October 5, 2009
Automating bending with a press brake tied to a robot isn't the only option. Panel benders and folding technologies have evolved to handle more parts and various lot sizes.
When fabricators think about automated bending, a robot tied to a press brake usually comes to mind. So do high volumes. But press brakes aren't the only automation option, and high volumes aren't always a prerequisite. Automated panel bending and folding systems hold one side of the blank while bending the flange up or down (see Figure 1 and Figure 2). Systems serve various environments, according to sources, including batch or kitted production, high or low volume, high or low part mix, and so on.
New iterations of the technology overcome previous limitations. For instance, manual folding systems, like their brake counterparts, could fold in only one direction. Today some automated folding systems offer single beams that articulate, altering their pivot point and moving around previously bent flanges to fold in positive and negative directions.
Part geometry also has thrown up some hurdles. Press brakes can handle extremely complex, small parts that both panel bending and folding systems historically couldn't touch. But new technology can indeed bend small parts automatically (see Figure 3) using hold-down tooling borrowed from folding and panel bending, and introducing a way to handle the part without articulated-arm robots, which can have difficulty grasping small workpieces.
Limitations remain. Systems can bend flange heights only so tall. Single-beam folding and most panel benders specialize in bending thin stock. But within those constraints, established and emerging technology may help remove those all-too-familiar bottlenecks in the bending area.
Some lighting fixture companies use panel bending lines to produce complex geometries within incredibly low cycle times, measured in seconds. Often connected to coil lines with blanking systems, these panel bending lines are modular, usually with two to four stations, each dedicated to particular bends (see Figure 4).
According to Matti Lukkari, director of technical sales at Finland-based Pivatic Oy, the return on investment for these large systems makes sense for volumes of 100,000 or more a year. One lighting fixture manufacturer, he said, produces up to 1 million panels a year on such systems.
In these systems, hold-down tooling and bending wings fold flanges up and down; the top wings move down to fold in the negative direction; the bottom wings move up to fold in the positive direction (see Figure 5). The machine can position parts to have bending wings on either side. Both sides of a part can be bent simultaneously—hence those fast cycle times. According to Lukkari, complex panels can be bent in as little as 20 seconds.
"The biggest benefit is that there is no movement between the workpiece and the folding tool," Lukkari explained. "That means there are no marks or scratches on the workpiece and no wear on the folding tools," making unattended bending of prepainted stock and other material possible.
The number of stations can be customized based on the product family needs, he said. A two-station system might have four wing formers for panels, suited for applications such as shelving, drawers, and other office furniture. A three-station setup could have six wing formers for wrappers and casings, suitable for products such as furnaces and coil casings.
In a typical setup, the first stations bend the panel's long sides, folding flanges up and down in any combination, within certain flange length limits. Then the panel moves on to the second set of stations, which bend the shorter side. "Now that the sides are already bent, the length of the hold-down tools in the second station must match between the already bent sides," Lukkari said.
Hold-down tool changes often are required for lines configured for varying part geometries. Manual and automated systems can accomplish this. In the manual setup, the operator presses a button that releases the hold-down tool hydraulic clamp, so he can then manually change the tool. "Typically, one operator can accomplish this in a few minutes," Lukkari said. "However, it is a manual operation that needs to be done."
The automated option involves a servo-driven system that removes the hold-down tools and places them in a magazine. "When equipped with this kind of hold-down tool changing system," he said, "the system is down for only 30 seconds to a maximum of 1 minute."
Such automated bending has part size and thickness limitations. Some stations are designed to perform bends for casing enclosures and the like. But in standard panel stations, flange heights need to be about 4.7 in. or less to clear the tooling. Specialized tools to perform corner bends reduce that flange height to a little more than 3 in. Because these systems have automatic blank positioners that can only get so close to the bend line, these systems have trouble dealing with sections less than 12 in. Maximum thickness is a little less than 0.050 in.
But, "if an end user works with a limited number of part families, such as those for lighting fixtures or office furniture," Lukkari said, "then he appreciates the flexibility and also the shortest possible cycle time."
Manufacturers producing parts in kits, with different parts flowing through cells to arrive as a complete kit at assembly, create special challenges for bending automation. Blanking has adapted by moving away from hard tooling in processes like stamping and toward flexible processes like laser cutting.
Kits present bending challenges, particularly in the press brake. Staged and segmented tooling arrangements have helped matters, but it doesn't alter the fact that brakes need different punches and dies for bend geometries and material thicknesses. A shop could run large batches and reduce the number of changeovers, but that means work-in-process would need to sit until all the product batches were complete before starting assembly. Say goodbye to single-piece part flow.
"In a panel bender, tool setup is automatic," said Bill Bossard, president of Salvagnini America, Hamilton, Ohio. "You can go from a panel that's 5 by 10 inches to one that's 5 by 10 foot, and you have zero [manual] setup, because the tools position themselves to allow for clearances of long and short flanges."
Changing out between parts happens extremely quickly, he said. Within six to eight seconds, a new program is pulled up (previously entered offline), reference blocks and devices are moved into place for the new blank size, the hold-down tooling rearranges itself to handle different part lengths, and the machine is good to go.
"This kind of equipment is ideal for getting closer to a lean, single-piece part flow," Bossard said. "You might need to make thousands of products a year, and each assembly might have 50 parts. There's no reason why you couldn't run part No. 1 through 50, then repeat."
The technology doesn't work for everything. Flanges again can be only so high. "We build machines that go up to 10 inches high, and a special system for 13-inch-high [flanges], designed for electrical box manufacturing," Bossard said. But most panel bending work concentrates on relatively low flanges.
Thin material dominates. Most systems don't bend material thicker than 1/8 in. Panel sizes range from 5 by 10 in. up to 60 by 157 in. or more, depending on the system. Parts smaller than 5 by 10 in. and thicker than 1/8 in. remain the press brake's forte.
New panel bending systems integrate a shear to help produce parts like stiffener rails welded onto the back side of panel enclosures. As Bossard explained, this "allows you to bend a narrow profile and shear it, with a shear blade underneath, and the bender then continues on to form the main panel."
He added that workpiece monitoring has been perfected over the years to ensure the correct material enters the bend area at the right time. System-makers use finite element analysis, among other things, to design bending components to minimize deflection; testing and diagnostic work have analyzed the tension and compression areas of myriad bent materials, and the knowledge has been integrated into panel bending design (see Figure 6).
Bending machines now have eddy-current sensors that detect material microstructure on-the-fly, with the machine's controls drawing from a database of material tables. When the blank moves to the bending area, the machine can detect mechanical properties, be it stainless steel, steel, or aluminum. Thickness also is measured twice, and if the thickness is outside the tolerance range for the part, the machine automatically updates the bend program to accommodate.
When adopting automation, many prefer seamless flow between blanking and bending, with part kits emerging continually, ready for assembly.
Michael Stock, manager of bending products for Prima Finn-Power North America, Arlington Heights, Ill., said this arrangement is often ideal, but it's not for everyone. What if parts require graining or deburring? What if the assembly area isn't near the blanking area? Transporting oddly shaped parts can be a bear, so some may prefer to move flat cut blanks from the laser and turret punch centers to a bending area that's adjacent to painting or assembly.
More often than not, the bending area consists solely of press brakes. But in high-mix or kitted production environments, "it's a constant struggle for the press brake," Stock said, "because you spend 80 percent of your day changing the machine over with different tooling, and 20 percent of the day actually bending parts."
Today specialized benders can help (see Figure 7). Though from a distance they may look like a press brake, and have a similar footprint, they in fact resemble panel benders without automated material handling. Instead of large tables with servo-driven blank manipulators, these stand-alone bending centers require an operator to call up the program, place the blank inside the work envelope, then stand back.
In this arrangement, the operator scans a blank's bar code for part tracking, places the blank in the work envelope, initiates the bend cycle, then repositions the part 90 or 180 degrees for subsequent bends. Like in panel bending, tool change happens automatically, this time with robotic units to the left and right of the bending bed. Individual hold-down tooling components come together to accommodate specific bend lengths. The tools are locked and unlocked into place hydraulically, resembling what happens in full-sized automated bending centers (see Figure 8). Specialized tools for corner reliefs and other forms can be used as well.
Advantages of conventional panel bending apply to this system too: "The standard tooling can bend through the entire capacity of the machine, up to 11 gauge," Stock said. "Also, the standard tools, though bumping, can do multiple radiuses and different angles, as well as hems."
Although double-beam folding systems can bend thick gauges in the positive and negative direction, single- beam folding systems primarily work with material 11 gauge and thinner, depending on the machine model. Automated single-beam systems now have a beam that can move inward and outward to change pivot points for both positive and negative bending, as well as automated part positioning and handling.
Automated folding systems "should be designed to run kits," said Rick Wester, vice president of RAS Systems LLC, Peachtree City, Ga.
In such systems, scanners measure incoming blanks to ensure the geometry matches the one in the program and that the part is within tolerance. The blank then is taken to the bend line, and the folding program starts.
"We then can put another part on the table, measure it and move it into position, then put a third part on the table and have it measured. As soon as the first part is cleared, the second part is only four seconds away from being in position for its first bend. And these could be different parts—a top, bottom, and a wrapper, for instance. So rather than running 50 of each, you have a product that you can bend, put together, then ship almost immediately."
But as in panel bending centers, automated folding systems can't handle small parts less than 10 in. wide or long (again, depending on the machine model). "The manipulator holds the part," said Wester, "so that means we only can get to within 6 inches from the bend line."
That's why small parts have been relegated to press brakes. From a part flow standpoint, this can present a challenge. For many electronic assemblies and enclosures, various units might share small internal brackets and other components. Unfortunately, since the same brackets may go on various enclosures, volumes are higher. Bending them can take serious time in the press brake area and require the operator's hands to be close to the bend line.
Last year a new kind of machine hit the European market, one that automatically bends parts with dimensions down to 1.5 by 2 in., flanges up to 5 in., and with thicknesses up to 11-gauge mild steel (see Figure 3). The part hold-down tools are like those on a folding center, but here the resemblance ends. To be released in North America in the near future, the system doesn't use a folding beam. Instead, a specialized part manipulator holds the middle of the small blank, clamping it from above and below. It then carries the blank to the work envelope and places it in between the hold-down tools. Behind these are two bending tools, one that moves upward for positive bends, another downward for negative bends—similar to an automated panel bender. The part manipulator and hold-down tools remain stationary as the bending tools form the part. To bend another side, the hold-down tools open, the part handler rotates the piece, and the process starts again (see Figure 9).
Like a panel bender, the system uses segmented hold-down and bending tools for different bend lengths and part geometries; for example, narrow tools to bend, a tabbed section up in between two flat portions (see Figure 10). Like in folding and panel bending, the angle isn't dependent on the tooling, but simply how far the bending tools push the material. This machine also scans parts to ensure it has the correct blank for compensation of any load tolerances.
Wester explained that this machine is designed for small parts: 24 by 24 in. would be the absolute maximum.
This unit, he added, was designed to complement larger folding setups. The large folders can handle the made-to-order panels, while the small-part bender can churn out those common internal brackets, though the system can be used for low and medium lot sizes as well.
Sources added that these machines often serve as a complement of, not a replacement for, the press brake. A shop may have an automated folder or panel bender for large, made-to-order parts, with a press brake for low-volume or thick plate not suitable for panel bending or single-beam folding. (Automated double-beam folding systems are available to handle relatively thick plate bending.) Sources added that robotic press brakes can be a good choice for blanks that don't fit within the part geometry constraints of an automated panel bender or folder.
All sources did make one point abundantly clear. In the bending arena, press brakes aren't the only machine tool available, and they're not the only machines that can be automated. Now more than ever, a manufacturer can have more than one sheet metal bending tool in the fabricating toolbox.
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