New innovations have unlocked new applications for electron beam welding
The manufacturing industry is spoilt for choice when it comes to welding techniques. Favourite methods such as submerged arc welding (SAW), flux core arc welding (FCAW) and shielded metal arc welding (SMAW or ‘stick’) have come to define the industry standard.
However, they come with a number of drawbacks. Consumable filler wires and shielding gases increase running costs while multi-pass welds can increase defect propensity and create weld flaws and speeds, while safety of use varies between techniques.
Electron beam (EB) welding escapes a number of these drawbacks. A beam of electrons transfers kinetic energy to two pieces of metal, transforming into heat energy upon impact. Once the metal is molten, the two pieces flow together, creating a metallurgically sound weld.
However, EB welding suffers from a major drawback – it must be performed in a vacuum in order to prevent the electron beam from dissipating, as well as preventing the formation of metal oxides, which could prevent the pieces of metal forming an adequate join.
This puts a limit on what EB welding can be applied to. It is expensive, requiring the installation of a vacuum chamber, which also limits where the welding takes place. Depending on the size of the chamber, it also limits the size of the components that can be welded.
However, Cambridge Vacuum Engineering (CVE), a UK-based EB welding system and vacuum furnace manufacturer, in association with The Welding Institute (TWI), has designed a portable and scaled-down EB welding system that mitigates some of the potential drawbacks with EB welding.
InnovOil spoke to CVE global development manager Grant Coghill about his company’s product, called EBFLOW.
“We’ve developed a local vacuum EB welding system that can be easily transported and operated on site and applied to structures significantly larger than can be accommodated in a traditional vacuum chamber,” Coghill said.
EBFLOW works by forming a local seal only around the area of the product being welded, instead of placing the entire component in a vacuum chamber. This means that EBFLOW can work on much larger products than EB welding could traditionally work on, as they do not have to be confined within a vacuum chamber.
“Using a system of sliding seals and precision handling enables fast longitudinal and circumferential welds on large work pieces. There is no filler wire, the weld is autogenous, it can be heat treated and the weld can be rendered metallurgically indistinguishable from the parent material,” Coghill added.
CVE designed a flexible sliding head to go around the electron gun, which produces the electron beam. A coarse vacuum is enabled at the weld/head seal interface and produces excellent welds of the highest quality.
Coghill said: “With traditional EB, it is the norm for industry to specify a very high vacuum in-chamber. However, we have around one millibar, which is sufficient and has been proven to work very successfully in a range of metals including steel, stainless steel, aluminium, titanium, etc.”
One millibar is roughly equivalent to a thousandth of the atmospheric pressure found at sea level, or the same atmospheric pressure found at the top of Mount Everest.
“What we’ve found is that we don’t need a very high vacuum to produce consistently sound welds, so the head allows us to give that vacuum level while still giving excellent weld properties,” Coghill added.
“The EBFLOW system has been manufactured to be very robust, which makes it much more able to work in a shop floor environment, shipbuilding, offshore, heavy engineering, etc.”
Submerged arc welding’s speed, versatility, safety and its ability to produce a high-quality weld has seen it established as an industry standard. EBFLOW will need to deliver some impressive results if it wants to compete with it.
“The submerged arc welding process on something 100 mm thick would need approximately 90 passes, which means 90 smaller runs one on top of each other,” Coghill said. “With the electron beam process, because it isn’t lots of little runs, it’s one big run, this substantially reduces weld completion time scales.
“That means, typically, the EBFLOW electron beam out of chamber scenario gives you 20-30 times faster welding speeds than the existing SAW fastest method currently available.”
For a recent project, EBFLOW produced a circumferential weld around a steel pipe that was 1,700 mm in diameter (5,300 mm linear length) in just 55 minutes. When compared with other common welding techniques, such as SAW, which can do it in around 14 hours, FCAW in 60 hours and stick welding in 80 hours, EBFLOW offers a massive time saving.
“With the utilisation of our product, we can show that in some cases an increase in production output on the same manufacturing/factory footprint of over 400%, contributing to a gross margin increase of up to 20% and associated reduction in final cost of the component leaving the factory. EBFLOW enables phenomenal cost savings and a massive increase in productivity compared to SAW.”
The big question then is what kind of a price does EBFLOW deliver these results at?
“Our pricing, typically, we’re looking at around GBP4 million (US$5.3 million) for a basic set up,” Coghill said.
“However, that is a big cost for most companies, but your return on investment (ROI) is a figure that’s normally unheard of. As an example, because of the speed time increases and the reduction in cost, capital equipment, which does usually cost in the six-figure-plus scenario, would be signed off by a financial director or a CEO based upon a three-to-five-year ROI ‘rule’.”
“With EBFLOW, ROI’s vary dependent upon specific applications; worse case would be a year to 16 months, but typically you’re looking at just six to eight months. So, the return on investment timeframe for a piece of capital equipment that a CEO or a financial director would normally OK for three to five years is reduced massively.”
Electron beam welding also produces radiation, which means that shielding has to be used. “Our machines go through rigorous safety checks prior to leaving the factory and prior to use on-site. To put it into perspective, radiation generated from EBFLOW is less than the background radiation surrounding us which we are all exposed to daily, therefore EBFLOW is very safe in this regard,” Coghill said.
At present, EBFLOW is mostly designed for handling longitudinal and circumferential welds. This means that there are specific tasks it is better at handling than others.
“Heavy wall thickness pressure vessels are one of the main targets because it’s a relatively simple application,” Coghill said. “The thickness of the weld joints is ideal for EBFLOW.”
He added that EBFLOW could be used on a number of other projects, such as civil engineering, shipbuilding, offshore oil and gas, renewable energy, etc. The benefit of EBFLOW really kicks in at joining metals with thicknesses greater than around 40 mm.
EBFLOW’s portability is another important feature, which opens up a number of options previously unavailable to traditional EB welding, due to the supporting infrastructure it requires.
CVE has also begun looking at ways to improve EBFLOW and expand it beyond its core capabilities.
“We’re already created a working prototype to weld what are called nozzle welds on pressure vessels,” said Coghill.