ONE OF the challenges of pressing, forming or clamping sheet metal can be to ensure secure and even grip across the workpiece without time-consuming complexity in setup and release.
Conventional hydraulic and pneumatic cylinders can be too slow to operate or have the drawback of applying their force in point loads, rather than across the surface of the product.
An alternative way of approaching the task is to employ Airstroke air spring actuators, which are highly engineered bellows manufactured by Firestone containing no rods, seals, pistons or other wear parts prone to breaking and leakage.
Rather than extending a piston to apply point force, the Airstroke extends itself to apply force over a broader area, says Jim Hine, product manager for Bridgestone New Zealand.
“Also valuable to a production engineer is the flexible air springs’ ability to arc without a clevis – to bend and to tolerate uneven and fluctuating loads. This built-in flexibility makes them suitable for materials handling tasks in which they must exert force across uneven surfaces, such as in different pressing and forming applications,” he says.
These qualities were put to the test in the manufacture of large heat exchangers, in which sheets of corrugated steel had to be welded and fitted together with very close tolerances.  Previously a C-clamp was used to hold the sheets for welding, but this was clumsy and time consuming.
To replace the C-clamp, a pneumatic clamp was designed using an Airstroke actuator and corrugated jaws. The actuator is simply inflated and deflated to open and close the jaws, to hold and release the steel sheets during the welding process.
“The actuator proved so simple to use that the manpower required to assemble the heat exchangers was reduced by 50 percent. Even after two years of use, the clamp operated flawlessly and never needed repair. In addition to being ideal for work in grimy environments because of their lack of wear parts, the Airstrokes’ angular capability allowed for action through an angle without a clevis,” says Hine.    
“The low profile of the single-convoluted Airstroke employed allowed for a compact design, which is also useful in applications such as pipe weld clamps and coil holders. The low profile design allows the actuators to fit into pipes with small diameters, where their powerful, short-stroke action provides consistent force to hold the pipes stationary and in alignment during welding. 
“Their low profile is also invaluable within coil holders, where they can be inflated quickly to spread clamping arms into the coils to provide consistent pressure to immobilize them. The quick inflate/deflate action is ideal for stopping and starting the coil for forming, coating and other processing, as well as making coil placement and removals easier on the manufacturing line.”
Because friction is reduced by there being no internal moving parts to break or wear within Airstrokes, they are very suitable for high-repetition tasks, such as powering stamping presses. Flexible Airstrokes are also far less affected by side loads generated by the material beneath them (they can bend with the load, rather than break down as a rigid cylinder may) and are impervious to dirt and contaminants the material or environment may carry. In addition, air springs are far more tolerant of shock loads then conventional pneumatic cylinders.
Such shock may damage conventional cylinders and, where they cannot absorb the bumps and grinds of production, the shock may transfer into the workpiece and damage that.
Airstrokes are available in capacities of 40 to 40,000kg of pressing, pushing or lifting power, with starting (uninflated) heights from just 16mm and strokes (extensions) of up to 350mm, powered by simple, basic compressor equipment found in nearly every factory.