How clamping kits save time and money.
For example, say you just bought a new CNC machine. The part you are machining has a 9-min floor-to-floor cycle time. Three minutes of the nine are for positioning and tightening four hold-down straps by hand with a hex wrench.
You paid a small fortune to speed up your machining, only to waste a third of your time by hand clamping. Hydraulic clamping would do the same task in 6 sec: 3 to clamp, and 3 to unclamp.
Pneumatic and hydraulic clamping has been around for over 40 years. Despite the obvious time savings, many people have shied away because it appeared too complicated to be practical for them.
Perhaps you have been hearing about hydraulic clamping for years, and have even seen it in action at the trade shows. Problem was, you didn't know anything about hydraulics; the idea of hooking up pumps, hoses, and regulators turned you off. Besides, there seemed to be lots of unfamiliar mathematics and plumbing involved. Enter the kits
Today, however, power clamping is more attractive, as simplified kits are being introduced. Clamping equipment manfuacturers have gathered the necessary hardware into sets targeted toward the most common clamping situations.
For example, Jergens, Inc, Cleveland, OH, offers two clamping kits: a basic kit for extended production work on a single fixture, and a flexible kit for both short and long runs that can be easily moved from fixture to fixture. Both kits use shop air as a power source for the hydraulic boosters that drive the system.
The kits are sold complete in a single box. The actual clamps themselves are not included in the kits, but are chosen from among a few dozen styles, all of which are kit compatible. Prices for the kits range from $500 to $1000. What's in a kit?
The heart of any clamping kit is its power source. In the case of Jergens' kits, the power source is an air-powered booster using low-pressure shop air. The booster converts low-pressure air to high-pressure hydraulic power.
Use of a low-pressure source simplifies the system, requiring only a single hydraulic line and relatively inexpensive pneumatic controls instead of hydraulic controls.
The work to be done determines which of the two types of boosters, and consequently which kind of kit, is needed. Permanent fixtures and OEM applications require only a small, dedicated booster because they normally do not call for a large number of clamps, and they are infrequently disconnected. The basic kit is designed for this type of application.
Larger numbers of clamps and fixtures that are freqeuntly changed require a "prefill" booster, a power source that offers high pressures and does not require the line to be bled when disconnected for reattachment to new fixtures. Many users of this power source have attached handles to the booster so it can be carried from fixture to fixture. Jergens calls the kit that contains a prefill booster their Flexible Kit.
The remaining hardware in a kit is used to connect and control the system. Hoses, both air and hydraulic, are included, as are the necessary mufflers, gages, hydraulic fluid, valves, fittings, and filters. In the case of Flexible Kits, quick-disconnect couplings are included to speed changeovers between fixtures. How to use a kit
The new kits are for off-the-shelf use by the general metalworking shop. Although they can be greatly expanded and customized for dozens of uses, in most cases they are for power clamping during milling, drilling, and broaching.
First, you choose your kit based on whether it will be for a dedicated operation or will be moved around. A broaching machine, for example, would use a dedicated system, as would a hydraulic vise that is never disconnected.
Next, you select the clamps. These are not included in the kits, but are picked to fit the job at hand. (See box containing drawings of clamps and their basic forces.)
Force calculations are sometimes required for unusual jobs, but in most simple cases a standard circuit diagram is available from the manufacturer. In some cases, manufacturers have toll-free telephone lines for assistance as well.
Then, with clamps, kit, and circuit plan in hand, you connect your system to your shop air supply. Big savings in time.
What are the benefits of power clamping with kits? Number one is speed. With hand clamping, only about 30 percent of the time it takes to machine a part is spent removing metal. The remaining 70 percent is required to move, load, clamp, unclamp, and unload the part. Obviously, any improvement in machining speed will affect only a small proportion of the overall production time.
Power clamping dramatically reduces this overall "floor-to-floor" time. Savings of 30 to 60 percent are not at all unusual, as a single lever can activate dozens of clamps at once. In this way, expensive idle time on high-speed CNC equipment is minimized.
One typical application involves a horizontal mill. Eight cutters were being use to cut keyways in eight shafts at once. By hand, a bracket with 5/8" stud and flange nuts were tightened for each cycle. A hammer was used to register the workpiece before final tightening.
It took 40 to 60 sec to clamp, and the total floor-to-floor cycle time of the operation yielded 100 pcs/hr.
With a power clamping kit in place, two hydraulic cylinders now hold the eight shafts. It takes 3 sec to clamp and 3 to unclamp; cycle time is now 200 pcs/hr, a 100 percent improvement.
Power clamping is not just for large or automated equipment. Routine and semiroutine work on older and smaller equipment is where hydraulics can really shine. Thanks to the new, lower-cost kits, slow setups on a drilling fixture vise, for example, can be sped along at rates unheard of with hand clamping. High speed is not all
Power clamping has a lot going for it in addition to speed. Pressures are consistent, eliminating over- and under- tightening problems stemming from operator fatigue or carelessness. There is no slippage and no part distortion because the pressure is alway exactly the same.
Scrap is cut way down, too, because of more accurate positioning. Finally, tool life is increased substantially because slippage and chatter are reduced or eliminated. Tool lives that are three times those experienced with hand clamping are not unusual.
In the horizontal mill example, the elimination of tool chatter meant that the mill's cutters had to be replaced only once a year versus the previous three times a year. The clamping system's cost of $1000 in this example was almost exactly equal to the savings in one year for cutters alone! Is power clamping for you?
If you mill, drill, or broach even as few as 50 pieces in a run, you should take a hard look at power clamping. If you machine fewer than 50 pieces at a time, but each piece requires many clamps, or clamps in hard-to-reach places, you should also investigate.
Finally, if you machine thin-section pieces that are easily distorted, power clamping may be the only way to properly hold your work.
For details from Jergens, circle E29.
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|Publication:||Tooling & Production|
|Date:||Apr 1, 1984|
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