Lecture notes on CNC.doc

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Chapter 1

NC Technology

1. Introduction:

Conventional machines used for operations like Turning, Drilling, Milling were commonly

used and operated manualy. the worker had to use a detailed working drawing sheet of the

workpart that included dimensions, tolerances, surface roughness,….

He also had to use process sheet, which includes production steps, cutting speed, feed,

feedrate, revolutions,…..

This sheet was used to develop the NC coded program.

2. Basic Components of NC Machine System:

To produce the program instruction we use the process sheet and convert it to NC coded

program.

The NC coded program is then punched into a tape to e transferred to the machine

control unit.

The machine control unit !MC"# contains a tape reader, it also has register and uffer,they are used to convert the data from the punched tape into electric signals that are sent

to the machine tool.

Machine

ControlUnit (MCU)(Computer

) Machine Tool

NC Machine

ProgramInstruction

3. lo! "iagram of the Steps in #rocessing NC #rogram:

$. #rogram of Instructions : It is the detailed step %y step commands that direct the actions of the processing

e&uipment. In machine tool applications 'the program of instruction is called part

program 'and the person !ho prepare the program is called a part programmer.

The program is coded on a suita%le medium for su%mission to the machine control

unit. The most common input mediums used are punched tape ' punched cards and

magnetic tape .

a. #unched Card:

#unched card is a plastic ( paper card !hich is ha)ing holes . It can

accommodate only fe! sentences of the program so there is restriction on the

si*e . The ad)antage of using card is that se&uence of operation can %e changed

%ecause each operation is on separate card .'program readers and

transportation de)ices for punched cards are more complicated than for punched tape.

%. #unched Tape :

"ifferent materials ha)e %een used for punched tape . These materials are

paper and foil . The follo!ing figure sho!s the shape and dimensions of the

punched tape

The follo!ing ta%les sho!s the standard +I, and IS- ,SCII/ codes for

numerical control programming originally designed for punched tape.

Tape Reader

Inormation Read! "ecode Machine Ta#le

Machine ControlUnit (MCU)

Machine$ctuatingRegisters

c. Magnetic Tape :

Magnetic tape is a plastic tape coated !ith iron o0ide and is similar to the tape

sed in tape recorders %ut small si*e/.magnetic tape can store much moreinformation per unit length as compared to punched cards or magnetic tapes .,lso

Information can %e easily stored and erased .This is the least preferred in

machining %ecause of the follo!ing reasons :

1. electrical and magnetic fields can easily distort program signals

2. any damage of the magnetic tape is not easy detecta%le %ecause no )isual

e0amination is possi%le.

3.tape gets damaged in dust in the shop floor.

.Machine Control nit :

Information is passed from the NC tape to the machine control unit %y means of

the tape reader in the machine control unit MC/ . ,fter the tape has %een read

%y the tape reader 'the coded information 'no! in the form of signals 'is passed on

to the control. egisters !ithin the control accept the information !hich consists

of proper coordinates ' preparatory functions and miscellaneous functions..This

information is transmitted to the respecti)e register sections !here actuation

signals are relayed to the machine tool dri)es. , fundamental s4etch of this process

is illustrated in the follo!ing figure .

$ % & ' ( )

* + ) - % $ *

Tape Reader

Inormation

Read!"ecode

Machine Ta#le

Machine ControlUnit (MCU)

Machine$ctuatingRegisters

Inormation Passed"irectl&

Most modern NC and CNC machine controls are euiped with uffer storage shown

in the following figure ,this feature allows the control to accept information into the

uffer registers while an operation is eing performed from the active machineregisters.when the operation is complete the information is transferred from the uffer

storage to the machine actuation registers.

Tape reader types/a.Mechanical Type/ as shown in following figure

• Consists of pins that read holes in the tape, such that a hole is read as % or

signal, tape is red as + or no signal.

• 0t is commonly used in point to point motion !like in drilling#• 0t is slow, reads only aout 1+ chr2sec

• 0t is reliale, ine3pensive, and easy maintainance.

$ % + - 1 (

* ) 4 & (

$ % & ' ( )

* + ) - %

. 5hoto6electric reader/ as shown in the following figure

• Consists of a light eam and photo electric cell that gives a signal when light

falls upon it, such that a hole is read as % or signal, tape is red as + or no signal.

• 0t is commonly used in contouring motion.• 0t is fast, reads '++6)++ chr2sec

• 0t is very e3pensive

• 0t has high sensitivity to dust

C. 5numatic reader / as shown in the figureTheir principle is similar to that of electromechanical tape reader . Here pressure on

the moving contact is e3erted y compressed air . 0f there is punched hole in front of

no77le , the compressed air passes and no pressure uilds up at the opening of no77le

.this pressure is utili7ed to otain an electric signal . these readers are relatively cheap

.They have the advantage that the dirt particales in the reading 7one are automatically

lown off thus providing more reliaility .

5. .,0is elationships:

• 8or Milling2Drilling

• for Turning/

9nce the NC tape has een read ,decoded and the machine actuation registers loaded ,the

Machine responds with its appropriate coordinate a3is movements and other commands

Machines with only $ and * position capaility are known as two a3is machines. 9n

Machines of this type distance in : direction is controlled y the operator or y preset

;tops similar to that of a conventional drill press.

The three asic motions are designed y the electronic industries association !<0=# are the

$,*,: , the $ motion is parallel to the longest dimension of the machine tale,the *motion

0s normally parrel to the shortest dimension of the machine tale.The : motion ecomes

Complicated y the fact that the NC macines are made with vertical and hori7ontal spindle so it can e said that the line through the centre of the machine spindle is actually the :

a3is ,it is only when the actual depth of cut : a3is is controlled y the tape ,the macine is

considered a true three a3is NC machine. Machine 2 a3es relationships can e seen in

figures /

>ertical Milling Machine Hori7ontal Milling Machine

Turning Machine

6. Types of Motion Control:

%. 5oint to 5oint Motion !5T5#/

• Tool moves to the defined points with only feed ack at the specific point.

• "sed in drilling operations.

&. Contouring Motion/

• $,*,: motion are always controlled and they have constant feedack.

•"sed in milling or turning operations.

'. ;traight Cut/

9nly one coordinated is monitored at a time.

•"sed in simple straight cutting operations.

7.ectangular Coordinates : ,%solute and Incremental 7.1. Cartesian Coordinate System :

The system of cartesian is illustrate in figure ' the 8 a0is is the hori*ontal left

,nd right / and the 9 a0is is )ertical up and do!n/ and the is perpendicular

To the paper !ith its point at the location !here the 8 and 9 lines cross each

-ther 'the intersection of the t!o a0es 8 and 9 is called orign or ero point.

our &uadrant are formed !hen the 8 and 9 a0es cross as sho!n in the figure

7.2 incremental System :

,n incremental system !or4s according to the same principle ' it positions the

;or4 or cutter in increments from the immediately preceding point. Calculations

,re made from the location of the tool or ta%le to !here it is going. ,s sho!n in figure the use of plus and minus signs in)ol)es a ne! aspect !hen used in the

incremental mode ' a <0 mo)e directs the tool to the left . Similarly a =9 mo)e

positios the cutter up from the present location and <9 is a command to mo)e

do!n . a = directs the cutter a!ay from the !or4piece'!hile a < is a mo)e

to!ard or into the !or4piece.

7.3 ,%solute Systems :

,n a%solute system operates similar to the a%solute dimensioning. ,ll positions

are figured and punched in the tape relati)e to the same *ero or reference point.

-ne ad)antage of a%solute systems o)er incremental systems concerns

positioning errors .if a positioning error occurs in an incremental system 'all

>. +ngineering ,nalysis of NC #ositioning Systems :

The NC positioning system converts the coordinate a3is values in the NC part

program into relative positions of the tool and work part during the processing .

Aet us consider the simple positioning system shown in figure .The system consists of

= cutting tool and worktale on which a work part is fi3ed .The tale is designed to

move the part relative to the tool . The worktale moves linearly y means of a

rotating leadscrew ,which is driven y stepping motor or servomotor .8or simplicity,

Be show only one a3is in our sketch .To provide 36y capaility ,the leadscrew has a

certain pitch 5 !in2thread , mm2thread#. Thus the tale moves a distance eual to the

pitch for one revolution. The velocity of the work tale ,which corresponds to the feed

ate in a machining operation is determined y the rotational speed of the leadscrew.

There are two types of positioning systems used in NC system / shown in figure

a. open loop system operates without verifying that the actual position achieved

in the move is the same as the desired position.

. Closed loop control system uses feedack measurements to confirm that the

final position of the worktale is the location specified in the program .

9pen loop cost less than closed loop systems and are appropriate when the force

esisting the actuating motion is minimal , closed loop systems are normally

specified for machines that perform continuous path operations such as milling or

Turning in which there are significant forces resisting the forward motion of the

cutting tool.

Chapter 2

CNC Machines

1.Introduction:

2.eatures of CNC Machines:

%. ;torage of more than one part program.

&. >arious form of program input

• Manual data input

• 8loppy diskette

• Communiction with e3ternal computer

'. 5rogram editing at the machine tool

(. 8i3ed cycles @ programming suroutines

). 0nterpolation

1. Cutter length and si7e compensation

-. =cceleration and deceleration calculation

. Communication interface

4. Diagnostics

Punched tape PunchedCard Magnetic tape

Computer as input data

Programperorms

interpolationcalculations

3. Machine Control nit of CNC:

$. CNC Soft!are:

%. 9perating system software/ is to interpret the NC part program and generate the

corresponding control signals to derive the machine tool a3es ,it is installed y thecontroller manufacturer and is stored in 9M in the MC". The operating system

software consists of the following /

• <ditor/ which permits the machine operator to input and edit NC part programs

• Control program/ which decodes the part program instructions,perform

interpolation and acceleration2deceleration calculations ,and accomplishes

other related functions to produce the coordinate control signals for each a3is.

• <3ecutive program/ which manage the e3ecution of the CNC software as well as

the 0 2 9 operations of the MC".

&. Machine interface software/ is used to operate the communication link etween theC5" and the machine tool to accomplish the CNC au3iliary functions !coolant

control ,tool changer ,fi3ture clamping device ,timers …#,as previousely indicated ,the

0 2 9 signals associated with the au3illiary functions are sometimes implemented y

means of a programmale logic controller interfaced to the MC" ,and so the machine

interface software is ofthen written in the form of ladder logic diagram

Memory1Main Memor& RM perating5&s R$M PartProgram

25econdar&Memor&Remo6a#lestorage

CPU1Control 5ection2$rithmetic 7ogicUnit ($7U)3Immediate $ccessmemor&

I/O Interface1perator Panel(8e&#oard CRT9)

2Tape Reader

Machine Tool Controls

Position Control (-.+)5pindle 5peed Control

Sequence Controls

Coolant:i;ture Clamping Tool Changer

5&stem<us

'. =pplication software/ consists of the NC part programs that are written for

machining.

. "irect Numerical Control "NC/:

DNC can e used for up to &)1 machines.

0t has two systems/

%. Aoad/

0ts where the machine is directly controlled from the central computer

&. Download/

0t is where the MC" attached to the machine downloads the NC code from the centralcomputer

5. "istri%uted Numerical Control "NC/:

CentralComputer

<ul= Memor&NC

Programming

"ata 5>itching<o;

5>itchingNet>or=

MCU MCU MCU

?,N @ey system6. ,pplications of NC A CNC:

%. Machine tool applicatioin/

• NC lathe

• NC oring mill

• NC drill press

• NC milling machine

• NC cylindrecal grynding

Non6machine tool application/

•Belding machining

•Thermal cutting machine

7. #art characteristcs to %e Suited to ,pplications of NC A CNC:

%. Eatch production of small to medium lot si7e !%6%++ products#

&. epeated order

'. Comple3 part geometry

(. Much metal needs to e removed

). 5art is e3pensive>. ,d)antages of using NC'CNC:

%. Freater accuracy

&. Aower scrap rates

'. More comple3 part geometry

(. Aess floor space is reuired

). 9perator skill level is redued

1. 0nspection reuirement is reduced

1."isad)antages of using NC' CNC:

%. Higher investment cost

&. Higher maintainance effort

"NC Computers MCU

5atelliteComputer MC

Chapter 3

NC Coding System

1.ormat of NC Coded #rogram:

Bord =dress 8ormat/

%. ;euence Numer !N6Bord#

&. 5reparatory word !F6Bord#

'. Coordinates !$,*,: Bord#

(. 8eed ate !86Bord#). ;pindle ;peed !;6Bord#

1. Tool ;election Bord !T6Bord#

-. Miscellaneous Command !M6Bord#

. <nd69f6Elock !<9E ;ymol#

2. NC coded #rogram in milling and drilling operations :

The follo!ing figure sho!s the a0es con)ention for the )ertical milling machine MC/ ,nd Dori*ontal milling machinesDMC/. ;hile the ta%les indicate a summary of the

EF codes'MF codes used in milling and drilling operations .The remaing part of this

section e0plains the method of using E codes .

Punched tape Punched

Card Magnetic tape

Computer as input data

3. NC coded #rogram in Turning operations :

The follo!ing figure sho!s the a0es con)ention for turning operations . ;hile the

ta%les indicate a summary of the EF codes'MF codes used in turning operations .The

remaing part of this section e0plains the method of using E codes .

Chapter .$

NC #art #rogram

NC part programming consists of planning and documenting the seuence of processing

;teps to e performed on an NC machines, the part programmer must have a knowledge

9f machining as well as geometry . The documentation portion of the part programming

involves the input medium used to transmit the program of instructions to the NC machine

Control unit !MC"#.

The traditional input medium !%4)+# to the NC machines is %6inch wide punched tape .

more recently ,the use of magnetic tape and floppy disks have een growing in popularity as storage technologies for NC .

5art programming can e accomplished using a variety of procedures ranging from highly

Manual to highly automated methods. These methodes are /

%. Manual 5art 5rogramming

&. Computer =ssisted 5art 5rogramming

'. 5art 5rogramming "sing C=D2C=M

(. Manual Data 0nput

The follo!ing are e0planations of the different methods of part programming !ith some

+0amples .

1 . Manual part programming :

In manual part programming 'the programmer prepares the NC code using the lo! le)el

machine language .the program is either !ritten %y hand on a form from !hich a

punched tape or other storage media is su%se&uently coded 'or it is entered directly into

, computer e&uipped !ith NC part programming soft!are '!hich !rites the program ontothe storage media .In any case 'the part program is a %loc4 %y %loc4 listing of the

machining instructions for the gi)en Go% 'formatted for the particular machine tool to %e

used .

Manual part programming can %e used for %oth pointFtoFpoint and contouring Go%s. It is

Most suited for point <toFpoint machining operations such as drilling . It can also %e used

for simple contouring Go%s' such as milling and turning !hen t!o a0es are in)ol)ed .

Do!e)er 'for comple0 three dimensional machining operations 'there is an ad)antage in

using computer assisted part programming .

The follo!ing are some e0ercises in drilling 'milling and turning machine operations

using the Bo0ford CNC machines:

a. "rilling and Milling +0ercises:

%. Turning +0ercises:

2 . Computer ,ssisted #art #rogramming :

3 . NC #art #rogramming using C,"(C,M :

$ . Manual "ata Input :

Chapter .

+0ercises and #re)ious +0aminations

Problem ONE : [10]

1.What are the basic components of NC System? 2.Explain the dierent !eros of NC machine tool ?

3.Explain the NC Proced"re?Problem #WO: [10]

1.Explain brie$y the %"nction controlled by NC?2.Explain the preparatory f"nctions?

3.Write a simple part pro&ram for the follo'in&

component ..(rillin& and tapin& t'o holes 'ith diameter 10mm 'ith

depth )0 mm *"sin& man"al + control .

1,Explain brie$y the %"nction controlled byNC -

2..o' to ad/"st the 'or2 plane - 3i4e an example ?3.Write a simple part pro&ram for the follo'in&

gher Technological Institute

0 th of amadan

chanial +ngineering

"epartment

Midterm +0amination

Term: H,N.(M,9 26

Co"rse : Control ofman"fact"rin&Code : 5#E)06Examiner :(r,7brahim Nasr #ime :1 .o"r

0 th of amadan

chanial +ngineering

"epartment

Midterm +0amination

Term: H,N.(M,9 26

Co"rse : Control ofman"fact"rin&

Code : 5#E)06Examiner :(r,7brahim Nasr #ime :1 .o"r

5aterial : Plastic#ool chan&ed at : 80*90*+)

e;"ired 1.5ill the steps [< mm diameter slot drill]

2.(rill the holes [ = mm diameter slot drill ]

3.5ill the 60 mm diameter poc2et [ < mm diameter slotdrill ]

Problem ONE : [10]

1.What are the basic components of NC System? 2.Explain the dierent !eros of NC machine tool ?

3.Explain the NC Steps?

0 th of amadan

chanial +ngineering

"epartment

Midterm +0amination

Term: M,9(,E. 26

Co"rse : Control ofman"fact"rin&Code : 5#E)06

Examiner :(r,7brahim Nasr #ime :1 .o"r

Problem #WO: [10]

1.(escribe the "sa&e of p"nched tape as inp"t medi"m for NCmachine?

2.Compare bet'een the p"nched tape readers operations -6,Explain the f"nctions of the follo'in& : (ecoder > ?"erstora&e

interpolator > (ri4e "nit =,Explain the basic types of motion control system?

%(ra' bloc2 dia&ram of NC system ?

Problem ONE : []

1.Explain the basic components of NC system?2.With dra'in&*explain machine re&isters and b"er stora&e

operations?3.What are the types of NC system?

Problem #WO: [10]

1.@sin& s2etches *explain ho' the +axis control can be done in

drillin&?2.Compare bet'een dierent !eros "sed in millin& and drillin&?

3.What are the f"nctions controlled by NC in millin& and drillin&?

Problem #.EE: []

1.Explain 'ith examples the dierent 3codes canned cycle "sed

in drillin& and millin&?2.(ra' s2etch and indicate the machine axes?

3.Explain the canned cycles "sed in t"rnin&? Problem %o"r: [)0]

Practical

0 th of amadan

chanial +ngineering

"epartment

inal +0amination

Term: H,N.(M,9 26

Co"rse: A"tomatic control in

man"fact"rin&Code : 5#E)06Examiner :(r,7brahim Nasr #ime :1, .o"r

Write the 3*5 coded pro&ram and sim"late the prod"ctionsteps onComp"ter

Select the s"itable tool * feed rate and c"ttin& speed

0 th of amadan

chanial +ngineering "epartment

inal +0amination

Term: -ct.(Han.27

Co"rse: A"tomatic control inman"fact"rin&Code : 5#E)06Examiner :(r,7brahim Nasr #ime :60 min,

Problem ONE : [10]1, What are the steps of NC system -

2?rie$y * compare bet'een NC*CNC* (NC machines?

3.Explain brie$y the components of NC system?!.s2etch and explain the NC coordinate system?

".Compare bet'een the types of +ero points?Problem #WO: [10]

1What are the types of motion control system?2Compare bet'een the dierent inp"t media in NC machine?

3What are the types of p"nched tape readers? 4Explain 'ith s2etches *the dierence bet'een open and closed

loop control systems?

Problem #hree: [Practical]

[)0]Write the 3*5 coded pro&ram and sim"late the prod"ctionsteps onComp"ter

Select the s"itable tool * feed rate and c"ttin& speed

0 th of amadan

inal +0amination

Term: -ct.(Han.27

Co"rse: A"tomatic control in

man"fact"rin&Code : 5#E)06Examiner :(r,7brahim Nasr #ime :1, .o"r

Problem ONE : [] 1Compare bet'een the

machine control"nit of NC and CNC machines? 2Explain the follo'in& "sin& s2etch

,NC coordinate system , +ero point

,#he 3<1 * 3<) *3<= * 3< *3B

Problem #WO: [1]

1Explain the #as2s in comp"ter assisted part pro&rammin&?2Write the AP# pro&ram to prod"ce the follo'in& sho'n

component

the re;"ired a, drillin& = holes 'ith feed rate 1)0 mmDmin, *c"ttin& toolspeed )000 rpm

b,millin& the o"ter s"rface 'ith c"ttin& tool diameter < mm *feed rate 1)0 mmDmin, and c"ttin& tool speed )000 rpm

0 th of amadan

inal +0amination

Term: Han.(May 27

Co"rse: A"tomatic control inman"fact"rin&Code : 5#E)06Examiner :(r,7brahim Nasr #ime :1, .o"r

Problem #hree: [Practical] [)0]

Problem ONE : [] 1 .o' NC collect informations?

2Explain the follo'in& "sin& s2etch ,,motion control system

,,$o' dia&ram of NC ,,interpolation 3codes

Problem #WO: [1]

1Explain the AP# lan&"a&e statements -&i4e examples?2Write the AP# pro&ram to prod"ce the follo'in& sho'n

component

the re;"ired a, drillin& the hole 'ith feed rate 1)0 mmDmin, *c"ttin& toolspeed )000 rpm

gher Technological Institute0 th of amadan

inal +0amination

Term: Han.(May 27

Co"rse: A"tomatic control inman"fact"rin&Code : 5#E)06Examiner :(r,7brahim Nasr #ime :1, .o"r

b,millin& the o"ter s"rface 'ith c"ttin& tool diameter < mm *feed rate 1)0 mmDmin, and c"ttin& tool speed )000 rpm

Problem #hree: [Practical] [)0]

Lecture notes on CNC.doc

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