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7/25/2019 April May 2014 Design of Jigs and Fixtures Anwer Key
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KARPAGAM INSTITUTE OF TECHNOLOGY, COIMBATORE 105
DEPARTMENT OF MECHANICAL ENGINEERING
IV YEAR - MECH VII - SEM
ANSWERS UNIVERSITY QUESTION PAPER NOV/DEC 01!
ME0" - DESIGN OF #IGS, FI$TURES AND PRESS TOOLS
PART - A
1. A situation in which a workpiece has more locating points than it
actually needs. Redundant locators increase the chances of errors in
manufacturing processes.2.
3. A xture is a work holding device which is used to locate, support and
hold the workpiece securely fastened to the machine tale during the
machining operation. !t does not guide the tool."xample# $urning %ixtures, &illing %ixtures
'. !ndexing (igs are used to drill series of holes in a circle on the
circumference of a cylindrical workpieces. $he indexing plate with aplunger is re)uired in the indexing (igs.
*. A press is a metal forming machine tool used to shape or cut metal y
applying force to carry out the various sheet metal operations.
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+. entre of pressure is a point, in which the summation of shearing
forces will e symmetrical. $his point is the centre of gravity of the line
that is the perimeter of the lank.
-. $he tendency of the metal tries to resume its original position causing
a decrease in end angle known as spring ack.
. A die in which a cutting operation is comined with non/cutting
operation is referred to as a comination die. $he cutting operations
may include lanking, piercing, trimming and cuto0 and are comined
with non/cutting operations which includes ending, extruding,
emossing and forming.
9. $he cutting of metal etween die and punch is a shearing process in
which the metal is stressed in shear etween two cutting edges
eyond its ultimate strength.iing is the secondary operation in which the extended portions are
removed in the lank.
1. 4okaYoke or mistake proofing or fool-proofing, is a Japanese word for the
concept of using simple mechanisms to prevent mistakes from being made by workers
without any special effort. The failsafe devices are called as oka yokes.
PART B11% (a) PRINCIPLES OF LOCATION:
5ocation must e related to the dimensional re)uirements stated on
the workpiece drawing. !t is preferale to use a more accurately machined surface than a less
accurate surface for location. $he workpiece should e prevented from moving along and rotating
around the 6, 7 and 8 axes. 5ocation system should facilitate easy and )uick loading and unloading
of the workpiece. Redundant locators must e avoided.
5ocation system should positively prevent wrong loading of the
workpiece y foolproong.
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DIFFERENT LOCATING METHODS:
A workpiece can e located from#
1. 4lane surface
2. ylindrical surface
3. 4role surface
Location from Plane Srface
A plane surface can e located with three points on the surface. A
rough un/machined surface can e located with three location pads having
point contact. $his can e done y providing three location pins having
spherical surfaces at the locating points as shown in %igure. $he pins should
e spaced as widely as possile for more accurate location. $he height of the
collar of the pins should e e)ual so that the located surface is parallel to the
ase plate resting on the machine tale. Although the three pins can dene a
plane, they cannot provide ade)uate support to the workpiece duringmachining operation such as milling. Additional ad(ustale supports are
necessary to prevent distortion and virations in the workpiece during
clamping and machining. $he numer of ad(ustale supports would depend
upon the shape, strength and sie of the workpiece.
Locatin! Plane Srface
Locatin! c"lin#rical $rface:
!n the cylindrical location, the workpiece surface or the support surface
may e circular. 5ocating the cylindrical surface is the e0ective and most
common method of the location. ince 9 degrees of freedom is arrested y
using the cylindrical locating pins and the remaining 3 degrees of freedom is
arrested y the clamping which is shown in the gure. $he cylindrical
locators may e short or long. &ost it is kept as short as possile to prvent
uckling during loading and unloading.
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Locatin! c"lin#rical $rface $in! c"lin#rical $rface
$he cylindrical surfaces of the workpieces are usually located using :;