Automatically precise pressure, more reliable clamping and adaptability to many different part shapes make hydraulic vises indispensable to many machine shops. Whether a shop is machining cumbersome parts or performing machining operations that require precision finishing of parts in a production environment, hydraulic vises and other related engineered workholding systems offer highly flexible and stable fixturing solutions that can speed up work cycles and cut down on waste.
When manual mounting becomes too difficult to apply the consistent-and-even clamping pressure that is necessary to hold a part in place, a machine shop cannot simply use traditional mechanical vises or other clamping devices that might move or vibrate and render the workpiece into scrap.
“One machine shop we competed with was having some difficulties using a mechanical vise setup to machine welded beams that were perfectly straight,” says Larry Johnson, the president of Special Machined Components (Mason, OH). “Due to the size of the beams, mechanical vises were tough to load and control. I understand that they had to scrap quite a few of the beams – perhaps 50 of them – during the first two or three months of production. At our shop, however, I don’t think we’ve had to scrap ten beams over the last 13 years thanks to our hydraulic workholding system. That’s certainly a huge improvement over the mechanical vises.”
Johnson refers back to 2001, when Special Machined Components first began machining beams for heavy-duty vertical lifting systems that normally use four or six of these beams to raise heavy vehicles such as trucks, buses and fire trucks overhead for maintenance purposes. Precise machine finishing is required for every beam, which needs to support approximately 15,000 lb to 40,000 lb each to provide a total lifting capacity of 160,000 lb.
One of the problems in using a mechanical vise for large or heavy parts such as these beams is the difficulty in setting up the machine tool for consistent clamping. For example, when a stout 300 lb operator works the first shift and a much smaller man takes over on the next shift, a difference in the clamping power between the two shifts becomes likely. Also, over-clamping or clamping a vise too hard can create workpiece distortions that result in wasted material and production time.
The hydraulic workholding system installed in 2001 was a six-vise stacked ProHold model manufactured by Planet Products (Cincinnati, OH), the same system used by some job shops for welding and riveting as well as machining operations. Shops quite often apply hydraulic vises to production runs where the consistent clamping grip and easy operating quickness are most important – the operator simply sets the pressure and the vise holds each production part the same way.
“Our hydraulic vises have a pre-set, automatic clamping and release mechanism,” explains Johnson. “Just open or close the valve on the vise and its jaws open and close. Because we use vises on our system, one valve controls the front three vises and another valve controls the back three vises. You just flip a valve and that opens and closes the entire system. It’s really that easy to operate.”
The powered opening allows a 400 lb beam to rest on the vise and always be open. This typically would not happen with a spring return vise. Johnson notes how a mechanical vise would be much more difficult to operate adequately for this application.
“Doing this kind of work would be a really tough job if you were using mechanical workholding fixtures,” he says. “Because the beams we machine weigh about 400 lb each, to use a mechanical vise you’d have to hammer around it to make sure it is tight enough. But with hydraulic vises we’ve got much better control and no concerns about operator errors. I’ve never had a problem with parts coming loose using the ProHold hydraulic. The hydraulic system is the only way to do it. It’s more expensive, but it pays for itself.”
ProHold hydraulic vises have a longer hydraulic stroke for quicker loading and can clamp a wide range of parts with same tooling. The long hydraulic stroke allows several different sized parts to be processed with the same top jaws to significantly reduce set up time and effort. “That definitely makes a difference in our application,” says Johnson. “The vises open up wide enough so that you can load those heavy beams quickly and easily.”
He adds that automatically closing the vises simultaneously saves time and efforts. Each set of jaws moves independently and can clamp different sized parts at the same time with uniform clamping pressure. “The hydraulic vises that I have will accommodate all three different sizes of the beams we machine,” Johnson says. “If a shop runs the same types of parts as these, the hydraulic vises are an easy setup. It’s just a matter of changing the jaws on them and you’re ready to go again.”
The full hydraulic control allows synchronized operation of multiple vise and even automated or remote control that eliminate operator variation and ergonomic issues. ProHold is one of the more established brands of hydraulic workholding systems that was acquired by Planet Products in recent years. Planet, known best for its live tools and “speeder” tool heads, purchased ProHold because the line accommodates individual setups, machining centers and automated centers, and also because ProHold workholding systems offer some distinct features.
For example, a new ProHold 6 in hydraulic self-centering vise is a fully hydraulic double-acting type with a total stroke of 4.25 in and 11,000 lb of clamping force at 3,800 lb of hydraulic pressure. Self-centering clamping is repeatable within .001 in. Internal pressure accumulators allow the vise to hold pressure even with the hydraulic supply removed, allowing use on palletized systems.
This double-acting vise permits either OD or ID self-centering clamping with no modification. The jaw opening stroke is fully powered to assure positive opening, even with heavy workpieces. Quick-change top jaws on the ProHold 6 in hydraulic self-centering vise are available with either hardened inserts, or machinable steel or aluminum blanks that can be tailored specifically for the workpiece. Standard Prohold Series quick-change top tooling will fit on the vise.
The vise is designed for high production machining and the hydraulic positive opening feature makes it ideal for automated loading. A hardened and ground chip cover eliminates chip accumulation to prevent chips from entering the vise cavity. Any coolant entering the vise is internally drained via weep holes. Vises may be used individually or linked together on a common fixture plate. Operation is by a control valve mounted on the vise, remote mount, or automated control for robotic loading.
The ProHold series hydraulic vise system is covered by U.S. Patent #7,156,384 and includes a 4 in flexible modular vise system, 4 in single station vise, 6 in double station vise, 4-axis indexing Trunnion vise and 4-sided vise columns for palletized operations. Hydraulic pump units and workholding accessories are also available.
Special Machined Components, 7626 Easy Street, Mason, OH 45040, 513-459-1113.
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