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Case in point: Turret punch

Controls are also used to boost punching-machine productivity. Consider the case of Specialty Fabricating Co., Omaha. The company purchased a used turret punch, and its mechanical components were in fine condition — but the controls were lacking. After determining that pricing to connect wiring was costly, Specialty Fabricating decided to replace the parts themselves. Owner Art Venteicher now uses components and software from Baldor Electric Co., Fort Smith, Ark., for positioning sheet-gauge work material and turret-mounted tooling. Baldor BSM 90 brushless servomotors drive X and Y axes, which move sheet metal on a flat, horizontal plane into a punching position.

Baldor 23H servo control amplifies the controller signal; Baldor's ISA bus, DSP motion NextMove/PC controller (loaded with the MINT programming language) instructs the motors to move from point to point. MINT receives standard RS-274 (G-Code) commands, and converts them into X-Y movements and punching actions. The program also helps with statistical process control functions by keeping track of total punches per tool, so the operator may change tooling after a designated number of punches. Explains Venteicher, “We've nearly doubled our productivity — from about 100 hits per minute to 200 on a given move.”

Other sheet considerations

Initially, before being fed to a press, sheets are separated. Suitable here are cylinders from Festo Corp., Hauppauge, N.Y., which have piston diameters to 125 mm and strokes from 10 to 2,000 mm. Sheets to be pressed are also handled with vacuum grippers in flat, bell, or bellows configurations — in conjunction with semi-custom connectors.

Appropriate vacuum valves smooth actuation, so for this portion of the operation, Festo offers multi-function vacuum-lifting cylinders tailored to confined workspaces. An oval piston, hollow piston rod, and endcap vacuum port create lifting vacuum; vacuum cup attachments serve to transport metal and protect workpieces against rotation.

Vibration mitigation

Pressing and stamping machines are often installed on custom-designed flooring and slabs, because the force and shock they produce is so great. Dampers are used in conjunction with these foundations, or sometimes to compensate for convertible designs.

One such product is heavy-gauge polymer and rubber supports: Kellett Enterprises Inc. Greenville, S.C., sells vibration-isolation pads that reduce transmitted shock and vibration in overly loud screw presses; injection molders that would otherwise tend to “walk” from vibratory movement; die casters that need protection; and metal stamping presses.

More specifically, Kellett's LP-13 custom-cut Shake Absorbers are sold as area pads, bumpers, and neoprene shims to stabilize (and sometimes level) machinery.

Another option for damping is friction springs. Friction springs consist of separate inner and outer mating tapered rings that stack together to form a column. Under compressive loading, the wedging action of the tapered rings expands the outer rings and contracts the inner rings allowing for axial deflection, thus absorbing the compressive load.

Friction springs are useful in stamping and punching, as they can be installed at various locations to absorb the huge dynamic forces of these applications. More specifically, friction springs manufactured by Ringfeder Power Transmission USA Corp., Westwood, N.J., also called RING springs, absorb forces from 0.1 to 10,000 kN and energy from 1 J to more than 100 kJ. They can be installed to damp motion on the normal machine axis in either the negative or positive direction — in other words, on the up or down stroke. “Friction springs with high capacity and low terminal force best protect stamping-machine structures,” explains Carl Fenstermacher, president of Ringfeder PT USA. Terminal force is that which the damping device exerts on the structure towards its stroke end.

A RING spring has a linear force-travel diagram, which means that the forces exerted on the machine structure are controlled and predictable during its entire stroke, unlike buffers of a different design. Larger impact forces are accommodated, and stroke length is a direct function of the number of rings in the stack height; more rings make for more stroke, and vice versa.

One caveat: “After a stamping machine completes the working portion of a cycle, it tends to recoil,” warns Fenstermacher. “Because friction springs damp two thirds of the force transmitted to them, approximately one-third of the compressive force is recoiled back into the system. Proper sizing of the spring is the key to protecting stamping machinery and supports.”

In contrast to velocity-dependent spring systems, friction springs also provide full spring work and damping, even when the load is applied quickly or very slowly.

FABTECH 2010 in Atlanta

FABTECH 2010 will be held November 2 to 4 at the Georgia World Congress Center, as the southeast is seeing expansion in metal fabricating and manufacturing. FABTECH 2010 will showcase metal forming, stamping, finishing, and welding equipment and technology. The event is expected to draw 22,000 attendees; 2,000 pieces of equipment in action; and more than 500 product debuts. Presentations and educational sessions abound; a Finishing Pavilion allows manufacturers to review metal manufacturing processes from beginning to end. The American Welding Society, Fabricators and Manufacturers Association International, Society of Manufacturing Engineers, and Precision Metalforming Association cosponsor the show. Registration is now open through fabtechexpo.com.

For more information

Baldor Electric Co.
(479) 646-4711
baldor.com

Precision Metalforming Association
(216) 901-8800
pma.org

TURCK Inc.
(800) 544-7769
turck.com

Kellett Enterprises Inc.
(864) 244-7248
kellettent.com

TRUMPF Inc.
(860) 255-6000
us.trumpf.com

Festo Corp.
(800) 993-3786
festo.us

Ringfeder Power Transmission USA Corp.
(888) 746-4333
ringfeder.com