CHAPTER8_1INTRODUCTION_TO_JIGS_PARt1.pdf

8/10/2019 CHAPTER8_1INTRODUCTION_TO_JIGS_PARt1.pdf

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JIGS



WHAT? WHERE? HOW?



IntroductionMass production aims at high productivities to reduce unit cost andinter-changea i!ites to "aci!itate eas# assem !#$Jigs are use"u! in mass production$The# provide a means o" manu"acturing interchangea !e parts since the#esta !ish a re!ationship% &ith predetermined to!erances % et&een &or'and too!$

E!iminate set up time "or each piece and thus reduce cost$

(asic re)uirements o" a good dri!! *ig are+$ ,uic' and accurate !ocation o" the &or' piece$

$ Eas# !oading and un!oading o" the &or' piece and prevention "rom o"!oading$

.$ /revention o" ending or movement o" &or' piece during dri!!ing$0$ Amp!e chip c!earance to "aci!itate "ast remova! and c!eaning$1$ 2ight &eight to minimi3e operator "atigue due to repeated hand!ing$





4RI22 (5SHES

These are used to guide dri!!s% reamers and other cutting too!s tothe &or'piece $

(ushes are made o" &ater hardening car on stee! &ith 6$71 to +8car on and 6$16 to 6$98 o" manganese and hardened to R:;6 to;0 to minimi3e &ear due to contact &ith hard rotating too!s$Jig ushings are used in dri!!ing and oring *igs$ Their use permitsgiving up the reduction o" dri!! run o"" and ho!e e<pansion$

The diametric accurac# o" ho!es in dri!!ing is 168 higher on the

average compared to that o" ho!es dri!!ed conventiona!!#$



GE=ERA2 =OTES O= 4RI22 (5SHES

(ushing are main!# used to guide dri!!% reamers and other machining too!in the proper positioning on the &or'piece$ 4ri!! ushes need to

/revent the ending moment o" the dri!!

He!ps etter accurac# minimi3e the time "or dri!!ing$

It protects the dri!! *ig p!ate$

To reduce the &andering o" !ong dri!!$The concentricit# o" the dri!! ushes is 6$6+$

The !ength o" ushing shou!d e appro<$ t&ice the diameter o" the ushho!e$

The diameter shou!d e ver# c!ose to the dia o" the dri!! ut not e tightas it &i!! cause drag in ushing$

Genera! ru!e "or c!earance et&een 6$6+. to6$6 ; mm$ High c!earancecauses chipped dri!! margin and inaccurac#$



MATERIA2S >OR 4RI22 (5SHES

• Made o" good )ua!it# case hardened stee! or too! stee!$

• :an a!so e made o" mi!d stee! car urised to give su""icient

case depth$

• :ommon materia! "or dri!! ushing is Water hardening stee!s&ith 6$71 to+$6 8 :%61 to 6$98 Mn and hardened to ;6to

;0Rc$



T@/ES O> 4RI22 (5SHES

+$ /ress "it ushesa Head!ess or p!ain ush

Headed or "!anged ushc Headed or co!!ared press "ir ush

$ Rene&a !e ushesa >i<ed ushes

S!ip ushes.$ 2inear ushes0$ Threaded ushes1$ Scre& or c!amping ush



S/E:IA2 (5SHES

+$ Oi! grove ushesa T#pe + Boi! &ith ho!e /-t#pe% H t#pe% s!ip "it t#pe

T#pe - &ith oi! ho!e and e<terna! groove

c T#pe .- &ithout oi! "eed

+$ Temp!ate ushes



OTHER T@/ES

• :ircuit oard dri!! ushes• :hip rea'er ushes•

4irect coo!ant ushes



The "actors to e considered &hi!e designing "or *ig - ushing%

o The ushes% used to guide and proper!# !ocate dri!!s% reamers etc$ are genera!!#made o" car on or a!!o# stee! and made &ear resistive # hardening to R: ;6 anda ove$ O"ten ushes are a!so made "rom gre# cast iron "or anti"riction andprotection o" the too!s$

o The hardened *ig ushes are "inished outside # grinding and inside # grindingand !apping i" high precision is insisted$

o The ushCs !ength shou!d e su""icient D t&ice dri!! diameter and its diametershou!d e s!ight!# !arger than the dri!! diameter

o 4esign and construction shou!d ena !e eas# and )uic' proper "itting and remova!or rep!acement o" the ushes

o (ushes shou!d not come out "rom its seat a!ong &ith the dri!! during its return$



/ress >it (ushing

/ressed # inter"erence "it in the ush p!atesD*ig p!ates

5sed in atch production &here ushes out!ast !i"e o" *ig

Emp!o#ed &here the centre distances o" ho!es are too c!ose

to permit the "itting o" !iners and rene&a !e ushes$ +$Head!ess OR /!ain (ush

$Headed OR >!anged ush

.$Headed :o!!ard OR /ress "it ush• Headed ushes are pre"era !e

:o!!ar provides positive s!op

:hance o" getting !oose and move a<ia!!# is !ess$





Rene&a !e (ushes• 5sed "or continuous OR "or !arge atch productionD5sed in

!inear ushings• Inside diameter is su *ected to severe &ear due to

continuous contact &ith cutting too!s$• Emp!o#ed &here the ushing &i!! &ear out e"ore *ig does• t#pes +$ >i<ed $ S!ip• Must e prevented "rom rotating and moving a<ia!!#

D(# provision o" a "!at on the co!!ar





S!ip (ushes• When a ho!e re)uires t&o operations such as dri!!ing and

reaming• =ecessar# to use t&o di""erent guide ushes "or the di""erent

too!s$• Are interchangea !e in a given si3e o" !iner$• 5sed &hen the component is sti!! in the *ig "or reaming

operation there # providing more accurac#$•

Fnur!ed in its head "or eas# remova!$





2iner (ushes• Fno&n as master ushingsC are permanent!# "i<ed into the *ig

od#$• 2iner ushings are avai!a !e in head OR head!ess t#pes and

are pressed into the *ig p!ate$• The# are hardened and so the# provide on!# a !itt!e chance o"

a""ecting the accurac# o" the too! # changing the ushings$





Threaded (ushes5sed "or c!amping the &or' piece are threadedon the outsideThe scre&ing o" the ush into the *ig od# ho!ds

the ush in p!ace ma'es ush ad*usta !e$Ad*usted to suite the !ength o" component$(ut its ver# di""icu!t to maintain accurac#

This is overcome # ma'ing the thread !oose andguiding the ushing # a ground c#!indrica!portion$





Scre& or c!amping (ushes

• 5sed &here &or' piece a!so c!amped$• When !ight &or' piece to e dri!!ed$•

The# have e<terna! threads• Rapid &ear o" thread% so not pre"erred "or

accurate &or'$





S/E:IA2 (5SHES



5sed "or specia! operations such as ottom o" a ushre)uires shaping to suit the pro"i!e o" the componentto prevent de"!ection o" too!

Minimi3e &eight # use o" thinner sections% man#dri!! *igs are ui!t up "rom stee! p!ates "rom sections$

It has the advantage o" econom# o" time since itavoids time necessar# to ma'e casting pattern





Specia! 4ri!! (ushes

Some o" the specia! dri!! ushing are temp!ate ushing%groove ushing% 'nur!ed and generated ushing$Some other t#pe o" specia! ushing are

+$4ri!! ho!es in inc!ined sur"ace$2ong ush is used i" ho!e eing dri!!ed is in recess$ Toreduce dri!! "riction% ush can e counter- ored$

.$T&o ushing &ith "!at can e used %i" it ecomes

impossi !e to provide dri!! ushes in *ig p!ate0$(ushing &ith ho!es can e used$



+$ Oi! grooved ushes◦ /ermit positive and comp!ete !u rication o" the ushing

"or continuous high speed dri!!ing operations◦ Give comp!ete dri!! &ith !u rication and coo!ing◦ 5sed &hen dri!!ing hardened stee! and used as earing$◦ 4i""erent T#pesa With oi! ho!e / t#pe% H t#pe% s!ip "it t#pe

With oi! ho!e and e<terna! groovec Without oi! "eed





$ Temp!ate ushes

5sed "or insta!!ation in thin *ig p!ates$

(ushing is pressed into the ho!e% and a !oc'ring is insta!!ed on the opposite side$

CHAPTER8_1INTRODUCTION_TO_JIGS_PARt1.pdf

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