CLAMPS

CLAMPING Principles

• Clamping elements must hold the work piece firmly engaged with locating elements during the operation.

• The clamping devices is to hold the position of the part against the locators throughout the machining cycle.

•The clamp must not damage or deform the part. The clamping force must not be less.

•Clamp should be fast acting and allow rapid loading an unloading of parts.

CLAMPING PRINCIPLES

CLAMPS

CLAMPING PRINCIPLES

• The clamp should press against a strong portion of the work piece without distorting the workpiece.

• It should hold the work firmly and transmit the clamping force throughout the cutting operation, directly over a fixed support.

• It should be capable of overcoming the maximum possible force exerted on it by the work piece

CLAMPING PRINCIPLES

•Simple clamps are always preferred than complicated clamps.

•Clamp should be easy to operate, positioned or loosened.

• Do not forget to estimate the cutting force and applied clamping force.

CLAMPING PRINCIPLES

CLAMPS

• When designed, they should be operated from the front side of the operator

• They should be designed such that they press down and tend to seat the work

• When cam or wedges are used, they should be designed so that loads or vibrations will tend to seat work.

CLAMPING PRINCIPLES

•The clamp should not damage the work piece surface, recommended to use clamping pad.

•It is best to over design the clamp if there is some doubt.

CLAMPING PRINCIPLES

CLAMPS

TYPESOF

CLAMPS

CLAMPS

TYPES OF MECHANICAL ACTUATION CLAMPS

Screw clamp C-clamp Strap clamp Swing clamp Swing strap clamp Pivoted clamp Hinged clamp Wedge clamp Latch clamp Toggle clamp

Cam action clamp Pinch clamp Equalizer clamp Plate type clamp Two way clamp Edge clamp Button clamp Differential clamp Hook clamp Two slot clamp Spider clamp

SCREW CLAMP

SCREW CLAMP

• These are simple clamps which make use of a threaded rod equipped with some method of tightening.

• They are used commonly in jigs and fixtures.

• Screw clamp uses the torque developed by screw thread to hold the workpiece.

• Table shown indicates the average holding force for screws of different sizes

SCREW CLAMP

They may consist of knurled collar, hand knob, Tommy bar or spanner flats for rotating and tightening the screw.

Simple screw clamp is shown in figure.

SCREW CLAMP

The clamping force of the screw clamp may be increased by provision of pad.

The clamp pad is free to rotate on the pivot. This eliminates the friction between workpiece and clamp (shown in next slide)

The clamping pad remains stationery on the workpiece while the screw rotates and rubs on the top face of the pad.

A swivel-type clamping pad provides a spherical joint between clamping pad and clamping screw.

This allows the clamping pad to swivel around the clamping screw.

The pad adjusts itself to suit the inaccuracies in the clamping face of the work piece

The cross pin pull the pad backwards when screw is retracted

SCREW CLAMP

CLAMPING ACTION OF SCREW CLAMP

SLIDE CLAMPING BAR TO CONTACT THE WORKPIECE

TURN AND APPLY CLAMPINGFORCE

AFTER MACHINING TURN TO UNCLAMP

SLIDE CLAMPING BAR BACK TO UNLOAD

SCREW CLAMP

Screw clamp with pressure pad

Ball and foot are threaded to allow easy installation and removal, a left-hand thread to positively prevent blackout when turning the screw

SCREW CLAMP

SCREW CLAMP

C-CLAMP

C-CLAMP

These are quick acting clamp.

The locking nut can release or lock the clamp in about one turn only ( shown in figure)

STRAP CLAMP

STRAP CLAMP

Simplest of all clamps.The basic operation is as same as that of a

lever.They can broadly classified as first class,

second class, third class each representing a form of lever.

When a strap clamp is used, the force on the workpiece is always proportional to the position of the fastener with respect to the workpiece and heel.

Manual devices include hex nut, hand knobs, cams.

The strap clamp is operated by either manual or power driven devices.

Power driven include hydraulic or pneumatic.

STRAP CLAMP

The fulcrum is placed between the work and the effort. Note the spherical washer

The work is placed between the fulcrum and the effort. This is principle of second class lever

STRAP CLAMP

In this type, the effort is placed between the work and the fulcrum.

STRAP CLAMP

Simple strap clamp arrangement

STRAP CLAMP

TAPPED HEEL STRAP CLAMP

CAM ACTUATED STRAP CLAMP

RETRACTABLE CLAMP

RETRACTABLE CLAMPWhen clamps fall in the path of loading and unloading they are made slotted to permit linear withdrawal.

Clamp strap with slotted underneath to allow sliding it straight back for clear loading. Two drill slots on sides are provide a secure grip while sliding

SWIVEL CLAMP

SWIVEL CLAMPAnother type of strap clamp

In this design the clamp is rotated by 90 to clear the passage for loading and unloading.

The clamp is swung to the position shown in chain-dotted line during loading and unloading the workpiece.

PIVOTED CLAMP

PIVOTED CLAMP

• In this type of ( PIVOTED ) design, clamps are pivoted at the center to simplify their operation.

• The clamp pivots around the central pin during operation.

• The point of operation should be noted, the screw has been shifted from centre to the end opposite the clamping point

• It is tightened and loosened by the knurled head screw.

PIVOTED CLAMP

Pivoted two way clamp

SWING CLAMP

SWING CLAMP

Swing clamp combine the screw clamp with swinging arm that pivots on its mounting stud.

The holding power with this clamp is generated by screw.

Swing clamp must be swung to the working position.

SWING CLAMP

Other arrangements of swing clamp

SWING CLAMP

STANDARD SWING CLAMP

SWING CLAMP

Long-reach swing clamp that can be hand tightened for medium clamping force. The post-mounted version is ideal for tight spaces, with a long mounting post for increased strength. Swing arm can be turned over for more clearance underneath

SWING CLAMP

HINGE CLAMP

HINGE CLAMP

Hinged clamp provides rapid clearance of loading an unloading passage.

It is generally clamped with swinging eye bolt.

The clamp is provided with open slot through which the eye bolt can be swung in position.

The hinged plate is swung aside during loading and unloading.

HINGE CLAMP

• HINGE CLAMP

• Hinged clamp can also be used for two way clamping.

• The work is pushed against locating pins by pivoted edge clamp which also houses a swinging eye-bolt.

• Tightening of knurled nut against hinge clamp first pushes the work against pins.

• This pushes clamping pad towards workpiece which is clamped simultaneously in two directions by edge clamp and pad in hinge.

• The knurled nut is loosened only by half a turn before swinging the eye bolt and hinge plate aside for loading and unloading the workpiece.

WEDGE CLAMP

WEDGE CLAMP

A plain wedge clamp consists of movable inclined plane which forces the workpiece against a fixed stop.

Plain wedge clamps tends to loosen under vibration.

The taper end of the plain wedge may range from 6 to 18 depending upon the coefficient of friction of the metal.

The wedge can be used with springs to form a pinch clamp.

WEDGE CLAMP

WEDGE ANGLE AND FORCES The diagram shows the forces acting on wedge

at instant removal begins. It is assumed that the wedge has previously been

inserted to exert a clamping force F2 on the workpiece with reaction F1 from the wedge block.

F1 & F2 act normal to the bearing surfaces. The taper angle of the top of the wedge is a. Two friction forces F3 & F4 resist removal of

wedge by pull P. For coefficient of friction designated by f. F3 = f F1

F4 = f F2

WEDGE CLAMP

WEDGE CLAMP

The angle a must have a tangent less than value of the coefficient of friction if wedge is to stay tight.

For coefficient of friction 0.15 is approximately 16. But it almost certain that a taper angle of over 16 will not stay in place. But in presence of oil and other slippery conditions, f may drop below 0.1 for which an angle less than 10 is required.

The practical working angle for tapered keys should be less than 7 ( Total angle)

WEDGE CLAMP

PLAIN WEDGE CLAMP IMPROVED WEDGE CLAMP

PINCH CLAMP

EDGE CLAMP

EDGE CLAMPAn important new clamping development!

These new mini edge clamps, are ideal for fixturing small parts.

Clamping force is applied by positive screw action with the easy turn of hex wrench.

Edge clamps exert downward thrust force on workpiece, to prevent it from lifting.

EDGE CLAMP

THE SERRATED FACE PROVIDES MAXIMUM GRIPPING WHILE SMOOTH FACE AVOIDS MARRING FINISHED PARTS

EDGE CLAMP

EDGE CLAMP ARRANGEMENT

HOOK CLAMP

HOOK CLAMP

Hook clamp are similar to swing clamps but smaller.

They are useful in tight places or where several clamps rather than one large clamp must be used.

HOOK CLAMP

HOOK CLAMP

UPTHRUST CLAMP

UPTHRUST CLAMP

Up-thrust clamp locate off of parts top surface and clamp from bottom

UPTHRUST CLAMP

UPTHRUST CLAMP

The lower jaw has two clamping surfaces 180 apart one for thinner parts, the other for thicker parts. The cam handle rotates to screw the lower jaw up or down for fine adjustment

ADJUSTABLE CLAMP

ADJUSTABLE CLAMP

ADJUSTABLE CLAMP

Adjustable clamping arrangement

DOUBLE END STRAP CLAMP

Clamp strap with two clamping ends, for holding two work pieces simultaneously

DOUBLE END STRAP CLAMP

Double end strap clamp arrangement

U-CLAMP

U-CLAMPSOpen U end allows totally removing clamp strap when unclamped. Clamp tips are beveled for extra clearance

TOGGLE CLAMP

TOGGLE CLAMP

A toggle clamp is a quick-acting mechanical linkage where two of the elements make up a Toggle action.

Actuating the clamp first moves it into position, then applies clamping forces by compressing or stretching the linkage elements after contacting the work piece, then positively locks it by moving the toggle action’s center pivot past centerline of other two pivots, against a stop.

Do not try to design a toggle clamp. It is advised to use only the standard clamp from reputed manufacturer.

TOGGLE CLAMP

LATCH CLAMPLatch clamp is limited to light work as it is difficult to secure rigidly.

The main advantage of latch clamp is in the speed of manipulation.

Simple latch clamp is shown in fig.

EQUALISER CLAMP

In multiple clamping, a pivoted equalizer is used for clamping two unequal workpiece simultaneously.

The equalizer clamp pivots around the pin to suit the workpiece.

Equalizer principle can be extended to facilitate clamping of many even number of work pieces simultaneously by a single clamp.

The main advantage of this type of clamp is that clamping force is equally distributed to all work pieces.

EQUALIZER CLAMP FOR UNEQUAL PIECES EQUALIZER FOR MANY

NUMBER OF PIECES

PLATE CLAMP

It holds the workpiece with Toe and Heel arrangements. The heel is held in position by a pin and spring arrangement.

TWO WAY CLAMP

TWO WAY CLAMP

This clamp has quick releasing action. When nut is released the clamp becomes loose.

An advantage of this type of clamp is that all clamping actuation is done from one central position

If separate clamp are used, the machine operator may be required to reach across the workpiece or travel to other side of the machine to operate the clamp

TWO WAY CLAMP

TWO WAY CLAMP

SOME OF TWO WAY CLAMPING METHODS

TWO WAY CLAMP

Centrally actuated clamp

TWO WAY CLAMP

DIFFERENTIAL CLAMPING

DIFFERENTIAL CLAMP

Differential clamp adjust themselves to suit the workpiece

The clamp does not subject the work piece to bending or distortion.

They clamp the workpiece without shifting its position

The lower jaws are closed or opened by turning screw which engages in t-slot in operating clamp

DIFFERENTIAL CLAMPING

DIFFERENTIAL CLAMP ARRANGEMENT

SPIDER CLAMP

SPIDER CLAMPIn spider clamp circular and symmetrical work pieces can be clamped well with a spider clamp having three clamping points.

As the clamp acts as a sort of rigid washer, no heel pin is required

MAGNETIC CLAMPING

MAGNETIC CLAMPING

Magnetic clamping force can be developed by permanent magnets and electromagnets.

Permanent magnets: are mounted on sliding member which can be moved under the non-magnetic material on the table to block the magnetic flux. This release the workpiece.

• For clamping work piece permanent magnets are moved under the magnetic part of the table. This allows magnetic flux to pass through work piece and hold it magnetically.

• The permanent magnets are slid in clamping and unclamping position.

• Electromagnetic tables use solenoid coils as temporary magnets

• When dc current is passed through the solenoid coil it acts like magnet

• Magnetic clamping leaves some residual magnetism in work pieces which can be removed by demagnetizing

MAGNETIC CLAMPING

VACUUM CLAMP

This is particularly convenient for securing thin flat sheets which are vulnerable to distortion under heavy clamping force. Vacuum clamping provides light clamping. The holding face is provided with 0.025mm deep grooves which create a vacuum all over the face.

The clamping face is circumscribed by rubber seal groove all round. The seal in the groove segregates the clamping vacuum area from space outside the seal. The vacuum pressure is usually limited to LESS THAN 1 kg/cm2.

VACUUM CLAMP ARRANGEMENT