the laser welder are necessary, as even a fraction of reflected light from a multi-kW laser is a high risk. Thermal characteristics and gas affinity influence the shape and quality of the final weld, dictating susceptibility to blowouts and porosity. Titanium, for example, is extremely susceptible to porosity when welded in anything other than an argon or vacuum environment. Copper, already very reflective, tends to exhibit high rates of material ejection from the melt pool when laser welded in standard atmospheric conditions.

These limitations can be overcome with optimisation of process parameters, narrower focal spots for reflective materials and copious inert shielding gas for porosity-prone materials, but these mitigations have associated cost and risk.

Electron beam welding does not suffer from many of the limitations of laser but does suffer from its own unique drawbacks. One technology able to eliminate some of the limitations of standard laser welding, without suffering electron beam welding’s unique challenges, is laser welding in vacuum.

How is Vacuum Laser Welding Different to Conventional Laser Welding?

Laser welding in vacuum (LV) was first trialled in Japan in the 80s and recent (2010s) advances in laser technology have reignited academic and industrial interest.

The method is now seeing industrial uptake, providing benefits over both laser in atmosphere and electron beam in certain applications.

The process of laser welding in a vacuum changes several physical phenomena governing weld formation for the better, giving a weld often indistinguishable from an electron beam weld, which until now, was the gold standard for weld quality.

The end results of laser in vacuum, compared to atmospheric laser, are:

  • Increased penetration depth for the same power and speed,
  • Reduced root porosity and gas entrapment, and
  • Stabilised weld pool.

The penetration depth increase is caused by two factors: the dispersal of the vapour plume increasing laser coupling-in efficiency and the reduction in boiling point caused by the reduced pressure of vacuum. Of these, the boiling point reduction is the dominant factor affecting penetration, with less energy required to vaporise more metal and the ratio of vaporised to molten metal increased, the welds take on a parallel-sided form previously only seen in electron beam welding. The lack of a vapour plume, due to its dispersion in vacuum, leads to a reduction in spatter and less energetic melt pool flow.

Vacuum also facilitates degassing, allowing porosity-forming bubbles to escape the melt pool before solidifying into pores. These factors combine to produce a very high-quality weld, this gives vacuum laser welding parity with electron beam in terms of weld quality on many applications.

On the process side, a laser in vacuum system offers excellent safety as a vacuum chamber also acts as photon containment. With interlocks connected to the vacuum system, making a vacuum laser welder into a Class 1 laser system is easily achievable.

Figure 3. Vacuum laser welds into stainless steel, power 1-4kW, speed 1m/min.

What Can Vacuum Laser Offer Over Electron Beam?

Electron beam has some challenges familiar to suppliers and end-users in the field:

  • Magnetism susceptibility
  • X-ray proofing, and
  • Filament replacement.

A beam of electrons, as a collection of charged particles moving rapidly, is subject to the Lorentz force in the presence of a magnetic field.

This means that even a small residual magnetic field in workpiece or tooling can deflect an electron beam away from the joint during welding, this can lead to a frustrating search for the guilty component, with the machine inactive all the while.

A laser, as a collection of photons, is entirely unaffected by magnetic fields. X-ray generation when an electron beam strikes matter necessitates installation of heavy lead shielding along with regular testing to ensure the shielding is effective. Lasers require no such shielding, with the vacuum chamber sufficient to protect from any stray reflections.

Filament wear and replacement has an associated time cost, in high-volume production especially this can become expensive. The analogous process of replacement of a protective cover glass in a laser system takes a matter of seconds, compared to up to an hour for an electron beam filament replacement. The protective cover glass replacement brings us to one of the most pressing questions facing laser in vacuum.

What about window contamination?

Window contamination is one of the thorniest hurdles facing laser in vacuum. The laser must be coupled-in to the vacuum chamber by a transparent vacuum-holding window of very high optical clarity. When this window becomes contaminated with weld debris, it begins absorbing the laser beam’s energy. This has a very detrimental effect on the weld and will lead to out-of-tolerance welds very quickly if left unchecked.

CVE has developed multiple active and passive systems to protect the window from weld vapour, along with a contamination detection system and a rapid exchange mechanism. These systems allow CVE to develop robust, reliable, and cost-effective laser in vacuum processes for a wide range of applications.

Electron beam, laser in vacuum, or standard laser welding?

This question is dependent on many factors and is specific to application and the customer’s priorities. Each of the three technologies have their own strengths and weaknesses and will be more and less suited to your requirements.

Here at CVE, we will work with you to find which process gives the best results for your application; we’ll then build your desired machine!

Contact us for further information, we’re here to help.

Electron Beam Welding for Defence Applications

Introduction

Electron beam welding is a well-established welding process within the defence industry due to the high-quality output that the application requires. A variety of components, ranging from small to large and simple to complex, can be welded on CVE electron beam welders.

The characteristic electron beam weld has deep penetration, a narrow fusion zone, near parent metal strength, and is made in an inert atmosphere (vacuum).

The low heat input, typically 5% of that required for other fusion welding processes, implies a small disturbance of metal near the weld zone and a correspondingly small distortion of piece parts so that you can join finished components.

 

Contents:

1. Bomblet Tails

2. Aluminium Alloys

3. Titanium Components

4. CVE’s Computer Control System

5. Special Systems

6. Joint Finding Options

7. Beam Probing

Bomblet Tails

Electron beam welding solved the problem of high production manufacture of bomblet tails. The material is maraging steel, and it is welded in a low vacuum (10-2  to 10-3 mbar range).

After welding, the tines are spread out and then heat-treated and pulled back to a cylindrical shape by a retaining ring for close packing within the main bomb from which the bomblets are ejected in mid-air.

Initially, CVE investigated alternative production methods from a tube and sheet. CVE found that the tube method was too expensive and difficult. Therefore, welding from a sheet was preferred. Electron beam welding is the only viable joining method because of the large quantities involved and the need for a high integrity weld with the smallest weld bead and the least distortion.

After application development and pre-production development, CVE specified a machine based on standard units with a fast production cycle.

The floor-to-floor time is 17 seconds per component.

A principal requirement was the roundness of the final tail and this involved careful fixture design. The fixture had to retain the component in the correct shape. The fixture also had to be simple and quick to load and unload quickly within the 17-second cycle.

The fixture also had to be robust and capable of thousands of weekly operations with minimum downtime for cleaning or adjustment.

Defence components

Figure 1. Components include transducers, relays, and aneroid capsules.

Figure 2. As-welded bomblet tails.

Aluminium Alloys

High strength enclosures are manufactured in aluminium, utilising a combination of extrusions, CNC machining, and electron beam welding to provide a cost-effective manufacturing method.

Other examples of aluminium parts made by electron beam welding include missile cases, launchers, and armour piercing parts.

In some instances, it is possible to modify the mechanical properties within aluminium components by using a wire-feed system. An example is the local alloying of pistons around the piston ring groove.

Figure 3. High integrity and dimensional stability are important requirements for this product made in 6082 TF (T6).

Figure 4. A selection of aluminium parts.

Waveguides and antennae are also manufactured using electron beam welding. A cost-effective method of manufacture is to weld a combination of machined parts, forgings, and extrusions. By this means, it is also possible to produce parts that cannot be fabricated viably by any other welding technique.

The impracticality of forging a one-piece structure led to the concept of fabrication using electron beam welding. Electron beam welding allows you to use simpler forgings and complete practically all machining operations before assembly.

Below is a typical system for welding aluminium parts. The system may be operated in either a high or low vacuum, and the switch mode power supply is ideally suited to the deep welding of aluminium alloys. It is a CW model with a 60kV, 15kW electron beam column and switch-mode power supply. The chamber is a 1-metre cube with CNC controlled X-Y worktable with an internal rotary tilt table and run-out platform.

 

Defence components

Figure 5. One-piece structures.

Figure 6. CVE’s CW model of electron beam welding system.

Titanium Components

Examples of titanium parts manufactured by electron beam welding include fuel propellant tanks.

Electron beam welding is used to fabricate a rigid but lightweight rotor in Titanium alloy 685.

Minimum heat input assures dimensional stability, and the close control available on weld geometry means that post-weld machining is applied only to end flanges and seal diameters.

Our XW range of electron beam welders include chamber sizes up to 5000 x 3000 x 3000mm and up to 30kW beam power at 150kV. CNC controlled work handling equipment includes an X-Y table, run-out platform, rotary tilt table, and horizontal rotary table.

Figure 7. Lightweight rotor in Titanium alloy 685.

Figure 8. CVE’s XW model of electron beam welding system.

CVE's Computer Control System

The human-machine interface (HMI) includes a PC (either industrial touch-screen or keyboard & mouse) to provide a fully integrated system for controlling the beam parameters and mechanical movement. To assist the operator during set-up, CVE provides a dynamic change function.

Since the computer system monitors the key process parameters, you can use it for data logging. Software options are available for quality assurance (QA) monitoring and reporting. The QA package allows viewing of historical weld data automatically recorded. The system can display the data in a graphical form. The user may specify which parameters and timescale is displayed. You can read values from the graph and dynamically adjust the scaling.

You can save areas of particular interest a file in a format compatible with Microsoft Excel and graphically display real-time data. All beam parameters and vacuum levels are available. A record of the last weld performed can be displayed and printed. It shows the demanded values of all beam parameters and the variance from these values during the weld. You can cross-reference this information against the historical graph.

A man in front of a HMI operating a CVE electron beam welder

Figure 9. CVE’s HMI computer control system.

Special Systems

Special systems are normally designed for maximum production output featuring:

  • Small chambers – no larger than necessary to hold one component
  • Fast evacuation – very large pumps, often low vacuum
  • Rapid work movement – component positioned in the chamber and manipulated very quickly
  • Complete production lines – can incorporate washers, dryers, demagnetisers, presses, automatic handling, measuring and testing equipment
Joint Finding Options

Teach and Replay

This option is useful with components that have non-linear or varying weld joints and require a CNC control function.

 

Joint Finding

This option assists the operator by automatically finding the joint using back scattered electrons and a detector mounted in the top of the chamber. It is useful where components have multiple weld joints with minor dimensional differences between individual parts.

 

Seam Tracking

Seam tracking can incorporate joint finding plus a teach and replay function described above to follow the joint. It is useful for large rotary welds to compensate for run-out of the weld joint. Special software however is required to follow the joint in real time and the joint requires special preparation to be “seen” by the system. In this mode the end user must be prepared to trust the system to take over the tracking and welding of a joint automatically in real time.

Beam Probing

Electron beam welding is widely applied to high-value components and before welding, the operator must be confident that the equipment will produce the best quality weld. Reproducibility and consistency of the weld are also extremely important.

Beam probing techniques are often used as a QA method prior to welding to ensure the equipment will produce the desired quality weld. Whilst welding test pieces can confirm good beam quality the process is time-consuming and the results, if not acceptable, are difficult to interpret in terms of changes to the machine setup that may be required.

The design is based on existing proven equipment developed by TWI.

Figure 10. Beam probing system.

Electron Beam vs Laser Welding

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.

 

Overview

  1. What is the difference between electron beam and laser welding?
  2. Vacuum environment
  3. Shielding gas
  4. Component size
  5. Welding speed
  6. Weld quality
  7. Single pass welding of thick sections
  8. Automated process
  9. Wearing components
  10. Power efficiency
  11. Cost comparison
  12. Turnkey solutions
What is the Difference Between Electron Beam and Laser Welding?

EB 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. Many have seen Star Wars, James Bond, and a host of other hi-tech sci-fi films that have been present on our screens over many years. Culture, coupled with the high profile many respected institutions have been putting forward, has unfortunately meant that the electron beam process has taken a back seat.

Vacuum Environment

EBW 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

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.

Component Size

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.

Welding Speed

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.

Weld Quality

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.

Single Pass Welding of Thick Sections

Electron beam welding in a vacuum can achieve 20mm penetration in stainless steel when using 6kW beam power at 60kV, achieving up to 300mm thicknesses can in a single pass.

Laser welding with shielding gas can achieve approximately 1kW per mm depth of weld in steel. However, limited availability and high cost of high-power laser systems is a factor.

Automated Process

Electron beam welding can be highly automated with the evacuation time of the chamber in a few seconds. A typical cycle time in the automotive industry is 40 seconds per component. But time is dependent upon the length and complexity of the weld.

Laser welding can also be highly automated with high production rates, in addition to there being no waiting time for chamber evacuation. Beam splitting and beam sharing are also possible.

Wearing Components

The main wearing component within the electron beam welding process is the filament. Metal vapours can deposit on the viewing prism, but this has no effect on weld characteristics, and you can clean the prism.

During laser welding, a metal vapour that the welding process produces can coat the optical devices such as mirrors and lenses, leading to a drop in beam power.

Power Efficiency

Electron beam welding is a very efficient process, typically converting 85% of electrical power.

Laser welding typically converts up to 40% when using modern fibre and disc lasers.

Cost Comparison

Electron beam welding is more expensive than Tungsten inert gas (TIG) and metal inert gas (MIG) welding.

Laser welding is also more expensive than TIG and MIG, with prices increasing steeply with increasing power.

Turnkey Solutions

Electron beam systems include a chamber, fully automatic vacuum system, work handling, and control system.

Laser welding usually requires a systems integrator to provide an integrated solution, as the laser source does not include a control system or work manipulation.

Conclusion

The best process to use, electron beam vs laser welding, is often dependent on the given welding application. If you are not sure which system is best for your application, please get in touch! Our machines are built to order and manufactured at our Cambridge Headquarters. With 60-years of process know-how in providing turnkey solutions, we can find the right solution for your application.

Electron Beam Welding for Aero Engine Applications

Introduction

The aero-engine industry has taken maximum advantage of the attributes of electron beam welding, the design of many components is based on its application.

The industry requires fabrications from various materials that are often difficult to weld by other methods such as forgings, pressings, or castings, often in a fully machined state. Although the finished fabrications may be complex, they will invariably be from relatively simple constituent parts. You can achieve lightweight yet rigid assemblies economically from the most appropriate materials.

You can perform electron beam welding reliably and repeatedly using established parameters and techniques that you can readily set up on a machine, even for small batches or one-off production.

Early Applications – Stator Blades

An early application within the aero engine industry was the welding of stator blades. The individual blades are cast in a range of steel or nickel-based alloys and are typically heat- and/or corrosion-resistant. The blade platforms also have varying sections, and there is a need to maintain close dimensional tolerances. Therefore, the range of joining methods that meet all criteria are strictly limited. The high-voltage beam of electrons is particularly successful in this type of application, where the thickness of the section may vary, yet throughout the progressive fusion, you can use the same weld parameters.

Fixtures are designed to accommodate several assemblies depending on component size. During the evacuation of the work chamber, the first joint is brought into view. As soon as the system reaches the correct pressure level, that joint is welded, and the X-Y table is indexed to the next joint. With several welds produced at each evacuation cycle, the total floor-to-floor time per weld may be less than 1 minute. Alternatively, a different approach would be to weld the complete ring in one evacuation cycle.

The welding procedure for each joint between blade platforms requires four weld passes: tack and finish weld for the outer platform, tack weld, and finish weld for the inner platform. Each weld pass requires a different set of beam settings and a different pattern of movement of the workpiece manipulator. Because of the complexity of the total weld programme, machines for this application incorporate teach-and-replay CNC, whereby the operator first teaches the system each of the subroutines for the four weld passes. He next teaches the system the angular position of each joint in a sequence that distributes the heat to minimise any possible distortion. From this point, the operator has only to initiate the welding cycle and for the machine to playback the complete sequence, with the operator taking on only a supervisory role.

 

Figure 1. Nickel-based alloy turbine blade.

Repair and Salvage

An equally important application for electron beam welding in the aero-engine industry is repair and salvage.

The general wear and tear on components within the arduous environment of the combustion gases, the strain on materials operating at high loads, often at high temperatures, create a continuous need for replacements.

High costs and long lead times are inevitable, but repair schemes can ensure a speedy, relatively low-cost turnaround of damaged or worn items. Because of the potential savings, most of the world’s airlines have installed their engine overhaul facilities and many of these incorporate electron beam welding. Repair schemes based on electron beam welding have approval for many components for both civil and military engines.

The welds are produced in a variety of materials and frequently in areas where access is limited. There is the added problem that, whilst in new parts, it is possible to ensure sufficient material to provide for any minor distortion; in repair work, you must base the scheme on the finished dimensions of the component you are repairing.

An interesting aspect of electron beam welding is its ability to weld together certain dissimilar metal combinations. This feature has been used within the industry to its advantage in several repair and salvage schemes where the added-on part has been produced in a material able to achieve a longer operational life than the original.

Figures 2 and 3. Nickel-based alloy turbine blade.

Electron Beam Welding of Stainless Steels

Introduction

This case study explores electron beam (EB) welding of stainless steels, including weld characteristics, joint design considerations, and examples of welded stainless steel components.

 

Contents:

1. Conventional Electron Beam Welding

2. Characteristics of an Electron Beam Weld

3. Joint Design Considerations

4. Welding Stainless Steels

5. Practical Examples

6. Industry Adoption

7. Conclusion

1. Conventional Electron Beam Welding

Electron beam welding uses a stream of finely focussed electrons to melt and fuse joint surfaces.  It is a contactless and reactionless process, as there are no forces engendered in the workpiece by the impinging electron beam, even though the concentrated energy density is very high.  Electron beam welding principles and some aspects of the technology, which permits intricate and complex fabrications in various materials and material combinations, are discussed below.

A conventional electron beam welding machine, as shown in Figure 1, consists essentially of a device for producing a focussed beam of electrons (an electron beam column) mounted on, or in, an evacuated chamber that contains devices for holding and moving a workpiece.

Electrons are generated and accelerated in the electron beam column to form a long, fine beam moving at a very high velocity. The magnetic lens then focuses the beam to produce an intense concentration of energy that can penetrate deeply into the metal.  The deflection coils, situated below the focus coil, move the electron beam in circles or more complex patterns for fusion zone improvement when supplied by appropriate voltages and waveforms. The electron beam travels through the abutting surfaces, and the joint surfaces are then progressively fused – creating a weld.

The specification and combination of weld parameters determine the maximum material thickness. The weld parameters, all of which are readily adjustable, are accelerating voltage, beam current, beam focus, and transverse speed.

The high heat intensity of electron beam welding results in a very narrow fusion zone with minimal distortion (Figure 2), so it is possible to weld machined components in the finished condition.

Figure 1. Schematic diagram of an electron beam welding machine.

Figure 2. Cross section of 75mm thick stainless steel alloys electron beam welded in a single pass wrought (L) and cast (R).

2. Characteristics of an Electron Beam Weld

The process results in high-quality welds associated with electronic control. This precise control of the beam allied to accurate manipulation of the workpiece provides a welding process that is readily capable of being fully automated.

CVE design systems to meet requirements with work chamber and work handling systems to suit product size and throughput. Selection of high vacuum (10-4 mbar) or partial vacuum systems (10-2 mbar) depends upon weld requirements.

The control system is also dependent upon production requirements and is fully computer-controlled. Figure 3 shows a typical medium-size chamber on a CVE electron beam welding machine.

Figure 3. CVE electron beam welding machine with a medium-sized chamber.

3. Joint Design Considerations

There are several aspects to consider when designing joints for the electron beam welding process. The joint must be satisfactorily strong in service and capable of being consistently produced in the quantities and the requisite quality desired. A reliable and simple inspection method is also desirable.

A designer will be disposed towards the electron beam process when there is a requirement for EB’s unique characteristics of a deep penetration weld and low total heat input. However, it is important to note the metallurgical factors to attain satisfactory quality. For instance, you should avoid welds that only partially penetrate, as these are prone to root porosity even when using beam deflection. A weld is usually stipulated to be of full penetration with a good sized under bead (in the context of the piece part dimensions), and as such, it has the merit of being easy to inspect.

There are advantages to be gained from specifying the simplest weld shapes since remote handling is an unavoidable feature of the electron beam welding process. The component must be fixtured and moved under the electron beam, as even though you can build in an extremely complex series of motions, simple tooling motions contribute to consistent and accurate alignment in the long term.

4. Welding Stainless Steel

So far as electron beam welding is concerned, high chromium content stainless steels, noted for their corrosion and temperature resistance, can be briefly categorised as the below.

 

Austenitic Steels

The ‘300’ series of steels are all readily welded by the electron beam process, exhibiting near parent metal strength and fusion zones free from cracks and porosity. The inert atmosphere of electron beam welding ensures an excellent piece part appearance after welding.

 

Ferritic Steels

These magnetic grades with a chromium content of 17-20% are not ideal for the electron beam process. So, they may require nickel addition to the fusion zone and/or pre or post-weld heat treatment to achieve acceptable joints.

 

Martensitic Steels

You can satisfactorily weld annealed material, although a tendency to solidification voids and root defects typically requires parameter selection. Some martensitic steels have high carbon content, and this is detrimental to good welding performance. Precipitation hardening stainless steels of the martensitic type have good weldability but require ageing to develop parent metal properties in the weld zone.

 

Duplex and Super Duplex Stainless Steels

Combining the optimum properties of both the ferritic and austenitic steels, these types are reported to have good weldability without preheating or post-weld heat treatment. The addition of nickel shim may also be useful to achieve the desired ratio of austenite to ferrite for corrosion protection.

5. Practical Examples

The following examples illustrate the remarkable versatility of the electron beam welding process in a range of weld penetrations and material combinations.

Figure 4 illustrates a range of small components fabricated using electron beam welding.

An application that exploits the small electron beam cross-section is the joining of precision bellows of stainless steel to a tapered coupling.

The fixturing required before welding is of the lightest construction as no forces are involved in the electron beam process. Other examples include relays, transducers, aneroid capsules, and diaphragms.

Figure 4. Stainless steel electron beam welded components.

 

Figure 5 shows a fuel spray nozzle for a gas turbine engine.

These nozzles are circumferentially disposed around the engine combustion chamber and spray atomised fuel at high pressure into the high-temperature burning zone.

The exit end of the nozzle is an assembly of Inconel 625 and Hastelloy, and the support stem is type 347 stainless steel.

Although Inconel may be prone to weld cracking, performing the electron beam process at a relatively slow speed ensures good mixing in the fusion zone and produces a crack-free joint.

 

Figure 5. Fuel spray nozzle.

6. Industry Adoption

The nuclear industry was the first to adopt electron beam welding of stainless steels on a large scale to exploit the properties of a small heat-affected zone, low incidence of defects, and near parent metal strength, to fabricate fuel and coolant containers of all sizes. The tubular fabrication in austenitic stainless steel type 304L shown above contains three pieces – a hexagonal base welded to a tube with the tube itself capped by a nosepiece. The whole assembly is some 2 m in length.

The requirement is for a straight assembly without significant drooping due to contraction distortion. The solution adopted involved pre-weld tacking at low power followed by 120° of full weld depth and completed by a full-circumference weld of full-depth commenced on the opposite side to the 120° of pre-weld. The various distortions engendered by this regime cancelled each other to produce straight assemblies. The weld fusion zone was made at a sufficient level of power to over-penetrate and produce a heavy consolidated internal bead. This process was sufficiently large to be machined to parent metal diameter and give a smooth bore.

7. Conclusion

In conclusion, the electron beam welding process has the merits of:

  • Deep penetration
  • Narrow fusion zone of controllable shape
  • Inert atmosphere (vacuum)
  • Near parent metal strength
  • Single-pass capability at high speed
  • Autogeny, no filler metal is required
  • Small heat input, low distortion

It is truly a high-quality process for joining high-quality materials.

If you are not sure which system is right for your application, please get in touch! Our machines are built and manufactured at our Cambridge Headquarters. With 60-years of process know-how in providing turn-key solutions, we can find the right solution for your application.

Utilising Electron Beams for Design Solutions

Overview

Cambridge Vacuum Engineering (CVE) has commissioned a unique electron beam system for Tokamak Energy Ltd, who will use the machine to find design solutions for divertor components and progress their pioneering work towards making commercial fusion energy a reality.

Fusion Energy

Based in Oxfordshire, UK, Tokamak Energy is striving to deliver a new source of clean energy to the world by utilising the potential of fusion power.

Fusion power is harnessed from the joining of small atomic nuclei to form larger ones, resulting in a release of energy. This is the same process that fuels the Sun, and Tokamak Energy want to recreate it here on Earth in their compact spherical tokamaks.  It is a scalable energy solution that is safe, clean, and plentiful.

Material Properties

As part of the manufacturing process, Tokamak Energy needs to find the best-suited material to use inside the divertor. The divertor is the exhaust system that extracts unwanted particles from the plasma inside of the Tokamak.

To achieve this, they required a solution to test and find materials and coolant configurations which optimise performance under high heat fluxes.

Advanced Electron Beam Technology

CVE designed a unique electron beam system that fit this requirement – a 60kV, 6kW machine able to produce 100mA of beam power.

The electron beam will rapidly deflect over a 30mm2 target,  simulating the heat loads on various components that Tokamak Energy will use in their tokamak.

These prototype tests will then be analysed using thermocouples and an infrared camera.

CVE’s rapid deflection technology and custom pattern generator make this process easier, allowing the beam to fire over the target area in the user’s defined pattern – at speeds of up to 10kHz. Including replicating the quasi-gaussian profile of the heat flux on divertor targets.

Typically, CVE design and manufacture electron beam machines for welding applications, so working on this project provided an exciting opportunity for knowledge transfer and innovation in a new field.

Tokamak Energy hopes to use their spherical Tokamak to form the basis of the commercial module that will deliver electricity into the grid.  You can find out more about their ground-breaking work on their website.

An electron beam welding machine custom-built by CVE for Tokamak Energy for use in the nuclear industry and nuclear fusion applications

Figure 1. Custom-built electron
beam system.

An Introduction to Electron Beam Welding

How Does Electron Beam Welding Work?

Electron beam welding works by generating high power electron beams that pass through an anode onto the workpiece.

 

Overview

  1. What is electron beam welding?
  2. How does electron beam welding work?
  3. Components of an electron gun
  4. How is the electron beam generated?
  5. How is the electron beam controlled?
  6. Electron beam welding machine schematic diagram
What is Electron Beam Welding?

Electron beam welding (EBW) is a fusion welding process that uses a high energy electron beam to join metals together, with a wide range of applications in many industries.

How Does Electron Beam Welding Work?

An electron beam welding machine consists of an electron gun, which is a device for producing a focused beam of high-speed electrons with velocities of between 0.3 and 0.7 times the speed of light.

The electron gun is normally mounted on, or in, a high vacuum chamber that contains tooling used for holding and moving a workpiece.

The electron beam passes through the anode and on towards the workpiece, using a focusing lens to focus the beam and achieve sufficient power density to weld the two metals.

This creates a high weld quality, with deep penetration and a narrow fusion zone.

Components of an Electron Gun

An electron beam is usually formed by employing a triode-style electron gun that consists of:

  • A cathode (also known as a filament)
  • A heated source (emitter) of electrons that is maintained at a high negative potential
  • A grid cup (also known as a bias cup)
  • A specially shaped electrode that can be negatively biased to the hot cathode emitter
  • An anode, a ground potential electrode through which the electron flow passes in the form of a collimated beam
How is the electron beam generated?

The hot cathode, or filament, is made from a high emission material such as tungsten or tantalum, with tungsten being the most common. A heating current is passed through to a filament that causes it to emit electrons. These are accelerated from the filament to the anode by applying a high negative voltage to the filament.

How is the electron beam controlled?

A control electrode, or grid, is situated close to the filament and is held at a negative potential in respect to it. As the voltage potential between the filament and grid is reduced, electrons are allowed to escape. These are then attracted to the anode, which has more positive potential than the electrons, or in the case of electron beam welding, the anode has a hole in its centre which allows the electrons to pass through the anode as a stream, and on towards the workpiece.

As the electrons travel to the workpiece, they pass through a focus coil or focusing lens (electromagnetic lens) so that the beam can be focused to a fine point to achieve sufficient power density to weld metals. The electron beam will also pass through a deflection coil (electromagnetic) at the bottom of the column which can manipulate the beam at very high speeds.

The addition of some hardware enables functions such as backscattered imaging, joint finding, real-time seam tracking, automatic beam alignment, engraving, beam splitting and Surfi-Sculpt™*.

Electron Beam Welding Machine Schematic Diagram

A schematic diagram of an electron beam welding machine with labels

Conclusion

Find out more about electron beam welding on our electron beam welding page, or watch our CGI animation video.

*Surfi-Sculpt is a trade mark of TWI Ltd.

Impact of Industry 4.0 in Automotive Manufacturing

What is Industry 4.0?

Industry 4.0, or the fourth industrial revolution, is the transition towards using artificial intelligence, cyber-physical systems, and other digital technologies in manufacturing processes and business models.

An industrial revolution is a transition within the manufacturing industry to a new production process.

The first industrial revolution saw the advent of mass production, utilising water and steam power, the second industrial revolution built on this by introducing electricity and assembly lines, with the third industrial revolution implementing computers and some automation practices.

Industry 4.0, first coined in the early 2010s, builds on all of the previous industrial revolutions by transforming existing manufacturing practices and factories into so-called ‘smart factories’ or ‘factories of the future.’

The Automotive Industry and Industry 4.0

Much of the automotive industry is being driven by the implementation of industry 4.0 technology: such as additive manufacturing (also known as 3D printing), internet of things (IoT), big data or smart machines – resulting in greater efficiency, traceability, and safety throughout the entire supply chain.

This has extended to the industrial internet of things (IIoT), which refers to networks of industrial devices that are all connected to the internet, collecting, exchanging, and analysing new insights.

Below we have explored some areas in which industry 4.0 has impacted the automotive industry and the production of motor vehicles – and how CVE’s welding machines and systems serve these requirements – consistently ensuring optimal production.

Manufacturing Execution Systems (MES)

Manufacturing execution systems (MES) are computerised systems used in manufacturing processes to monitor the transformation of materials throughout their production process.  An MES allows you to track parts, providing traceability throughout the entire product lifecycle and the ability to use big data to improve decision-making processes in the real-world.

This is an effective way to track parts from raw material to a component to use in commercial vehicles.

DMX code on automotive component 1

Figure 1 and 2: Example automotive components with DMX code engraving made using a CVE EB welding machine.

High-Speed Data Capture

CVE’s electron beam and laser welding machines can be enhanced with our high-speed data capture.

A dedicated PC integrates into the welder, enabling high-speed and high-channel-count logging of welding parameters: up to 3m samples per section (single channel), with counts up to 80 channels.

Other benefits include:

  • Capture up to 32 channels of high-resolution data up to 20,000 times per second
  • Data log file and report for traceability
  • Intuitive review programme providing detailed analysis of welds
  • User-definable channels are available, including thermocouples and strain gauges

The data capture logs every weld in its own file for easy review – you can also generate a serial weld report for traceability, with a review programme for easy data review and real-time data export capability to Excel or CSV.

Electrification and Electric Vehicles

A shunt resistor measures electrical current by calculating the voltage drop over the resistor.

The main application for shunts is within the battery management systems of most type of automobiles: including standard fuel, hybrid, and electric vehicles. Shunt resistors ensure the batteries are performing optimally and prolong battery life.

With the global trend in the automotive market towards electrification, the demand for battery and battery-related products has never been greater.

CVE has experience in welding machines for this application and below you can find an example weld of material used for shunt resistors in electric vehicles.

Copper manganin strip welded cross section

Figure 3: Weld cross-section of copper manganin for electric vehicle shunt resistors.

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