Introduction to CNC machine and Hardware.

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 are
Part 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

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?

Introduction to CNC machine and Hardware.

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…

Introduction to CNC machine and Hardware.

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