Page 20 - MetalForming April 2011

Hydraulic Presses
“Like mechanical presses, bed sizes are increased on hydraulic presses to handle more complex and larger tool- ing and parts,” says Eagle Press account executive Tom McCarthy. “Press manufacturers also utilize developments in 3D engineering, simu- lation and structural analysis to engi- neer more reliable presses that deliver the rated tonnage with minimal stipu- lated deflection.”
The issue of flexibility continues to become more important as part vol- umes continue to diminish, leading to more frequent changeovers. Quick-die- change systems and programmable control systems with recipe handling are two popular methods for reducing changeover time. Other options for optimizing flexibility include purchas- ing presses with larger bed sizes and stroke capacity, and adding the ability to operate under pressure or position setpoint control.
Raye: For half a century, ram speed, position and force were con- trolled by limit and proximity switch- es, relays, linear potentiometers and other analog/mechanical devices. Today, press controls are almost
entirely electronic. They boast super- visory PLCs receiving input from lin- ear and pressure transducers, load cells and programmable motion con- trollers. It now is common for process parameters to be entered into machine memory as individual part recipes, accessible through a touchscreen operator interface.
Modern hydraulic presses are engi- neered to integrate with new shop- floor technology, including communi- cation with central production-control systems. Faster speeds are being required for high-volume production of smaller parts. We recently designed an indexer press with a cycle time of 0.5 sec.
McCarthy: Press manufacturers are leveraging developments in 3D engi- neering, simulation and structural analysis to engineer more reliable presses that deliver the rated tonnage with minimal stipulated deflection. Press tonnage capacity is increasing to handle higher-strength steels, and cus- tomers request faster speeds—not just for increased production. For exam- ple, in hot-stamping applications, faster approach (nonworking) speeds are critical to begin forming the com- ponents immediately after they leave the oven.
Improved electronic controls and hydraulic components have enhanced control and accuracy of slide velocity and tonnage during the working por- tion of the stroke. This improves part quality and avoids material thinning and other quality issues. Even tryout and spotting presses are more com- plex—it’s common to see rolling bol- sters and booking platens to allow tool and die makers optimized access for repairs and modifications.
Murphy: Today’s presses are faster, have less leakage points and incorpo- rate the latest software packages for traceability and part quality.
Walkin: The market demands high- er output, energy savings and increased accessibility, which leads press manu- facturers to provide improved hydraulics, software, positioning and pressure control.
Gardner (Phoenix): Ram control represents a considerable improve- ment, providing the ability to match ram control to a customer’s applica- tions. Examples include:
• Returning the ram on pressure, distance, pressure with dwell.
• Controlling ram speed, switching from fast advance to a slower pressing speed. This can be done manually using adjustable limit switches or elec- trically using a linear transducer.
• Electronically monitoring force and distance.
Q:
Murphy: Industrial computers rather than PLCs are being used more often due to their processing speeds and memory storage. Hydraulic cir- cuits are being designed to offer lower- power solutions while still providing high speeds and cycle rates. Integrating servo motors, drives and other control devices is more common due to cus- tomer requests to provide a more ver- satile machine.
Debus: It would be misleading to state that a plethora of new technology has been hitting the hydraulic-com- ponent and drive marketplace. Per- formance improvements and afford- ability should be headlines associated with higher-tech components.
A good example is the performance of modern servo-proportional valves. These components offer performance characteristics similar to true servo valves but without the associated cost and tight operational requirements, such as fluid conditions. Press manu- facturers can use these components within standard product offerings to provide customers with more bang for their buck. Five to 10 years ago, if customers wanted programmable press speed, this functionality typi- cally carried a decent cost adder. Today, it is more a matter of setup and component selection rather than addi- tions to the cost and complexity of the total system.
18 MetalForming/April 2011
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