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Dept. of mechanical Engineering, GIET,BBSR

Highlights

HISTORY OF CNC1

ABOUT CNC2

CNC PART PROGRAM3

ADVANTAGE & DISADVANTAGE4

APPLICATION AND IMPROVEMENT5

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Dept. of mechanical Engineering, GIET,BBSR

HISTORY OF CNC

The concept is credited to John Parson (1947). Using punched cards he was able to control the position of a machine in an attempt to machine helicopter blade.

US Air Force teamed up with MIT to develop a programmable milling machine (1949).

In 1952, a three-axis Hydrotel milling machine was demonstrated. The term Numerical Control (NC) originated. The machine had an electromechanical controller and used punched cards.

A new class of machines called machining centers and turning centers that could perform multiple machining processes was developed.

Modern NC machine has a computer on board, Computer Numerical Control (CNC). They can run unattended at over 20,000 rpm (spindlier speed) with a feed rate of over 600 rpm and an accuracy of .0001

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HISTORY OF CNC

More recently, microprocessors have made CNC controls even

cheaper. The Enhanced Machine Controller project, or EMC2, was a

project to implement an Open Source CNC controller that was started

by NIST, the National Institute of Standards and Technology as a

demonstration. Some time in 2000, the project was taken into the

public domain and Open Source, and EMC2 appeared a short time

later in 2003.

Dept. of mechanical Engineering, GIET,BBSR

(1959 CNC Machine: Milwaukee-Matic-II was first machine with a tool changer)

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ABOUT CNC

Dept. of mechanical Engineering, GIET,BBSR

Computer

Numerical

Control

CNC Stands for

Numerical control is a method of automatically operating a

manufacturing machine based on a code of letters, numbers, and

special characters.

The numerical data required to produce a part is provided to a

machine in the form of a program, called part program or CNC

program.

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ABOUT CNC

The program is translated into the appropriate electrical signals for

input to motors that run the machine.

A CNC machine is an NC machine with the added feature of an on-

board computer.

Dept. of mechanical Engineering, GIET,BBSR

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ABOUT CNC

Dept. of mechanical Engineering, GIET,BBSR

HAAS CNC Machines

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ABOUT CNC

Dept. of mechanical Engineering, GIET,BBSR

Basic Components

An NC system consists of the machine tools, the part-program, and the

machine control unit (MCU).

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ABOUT CNC

Dept. of mechanical Engineering, GIET,BBSR

Machine Tools

The machine tools perform the useful work.

A machine tool consists of.

A worktable,

One or more spindles, motors and controls,

Cutting tools,

Work fixtures, and.

Other auxiliary equipment needed in the machining operation.

The drive units are either powered by stepping motors (for open-loop

control), servomotors (for close-loop control), pneumatic drives, or

hydraulic drives.

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CNC PART PROGRAM

The part-program is a collection of all data required to produce the

part. It is arranged in the form of blocks of information.

Each block contains the numerical data required for processing a

segment of the work piece.

Dept. of mechanical Engineering, GIET,BBSR

PART PROGRAM

MANUAL PROGRAM COMPUTER ASSITED

PART PROGRAM

Part program is of two type:

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

PART PROGRAM PROVING

CUTTING PROCES PARAMETER PLANNING

PART PROGRAM WRITTING

TOOL SELECTION

MACHINING PATH PLANNING

AXES SELECTION

JOB & TOOL SET UP PLANNING

PROCESS PLANNING

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CNC PART PROGRAM

MANUAL PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

Manual part program is written in a special set of instruction

called manuscript.

The instruction are prepared in précised manner because the

typist prepare the NC tape directly from the manuscript

Manuscript includes instructions and also other data such as

other preparatory commands, miscellaneous instructions and

speed/feed specifications all of which need to operate the machine

under tape control .

MANUAL PART PROGRAM

PTP JOBS

COUNTOURING JOBS

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

COMPUTER ASSISTED PART PROGRAMMING

Programmers Activities:

Geometry workspace entry

Entry of sequence of operation

Computer Activities:

Input Translation

Advance computation

Cutting tool offset calculation

Post processing

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

Preparatory command (G code)

The G codes prepare the MCU for a given operation, typically involving a

cutter motion.

G00 rapid motion, point-to-point positioning

G01 linear interpolation (generating a sloped or straight cut)

G06 parabolic interpolation (produces a segment of a parabola)

G17 XY plane selection

G20 circular interpolation

G28 automatic return to reference point

G33 thread cutting

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

Miscellaneous commands (M code)

M00 program stop

M03 start spindle rotation (cw)

M06 tool change

M07 turn coolant on

Feed commands (F code)

Used to specify the cutter feed rates in inch per minute.

Speed commands (S code)

Used to specify the spindle speed in rpm.

Tool commands (T code)

Specifies which tool to be used, machines with automatic tool

changer.

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

CNC Machine Axes of Motion

The coordinate system used for the tool path must be identical to the

coordinate system used by the CNC machine. The standards for machine

axes are established according to the industry standard report EIA RS-267A.

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

CNC Machine Axes of Motion

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CNC PART PROGRAM

CNC MOTION CONTROL

POINT TO POINT MOTION

STRAIGHT CUT MOTION

COUNTORING MOTION

Dept. of mechanical Engineering, GIET,BBSR

1. Point-to-point (PTP) MOTION

The cutting tool is moved relative to the work piece (i.e. Either the cutting

tool moves, or the work piece moves) until the cutting tool is at a

numerically defined position and then the motion is paused.

The cutting tool then performs an operation.

When the operation is completed, the cutting tool moves relative to the

work piece until the next point is reached, and the cycle is repeated.

The simplest example of a PTP NC machine tool is the NC drilling

machine.

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

Straight-cut MOTION

Straight-cut system are capable of moving the cutting tool parallel to one of

the major axes (X-Y-Z) at a controlled rate suitable for machining.

It is appropriate for performing milling operations to fabricate work pieces

of rectangular configurations.

Straight-cut NC systems can also perform PTP operations.

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

Contouring NC

In contouring (continuous path) operations, the tool is cutting while the

axes of motion are moving.

The axes can be moved simultaneously, at different velocity.

The path of the cutter is continuously controlled to generate the desired

geometry of the work piece.

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CNC PART PROGRAM

Dept. of mechanical Engineering, GIET,BBSR

N1 G00 X-35 Z-5

N2 G01 X10 Z0 F100

N3 G01 X0 Z-30 F100

N4 G01 X10 Z0 F100

N5 G01 X0 Z-30 F100

N6 G01 X10 Z-0 F100

N7 G01 X0 Z-40 F100

N8 G00 X-35 Z-5

M30

Example of a part program

(This is a manual part program for lathe machining)

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P1

P2

P3P4

+X

+Z

-X

-Z

ADVANTAGE & DISADVANTAGE

ADVANTAGE

CNC machines can be used continuously 24 hours a day, 365 days a

year and only need to be switched off for occasional maintenance.

CNC machines are programmed with a design which can then be

manufactured hundreds or even thousands of times. Each

manufactured product will be exactly the same.

Less skilled/trained people can operate CNCs unlike manual lathes /

milling machines etc.. which need skilled engineers.

CNC machines can be updated by improving the software used to

drive the machines

Training in the use of CNCs is available through the use of ‘virtual

software’. This is software that allows the operator to practice using

the CNC machine on the screen of a computer. The software is similar

to a computer game.

Dept. of mechanical Engineering, GIET,BBSR

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ADVANTAGE & DISADVANTAGE

CNC machines can be programmed by advanced design software

such as Pro/DESKTOP®, enabling the manufacture of products that

cannot be made by manual machines, even those used by skilled

designers / engineers.

Modern design software allows the designer to simulate the

manufacture of his/her idea. There is no need to make a prototype or a

model. This saves time and money.

One person can supervise many CNC machines as once they are

programmed they can usually be left to work by themselves.

Sometimes only the cutting tools need replacing occasionally.

A skilled engineer can make the same component many times.

However, if each component is carefully studied, each one will vary

slightly. A CNC machine will manufacture each component as an

exact match.

Dept. of mechanical Engineering, GIET,BBSR

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ADVANTAGE & DISADVANTAGE

DISADVANTAGES

CNC machines are more expensive than manually operated machines,

although costs are slowly coming down.

The CNC machine operator only needs basic training and skills,

enough to supervise several machines. In years gone by, engineers

needed years of training to operate centre lathes, milling machines and

other manually operated machines. This means many of the old skills

are been lost.

Less workers are required to operate CNC machines compared to

manually operated machines. Investment in CNC machines can lead

to unemployment.

Many countries no longer teach pupils / students how to use manually

operated lathes / milling machines etc... Pupils / students no longer

develop the detailed skills required by engineers of the past. These

include mathematical and engineering skills

Dept. of mechanical Engineering, GIET,BBSR

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ADVANTAGE & DISADVANTAGE

Dept. of mechanical Engineering, GIET,BBSR

COMPUTER NUMERICAL CONTROL - MACHINE MANUALLY OPERATED CENTRE LATHE

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APPLICATION AND ADVANCEMENT

APPLICATION

CNC machine is used

In the metal removal industry

In the metal fabrication industry

In the electrical discharge machining industry

In the woodworking industry

Laser welding in automobile industry

Laser machining and Cutting

Dept. of mechanical Engineering, GIET,BBSR

Small parts made using

EDM

LASER MACHININGLaser welding in automobile industry26

APPLICATION AND ADVANCEMENT

Dept. of mechanical Engineering, GIET,BBSR

Other Industries where CNC machines are used:

Many forms of lettering and engraving systems use CNC

technology. Water jet machining uses a high pressure water jet

stream to cut through plates of material. CNC is even used in the

manufacturing of many electrical components. For example, there

are CNC coil winders, and CNC terminal location and soldering

machines.

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APPLICATION AND ADVANCENENT

ADVANCES OF CNC:

CNC are operated using DNCs

Reverse engineering is possible only because of CNC

Robotics technology is introduced in CNC technology

3D printing is done using CNC. Advance machining process such

as EDM,LBM, Stereolithography (SLA), Fused Deposition

Modeling (FDM)

Rapid prototyping, Rapid manufacturing concepts are developed

after CNC .

Dept. of mechanical Engineering, GIET,BBSR

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A rapid prototyping machine

using selective laser sintering

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29Dept. of mechanical Engineering,

GIET,BBSR

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