INTRODUCTION TO CNC

& HARDWARE

Submitted By:

Aman Kumar

1

A sequence of operations and processes designed to create a

specific product .

The process of turning raw materials into a product .

Examples:

welding, casting, cutting, assembling, etc.

Typical product cost breakdown

What is manufacturing process ?

The first NC machines were built in the 1940s and

1950s by Prof. John T Parson.

CNC machine came into existence after evolution of

computer around 1980.

Modern CNC Machine are improving further as the

technology is changing with a variety of functions

according to applications.

In the early 1950s the Massachusetts Institute of

Technology developed a more advanced vacuum tube

computer called Whirlwind.

History

To ensure that all U.S. military airplanes were manufactured identically after world war II the

US Air Force invited several top companies to develop and manufacture numerical control

systems which can handle the quantity and repeatability of machine.

In 1952, The first three axis, Numerically controlled, tape-fed machine tool was created. A

Cincinnati Milacron Hydro-Tel Vertical Spindle Milling (VMC) machine was retrofitted and

controlled by the Whirlwind Computer. The controller was equipped with optical sensors and

used a straight binary perforated tape to hold the instructions; The tape was read via a

mechanical feeding mechanism. In 1954, Numerical control was announced to the public, and

after three year the first Production NC machine was delivered and Installed.

Cont…

Numerical Control Machine(NC)

Form of programmable automation.

Mechanical actions of machine tool are

controlled by program.

The program is in form of alphanumeric

data.

After a job is finished the program of

instructions can be changed to process a

new job.

Numerical Control Machine(NC)

Advantages

Reduces non productive time

Reduces manufacturing lead time

Greater manufacturing flexibility

Improves quality control

Reduced inventory

Disadvantages

High investment cost.

High maintenance effort.

Part programming.

Higher utilization of NC Equipment's.

CNC Machine

To overcome the shortcomings of the NC machines CNC machines evolved.

CNC machines are the NC machines whose MCU is based on the micro computer

rather than the hardwired controller.

Elements of CNC

machines arePart program

Machine Control Unit

Machine tool

Features of CNC

machines are:

Storage of more than one part

program

In-process compensation

Improved programming and operating

features

Adaptive control adjustments

Block diagram of CNC Machine

Elements of CNC machines

Elements of CNC machine tool essentially consists of the following parts:

Part Program

Program Input Device

Machine Control Unit (MCU)

Drive System

Machine Tool

Feedback System.

Part Program

It controls the movement of the machine

tool and on/off control of auxiliary

functions such as spindle rotation and

coolant.

The coded instructions are composed of

letters, numbers and symbols.

A part program is a series of coded instructions required to produce a part.

Program Input Device

The program input device is the means for

part program to be entered into the CNC

control.

Three commonly used program input

devices are punch tape reader, magnetic

tape reader, and computer via RS-232-C or

USB communication.

Machine Control Unit (MCU)

The machine control unit (MCU) is the heart of a CNC system. It is used to perform the

following functions

a) To read the coded instructions.

b) To decode the coded instructions.

c) To implement interpolations (linear, circular, and

helical) to generate axis motion commands.

d) To feed the axis motion commands to the amplifier

circuits for driving the axis mechanisms.

e) To receive the feedback signals of position and

speed for each drive axis.

f) To implement auxiliary control functions such as

coolant or spindle on/off and tool change.

Drive System

A drive system consists of amplifier circuits,

drive motors, and ball lead-screws.

The MCU feeds the control signals (position and

speed) of each axis to the amplifier circuits.

The control signals are augmented to actuate

drive motors which in turn rotate the ball lead-

screws to position the machine table.

Feedback System

The feedback system is also referred to as the

measuring system.

It uses position and speed transducers to

continuously monitor the position at which

the cutting tool is located at any particular

instant.

The MCU uses the difference between

reference signals and feedback signals to

generate the control signals for correcting

position and speed errors.

Machine Axis Designation

Machine axes are designated according to the "right-

hand rule“.

When the thumb of right hand points in the direction

of the positive X axis, the index finger points toward

the positive Y axis, and the middle finger toward the

positive Z axis. The main axes to be designated are

the linear axes and the rotary axes.

First axis to be identified is the Z-axis. This is then followed by

the X and Y axes respectively.

1. Z-axis

Positive (+) Z direction increases the clearance between the cutting tool and the workpiece. For example, in

a drilling machine the drill movement towards the workpiece is the negative Z direction. This helps in

reducing the possible accidents because of wrong part program entry in the coordinate signs.

•The main spindle (axis of tool spindle or w/p rotates) is treated –Z axis.

•+ve direction away from the w/p and towards tool spindle holder.

•in case of multiple spindles –one spindle is selected as principal spindle & its axis as Z axis.

2. X-axis

The X axis is the principle motion direction in the positioning plane of the cutting tool or the workpiece. It

is perpendicular to the Z axis and should be horizontal and parallel to the work-holding surface wherever

possible.

•Horizontal & parallel to the working surface.

•When Z -axis is horizontal: +ve X-axis to the right when looking from spindle towards the w/p

•When Z -axis is vertical: +ve X-axis towards right looking from the spindle towards supporting column.

3. Y-axis

It is perpendicular to both X and Z axes and the direction is identified by the right hand Cartesian coordinate

system.

Perpendicular to both X-and Z -axis.

For +ve Y direction rotate x axis advance right hand screw in +ve Z direction

VMC (Vertical Machining Center)

HMC (Horizontal Machining Center)

Common types of CNC machines

CNC Lathe machine

CNC Milling machine

CNC Drilling machine

CNC Grinding machine

CNC Laser cutting machine

Water jet cutting machine

Electro discharge machine

1. Numerical Control Machine

The program is fed to the machine through magnetic tapes or other such media.

The original NC machines were essentially basic machine tools which were modified to have motors for

movement along the axes.

An NC machine is numerically controlled but has no memory storage and is run off of the "tape" each

time the machine cycles

2. Computer Numerical Controlled machine

The machines are interfaced with computers.

This makes them more versatile in the sense that, suppose a change in dimension of a part is required.

A CNC machine has memory storage and the program can be stored in its control.

3. DNC

Number of machines are controlled by a central computer.

DIFFERENCE BETWEEN NC, CNC AND DNC

Applications

Parts needed in a hurry

Parts with complicated contours

Parts requiring expensive jigs and fixtures

Parts those have several engineering changes

Cases where human errors can be extremely costly

Parts requiring close tolerance or good repeatability

AUTOMATION

Productivity

Machine utilization is increased because more time is spent cutting and less time

is taken by positioning. Reduced setup time increases utilization too.

PROFIT increases as COST decreases and as PRODUCTIVITY increases.

PRODUCTIVITY through AUTOMATION

helping the workers to

perform their tasks more

efficiently

Transfer of the skill of the

operator to the machine

ADVANTAGES OF CNC MACHINE

Quality

1. Parts are more accurate.

2. Parts are more repeatable.

3. Less waste due to scrap.

Machining Complex shapes

1. Slide movements under computer control.

2. Computer controller can calculate steps.

Management Control

1. CNC leads to CAD

2. Process planning

3. Production planning

Increased dimension precision of the work part through high basic precision of the

machine tool (1/1000mm).

Higher accuracy

Reduce lead time

Higher flexibility

Reduce scrap rate

Reliable operation

Consistent quality

Reduced manpower

Increased productivity

Reduced non productive time

Cont…

1. Machine Cost is Higher than Conventional Machine.

2. Higher Maintenance Costs .

3. Higher Labor Costs .

4. Higher Machine Attachment Costs.

5. Higher Tooling Costs.

6. High maintenance requirements

DISADVANTAGE OF CNC MACHINE

HARDWARE OF CNC MACHINE

The drive units of the carriages in NC machine

tools are generally the screw & the nut

mechanism.

There are different types of screws and nuts

used on NC machine tools which provide low

wear, higher efficiency, low friction and better

reliability.

Recirculating Ball Screw

The recirculating ball screw assembly has the flanged

nut attached to the moving chamber and the screw to

the fixed casting. Thus the moving member will

move during rotational movement of the screw.

In these types of screws, balls rotate between the

screw and nut and convert the sliding friction (as in

conventional nut & screw) to the rolling friction. As a

consequence wear will be reduced and reliability of

the system will be increased. .

The traditional ACME thread used in conventional

machine tool has efficiency ranging from 20% to

30% whereas the efficiency of ball screws may

reach up to 90%.

There are two types of ball screws.

In the first type, balls are returned through an

external tube after few threads.

In another type, the balls are returned to the start

through a channel inside the nut after only one

thread.

Cont…

Roller Screw

These types of screws provide backlash-free

movement and their efficiency is same as that of ball

screws.

These are capable of providing more accurate

position control.

Cost of the roller screws are more compared to

ball screws.

The thread form is triangular with an included

angle of 90 degrees.

There are two types of roller screws: Planetary

and Recirculating screws.

Planetary Roller Screw

The rollers are threaded with a single start thread.

Teeth are cut at the ends of the roller, which

meshes with the internal tooth cut inside the nut.

The rollers are equally spaced around and are

retained in their positions by spigots or spacer

rings.

There is no axial movement of the rollers relative

to the nut and they are capable of transmitting

high load at fast speed.

Cont…

Recirculating Roller Screw

The rollers in this case are not threaded and are provided with a

circular groove and are positioned circumferentially by a cage.

There is some axial movement of the rollers relative to the

nut.

Each roller moves by a distance equal to the pitch of the

screw for each rotation of the screw or nut and moves into an

axial recess cut inside the nut and disengage from the threads

on the screw and the nut and the other roller provides the

driving power.

Rollers in the recess are moved back by an edge cam in the

nut. Recirculating roller screws are slower in operation, but

are capable of transmitting high loads with greater accuracy.

An Automatic Tool Changer is equipment that reduces cycle

times by automatically changing tools between cuts.

Automatic tool changers are differentiated by tool-to-tool time

and the number of tools they can hold.

CNC tool changers allow a machine to perform more than one

function without requiring an operator to change the tooling.

A CNC tool changer can quickly change the end effectors

without the requirement of multiple robots.

Tool changers can be a manual tool changers or automatic tool

changers.

A CNC tool changer ful fills the requirement of multiple tooling

for a wide variety of machine tools

AUTOMATIC TOOL CHANGER

Tool changer is equipment which is used in CNC machines to reduce the cycle time.

The term applies to a wide variety of tooling, from indexable insert, single

point tools to coded, preset tool holders for use in automatic tool changers. It includes power-

actuated, cross-slide tooling and turret tool holders for single spindle chuckers, interchangeable-

block boring tools.

A number of basic types of tool holders are available that accommodate

most face mills, end mills, drills, reamers, taps, boring tools, counter bores, countersinks, and spot

facers.

Arbor type cutters such as face mills and shell end mills are held in anarbor type tool holders.

Shank type mills are held in positive lock holder. Drills, reamers and boring tools are held in a

straight shank collet type holder. Taps are held in a tension and compression collet type holders.

Why Tool Changer is needed?

1.Tool change system with gripper arm

2.Tool change system with chain magazine

3.Tool change system with disc magazine

TYPES OF AUTOMATIC TOOL CHANGER

There are mainly three kinds of tool changers available in market according to the tool

magazine arrangements provided

In this system, a disc is provided with magazine, in which

different types of tools are loaded.

It can hold maximum 32 tools. In magazines, all the tools which

are required are fixed in the magazines.

The tool which is programmed in controller according to the

program will be indexed in front of the gripper arm and then the

gripper arm grips the tool and performs the operation.

After completion of the operation by each tool, the gripper arm

places the tool back in to the magazine

Tool change system with gripper arm

In this system, there are mainly two elements,

Disc with magazine

Gripper arm

Tool Change system with chain magazine

In this kind of system, a chain is provided with magazines for

toolholding. This chain can hold numerous tools so it is used in

heavy machineries. Starting from 32 it can hold more than 100

tools.

These chain is indexed in front of the head stock directly as per

the tool programmed position.

In this kind of system there is no arrangement like gripper arm.

The chain itself is indexed and the machining is done while

keeping the tool in the chain only

Tool change system with Disc magazine

In this system, the tools are held in a big disc. This

disc is not similar to the disc provided in gripper

arm mechanism.

In this disc, there are tool grippers provided

separately for each magazine these grippers holds

the tool and performs machining operation as well.

This system disc can hold 32 to maximum of 64

tools. These type of tool changers are used in

medium capacity machineries.

Automatic Guided Vehicle (AGV)

What is an AGV?

A Computer-Controlled, Non-manned, Electric Powered Vehicle Capable of Handling Material.

Different Types of AGVs

1. Fork

2. Tow/Tugger

3. Unit Load

4. Custom

What is a good use for AGVs?

Repetitive motion

Distances over 150 feet

Multi-shift operation

Desire to save costs and improve efficiency

• Not a permanent obstacle

• Paths can be changed easily

• System can be expanded

easily

• Does not represent a single

point of failure - system has

built-in redundancy

• Favorable cost/benefit

compared to other automated

material handling solutions

Why use Guided Vehicles?

How are they powered?Charge it!

• Standard Charging

(battery swap)

• In-Vehicle

(opportunity)

Charging

• Inductive Charging

How do they know where to go?

Guidance Methods

• Optical – Tracks contrasting color

• Wire – Embedded in floor

• Inertial – Gyro with magnets in floor

• Laser – Triangulation from reflective targets

Cont…