Presentation On CNC Machines Presented To:- Presented By:- Mr. Pawan Kamboj Chetan Gosain (Lect. In...
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- Slide 1
- Presentation On CNC Machines Presented To:- Presented By:- Mr.
Pawan Kamboj Chetan Gosain (Lect. In Mechanical Department) Roll
No:-10512 4 th Year, 7 th Sem.
- Slide 2
- Aim To Discuss The CNC Machines.
- Slide 3
- CONTENTS 1. WORKING PRINCIPLE OF CNC 2. CONSTRUCTIONAL FEATURES
OF CNC 3. KEYS OF CNC 4. TYPES OF CNC 5. SAFETY CHECKING ON CNC 6.
PROGRAMMING OF CNC 7. FUNDEMENTALS OF CNC PROGRAM 8. PROGRAM
STRUCTURE 9. EXAMPLE OF CNC PROGRAMMING 10. CO-ORDINATE SYSTEM 11.
ADVANTAGES OF CNC MACHINES
- Slide 4
- INTRODUCTION Computer numerical control machine is a numerical
control system that utilizes a dedicated, stored program computer
to perform some or all of the basic numerical control functions.
The external appearance of a CNC machine is very similar to that of
a conventional NC machines. PART PROGRAM~> PUNCHED TAPE READER
OR ANY OTHER SIMILAR DEVICE~> STORED IN COMPUTER PROGRAM.
- Slide 5
- WORKING PRINCIPLE OF CNC By controlling the relative movements
between the tool and the work piece geometrical shapes are
machined. Control of these relative movements through coded letters
numbers is known as Numerical Control of machine tools.
- Slide 6
- Constructional features of CNC machine tools CNC machine tools
differ from conventional machine tool in a number of respects. The
special constructional features of CNC machine include: 1.)Rigid
structural design. 2.)Infinitely variables spindle and feed drive.
3.)Slide ways fitted with plastic inserts. 4.)Linear bearings for
axis drive. 5.)Automatic tool changers.
- Slide 7
- KEYS OF CNC
- Slide 8
- MACHINE STRUCTURE To meet the requirements of high efficiency
the numerically controlled machine tools should have a structure
that is correctly designed to withstand normal weight distribution.
BECAUSE The higher cutting speeds and feeds in CNC machine results
in rapid acceleration and deceleration of the slides and the
machines are subjected to fluctuating and variables forces during
the machining operation. Also the machine structure design should
be such that removal of chips do not on the slide ways.
- Slide 9
- Linear motion bearings The sliding friction due to direct metal
to metal contact between the slides and slide ways is replaced with
rolling friction by the use of antifriction ball or bearings.
Rolling element when applied to reciprocating motion has followed
advantages. Reduce the drive power to be used. Stick slip problem
is completely eliminated. Require only small amount of lubricant.
Absorb the machine vibration.
- Slide 10
- Hydrostatic slide ways Hydrostatic slide ~> Oil
pumped~>Cavities or Pockets~>Carriage on slides contact with
Slide way with continous supply of thin film of fluid. The
hydrostatic slide way provides almost a frictionless condition for
the movement of the slide. For efficient operation it is very
important that the fluid and slide ways are kept clean. Also the
hydrostatic slide ways need a very large surface area to provide
adequate support.
- Slide 11
- Measuring systems In CNC machines the electronic measuring
systems are used on each controlled axis and to monitor movement
and compare the position of the slide and the spindle. To Measuring
system used in the CNC machines are of two types To measure the
position of the slide (linear measurement ) measure the spindle
speed (rotary measurement) A linear scale is used as a linear
measuring device which is used very often. In this method linear
displacement is measured directly at the slide. The measuring
device is fixed on to the moving machine element, which detect the
actual distance traveled by the machine slide. One of the rotary
measuring devices is an incremental rotary encoder. Incremental
measurement means measurement by counting. The out put signal of
incremental rotary encoders is fed to an electronic counter which
provides the corresponding values.
- Slide 12
- Work holding device and tooling The CNC machines are capable of
performing a number of operations using different tools, on
different faces of the component in a single setting. This requires
that the component should be accessible from different sides
without changing of clamps or repositioning of components. The
multidirectional cutting forces to reduce the clamping and
unclamping time. A work holding devices for a CNC application
should have the following function. It should restrict the linear
and rotary motion of the component. The component should not
distort or deflect due to cutting forces process. It should
facilitate quick loading and unloading of the component. It should
not interfere with the cutting tools. It should provide easy
removal of chips. It should be safe.
- Slide 13
- Automatic tool changers The CNC machines are designed to
perform a number of operations in a single setting of the
work-piece. To reduce the down time in change over from one
operation to the next, the CNC machines are equipped with automatic
tool changing facility.
- Slide 14
- WORKING PRINCIPLE OF CNC MACHINES WORKING PRINCIPLE OF CNC
MACHINES Types of CNC machines TYPES OF CNC MACHINES There are
mainly two types of CNC machine : (1) Machining centers There are
very important types of CNC machine and are multi-functioning
machine equipped with automatic tool changes and are capable to
carrying out, milling, and drilling, reaming, taping, boring,
counter boring. In this type of machines there are three types of
axis X axis, Y axis, Z axis. Here the tools are rotated clockwise
or anticlockwise the works still fixed. (2)Turning centers/ CNC
lathes CNC lathes have only two axes X and Z, X axis for
longitudinal movement and Z axis for crosswise movement. Tools are
arranged in turret with a number of stations some lathes have
rotating tools in the turret to facilitate off-axis machining such
as drilling, milling etc These machines have additional controller
for spindle rotation such machines are known as turning
centers
- Slide 15
- Safety check on the CNC machine Check the main pressure of the
hydraulic and pneumatic system. Check the clamping pressure of the
hydraulic and pneumatic system. Check the sliding movement. Check
the tool position with respect to the program Check the program
control levels try to cut job in a single block. Do not use
compressed air for cleaning. Check the coolant supply by pressing
appropriate switch manually. Check the speed over the ride
position.
- Slide 16
- PROGRAMMING OF CNC MACHINES CNC programming is a term that
refers to the methods for generating the instruction that drive the
CNC machine tool. Part program is a set of instructions which
instructs the machine tool about the processing step to be
performed for the manufacture of a component. There are two
distinct techniques adopted for creating CNC programs. i.) Manual
programming ii.) Computer assisted programming
- Slide 17
- Manual programming 1). Positioning A dimensional instruction
that move and position the tools or work pieces to produces the
required work 2.) Motion The relative velocity of the tool with
respect to the work piece is to be controlled, in both spindle
drive and positioning drive 3.) Switching function: - The auxiliary
function of the machine such as coolant, tool changes and program
stop. The following should take into account when writing a part
program. The machine features and capacity. The size if the
component. The material to be machined. Machine co-ordinates. The
sequence of operation. The tooling to be used. Component holding
and location.
- Slide 18
- Computer Aided part programming CNC machines of complex 3
dimensional components require thousands of instructions and with
out computer assistance it would be impractical to write part
programs for the production of such components. NC part programming
languages and the processors and post processors that translate the
language instruction into NC programs. There are several NC
languages in use. Some of them are v APT v ADAPT v EXAPT v UNIPAT v
SPLIT v PROMPT
- Slide 19
- FUNDAMENTALS OF PART PROGRAMMING A program is a set of encoded
information giving coordinate values and other details to indicate
how a tool should be moved in relation to a work-piece in order to
achieve a desired machining form.
- Slide 20
- A part programmer has to do the following while write a program
Study the drawing of component thoroughly. Identify the type of
material to be used. Determine the specification and functions of
machine to be used. Decide the dimensioning units metric or inch.
Determine the cutting parameters for the job/tool combination.
Establish the sequence of machining operation.
- Slide 21
- PROGRAM STRUCTURE In manual part programming the programmer has
to determine the machining parameters and the sequence of
operations to be performed. Based upon this sequence, the tool path
is calculated and program is written. The basic unit of a program
input to the control is called a block. The term block structure of
format refers to the rules for writing a program block. A block
contains any or all of the following. Sequence or block number ( N)
Preparatory function(G) Dimensional information (XYZ etc) Decimal
point (.) Feed rate(F) Spindle speed (S) Tool number (T) Tool
offset function(D) Miscellaneous function(M) End of
block(EOB/*)
- Slide 22
- Example of CNC Programming What Must Be Done To Drill A Hole On
A CNC Vertical Milling Machine
- Slide 23
- Top View Front View Tool Home 1.) X & Y Rapid To Hole
Position
- Slide 24
- Top View Front View 2.) Z Axis Rapid Move Just Above Hole 3.)
Turn On Coolant 4.) Turn On Spindle.100
- Slide 25
- Top View Front View 5.) Z Axis Feed Move to Drill Hole
- Slide 26
- Top View Front View 6.) Rapid Z Axis Move Out Of Hole
- Slide 27
- Top View Front View 9.) X&Y Axis Rapid Move Home 7.) Turn
Off Spindle 8.) Turn Off Coolant
- Slide 28
- 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 Heres The CNC
Program!
- Slide 29
- Top View Front View Tool At Home O0001 Number Assigned to this
program
- Slide 30
- 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 Direction
- Slide 31
- Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0
Y1.0 G00Rapid Motion X1.0X Coordinate 1.0 in. from Zero Y1.0Y
Coordinate 1.0 in. from Zero
- Slide 32
- Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0
Y1.0 N015 G43 H01 Z.1 M08 G43Tool Length Compensation H01Specifies
Tool length compensation Z.1 Z Coordinate.1 in. from Zero M08Flood
Coolant On
- Slide 33
- 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 G01Straight Line
Cutting Motion Z-.75Z Coordinate -.75 in. from Zero F3.5Feed Rate
set to 3.5 in./min.
- Slide 34
- 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 G00Rapid Motion Z.1Z
Coordinate.1 in. from Zero M09Coolant Off N025 G00 Z.1 M09
- Slide 35
- 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
G91Incremental Programming Mode G28Zero Return Command X0, Y0, Z0
X,Y,& Z Coordinates at Zero N025 G00 Z.1 M09
- Slide 36
- 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 M30End of Program
- Slide 37
- FunctionMeaning G00Point to point positioning G01Leaner
interpolation G02Circular interpolation G03Circular interpolation
(Anti clockwise) G70Dimensioning in inch G71Dimensioning in mm
G90Absolute dimensioning G91Incremental dimensioning G96Constant
surface speed G97Spindle speed Preparatory function (G-words ) They
are the commands, which prepare the machine for different modes of
movement like positioning, contouring, thread cutting etc and for
presetting the machine.
- Slide 38
- FunctionMeaning M00Program stop M01Optional stop MO5Spindle
stop MO6Tool turret index M09Coolant off M10Clamp work piece
M11Release work piece M30End of program Miscellaneous function The
miscellaneous function word is used to specify certain
miscellaneous or auxiliary functions which do not relate to the
dimensional movements of the machine. The miscellaneous functions
may be spindle start, spindle stop, coolant ON/OFF, etc.
- Slide 39
- METHODS OF LISTING THE COORDINATES OF POINTS The coordinate
systems are used to define and control the position of the tool in
relation to the work piece. Each system has its own applications
and the coordinate systems may be used indecently or may be mixed,
within a CNC part program according to the machining requirements
of the component. The co- ordinate systems used in CNC machines are
as follows. a) Absolute co-ordinates b) Incremental
co-ordinates
- Slide 40
- Absolute co-ordinates In the absolute co-ordinate system the
co-ordinates of a point are always referred with reference to the
same datum. The datum position in X axis and Y-axis and Z axis are
defined by the program before starting the operation of the
machine. A major advantage of this system is that it is very easy
to check and correct a program written is made in the value of any
dimension in a particular block.
- Slide 41
- Incremental co-ordinate In the incremental co-ordinate system
the co- ordinates of the any point are calculated with reference to
the previous point i.e., the point at which the cutting tool is
positioned is taken as a datum point for calculating the
co-ordinates of the next point to which movement is to be made. It
is difficult to check a part program written in incremental
dimension in a particular block, it will affect subsequent
blocks.
- Slide 42
- Advantages of Computer Numerical Control Machines Accuracy and
repeatability is very high as compared to the NC machines. Reduced
scrap and rework. Reduced inspection time. Reduced material
handling. Easy of inter changeability of machine parts. Complicated
shapes and curves are easily manufactured with quality assurance
and better production. Reduced skilled operators can work in CNC
machines. It can work 24 hours a day because the resting times are
very low. Time taken to complete the works is minimum as compared
to manual machines. Program editing at the machine site.
- Slide 43