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Press Brakes of a Different Color

By: Casey Schlachter

Casey Schlachter is national press brake sales manager, Mitsubishi Laser/MC Machinery Systems Inc., Wood Dale, IL: 630/860-4210; www.mitsubishi-world.com.

Saturday, January 01, 2011
 
Traditional, hydraulic press brakes use gear
Electric Press Brakes
Electric press brakes prove reliable and efficient, and accurate—down to
1 micron.
pumps to pressurize lines that deliver oil to pistons. While the pumps prove fairly reliable, they have some disadvantages. For starters, they continuously draw power even when the press brake sits idle. They also are noisy and can cause machine vibration.

Worst of all: During production, temperature changes to the hydraulic oil can cause perceptible shifts in the ram, interfering with the ability to meet tight production specifications.

To eliminate the gear pump and other troublesome elements of traditional press brakes, manufacturers have developed electric and hybrid press brakes. Hybrids employ hydraulic and electric technologies—hydraulic power still moves the ram, but a hybrid pump only is energized for a fraction of the day, and delivers exact positioning that does not rely on valve operation for control. This design also avoids the problems caused by changes in oil temperature.

How Green Press Brakes Work

The most common hybrid press brakes work with a motor that features a sealed shaft that reaches into a hydraulic tank. The shaft is attached to and has direct control over a piston pump, which delivers hydraulic pressure to move the ram—but only when the operator steps on the foot pedal.

With electric press-brake technology, electric motors directly control ram movement with help from belts or gear mechanisms that drive heavy-duty ballscrews. Belt-driven ballscrew designs incorporate timing belts that encircle the motor’s pinion gear and another gear that sits directly above the screw. The ballscrew turns in and out of a nut attached to the ram, or the nut spins around the screw, controlling ram movement.

Gear-driven screw designs are similar, except that the pinion gears are in direct contact with each other. A motor rotates the pinion gears, which in turn rotate the ballscrew to operate the ram. Because of the metal-to-metal contact, this design is slightly noisier than belt-driven designs.

Some systems use pulleys to drive the ram. In a pulley-driven design, pulleys line the upper ram, wound on a common belt that pulls the ram down thanks to the force-multiplying effect of the pulleys.

3D modeling and interactive process simulation
The latest bending software for press brakes features 3D modeling and interactive process simulation to help guide the bending process.
The pulleys pull down against springs that push the ram up after the bend. Ram repeatability is slightly lower with pulley systems than with ballscrew designs.

More Efficient, More Accurate

The benefits of trading up to an electric or hybrid machine are widespread. The most obvious advantage is the environmentally friendly and energy-saving aspects of the technology. Electric press brakes eliminate the need for hydraulic oil and can reduce energy costs by as much as 50 percent. That means no messy oil changes or detrimental effects to the environment caused by disposing of old oil. Using typical industrial energy costs, a 100-ton hybrid brake can save a fabricator about $900/yr. Hybrids also are efficient, using one-third the amount of oil as hydraulic brakes.

While greater efficiency has helped fuel interest in electric and hybrid designs, the improved accuracy and repeatability from the machines also has fabricators taking interest. They know well that when using hydraulic press brakes, ram repeatability becomes compromised as the hydraulic fluid warms over time—typically by around 50 F in 2 hr.—which transmits heat to the frame. This can cause the ram to shift by as much as 0.006 in. In addition to this worrisome shift, warming also can cause seal weeping and radiant heating of the shop floor. Electric and hybrid models avoid these problems, ensuring accuracy within 1 to 5 microns.

Some hybrid and electric press brakes go one step further to ensure accuracy: they’ll employ automatic thickness sensors to gauge sheet thickness at each pinch point during bending.

Unforeseen Savings

Some fabricators might argue that they don’t need the high level of speed and accuracy that hybrid or electric press brakes offer. But if they consider all of the indirect and long-term cost savings possible with electric and hybrid press brakes, the return on investment quickly becomes apparent.

For many fabricators, the peace of mind they gain knowing that their press brakes will produce bends to exact specifications—without needing adjustment due to changes in oil temperature—is reason enough to make the switch to electric or hybrid. For others, the frustrations they’ve endured from

Software Takes Bending to a New Level
Hybrid and electric technologies aren’t the only innovations shaping the press-brake market. New programming software is improving the usability and accuracy of press brakes, in a very cost-efficient way.Some software systems feature 3D modeling and simulations that simplify press-brake programming and operation, even for relatively inexperienced operators. These sophisticated systems can automatically position backgauges and compute optimal bend sequences. What’s more, some software features interactive process simulation that can provide detailed, configurable simulations of any press-brake operation. Operators and programmers can view (and adjust) animated backgauge movement, ram stroke, and part insertion and retraction, as well as potential collisions.
problems with inaccurate bending, such as unnecessary costs and stress, are what push them to upgrade.

For example, if a manufacturer forms a part designed to fit precisely into an assembly with one or more additional components, the smallest degree of variance can make a huge difference in assembly time. If the parts don’t fit together properly because the press-brake ram may have shifted slightly, additional work, or even total rework, may be required to bring a component up to par. While this scenario is particularly relevant to fabricators that bend complex parts from thin sheetmetal, where even tiny inconsistencies can ruin an entire batch of parts, most manufacturers can benefit from using a more precise press brake.

Put simply: Hybrid and electric press brakes can help fabricators substantially streamline downstream operations, saving time and money and increasing customer satisfaction.

Added Bonuses

While accuracy and fuel efficiency are driving fabricators to invest in hybrid or electric press brakes, other benefits await. First, hybrid and electric technologies deliver much faster cycle times, making shops more productive and profitable.

Also, fabricators using hydraulic brakes must invest time and money to inspect and maintain valves, tanks, pumps, filters and seals. Hybrid press brakes require much less maintenance as they use significantly fewer valves; electric press brakes are virtually maintenance-free.

Electric and hybrid press brakes also make for a much nicer shop-floor atmosphere. They operate more quietly than do hydraulic press brakes, and don’t cause messy oil leaks or generate residual heat. MF

 

See also: Mitsubishi EDM/Laser

Related Enterprise Zones: Fabrication

 


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