04-clamping principles & clamps..ppt
TRANSCRIPT
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