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In a high-production workholding environment there are different types of clamping. The traditional method of hydraulic clamping and unclamping still remains very popular. Within that family of hydraulic clamping there are several different slices or different flavors of hydraulic clamping that you can have. One of those is single acting clamp. Basically what that means is you use hydraulics to clamp the part and then you use springs inside the hydraulic clamps to return them. It's the simplest hydraulic circuit that you can design; it is also probably the least reliable. So while its simplicity it makes it very convenient from a hydraulic standpoint, it's also the least reliable in a long-term high production volume situation.

You can go full double acting, which is more of a sure way to ensure full double acting. What that means is you're using hydraulics to clamp and unclamp, so you're using positive pressure on both sides of the cylinder to actuate, a positive way of moving the clamps. Traditionally in CNC workholding we've had to use accumulators. Once the pressure is locked into the fixture via a check valve the accumulator is used to stabilize the pressure inside the fixture to take away any variations in pressure due to temperature or small leakage considerations.

Another example would be mechanical clamp and hydraulic unclamp. Again we're using mechanics this time to clamp the part, such as a Belleville washer stack. A lot of people feel that using Belleville washer springs to clamp is a more reliable way. If during your cutting process you happen to accidentally machine a hydraulic line or spring a hydraulic leak and evacuate the fixture of all pressure, the Belleville washer stack will not unclamp your part; and will not have a catastrophic failure. And then you use hydraulics to unclamp those mechanical clamps. The limitation of Belleville washer stacks or that type of clamps is that you have a very small stroke. It's very difficult to do any type of swing clamping. Your ability to handle various part numbers on the same fixture is limited because of the small strokes of the clamps, although a benefit of that obviously is that there's no accumulator or check valve needed because you don't have a hydraulic actuation of the clamping.

A different example again is a mechanical clamp using a nut runner or a similar type of application where you're using a mechanical nut to clamp and unclamp the fixtures. No hydraulics are involved, but it requires more operator intervention or a mechanical station for the nut runner, wrench assembly, or something of that nature. It's certainly not as automatic as we would like to see in a high-volume environment. So that are some of the traditional methods that we've used for clamping in the past, and now Tim Jones will talk to you about some new technology available in CNC workholding.