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CNC GOVT POLYTECHNIC AMBALA CITY CNC GOVT POLYTECHNIC AMBALA CITY

CNC GOVT POLYTECHNIC AMBALA CITY - PowerPoint Presentation

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CNC GOVT POLYTECHNIC AMBALA CITY - PPT Presentation

CHAPTER 1 INTRODUCTION Introduction to NC Production of machined parts whose production is controlled by a computer Definition NC A method of accurately controlling the operation of a machine tool by a series of coded instructions consisting of numbers letters of the alphabet and sym ID: 701618

view cnc tool machine cnc view machine tool guide amp machines g00 top front programming axis control part motion

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Slide1

CNC

GOVT POLYTECHNIC

AMBALA CITYSlide2

CHAPTER 1

INTRODUCTIONSlide3

Introduction to NC

Production of machined parts whose production is controlled by a computer

.

Definition:

NC - A method of accurately controlling the operation of a machine tool by a series of coded instructions, consisting of numbers, letters of the alphabet, and symbols that the machine control unit can

understand

The concept of NC was proposed in 1940s by

JohnParsons

who recommended a method of automatic machine control that would guide a milling cutter to produce a curvilinear motion in order to generate smooth profiles on the work-pieces.Slide4

Components of NC machinesSlide5

Evolution of NC/CNC

Single

items produced by craftspeople

Interchangeable Parts

Eli Whitney (Cotton Gin)

Manual labor was still the most cost effective method.

WW II manufacturers could not maintain quantity & quality parts.Slide6

Conventional vs. CNC machine Slide7

Item

Conventional machine

CNC

machine

1. Movement

Acme screw

Ball screw

2. Feed

manual

motor

3.measurement

manual

Linear scaleSlide8

Three basic components of an NC system:

Input

medium:

- Part

program or instructions needed to drive the machine tool components - Instructions are prepared manually or by use of computer - Instructions include machining parameters (feed rate, cutting speed); sequence of actions (e.g., positioning & machine functions) - Instructions are stored in the form of tape (paper, magnetic); floppy diskettes; DNC download to CNC RAM

2

. Machine control unit (MCU): - Electronics & control hardware - Interpret instruction set - Execute instructions - Monitor results & correct where appropriate

3

. Machine tool: - Mechanical structure that performs the machining, including the components that drive each axis of motion (e.g., AC or DC motor; hydraulic actuator; stepper motor — choice affects speed of response, accuracy and power capacity).Slide9

INPUT UNIT

Input data includes information about the control medium, information about computer programs should also be given.

Control medium: perforated tape,

magnatic

tape, etc.

Type of dimensional programming: Absolute, Incremental or both etc.,

Number of digits in each dimensional word etc., Input resolution Information about programming methods and languages

Tape reader type - Mechanical or photo electric etc., Tape code - ISO, EIASlide10

MCU

MCU - Machine Control Unit - decodes NC codes to drive and monitor servo motor movements.Slide11

CNC Advantages vs. NC 

Programs could be stored in computer memory.

Easier to edit.

More complex parts could be manufactured.

Use of 3d geometry.

Networking/

filesharing

w/ other computers.Slide12

Limitations of NC

Relatively high initial cost of equipment.

·

Need for part programming.

·

Special maintenance requirements.

·

More costly breakdowns.Slide13

Advantages Of CNC 

Increased productivity after  programming is completed

Reliability - reduces human error

Often eliminates need for special jigs and fixtures

Reduces location of part features

Makes possible the machining of complex shapes requiring simultaneous 3 axis

motion

Single part and production runs can be programmed and machined with minimum effort and cost.

Programs can readily be altered and re-run

Reduced inspection costs (more reliable)

Once programming, setup and verified the equipment can be operated by a less skilled operator.Slide14

Disadvantages 

of CNC

Initial cost of CNC machine tools

Servicing of equipment

Larger machines require more space

Personnel must be trained in the programming and operation of this equipment.Slide15

Computer Numerical Control (CNC) Slide16

Direct Numerical Control (DNC)

Distributed (Direct) Numerical Control (DNC): ·

(

Direct) Central computer stores programs & directs NC operations; NC machines dependent on central computer.

(Distributed) Central computer stores programs and transfers programs to CNC machines.

Central computer provides management functions (e.g., part of MIS) Programs stored as cutter location (CL) files and post-processed for the machine assigned the job.

Major components: central computer; bulk memory; telecommunication (EDI); CNC machine tools.Slide17

DNCSlide18

Selection of components for NC/CNC

1. Parts from similar raw material, in variety of sizes, and/or complex geometries.

2

. Low-to-medium part quantity production.

3

. Similar processing operations & sequences among work pieces.

4

. Frequent changeover of machine for different part numbers.

5

. Meet tight tolerance requirements (compared to similar conventional machine tools).Slide19

Application of CNC Machine Tools

CNC mills and machining centers,

CNC lathes and turning centers

CNC electrical discharge machining (EDM)

CNC grinding machines

CNC cutting machines (laser, plasma, electron, or flame)

CNC fabrication machines (sheet metal punch press, bending machine, or press brake)

CNC welding machinesSlide20

AXIS IDENTIFICATION

2&3

axes CNC Machines

CNC lathes will be coming under 2 axes machines. There will be two axes along which motion takes place.

The saddle will be moving longitudinally on the bed (Z-axis) and the cross slide moves transversely on the saddle (along X-axis).

In 3-axes machines, there will be one more axis, perpendicular to the above two axes. Slide21

RIGHT HAND RULE FOR LINEAR AXIS IDENTIFICATIONSlide22

AXIS IDENTIFICATION(Lathe)Slide23

Axis identification (milling)Slide24

CHAPTER 2

CONSTRUCTION AND TOOLINGSlide25

MAIN ELEMENTS OF CNC MACHINES

To enable electronic automation with high rate of metal removal at optimum cutting conditions, maintaining high repetitive accuracies with utmost safety to the operator and the machine, CNC machines are specially designed.Slide26

MAIN ELEMENTS OF CNC MACHINES

i

) Machine structure

ii) Guide ways

iii) Spindle bearings & mounting

iv) Drive units

v) Mech. Power transmission

vi) Position feed back elements / systems

vii) Additional accessories / equipment

viii) Control software

ix) Chip removal system

x) Safety features Slide27

Machine structure

Structures are designed to withstand static, dynamic & thermal loads providing high stiffness, rigidity & damping properties. The material used is generally

mechanite

cast iron / special casting with nickel & copper elements. Welded structures also in wide usage.Slide28

Guide ways

TYPES OF GUIDE WAYS

1. Friction Guide ways: The relation between moving part (Guide) and stationary part (Guide way) contacting directly each other.

2. Anti Friction Linear Motion Guide ways: Here the contact between guide and guide way may be separated by the third element i.e. Ball, Roller or hydraulic oil film in case of Hydro dynamic or hydrostatic guide way systems. Slide29

1) HYDROSTATIC GUIDE WAY

2) AEROSTATIC GUIDE WAY

In Hydrostatic guide ways, the surface of slide is separated from the guide way by a very thin film of fluid supplied at pressure as high as 300 bar. Frictional wear and stick slip are entirely eliminated. A high degree of dynamic stiffness and damping are obtained with these guide ways, both characteristics contributing to good machining capabilities. Their application is limited due to high cost and difficulty in assembly.

In Aerostatic guide ways, the slide is raised on a cushion of compressed air which entirely separates the slide and the guide way surfaces. The major limitation of this type guide ways is a low stiffness, which limits its use for positioning application only. e.g. CMM and other measuring instruments. Slide30

RE CIRCULATING BALL BUSHINGS

The following are the advantages of the ball screws:

1) Low frictional resistance.

2) Low drive power requirement.

3) Lesser temperature rise.

4) Less wear hence longer life.

5) No stick slip effect.

6) High traverse speed.

7) High efficiency Slide31

There are two types of roller screws used planetary and re circulating. Both types provide backlash-free movement and their efficiency is of the same order (90 %) as ball screws. An advantage of roller screws is that because the pitch of the screw is smaller that the minimum pitch of the ball screw, the less complex electronic circuitry will provide more accurate positional control. Roller screws are much costlier than the ball screws. The rollers of both types of screw are positioned between the nut and the screw, and engage with the thread from inside the nut and on the outside of the screw. Slide32
Slide33

Guideways

The

guideways

of CNC machines are made of steel. To reduce the frictional forces, they are coated with a strip of PTFE (Poly Tetra

Fluoro

Ethylene).Slide34

Ballscrews

On conventional lathes a

leadscrew

is used to converts the rotary motion of the hand wheel into linear motion of the slides.

Leadscrews

have a high coefficient of friction and backlash. On CNC machines a

ballscrew

is used instead of a

leadscrew

. Friction and backlash are much less than on

leadscrews

.Slide35

Swarf Removal

Efficient chip removal system eliminates thermal effects & thus improves the quality of cutting and the job being machined.

Centrifuging of chips at source integrated into a

swarf

blowing system

Airflow isolation slide damper

Rotary valve

Blowline

inlet connectionSlide36

Safety

Suitable covers for guide-ways etc., and electronic interlocks for the safety of the operating personnel and machine are provided.Slide37

AUTOMATIC TOOL CHANGER

HYDROMOTOR IS USED FOR THE ROTATION OF THE MAGAZINE.

MAGAZINE

MOVES IN RAPID ONE TOOL AHEAD (SENSED BY PROXIMITY SWITCH)

MAGAZINE CREEPS TO THE POSITION IN A VERY LOW

SPEED

(SENSED BY PROXIMITY SWITCH).

WHEN THE MAGAZINE IS IN POSITION, LOCATING PIN ENTERS THE HOLE IN THE MAGAZINE AND POSITIONS THE MAGAZINE ACCURATELY. Slide38

ATC

Simple CNC machines work with a single tool. Turrets can work with a large number of tools. But if even more tools are required, then ATC is provided. The tools are stored on a magazine. It allows the machine to work with a large number of tools without an operator. The main parts of an automatic tool changer are the base, the gripper arm, the tool holder, the support arm and tool magazines.Slide39

Types of ATC

Depending on the shape of the magazine, ATC can be of two types: Drum Type changers are used when the number of tools is lower than 30. The tools are stored on the periphery of the drum. Chain type changers are used when the number of tools is higher than 30(The number is different depending on the design and manufacturer. It is important to note that the number of tools for the drum type is fewer than the chain type). But the tool search speed will be lower in this caseSlide40

SPINDLE DIRECT ATCSlide41

ATC TYPESlide42

WORKING OF ATCSlide43
Slide44

Programming Methods-APT

Part definition

P1=Point/12,20,0

C1=Circle/Center,P1,Radius,3

LN1=Line/C1. ATANGL,90

Cutter Commands

TLRT,GORT/LN1.TANTO,C1

GOFWD/C1,TANTO,L5Slide45

Programming Methods-CAM

Computer Aided Machining (CAM) Systems

Graphic representation of the part

PC based

Integrated CAD/CAM functionality

“Some” built-in expertise

Speed & feed data based on material and tool specifications

Slide46

Programming Methods-CAM

Tool & material libraries

Tool path simulation

Tool path editing

Tool path optimization

Cut time calculations for cost estimatingSlide47

Programming Methods-CAM

Import / export capabilities to other systems

Examples:

Drawing Exchange Format (DXF)

Initial Graphics Exchange Standard (IGES)Slide48

The Process CAD to NC File

Start with graphic representation of part

Direct input

Import from external system

Example DXF / IGES

2D or 3D scan

Model or Blueprint

(At this point you have a graphics file of your geometry)Slide49

The Process CAD to NC File

Define cutter path by selecting geometry

Contours

Pockets

Hole patterns

Surfaces

Volume to be removed

(At this point the system knows what you want to cut)Slide50

The Process CAD to NC File

Define cut parameters

Tool information

Type, Rpm, Feed

Cut method

Example - Pocket mill zig-zag, spiral, inside-out

Rough and finish parameters

(At this point the system knows how you want to cut the part)Slide51

The Process CAD to NC File

Execute cutter simulation

Visual representation of cutter motion

Modify / delete cutter sequences

(At this point the system has a “generic” cutter location (CL) file of the cut paths)Slide52

The Process CAD to NC File

Post Processing

CL file to machine specific NC code

Filters CL information and formats it into NC code based on machine specific parameters

Work envelope

Limits - feed rates, tool changer, rpm’s, etc.

G & M function capabilitiesSlide53

Output: NC Code

Numerical Control (NC) Language

A series of commands which “direct” the cutter motion and support systems of the machine tool.Slide54

Output: NC Code

G-Codes (G00, G1, G02, G81)

Coordinate data (X,Y,Z)

Feed Function (F)

Miscellaneous functions (M13)

N - Program sequence number

T - Tool call

S - Spindle commandSlide55

Output: NC Code

NC Program Example

N01G90 G80

N03 GOO T12 M06

N05 GOO X0 Y0 Z.1 F10 S2500 M13

N07 G1Z-.5

N09 G02 X-10. I0J0F20

N13 X0Y10

N17 X10Y0

N19 X0Y-10

N21 X-10Y0

N23 M2Slide56

Example of CNC Programming

What What Must Be Done To Drill A Hole On A CNC Vertical Milling MachineSlide57

Top

View

Front

View

Tool Home

1.) X & Y Rapid To Hole PositionSlide58

Top

View

Front

View

2.) Z Axis Rapid Move

Just Above Hole

3.) Turn On Coolant

4.) Turn On Spindle

.100”Slide59

Top

View

Front

View

5.) Z Axis Feed Move to

Drill HoleSlide60

Top

View

Front

View

6.) Rapid Z Axis Move

Out Of HoleSlide61

Top

View

Front

View

9.) X&Y Axis Rapid

Move Home

7.) Turn Off Spindle

8.) Turn Off CoolantSlide62

Top

View

Front

View

Tool At Home

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

N015 G43 H01 Z.1 M08

N020 G01 Z-.75 F3.5

N030 G91 G28 X0 Y0 Z0

N035 M30

N025 G00 Z.1 M09

Here’s The CNC Program!Slide63

Top

View

Front

View

Tool At Home

O0001

O0001

Number Assigned to this programSlide64

Top

View

Front

View

Tool At Home

O0001

N005 G54 G90 S600 M03

N005 Sequence Number

G54 Fixture Offset

G90 Absolute Programming Mode

S600 Spindle Speed set to 600 RPM

M03 Spindle on in a Clockwise DirectionSlide65

Top

View

Front

View

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

G00 Rapid Motion

X1.0 X Coordinate 1.0 in. from Zero

Y1.0 Y Coordinate 1.0 in. from ZeroSlide66

Top

View

Front

View

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

N015 G43 H01 Z.1 M08

G43 Tool Length Compensation

H01 Specifies Tool length compensation

Z.1 Z Coordinate .1 in. from Zero

M08 Flood Coolant OnSlide67

Top

View

Front

View

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

N015 G43 H01 Z.1 M08

N020 G01 Z-.75 F3.5

G01 Straight Line Cutting Motion

Z-.75 Z Coordinate -.75 in. from Zero

F3.5 Feed Rate set to 3.5 in./min.Slide68

Top

View

Front

View

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

N015 G43 H01 Z.1 M08

N020 G01 Z-.75 F3.5

G00 Rapid Motion

Z.1 Z Coordinate .1 in. from Zero

M09 Coolant Off

N025 G00 Z.1 M09Slide69

Top

View

Front

View

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

N015 G43 H01 Z.1 M08

N020 G01 Z-.75 F3.5

N030 G91 G28 X0 Y0 Z0

G91 Incremental Programming Mode

G28 Zero Return Command

X0, Y0, Z0

X,Y,& Z Coordinates at Zero

N025 G00 Z.1 M09Slide70

Top

View

Front

View

O0001

N005 G54 G90 S600 M03

N010 G00 X1.0 Y1.0

N015 G43 H01 Z.1 M08

N020 G01 Z-.75 F3.5

N035 M30

N030 G91 G28 X0 Y0 Z0

N025 G00 Z.1 M09

M30 End of ProgramSlide71

Output: NC Code - Canned CyclesSlide72

CAD to NC CodeSlide73

THANK YOU