Clamping and Clamping Devices

Clamping&

Clamping Devices

Clamping System• A clamping system must hold the workpiece firmly against the

locating elements and the cutting forces developed duringoperation without causing damage to it.

• Speed of operation, operator fatigue and strategic positioning are considerationwhile designing clamping system

• Clamping device should be incorporated into the jig or fixture, proper clamping ina fixture directly influence the accuracy and quality of the work done andproduction cycle time.

Principles of Clamping• Position

• Strength

• Productivity

• Operator fatigue

Principles of ClampingPosition:

• Clamping system should be positioned at thick sections of the workpiece.

• Clamping should be positioned to direct the clamping force on a strong, supportedpart of the workpiece.

• Clamping on unsupported part bends slender workpieces, affects accuracy ofoperation.

• Clamping system should not obstruct loading and unloading of the workpiece.

• Clamping system should not obstruct the paths of cutting tool.

• Operator should be able to operate clamps easily and safely

• A vertical hole drilled in the bent workpiece would become angular when theunclamped workpiece springs back to its original shape.

Distortion of unsupported workpiece

• Clamping force shall be directed towards support / locators.

Principles of Clamping

• Clamp shall be directly in line with the support


• Clamping force shall be directed towards support / locators.


• Clamps shall apply force against supported area of work piece


Good Bad

Principles of ClampingStrength:

• The clamping system should be capable to hold the workpiece securely againstthe forces developed during operation.

• Clamping device should be capable to be unaffected by the vibrations generated during an operation.

• The clamping force should not dent or damage the workpiece with excessivepressure.

• For clamping weak and fragile workpiece, clamping force should be equallydistributed over a wider area of the workpiece.

• While clamping soft workpiece, clamps should be fitted with pads or softermaterials such as Nylon or Fibre to prevent damage and denting of theworkpiece.

• Clamping faces should be hardened by proper treatments to minimize their wearing out.

Principles of ClampingProductivity:

• Clamping time should be minimised byusing hand knobs, tommy bars, knurledscrews, handwheels and handles, sothat clamp can be tightened or loosenedmanually without using spanners.

• Most of the clamps use hexagonal nut orhand nut

Hand operated clamping devices


Hand operated clamping devices

Principles of ClampingOperator Fatigue:

• Operator fatigue should be taken into account.

• Clamping should be operator friendly.

• Clamping and releasing should be easy and less time consuming.

• Maintenance should be easy.

• If considerable number of clamps are to be tightened or loosened repeatedly, it isbetter to use pneumatic or hydraulic clamping which reduces operator fatigueand saves clamping time.

• Hand nuts are more convenient for the operator than hexagonal nuts because aspanner is not required to tighten them.

Types of Clamping• Mechanical Actuation Clamps

• Pneumatic and Hydraulic Clamps

• Vacuum Clamping

• Magnetic Clamping

• Electrostatic Clamping

• Non Mechanical Clamping

• Special Clamping Operations

Types of Clamps• Screw clamps

• Strap clamps

• Pivoted clamps

• Hinged clamps

• Swinging clamps

• Quick action clamps

• Power clamps

• Non-conventional clamps

Methods of ClampingClamping method and system are basically of two categories:

1. General type without much consideration of the speed of clamping operations.

2. Quick acting clamping method / quick action clamps.

Screw Clamps• They are threaded devices with knurled collar, hand knob, Allen keys, tommy bar

or spanner flats for rotating and tightening the screw.

• They are used for light clamping.

Screw Clamp

Screw Clamps• The clamping area of screw is increased by providing a pad.

• The clamping pad remains stationary on the workpiece while the screw rotatesand rubs on the conical seat of the pad.

Floating Pad

Screw Clamps• A floating pad is used to prevent damage to the workpiece by allowing the screw

to rotate at the point of clamping on the workpiece.

• The swivel type clamping pad provides a spherical joint between the clampingpad and the clamping screw.

• The swivelling pad adjusts itself to suit the inaccuracies in the clamping face ofthe workpiece.

• The cross pin engages the pad with the screw.

Floating Pad

Screw Clamps• The disadvantage of screw clamp is, the clamping pressure largely depends on the

workpiece, it varies from one workpiece to other.

• It is more time consuming and more efforts are required.

Screw Clamps

Clamping Screw

Screw Clamps

Strap or Plate Clamps

Strap / Plate / Bridge Clamps• It is very simple and reliable clamping device.

• The clamping force is applied by spring loaded nut.

Strap Clamp

Strap / Plate / Bridge Clamps• These are made of rectangular plates and act like levers.

• The clamps are tightened by rotating a hexagonal nut on a clamping screw.

• One end of the clamp presses against the workpiece and the other end on theheel pin.

• The toe i.e. clamping face of the clamp is curved and the pressure face of the heelpin is made spherical to take care of any variations in the workpiece.

• Spherical washers permits the clamp to tilt with respect to the screw and the nut.

Simple Plate Clamp

Strap / Plate / Bridge Clamps• Strap clamps are provided with a washer and spring below the clamp.

• The spring lifts the clamp as the nut is loosened and workpiece becomes free.

• The Spring holds the clamp in a raised position during loading and unloading ofthe workpiece.

• Washer prevents the entry of the spring in the hole of the clamp.

• Clamp is rotated about the stud to release the workpiece.

Simple Plate Clamp

Strap Clamp: Workpiece Variation• The clamp is prevented from rotating during clamping by providing pin at the

heel-end.

• The clamp stud is usually at least 10mm in diameter and nearer to the toe-endthan heel-end of the clamp.

Strap Clamp: Workpiece Variation• The heel pin engages the clamp plate to prevent it from rotating during clamping.

Strap / Plate / Bridge Clamp

Bridge Clamp

Retractable Strap Clamp• When clamps fall in the path of

loading and unloading, they aremade slotted to permit linearwithdrawal.

• The clamp is retraced to the positionshown by chain dotted line duringloading and unloading of theworkpiece.

• Slotted clamp plate so that theworkpiece can be released withoutclamp rotation.

• Adjustable heel pin is used whereworkpiece height is likely to varymore considerably.

Slotted Strap Clamp with adjustable heel pin

Retractable Strap Clamp

“U” Clamp• U Clamp can be removed altogether to facilitate loading and unloading of the

workpiece.

U Clamp with open slot

Two Point Clamp• It is used to clamp two workpieces or to clamp a single workpiece at two

locations.

Swinging Strap Clamp• This type of clamp can be rotated by 90o to clear the passage for loading and

unloading the workpiece.

• The clamp is swung to the position shown by the chain dotted line during loadingand unloading of the workpieces.

Swinging Strap Clamp

Special Strap Clamp• The clamp shape can be changed to suit the workpiece and the operation.

• Clamps can be made slotted in centre to permit passage of the cutter.

Tool slot in clamp

Special Strap Clamp• The clamp shape can be changed to suit the workpiece and the operation.

• Circular and symmetrical workpieces can be clamped well with a spider clamphaving three clamping points, no heel pin is necessary.

Spider Clamp or Three-point Clamp

Swinging Strap Clamp• Figure shows a 45o swinging diagonal

clamp developed for clamping theworkpiece to the jig.

• The ends of the clamp are chamferedto enable loading and unloading of theclamp.

• The stop pin is fitted in the jig platefacilitate bringing the clamp blindly inthe clamping position andloading/unloading positions.

• The clamping bolt is welded to theclamp to simplify swinging of the clampalong with the bolt.

Special swing clamp for drill jig for Terminal Box holes in electrical motor body

• Gooseneck Clamp can reduce the clamp height with respect to the work pieceheight.

Strap Clamp

Gooseneck Clamp

• Strap Clamp clamping two work pieces

Strap Clamp

Strap Clamp

Strap Clamp: Workpiece Variation• Spherical washers are used in pairs. The spherical seat of washers transmits the

clamping pressure from the nut to the clamp.

• Heel pin pressure surface should also be made spherical to permit some tilting ofthe clamp.

• Misalignment between the clamp surface and the clamping nut due to tilting ofthe clamp can be countered by use of spherical washers between the clamp andthe nut.

Clamping variable workpieces

Strap Clamp: Workpiece Variation

Universal Clamp with cylindrical washer

Edge Clamps

Edge Strap Clamp• Edge Clamps are used for clamping workpieces on the edges during facing

operations or when only horizontal surface is to be machined.

• Tightening of the hexagonal nut wedges the clamp between the workpiece andthe angular heel surface.

Edge Strap Clamp

Edge Jaw Clamp• Edge jaw clamp slides down the inclined heel as the hexagonal nut is tightened.

• Tightening of the hexagonal nut pushes the jaw against the workpiece to clamp itsedge.

Edge Jaw Clamp

Pivoted Clamps

Pivoted Strap Clamp• Clamps are often pivoted at the centre to simplify their operation.

• The knurled headed screw is used to loosen and tighten the clamp.

Pivoted Strap Clamp

Pivoted Edge Clamp• The pivot pin is nearer to the clamping point.

• The screw is shifted to the end opposite the clamping point.

• The clamping screw becomes more accessible to the operator.

Pivoted Edge Clamps

Pivoted Two-way Clamp• Pivot action can be used for two-way clamping of the workpiece.

• Tightening of the screw makes the curved surface of the clamp touch theworkpiece and further tightening of the screw clamps the workpiece verticallyand horizontally.

• Two-way clamp also pushes the workpiece against two locators.

Pivoted Two-way Clamp

Hinged / Latch Clamps

Hinged Clamp• Hinged clamp provides rapid clearance of the passage for loading and unloading.

• It is clamped with swinging eyebolt. The clamp has open slot through which theeyebolt can be swung into position.

• Tightening of the hexagonal nut clamps the workpiece.

• For loading and unloading the workpiece, the hexagonal nut is loosened half-a-turn and the eyebolt is swung out of the open slot to free the hinged plate.

Hinged Clamp

Hinged Clamp• The latch and the stud movements are controlled.

• The latch is in fully open position when the faces indicated by “X” are in contact.

• Hand nut is used to clamp the workpiece.

Hinged Two-way Clamp• The workpiece is pushed against the location pins by the pivoted edge clamp

which also houses the swinging eyebolt.

• The knurled nut is used to clamp the workpiece against the location pins.

• Workpiece is clamped in two direction by the edge clamp and the pad in thehinge.

• For loading and unloading the workpiece, the knurled nut is loosened half-a-turnand the eyebolt is swung out of the open slot to free the hinged plate.

Hinged Two-way Clamp

Hinged Clamp

Hinged Clamp with pivoted clamping block

Hinged Clamp• Two-way clamp is an extension of the latch-type clamp.

Button Clamps• These may be fixed at one point or removable as required.

C Washer

C Washer• It is a strap clamp with an open slot.

• It is simple and quick in operation.

• The slot permits quick removal of C Washer after a slight loosening of thehexagonal nut.

• The C washer is often chained to the fixture or pivoted around a shoulder screwto prevent its loss.

• The pivot shoulder screw makes the C washer captive.

Swing Washer• To load or unload the work piece, the locking nut is rotated by giving it about one

turn.

• The stud and bolt sizes are selected in such a manner that when the C Clamp isremoved, the work piece can freely pass over the nut

Swinging Clamps

Swinging Clamps• Theses clamps are swung to the position.

• They rotate in the plane of the plate.

• Figure depict the swinging clamp pivotedabout the shoulder screw.

• Workpiece is clamped by knurled headscrew.

Swinging Clamps

Swinging Clamps• Swinging latch with an open slot at one end..

• The latch is swung around pivot P at the other end.

• Shoulder screw S enters the open slot during operation.

• The workpiece is clamped by knurled head screw.

Swinging Clamps• Types of latches and their methods

of operation.

• Chain-dotted line shows the latchesin their clear loading and unloadingposition.

• Shoulder screws are often used aspivots for thrust pads.

• The shoulder diameter must bebigger than the thrust diameter sothat the shoulder face acts as a stopwhen the screw is tightened.

Swinging Clamps• Swinging clamp with C Washer

Quick Action Clamps

Toggle Clamp• They provide considerable distance for

loading and unloading of theworkpiece.

• The C frame clamp can be swung to thechain dotted position during loadingand unloading.

Toggle Clamp• The pusher-type toggle clamp withdraws backwards during unclamping.

• Toggle clamps are provided with clamping screws to accommodate workpiecevariations.

Toggle Clamp

Quick Turn Screw / Thumb Screw• It is used to clamp hinged jig plates and

latches within a quarter turn.

• In unclamped position head of the thumbscrew can pass through the slot provided inthe jig/latch plate.

• The plate can swung clear of the thumbscrew head.

• For clamping, the thumb screw is turned90o so its head is right angles to the slot inthe plate.

• The mating surface of the thumb screwhead must be filed for proper clamping.

• Quarter-turn screws are suitable for lightloads only.

• For heavy loads, swinging eyebolt and knobcombination is used.

Quick Action Hand Nut

Cast Hand Nut

• They are available with the manufacturers of standard parts.

• Cast hand nuts are more convenient and less expensive than the turned nuts

Cam• Quick clamping by cam is very effective and very simple in operation.

• The cam type clamping system is used for clamping through some interior partswhere other simple system will not have access.

Cam• Cam shifts its mating surfaces to clamp or unclamp the workpieces.

Multiple Clamping

Double Clamping• Two workpieces with limited variation can be clamped by a single strap clamp.

• The spherical washers are provided between the nut and the clamp which allowthe clamp to tilt slightly to suit the variation in the two workpieces.

Equaliser• Clamp is pivoted around a pin.

• Equaliser clamp pivots to suit the variation in the workpieces.

• Equaliser principle can be extended to clamp more than two workpieces.

Equaliser• In multiple clamping, a pivoted equaliser is used for clamping two unequal

workpieces simultaneously.

• A pivot pin is used to pivot the equaliser.

Equaliser for two workpieces

Equaliser


Equaliser• Many even number of workpieces can be clamped simultaneously by a single

clamp.

Equaliser for four workpieces

Equaliser• Only an even number of workpieces can be clamped by an equaliser.


Equaliser for four workpieces

Stacking• Workpieces can be staked together and the entire stack can be secured by a single

clamp.

• Workpieces can be sandwiched between locators and the multi-layered sandwichcan be secured by a single clamp.

• All the workpieces are clamping together by hexagonal head bolt and one end ofthe fixture.

Stacking• In string milling fixture, round workpieces are sandwiched between V locators.

Power Clamping

Power Clamping• Power clamping is used to simultaneously operate a number of clamps.

• Power clamping can be broadly divided in to the following categories:

• Fluid power clamping

o Pneumatic clamping

o Hydraulic clamping

• Vacuum clamping

• Magnetic clamping

• Electrostatic clamping

Summary: Principle of Clamping• Positon clamp on strong supported part of the workpiece, clear of the workpiece

loading / unloading and cutting tool paths.

• Clamp strength should be adequate to withstand operational forces withoutdamaging the workpiece.

• Quick operation without spanner, levers, knobs.

• Pneumatic / hydraulic operation for simultaneous actuation of numerous clamps.

• Compensation for variation in the workpiece through radii at clamping point andon the heel pin, use of spherical washers and equalisers.

References1. Jig and Fixture Design Manual, Erik K. Henrikson, Industrail Press.

2. Jigs and Fixture, P.H. Joshi, THM.

3. An introduction to jig and tool Design, M.H.A. – Kempster, III Ed.Pub ELBS.

Thank You!

Clamping and Clamping Devices

Engineering

Transcript of Clamping and Clamping Devices