Jigs and fixtures imp

ppt for jig and fixture and their types

1. Jigs
and
Fixtures

2. Definitions
Jig: A device that holds
the work and locates
the path of the tool.

Fixture: A device fixed
to the worktable of a
machine and locates
the work in an exact
position relative to the
cutting tool.
Superior Jig
Flexible Fixturing Systems

3. What are Jigs and Fixtures
Anything used to
hold a work piece in
a desired location
Locate parts for
precision
Repeating process
on a series of parts
Holding parts for
machining, painting,
assembly

4. Components used in Jigs:

5. Drill jig terms
Drill bushings
Precision tools that
guide cutting tools
such as drill and
reamers into
precise locations in
a workpiece.
Accurate Bushing Co.

6. Drill jig components
Jig body
It is a plate or frame which Holds the
various parts of a jig assembly.
Cap screws and dowel pins
Hold fabricated parts together

7. Drill jig components
Locating devices
Pins, pads, and recesses used to locate
the workpiece on the jig.

8. Drill jig components
Clamping devices

9. Drill jig components
Locking pins
Inserted to lock or
hold the work piece
securely to the jig
plate while
subsequent holes
are being drilled.

10. Elements of Jig and fixture
Sufficiently rigid bodies (plate, box or
frame structure
Locating elements.
Clamping elements.
Tool guiding elements.
Elements for positioning or fastening
the jig or fixture.

11. Two main
types of jigs:
For machining purposes
Locates the component,
holds it firmly in place,
and guides the cutting
tool.
For assembly purposes
Locates separate
component parts and
holds them rigidly in their
correct positions while
they are being connected.
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12. Drill jig terms
Open jig (also called plate jig or drill
template)
The simplest type of drill jig
Consists of a plate with holes to guide the
drills, and may have locating pins that
locate the workpiece on the jig

13. Channel
•Permit drilling in more than
one surface
•Reduces number of setups but
increase in design and
manufacturing cost of jigs

14. Leaf/Latch jig:
Small and incorporates a hinged leaf that carries
bushings, and through which clamping forces is applied.
The plate can swung aside to allow for loading and
unloading the work piece from top.

15. Uses of Jig and fixture
Reduce cost of production.
Increase the production.
To assure high accuracy of parts
Enable heavy and complex parts to
machine
Reduced quality control expenses.
Increased versatility of machine tool.
Less skilled labour.
Saving labour.
Partially automates the machine tools
Use improve the safety, accidents low

16. Type of Fixtures
Milling fixtures
Turning Fixture
Fixture design
considerations
Sequence in laying
out a fixture
Standard Parts Co.

17. Turing Fixture
•When workpiece can not
held on lathe easily by
using of standard holding
devices ,then a turning
fixtures are used.
•It is either held in a chuck or
fixed to a face plate.
•It consists base location
and clamping devices as
usual and an arrangement
to fasten the fixture to the
lathe.
•A turning fixture mounted
on a lathe machine spindle.

18. Milling Fixture
•It is work holding device
which is clamed to table
of the milling machine.
• It is solid casting that
absorb vibrations
resulting from cutting
action of milling cutter.
•It consists heavy base
,locating and clamping
element.

19. Fixture components
Fixture base
Fixture components and the workpiece are
usually located on a base, which is
securely fastened to the milling machine
table.
Standard Parts Co.

20. Fixture components
Clamps
Clamps counteract forces from the feed of
the table and rotation of the cutter.
American Drill Bushing Co.

21. Clamps
The process of holding the position of the workpiece in the
jig or fixture is called clamping. The primary devices used
for holding a workpiece are clamps.
To perform properly, both the clamping devices and their
location on the workholder must be carefully selected.

22. Factors in Selecting Clamps
Clamps serve two primary functions. First, they must hold the workpiece
against its locators.
 Second, the clamps must prevent movement of the workpiece.
In drilling, for example, the primary cutting forces are usually directed
down and radially about the axis of the drill. So, the clamps selected for an
application need only be strong enough to hold the workpiece against the
locators and resist the secondary cutting forces.
Holding Securely Under Vibration, Loading, and Stress. The next factors
in selecting a clamp are the vibration and stress expected in the operation.
Cam clamps, for example, although good for some operations, are not the
best choice when excessive vibration can loosen them. It is also a good idea
to add a safety margin to the estimated forces acting on a clamp.
Preventing Damage to the Workpiece. The clamp chosen must also be one
that does not damage the workpiece. Damage occurs in many ways.
 Too much clamping force can warp or bend the workpiece.
 Surface damage is often caused by clamps with hardened or non-rotating
contact surfaces Improving Load/Unload.
The speed of clamping and unclamping is usually the most-important factor
in keeping loading/unloading time to a minimum.

23. CLAMPING GUIDELINES

24. 1.Solid clamp
•It is also called as heel clamp.
•It is simple type of clamp which is tightened by
rotating a hexagonal nut on a stud.
•One end of clamp is pressed against the work
piece and another end is on the pin.
•The washer is provided below the nut and
compression spring is provided below the clamp.
•
Types of clamp

25. 2.Latch swinging clamp
•It can be pivoted on one end and swung around the
pivot.
•The plate can be clamped during operation by
tightening the shoulder screw.

26. 3.Slotted Strap clamp
•Its plate is used to allow
linear movement when
it falls in the path of
loading and unloading.
•Its construction is
similar to heel clamp.

27. Slotted clamp:

28. 4.Cam clamp
•Direct – tendency to loosen during machining
•Fast operating clamping devises by simply actuating the
handle up and down which lock and unlock the plate.

29. 5.Hinged clamp:
•It is similar to swinging the latch clamp , but the hinge clamp is used
when it is not possible to rotate the latch.
•In hinge clamp the plate is hinged at one end which can be swung
aside during loading and unloading.
•The work piece can be clamped by tightening the nut on the stud .
•The stud also permit adjustment to accommodate work piece of
varying height.

30. Advantages and disadvantages of
clamp:
Advantages:
1.They are hold workpiece.
2.Less chances of damage.
3.They are unaffected by vibration.
 Disadvantages:
1.It may be damage the workpiece due to variable pressure.
2.It take more time clamp the workpiece.
3.More effort for operator for repetitive nature disturb the clamping

31. 1. External locators
Devices used to locate the part from
external surface.
Two basic forms of external locators are
fixed or adjustable.


32. Internal locators
For locating holes and bored diameters –
usually located internal surfaces.
Fixed locators – machined to suit specific size
when the size variations are not large –
example: base plate
Compensating locators: conical and self
adjusting

33. 1.Cylindrical locators
•It is used in to hole
available in a workpiece for
the insertion of locator.
•Top portion of this pin is
given sufficient chamfer to
facilitate loading of the
workpiece as shown in fig.

34. 2.Conical locators:
A conical locator is similar to cylindrical
locators but shoulder is similar to cone
shaped.
It is used to locate workpiece which is
cylindrical with or without hole.
Any variation of hole size can be easily
adjust due to conical shape of the pin.

35. Conical locators

36. 3.Diamond Pin locator
The second locator is used
only to restrict the rotational
degree of freedom.
The second locator is
diamond pin which is
slightly smaller than
workpiece hole.
The principle locator should
be longer than locator so
that the work piece can be
pivoted around it before
engaging with the diamond
pin.

37. 4.V locators
It used to locate cylindrical or
semi cylindrical surface.
It allow workpiece with
varying diameter.
Generally a fixed v or sliding
v used to locate workpiece
and combination of fixed v
used to clamp a workpiece.

39. General principle of Jigs and Fixtures
Reduction of idle time – Should enable easy
clamping and unloading such that idle time is
minimum
Cleanliness of machining process – Design must
be such that not much time is wasted in cleaning of
burrs, chips etc.
Replaceable part or standardization – The locating
and supporting surfaces as far as possible should be
replaceable, should be standardized so that their
interchangeable manufacture is possible
Provision for coolant – Provision should be there so
that the tool is cooled and the chips are washed
away

40. General principle of Jigs and Fixtures
 Hardened surfaces – All locating and supporting
surfaces should be hardened materials as far as
conditions permit so that they are not quickly worn
out and accuracy is retained for a long time
 Fool-proofing – Pins and other devices of simple
nature incorporated in such a position that they will
always spoil the placement of the component the
fitting of the cutting tool until the latter are in correct
position.

41. General principle of Jigs and Fixtures
Economic soundness – Equipment should be
economically sound, cost of design and manufacture
should be in proportion to the quantity and price of
producer
 Easy manipulation – It should be as light in weight
as possible and easy to handle so that workman is
not subjected to fatigue, should be provided with
adequate lift aids
 Initial location – Should be ensured that workpiece
is not located on more than 3 points in anyone plane
test to avoid rocking, spring loading should be done
 Position of clamps – Clamping should occur
directly above the points supporting the workpiece to
avoid distortion and springing

42. General principle of Jigs and Fixtures
Clearance – Sufficient amount of clearance should be
provided around the work so that operator’s hands
can easily enter the body for placing the workpiece
and any variations of work can be accommodated
 Ejecting devices – Proper ejecting devices should
be incorporated in the body to push the workpiece
out after operation
 Rigidity and stability – It should remain perfectly
rigid and stable during operation. Provision should be
made for proper positioning and rigidly holding the
jigs and fixtures
 Safety – The design should assure perfect safety
of the operator