Air Hydraulic Unclamping Cylinders: Enhancing Efficiency and Precision

On a CNC machining center, every automatic tool change depends on one short, powerful push: the drawbar has to be pushed against the spindle's disc springs to release the tool holder. Air hydraulic unclamping cylinders deliver that push using nothing but the plant's compressed air. This article explains how they work, what they are made of, and where HINAKA's units fit.

What Are Air Hydraulic Unclamping Cylinders?

An air hydraulic unclamping cylinder uses compressed air to drive a large piston, which pressurises hydraulic oil through a much smaller plunger. The resulting hydraulic force pushes the spindle drawbar and releases the tool. Clamping itself is done by the spindle's disc springs: once the tool change is complete, the cylinder retracts and the springs clamp the new tool. The unclamping cylinder only unclamps.

How the System Is Built

Depending on the spindle type, the booster and the unclamping cylinder are either combined in one unit or installed separately:

• Integrated type (BPT series): the air-oil booster is built into the unclamping cylinder itself and mounts at the rear of belt- and gear-driven spindles.
• Separate type (BPF booster + HUC cylinder): on direct-drive and built-in spindles the rear of the spindle is occupied by the motor, so a hollow HUC hydraulic cylinder sits at the spindle and a BPF booster, mounted nearby, supplies the oil through a high-pressure hose.

The main components are:

1. Air piston and oil plunger: the area ratio between them sets the boost ratio (output oil pressure = air pressure × ratio).
2. Solenoid valve: switches the air supply for unclamping and return.
3. Oil cup with level sensor: tops up small oil losses and signals the machine controller when the level is low.
4. Unclamping cylinder: pushes the drawbar; the HUC is hollow so it can be used with or without coolant through the spindle.
5. Anti-rotation and sensor brackets: keep the cylinder aligned and allow the unclamp position to be detected.

Benefits

• High force from shop air: the boost ratio turns 0.6 MPa compressed air into the hydraulic pressure needed to overcome the disc springs.
• No hydraulic power unit: no separate pump, motor or oil tank is needed for tool change.
• Works only during tool change: the unit uses no air and generates no heat on standby.
• Compact installation: the unclamping function fits at the spindle without a large hydraulic system around the machine.

Where They Are Used

Air hydraulic unclamping cylinders are used on CNC machining centers and other machine tools with automatic tool changers, for BT30, BT40 and BT50 tool holders. The choice between the integrated and separate types depends on the spindle:

• Belt- and gear-driven spindles: BPT, or BPTQ where tool change time is the bottleneck.
• Direct-drive and built-in spindles: BPF or BPFQ booster with a HUC unclamping cylinder.
• Horizontal mounting or humid environments: the Dual-Oil BPT-D and BPF-D series, which run on oil in both directions.

Why HINAKA

• Focused on spindle unclamping: HINAKA, founded in 1988 in Kaohsiung, Taiwan, has built boosting unclamping cylinders for machine tool builders for many years.
• A full range for every spindle type: integrated BPT, separate BPF + HUC, high-speed Q versions with a quick-exhaust valve, and the Dual-Oil series.
• Faster tool change: HUC cylinders use enlarged air and oil ports, and the Q versions unclamp over 40% faster than the standard versions.
• Sized to your spindle: boost ratio and oil volume are selected for your drawbar force and stroke.

Conclusion

An air hydraulic unclamping cylinder gives a machining center the force it needs to release tools, using the compressed air already in the plant. Choosing the right type starts with one question: is your spindle belt-driven or direct-drive? Contact us with your spindle type, drawbar force and unclamp stroke, and we will recommend the right unit.

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BPF or BPT? A Quick Guide to Choosing the Right Unclamping Cylinder for Your Spindle

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