With simple structure, easy to mount.
The workpiece can be loaded and unloaded quickly, easy to operate.
All parts are anti-rust treated, the surface is clean.
For heavy duty clamps, the critical part are heat treated to obtain high strength and wear resistance ability.
In manual clamping devices, toggle clamps offer simplicity and design adaptability that is hard to beat.
These clamps, in fact, are practically universal workholders, with an exceptional ratio of holding force to application force, combined with rapid operation, positive locking action and simplified installation. Although they are fairly simple devices, choosing the right manual toggle clamp for a job is a three-step process: Selecting the appropriate clamp action; determining tool forces and required holding capacity (and its direction); and deciding upon the number of clamps to use.
Of these three steps, shops should focus on selecting the most suitable clamp action and ascertaining the number of required clamps. Determining tool forces is a complex issue and should be the responsibility of the fixture designer. That's because tool forces should be absorbed by fixed stops, not the clamps.
The four basic toggle actions are latch, plier, hold-down and plunger. Each type uses a mechanical over-center, toggle-locking action.
Manual toggle action offers a number of advantages. It's faster than tightening nuts and bolts, relatively inexpensive and widely available. Also, it maintains a positive mechanical lock unless stressed beyond its rating. These clamps are limited in that the clamping point must be consistent and the exerting force can be difficult to calculate.
Holding capacity versus exerting force must be understood in selecting a toggle clamp. Exerting force is the amount of force the clamp applies to the workpiece. This variable force depends on the relative position of the clamp components, the adjustment of the spindle or the hook, part variation and point of application on the bar. The maximum exerting force that a clamp generates, for any given set of variables, occurs just as the clamp is going over center into a mechanical lock position. The exerting force shouldn't exceed the rated holding capacity of the clamp.
Holding capacity is the maximum force that the clamp sustains in its closed and locked position without permanent yielding and damage of clamp components. Holding capacity is relevant only when the clamp is in its over-center condition. With hold-down action clamps, holding capacity is rated at a point of application on the clamp bar closest to the base. If the application point moves along the bar away from the base, the holding capacity decreases. The relationship between holding capacity and application point is not linear.
Operator safety is a paramount concern, so clamp style and position should be selected to avoid possible pinch points. A clamp's rated holding capacity should never be exceeded.
Users should not adjust spindles so tightly that clamps become difficult to operate. A rule-of-thumb is that 60 lb. is the maximum force that an operator can repetitively exert on a clamp handle. An average value during the course of a workday is probably closer to 40 lb. If the clamp is too hard to operate, the operator's hand may slip, causing injury. In addition, end users should avoid use of cheater bars to increase leverage. These could slip and cause injury; therefore, if a longer handle is necessary, it should be welded to the original clamp handle. However, a longer handle can permit excessive exerting force, which could cause the clamp to be overstressed -- resulting in a greater tendency to pop out of its mechanical over-center lock. This is especially true if vibration is present and the handle oriented such that it falls open due to gravity. If a positive lock is required, users should drill a cross-hole through the clamp assembly and install a pin to prevent opening.
Also, various devices can be used to preload a clamp arm or plunger if it is used as a locator. This creates an artificial load on the arm or plunger as if it were clamping a part and keeps the clamp in its locked condition.
Most clamps are metallic and will conduct electricity and heat so end users should take precautions against the possibility of shock or burns.
While the action of operating a clamp is of short duration, many repetitive actions can lead to fatigue and related problems. Shops should ensure clamps are used in such a way that they complement the structure of the human body by keeping the operator's wrist straight. Most clamp handles are easily modified to position the handle in a bent position to do so. The optimal handle width or diameter is 1.5 in. for a male hand and 1.343 in. for a female hand.
If required exerting forces or cycle rates are such that operator fatigue and therefore safety, is involved, a better choice for the application could be a pneumatically or hydraulically operated.
Toggle-action clamps can accommodate only small variations in part thicknesses, so part tolerances and repeatability are key considerations. This is because the over-center point of the toggle action is closely controlled. Part thicknesses varying on the low side reduce exerting force. Conversely, part thicknesses varying on the high side increase exerting force, making clamps difficult to operate and even overstressed. A neoprene-tipped spindle will help adapt the clamp to part variations. Spring-loaded spindles can also adapt to variations, but the exerting force is limited to the spring force.
For large variations in part thickness, a cam-action clamp or hydraulic clamp is a good choice. The repeatability of the over-center stop point makes the straight-line action clamp a good locator if fitted with a pre-stop.
Part position and orientation should be such that parts are positioned against a fixed stop so that tool forces are resisted by the stop, not the clamp. Shops should consider how parts will be loaded and unloaded to be sure the clamp bar, including the spindle, will clear the area. If clamping points are not supported underneath, part distortion is likely and the part could vibrate and move out of position. Many clamps have different, easily modified handle styles with lower profiles to avoid tool-path obstruction or to clear machine movements.
Environmental concerns can affect the choice of clamp material. Standard clamp materials are zinc-plated, low-carbon steel for stampings and stainless steel for pivot points. Corrosive liquids or gases or even high humidity, can cause corrosion. Many standard clamp models are available in 302/303 stainless steel for corrosion resistance. In many cases, low-carbon steel clamps can be plated with electroless nickel, cadmium or chromium for corrosion resistance or for aesthetic purposes.
Above 500 degrees F, stainless steel clamps provide better service than low-carbon steel clamps. The limit for plastic grips is 150 degrees F and neoprene on spindle assemblies can be used to 225 degrees F.
How many clamps?
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Shops determine the number of clamps needed by dividing the resultant forces applied against the clamp arm by the holding capacity of the clamp. Manufacturers list maximum values for holding capacity; however, these values must be reduced as the clamping point moves away from the base.
If the number of clamps required is a fraction, the next largest whole number should be selected, which also provides a safety factor. Each clamp must be properly adjusted to ensure that it carries its fair share of the load.
Contact Information
Company :
Shenzhen Tiptop Industries Development Co., Ltd.
Country :
China
Contact person :
Walt Wu
2008-10-11 03:54 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html) @208.185.167.108
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