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Press Brakes

Holding the line

By Lynn Stanley

Above: Ursviken’s new crowning control system simultaneously solves all of the problems associated with bending heavy  plate, including AHSS.

Heavy, high-strength plate meets its match with evolved crown control technology

September 2015 - Dry docking an Ohio-class ballistic missile submarine that is a few feet longer than the Washington Memorial, seven stories high and 42 ft. wide, takes careful planning and precise positioning. Tide, current and wind govern the parameters for safe docking—leaving the pilot, tug masters and crew with a small window of opportunity to maneuver the behemoth into the dock’s narrow basin and bring it to rest on the keel blocks. 

Though not as cumbersome as a fast attack sub, forming long bends in high-strength steel plate also requires meticulous preparation. Press brake operators must grapple with machine deflection, concentrated load and material springback while fighting the clock to achieve an accurate bend. And they have just one chance to get it right. Overbending by one or two degrees can mean costly rework, production delays or worst case scenario–a scrapped part. Words no manufacturer in the heavy plate sector wants to hear. 

“Plate that is 1 in. thick, 24 in. wide and 24 ft. long can cost up to several thousand dollars so the bend has to be right,” says Marten Weidgraaf, general manager for Ursviken Inc. Based in Elgin, Illinois, Ursviken is part of Sweden’s Ursviken Group. The company studies heavy plate applications used by industries like shipbuilding, construction equipment and tube and pole manufacturing in order to engineer press brake technology for machines up to 10,000 tons that can help fabricators improve production, accuracy and ergonomics while minimizing setup time.

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Taming AHSS

The use of advanced high-strength steels (AHSS) has become increasingly popular for fabricating parts like telescoping boom crane arms which have the longest reach in the industry and use heavy-duty components. AHSS offers weight reductions without sacrificing strength but the materials pose several challenges for conventional bending operations. 

Prone to fractures, these grades tend to produce batch-to-batch inconsistency and have a significantly larger range of springback–10 to 25 degrees. Individual plate for these parts can weigh as much as 5 tons and require a press brake with a bed as long as 40 ft. To achieve an even angle over the full length of the part, operators have to measure every second foot, sometimes measuring again. This process can take up to an hour for one part.

This type of manual setup and angle measurement also requires an experienced operator, Ursviken National Sales Manager Mike Rose says. “It’s more of an art form than science,” he notes. “Parts typically are formed using a template. If the part is too tight, the template won’t fit. This means the operator has to guesstimate the angle on the first few bends and then correct later.”

This approach is possible, he continues, “if you are bump bending but if the operator is performing a single hit for a 90-degree bend it gets even more challenging. If you overbend a small part, you can scrap it and start over. With big plate there is no such thing. Operators will do whatever it takes to correct the error.”  What it often takes, he adds, is hours of rework and associated costs.

For Ursviken the challenges inherent with producing parts like very large crane arms has provided a proving ground for its latest innovation: the crowning control system (CCS). 

“Whether it’s ship building, mining or construction equipment, the single most important thing for these customers is to get that first bend right the first time,” says Weidgraaf. “In a conventional bending approach large plate will automatically lay flat when the ram returns to top dead center (TDC).” The operator then must rebalance the plate in the Vee opening using a jib crane to hold the material in place while attempting to relocate the original bend line. Hopefully, when the ram cycles back down, the punch radius strikes in precisely the right location. “It’s tricky work and it requires highly skilled operators. With CCS we’ve eliminated the guesswork that up until now has plagued heavy plate bending operations.”

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Pedigree

The science behind CCS has been built on a foundation of intellectual property. The conventional press brake has always been capable of adjusting bottom dead center (BDC). Ursviken took that function a step further by developing the ability to control BDC by programming the Y1 and Y2 axes to operate independently–making true air bending of heavy plate possible for the first time. CNC crowning designed with a mechanical CNC axis followed, allowing the operator to receive feedback of the plate’s position and make controlled adjustments of the machine bed to compensate for deflection while maintaining accuracy over the full bending length of the part, even outside the side frames in larger press brakes.

Next, a three-point angle correction was introduced to automatically or manually measure bend angles at the right and left ends and center of the workpiece to eliminate an uneven canoe shape across the length of the part.

Ursviken launched FlexiCrown in 1994. Impervious to the forces of springback, FlexiCrown provides an FEM calculated curve that matches machine deflection in each bending process, yet allows the operator to measure different areas and modify crowning every 2 ft. if necessary. In 2000 the company launched its active mechanical or optical laser angle control system which automatically measures springback and adjusts BDC.

FFJ 0915 pressbrakes image4The next evolutionary step has CCS using FlexiCrown to combine the BDC setting with local crowning. “By solving all of the forming problems associated with advanced steels at once, the system helps the operator create a good part the first time,” explains Weidgraaf.  “It’s a type of forming capability that is not available elsewhere in the marketplace.”

Optical laser angle reading devices scan the entire part reading from the front and back side, giving the operator a true angle every second foot. When springback is detected, the system holds the part in position with plate supports and material followers so it can’t slide away from the initial hit of the punch. Upon release of the part, the crowning is reset according to each measurement taken and a final calculation generated for BDC. 

Thus, “The first bend is a perfect bend without the need for manual corrections, shimming or reworking,” Weidgraaf says. “We’ve tested the laser scanning unit’s ability to measure angles along the length of the part at 1 meter per second. And we’ve proven the technology in the harsh fabrication environment used to produce telescoping boom crane arms. The columns for that part have to be perfectly straight and accurate.”

Limiting idling

Without a material handling system that can hold the part in the proper location and effectively measure angles, big press brakes tend to sit idle 50 percent of the time because of the logistics work operators have to perform on the parts. “With CSS we’ve created a fully integrated material handling system to ensure the part doesn’t slip during forming,” says Weidgraaf.

“Part-to-part consistency and accuracy are significantly improved. The CNC variable die tool’s (VDT) ability to accommodate different die openings makes setup time negligible and retrieves lost production time for the manufacturer. These options can also be used in combination with one another,” he says.

Its sparing energy consumption offers additional savings for fabricators. As soon as the operator gives the order, the motor begins to ramp up during a supervised free-fall, reaching full speed to bend the part before transitioning to a low rpm once the press beam arrives at TDC. “The Eco pump or stop-start function offers 20 to 25 percent additional up speed,” says Weidgraaf. “On a conventional press brake it can be a slow process waiting for the beam to return. Our system allows the operator to remove the part quicker.” 

“Efficient press brake operation can be a fateful question,” says Ursviken Application and Sales Engineer Mikael Linderot. “Very often when you talk to people who are not familiar with the technology, they tend to see a machine that goes up and down and they are satisfied with knowing the machine’s length and tonnage. We’re asking manufacturers to go beyond that thinking and explore possible avenues toward making their press brake operations more efficient because when you buy a large press brake it’s a very long-term investment.” 

Ursviken’s goal, adds Wiedgraaf, “is to continually evolve our technology through pioneering research that can do the problem solving for customers so that they can focus on their bottom line.” FFJ

Sources

  • Ursviken Inc.
    Elgin, Illinois
    phone: 866/872-4868
    fax: 847/214-8705
    www.ursviken.com
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