The KSK plant at Schwerte, part of the Vlassenroot group, has expanded its capacity for the production of mobile crane booms with the installation of a new LVD PPEB-H 2000t 14m press brake.

Vlassenroot is one of the world’s major manufacturers of critical components for mobile cranes and operates across four sites in Belgium, Germany and Poland. One of the strengths of the group is that it has all of its production processes in-house and can offer crane manufacturers a complete fully welded boom and chassis from one supplier.

In fact, the acquisition of KSK in 1999, which had extensive welding facilities, was driven by the demand from crane manufacturers for complete welded booms.

Production starts with high strength steel delivered to Vlassenroot’s Brussels plant where blanks for the formed components are laser cut. The Belgian plant forms some of the boom components that are required as unwelded profiles and ships the other blanks to Schwerte in Germany and Gliwice in Poland, where it produces smaller welded assemblies. The welded structures come together at Vlassenroot’s plant in Bochum, Germany, for final assembly and despatch to the customer.

“We have complete control of the whole process, from steel to welded boom section, and we are the only one in the world that can offer that,” says Ludwig Deckers, plant manager at Schwerte. “That gives us a lot of advantages and it gives the crane manufacturers a lot of advantages too.”

He adds that in recent years the strongest part of the market has been in cranes for the wind power sector, which puts Vlassenroot at an advantage because its LVD press brakes – two in Belgium and the one at Schwerte – give it the large-scale production capability to meet this demand.

“The largest crane we build parts for has a 500t capacity and the longest section we produce at Schwerte is 14.55m long. We supply all leading crane companies throughout the world, exporting to Europe, the US, Africa, Russia, China, Japan – there’s not a lot of competition in this business.”

Herr Deckers explains that the partnership with LVD goes back a number of years to the time when Vlassenroot only had conventional press brakes.

“Our first link with LVD came when we asked them to rebuild one of these as a CNC machine with new hydraulics and controls. It all went exceptionally smoothly so we asked them to rebuild all our press brakes. So when we needed new capacity in Belgium it was a natural step for us to go to them for new machines too. We now have two 2000t LVD PPEB 14m press brakes at our Belgian plant.

“We went to LVD for this new machine in Schwerte too because of the good experience we’d had with them and the service they provide.”

The new machines LVD built for Vlassenroot – and now KSK – were designed specifically to be the optimum configuration for crane boom forming in high strength steels. In fact, Vlassenroot gave LVD all of its component drawings and asked it to build a machine around them.

The latest machine includes a couple of further refinements. The first is a series of CNC pushers at the front of the machine that ensure the plate is firmly located on the back gauges.

“It was a hell of a job for the operators to push these long and heavy components up against the back gauges, so we asked LVD to come up with an automatic system rather than using manpower. It has worked very well,” says Herr Deckers.

The second special feature is a bottom die that can be adjusted in 10mm increments from 110mm up to 320mm. This is to allow KSK to cope with some of the very large bend radii required on the higher strength steels.

Bending these materials requires special expertise and the highest quality equipment says Mr Deckers.

“On a normal steel, to bend an angle of 90 degrees you may have to bend to 89 or 88 degrees to allow for springback. With the 1100 Newton tensile strength material we commonly bend you may have a springback of 30 degrees – so you have to bend to 60 degrees. So you need a lot of force to go into the die to bend the material.”

The stronger the material, the lighter and taller the crane builders can make their telescopic booms. There is currently talk of 1300 Newton or even 1600 Newton tensile strength steel in the future – but that would require designs and welding materials that have yet to be developed.

To form these extremely strong materials accurately, a number of factors have to be intrinsic to the design of the machine. The geometry is particularly important, and the frame must be carefully designed to ensure that the bending forces act through the centre line of the die. Crowning control is also extremely important to compensate for any deflection in the frame due to the forces being applied to the workpiece – if that is not accurate then the press brake will not be able to bend accurately along the length of the part. On the LVD machines, crowning is an automatic NC axis driven from the machine control.

“The bend accuracy is crucially important to us because of the requirements of the end product. Although we are making very large components – up to more than 14m long – the tolerances the customers are asking for are very tight. On a boom section 1.6m in diameter, the height and the width have to be within plus or minus 2mm on the welded fabrication. Otherwise, the telescopic boom sections won’t slide in and out properly,” says Herr Deckers.

“After only a few weeks of operating the new machine it has proved itself to be more accurate and more productive than the machine we had before. I didn’t expect such positive results so quickly.”