Hydraulics vs. Electrics: Selecting the Right Press Brake
- October 7, 2011
by Mary Scianna
If the press brakes in your fabrication shop are more than a decade old - not uncommon given the solid construction of most press brakes - and you're in the market for new replacement equipment, you may be surprised by the technological developments on today's press brakes.
For one thing, the standard heavy duty hydraulic workhorses of the past are equipped with energy-saving features, new pump mechanisms and energy efficient electrical motors, and there's a wider variety of hybrids and electric models too that promise higher energy efficiencies, faster speeds and higher accuracies.
So if all of today's press brakes offer machining improvements, is one technology better than the other or is there room--and necessity - for hydraulics, hybrids and electrics?
"Hydraulic press brakes use gear pumps that gently push the oil from side to side. They're reliable but they run all day long while the machine is on, even when you're not cycling the machine,” explains Casey Schlacter, press brake sales manager for Mitsubishi, Wood Dale, IL. "The machine idles and the gear pumps consume about 1600 W of energy continuously. And depending on where you live, the cost of that power can get expensive.
Yet other suppliers of hydraulic press brakes say that's not the case with today's modern units, which offer energy saving enhancements.
"Energy-saving enhancements can be added to straight hydraulic press brakes,” says Paul LeTank, bending product manager for LVD Strippit, Akron, NY. Timers can be used to stop the main motor to reduce idle time. Variable displacement pumps can improve hydraulic efficiency. Variable speed drives can improve electrical efficiency.”
Indeed, John Kemp, applications and training manager for Bystronic, Elgin, IL, adds that electric press brakes actually use about twice as much electrical energy as a hydraulic press brake to generate the same amount of tonnage.
"The advantage of the electric machine is that the motors are used only during bending and go off during standby. If you take the same approach on a hydraulic machine and run the hydraulics only during bending, you use about half as much electrical energy as an electric press brake of the same tonnage.”
Bystronics uses a hydraulic pump and control valves that turn off when the hydraulics are not in use. "To generate 150 tonnes we use an 11 kW electrical motor. For an electric only press brake, you neeed about 22 kW to generate the same 150 tonnes.
Hybrids also use hydraulics, but instead of gear pumps, hybrids typically use a servo electric drive to control the hydraulic flow to the cylinders. On electric press brakes, electric motors control the ram movement via belt or gear mechanisms that drive ball screws. Proponents of hybrids and electrics say the main advantages of the technology are energy savings, faster speeds and higher accuracies.
While all suppliers readily concur on this, today's modern hydraulics offer other advantages beyond energy-saving features. They're still better machines for larger parts in the 300-plus tonnes range. Electrics and hybrids are better suited to smaller tonnages ranging from 30 to 80 tonnes for electrics and 90 to 250 for hybrids.
"Typically, a hybrid or electric press brake can be up to 20 to 30 per cent more energy efficient than a traditional hydraulic press brake. Electric machines have relatively high bending speeds, but they are not as fast as hydraulic machines in approach or retraction speed,” says Bystronic's John Kemp.
Hybrids: The Best of Both Worlds?
It seems that each type of machine offers some advantages depending on the size of the part being bent, so it's not surprising that some suppliers would choose to focus on the hybrid
Mitsubishi is one example. The company is launching a new generation of hybrid press brakes, the BH series, that will make their debt at the upcoming FABTECH in November in Chicago, IL.
"We have ball screws and hydraulics on one machine and no one has ever done this before,” says Mitsubishi's Casey Schlacter. "So when you step on the pedal a ball screw moves the ram down at high speed and a ball screw is pulling the ram up at high speed. But only wheyou get to 1 mm above the touch point of the tooling and material you want to form does the machine go into a slow bending speed and hydraulics kick in and you bend with hydraulic force. So you can bend as big as you want with hydraulics, but ram speed is lightening fast because it's driven by ball screws.”