By Kip Hanson, Contributing Editor
Article from May 2014 issue of Cutting Tool Engineering.
(Partial article. Use this link to read it in full): It’s ironic. Tell a shop owner or production engineer to mount a mechanical 3-jaw chuck on a CNC lathe and they’ll look at you as though you’re wearing a duck on your head. Why do they then turn around and put old-fashioned, hand-cranked vises on vertical machining centers? A basic hydraulic vise setup for a VMC can cost between $1,700 and $4,000—roughly the same price as a hydraulic workholder on a lathe—and provide far more reliable and consistent clamping than mechanical units. So what gives?
Fewer than 10 percent of shops use hydraulic vises on their machining centers. This lack of acceptance is due largely to shops going with what they know. Most machine shops have always used mechanical vises. There’s a comfort factor there.
Machine tool builders are partially to blame for the lack of acceptance of hydraulic vises. Money is a big consideration. A fully plumbed trio of hydraulic vises equipped with automatic clamping can set you back $40,000 or more. If your needs are more modest, a basic hydraulic starter kit and 6″ vise sells for significantly less. Either way, it’s a lot of money, considering you can buy 20 commodity mechanical vises for the price of a starter package.
The benefits of hydraulic workholding include reduced setup time, clamping consistency and improved part quality. In addition, predictable clamping forces are a key determinant of part quality. But perhaps the biggest benefit is improved productivity. Pushing a button to clamp four vises at once takes less than a second. These small gains add up. A 2 hour savings a day could gain 500 hours of extra machining time a year.
All Pumped Up
Long stroke or short, most hydraulic vises allow the movable jaw to slide close to the workpiece and lock into place. This minimizes jaw travel and cuts the load or unload time to less than 1 second. The primary consideration in vise selection, however, isn’t stroke length, but pump type, because vises require sufficient oil and pressure to do their job. As pressure and/or volume needs increase, a commensurately stronger pump is called for.
Pump size and type ultimately come down to the pressure and volume required for an application. Yet David Vilcek, engineering project manager for Carr Lane Roemheld Manufacturing Co., Fenton, Mo., might tell you to ditch all those pumps and lines and select its hydra-mechanical vises, which offer the benefits of hydraulic workholding without the plumbing.
“Hydra-mechanical vises utilize a self-contained hydraulic system,” Vilcek said. “Like a mechanical vise, you turn a crank until the movable jaw touches the part.” Once it touches the part, however, the similarities change—hydra-mechanical vises have a small detent on the side of the vise. “It just takes a little pop with your hand to engage. When you turn the crank, it advances an internal piston that builds hydraulic pressure, resulting in a very high clamping force of up to 12,000 lbs. on our 160mm vise.”
This isn’t a one-trick pony for the company. Like its competitors, Carr Lane Roemheld also offers externally powered hydraulic vises. Regardless of the brand, it’s important to select the same qualities in a hydraulic vise as a mechanical one. “One key feature is the vise base itself,” Vilcek said. “Those machined out of steel rather than cast iron are more robust. Look for precision-ground guide ways and locating surfaces, casehardened to several millimeters deep.”
Vilcek considers hydraulic workholding a flexible tool for fixturing—not just some “plain old vise”—and a good intermediate step between pure mechanical systems and dedicated fixtures. Hydraulic workholders quickly adjust to part sizes from ½” (12.7mm) or smaller to 10″ (254mm) or more across, he added. “With delicate parts, you can dial the pressure down for a gentle touch. When you need to rip, crank it up. Either way, you’re sure to get the same clamping force every time.”
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