april may 2014 design of jigs and fixtures anwer key

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 :;

april may 2014 design of jigs and fixtures anwer key

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