Built in Austria by robots

Responsible for the fabrication of all Liebherr crawlers up to the 300t capacity class, the facility is fast approaching its 35th anniversary this September, and as times are changing so has the focus.

Accounting for 32% of Liebherr-Werk Nenzing’s turnover last year, along with duty-cycle, piling and drilling rigs, crawler cranes have become an important staple of the business there.

For larger crawlers above 300t Liebherr Ehingen handles the fabrication, partly due to the size of the manufacturing facilities there, but also because Nenzing’s history of manufacturing pure lifting cranes is markedly shorter than at Ehingen.

Head of marketing at Liebherr Nenzing, Wolfgang Pfister explains: “The reason for this is that Ehingen has always manufactured lift cranes, but we started with duty cycle crawler cranes for dynamic applications, so exploration, demolition, recycling, material handling, foundation works, etc.

“From a market point of view there wasn’t really a need from Ehingen’s customer base to go into smaller sizes, and when our customers at that time were asking for pure lift cranes we didn’t have them [in smaller capacities]. We were selling a duty cycle machine as a lift crane.

“A duty cycle machine is a workhorse, it has high engine power, high winch power. It’s made for dynamic applications. That’s why we came up with a new product line of pure lift cranes in a [capacity] range where Ehingen didn’t have any offering and that’s why we came up with [the smaller capacity cranes of] the LR series.”

The largest crane Nenzing manufactures, the LR 1300, is, according to Liebherr, one of the most popular cranes in the world in the 300t capacity class, with roughly 50% of the market share for mid-sized crawler cranes in 2010.

Liebherr attributes the crane’s success to its placement near the top of the mid-size capacity range while still retaining the roadability and setup advantages of a smaller taxi crane.

Despite the steep drop in demand across the world market for crawler cranes in 2009, a slow-blossoming recovery has already seen Nenzing’s crawler sales increase during the first quarter of 2011.

With Nenzing’s crawler segment’s core European market recovering, and prospects in Australia and Asia rapidly increasing to cumulatively rival Europe’s importance, Liebherr Nenzing has almost completed a programme of upgrades and expansions to position themselves for the upswing.

At Liebherr’s Rostock facility in Germany, which falls under the managerial control of Liebherr-MCCtec at Nenzing along with Liebherr’s plant in Sunderland, UK, the final third of a 700m-long production hall is being constructed for offshore crane manufacture.

And having already identified the trend towards mid-sized and larger crawlers, Nenzing intends to boost it’s production capacity with a new production line enhanced by the presence of robotic welding machines.

Liebherr Nenzing’s newest production hall, built in 2007, provides 12,160sq m of factory floor space for the production of lattice boom sections.

The new production hall makes use of handling and welding robots to assist the manufacture of the main boom sections, a first for lattice boom crawler production at Liebherr, and a system they believe is industry-leading for production methods.

Pfister says: “It’s really new for the crane industry, because no crane manufacturer is manufacturing boom sections the way we are doing it.

“Robot technology is nothing new to the industry, but the way it is done from a logistics point of view, nobody is doing it to such an extent as a closed circuit, it’s a full entity working on its own.”

However the closest example of a similar system is the robotic welding production line at Liebherr’s Pamplona facility where their tower crane line is manufactured.

Liebherr Nenzing managing director, Gerhard Frainer, explains: “Our sister company in Pamplona, for tower crane manufacturing, there they use robots. They have a very different boom system but they use robots for welding boom sections for tower cranes.

“Our lattice booms are all manufactured out of tubes unlike tower cranes. The main tubes and the diagonals they are all round tubes, so that makes the welding very complicated. As one tube is welded onto the next tube it’s a very special profile, and in the tower crane products you don’t have this.

“So in the Liebherr Group we are the first to do that for this type of lattice boom crane.”

The production hall at Nenzing only requires four people working to manage the robotic assembly process and achieve full capacity at any one time.

But along with the reduction in assembly line technicians needed to achieve full productivity, the main benefit is much more impressive.

Frainer says: “Production time itself is significantly shorter; from putting the production order into the system until delivery it does not take more than two weeks, and that’s the significant advantage,” says Frainer.

“One of the main driving issues behind the investment is that we have whatever boom configuration we have sold and which we need to deliver manufactured within two weeks.”

A production manager runs the operation mainly from the control centre in the centre of the hall, only leaving it to load the metal tubes, from which the lacing will be cut, onto the initial section of the production line.

Along with the production manager and one control room manager, two technicians are needed to use the plasma cutters that cut each tube into the correct sizes.

Firstly 6t loads of 12m-long metal tubing are moved into the facility and placed in racks by overhead crane, ready for selection as needed.

A worker will place plastic caps over each end of each tube to ensure that no material gets inside the tube during sandblasting prior to welding.

Once a production order has been received identifying how many tubes of a particular diameter are needed, the production manager can select the number of tubes and load them onto the production line, with re-stocking taking place automatically.

From here the system takes over and conveys the tubes through a cleaning machine that removes excess debris from the outside of each tube before it moves through the sandblaster.

After sandblasting, the tubes reach the plasma cutters where different diameters are cut into different sizes according to the boom section being constructed.

At this point the cut tubes are moved by forklift to one of two production lines for the next part of the process. If space is limited due to tubing coming through faster than it can be cut, the automated system detects the available floor space and shuts down if it is below pre-defined parameters.

The forklift will either take the tubing to the loading zone of the robotic welding area, or if a boom head or foot section is being constructed this is welded manually in a separate production line running alongside the robotic line.

Manual welding is still needed at this hall to ensure the whole boom manufacture process remains inside the one hall.

All welding for the four corner tubes of the lattice boom, the chords, between which the lacing will be welded, are done on the manual production line. This is also the case for the boom head and foot sections, with finger and fork endings also welded on at this point.

For tubing placed at the start of the robotic welding area, once a worker initiates the programme—using an ID number uniquely assigned to that batch of tubes when they entered the hall—one of two handling robots in this area will select a tube and take it to a measuring machine.

After it has been measured to ensure it has the correct diameter and cut for use as lacing, that information is fed to the second handling robot. This robot then places the lacing in the position on the main boom— which already has finger and fork endings welded—indicated by the data received from the measuring machine.

One of the welding robots then measures its positioning to make sure it is correct before welding to fix the lacing in place.

Once the lacing is placed on one side of the boom, the boom is rotated 180° so the other side can be completed, before the procedure is repeated following a 90° turn and one more 180° rotation to complete placement of the lacing.

The constructed boom then goes through quality control before being painted, dried and finally lifted through an opening in the roof to the upper floor of the production facility for storage. Here the completed booms will remain until the time comes to lift them across into the dispatch area on to the back of a waiting truck to continue the crane’s fabrication.

This storage area while fairly spacious does not need to be. As Frainer explains, one of the benefits of using robotic assembly to halve lattice boom production time is that they can utilise ‘just-in-time’ manufacturing and cut a number of costs.

“We don’t have any storage issues anymore,” says Frainer. If you don’t have this flexibility you need to have each different type of boom section, and many of them, in stock, so it consumes a lot of open storage space and a lot of handling.

“Because it goes directly out of the building onto the lorry, there is no additional handling for storage, no internal transport, less handling damage risk, no transportation time, nothing like that, that has all disappeared.”