introduction to cnc m4 u11

7/23/2019 Introduction to CNC M4 U11

http://slidepdf.com/reader/full/introduction-to-cnc-m4-u11 1/90

Trade of Metal Fabrication

Module 4: Structural SteelFabrication

Unit 11: Introduction to CNC

Phase 2



Trade of Metal Fabrication – Phase 2

Module 4 Unit 11

Table of Contents

List of Figures.....................................................................................................................6

List of Tables......................................................................................................................7

ocu!ent "elease #istor$................................................................................................%

Module 4 – &tructural &teel Fabrication.........................................................................'

Unit 11 – Introduction to CNC........................................................................................

!earnin" #utco$e:......................................................................................................

%e& !earnin" Points:...................................................................................................

Trainin" 'esources:.....................................................................................................

%e& !earnin" Points Code:..........................................................................................

C(C Machine Tools.........................................................................................................1)

NC and CNC ()*lained................................................................................................1+

Nu$erical Control,....................................................................................................1+

Co$*uter Nu$erical Control,...................................................................................1+

Constructional Features of CNC Machines...................................................................11

Machine Structure......................................................................................................11

Slide-a&s...................................................................................................................12

!eadscre-s.................................................................................................................1Machine /uardin" and S-arf Control.......................................................................14

S-arf Control.............................................................................................................10

Machine )es................................................................................................................1

'i"ht3and 'ule 56ertical Millin" Machine7............................................................18

Control of Slide Mo9e$ent on CNC Machines............................................................1

d9anta"es of CNC Machines......................................................................................2+

Part Progra!!ing...........................................................................................................21

Part Pro"ra$$in"..........................................................................................................21

Cartesian Coordinates................................................................................................21

;< = > ? )es...........................................................................................................22

Polar Coordinates.......................................................................................................2

Selection of ?ero Point..................................................................................................24

@uadrantal use for Millin".........................................................................................2

@uadrantal use for Turnin"........................................................................................28

Aefinition of Points on a Surface...............................................................................2

Aocu$entation...............................................................................................................1

Unit 11 2




Module 4 Unit 11

Pro"ra$ Sheets..........................................................................................................1

Coordinate Sheets......................................................................................................1

#*eration Sheet..........................................................................................................1

Part3Pro"ra$ For$at.....................................................................................................

Fi)ed SeBuential For$at............................................................................................Tab SeBuential For$at...............................................................................................

ord ddress.............................................................................................................4

!eadin" ?ero Su**ression.........................................................................................4

Trailin" ?ero Su**ression..........................................................................................0

Part Pro"ra$ Code !istin"s.......................................................................................0

M: Miscellaneous Functions......................................................................................0

/: Pre*arator& Function ddresses...........................................................................

Control of Slide Mo9e$ent.......................................................................................!inear Inter*olation...................................................................................................8

/eo$etr& and Tri"ono$etr&.........................................................................................4+

I$*ortant /eo$etrical Theore$s..............................................................................4+

Intersectin" Strai"ht !ines.........................................................................................42

Trian"les........................................................................................................................4

P&tha"oras Theore$..................................................................................................40

Tri"ono$etr&.............................................................................................................4

Tri"ono$etrical 'atios..............................................................................................4

Solution of 'i"ht3n"led Trian"les...........................................................................48

Sine 'ule....................................................................................................................48

The Cosine 'ule.........................................................................................................4

ata *n+ut,&torage and Progra! Pro-ing....................................................................)

Aata In*utDStora"e and Pro"ra$ Pro9in"......................................................................0+

Ma"netic Ta*es and Aiscs.........................................................................................01

Ma"netic Aiscs..........................................................................................................01

ost Co$*uter...........................................................................................................01Manual Aata In*ut 5MAI7..........................................................................................01

Pro"ra$ Pro9in"........................................................................................................02

Ar& 'un......................................................................................................................02

Plotter.........................................................................................................................02

Sin"le Ste* or Ste**in"..............................................................................................02

Co$*uter /ra*hics....................................................................................................02

C(C &etting / 0+eration...............................................................................................

orE*iece and Tool Settin"...........................................................................................0

Unit 11




Module 4 Unit 11

Settin" )is Aatu$s..................................................................................................04

orEholdin" Ae9ices....................................................................................................00

Cate"or& 1..................................................................................................................00

Cate"or& 2..................................................................................................................08

Machine #*eratin" Considerations...............................................................................+($er"enc& Shutdo-ns...............................................................................................+

Feed #9erride Control...............................................................................................+

&elf ssess!ent.................................................................................................................61

ns3ers to uestions 15. Module 4. Unit 11................................................................6

*nde..................................................................................................................................6'

Unit 11 4




Module 4 Unit 11

List of Figures

Fi"ure 1 3 nti3Friction Slide-a&s....................................................................................11

Fi"ure 2 3 &drostatic Slide-a&........................................................................................12

Fi"ure 3 'e3circulatin" all !eadscre-..........................................................................1

Fi"ure 4 3 Machine /uardin"............................................................................................1

Fi"ure 0 3 S-arf 'e$o9al Con9e&ors...............................................................................14

Fi"ure 3 ;< =< ? )es......................................................................................................10

Fi"ure 8 3 'i"ht3and 'ule...............................................................................................1

Fi"ure 3 #*en !oo* Control...........................................................................................18

Fi"ure 3 locE Aia"ra$ Closed !oo* Control S&ste$..................................................1Fi"ure 1+ 3 T-o3Ai$ensional 'ectan"ular Coordinates...................................................2+

Fi"ure 11 3 ;< = and ? )es..............................................................................................21

Fi"ure 12 3 bsolute and Incre$ental Ai$ensionin"........................................................21

Fi"ure 1 3 Ai$ensionin" in Polar Coordinates................................................................22

Fi"ure 14 3 Pitch Circle Aia$eter......................................................................................22

Fi"ure 10 3 ()a$*le of ?ero Point #*tions on orE*iece...............................................2

Fi"ure 1 3 ()a$*les of Co$*onent -ith ?ero Point in orE*iece Centre.....................2Fi"ure 18 3 ;+ ?+ Positions for Turnin" #*erations.........................................................24

Fi"ure 1 3 bsolute Si"ns for Four @uadrants.................................................................20

Fi"ure 1 3 'ear Tools Post !athe.....................................................................................2

Fi"ure 2+ 3 Front Tool Post !athe......................................................................................28

Fi"ure 21 3 Aefinition of Points on a Surface 1.................................................................2

Fi"ure 22 3 Aefinition of Points on a Surface 2.................................................................2

Fi"ure 2 3 Aefinition of Points on a Surface .................................................................2

Fi"ure 24 3 Pro"ra$$in" Sheet.........................................................................................1

Fi"ure 20 3 !inear Inter*olation........................................................................................

Fi"ure 2 3 ()a$*le of /+ Co$$and in use..................................................................8

Fi"ure 28 3 ()a$*le of /+2 Co$$and in use..................................................................

Fi"ure 2 3 I$*ortant /eo$etric Theore$s......................................................................

Fi"ure 2 3 Intersectin" Strai"ht !ines..............................................................................41

Fi"ure + 3 Trian"les..........................................................................................................42

Unit 11




Module 4 Unit 11

Fi"ure 1 3 Section of Punched Ta*e.................................................................................4

Fi"ure 2 3 Machine Aatu$ and orE*iece Aatu$..........................................................02

Fi"ure 3 Collet Aetails..................................................................................................00

Fi"ure 4 3 Cla$*in" Set #*eration..................................................................................08

List of Tables

Table 1 3 Fi)ed SeBuential For$at.....................................................................................2

Table 2 3 Tab SeBuential For$at........................................................................................2

Table 3 ord ddress......................................................................................................

Unit 11 6




Module 4 Unit 11

ocu!ent "elease #istor$

ate ersion Co!!ents

2D+1D+ First draft

1D12D1 S#!S transfer

Unit 11 7




Module 4 Unit 11

Module 4 – &tructural &teel Fabrication

Unit 11 – *ntroduction to C(C

uration – 4 #ours

Learning 0utco!e8

& the end of this unit each a**rentice -ill be able to:

• !ist the technolo"ical de9elo*$ents -hich ha9e led to the de9elo*$ent of$odern CNC $achines

• !ist the constructional details -hich distin"uish a CNC $achine tool fro$ acon9entional $achine tool

• State the ad9anta"es of CNC $achines co$*ared -ith con9entional $achines

9e$ Learning Points8

Rk - Requirement for complex components

microprocessors –computer technology.

- Differences between NC and CNC machines.

- Machine structure and frame location of

servo motors, stepping motors, machine

Rk - Repeatability.- Set-up of times, flexibility in changes of

component design. Reduction of operation

P - Communication, information gathering,

adaptability, quality awareness.

Training "esources8

•

Ae$onstration $achine or 9isit to -orE*lace to 9ie- CNC $Dc in o*eration• Ara-in"s and illustrations of CNC $achines

• Sa$*le co$*onents or dra-in"s of co$*le) *arts *roduced on CNC$achines

• Manufacturers s*ecifications for 9arious $achines

• Course notesDhandoutsD9ideos

9e$ Learning Points Code8

M G Maths AG Ara-in" '% G 'elated %no-led"e Sc G Science

Unit 11 %




Module 4 Unit 11

P G Personal SEills SE G SEill G aHards

Unit 11 '




Module 4 Unit 11

C(C Machine Tools

(C and C(C :+lained

(u!erical Control;

Nu$erical Control 5NC7 is the techniBue of "i9in" instructions to a $achine in the for$of a code -hich consists of nu$bers< letters of the al*habet< *unctuation $arEs andcertain other s&$bols. The $achine res*onds to this coded infor$ation in a *recise andordered $anner to carr& out 9arious $achinin" functions.

Instructions are su**lied to the $achine as a series of blocEs of infor$ation. blocE ofinfor$ation is a "rou* of co$$ands sufficient to enable the $achine to carr& out oneindi9idual $achinin" o*eration e.". $o9e cutter fro$ *osition 1 to *osition 2 at a

s*ecified feed rate.

(ach blocE is "i9en a seBuence nu$ber for identification. The blocEs are then e)ecuted instrict nu$erical order. n e)a$*le of a blocE is as follo-s:

NI /++ ;1+ ) =2+

The $eanin" of this infor$ation is as follo-s: NI is blocE nu$ber 1 /++ directs the$achine or cutter to $o9e at the ra*id tra9erse rate. ;1+ and =2+ are the coordinate9alues of the tar"et *oints of the $o9e$ent.

hen the instructions are or"anised in a lo"ical $anner the& direct the $achine tool tocarr& out a s*ecific tasE 3 usuall& the co$*lete $achinin" of a -orE*iece or J*artJ. It isthus ter$ed a *art *ro"ra$.

Co!+uter (u!erical Control;

Co$*uter Nu$erical Control 5CNC7 is based on the conce*ts of NC but utilises adedicated co$*uter -ithin the $achine control unit to store the *ro"ra$. CNC is lar"el&the result of technolo"ical *ro"ress in $icroelectronics 5the $iniaturisation of electronicco$*onents and circuitr&7< rather than an& radical de*arture in the conce*t of NC.

CNC control units< liEe the co$*uters on -hich the& are based< o*erate accordin" to astored *ro"ra$ held in co$*uter $e$or&. This $eans that *art *ro"ra$s are no- able to

beco$e totall& resident -ithin the $e$or& of the control unit< *rior to their e)ecution. No lon"er do the $achines ha9e to o*erate on the Jread3blocEDe)ecute blocEKK *rinci*le as

Unit 11 1)




Module 4 Unit 11

in an NC $achine. CNC $achines ha9e no- co$*letel& su*erseded the older NC$achines fro$ -hich the& are deri9ed.

Unit 11 11




Module 4 Unit 11

Constructional Features of C(C Machines

con9entional $achine tool has an intelli"ent source for error co$*ensation 5theo*erator7. Aurin" $achinin" a sEilled o*erator can 9ar& the cuttin" conditions toco$*ensate for deflection< 9ibration< etc. to "enerate the desired sha*e< siHe and finish.

The CNC $achine can onl& co$*ensate for an error that is detected and co$$unicatedto the control. Aeflection< 9ibration etc. cannot< as &et< be easil& $onitored. For thisreason NC $achines are $ade stron"er and stiffer to *erfor$ to a $ore accurate standardthan their con9entional counter*arts.

The ca*acit& for 9ar&in" the conditions -hile $achinin" is therefore li$ited. s far as *ossible the conditions ha9e to be established as the *ro"ra$ is *roduced.

In addition to this< CNC $achines are s*endin" $ore ti$e *er shift cuttin" thancon9entional $achines did in the *ast. This hi"her *ercenta"e of cuttin" ti$e results infaster -ear rates on the slides and trans$ission s&ste$s.

Con9entional $achine tools are also desi"ned -ith the 9ie- to ha9in" the sEilledo*erator standin" directl& in front controllin" the $achine. This is no lon"er reBuired for

CNC since the $achine is o*eratin" under *ro"ra$ control.

#*ti$u$ cuttin" s*eeds and feeds< continuous *ath $achinin"< ra*id slide $o9e$ent to brin" the tool close to the -orE and then sudden sto**in"< all subLect the $achine toforces -hich are not encountered on con9entional $achines.

Machine &tructure

Since ri"idit& *la&s a $aLor *art in the accurac& of a $achine tool< $odern CNC

$achines tend to ha9e o9er3*ro*ortionated slide -a&s< "uides and s*indles. ThicEer castsections than con9entional $achines are also used. The use of s&$$etrical castin"sassists in reduction of ther$al stresses -ithin the $achine. These structural desi"nfeatures are e$*lo&ed to co*e -ith the torsional forces and hea9& dut& cuttin" i$*osedon these $achines.

Unit 11 12




Module 4 Unit 11

&lide3a$s

Con9entional $achine tool slide-a&s o*eratin" under conditions of slidin" friction donot e)hibit a constant coefficient of friction. Friction coefficient is hi"hest at lo- 9elocit&.This condition "i9es rise to KsticE3sli*K -hich *roduces LerE& slide action -hen $o9e$ent

taEes *lace at lo- 9elocities. Nu$erical control also reBuires a ra*id res*onse of theslides to co$$and si"nals fro$ the $achine control.

To eli$inate these *roble$s rollin" friction can be used instead of slidin" friction. Fi"ure1 sho-s a nu$ber of -a&s of achie9in" this.

Figure 1 5 nti5Friction &lide3a$s

(ach of these $ethods considerabl& reduces frictional resistance "i9in" ra*id slideres*onse and eli$inates KsticE3sli*K. This t&*e of slide-a& is *articularl& suitable for$achines -hich are not reBuired to $achine -hile the slide is $o9in" e.". drillin" etc.hen the slide reaches the *oint -here drillin" taEes *lace it is cla$*ed in *osition. The$ain disad9anta"e of this desi"n is the load bearin" and cla$*in" ca*abilities are not as"ood as a con9entional slide-a&. Machines -hich are reBuired to $achine -hile theslide-a& is $o9in" such as $illin" often utilise a h&drostatic s&ste$. See Fi"ure 2 -here

fluid is *u$*ed in bet-een the slide surfaces at hi"h *ressure u* to +<+++ %nD$.Frictional -ear and sticE3sli* are entirel& eli$inated. n alternati9e desi"n is to coat the

Unit 11 1




Module 4 Unit 11

sides -ith Pol&tetrafluoroeth&lene 5P.T.F.(.7. This $aterial has a 9er& lo- coefficient offriction.

Unit 11 14




Module 4 Unit 11

Figure 2 5 #$drostatic &lide3a$

Leadscre3s

The lead scre-s used on con9entional $achine tools are usuall& of the c$e thread for$.These threads are 9er& inefficient because of the hi"h frictional resistance bet-een theflanEs of the scre- and the nut. The& also e)hibit hi"h bacElash< because there $ust beclearance bet-een the flanEs of the nut and the scre-. This -ould not be acce*table onCNC $achines.

The alternati9e $ost co$$onl& used is the re3circulatin" ball leadscre-. This t&*e ofleadscre- re*laces slidin" friction -ith rollin" friction. oth the lead scre- and nut ha9ea *recision "round for$ into -hich an endless strea$ of re3circulatin" balls -hich

co$*letel& fill the tracE is inserted. This t&*e of leadscre- has an efficienc& of u* to+.

The ad9anta"es of recirculatin" ball scre-s o9er c$e scre-s are:

517 lon"er life

527 less frictional resistance

57 lo-er torBue reBuired

547 $ore *recise *ositionin" of slides because bacElash is al$ost co$*letel&eli$inated

Unit 11 1




Module 4 Unit 11

Figure 5 "e5circulating <all Leadscre3

Machine =uarding and &3arf Control

Man& CNC $achines *articularl& turnin" centres are al$ost totall& enclosed b& anen9elo*e of elaborate "uardin". This is considered necessar& for the follo-in" reasons:

• lar"e a$ounts of s-arf and cuttin" fluid are *resent in the cuttin" Hone.

• the hi"h s*indle s*eeds and feed rates create hi"h forces -hich could cause seriousinLur& in the e9ent of a collision or tool breaEa"e.

• these "uards are usuall& interlocEed -ith the control s&ste$ throu"h li$it s-itchesi.e. the s*indle -ill onl& o*erate -hen the "uards are full& closed see Fi"ure 4.

Figure 4 5 Machine =uarding

Unit 11 16




Module 4 Unit 11

&3arf Control

In con9entional $achiner& s-arf re$o9al is "i9en little consideration< it is usuall&re$o9ed b& hand b& the $achinist. ith the hi"h rates of $etal re$o9al< heat build u*and the trend to-ards un$anned o*eration the *roble$ of s-arf re$o9al reBuires

consideration for CNC $achinin".Man& $anufacturers build in s-arf re$o9al eBui*$ent as *art of the $achine such asrotar& scre- or linear con9e&ors 5see Fi"ure 07 .C. o-e9er< to a lar"e e)tent< the basicdesi"n of the $achine can assist "reatl& in s-arf control e.". slant3bed lathes 5Fi"ure 0a7allo- the s-arf to fall a-a& fro$ the cuttin" Hone naturall&. S-arf re$o9al b& "ra9it&alone is not al-a&s sufficient in itself. This can be assisted b& $ulti*le coolant Letsaround the cuttin" Hone -hich Eee* the tool free fro$ accu$ulated s-arf. t the end of a$achine c&cle and before a ne- co$*onent is loaded the area can often be cleaned ofs-arf b& co$*ressed air Lets.

Figure 5 &3arf "e!o-al Con-e$ors

Unit 11 17




Module 4 Unit 11

Machine es

The *ri$ar& a)es of a $achine are desi"nated as ;< =< ? and can ha9e *ositi9e orne"ati9e 9alues.

The ?3a)is is al-a&s *arallel to the $ain s*indle of the $achine 5see Fi"ure 7. It doesnot $atter -hether the s*indle carries the -orE*iece or the toolin"< therefore the ?3a)iscan be either 9ertical or horiHontal. #n $illin"< borin" and drillin" $achines the s*indleis the tool rotatin" $eans -hile on c&lindrical "rinders and lathes the s*indle is the -orErotatin" $eans. Positi9e ?3$o9e$ent al-a&s increases the distance bet-een the -orEand the tool.

The ;3a)is of $otion is horiHontal and *arallel to the -orE3holdin" surface. If ? ishoriHontal< *ositi9e ; is to the ri"ht looEin" fro$ the s*indle to-ards the -orE*iece. If ?is 9ertical< -hen looEin" fro$ the s*indle to-ards its su**ortin" colu$n< *ositi9e ; is tothe ri"ht.

The =3a)is of $otion is *er*endicular to both the ; and ? a)es. Positi9e = is in thedirection -hich -ould $aEe a ri"ht3handed set of coordinates.

CNC lathes onl& ha9e t-o $aLor a)es ; and ?. There is no =3a)is.

Figure 6 5 >? @? A es

So$e CNC $achines ha9e additional a)es runnin" in *arallel -ith the $ain a)es.

Unit 11 1%




Module 4 Unit 11

here there is $ore than one $o9in" ele$ent in the sa$e a)is one is called the *ri$ar&a)is and is desi"nated as ; = or ?. Secondar& $o9e$ents in the sa$e a)is are desi"ned

b& U 6 in u**er case letters.

Unit 11 1'




Module 4 Unit 11

"ight5#and "ule Bertical Milling Machine

The directions of the $achine a)es are eas& to re$e$ber b& the ri"ht3hand rule:

Face the $achine and hold &our ri"ht hand as sho-n belo-< -ith the $iddle fin"er in thedirection of the tool a)is 5?7: the thu$b -ill *oint in the direction of the ; a)is and theforefin"er in the direction of the = a)is.

Figure 7 5 "ight5#and "ule

Unit 11 2)




Module 4 Unit 11

Control of &lide Mo-e!ent on C(C Machines

The control of slide *osition and 9elocit& of $o9e$ent can be either acco$*lished b&o*en loo* 5non3ser9o7 or closed loo* 5ser9o7 $eans. In an o*en loo* s&ste$ the *ositionand 9elocit& of the slides are not $easured.

blocE dia"ra$ of an o*en loo* control is sho-n in Fi"ure .

Figure % 5 0+en Loo+ Control

#*en loo* s&ste$s ha9e no $eans of co$*arin" the final slide *osition -ith the *ositionin -hich it -as co$$anded to "o. s*ecial t&*e of electric $otor Eno-n as a ste**er$otor is usuall& used in o*en loo* s&ste$s to *ro9ide accurate *ositionin" and 9elocit&control of slide $o9e$ent.

The *rinci*le of the ste**er $otor is that< u*on recei*t of a di"ital si"nal 5a *ulse7 the

s*indle -ill rotate throu"h a s*ecified an"le 5the ste*7. The ste* siHe is deter$ined b& thedesi"n of the $otor but -ill t&*icall& be bet-een 1. and 8.0 de"rees. Thus< if t-o di"ital

*ulses are a**lied< then the s*indle rotor -ill rotate b& 2 ste*s< or b& bet-een . and 10de"rees de*endin" on the $otor desi"n. Thus< b& countin" 5electronicall&7 the nu$ber of

*ulses sent to the ste**er $otor< and b& Eno-in" the lead of the a)is leadscre-< thedistance tra9ersed can be accuratel& *redicted. There is no need for *ositional feedbacE.

6elocit& of the a)is $o9e$ent is deter$ined b& ho- BuicEl& the *ulses are sent to theste**er $otor 5the *ulse freBuenc&7. If the *ulses are sent 9er& ra*idl&< then the feed3rate

-ill be hi"h if the *ulses are sent 9er& slo-l& then the feed3rate -ill be lo-. The s*eed at-hich the *ulses are trans$itted can be accuratel& "o9erned b& the CNC control s&ste$.Therefore there is no need for 9elocit& feedbacE.

In s*ite of these ad9anta"es of no feedbacE bein" necessar& there are so$e seriousdisad9anta"es in usin" ste**er $otors on CNC $achine tools< i.e.:

• If the $achine a)is is stalled throu"h o9erload the *ulses -ill continue to count and aloss of *osition -ill occur

• The $a)i$u$ *o-er out*ut fro$ ste**er $otors is relati9el& lo-

Unit 11 21




Module 4 Unit 11

• ecause *ulse rate 5freBuenc&7 is li$ited the $a)i$u$ a)is feed rate is also restrictedtherefore the ra*id tra9erse s*eeds achie9able are lo-

Unit 11 22




Module 4 Unit 11

ecause of these li$itations the ste**er $otor is onl& found on s$all lo- *o-ered$achines and on retro3fitted $achines. 'etro3fitted $achines are con9entional $achinetools -hich ha9e been fitted -ith CNC controllers.

Ser9o control reBuires both *ositional and 9elocit& feedbacE< i.e. the actual 9elocit& and *osition of the slide-a& $ust be co$*ared to the co$$anded 9alues. ser9o s&ste$al-a&s for$s a closed loo* 5see Fi"ure 7. The de9ices -hich are used to *ro9ide thefeedbacE in the closed loo* are called transducers. transducer is a de9ice -hichcon9erts one for$ of ener"& into another for$< e.". $echanical dis*lace$ent into anelectrical si"nal.

T-o t&*es of transducers are used on CNC $achines:

• 6elocit& transducer: The $ost co$$on 9elocit& transducer is the tacho3"enerator.This is a de9ice si$ilar to a bic&cle d&na$o. It *ro9ides a 9olta"e *ro*ortional to itss*eed. Tacho3"enerators usuall& co$e as an inte"ral *art of a ser9o $otor. The9olta"e is used to *ro9ide feedbacE fro$ $otor s*eed and hence slide 9elocit&.

• Position transducers: Slide-a& *osition is $easured b& transducers -hich can beeither linear or rotar&. !inear transducers o*erate b& $easurin" slide $o9e$ent.'otar& transducers o*erate indirectl& b& $easurin" leadscre- rotation or $otor shaftrotation and relatin" this to linear slide $o9e$ent.

The t&*es of $otor used for electrical ser9o s&ste$s can be either C or AC ser9o$otors. &draulic ser9o s&ste$s are also used on so$e CNC $achines.

Figure ' 5 <locD iagra! Closed Loo+ Control &$ste!

Unit 11 2




Module 4 Unit 11

d-antages of C(C Machines

Aes*ite the e)tra costs in9ol9ed CNC $achines ha9e $an& ad9anta"es. These can besu$$arised as follo-s:

•"educed lead ti!e!ead ti$e is the ti$e bet-een the recei*t of a desi"n s*ecification and the ti$e in-hich $anufacture is read& to co$$ence. In $an& cases standard toolin" is all that isreBuired. The need for s*ecial Li"s and fi)tures is al$ost co$*letel& eli$inated.Si$*le -orE cla$*in" arran"e$ents are usuall& sufficient.

• :li!ination of o+erator errors

'es*onsibilit& is transferred fro$ the o*erator to the *art *ro"ra$. Pro9ided the *ro"ra$ is correct< this is al-a&s *ro9ed in ad9ance of *roduction and the $achine is

set u* *ro*erl& no errors -ill occur in the -orE. #*erator fati"ue< boredo$ orinattention -ill not affect the Bualit& or the duration of $achinin".

• Fleibilit$ in changes of co!+onent design

The $odification of a co$*onent desi"n can be 9er& easil& acco$$odated b&alterin" the *art *ro"ra$. There $a& be no chan"es reBuired to Li"s and fi)tures-hich -ould t&*icall& be the case for con9entional $achinin".

• "educed scra+ and ins+ection

()tre$e accurac& and re*eatabilit& of co$*onents *roduced are features of CNC$achinin". It is usuall& onl& necessar& to ins*ect the first co$*onent. #nce the

*ro"ra$ has been *ro9ed the re*etiti9e accurac& of the $achine $aintains aconsistent *roduct.The cost associated -ith ins*ection< re3-orE and scra* are al$ost eli$inated.

• Co!+le one5offs and s!all batch Euantities

CNC finds its "reatest ad9anta"es in s$all batch Buantities and co$*le) one3offs.Machinin" a s$all batch Buantit& is found to be econo$ical -ith CNC $achines

because of the fast chan"e3o9er ti$es. *art *ro"ra$ can be *re*ared a-a& fro$ the$achine -hile the $achine is still in *roduction. Stora"e of *ro"ra$s is not a

*roble$ and chan"e o9er fro$ one batch to another is achie9ed b& loadin" the correct *art *ro"ra$. For co$*le) sha*ed one3off co$*onents and *roto3t&*es the CNC$achine finds $an& a**lications because of the difficult& often encountered in

*roducin" these sha*es on con9entional $achines.

• Lo3er Labour Cost

CNC $achines do not necessaril& o*erate at faster cuttin" s*eeds than con9entional

$achines< but $ore ti$e is nor$all& s*ent in actuall& cuttin" $etal because the set u*ti$es are less. It is also *ossible for one o*erator to attend to $ore than one CNC

Unit 11 24




Module 4 Unit 11

$achine at a ti$e.

• ccurate Costing and &cheduling

The ti$e taEen in $achinin" is *redictable and consistent -hich results in "reateraccurac& in esti$atin" and costin".

Unit 11 2




Module 4 Unit 11

Part Progra!!ing

Part Progra!!ing

Cartesian Coordinates

The $ain difference bet-een CNC and con9entional is that CNC dra-in"s are usuall&di$ensioned in Cartesian coordinates because this $aEes *ro"ra$$in" easier. TheCartesian 'ectan"ular Coordinate S&ste$ for$s the basis of NC $easure$ent.

Usin" rectan"ular coordinates< an& s*ecific *oint in *h&sical s*ace can be described in$athe$atical ter$s alon" t-o a)es 5; and =7. ith this s&ste$< the location of an& *ointon a flat surface or *lane can be defined $athe$aticall& -ith reference to t-o lines5a)es7 in the sa$e *lane and *er*endicular to each other.

This coordinate s&ste$ can be e)tended to *er$it definin" the location of an& *oint in

three3di$ensional s*ace relati9e to three $utuall& *er*endicular *lanes. The *oint -ould be defined b& three i$a"inar& *er*endicular *lanes -ith each a)is bein" the line ofintersection of t-o *lanes.

The intersection *oint of t-o a)es $arEs the ori"in *oint. The ori"in is surrounded b&four Buadrants. (ach Buadrant consists of *ortions of the nu$ber lines for$in" each a)is.The location of a coordinate *oint is s*ecified in relation to the *oint of ori"in -here thea)es intersect. t-o3di$ensional a**lication of this s&ste$ of coordinates is illustratedin Fi"ure 1+.

Figure 1) 5 T3o5i!ensional "ectangular Coordinates

Unit 11 26




Module 4 Unit 11

>? @ / A es

NC $illin" is carried out -ithin t-o *lanes defined b& three3a)es 5;< = and ?7. The ;and = a)es consist of indi9idual nu$ber lines that are *er*endicular to each other and la&-ithin the sa$e *lane. The ? a)is is created b& e)tendin" *lanes into s*ace abo9e< belo-

and *er*endicular to the ; and = a)es 5see Fi"ure 117.

Figure 11 5 >? @ and A es

In the Cartesian or ri"ht an"le coordinate s&ste$ all *oints can be described as eitherincre$ental or absolute. In absolute $easure$ent each *oint is al-a&s taEen fro$ thesa$e Hero. This *re9ents build u* of tolerances bet-een each di$ension.

In incre$ental di$ensionin" also Eno-n as chain di$ensionin" each *oint is taEen fro$the *recedin" *osition. Fi"ure 12 sho-s the sa$e co$*onent di$ensioned in absoluteand in incre$ental.

Unit 11 27




Module 4 Unit 11

Figure 12 5 bsolute and *ncre!ental i!ensioning

Unit 11 2%




Module 4 Unit 11

Incre$ental di$ensionin" is often discoura"ed because of the *ossibilit& of build u* intolerances bet-een indi9idual features. o-e9er on CNC $achines this *roble$ isreduced because of the inherent accurac& and re*eatabilit& of the $achines.

In so$e cases incre$ental di$ensionin" is ad9anta"eous such as -here a *attern of holes

is re*eated at different locations on a -orE*iece. Most $achines can be *ro"ra$$edeither in incre$ental or absolute $ode or s-itched fro$ one $ode to another durin" *ro"ra$$in".

In absolute *ro"ra$$in" all a)is $o9e$ents are s*ecified in relation to a fi)ed datu$ *oint.

In incre$ental *ro"ra$$in" each a)is $o9e$ent is $easured fro$ the last *osition.(ach *oint 9isited -hen $achinin" ser9es as the datu$ *oint for the ne)t *oint or

*ositional $o9e.

Polar Coordinates

This is -here features on a dra-in" are described b& a len"th and an an"le $easuredfro$ a s*ecific *oint. Fi"ure 1 sho-s an e)a$*le of Polar coordinate di$ensionin".

Figure 1 5 i!ensioning in Polar Coordinates

Man& of the $ore $ode$ $achines allo- the use of *olar coordinates -hile *ro"ra$$in". This can sa9e a considerable a$ount of ti$e in *ro"ra$$in" e.". if anu$ber of holes around a Pitch Circle Aia$eter 5PCA7 are to be drilled 3 see Fi"ure 14.

Figure 14 5 Pitch Circle ia!eter

Unit 11 2'




Module 4 Unit 11

If &ou -ere usin" Cartesian coordinates for this *ro"ra$ &ou -ould ha9e to -orE out thecoordinates for each of the hole centres usin" sine and cosine.

Unit 11 )




Module 4 Unit 11

&election of Aero Point

In order to define certain *oints on a -orE*iece in this $anner< &ou -ill first ha9e todecide -here to *ut the coordinate s&ste$ on the -orE*iece< es*eciall& -here to *lacethe Hero *oint.

For $illin"< the Hero *oint 5or reference *oint7 of all di$ensions $a& be *laced an&-hereon the -orE*iece. !etKs call this Hero *oint K-orE*iece HeroK 5?7 or -orE*iece datu$.

To sa9e trouble of unnecessar& calculations it is ad9isable to *lace -orE*iece Hero at that *oint on a *art dra-in" on -hich $ost of the di$ensions are based. See e)a$*les Fi"ure10 and Fi"ure 1.

-orE*iece datu$ $a&be defined as a *oint< line or surface fro$ -hich di$ensions arereferenced. It $a&or $a& not be -ithin the -orE*iece area.

The s&$bol used to denote -orE*iece Hero is:

Figure 1 5 :a!+le of Aero Point 0+tions on orD+iece

Figure 16 5 :a!+les of Co!+onent 3ith Aero Point in orD+iece Centre

Unit 11 1




Module 4 Unit 11

For turnin" o*erations the ; a)is Hero is nor$all& *ositioned on the centreline of thes*indle a)is. The ? a)is Hero can be *ositioned on the front face of the -orE*iece or onthe face of the -orE*iece or on the face of the chucE. See Fi"ure 18.

Figure 17 5 >) A) Positions for Turning 0+erations

Unit 11 2




Module 4 Unit 11

uadrantal use for Milling

In *ro"ra$$in" it is easier to i$a"ine the tool is $o9in" around the -orE*iece ratherthan the slide-a&s $o9in". Fi"ure 1 belo- sho-s ho- the O and 3 si"ns chan"e for ;and = as &ou $o9e around the four Buadrants. ; 9alues to the ri"ht of the datu$ are

*ositi9e 5O7 and those to the left are ne"ati9e 537. = 9alues abo9e the datu$ are *ositi9e5O7 and those belo- are ne"ati9e 537. ? 9alues abo9e the datu$ are *ositi9e and -hen thetool $o9es belo- the datu$ it is ne"ati9e.

Figure 1% 5 bsolute &igns for Four uadrants

In incre$ental *ro"ra$$in" ; O tells the tool to $o9e to the ri"ht fro$ -here it is no-and ; 3 to the left. = O tells the tool to $o9e u* fro$ its *resent *osition and = 3 tells it to$o9e do-n.

? O tells the tool to $o9e a-a& fro$ the -orE*iece and ? 3 tells the tool to $o9e to-ardson into the -orE*iece.

Unit 11




Module 4 Unit 11

uadrantal use for Turning

The Buadrant in use durin" *ro"ra$$in" de*ends on -hether the $achine has a front orrear $ounted tool *ost and -hether the *ro"ra$ Hero is on the chucE face or the-orE*iece front face.

Figure 1' 5 "ear Tools Post Lathe

bsolute di$ensions: If ;+ is on the chucE centreline and ?+ is on the chucE face then:? $o9e$ents to-ards the chucE are ne"ati9e.

• ? $o9e$ents a-a& fro$ the chucE are *ositi9e

• ; $o9e$ents on the other side a-a& fro$ the o*erator are *ositi9e

• ; $o9e$ents to-ards the o*erator are ne"ati9e.

Incre$ental ; $o9e$ents to-ards the centreline are ne"ati9e. Incre$ental ; $o9e$entsa-a& fro$ the centreline are *ositi9e.

Unit 11 4




Module 4 Unit 11

Unit 11




Module 4 Unit 11

Figure 2) 5 Front Tool Post Lathe

Front $ounted tool *ost lathe ref. Fi"ure 2+.

bsolute di$ensions:

• ? $o9e$ents to-ards the chucE are ne"ati9e

• ? $o9e$ents a-a& fro$ the chucE are *ositi9e

• ; $o9e$ents to-ards the o*erator on the side of the centreline nearest the o*eratorare *ositi9e

• ; $o9e$ents a-a& fro$ the o*erator are ne"ati9e.

Incre$ental ; $o9e$ents to-ards the centreline are ne"ati9e. Incre$ental ; $o9e$entsa-a& fro$ the centreline are *ositi9e.

Unit 11 6




Module 4 Unit 11

efinition of Points on a &urface

The sa$e identification letters 5;< =< ?7 can be used for definin" an& *oint on a-orE*iece b& *lacin" the three a)es on the *art dra-in" as sho-n belo-:

Figure 21 5 efinition of Points on a &urface 1

ll *oints on the -orE*iece surface are defined b& ; and = 9alues< -hile ? 9alues denotethe de*th of tool infeed.

Figure 22 5 efinition of Points on a &urface 2

!ets start b& definin" *oints on the -orE*iece surface and for"et about the cuttin" de*th

5infeed7 for the $o$ent.

Unit 11 7




Module 4 Unit 11

hat -e need is a t-o3di$ensional coordinate s&ste$ constituted b& the ; a)is and the= a)is.

Figure 2 5 efinition of Points on a &urface

s alread& stated the *oint of intersection of these t-o a)es is called Hero. The arro-sindicate the direction of *ositi9e $otions 5;O and =O7.

If a "raduated scale is *laced alon" each a)is< -e can define an& *oint on a surface b&$eans of its ; and = 9alues.

ll nu$erical 9alues in the directions of the arro-s carr& a *ositi9e si"n all 9alues in theo**osite directions a ne"ati9e si"n.

:a!+le:

The *oints ha9e the follo-in" coordinates:P1: ;1 =00

P2: ;40 =10

P: ;8+ =0+

Unit 11 %




Module 4 Unit 11

ocu!entation

Progra! &heets

Part *ro"ra$$in" is nor$all& carried out b& usin" *re3*rinted *art *ro"ra$ sheets. These

sheets *ro9ide a neat and orderl& -a& of settin" out the *ro"ra$. The& also *ro9ide *er$anent docu$entation of the Lob to be $achined. n e)a$*le of a *art *ro"ra$ sheetis sho-n in Fi"ure 24. The sheets are laid out in such a -a& that the infor$ation can be-ritten in b& hand and then the sheet can be *laced in a telet&*e and the *ro"ra$ can beco*& t&*ed onto the second line and a *unched ta*e is *roduced at the sa$e ti$e. SeeFi"ure 24.

Coordinate &heets

Coordinate sheets are used as a su**le$ent to the *ro"ra$ sheet. ll rele9ant coordinatesare laid out on this sheet. se*arate coordinate *oint -ill be s*ecified for each *oint-here the cutter needs to chan"e direction. The sheet is useful as an aid in *ro"ra$

*ro9in" and for locatin" and editin" errors -hen the& occur.

0+eration &heet

This sheet is intended as an aid to the o*erator. It ite$ises each o*eration in seBuence andidentifies the tools reBuired for each o*eration and the tool settin"s.

Unit 11 '




Module 4 Unit 11

Unit 11 4)




Module 4 Unit 11

Figure 24 5 Progra!!ing &heet

Unit 11 41




Module 4 Unit 11

Part5Progra! For!at

The $achine control unit 5MCU7 controls the $achine in res*onse to coded co$$ands-hich $aEe u* the *art *ro"ra$. These co$$ands are identified b& a ca*ital letter -hichis referred to as an address. The co$$ands also contain nu$bers -hich follo- the letters.

The co$bination of the letter address and the nu$erical infor$ation is Eno-n as a -ord.(ach line of a *ro"ra$ is called a blocE. blocE $a& contain a nu$ber of -ords.

The for$at in -hich the -ords are arran"ed -ithin a blocE is Eno-n as the *art *ro"ra$for$at. The order in -hich the -ords a**ear in a blocE $a& be fi)ed or 9ariable.

Fied &eEuential For!at

The instructions in a blocE are al-a&s "i9en in the sa$e seBuence. ll instructions $ust be "i9en in each blocE includin" instructions that do not chan"e fro$ blocE to blocE e.".

Table 1 5 Fied &eEuential For!at

Tab &eEuential For!at

The instructions in a blocE are al-a&s "i9en in the sa$e seBuence as in the fi)edseBuential for$at. o-e9er if instructions re$ain unchan"ed in succeedin" blocEs theinstructions need not be re*eated but the tab character $ust be *unched to ensure that thesa$e nu$ber of tab characters a**ear in each blocE e.".

Table 2 5 Tab &eEuential For!at

Unit 11 42




Module 4 Unit 11

ord ddress

(ach -ord is *receded b& its letter address. This s&ste$ enables instructions -hichre$ain unchan"ed fro$ the *recedin" blocE to be o$itted fro$ successi9e blocEs. Thisfor$at is ado*ted b& $ost CNC $achine control units e.".

Table 5 ord ddress

The address for$at refers to the for$ in -hich the -ords $ust taEe for e)a$*le:

N4: 4 di"its after N

/2: *re*arator& function K/K follo-ed b& 2 di"its

;4: ;3di$ension follo-ed b& 4 di"its before the deci$al *oint and three di"itsfollo-in" the deci$al *oint.

There is usuall& a $a)i$u$ of 8 di"its that can be -ritten for ;< = and ? a)es. o-e9ernot e9er& CNC control -ill allo- a deci$al *oint to be used and there are t-o other$ethods of re*resentin" di$ensions as follo-s.

Leading Aero &u++ression

This is the re$o9al or su**ression of an& Heros on the left of the nu$ber -hen -rittenout in the se9en di"it for$at< e.". the di$ension 1+.80 $$ -ritten in leadin" Herosu**ression for$at 58 di"it entr&7.

8 di"it entr& 4 before< after G +1+ . 80+

deci$al *oint *osition of i$a"inar& deci$al *oint

-ith !eadin" Hero su**ression G 1+80+

:. For a $achine control of this t&*e an ; di$ension of 1+.80 -ould be -ritten as

>1)7)

Unit 11 4




Module 4 Unit 11

Trailing Aero &u++ression

ith this s&ste$ an& Heros to the ri"ht of the deci$al *oint are re$o9ed or su**ressed.So an ; di$ension of 1+.80 -ould beco$e ;+1+80 for a control -hich acce*tstrailin" Hero su**ression.

The $aLorit& of $ode$ CNC $achines allo- the use of deci$al *oint *ro"ra$$in" i.e.&ou Lust -rite the di$ension u* to a $a)i$u$ of 8 di"its.

Part Progra! Code Listings

• N: locE seBuence nu$ber address. locEs are often inserted in ste*s of 0 toallo- for blocEs to be inserted if accidentall& o$itted.

• ;< =< ?: These addresses si"nif& the ;< 6< ? a)es $o9e$ents.• I< Q< %: These addresses are used for *ro"ra$$in" circular $o9es

• T: Tool nu$bers address. The *ro"ra$$er $ust assi"n a nu$ber e.". T+1 toeach tool used in the *ro"ra$.

• S: S*indle s*eed address. The letter is follo-ed b& nu$bers -hich indicatethe s*indle s*eed.

• F: Feed rate address 3 follo-ed b& nu$bers as in s*indle s*eed.

M8 Miscellaneous Functions

These are $achine $ana"e$ent functions such as startin" and sto**in". The M letter isfollo-ed b& 2 di"its. The co$$on standardised M functions are as follo-s:

• M++: *ro"ra$ sto*

• M+2: end of *ro"ra$

• M+: end of *ro"ra$ -ith re-ind to *ro"ra$ start

• M+: flood coolant on

• M+: coolant off

• M+: tool chan"e

• M+: s*indle on clocE-ise

• M+4: s*indle on anti3clocE-ise

• M+0: s*indle off

• M+8: $ist coolant on

Unit 11 44




Module 4 Unit 11

=8 Pre+arator$ Function ddresses

/ functions are *re*arator& functions used to chan"e the $ode of $o9e$ent of the$achine< such as ra*id slide $o9e$ent< circular $o9e$ent< controlled feed rate< absoluteor incre$ental $o9e$ent etc. The code consists of the letter / follo-ed t-o di"its. So$e

co$$on standardised / functions are as follo-s:• /++: ra*id slide $o9e$ent

• /+1: linear inter*olation

• /+2: circular inter*olation clocE-ise

• /+: circular inter*olation anti3clocE-ise

• /+4: d-ell

• /4+: cancel cutter radius co$*ensation

• /41: cutter co$*ensation left

• /42: cutter co$*ensation ri"ht

• /8+: inch units

• /81: $etric units

• /+: absolute coordinates

• /1: incre$ental coordinates

Pro"ra$ start character. Used at the be"innin" of a *ro"ra$ to indicate the start.

So$e co$$and functions are $odal -hich $eans that the co$$and re$ains in effectuntil cancelled or su*erseded b& a co$$and of the sa$e t&*e.

Control of &lide Mo-e!ent

There are t-o basic t&*es of slide $o9e$ent -hich are usuall& a**lied on CNC $achines

as follo-s:

• *oint3to3*oint control

• continuous *ath

Point3to3Point Control is used -here the $achine slide is reBuired to reach a *articular *oint in the shortest *ossible ti$e. N# $achinin" taEes *lace -hile the slide is $o9in".

Point3to3Point Control -ould be suitable for $achines -hich are onl& used for drillin" or

borin" i.e. no $achinin" is taEin" *lace as the slide is $o9in" fro$ the centre line of onehole to the coordinate *osition of the ne)t. The *ath the tool or slide taEes in "ettin" fro$

Unit 11 4




Module 4 Unit 11

one *oint to the ne)t is uni$*ortant. hen the $achine is o*eratin" in *oint3to3*oint$ode the /++ *re*arator& function is o*erational.

Continuous Path Control can taEe the for$ of !inear or Circular Inter*olation.Inter*olation is the *rocess of Loinin" u* *ro"ra$$ed *oints to "enerate a s$ooth *ath.

Unit 11 46




Module 4 Unit 11

If the se"$ents Loinin" the *oints are strai"ht lines the *rocess is called !inearInter*olation. If the se"$ents Loinin" the *oints are arcs of circles the *rocess is calledCircular Inter*olation. n& $achinin" o*eration -here the tool is cuttin" as the slides are$o9in" in a controlled $anner reBuires continuous *ath control.

Linear *nter+olation

!inear inter*olation $eans $achinin" in a strai"ht line. This can be either horiHontal<9ertical or at an an"le in an& direction. The /+1 code is entered into the control -ith afeed rate 9alue e.". N2< /+1< ;2++< =14+< F4++.

Figure 2 5 Linear *nter+olation

In blocE No.2 the tool tra9els alon" a strai"ht line fro$ current *osition 5S7 to P2 at afeed rate of 4++ $$D$in. 5see Fi"ure 207.

Circular inter*olation refers to the *ro"ra$$in" of circular arcs u* to a co$*lete circle.In order to *ro"ra$ an arc -ith in*ut in Cartesian coordinates the data in*ut is "uided b&the control u*on in*uttin" the co$$and /+2 or /+. The control -ill reBuest:

• ;: 1st coordinate of tar"et *oint

• =: 2nd coordinate of tar"et *oint

• I: 1st coordinate of circle centre

• Q: 2nd coordinate of circle centre

I is used to s*ecif& the centre of the arc in the ; direction

Q is used to s*ecif& the centre of the arc in the = direction

% is used to s*ecif& the centre of the arc in the ? direction

Note: So$e $achine control units reBuire the I< Q and % 9alues to be "i9en incre$entall&.

Unit 11 47




Module 4 Unit 11

Unit 11 4%




Module 4 Unit 11

Figure 26 5 :a!+le of =) Co!!and in use

Unit 11 4'




Module 4 Unit 11

Figure 27 5 :a!+le of =)2 Co!!and in use

Unit 11 )




Module 4 Unit 11

=eo!etr$ and Trigono!etr$

*!+ortant =eo!etrical Theore!s

Chords and Circles: If t-o chords of a circle intersect< either -ithin or -ithout the circle<

the *roduct of the t-o se"$ents or one chord is eBual to the *roduct of the t-o se"$entsof the other chord.

Fi"ure 2 sho-s at 5a7 the chords intersectin" inside the circle< at 5b7 the chordsintersectin" outside the circle< and at 5c7 the s*ecial case of one chord Lust touchin" acircle so that the chord is a tan"ent.

Figure 2% 5 *!+ortant =eo!etric Theore!s

In Fi"ure 25a7 and 5b7: # ) # G #C ) #A

In Fi"ure 25c7: 5#7 G #C ) #A

n i$*ortant a**lication occurs -hen one chord is the dia$eter of the circle< the other

chord intersectin" the dia$eter at ri"ht an"les -ith the circle< as sho-n in Fi"ure 2.

The chord is bisected and # G #.

!et A G dia$eter of circle<

G len"th of chord < and h G hei"ht of se"$ent.

Unit 11 1




Module 4 Unit 11

Unit 11 2




Module 4 Unit 11

# ) # G #( ) #C

:. D2 ) D2 G 5A – h7 h

and D4 G Ah 3 h

:. G 4 5Ah 3 h7

and G 2R 5Ah 3 h7

If A is reBuired< usin" D4 G Ah 3 h

Ah G D4 O h

A G D4h O h

Unit 11




Module 4 Unit 11

*ntersecting &traight Lines

If t-o strai"ht lines intersect< 9erticall& o**osite an"les are eBual. In Fi"ure 25a7 an"les are eBual< and an"les are eBual.

If a strai"ht line intersects t-o *arallel strai"ht lines< corres*ondin" an"les on the sa$e

side of the line are eBual. In Fi"ure 25b7< an"les are eBual< and an"les are eBual.

Figure 2' 5 *ntersecting &traight Lines

If the abo9e t-o theore$s are co$bined< then in Fi"ure 25c7 all four an"les are eBual

and all four an"les are eBual.

Unit 11 4




Module 4 Unit 11

Triangles

trian"le is a *lane area bounded b& three strai"ht lines. Trian"les can be classified intothree t&*es. (Builateral trian"les ha9e sides of eBual len"th isosceles trian"les ha9e t-osides of eBual len"th< -hilst scalene trian"les ha9e sides of different len"ths. trian"le

-hich contains a ri"ht3an"le is ter$ed a ri"ht3an"led trian"le. Such a trian"le -ould beisosceles if the sides containin" the ri"ht3an"le -ere of eBual len"th.

Fi"ure + sho-s a trian"le C< -ith C continued to A. and C( dra-n *arallel to .& use of the theore$s stated earlier:

C( G C

and (CA G C

Figure ) 5 Triangles

The su$ of the three an"les in the trian"le therefore is the sa$e as

C O C( O (CA G CA

CA is a strai"ht line of 1+ 5i.e. t-o ri"ht3an"les7 hence the su$ of the three an"les ina trian"le is 1+.

Si$ilar trian"les are trian"les -hich ha9e the three an"les in one trian"le eBual to the

three an"les of the other< -hereas con"ruent trian"les are eBual in all res*ects.

Unit 11




Module 4 Unit 11

ConseBuentl&< the areas of con"ruent trian"les are eBual< but the areas of si$ilar trian"lesare not. The corres*ondin" sides of si$ilar trian"les are *ro*ortional to each other.

Unit 11 6




Module 4 Unit 11

T-o si$ilar trian"les are sho-n belo-< for -hich:

G C G C

1 1 1 C1 C1 1

Tri"ono$etr& literall& $eans the $easure$ent of trian"les. In order that *articular an"les

andDor sides $a& be indicated *recisel&< it is con9entional *ractice to letter the an"les-ith ca*ital letters and the sides -ith s$all letters. Further$ore< side a is o**osite an"le< side & o**osite an"le = and so on. This standard con9ention is illustrated in the fi"ure

belo-.

Unit 11 7




Module 4 Unit 11

P$thagoras Theore!

This theore$ can be used to find the len"th of one side of a ri"ht an"led trian"le if thelen"ths of the other t-o sides are Eno-n.

The theore$ states that if -e taEe the len"ths of the t-o s$aller sides of a ri"ht an"ledtrian"le< sBuare the$ and then add the$ to"ether the result -ill be eBual to the len"th ofthe lon"est side 5the h&*otenuse7 sBuared.

In the trian"le C belo- this can be e)*ressed $athe$aticall& as follo-s:

G C O C

:. In order to find the len"th of -e can sa&:

G RC O C

& trans*osin" the for$ula -e can find the len"th of an& side if the len"ths of the othert-o are Eno-n.

The Theore$ of P&tha"oras states that the sBuare on the h&*otenuse of a ri"ht an"le iseBual to the su$ of the sBuares on the other t-o sides.

()a$*le: In the trian"le C sho-n< the len"th C G 10 and C G 2+. Calculate thelen"th of 5h&*otenuse7:

G C O C G 220 O 4++

Unit 11 %




Module 4 Unit 11

G R20

G 20

Unit 11 '




Module 4 Unit 11

Trigono!etr$

The ratios of the len"ths of the sides in si$ilar ri"ht3an"led trian"les are al-a&s the sa$e< *ro9ided the an"les in each case are the sa$e. The& ate called tri"ono$etrical ratios. Inorder to be able to differentiate -hich sides and -hich an"les are bein" considered a

s*ecial notation and -ordin" is used as follo-s:

Trigono!etrical "atios

sine of an"le G o**ositeh&*otenuse

cosine of an"le G adLacent

h&*otenuse

tan"ent of an"le G o**osite

adLacent

The use of tri" ratios is li$ited to the solution of ri"ht an"led trian"les onl&.

Unit 11 6)




Module 4 Unit 11

&olution of "ight5ngled Triangles

In sol9in" *roble$s in9ol9in" the use of tri"ono$etr& a useful $ethod of a**roach is toasE t-o Buestions:

5a7 is there a ri"ht3an"led trian"le< if so

5b7 b& -hat ratio $ust I $ulti*l& the Eno-n side to obtain the unEno-n side i.e. -hatit unEno-n

ratio G unEno-nEno-n side

()a$*le:

In a ri"ht3an"led trian"le< the h&*otenuse is of len"th

12 $$ and one an"le is 8. hat is the len"th of theshortest side,

#ne an"le is +< another is 8< since the an"les in a trian"le add u* to 1+< the otheran"le is: 1+ 3 5+ O 87 G 1+ 3 1 G 18.

The shortest side -ill be o**osite the s$allest an"le it -ill be side a in the fi"ure abo9e.The reBuired $ulti*lier of the Eno-n side is:

ratio G unEno-n G side o**osite G sin G sin 18

Eno-n side h&*otenuse

The ans-er is:

Eno-n side ) sin 18 G 12 sin 18 G 12 ) +.224 5fro$ Tri". tables7

ns-er: G .0+

&ine "ule

The sine rule can be used to sol9e *roble$s of trian"les that are not ri"ht an"ledtrian"les. The sine rule states:

a G b G cSin Sin Sin C

a is the line o**osite an"le

b is the line o**osite an"le

c is the line o**osite an"le C

Unit 11 61




Module 4 Unit 11

n& t-o ter$s can be used to"ether:

i.e. a G cSin Sin C etc.

Unit 11 62




Module 4 Unit 11

To find the len"th in the trian"le abo9e *roceed as follo-s:

an"le C G 1+ 3 51++ O 4+7 G 4+

a G c fro$ Sine 'uleSin Sin C

C G sine rule a**liedSin Sin C

G Sin C ) C re3arran"ed for

Sin

G 4+ ) + substitute Eno-n 9aluesSin 1++

G +.42 ) + fro$ sine tables.4

G .1 $$

Unit 11 6




Module 4 Unit 11

The Cosine "ule

The cosine rule states that in an& trian"le -hether it is ri"ht3an"led or not< the sBuare of a *articular side is the su$ of the sBuare of the other t-o sides $inus t-ice the *roduct ofthe other t-o sides and the cosine of the an"le o**osite the *articular side. ritten as an

eBuation this beco$es:

a G b O c 3 2bc cos

or

b G a O c 3 2ac cos

or

c G a O b 3 2ab cos C

This for$ of the eBuation is used to find the third side of a non ri"ht3an"led trian"le -henthe other t-o sides and the included an"le is Eno-n.

()a$*le:

c G a O b 3 2bc cos C

G 1+. O .8 3 251+.7 5.87 cos

c G R1+. O .8 3 251+.7 5.87 cos V

G 11.+ $$

Unit 11 64




Module 4 Unit 11

ata *n+ut,&torage and Progra! Pro-ing

ata *n+ut,&torage and Progra! Pro-ing

The $ain $ethods -hich can be used to in*ut data into a CNC control unit are:

• Punched ta*e and ta*e reader

• Ma"netic ta*e

• Ma"netic disc

• ost co$*uter

• Manual data in*ut

Punched Ta*e: This is a lo- cost $ethod of data in*ut. The ta*e is a9ailable in rolls orcan be fan folded.

Figure 1 5 &ection of Punched Ta+e

Punched ta*e is a9ailable $ade fro$ *a*er< *ol&ester< *a*erD*ol&ester la$inates< or *ol&esterDalu$iniu$ foil la$inates.

Unit 11 6




Module 4 Unit 11

Punched ta*e has certain ad9anta"es such as: sho* floor suited i.e. insensiti9e to $a"neticfields or oil conta$ination. It can also be read 9isuall& b& an e)*erienced *erson. Ta*eda$a"e is also i$$ediatel& noticeable.

Unit 11 66




Module 4 Unit 11

The disad9anta"es of *unched ta*e are the s*rocEet holes tend to -ear or tear -ith use.The stora"e densit& is lo- and the ta*e is not erasable and re3usable.

Ta*e readers: The function of the ta*e reader is to detect the *resence and *osition of

holes in the ta*e. There are three different t&*es of ta*e reader:

1. Pneu$atic

2. Mechanical

. Photo3electric

Magnetic Ta+es and iscs

Ma"netic ta*e is a chea* and con9enient $ethod of storin" lar"e 9olu$es of data in a

s$all s*ace. Ta*e cassettes are eas& to handle and store. It can also be erased and re3-ritten as reBuired. The ta*e recorder fulfils the tasE of both the ta*e *unch and ta*ereader since it can record and *la&bacE.

o-e9er it is i$*ossible for an o*erator to Eno- if a ta*e contains an& infor$ation or not b& 9isual ins*ection. Ma"netic ta*es can also be erased accidentall& in the *resence of a$a"netic field.

Magnetic iscs

The data transfer rate is faster for a disc than $a"netic ta*e. The access ti$e< to storeddata is faster because the disc is a rando$ access de9ice. That is an& sin"le *iece of datarecorded on the disc can be accessed as easil& and as BuicEl& as an& other.

#ost Co!+uter

The *rocess of transferrin" *art *ro"ra$s fro$ a host co$*uter into the $e$or& of aCNC $achine tool is called Airect Nu$erical Control 5ANC7. nu$ber of $achine toolsof different t&*es can be in9ol9ed.

Manual ata *n+ut BM*

This is a ter$ used to describe the $ethod of enterin" data into the $achine control unitusin" the console Ee&*ad. The enterin" of co$*lete *ro"ra$s other than relati9el& shortones is not *ractical as the $achine is idle -hile data is bein" entered on $ost $achines.The $ost co$$on use of MAI is for editin" *ro"ra$s and for $achine setu*. This hasthe ad9anta"e that once edited the ne- *ro"ra$ can be sa9ed or re3*unched

auto$aticall& b& out*uttin" to the ta*e *unch.

Unit 11 67




Module 4 Unit 11

Progra! Pro-ing

efore a *ro"ra$ is used it should be K*ro9edK to checE that the desired o*eration -illtaEe *lace. The conseBuences of not *ro9in" a *art *ro"ra$ ran"e fro$ da$a"e to theco$*onents and toolin"< catastro*hic da$a"e to the $achine tool or serious inLur& to the

o*erator or other obser9ers. The follo-in" $ethods can be used to *ro9e a *ro"ra$.

r$ "un

This in9ol9es runnin" the *ro"ra$ in auto$atic $ode -ithout the co$*onent installed inthe chucE or on the $achine table. The *ur*ose is to 9erif& the tool *ath.

Plotter

relati9el& si$*le -a& of checEin" the *ro"ra$$ed co$*onent *rofile is to substitute a *en ti* for the cuttin" tool. For a $illin" o*eration a t-o di$ensional trace of the cutter *ath $a& be *roduced on *a*er b& *lacin" a board on to* of the $achine table.

&ingle &te+ or &te++ing

This in9ol9es the o*eration Jste**in"J throu"h the *ro"ra$ line b& line and actuall&cuttin" a co$*onent one ste* at a ti$e. fter each ste* the ne)t $o9e$ent is carefull&checEed before e)ecution.

Co!+uter =ra+hics

The *ro"ra$ is fed into a co$*uter usin" the Ee&board< flo**& disc or ta*e. The

co$*uter "ra*hics are then used to si$ulate a test run. The correct siHed blanE a**ears onthe screen and usin" ani$ated tool $o9e$ents it is $achined to final sha*e and siHeaccordin" to the *ro"ra$ data.

Unit 11 6%




Module 4 Unit 11

C(C &etting / 0+eration

orD+iece and Tool &etting

The $achine datu$ is the *oint -ithin the $achineKs ran"e of $o9e$ent fro$ -hich the

$achine $aEes its *ro"ra$$ed di$ensional $o9es. It is an e)act *oint on each a)is thatthe $achine can find e9en after *o-er loss 3 this is the *oint the $achine slides $o9e to-hen &ou reference the $achine. It is often called the Hero datu$ or the $achinereference *oint. Three a)is $achines usuall& ha9e the ? a)is datu$ *osition as thes*indle full& retracted. hen a -orE*iece is cla$*ed on the $Dc table the -orE*iecedatu$ and the $achine datu$ -ill not nor$all& coincide. In order to relate the t-o afloatin" Hero facilit& is *ro9ided. This $eans that the o*erator can arbitraril& desi"nate asHero an& *oint on each a)es -ithin the ran"e of slide dis*lace$ent.

Figure 2 5 Machine atu! and orD+iece atu!

Unit 11 6'




Module 4 Unit 11

&etting is atu!s

#n CNC $achines e$*lo&in" full& floatin" datu$ facilities it is co$$on to *osition the-orE*iece or -orEholdin" de9ice on the $achine table< for con9enience. The tool< orsettin" *robe< is then Lo""ed $anuall& to touch the co$*onent in each a)is in turn. ith

the tool or settin" *robe in the correct settin" *osition 5co$*onent datu$ *osition7< oneof t-o actions $a& be taEen. The choice -ill de*end on the $achine tool.

The first action in9ol9es settin" the rele9ant a)is re"ister to Hero< b& enterin" at theconsole. button $arEed Ka)is HeroK $a& also ha9e to be de*ressed to confir$ the action.Thereafter< the $achine Hero *osition is assu$ed to be that *oint. ll subseBuentl&

*ro"ra$$ed *ositional $o9es -ill be $ade -ith reference to this Hero *oint.

The second action is *erha*s $ore *re9alent on CNC turnin" centres. t start3u*< $an&turnin" centres send their slides to a Eno-n *osition nor$all& at the e)tre$es of theira)is $o9e$ents. hen at this *osition< indicated b& li$it s-itches detectin" the li$its oftra9el< the control unit KEno-sK that the slides are at Eno-n di$ensions fro$ the $achinedatu$ *oint. This $a& be< for e)a$*le< ++ $$ fro$ the bacE face of the chucE in the ?3a)is< and 0++ $$ fro$ the centre3line of the s*indle in the ;3a)is. The e)act di$ensions-ill< of course< 9ar& fro$ $achine to $achine. The tool can then be Lo""ed to touch onthe co$*onent as *re9iousl& described. The di$ensions sho-in" on the a)is read3outsare then subtracted fro$ the Eno-n Kli$its of tra9elK di$ensions. The resultin" 9alues are

then entered into a)is offset re"isters -ithin the CNC control unit. In a roundabout -a&this creates the datu$ *osition for the tool ti*. The datu$ *ositions are not initialised to;+ and ?+ ho-e9er the& are co$*uted 5-ithin the control unit7 fro$ the Eno-n Kli$itsof tra9elK di$ensions< and the 9alues contained in the a)is offset re"isters.

'e"ardless of the actual *rocedure< the *art *ro"ra$$er *ro"ra$s the *art fro$ a datu$ *oint relatin" to the co$*onent. The *ositionin" of the co$*onent at the $achine< and asi$ilar $anoeu9re to those described abo9e and then reconciles the *osition of theco$*onent to the datu$ *ositions set at the $achine tool. @uite ob9iousl&< the correct

*rocedure for each indi9idual $achine $ust be follo-ed. To this end< theo*eratin"Dsettin" $anual for the indi9idual $achine $ust be thorou"hl& studied.

Unit 11 7)




Module 4 Unit 11

orDholding e-ices

orEholdin" de9ices can be broadl& di9ided into t-o cate"ories:

1. those -hich hold rotatin" -orE*ieces and

2. those -hich hold fi)ed -orE*ieces on $achines -hich use rotatin" cuttin" tables.

Categor$ 1

ChucDs

ChucEs $a& be $anuall& o*erated or *o-er assisted. It is $ore co$$on for *o-er3assisted chucEs to be used for CNC -orE -here the e$*hasis is on s*eed of loadin" andunloadin". Po-er assistance $a& be b& *neu$atic or h&draulic o*eration< the latter bein"used for lar"er a**lications. /reater "ri**in" *o-er is obtained usin" h&draulics since theh&draulic fluid is essentiall& inco$*ressible. Such chucEs ha9e a La- $o9e$ent of onl& afe- $illi$etres and so $ust be initiall& set for the dia$eter of -orE*iece bein"$achined. uto$atic chucEs are nor$all& o*erated b& a foot *edal but a KchucE enableK

button< on the o*eratin" console< has to be de*ressed before the chucE can be released.This is a safet& de9ice to *re9ent accidental $is3o*eration of the chucE. ar feeders $a&

be e$*lo&ed -here $an& identical co$*onents are reBuired< and the ra- $aterial can beobtained in bar stocE for$.

hen loadin" co$*onents into chucEs< it is desirable to locate the co$*onent a"ainst the bacE face of the chucE< or a suitabl& desi"ned s*acer. This ensures *ositi9e location toresist the a**lied cuttin" forces. here the co$*onent is not bacEed u* in this -a&< theo*eration is rel&in" on the frictional location *ro9ided b& the chucE La-s alone.

Collets

Collets or collet chucEs are BuicE3actin" fi)ed3dia$eter -orE3holdin" de9ices. The& aredesi"ned for holdin" close dia$eter round co$*onents. If co$*onents are to be$achined fro$ len"ths of bri"ht bar< the bar stocE can be fed throu"h the centre of thecollet onto a fi)ed sto*. Collets offer BuicE< *ositi9e and constant re3chucEin" and afforda -ide area of contact for "ri**in". ecause the& are of fi)ed dia$eter< a set is reBuiredto acco$$odate different3dia$eter -orE*ieces. Collets $a& ha9e La-s of different for$sto acco$$odate different sections of co$*onents.

Unit 11 71




Module 4 Unit 11

Unit 11 72




Module 4 Unit 11

Figure 5 Collet etails

Collets o*erate on the *rinci*le of $o9in" alon" a ta*er. There are different desi"ns inthat the ta*er $a& be *ushed 5as in a *ush3out collet7< or *ulled 5as in a dra-3bacE collet7.

The& $a& be $anuall& o*erated or *o-er assisted.

ar feeders are useful additions to a collet set u* for s*eed of co$*onent feedin". The bar stocE is fed throu"h the collet auto$aticall& for each ne- co$*onent.

Collet details are illustrated in Fi"ure .

Turning Fitures

here the co$*onent is unusuall& lar"e or irre"ular 5as in the case of castin"s orfor"in"s7< s*ecial3*ur*ose turnin" fi)tures $a& ha9e to be desi"ned. The fi)tures -illthen be $ounted directl& onto the s*indle of the $achine itself< or on a face*late $ountedon the s*indle. It -ould be unusual to e$*lo& face*lates alone on CNC $achines sincethe settin"3u* ti$e -ould be *rohibiti9el& lon". 'obotic de9ices can easil& co*e -ithloadin" and unloadin" *ur*ose3desi"ned fi)tures e$*lo&in" *o-er o*erated cla$*in"de9ices.

Unit 11 7




Module 4 Unit 11

Categor$ 2

orDholding e-ices on Machines :!+lo$ing "otating Cutters

In all cases the -orEholdin" de9ice should be *ositioned at the centre of the -orEtable inthe ;3a)is on $achinin" centres and $illin" $achines. This ensures the "reatest su**ort

and $ini$ises an& static deflection of the $achine table due to the -ei"ht of theco$*onent and the -orEholdin" de9ice. Si$ilarl&< *ositionin" the -orEholdin" de9ice asnear to the colu$n of the $achine as *racticable $ini$ises an& deflection of the $achinetool structure due to the effects of o9erhan". The direction of the cuttin" forces shouldal-a&s be directed to-ards a *ositi9e< fi)ed location. Ao-els are useful location de9icesin this res*ect since the& offer *ositi9e location in all directions. Finall&< if there isfle)ibilit& to *osition the -orE*iece or the table< other factors that $i"ht be consideredconcern the ease of loadin" and unloadin" and the ease of s-arf re$o9al fro$ the cuttin"Hone. The co$*onent should be *ositioned such that the cuttin" action directs the

$achined s-arf a-a& fro$ the o*erator. So$e co$$on -orEholdin" $ethods arediscussed belo-.

Machine ice: The $ost 9ersatile -orEholdin" de9ice for s$all *ris$atic co$*onents isthe fa$iliar $achine 9ice. This offers si$*licit&< 9ersatilit&< ri"idit& it can easil& beada*ted to *o-er3assisted o*eration and it is readil& a9ailable in a ran"e of siHes at areasonable cost. ()tra fle)ibilit& $a& be offered b& the use of a s-i9el 9ice 5allo-in"

rotation in the horiHontal *lane7< or a uni9ersal 9ice 5allo-in" rotation in both horiHontaland 9ertical *lanes7. The 9ice should be cla$*ed to the -orEtable in such a -a& that theco$*onent is *ositi9el& located 5to resist cuttin" forces7 a"ainst the fi)ed La- of the 9ice.'el&in" on the frictional location of the 9ice La-s is not reco$$ended. S*eciall&$achined re*laceable 9ice La-s can enhance the location and cla$*in" abilit& of the$achine 9ice< at $ini$al cost.

Cla!+ing :le!ents: Cla$*in" ele$ents co$*rise a ran"e of $odular co$*onents

-hich can be asse$bled to for$ -orEholdin" de9ices. $ini$u$ set -ould include aran"e of studs< nuts< -ashers< cla$*in" stri*s< *acEin" *ieces or ste**ed blocEs< tee3nutsDbolts< etc. The&Kre nor$all& used in conLunction -ith other standard ite$s of-orEsho* eBui*$ent for su**ortin" the -orE 3 for e)a$*le< *arallel bars< 9ee3blocEs<an"le *lates and so on.

Unit 11 74




Module 4 Unit 11

Unit 11 7




Module 4 Unit 11

Figure 4 5 Cla!+ing &et 0+eration

The $ost co$$on set3u*s are those of the Kbrid"eK or Kstra*K cla$*in" arran"e$ent or anKed"eK cla$*in" arran"e$ent. The latter is *referred -here it is reBuired to $achine the

-hole of the to* face of a co$*onent -ithout necessitatin" an inter$ediate cla$*chan"e. These are illustrated in Fi"ure 4. hen used in these confi"urations< certain

*oints should be obser9ed:

• Position studsDbolts as close as *ossible to the -orE*iece.

• PacE the rear of the cla$* until it is le9el -ith< or sli"htl& hi"her than< the hei"ht ofthe -orE*iece – ne9er lo-erW

• Position cla$*s so that the stud is closer to the -orE*iece than it is to the *acEin" blocE.

• Select studs that are as short as *ossible but lon" enou"h for the nut to be full&en"a"ed on the thread.

• l-a&s use s*herical cla$*in" -ashers underneath the cla$*in" nuts.

• (nsure that all cla$*s and *acEin" are clear of< and do not i$*ede< the intendedcutter *ath.

• l-a&s cla$* on a solid *art of the -orE*iece use su**ortin" de9ices -herenecessar&.

• Use $ore than one cla$*.

• efore $o9in" cla$*s< after *artial $achinin"< ensure that one or $ore other cla$*sare still holdin" the -orE*iece in *osition.

• S*rin"s should be inserted bet-een the $achine table and the stra* cla$* to su**ortthe cla$* durin" loadin" and unloadin".

Unit 11 76




Module 4 Unit 11

The selection and usa"e of cla$*in" sets is lar"el& a $anual o*eration. It is *ossible toauto$ate the o*eration b& usin" s$all *neu$atic c&linders instead of cla$*in" nuts.The& find "reatest a**lication in CNC -orE -here co$*onents can be loaded a-a& fro$the $achine on sub3tables or *allets. 'ead&3loaded *allets can then be e)chan"ed ra*idl&at the $achine tool.

Fitures

S*ecial3*ur*ose fi)tures are often e$*lo&ed. The decision to desi"n and $anufacturesuch a fi)ture -ill de*end on such factors as:

5a7 The siHe< sha*e and for$ of the co$*onent or ra- $aterial.

5b7 Suitabilit&< or other-ise< for efficient -orEholdin" 5and settin"7 b& other $eans.

5c7 The nu$ber of co$*onents reBuired and the liEelihood of re*eat orders.

5d7 ntici*ated increase in *roducti9it&.

5e7 ProLected cost of *roducin" the fi)ture.

5f7 The need to coordinate -orEholdin" -ith auto$ated loadin" and unloadin" ofco$*onents.

5"7 The *ossibilit& of $achinin" a nu$ber of co$*onents at the sa$e set3u*.

5h7 The need to *ro9ide e)tra de"rees of $o9e$ent not *ro9ided b& the $achine tool

itself. For e)a$*le< rotar& inde)in" of co$*onents.

If a fi)ture is to be s*eciall& desi"ned< it is a "ood idea to incor*orate so$e $eans forestablishin" the ;+< =+< ?+ datu$ *osition for settin" the cuttin" tool. This could taEe thefor$ of a si$*le hardened and "round settin" blocE -hich for$s *art of the fi)ture butdoes not interfere -ith the $achinin" o*erations. The o*erator -ould then KtouchK on tothe settin" blocE and set the a**ro*riate a)is re"isters to Hero.

0ther orDholding e-ices

Man& ad9anced CNC $achinin" centres are eBui**ed -ith the ca*abilit& to *erfor$si$ultaneous $achinin" o*erations in $ore than three a)es. ()tra a)es of $otion $a&include rotar& $otions about the *ri$ar& linear a)es ;< = and ?. here such ca*abilit&e)ists< e)tre$e fle)ibilit& for the *roduction of co$*le) co$*onents is *ro9ided. hereit does not e)ist< it $a& be necessar& to fall bacE on traditional -orEholdin" de9ices to

*ro9ide the e)tra a)es of $o9e$ent. In this cate"or& are the di9idin" head< rotar& table<adLustable an"le *late< and so on.

Unit 11 77




Module 4 Unit 11

In "eneral< such de9ices are not full& co$*atible -ith the conce*t of CNC $achinin"techniBues. o-e9er the s*ecific a**lication -ill deter$ine their use.

Unit 11 7%




Module 4 Unit 11

Machine 0+erating Considerations

S-arf re$o9al fro$ the cuttin" area $a& ha9e to be carried out durin" $achinin". The *ro"ra$ c&cle $a& ha9e to be sto**ed at *re3deter$ined inter9als usin" *ro"ra$ codesto enable the o*erator to clean a-a& s-arf.

:!ergenc$ &hutdo3ns

efore usin" the $achine the o*erator $ust be a-are of the location of the e$er"enc&sto* button or buttons. ($er"enc& sto*s in9ariabl& reBuire the *ro"ra$ and cuttin" toolto be re3set at the *ro"ra$ start *osition before $achinin" can re3start.

Feed 0-erride Control

This control usuall& *ro9ides for a feed rate o9erride fro$ + 3 10+. This allo-s theo*erator to $anuall& correct *ro"ra$$ed feed rates -ithin these li$its. Feed rateo9erride can also be used to re"ulate Lo" feed -hen settin" u* tools.

Unit 11 7'




Module 4 Unit 11

&elf ssess!ent

@uestions on acE"round Notes – Module 4.Unit 11

1. riefl& e)*lain Nu$erical Control in relation to a CNC Machine.

2. !ist t-o of the Constructional Features of a CNC Machine.

Unit 11 %)




Module 4 Unit 11

. Na$e so$e of the ad9anta"es of a CNC Machine.

4. In Part Pro"ra$$in" -hat does selection of ?ero Point $ean,

. hat does the Settin" of )is Aatu$ $ean,

Unit 11 %1




Module 4 Unit 11

ns3ers to uestions 15. Module 4. Unit 11

1.

Unit 11 %2




Module 4 Unit 11

(u!erical Control8

Nu$erical Control 5NC7 is the techniBue of "i9in" instructions to a $achine in the for$ of a code -hich consists of nu$bers< letters of

the al*habet< *unctuation $arEs and certain other s&$bols. The $achine

res*onds to this coded infor$ation in a *recise and ordered $anner to

carr& out 9arious $achinin" functions.

Instructions are su**lied to the $achine as a series of blocEs of

infor$ation. blocE of infor$ation is a "rou* of co$$ands sufficientto enable the $achine to carr& out one indi9idual $achinin" o*eration

e.". $o9e cutter fro$ *osition 1 to *osition 2 at a s*ecified feed rate.

(ach blocE is "i9en a seBuence nu$ber for identification. The blocEs

are then e)ecuted in strict nu$erical order. n e)a$*le of a blocE is

as follo-s:

NI /++ ;1+ ) =2+

The $eanin" of this infor$ation is as follo-s:

NI is blocE nu$ber 1 /++ directs the $achine or cutter to $o9e at the

ra*id tra9erse rate. ;1+ and =2+ are the coordinate 9alues of the tar"et

*oints of the $o9e$ent.

hen the instructions are or"anised in a lo"ical $anner the& direct the

$achine tool to carr& out a s*ecific tasE 3 usuall& the co$*lete $achinin"

of a -orE*iece or X*art. It is thus ter$ed a *art *ro"ra$.

2.

Unit 11 %




Module 4 Unit 11

Unit 11 %4

Constructional Features of C(C Machines8

con9entional $achine tool has an intelli"ent source for errorco$*ensation 5the o*erator7. Aurin" $achinin" a sEilled o*erator

can 9ar& the cuttin" conditions to co$*ensate for deflection< 9ibration

etc. to "enerate the desired sha*e< siHe and finish.

The CNC $achine can onl& co$*ensate for an error that is detected

and co$$unicated to the control. Aeflection< 9ibration etc. cannot

as &et< be easil& $onitored. For this reason NC $achines are $adestron"er and stiffer to *erfor$ to a $ore accurate standard than their

con9entional counter*arts.

The ca*acit& for 9ar&in" the conditions -hile $achinin" is therefore

li$ited. s far as *ossible the conditions ha9e to be established as the

*ro"ra$ is *roduced.

In addition to this< CNC $achines are s*endin" $ore ti$e *er shift

cuttin" than con9entional $achines did in the *ast. This hi"her

*ercenta"e of cuttin" ti$e results in faster -ear rates on the slides

and trans$ission s&ste$s.

Con9entional $achine tools are also desi"ned -ith the 9ie- to ha9in"

the sEilled o*erator standin" directl& in front controllin" the $achine.

This is no lon"er reBuired for CNC since the $achine is o*eratin" under

*ro"ra$ control.

#*ti$u$ cuttin" s*eeds and feeds< continuous *ath $achinin"< ra*id

slide $o9e$ent to brin" the tool close to the -orE and then sudden

sto**in"< all subLect the $achine to forces -hich are not encountered

on con9entional $achines.




Module 4 Unit 11

.

d-antages of C(C Machines8

'educed !ead Ti$e.

(li$ination of #*erator (rrors.

Fle)ibilit& in chan"es of Co$*onent Aesi"n.

• 'educed Scra* and Ins*ection.

• Co$*le) #ne3#ffs and S$all atch @uantities.

• !o-er !abour Cost.

• ccurate Costin" and Schedulin".

4.

&election of Aero Point8

In order to define certain *oints on a -orE*iece in this $anner< &ou

-ill first ha9e to decide -here to *ut the coordinate s&ste$ on the

-orE*iece< es*eciall& -here to *lace the Hero *oint. For $illin"

the Hero *oint 5or reference *oint7 of all di$ensions $a& be *lacedan&-here on the -orE*iece. !etKs call this Hero *oint K-orE*iece HeroK

5?7 or -orE*iece datu$. To sa9e trouble of unnecessar& calculations

it is ad9isable to *lace -orE*iece Hero at that *oint on a *art dra-in"

on -hich $ost of the di$ensions are based.

Cont.

Unit 11 %




Module 4 Unit 11

4. Continued.

-orE*iece datu$ $a&be defined as a *oint< line or surface fro$

-hich di$ensions are referenced. It $a& or $a& not be -ithin the

-orE*iece area.

The S&$bol used to denote orE*iece ?ero is:

Figure 18 ()a$*le of ?ero Point #*tions on orE*iece.

Figure 168 ()a$*le of Co$*onent -ith ?ero Point in orE*iece

Centre.

Unit 11 %6




Module 4 Unit 11

.

Unit 11 %7




Module 4 Unit 11

&etting is atu!s8

#n CNC $achines e$*lo&in" full& floatin" datu$ facilities it is

co$$on to *osition the -orE*iece or -orEholdin" de9ice on the $achine table< for con9enience. The tool< or settin" *robe< is then

Lo""ed $anuall& to touch the co$*onent in each a)is in turn. ith

the tool or settin" *robe in the correct settin" *osition 5co$*onent

datu$ *osition7< one of t-o actions $a& be taEen. The choice -ill

de*end on the $achine tool.

The first action in9ol9es settin" the rele9ant a)is re"ister to Hero

b& enterin" at the console. button $arEed Ka)is HeroK $a& alsoha9e to be de*ressed to confir$ the action. Thereafter< the $achine

Hero *osition is assu$ed to be that *oint. ll subseBuentl&

*ro"ra$$ed *ositional $o9es -ill be $ade -ith reference to this

Hero *oint.

The second action is *erha*s $ore *re9alent on CNC turnin" centres.

t start3u*< $an& turnin" centres send their slides to a Eno-n *osition

nor$all& at the e)tre$es of their a)is $o9e$ents. hen at this *osition

indicated b& li$it s-itches detectin" the li$its of tra9el< the control unit

KEno-sK that the slides are at Eno-n di$ensions fro$ the $achine datu$

*oint. This $a& be< for e)a$*le< ++ $$ fro$ the bacE face of the

chucE in the ?3a)is< and 0++ $$ fro$ the centre3line of the s*indle in

the ;3a)is. The e)act di$ensions -ill< of course< 9ar& fro$ $achine to

$achine. The tool can then be Lo""ed to touch on the co$*onent as

*re9iousl& described. The di$ensions sho-in" on the a)is read3outs are

then subtracted fro$ the Eno-n Kli$its of tra9elK di$ensions. The

resultin" 9alues are then entered into a)is offset re"isters -ithin the

CNC control unit. In a roundabout -a& this creates the datu$ *osition

for the tool ti*. The datu$ *ositions are not initialised to ;+ and ?+

ho-e9er the& are co$*uted 5-ithin the control unit7 fro$ the Eno-n

Kli$its of tra9elK di$ensions< and the 9alues contained in the a)is offset

re"isters.

Unit 11 %%




Module 4 Unit 11

. Continued.

'e"ardless of the actual *rocedure< the *art *ro"ra$$er *ro"ra$s the

*art fro$ a datu$ *oint relatin" to the co$*onent. The *ositionin" of the

co$*onent at the $achine< and a si$ilar $anoeu9re to those described

abo9e and then reconciles the *osition of the co$*onent to the datu$

*ositions set at the $achine tool. @uite ob9iousl&< the correct *rocedure

for each indi9idual $achine $ust be follo-ed. To this end the o*eratin" Dsettin" $anual for the indi9idual $achine $ust be thorou"hl& studied.

Unit 11 %'




Module 4 Unit 11

*nde

introduction to cnc m4 u11

Documents