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INSIGHT YOUNGSVILLE, N.C To maximize up-time on expensive machine tools, many production machine shops are set up to deliver raw parts to the tool on workholding palletized fixtures. Hydraulic clamps mounted on the pallet hold workpieces securely in place during machining. At a separate load/unload station, the operator unclamps and removes finished parts from the pallet, then loads and clamps new parts. By using a number of pallets, the machine tool spends more time cutting metal and less time waiting for parts to be unloaded and loaded. At a typical load/unload station, the operator first connects hoses fitted with quick-acting couplers to the pallet, then uses hydraulic power to release the clamps, and later to re-apply them on the next part. After this, the couplers are disconnected. A fixture- mounted check valve and accumulator maintain clamping pressure during the machining cycle. Such systems have worked well, but the couplings have some shortcomings in this application. Connecting and disconnecting them requires physical effort by the operator. During the time they are disconnected, chips and other contaminants can enter the system via the exposed coupler faces. Further, frequent opening and closing of these couplers causes them to wear, eventually leading to leakage and possibly adding metal-chip contaminants to the fluid. Even the normal flexing of the hoses can produce elastomer particle contamination and eventually cause leaks. Enerpac's hydraulic Wand cylinder activates fixture-mounted, passive Booster cylinder to clamp casting before fixture is positioned for final machining. As an alternative arrangement, the Wand and Booster system -- designed and produced by Enerpac - pressurizes workholding fixtures mechanically - eliminating the need for quick-acting couplings and avoiding their problems. The system consists of two hydraulic cylinders. The first, referred to as the wand, is located at the load/unload station, and is connected to a hydraulic pump there. The second, called the booster, is mounted in the workholding future. When a pallet arrives at the load/ unload station, the operator simply places the wand into a cradle that is built into the booster. The cradle holds the wand securely and aligns the two cylinders. When ready to activate the clamps, the operator starts the pump. The wand extends and begins to mechanically stroke the piston in the booster cylinder forward. The oil in the booster cylinder is pushed through the tubing into the clamping cylinders. This movement of oil strokes the clamp cylinders into position. Once they are positioned, the wand stops, but now begins to build pressure in the booster. When the operator sees that the proper clamping pressure is generated, he or she can close the fixture-mounted holding valve and stop the pump. The single-acting wand automatically retracts. The holding valve and an accumulator maintain pressure in the clamping cylinders. The fixture now can now be sent for machining with the workpiece held securely in place. Once the part is machined, the pallet returns to the load/unload station. To unclamp, the operator simply releases the holding valve that is mounted on the fixture. The clamps relax, allowing the part to be removed. A new part now can be loaded, and the wand re- positioned to apply pressure for clamping once again. The wand and booster system incorporates a closed hydraulic circuit in the pallet. The connection between the wand and booster is purely mechanical. The hydraulic circuit never opens, thus eliminating the chance for external leakage. This feature also avoids the ingestion of loose particles from the pump circuit into the pallet. The placement of the wand against the booster also can be more easily automated - compared to trying to connect small hydraulic couplers automatically. The system is truly versatile, and can be adapted to any single-acting pallet fixture using ouick disconnects. Thomas Eggert, global marketing manager - workholding, Enerpac, Milwaukee, provided this discussion. Phone Enerpac at 262 / 781-- 6600 or visit www.enerpac.com.
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Source: Hydraulics & Pneumatics
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