Ask any manufacturer: the boom of an all-terrain crane is the single most complicated and finely-wrought part of the entire machine. Almost all booms are bent in complex oviform shapes; many use a pinning system to reduce tip loadings. A huge amount of effort goes into reducing boom weight to keep axle loadings below the magic sum of 12t per axle.
What may not be so well known is that many booms are made by sub-suppliers. All four of the major European mobile crane manufacturers – Grove, Liebherr, Tadano-Faun and Terex-Demag – buy booms for at least one of their current production models from Vlassenroot.
Liebherr Ehingen head of sales promotion Wolfgang Beringer says, “One main reason for us for outsourcing steel components to suppliers is the limited capacity in our works in Ehingen. In 2008 we produced almost 1,800 cranes; only a few years ago we manufactured less than 1,000 cranes per year. We would not be able to manufacture all the required steel components by ourselves. So another reason for outsourcing is that this gives us a high level of flexibility to be able to balance fluctuations in the market.
“But its very important for us that steel fabrication, welding, of these high quality steels remains a core competence for us. Prototypes and complex components are manufactured by ourselves,” Beringer says. “We have developed manufacturing and welding technologies and we will maintain and further develop these sophisticated technologies. Corresponding specifications are passed over to our suppliers.”
Vlassenroot’s history stretches back more than 80 years, to 1926. Outside its Belgian factory stand one of the world’s first bending presses: the company started off in the flattening business: it bought steel coils, and decoiled it. Now, while it still produces steel for bridges (one of its biggest jobs here was for the iconic Millau Viaduct) and occasional architectural projects, around 98% of its business is focused on booms.
Investor Jean-Charles (JC) Wibo bought into the company in 1996, when it employed just 45 people. Working with general manager Eddy Buyst, Wibo has entered into an ambitious programme of vertical integration, expanding the company’s business with a series of acquisitions in Germany and Poland. Each acquisition has added a new step in the company’s production chain, and a new opportunity for adding value to its finished products.
Shells are cut and bent in Brussels, Belgium. Top and bottom shells are welded together at the former KSK facility in Schwerte, Germany. Gliwice, Poland manufactures other components for booms, along with mobile crane chassis and upper structures. Finished booms are assembled at Bochum, Germany.
Wibo says, “One of our aims is to help customers with a lack of capacity: that was one of the reasons for buying in Poland. Gliwice currently has 500 people, but this is due to increase to 600 by the end of the year, taking Vlassenroot’s total staff to more than 1,000.
Gliwice is also used to manufacture crane chassis and uppers, a new product for Vlassenroot. Brussels plant manager Bart Deumens says, “We’re interested in areas where we can add value, where we can use our know-how in steel bending and welding.” In terms of crane capacity, the booms Vlassenroot makes are used in all terrains and rough terrains from 30t to 500t. It could make booms for bigger cranes, Deumens says, but it looks to products where it can see the benefits of serial production.
Deumens explains that one of Vlassenroot’s advantages over its competitors is that it is able to deliver complete products: “Our competitors are cutting and bending companies who collaborate with welding companies, or welding companies who buy parts from other suppliers. We are the only company making complete booms. Everything is overseen by one general manager, Eddy Buyst.”
Deumens says that of almost 4,000 booms bent in Brussels this year, about two-thirds will be delivered to customers incomplete. Only about 1,200-1,300 were completed by Vlassenroot (in Bochum). The company aims to grow in the immediate future, not by increasing the number of booms it bends in Brussels, but by increasing the number it completes in Germany: increasing the value it adds to the products.
Bending steel in Brussels
Every Vlassenroot boom starts as plate steel shipped via Antwerp from SSAB Oxelösund in Sweden. Plates of steel are grouped together for each order at the factory. The crane builders’ designers will often ask for different thicknesses of steel to be used; not just in each boom but sometimes even in each section. A millimetre of thickness shaved from half a boom shell may reduce the weight of the boom by 200kg. Over a five section boom, that could cut the gross weight of the crane by a tonne, keeping it within tight road travel limits, or adding to the load chart.
Deumens explains that one of the reasons Vlassenroot uses steel from SSAB is that it is manufactured to fine tolerances of flatness and thickness. The tolerances for thickness range from
-0.2mm to +0.3mm. Vlassenroot works to equally tight tolerances: each boom section is bent to tolerances of no more than 1º and the flatness of each boom section will vary for no more than 3mm along its length.
Most of the steel used by Vlassenroot in Brussels is SSAB’s 960 and 1100 types (the numbers refer to the steels strength in megapascals, or N/sq mm). Structural steel used in automobiles has a rating of 335 N/sq mm, that is, a third as strong as these steels. Deumens says end users are looking to shave every millimetre from the thickness of crane booms, to get the best balance of strength and weight. However, stronger steels cost more to cut, and to bend. So far, the cost increase doesn’t justify using the new steel for mobile cranes: that doesn’t mean it won’t in future.
With this strength comes flexibility. You can see that flexibility best on the biggest mobile cranes, when an extended boom bends like a fishing rod under its own weight. In the bending plant, the flexibility is demonstrated when it springs back after each pressing. Handling this flexibility is a key part of Vlassenroot’s job, and the skills of its employees.
Deumens says, “You need what the Germans call fingerspitzengefühl, the feeling you get in the tips of your fingers. We can train someone to use a bending machine in three or four months, but to know what the steel will do every time, takes years.”
A boom section is made up of an upper and lower shell of bent plate steel whose long edges are welded together. On the bottom shell of a 250t crane boom section, the plate steel is bent 25 times, springing back each time, and making the bending machine operator’s craft far more of an art than a science.
The bending machines Vlassenroot uses are amongst the world’s biggest. One machine, made up of three separate presses working together, can bend sections measuring up to 24m. It was this machine that bent the bridge pieces for Millau. Elsewhere in the factory, two more machines work together to press down on 15m-long steel plates with a force of 4,000t.
From Brussels, Vlassenroot’s shells travel around the world. Some are sent to well known European and Japanese crane manufacturers, or to other crane builders in Turkey, Russia, Algeria, and China. Many are grouped together next to that 4,000t bending machine, ready to be shipped to mobile crane factories in the USA at a rate of ten to twelve containers a week. Many (and, if Vlassenroot has its way, many more soon) will be shipped to Schwerte to be welded together, and then on to Bochum for final assembly into complete booms.
Welding shells in Schwerte
Vlassenroot bought KSK, and its Schwerte plant, at the end of 1999. The new facility allowed the company to move from bending plate steel in Brussels, to welding it together into bare boom sections. When Vlassenroot first bought the plant, it employed 45 people. Today, it employs 150. As in Brussels, the factory works continuously, 24 hours a day and seven days a week.
The two existing halls at Schwerte are working at maximum capacity, with barely enough room to walk around the plant. Only a couple of days before Cranes Today’s visit, however, Vlassenroot received permission to extend both halls out into a vacant space, currently used for storage. Building the new halls will take up to seven months, but the company hopes to be ready to start production in them by July 2009. As well as the new production facility, the company is building a new employee facility.
At Schwerte, the shells bent at Vlassenroot’s Brussels plant are welded together into boom sections. Inside the boom, longitudinal welds are made using metal active gas (MAG) welding; outside the weld is made using submerged arc welding. Where different widths of steel need to be joined together on the same boom (to save weight), cross welds are made manually.
As the external weld is made, the metal will buckle and wave from the heat. Some of these changes in the shape of the boom will be fixed by the metal springing back. However, to get the precise tolerances Vlassenroot aims for, the boom will need to be levelled again when it reaches Bochum.
Once the bare boom sections have been welded together at Schwerte and certified free from defects, they are carefully marked up and sent 30km away to Bochum. There, along with parts from the new Gliwice facility in Poland, they are assembled into complete booms.
Fabrication in Gliwice
Vlassenroot’s newest plant, Vlassenroot Polska in Gliwice, manufactures boom heads and cups, alongside chassis for mobile cranes. The plant welds 12,000 boom components a year: roughly five pairs of boom heads and cups for each completed boom assembled in Bochum.
The plant started building chassis for mobile cranes for Liebherr and Manitowoc in 2008. For Liebherr, it is building chassis for mid-size ATs (Liebherr’s own Ehingen, Germany factory makes chassis for its eight- and nine-axle ATs, Beringer says). For Manitowoc, it has begun with a smaller-capacity crane. Currently, the plant is building 10-12 chassis a month, but is aiming at increasing this to 20 per month (or 200 a year) soon. It is also building turning tables—the section above the slew ring that supports the boom—at a rate of around 40 a year currently, but plans to increase this amount substantially. Vlassenroot Polska will install two new machines for turning tables by 2010.
Vlassenroot started the new operation up, pretty much from scratch, at the end of 2006. Over two years, it has recruited almost 600 people, and built a 15,000 sq m production hall. This is now running at full capacity. This year, the new plant will use more than 8,000t of high strength steel (generally Weldox 960), with around 3,500t used for boom components, 2,000t for chassis, and the remainder for turning tables.
In the first half of 2009, the company hopes to start construction of a new hall running alongside the existing building, giving the company another 6,700 sq m of production space. This will be dedicated to chassis and turning table manufacture, but will be flexible enough that new products could be added. The new facility will allow the company to produce 400 chassis a year in 2010.
General manager of the group Eddy Buyst explains that the company aims to install new, state-of-the-art, equipment, including robotic welding systems, milling centres and laser cutting tables. The first of two new LVD presses, similar to those used in Brussels, is currently being installed.
JC Wibo says, “We generated revenues of EUR32m in Poland this year, and are aiming for EUR45m in 2009. We expect about EUR10m in revenues from chassis in Poland by year end, but this will grow. The new hall in Poland will add another 7,600 sq m to the plant, and another 200 or 250 people to the staff. It will cost EUR13m in additional investment. The new hall will be used to manufacture chassis and turning tables.”
The project to develop robotic welding processes for boom components is being developed by project manager Tom Thomas. The new equipment will use twin rotating tables: while the robotic welder works on one component, staff are able to mount the next component on the second table. When the first component is completed, the tables switch positions, allowing the robot to work continuously. Thomas says that the company has sent two boom components, assembled with temporary welds, to a potential supplier in Germany. This will allow the supplier to design a welding programme for the robots. Tests of the process are expected to take place in the first week of January 2009.
Once all of the pieces of steel have been prepared, they are sent on to be welded. As well as investing in new equipment, Vlassenroot Polska is investing in people, with a new welding school training all of its Polish welding staff. Currently, all of the welding is done by hand. The chassis are assembled on huge circular frames, allowing them to be rotated for welding. The company has a pair of 2.5m x 2.5m milling tables and one 2.5m x 12m milling centre, and will be adding more next year, for preparing the turning tables.
Assembly in Bochum
Vlassenroot bought two buildings in Bochum in 2002. It took over two more production halls on the same site in 2004, another two in 2006, and a seventh in 2007. Today, the seven halls have a total floor space of 13,000 sq m. Each hall is dedicated to working on completed booms for just one or two manufacturers,
The welded shells arrive from Bochum to be made into complete boom sections. The first stage of assembly is to ensure that the shells are completely straight. The waves introduced to the steel plates as they were welded are removed using a levelling machine. The machine uses hydraulic rams mounted inside and outside of the boom to carefully adjust shape of the boom. Like the bending machine operators in Belgium, the workers on the levelling machine need to develop an intuitive feel for the steel.
Once the welded booms have been levelled, the boom heads and cups are welded in place. With the other components welded to the boom shells, the assembled boom sections are assembled into complete booms, ready to be sent to the manufacturers, who will add skid shoes and hydraulics.
Vlassenroot has grown from bending steel to fabricating many of the key structural components for some of the world’s biggest crane builders. JC Wibo says, “Next year, in 2009, will be a year of consolidation. We made a large, EUR20m investment in Poland, starting with a greenfield site, and ending 2008 with more than 500 employees. In 2009, we have to train those people. In 2010, we will look to grow both internally and externally. We want to develop new products close to what we already do. That could be outriggers, it could be cabins, it could be counterweights.”
