ESAB welding facility ‘breaks new ground’

ESAB’s flagship facility is claimed to break new ground in welding. Berenice Baker reports

When the radiation-proof doors roll down on the hybrid laser facility in ESAB’s Process Centre and visitors are invited to watch the searing glare over CCTV, you almost expect to hear Auric Goldfinger sneer: ‘No, Mr Bond, I expect you to die.’

The hybrid laser station is just one of the many manual, automated, mechanised and robotic welding stations at the Gothenburg, Sweden-based facility designed to trial new technology and processes and to replicate customers’ own operations to solve problems and educate professional welders. ESAB has a dozen similar facilities across the globe, with the UK’s based in Waltham Cross, Hertfordshire, but claims the Swedish version — open for less than a year — is the most advanced and comprehensive of its type.

ESAB’s Process Centre has more than 1,000 customers from the energy, transport and shipbuilding sectors, and the facility is divided accordingly, supported by 29 skilled welders and engineers including Karl Johansson, who boasts the unlikely accolade of Nordic welding champion after winning a competition. Its fastest-growing area is wind turbines.

The main welding types available are: MMA (manual metal arc), otherwise known as stick electrode; SAW (submerged arc welding) carried out through flux powder instead of using shielding gas; hybrid laser, which uses laser welding; MIG/MAG (metal inert gas/metal active gas); and robotic, which is MIG/MAG welding with a degree of automation. Friction-stir welding is also beginning to be more widely adopted. According to the company, the only types of welding ESAB does not support are spot welding, electron beam welding and explosion welding.

Jim Boot, global customer services manager, said: ‘We look at customers’ processes, procedures and materials and make them competitive. For example, when they move from manual to automatic welding, much of the time they don’t think about redesigning the product or the way it is made to increase the productivity and benefit from the process.’

For example, shipbuilders and manufacturers of chemical and drinks carriers need their containers made from high-strength steel but lined with non-toxic, non-corrosive stainless steel — a combination known as duplex stainless steel. Modern laser and MIG techniques provide full penetration, which minimises defects and reduces thickness to save material and time.

Sometimes it is bottlenecks in the process, not the product that causes problems. When a Swedish wind-tower manufacturer introduced a new painting machine, it moved the process bottleneck to the welding station, where the introduction of a two-wire weld speeded up the entire production time.

Inside the Process Centre, the technology can be considered in terms of increased complexity. One of the simplest is Railtrac, a semi-automatic process using flux-core wire fed into the arc. Flux core is a hollow wire with a non-conducting centre, meaning there is a higher current per square metre of the wire tip, giving a higher deposit rate. This can be used in a set-up called tandem twin, with two wires in each of two torches, which allows a lot of weld at one time. This is a solution for high-productivity environments such as wind-tower welding.

One of ESAB’s consumable solutions comes into play here: a self-adhesive ceramic strip that holds the two metal plates to be welded with a relatively large gap in between. It can be removed along with the slag when the weld has set.

At the next level is a strip-cladding station, a solution used for lining tanks, which can be built in sturdy mild steel and then have a layer of stainless steel added. A wide metallic strip is melted onto the surface using MIG/MAG torches. As it is very fluid when it melts, it is lined up with electro magnets, which keep it in place. It is carried out through a pile of flux powder, which can be mixed to customer specifications. Usually 25-35 different ingredients are used, out of a potential 3,500.

Next is robot welding, where ESAB has a tendon robot and a single MAG robot supplied by ABB and Automan that are used widely in customer support as single-wire gas-shielded MAG welding is used widely in ship building and remanufacture. Although moving from a solid wire to flux-cored wire can offer an extra 10 to 15 per cent increase in weld speed or thickness, the set-up demonstrates that an upgrade to two wires does not double the speed as the gas protection can not keep up with it.

Each wire has a separate power source, so the first can give a deep penetration and the second a nice finish. Each wire carries 800A and 32V, which give a 16kg/hr deposition rate, meaning it has to work with gravity — anything sideways or upside-down would cause the liquid metal to slide off.

Finally, the most advanced technology — the hybrid laser — combines laser and commercial MIG/MAG gas-shielded welding at the same spot. The laser produces a keyhole that penetrates deeply and the MIG/MAG fills it, giving a weld with a cross-section shaped like a drawing pin.

Pål Dyberg, deputy process and application manager, said: ‘It combines the benefits of both and goes some way to counteracting the disadvantages. Arc welding is cost-efficient, cheap and best for bridging gaps. Laser is fast but expensive and cannot bridge gaps. Hybrid is fast and can bridge gaps. The weld can be steered, but you can’t go too fancy as the arc has to follow the laser very closely.’

Heat deformation can occur in large welding jobs such as shipyard applications using commercial SAW. Hybrid laser goes some way towards reducing this. Although the machinery is considerably more expensive, it saves time and wasted materials spent straightening. Also, for a T-shaped join, fillet welds are traditionally carried out from two sides for strength, but the hybrid process only needs to be approached from one side due to the high penetration, increasing the speed of welding.

It is at this most advanced end of the Process Centre that ESAB’s engineers are looking at producing quantifiable quality measures that to date have been reliant on the expertise and experience of welders.

‘When welders talk about stability, it means different things,’ said Dyberg. ‘When there is a stable process, an experienced welder can hear the sound of the weld going right and feel the vibration in the gun.’

ESAB is using a high-speed film illuminated with a millisecond fixed-pulse laser, which shows the small droplets of solder created at the point of peak current. This method shows that the shielding gas used to prevent excessive oxidation can cause turbulence and spatter if it is set to flow too fast.

ESAB is also experimenting with including a microphone to record the welding process. By producing a graph showing the pulsed current, the corresponding voltage and the sound signal, a stable weld shows pulses at the same time.

If the system briefly short circuits, it manifests as a small vibration in the gun, traditionally felt by the welder. ESAB is now looking at including a sensor to detect the vibration in the torch.

Using all the resources at its disposal, ESAB is currently investigating a problem for a client using hybrid laser. Though the exact details are under wraps, aluminium with a difficult coating needs to be welded to another metal surface. ESAB’s Process Centre has just three days to solve the problem but, with the wealth of expertise under its roof, you wouldn’t bet against it.