Clamping Cylinders
Types of Clamping Cylinders
| Single and double-acting | |||
| Single-acting cylinders deliver hydraulic power in only one direction of travel, utilizing an internal spring to provide plunger return when hydraulic pressure is removed. They require less valving and plumbing than double-acting cylinders, resulting in a less complex hydraulic circuit and minimal fixture congestion. However, single-acting cylinders deliver slower operating speeds than double-acting cylinders. Additionally, the spring return means that hydraulic fluid must have an easy return path with few restrictions, and only a few cylinders may retract simultaneously. |
A Single-acting clamping cylinder |
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| Double-acting cylinders use hydraulic power to move the plunger in either direction, so they are more complex. The payback for slightly more plumbing and control devices is high speed operation in either direction and precise control of the plunger. This is important when greater control is required during the unclamp cycle. The tighter control provided by double-acting cylinders is also helpful when timing sequences are critical, because they are less sensitive to system back pressures that can arise from long tube lengths or numerous cylinders retracting simultaneously. | A double-acting clamping cylinder |
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| Swing cylinders The swing cylinder is without doubt the most widely used hydraulic clamping device. The plunger of the swing cylinder and the attached arm rotate 90 degrees in either a clockwise or counter clockwise direction at the beginning portion of the stroke. They then travel down an additional distance to clamp against the fixtured part. Upon release of clamping pressure, the clamp arm raises and rotates back to 90 degrees in the opposite direction to allow for removal of the part removal and placement of the next part. |
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| Most swing cylinders are available in either single- or double-acting form. Stroke length is selected according to the geometry of the part to be clamped. Capacity, the clamping force, is selected according to the machining forces that must be resisted. A variety of arm lengths provides design flexibility. (The System Considerations section of this chapter provides more information.) | |||
| Upper flange mounting | Lower flange mouting | Threaded body mounting | Cartridge mounting |
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| Pull cylinders Fitted with a variety of plunger end-effectors, pull cylinders can be used to pull a part into place, pull it down, or push it via a clamp arm fitting. Pull cylinders are offered in single-and double-acting configurations and mounting styles such as illustrated for swing cylinders. |
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| Pull cylinders Fitted with a variety of plunger end-effectors, pull cylinders can be used to pull a part into place, pull it down, or push it via a clamp arm fitting. Pull cylinders are offered in single-and double-acting configurations and mounting styles such as illustrated for swing cylinders. Block cylinders In addition to clamping, block cylinders are used for punching, pressing, riveting, and bending applications. They are available in numerous mounting, stroke, and connection arrangements. |
 The block cylinder performing a clamping function |
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| Block cylinder holds workpiece against fixed stop, with further clamping by swing cylinder |
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| Pull down clamps Enerpac pull down clamps allow unobstructed top face machining. Independent horizontal and vertical movement achieve high lateral and pull down forces to hold the workpiece firmly against the fixture. The pull down force is equal to approximately 1/3 of the clamping force. |
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| Positive clamping cylinders A conventional hydraulic workholding system requires either special valving or a continuous power source to maintain clamping force. There is another way to accomplish positive clamping: Enerpac’s Collet-Lok® system. Collet-Lok combines the benefits of hydraulic workholding with the long-term stability of bolted mechanical fixturing. Once the part is positioned, supported, and clamped, the cylinders are mechanically locked in place so that all hydraulic pressure can be removed for any length of time. A Collet-Lok cylinder is locked by hydraulic pressure supplied to a lower port to drive a wedge upward to mechanically lock a collet chuck around the cylinder plunger. The collet releases the cylinder plunger only when hydraulic pressure is supplied to the opposite end of the wedge via an upper port. For full details, refer to Chapter 4. |
a collect-lock cylinder |
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