Page 40 - MetalForming February 2019

Ways to Decrease Cycle Time on
Hydraulic Presses
In any metalforming operation, press cycle time ultimately depends on the operations to be performed, and the material to be worked. There’s just no getting around material prop- erties, the need for dwell time, and the actions—and time—required to shape- shift a blank and achieve a desired part.
That said, wasted time exists in a cycle. Tinkering with this time, via a variety of methods, can cut a precious second or two, or more, which adds up to increased productivity and prof- itability across a job run. To discuss these methods, MetalForming tapped the expertise of Tim Wilson, mechan- ical engineer at Greenerd Press & Machine Co., Nashua, NH. Here, Wilson answers questions on how metalform- ers can speed the cycle.
MetalForming: The slowdown posi- tion of the ram may offer a means to achieve time savings. How can metal- formers optimize the location where the ram transitions from a rapid advance to pressing speed just above
the work location?
Wilson: The transition can be opti-
mized through a variety of actions. Modern hydraulic presses employ linear transducers, which provide the exact location of the ram throughout the entire stroke. An older press, with- out this technology, begins shutting off valves at a set position in order to slow ram speed to what is needed for
pressing.
Proportional valves can save some
time here, given proper setup and knowledge of where to begin the slow- down. We know the slowdown position from a job recipe. The valves must start turning off completely or proportion- ally, reducing flow so that the ram reaches the correct speed at that actual position. With faster, more advanced valves, transition time can be reduced. Existing equipment on a press limits that capability, but upgrades provide an option. If scheduling an older press for a new electrical enclosure or a PLC upgrade, that’s the time to consider
This Q&A with an industry expert details how setpoint adjustment, equipment upgrades and improved line communication can speed press operation.
BY LOUIS A. KREN, SENIOR EDITOR
Proportional valves, along with linear transducers, save time in transitioning a hydraulic-press ram from rapid advance to pressing speed.
control capability that delivers the needed flexibility to quickly transition to pressing speed.
MetalForming: Can ram reversal be manipulated to reduce cycle time?
Wilson: If the part does not require dwell under pressure, position reversal can be a good option, with reversal based on ram position instead of pres- sure. Consider a high-speed 900-ton press advancing at 1400 in./min. that must achieve a 53 in./min. pressing speed. The metalformer programs hard stops, so the ram travels downward farther than it needs to go to reach a hard-stop point, with a cushion helping to absorb force. Then the press builds tonnage to reverse back up. But once a certain downward position is attained, the extra travel to a hard stop means wasted time. And, the press builds more tonnage than is needed to form the part.
Or, if the work material only requires 300 tons of force to form, metalformers may, to prevent premature reversal, set
38 MetalForming/February 2019
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