Press Brake

The sheet metal bending department evolves

A decade ago most spending in precision metal fabrication—outside welding and consumables—occurred in the cutting department as the industry transitioned from low-powered CO2 lasers to high-powered CO2 and, finally, to solid-state technology. For the right application, a fiber laser today can run circles around a high-powered CO2 laser purchased a decade ago.

Each November at the FABTECH® tradeshow, the Fabricators & Manufacturers Association International publishes its “Capital Spending Forecast,” and for the past two years, the survey has tracked a noticeable shift in spending. Collectively, shops are spending more on bending than they are on laser cutting. Driving a lot of this increase is the industry’s push toward high-end press brake technology, including offline programming software, intuitive controls, angle measurement and correction, and automated tool changing (ATC). These days, a single press brake can be a major investment.

But there’s another reason: Spending on press brake alternatives has increased too. According to FMA, purchases of other sheet metal bending equipment, including panel bending and folding, jumped by a whopping 70 percent between 2012 and 2014, to a projected amount of $134 million. The 2016 forecast number is a little lower, at $104 million, but that’s still a historically high level.

The increase really isn’t a surprise, considering the unprecedented levels of throughput coming from the cutting department. Lasers cut more parts in less time and send that work to forming—and for many, this creates a bending bottleneck they need to free.

Luckily, fabricators have options. They can upgrade to a brake with advanced control, offline programming, and angle correction, shortening cumbersome changeovers. They also can invest in press brakes with ATC, which shortens those changeovers even more.

Still, no matter how short changeovers are, bending operators still run into problems when it comes to certain part sizes and bend geometries. Big parts are still a pain to lift. Two operators may spend half the day lifting large workpieces high into the air to bend a shallow edge flange. Robotized bending is an option, depending on the mix of parts and part volumes, but it’s not the only option.

Two alternatives to the press brake, panel bending, and folding, are opening up opportunities for shops, but they also give operation managers more options to weigh and more questions to ask. Does it make sense to send a part to a panel bender or folder, even though those parts need to be sent to a press brake for a few remaining bends? Does it make sense to send parts to a folding machine in another area, or should the work stay in one area to simplify routing, even though the bending process itself isn’t quite as efficient?

According to several managers who work in bending operations with various forming technologies, the answers to all these questions depend, as they so often do, on the application. 

Panel Bending and Folding Basics

In a press brake, the force from the punch pushes sheet metal into the V-die opening to make a radius. In air forming, the process has three points of contact: the punch tip on the top surface of the sheet metal and the leading radii of the two die shoulders underneath. Different materials may require different tools, depending on the tensile strength, thickness, and required radius and angle. Modern controls, simulation, angle correction, and ATC all make changeovers less arduous, but the technology still requires changing over tools with different die openings and punch-tip radii.

In panel bending, blank holder tools clamp the sheet in place so that the material protrudes on the other side. Next, bending blades from above and below the workpiece fold the metal. For most operations, the motion of the bending blade, not the shape of the tools, determines the final bend angle and radius. The segmented blank holder tools automatically change out to match the required bend lengths.

Panel bending limitations include flange height and material thickness, which depend on the machine and the depth of its throat, or the area behind the blank holder tool. A deep throat can form a deep flange.

Like a panel bender, a folder clamps the workpiece with tooling; on a folding machine, they’re referred to as clamping beam tools. But unlike a panel bender, a folder uses a swinging beam with a blade tool that contacts the sheet metal to make the bend. The height of the clamping beam tools generally determines the height limit for a perpendicular flange.

Historically, folding beams have swung upward only; to make both positive and negative bends, an operator needed to flip the workpiece. In recent years, though, bidirectional folding systems have become more popular. In these machines, the beam pivot point changes based on the width of the bending blade tool on the beam.

Say the beam blade is 0.6 inches wide. For the first upward bend, the top edge of the blade contacts the sheet to make the bend. To bend downward, the blade’s bottom edge must fold the material surface. This requires the beam’s pivot point to move 0.6 in.

The beam’s position determines the angle, and segmented clamping beam tools are arranged to handle different bend lengths. In recent years, folding systems with automatic clamping beam tool changeover have hit the market. In these machines, robotic manipulators change and rearrange clamping beam tools for the job at hand. 

A machine may not have to change clamping beam tools often; one setup may be able to handle a wide variety of bends of different geometries, material types, and thicknesses. But if a series of jobs have different bend lengths and situations in which previously formed flanges would collide with clamping beam tools, ATC can help shorten the setup time between jobs.

Quick Change

Over the past six years the fabrication department at A.J. Antunes & Co., a food preparation equipment-maker in Carol Stream, Ill., has undergone five big changes. First came lean manufacturing, 5S, and better tool organization. Second, came a Salvagnini panel bender, which reduced the bending cycle times and eliminated lengthy setups for many jobs. Third came offline press brake programming. Fourth came a new Amada fiber laser, which increased throughput and available cutting capacity—and increased demand on downstream bending. Fifth, and most recently, came a press brake with ATC.

“Bending has always been our bottleneck,” said Jorge Montalvo, manager, fabrication. “We started with 5S and lean. The setups went from an hour to 45 minutes. Then we saw the Salvagnini panel bender, and we thought it was great because we do a lot of box bending. Once we got that, everything took off.”

Montalvo added that the panel bender doesn’t work for every part. A part needs a flat surface to be positioned for a bend, and flanges can be only so high. But having the machine does allow the company to produce extremely complex bends in fewer setups. 

To increase its panel bending flexibility, the fabrication department now has a press brake directly adjacent to the panel bender. “Say a complex part requires five different setups on the press brake,” Montalvo said. “Now the panel bender does four of those five setups, and the operator turns around and finishes the part on the press brake.” He added that using another machine does increase handling time, but that slight increase in handling time is more than offset by all the setup time that the panel bender has eliminated.

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