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Press Brakes for Giants

They’re the monsters of the press brake world. But they operate like their smaller cousins, with a little help to handle the big work.

Zipping out small parts, looking like a demo version of a “real” press brake, LVD Strippit’s Dyna-Press electric press brake was a highlight of the Fabtech show a few years ago. It’s small and light enough to move around the shop with a forklift, and, within its size range, it was demonstrating the many virtues of electric drive. It looked like fun. We wanted to load one in the back of a truck and take it home.

Then they showed us some photos of what they build at the other end of the size scale. There was a machine being assembled with cranes, out of doors, in the Middle East desert. The base of the machine was secured to its foundation 18 feet below the ground. Parts of the brake were swinging from steel cables, like pre-cast parts of a skyscraper, while workers guided the crane operator to place them in position. The machine was too big to assemble inside of a building. So they assembled the press brake first, and then built a building around it.

What struck us, besides the staggering scale of the giant press brakes, was how much alike they were to the small ones. If you took a close-up photo of each, with nothing in the photo to indicate scale, like a human or a capscrew, you’d have to look at them for a moment before you could figure out their size. Press brakes are press brakes, even if they’re so big that you have to build the machine first and then erect the building that surrounds it. It’s an uncommonly scalable technology.

You may find it interesting that, even in lengths measured in dozens of feet, with machines that often are assembled in pieces, with two or even three self-contained machines lined up to make one big one, and with forces measured in thousands of tons, they operate in fundamentally the same way. The biggest questions then become how they handle those enormous workpieces, and who uses them.

“Most of them are bought by truck-chassis builders, light-pole and power-pole manufacturers, crane builders and shipyards,” says Lieven Vanhoenacker, LVD sales manager. “We build roughly 20 of them each year, year after year, and every one is customized to specific requirements.”

They are, in other words, much more tailored to particular and limited classes of work than are ordinary, mid-size press brakes. “A lot of the material being bent is pretty exotic, high-strength alloys. For example, the Weldox and Hardox alloys from Sweden’s SSRB.” These alloys range from just under 100 kpsi to over 190 kpsi yield strength and the springback can be 30%. They’re several times stronger than mild steel, and are being used in vehicle lightweighting applications and in building crane booms, among others. “Instead of making a truck chassis frame from 10 or 12mm material, they might use four-to-six millimeter stock in the strong alloys,” says Vanhoenacker.

Custom work pushers of various types are used in most cases, because the work is either too dangerous to handle, or too heavy to push against a backgauge.

As an extreme, a manufacturer of power-transmission poles wanted to make them of 30mm (1.2 in.) steel. “With material that thick, you need 250 tons per meter of length. It required 3,000 tons of force to make the 30-meter-long poles, in sections.”

This is a global business, with a concentration in areas that are expanding their infrastructure and building. “Our biggest market concentration at the moment is the Middle East,” says Vanhoenacker. An example is Galva Coat, based in Abu Dabi. They’ve grown rapidly with some big investments, and now have, they say, 65% of the regional market for these really big pieces.

And they can handle the biggest. A 3,000 ton LVD PPEB press brake complements a 1,400-ton, 14m-long tandem brake. The heavy one is used to form posts and pipelines up to 15m long in thicknesses to 25mm. Servo controlled with state-of-the-art hydraulics and electronics, the PPEB press brake is the largest machine of its kind in the Middle East, says LVD, and it is a turnkey system that includes press brake, automation, part evacuation and bending tools. 

This installation in Abu Dabi uses multi-part pushers to handle heavy plate.

For 90% of the day, the custom press brake is forming light poles. It incorporates a programmable V-axis crowning system, integrated and synchronized with the machine’s control system, to keep the ram and the table parallel during bending, for high accuracy. Rework is kept to a minimum. “We make about 50,000 to 60,000 poles a year with only 0.5% rework, which shows just how consistent the technology is” said Mohammed Botma, factory manager at Galva Coat.

Another continent, another application, this time for making crane booms. 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. The company expanded its capacity with the installation of a 2000-ton, 14m LVD PPEB-H 2000T press brake for producing mobile crane booms. Vlassenroot has all of its production processes in-house, so they can offer crane manufacturers a complete, fully welded boom and chassis from one supplier.

Ludwig Deckers, plant manager at the Schwerte plant, says that in recent years the strongest part of the market has been in cranes for the wind-power sector. Its big LVD press brakes give it the large-scale production capability for this market. The largest crane for which they build parts has a 500-ton capacity, and the longest section they produce at Schwerte is over 14m long. They supply all leading crane companies throughout the world.

The new machines LVD built for Vlassenroot were designed specifically to be the optimum configuration for crane-boom forming in high strength steels. 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 Deckers.

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

“In 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 Mpa (160 kpsi) tensile strength material we commonly bend, you may have a springback of 30 degrees – so you have to bend to 60 degrees. You need a lot of force.”

“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 Deckers.

LVD’s Vanhoenacker says that Vlassenroot’s work-handling issue is a very important part of designing and building these big machines. “How can I push feed my material to position, with front supports, back supports, front pushers, back pushers, and sheet followers? All these options are functions of the length and the weight and the product that the customer wants to make. So we do the complete study, of course, and look at all the options Most of these machines have tight access and CNC controlled back stops.”

This is where much of the customization comes in, he says. “We have sheet followers, front supports that follow and support the material during bending, that can support 600 kilograms. We actually can support 1,200 kilograms per support, so if you put in three of these, you can support a lot of weight during bending. So there aren’t many limitations.”

There are some caveats. The poles can be, and often are, conical or tapered. So feeding and backstop adjustment has to be programmed for that. And the tooling, as noted by Ludwig Deckers, may involve adjustable dies that allow for different radii. In fact, some poles are multi-faceted (octagonal or more), and some are cylindrical. Getting the adjustments right to air-bend a series of blended radii for round poles, with high levels of springback, begs for adjustable dies. But such dies are used in normal-sized machines, as well. Salvagnini makes an entire machine based on them.

Back to the company’s little electric Dyna-Press brake, we imagined making something like, say, an electrical junction box on one. And then, within the same electrical-power industry, we can use a giant press brake to make the poles that carry the electricity to the box. So LVD Strippit covers both ends of the industry. We may be pushing analogies and connections too far, but not by much. They’re all in the same family.

LVD-Strippit