February 24, 2009
At nearly half the cost of conventional stamping equipment and a small footprint (3 to 210 tons), the pneumatic press may be the answer for some operations. Traditionally, the technology has been associated with roll forming operations, but advances in the technology have made it an option for day-to-day stamping operations as well.
As global market price pressures continue to rise, stampers are looking for ways to reduce capital equipment and labor costs. At nearly half the cost of conventional stamping equipment and a small footprint (3 to 210 tons), a pneumatic press may be the answer for some operations. Traditionally, the technology has been associated with roll forming operations, but advances have made it an option for day-to-day stamping operations as well.
Today an air-driven press can be programmed with a PLC, equipped with an automated feed system, and grouped to create a transfer line. Gaining a better understanding of pneumatic press characteristics can help stampers decide if this machine is an appropriate choice for them.
Basically, a pneumatic press is a four-post or two-post precision die set (nominal tonnage rated at 100-PSI input pressure) that uses air pressure on the downstroke and mechanical springs for the upstroke of the press ram.
On the downstroke, the air tube/elastomeric actuator is filled with air at the signal from the control system, forcing the air tube to expand and apply pressure to perform the required work. When the blanking or forming is complete, the control signals the valves to shift (exhausting the air), and the mechanical springs return the press ram to top of stroke, completing the cycle. Air offers the same characteristics as oil, but eliminates the potential problem of leaks.
Construction typically is a rectangular assembly with a low profile and flat underside. This configuration makes the machine suitable for integration into automated processing systems. It can be mounted in unconventional attitudes at any angled position, including an inverted upside-down mounting at 180 degrees, or with a fixed horizontal stand for hand-fed operations.
While a pneumatic press offers an option for day-to-day stamping operations, it is not suitable for deep-draw work deeper than 2 inches or for jobs requiring extremely long press strokes more than 12 in.
Full Tonnage. Pneumatic presses provide full tonnage through the entire stroke length by keeping air pressure constant during operation. Without a rotational drive or linkage, the presses can achieve full tonnage without stalling at bottom dead center (BDC) and damaging the press or the die.
In the automotive arena, trends continue to dictate the use of laser-welded part blanks and panels fabricated with different material thicknesses. Full tonnage can be a production advantage for stampers making these types of components, whether the stroke length is 3 in. or 0.05 in.
Adjustable Stroke, Shut Height. Adjustable stroke length and shut height capabilities also are suited to forming applications requiring different heights or tonnages.
The adjustable stroke length is effective for forming complex shapes, such as a formed step. Such a part, with its multiple levels, requires the press to strike the material higher off the bottom of the stroke. The pneumatic press makes this possible (See Figure 1).
Few Moving Parts. Few moving parts and the direct actuation created by the air tube allow stampers to achieve a high ram velocity for increased speed. Because the pneumatic press design does not convert rotary motion to linear motion, there is no flywheel to store energy and no clutch needed to engage a drive to permit motion. This feature makes press maintenance simple and cost-effective.
Accuracy. Instead of a single-point, two-point, or four-point connection, the pneumatic press ensures uniform ram pressure. Deflection characteristics are comparable to other press types on the market, except the pneumatic press does not need extra frame structure to house the drive and gibbing configuration normally required for low deflection. Press rigidity also contributes to part accuracy.
Up to 400 SPM. Stroke cycles for a pneumatic press can be as fast as 400 strokes per minute (SPM). Since SPM can be varied with the size and stroke length of the press, the capability and capacity for press configuration are unlimited.
Automation. Pneumatic presses with a four-post or gap-frame design can be retrofitted or equipped upfront with robots, pick-and-place units, or transfers to create an automated line. Automation allows stampers to operate the press or presses at a high rate of production because of a minimally restrictive feed timing diagram. Multiple presses can be mounted on a common base to provide simultaneous cycling of each press ram, and different cycle times can be programmed through a centralized PLC.
Controlled Flow Rate. Stamping operations in which material flow rate (ram velocity) is critical, such as drawing and forming, can be performed with a pneumatic press. It is the ability to achieve a high ram velocity using unrestricted airflow that provides high-speed capability and full tonnage through the entire stroke length. Because the press stroke can dwell at BDC for a programmed length of time—anywhere from milliseconds to minutes—the production system is suitable for embossing, coining, assembly press fit, welding, and other specialized stamping operations.
Operators also can use the dwell feature with heated dies for lamination jobs that specify height requirements. Sensors can be installed to measure and ensure desired heights are achieved.
For low- or high-volume part runs, a pneumatic press, when combined with an automatic coil feed, may offer increased productivity for a low-cost investment. Gap-frame pneumatic press designs also are well-suited for low-, medium-, and high-volume part production that may not be appropriate for a hydraulic press because of pump drive or clutch heat problems.
Large Blanks, Low Tonnage. The pneumatic press also can be used for part production requiring relatively low tonnage (50 to 150), such as large blank panels manufactured for the appliance industry. Because of the reduced frame size of the pneumatic press, the equipment requires about 40 percent less floor space than conventional press models, yet it is able to perform jobs requiring large bed sizes and low to moderate tonnage effectively.
Auxiliary Functions. A versatile air-fed press can be used as a scrap cutter mounted adjacent to any type of press or in an automated cut-to-length line for processing blanks, and it can be easily disconnected from the base and used for other applications.
For stampers who need to optimize pressroom operations and meet cost constraints, the pneumatic press may provide the right combination to meet current job requirements as well as future contracts.
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