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DEPARTMENT OF MECHANICAL ENGINEERING 11
1. INTRODUCTION TO NC DNC AND CNC
1.1 NUMERICAL CONTROL (NC)
Fig.1.1 Numerical Control Systems.
Numerical control (NC) systems are hardware controls in which most of functions are carried out
by electronic hardware based upon digital circuit technology. Numerical Control is a technique for
controlling machine tools or processes using coded command instructions. These coded command
instructions are interpreted and converted by NC controller into two types of signals namely; motion
control signals and miscellaneous control signals. Motion control signals are a series of electric
pulse trains that are used to control the positions and the speed of the machine table and spindle,
whereas miscellaneous control signals are set of ON/OFF signals to execute the spindle rotation
and direction, control of coolant supply, selection of cutting tools, automatic clamping and
unclamping, etc. In motion control signals, each pulse activates a motion of one basic length-unit
(BLU).
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1.2 DIRECT NUMERICAL CONTROL (DNC)
Direct numerical control (DNC), also known as distributed numerical control (also DNC),
is a common manufacturing term for networking CNC machine tools. DNC networking or DNC
communication is always required when CAM programs are to run on some CNC machine control.
1.3 COMPUTERNUMERICAL CONTROL (CNC)
Fig.1.3 Block diagram of Computer Numerical control system
CNC controls are soft-wired NC systems as control functions are controlled by software
programs. Alternatively, Computer Numerical Control is the numerical control system in which
dedicated, stored program microprocessors are built into the control to perform basic and advanced
NC functions. Control signals in CNC systems are in the form of binary words, where each word
contains fixed number of bits, 32 bits or 64 bits are commonly used, representing different axial
positions.
A CNC system consists of the following 6 major elements:
a. Input Device
b. Machine Control Unit
c. Machine Tool
d. Driving System
e. Feedback Devices
f. Display Unit
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1.3.1 PROGRAMME 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 communication.
1.3.2 MACHINE CONTROL UNIT
The machine control unit (MCU) is the heart of a CNC system. It is used to perform the following
functions:
It read the coded instructions, decode the coded instructions. Implement interpolations (linear,
circular, and helical) to generate axis motion commands. and feed the axis motion commands to the
amplifier circuits for driving the axis mechanisms. And it receives the feedback signals of position
and speed for each drive axis. To implement auxiliary control functions such as coolant or spindle
on/off and tool change.
1.3.3 MACHINE TOOL
CNC controls are used to control various types of machine tools. Regardless of which type of
machine tool is controlled, it always has a slide table and a spindle to control position and speed.
The machine table is controlled in the X and Y axes, while the spindle runs along the Z axis.
1.3.4 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.
1.3.5 DRIVE SYSTEM
Drives are used to provide controlled motion to CNC elements 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 motors used for CNC system are of two kinds-
1. Electrical –DC or AC Stepper motors and DC or AC servo motors
2. Fluid - Hydraulic or Pneumatic
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2. CONTROL PANEL OF CNC
Fig.2 Control Panel
A CNC machine is normally controlled by a computer and software. However, most CNC
machines have a range of controls for manual use. It is rare for a CNC machine to be used manually
as simple operations are best carried out on cheap/basic/manual machines. When a CNC machine
is used manually it is being used well below its capability and specification.
2.1RESET BUTTON
The most important control button is usually the reset button. When the CNC machine is turned
on, the reset button is pressed by the machine operator. This zero the cutter, moving the cutter to
coordinates 0, 0, 0 on the X, And Z axis. In simple terms, the reset button moves the cutter to the
corner of the machine, above the work table.
2.2 MANUAL CONTROL
The cutter can be controlled manually although this is rarely needed. The ‘X’ and ‘Y’ buttons
control the movement of the cutter along the horizontal surfaces. The ‘Z’ buttons control depth and
up / down movement.
2.3 STOP BUTTON
Most control panels have stop buttons. When pressed these stop the machine very quickly.
2.4 SPEED AND FEED
On some CNC machines it is possible to manually vary the speed and feed of the cutter.
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DEPARTMENT OF MECHANICAL ENGINEERING 15
3. CNC MACHINERIES
The CNC machines which we worked at GTTC are:
CNC Lathe.
CNC Milling.
CNC Wire EDM.
3.1 CNC LATHE (FANUC SERIES OI-TC)
3.1.1 SPECIFICATIONS
Table.3.11 CNC Lathe Specification
EQUIPMENT UNIT RANGE
Made = Fanuc ---- ----
Chuck diameter mm 200
Max. cutting diameter mm 200
Max. cutting length mm 500
Spindle bore diameter mm 55
Spindle rotating speed rpm 45-4000
Main motor
power(AC)
kW 11
Hydraulic unit power
motor
kW 1.5
Chip conveyor motor kW 0.2
Coolant pump motor kW 0.55
Weight Kg 5000
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DEPARTMENT OF MECHANICAL ENGINEERING 16
Fig.3.11 CNC Lathe.
3.1.2 ABOUT CNC LATHE
Some view lathes as the only universal CNC machine tool because a lathe can make all of
the parts needed for another lathe. A lathe spins the work-piece in a spindle while a fixed cutting
tool approaches the work-piece to slice chips off of it. The act of cutting a work-piece on a lathe is
called "Turning".
Computer numerical control (CNC) has been incorporated into a variety of new technologies and
machinery. One such machine of this sort that is used for a wide array of production processes is
known as a CNC lathe.
Due to technological advancements, CNC lathes are quickly replacing some of the older and
more traditionally used production lathes, such as the multi-spindle. CNC lathes come with a
number of benefits. They can be easily set up and operated. They offer tremendous repeatability,
along with top-notch accuracy in production.
A CNC lathe is typically designed to utilize modern versions of carbide tooling and
processes. A part can be designed for customization, and the machine’s tool paths are often
programmed using the CAD or CAM processes some prime examples of finished items as a result
of using CNC lathe machines include:
Baseball Bats, Bowls, Camshafts, Crankshafts Cue, sticks Dining, Room Table and Chair Legs,
Gun Barrels, Musical Instruments
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3.1.3 PREPARING AND USING OF CNC LATHE
Checking to make sure the lathe is lubricated and learning to schedule routine maintenance
in accordance with workplace standards.
Learning to translate product specifications and work instructions into a machine-readable
format.
Establishing criteria for tool selection with efficiency and safety in mind.
Installing work-piece handling devices and inserting tools into their corresponding slots.
Learning to load a machining program into the CNC lathe and aligning its data points
according to project requirements.
Producing sample parts to verify if they match specifications and operator instructions.
3.2 CNC MILLING MACHINE (SEIMENS CONTROLLER)
Fig.3.2 CNC Milling Machine
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3.2.1 SPECIFICATIONS
Table.3.21 CNC Milling specification
CNC controller Siemens control
Axis Motor & Drive AC Servo (1.3 Nm)
Spindle Motor 1 HP with VFD (3PH).
Spindle Motor Speed 100 to 3000 rpm.
Lubrication System Automatic (Motorized).
Max. Depth Of Cut 1 mm Possible.
Axis Control 3 axis.
Axis Plane XY, XZ & YZ.
Max. Rapid Feed 4000 mm/min.
Table Load Capacity 100 Kg.
3.2.2 ABOUT CNC MILLING
CNC milling is a specific form of computer numerical controlled (CNC) machining. Milling
itself is a machining process similar to both drilling and cutting, and able to achieve many of the
operations performed by cutting and drilling machines. Like drilling, milling uses a rotating
cylindrical cutting tool. However, the cutter in a milling machine is able to move along multiple
axes, and can create a variety of shapes, slots and holes. In addition, the work-piece is often moved
across the milling tool in different directions, unlike the single axis motion of a drill.
CNC milling devices are the most widely used type of CNC machine. Typically, they are
grouped by the number of axes on which they operate, which are labelled with various letters. X
and Y designate horizontal movement of the work-piece (forward-and-back and side-to-side on a
flat plane). Z represents vertical, or up-and-down, movement, while W represents diagonal
movement across a vertical plane. Most machines offer from 3 to 5 axes, providing performance
along at least the X, Y and Z axes. Advanced machines, such as 5-axis milling centres, require
CAM programming for optimal performance due to the incredibly complex geometries involved in
the machining process. These devices are extremely useful because they are able to produce shapes
that would be nearly impossible using manual tooling methods. Most CNC milling machines also
integrate a device for pumping cutting fluid to the cutting tool during machining.
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DEPARTMENT OF MECHANICAL ENGINEERING 19
3.2.3 PREPARING AND USING CNC MILLING
Work safely at all times, complying with health and safety legislation, regulations and other
relevant guidelines.
Plan the CNC machining activities before you start them.
Load/input the program to the machine controller and check the program for errors using
the approved procedures.
Mount and set the required work holding devices, work-piece and cutting tools.
Check that all safety mechanisms are in place, and that the equipment is set correctly for the
required operations
Run the operating program, and check and adjust the machine tool speeds, feeds and
operating parameters to achieve the component specification.
Measure and check that all dimensional and geometrical aspects of the component are to the
specification.
Deal promptly and effectively with problems within your control, and seek help and
guidance from the relevant people if you have problems that you cannot resolve.
Shut down the equipment to a safe.
3.3 CNC WIRE EDM (MITSUBISHI CONTROLLER)
Fig.3.3 CNC Wire EDM
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3.3.1 SPECIFICATION
Table.3.31 CNC Wire EDM specification
DESCRIPTION MITSUBISHI RA90M
(AT)
MITSUBISHI RA90M
Max. work piece
dimension [mm] (in)
860 x 760 x 160 860 x 760 x 160
Maximum work piece
weight
350 350
Table dimensions 572 x 478 572 x 478
Machining range (X x Y) 320 x 250 320 x 250
Table rapid-feed speed
[mm/min] (in/min)
1300 1300
Wire diameter [mm] (in) 0.2 - 0.3 0.2 - 0.3
Maximum wire feed rate
[m/min] (in/min)
15 15
Maximum work piece
thickness [mm] (in)
160 -----
Taper machining device Standard Standard
Z-Axis stroke (manual
operation)
150 150
Max. taper angle [mm] (in) 15 for work piece 100 mm
thick
15 for work piece 100 mm
thick
Max. machining current 50A 50A
Minimum drive unit [u m]
(in)
0.05um 0.05um
CNC Controller Mitsubishi 64 bit Mitsubishi 64 bit
3.3.2 ABOUT WIRE EDM
Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used
to remove metal by means of electric spark erosion. In this process an electric spark is used as the
cutting tool to cut (erode) the work piece to produce the finished part to the desired shape.
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DEPARTMENT OF MECHANICAL ENGINEERING 21
The wire-cut type of machine arose in the 1960s for the purpose of making tools (dies) from
hardened steel. The tool electrode in wire EDM is simply a wire. The first CNC EDM machine was
produced in 1976. EDM wire cutting uses a metallic wire to cut a programmed contour in a work
piece. Extrusion dies and blanking punches are very often machined by wire cutting. Cutting is
always through the entire work piece. To start machining it is first necessary to drill a hole in the
work piece or start from the edge. On the machining area, each discharge creates a crater in the
work piece and an impact on the tool. The wire can be inclined, thus making it possible to make
parts with taper or with different profiles at the top and bottom. There is never any mechanical
contact between the electrode and work piece. The wire is usually made of brass or stratified copper,
and is between 0.1 and 0.3 mm diameter. Depending on the accuracy and surface finish needed, a
part will either be one cut or it will be roughed and skimmed. On a one cut the wire ideally passes
through a solid part and drops a slug or scrap piece when it is done. This will give adequate accuracy
for some jobs, but most of the time, skimming is necessary. A skim cut is where the wire is passed
back over the roughed surface again with a lower power setting and low pressure flush. There can
be from one to nine skim passes depending on the accuracy and surface finish required. Usually
there are just two skim passes. A skim pass can remove as much as 0.002" of material or a as little
as 0.0001". During roughing (i.e. the first cut) the water is forced into the cut at high pressure in
order to provide plenty of cooling and eliminate eroded particles as fast as possible. During
skimming (accuracy / finish cuts) the water is gently flowed over the burn so as not to deflect the
wire.
3.3.4 PREPARING AND USING OF WIRE EDM
Work safely at all times, complying with health and safety legislation, regulations and other
relevant guidelines.
Plan the CNC machining activities before you start them.
Load/input the program to the machine controller and check the program for errors using
the approved procedures.
Mount and set the required work holding devices, work-piece and cutting tools.
Check that all safety mechanisms are in place, and that the equipment is set correctly for the
required operations
The whole operation should take place inside water.
Run the operating program, and check and adjust the machine speeds, feeds and cutting
parameters to achieve the component specification.
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DEPARTMENT OF MECHANICAL ENGINEERING 22
Measure and check that all dimensional and geometrical aspects of the component are to the
specification.
Deal promptly and effectively with problems within your control, and seek help and
guidance from the relevant people if you have problems that you cannot resolve.
Shut down the equipment to a safe
4. STRUCTURE OF NC PART PROGRAM
In general, several commands are grouped together to accomplish a specific machining
operation, hence the use of a block of information for each operation. Each command gives a
specific element of control data, such as dimension or a feed rate. Each command within a block is
also called a word. The way in which words are arranged within the block is called block format.
Three different block formats are commonly used, (Fixed sequential format, Tab sequential format
and Word address format) With this type of format, each type of word is assigned as address that is
identified by a letter code within the part program. Thus the letter code specifies the type of word
that follows and then its associated numeric data is given. For example, the code T represents a tool
number. Thus a word of the form T01 would represent tool number 1. Theoretically, with this
approach, the words in a given block can be entered in any sequence and the controller should be
able to interpret them correctly. With the word address format only the needed words for a given
operation have to be included within the block. The command to which the particular numeric data
applies is identified by the preceding address code. Word format has the advantage of having more
than one particular command in one block something that would be impossible in the other two
formats.
N-CODE: Sequence number, used to identify each block with in an NC program and
provides a means by which NC commands may be rapidly located. It is program line
number. It is a good practice to increment each block number by 5 to 10 to allow additional
blocks to be inserted if future changes are required.
G-CODE: Preparatory Word, used as a communication device to prepare the MCU. The G-
code indicates that a given control function such as G01, linear interpolation, is to be
requested.
X, Y & Z-CODES: Coordinates. These give the coordinate positions of the tool.
COMMONLY USED WORD ADDRESSES
F-CODE: Feed rate. The F code specifies the feed in the machining operation.
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DEPARTMENT OF MECHANICAL ENGINEERING 23
S-CODE: Spindle speed. The S code specifies the cutting speed of the machining process.
T-CODE: Tool selection. The T code specifies which tool is to be used in a specific
operation.
M-CODE: Miscellaneous function. The M code is used to designate a particular mode of
operation for an NC machine tool.
I, J & K-CODES: They specify the centre of arc coordinates from starting.
Sequence and format of words:
N3 G2 X+1.4 Y+1.4 Z+1.4 I2.0 J2.0 K2.0 F5 S4 T4
4.1 M-CODES
M00Mandatory Program Stop
M01 Optional Program Stop
M02 Program End
M03 Spindle Forward/Clockwise
M04 Spindle Reverse/Counter clockwise
M05 Spindle Stop
M06 Tool change
M07 Mist Coolant On
M08 Flood Coolant On
M09 All Coolant Off
M19 Spindle Orient
M30 Program End and Rewind
M40-M45 Gear Change
M47 Repeat Program from First Line
M48 Enable Feed/Speed Overrides
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M49 Disable Feed/Speed Overrides
M98 Subprogram Call
M99 Return from Subprogram / Rewind
4.2 G-CODES
Table.4.2 G-CODES
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DEPARTMENT OF MECHANICAL ENGINEERING 25
4.3 CNC Machine Start Procedure
Fig.4.3 Steps involved in starting CNC machine.
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DEPARTMENT OF MECHANICAL ENGINEERING 26
4.4 Method of inserting new program
Fig.4.4 Steps for inserting new program to CNC machine
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DEPARTMENT OF MECHANICAL ENGINEERING 27
5. TYPICAL SAMPLE PROGRAMS
5.1 Sample program on Milling
Write a part program for milling operations being carried out on a CNC milling machine for the
figure shown below.
Fig.5.1 Milling sample
Program:
%1000
N1 G90 G54 G43 G17 G0 H1 Z50
N2 M03 S1500
N3 G0 X0 Y0
N4 G01 Z0 F500
N5 M98 P700 L15
N6 G0 G90 Z250
N7 M30
%700
N1 G92 Z-1 G0 F500
N2 G90 X0 Y25
N3 G03 X0 Y75
N4 G01 Y100
N5 X25
N6 G03 X75 Y100 R25
N7 G01 X100
N8 Y75
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N9 G03 X100 Y25 R25
N10 G01 Y0
N11 X75
N12 G03 X25 Y0 R25
N13 G0 X0
M99
5.2 SAMPLE PROGRAMME ON TURNING
Write a part program for turning operations being carried out on a CNC turning center. Let us take
an exercise: Figure shows the final profile to be generated on a bar stock by using a CNC turning
center. After studying the required part geometry and features, the main program can be written as
follows.
Fig. 5.2 Turninig Sample
N1 G21 G99 G40
N2 G28 U0W0
N3 T0101 M06
N4 G92 S1200
N5 G96 M04 S200
N6 G0 X75 Z2
N7 G71 U0.2 R1
N8 G71 P9 Q15 U0.2 W0.2 F0.1
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N9 G01 X0 Z0 G42
N10 G01 X20.0 Z-20.0
N11 X20.0 Z-45.0
N12 X40.0 Z-80.0
N13 X40.0 Z-105.0
N14 G03 X70.0 Z-120.0 R15.0
N15 G01 X70.0 Z-160
N16 G01 X100 Z2.0
N17 G28 UO WO
N18 M06 T0202
N19 G92 S2500
N20 G96 M04 S200
N21 G70 P9 Q13 F0.01
N22 X100 G40
N23 M09
N24 M30
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6. ADVANTAGES, DISADVANTAGES AND APPLICATIONS OF
CNC SYSTEMS
6.1 ADVANTAGES
The manufacturing process can be simulated virtually and no need to make a prototype or a
model. This saves time and money.
Once programmed, these machines can be left and do not require any human intervention,
except for work loading and unloading.
These machines can manufacture several components to the required accuracy without any
fatigue as in the case of manually operated machines.
Savings in time that could be achieved with the CNC machines are quite significant.
6.2 DISADVANTAGES
CNC machines are generally more expensive than manually operated machines.
The CNC machine operator only needs basic training and skills, enough to supervise several
machines.
Increase in electrical maintenance, high initial investment and high per hour operating costs
than the traditional systems.
Fewer workers are required to operate CNC machines compared to manually operated
machines. Investment in CNC machines can lead to unemployment.
6.3 APPLICATIONS
CNC was initially applied to metal working machinery: Mills, Drills, boring machines,
punch presses etchant now expanded to robotics, grinders, welding machinery, EDM's,
flame cutters and also for inspection equipment etc.
CNC electrical discharge machining (EDM).
CNC fabrication machines (sheet metal punch press, bending machine, or press brake)
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I. NARRATION
The internship started on 10th
January 2018. In the first day of training all the students were asked
to assemble and campus tour was held. Introduction about various machines present in the GTTC
and their applications was taught. The next day, the students were divided into 2 batches and timings
were decided. The batches were allotted a trainer. Mr. Kotrappa , our trainer, conducted classes for
4 hours from 9.30 am to 1.30 pm every day . Lectures were given on the theory of NC, mainly CNC
machines during the first few days. Various preparatory functions (G codes) and miscellaneous
functions (M codes) were taught. Basic programs on turning, milling using G codes and M codes
were taught. The theory sessions were followed by laboratory sessions on simulation. After some
days, we were given hands on training on CNC machines to perform basic turning and milling
operations. Demo on wire EDM operations were also shown. The internship ended on 08th
of
February 2018 and the students were awarded with 4 weeks of internship certificate.
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DEPARTMENT OF MECHANICAL ENGINEERING 32
II. SELF EVALUATION
During 4 weeks of internship at GTTC Hassan, I was given training on CNC machines operations
and their applications. I was eager to see the CNC operations as I was seeing it for the first time. It
was a new experience for me to see such huge machines in working condition. The training started
with some basic introduction to CNC machines. I could gain a decent knowledge about preparatory
functions (G codes) and miscellaneous functions (M codes). I came to know about the differences
between NC, CNC and DNC, and their operations, applications. Practical sessions were the most
interesting ones. After 2 hours of theory sessions, we used to have practical sessions where I was
allowed to have hands on experience on the machines. I also had laboratory sessions in the
simulation lab which was comparatively a bit boring. Working in CNC machines was one of my
most favourite parts. Our Trainer taught to write the programs really well which helped me to do
well in the practical. Simulation lab was a bit boring since it was not that easy to understand. Even
after trying for more than half an hour, I could not get the output. Another thing which was not
satisfactory was complexities in programming for different types of machines. There are various
types of machines such as SIEMENS, FANUC etc., for which we need to write different programs
since the machines have differences in specifications. In spite of these drawbacks, it was a
wonderful experience working as an intern in GTTC.
Hence I have successfully studied about the CNC machine tool and their function. With their G &
M codes and operation performed on these type of machine tool. The importance of lathes and
milling machines even if they are conventional cannot be undetermined. These machines have
played a vital role in bringing about industrial revolution and have laid the foundations. But the
bringing about of the new technology in the present era is very important. The conventional
machines are required in small quantities whereas the CNC machines must be increased to improve
the quantity and quality of production.
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III. APPENDIX
Samples of work:
Milling samples
Turning samples
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DEPARTMENT OF MECHANICAL ENGINEERING 34
IV. REFERENCES
http://en.wikipedia.org/wiki/computer_numerical_control.
http://www.seminarprojects.com/cnc.
http://www.slideshare.net

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IV REPORT.doc

  • 1. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 11 1. INTRODUCTION TO NC DNC AND CNC 1.1 NUMERICAL CONTROL (NC) Fig.1.1 Numerical Control Systems. Numerical control (NC) systems are hardware controls in which most of functions are carried out by electronic hardware based upon digital circuit technology. Numerical Control is a technique for controlling machine tools or processes using coded command instructions. These coded command instructions are interpreted and converted by NC controller into two types of signals namely; motion control signals and miscellaneous control signals. Motion control signals are a series of electric pulse trains that are used to control the positions and the speed of the machine table and spindle, whereas miscellaneous control signals are set of ON/OFF signals to execute the spindle rotation and direction, control of coolant supply, selection of cutting tools, automatic clamping and unclamping, etc. In motion control signals, each pulse activates a motion of one basic length-unit (BLU).
  • 2. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 12 1.2 DIRECT NUMERICAL CONTROL (DNC) Direct numerical control (DNC), also known as distributed numerical control (also DNC), is a common manufacturing term for networking CNC machine tools. DNC networking or DNC communication is always required when CAM programs are to run on some CNC machine control. 1.3 COMPUTERNUMERICAL CONTROL (CNC) Fig.1.3 Block diagram of Computer Numerical control system CNC controls are soft-wired NC systems as control functions are controlled by software programs. Alternatively, Computer Numerical Control is the numerical control system in which dedicated, stored program microprocessors are built into the control to perform basic and advanced NC functions. Control signals in CNC systems are in the form of binary words, where each word contains fixed number of bits, 32 bits or 64 bits are commonly used, representing different axial positions. A CNC system consists of the following 6 major elements: a. Input Device b. Machine Control Unit c. Machine Tool d. Driving System e. Feedback Devices f. Display Unit
  • 3. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 13 1.3.1 PROGRAMME 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 communication. 1.3.2 MACHINE CONTROL UNIT The machine control unit (MCU) is the heart of a CNC system. It is used to perform the following functions: It read the coded instructions, decode the coded instructions. Implement interpolations (linear, circular, and helical) to generate axis motion commands. and feed the axis motion commands to the amplifier circuits for driving the axis mechanisms. And it receives the feedback signals of position and speed for each drive axis. To implement auxiliary control functions such as coolant or spindle on/off and tool change. 1.3.3 MACHINE TOOL CNC controls are used to control various types of machine tools. Regardless of which type of machine tool is controlled, it always has a slide table and a spindle to control position and speed. The machine table is controlled in the X and Y axes, while the spindle runs along the Z axis. 1.3.4 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. 1.3.5 DRIVE SYSTEM Drives are used to provide controlled motion to CNC elements 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 motors used for CNC system are of two kinds- 1. Electrical –DC or AC Stepper motors and DC or AC servo motors 2. Fluid - Hydraulic or Pneumatic
  • 4. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 14 2. CONTROL PANEL OF CNC Fig.2 Control Panel A CNC machine is normally controlled by a computer and software. However, most CNC machines have a range of controls for manual use. It is rare for a CNC machine to be used manually as simple operations are best carried out on cheap/basic/manual machines. When a CNC machine is used manually it is being used well below its capability and specification. 2.1RESET BUTTON The most important control button is usually the reset button. When the CNC machine is turned on, the reset button is pressed by the machine operator. This zero the cutter, moving the cutter to coordinates 0, 0, 0 on the X, And Z axis. In simple terms, the reset button moves the cutter to the corner of the machine, above the work table. 2.2 MANUAL CONTROL The cutter can be controlled manually although this is rarely needed. The ‘X’ and ‘Y’ buttons control the movement of the cutter along the horizontal surfaces. The ‘Z’ buttons control depth and up / down movement. 2.3 STOP BUTTON Most control panels have stop buttons. When pressed these stop the machine very quickly. 2.4 SPEED AND FEED On some CNC machines it is possible to manually vary the speed and feed of the cutter.
  • 5. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 15 3. CNC MACHINERIES The CNC machines which we worked at GTTC are: CNC Lathe. CNC Milling. CNC Wire EDM. 3.1 CNC LATHE (FANUC SERIES OI-TC) 3.1.1 SPECIFICATIONS Table.3.11 CNC Lathe Specification EQUIPMENT UNIT RANGE Made = Fanuc ---- ---- Chuck diameter mm 200 Max. cutting diameter mm 200 Max. cutting length mm 500 Spindle bore diameter mm 55 Spindle rotating speed rpm 45-4000 Main motor power(AC) kW 11 Hydraulic unit power motor kW 1.5 Chip conveyor motor kW 0.2 Coolant pump motor kW 0.55 Weight Kg 5000
  • 6. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 16 Fig.3.11 CNC Lathe. 3.1.2 ABOUT CNC LATHE Some view lathes as the only universal CNC machine tool because a lathe can make all of the parts needed for another lathe. A lathe spins the work-piece in a spindle while a fixed cutting tool approaches the work-piece to slice chips off of it. The act of cutting a work-piece on a lathe is called "Turning". Computer numerical control (CNC) has been incorporated into a variety of new technologies and machinery. One such machine of this sort that is used for a wide array of production processes is known as a CNC lathe. Due to technological advancements, CNC lathes are quickly replacing some of the older and more traditionally used production lathes, such as the multi-spindle. CNC lathes come with a number of benefits. They can be easily set up and operated. They offer tremendous repeatability, along with top-notch accuracy in production. A CNC lathe is typically designed to utilize modern versions of carbide tooling and processes. A part can be designed for customization, and the machine’s tool paths are often programmed using the CAD or CAM processes some prime examples of finished items as a result of using CNC lathe machines include: Baseball Bats, Bowls, Camshafts, Crankshafts Cue, sticks Dining, Room Table and Chair Legs, Gun Barrels, Musical Instruments
  • 7. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 17 3.1.3 PREPARING AND USING OF CNC LATHE Checking to make sure the lathe is lubricated and learning to schedule routine maintenance in accordance with workplace standards. Learning to translate product specifications and work instructions into a machine-readable format. Establishing criteria for tool selection with efficiency and safety in mind. Installing work-piece handling devices and inserting tools into their corresponding slots. Learning to load a machining program into the CNC lathe and aligning its data points according to project requirements. Producing sample parts to verify if they match specifications and operator instructions. 3.2 CNC MILLING MACHINE (SEIMENS CONTROLLER) Fig.3.2 CNC Milling Machine
  • 8. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 18 3.2.1 SPECIFICATIONS Table.3.21 CNC Milling specification CNC controller Siemens control Axis Motor & Drive AC Servo (1.3 Nm) Spindle Motor 1 HP with VFD (3PH). Spindle Motor Speed 100 to 3000 rpm. Lubrication System Automatic (Motorized). Max. Depth Of Cut 1 mm Possible. Axis Control 3 axis. Axis Plane XY, XZ & YZ. Max. Rapid Feed 4000 mm/min. Table Load Capacity 100 Kg. 3.2.2 ABOUT CNC MILLING CNC milling is a specific form of computer numerical controlled (CNC) machining. Milling itself is a machining process similar to both drilling and cutting, and able to achieve many of the operations performed by cutting and drilling machines. Like drilling, milling uses a rotating cylindrical cutting tool. However, the cutter in a milling machine is able to move along multiple axes, and can create a variety of shapes, slots and holes. In addition, the work-piece is often moved across the milling tool in different directions, unlike the single axis motion of a drill. CNC milling devices are the most widely used type of CNC machine. Typically, they are grouped by the number of axes on which they operate, which are labelled with various letters. X and Y designate horizontal movement of the work-piece (forward-and-back and side-to-side on a flat plane). Z represents vertical, or up-and-down, movement, while W represents diagonal movement across a vertical plane. Most machines offer from 3 to 5 axes, providing performance along at least the X, Y and Z axes. Advanced machines, such as 5-axis milling centres, require CAM programming for optimal performance due to the incredibly complex geometries involved in the machining process. These devices are extremely useful because they are able to produce shapes that would be nearly impossible using manual tooling methods. Most CNC milling machines also integrate a device for pumping cutting fluid to the cutting tool during machining.
  • 9. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 19 3.2.3 PREPARING AND USING CNC MILLING Work safely at all times, complying with health and safety legislation, regulations and other relevant guidelines. Plan the CNC machining activities before you start them. Load/input the program to the machine controller and check the program for errors using the approved procedures. Mount and set the required work holding devices, work-piece and cutting tools. Check that all safety mechanisms are in place, and that the equipment is set correctly for the required operations Run the operating program, and check and adjust the machine tool speeds, feeds and operating parameters to achieve the component specification. Measure and check that all dimensional and geometrical aspects of the component are to the specification. Deal promptly and effectively with problems within your control, and seek help and guidance from the relevant people if you have problems that you cannot resolve. Shut down the equipment to a safe. 3.3 CNC WIRE EDM (MITSUBISHI CONTROLLER) Fig.3.3 CNC Wire EDM
  • 10. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 20 3.3.1 SPECIFICATION Table.3.31 CNC Wire EDM specification DESCRIPTION MITSUBISHI RA90M (AT) MITSUBISHI RA90M Max. work piece dimension [mm] (in) 860 x 760 x 160 860 x 760 x 160 Maximum work piece weight 350 350 Table dimensions 572 x 478 572 x 478 Machining range (X x Y) 320 x 250 320 x 250 Table rapid-feed speed [mm/min] (in/min) 1300 1300 Wire diameter [mm] (in) 0.2 - 0.3 0.2 - 0.3 Maximum wire feed rate [m/min] (in/min) 15 15 Maximum work piece thickness [mm] (in) 160 ----- Taper machining device Standard Standard Z-Axis stroke (manual operation) 150 150 Max. taper angle [mm] (in) 15 for work piece 100 mm thick 15 for work piece 100 mm thick Max. machining current 50A 50A Minimum drive unit [u m] (in) 0.05um 0.05um CNC Controller Mitsubishi 64 bit Mitsubishi 64 bit 3.3.2 ABOUT WIRE EDM Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the work piece to produce the finished part to the desired shape.
  • 11. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 21 The wire-cut type of machine arose in the 1960s for the purpose of making tools (dies) from hardened steel. The tool electrode in wire EDM is simply a wire. The first CNC EDM machine was produced in 1976. EDM wire cutting uses a metallic wire to cut a programmed contour in a work piece. Extrusion dies and blanking punches are very often machined by wire cutting. Cutting is always through the entire work piece. To start machining it is first necessary to drill a hole in the work piece or start from the edge. On the machining area, each discharge creates a crater in the work piece and an impact on the tool. The wire can be inclined, thus making it possible to make parts with taper or with different profiles at the top and bottom. There is never any mechanical contact between the electrode and work piece. The wire is usually made of brass or stratified copper, and is between 0.1 and 0.3 mm diameter. Depending on the accuracy and surface finish needed, a part will either be one cut or it will be roughed and skimmed. On a one cut the wire ideally passes through a solid part and drops a slug or scrap piece when it is done. This will give adequate accuracy for some jobs, but most of the time, skimming is necessary. A skim cut is where the wire is passed back over the roughed surface again with a lower power setting and low pressure flush. There can be from one to nine skim passes depending on the accuracy and surface finish required. Usually there are just two skim passes. A skim pass can remove as much as 0.002" of material or a as little as 0.0001". During roughing (i.e. the first cut) the water is forced into the cut at high pressure in order to provide plenty of cooling and eliminate eroded particles as fast as possible. During skimming (accuracy / finish cuts) the water is gently flowed over the burn so as not to deflect the wire. 3.3.4 PREPARING AND USING OF WIRE EDM Work safely at all times, complying with health and safety legislation, regulations and other relevant guidelines. Plan the CNC machining activities before you start them. Load/input the program to the machine controller and check the program for errors using the approved procedures. Mount and set the required work holding devices, work-piece and cutting tools. Check that all safety mechanisms are in place, and that the equipment is set correctly for the required operations The whole operation should take place inside water. Run the operating program, and check and adjust the machine speeds, feeds and cutting parameters to achieve the component specification.
  • 12. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 22 Measure and check that all dimensional and geometrical aspects of the component are to the specification. Deal promptly and effectively with problems within your control, and seek help and guidance from the relevant people if you have problems that you cannot resolve. Shut down the equipment to a safe 4. STRUCTURE OF NC PART PROGRAM In general, several commands are grouped together to accomplish a specific machining operation, hence the use of a block of information for each operation. Each command gives a specific element of control data, such as dimension or a feed rate. Each command within a block is also called a word. The way in which words are arranged within the block is called block format. Three different block formats are commonly used, (Fixed sequential format, Tab sequential format and Word address format) With this type of format, each type of word is assigned as address that is identified by a letter code within the part program. Thus the letter code specifies the type of word that follows and then its associated numeric data is given. For example, the code T represents a tool number. Thus a word of the form T01 would represent tool number 1. Theoretically, with this approach, the words in a given block can be entered in any sequence and the controller should be able to interpret them correctly. With the word address format only the needed words for a given operation have to be included within the block. The command to which the particular numeric data applies is identified by the preceding address code. Word format has the advantage of having more than one particular command in one block something that would be impossible in the other two formats. N-CODE: Sequence number, used to identify each block with in an NC program and provides a means by which NC commands may be rapidly located. It is program line number. It is a good practice to increment each block number by 5 to 10 to allow additional blocks to be inserted if future changes are required. G-CODE: Preparatory Word, used as a communication device to prepare the MCU. The G- code indicates that a given control function such as G01, linear interpolation, is to be requested. X, Y & Z-CODES: Coordinates. These give the coordinate positions of the tool. COMMONLY USED WORD ADDRESSES F-CODE: Feed rate. The F code specifies the feed in the machining operation.
  • 13. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 23 S-CODE: Spindle speed. The S code specifies the cutting speed of the machining process. T-CODE: Tool selection. The T code specifies which tool is to be used in a specific operation. M-CODE: Miscellaneous function. The M code is used to designate a particular mode of operation for an NC machine tool. I, J & K-CODES: They specify the centre of arc coordinates from starting. Sequence and format of words: N3 G2 X+1.4 Y+1.4 Z+1.4 I2.0 J2.0 K2.0 F5 S4 T4 4.1 M-CODES M00Mandatory Program Stop M01 Optional Program Stop M02 Program End M03 Spindle Forward/Clockwise M04 Spindle Reverse/Counter clockwise M05 Spindle Stop M06 Tool change M07 Mist Coolant On M08 Flood Coolant On M09 All Coolant Off M19 Spindle Orient M30 Program End and Rewind M40-M45 Gear Change M47 Repeat Program from First Line M48 Enable Feed/Speed Overrides
  • 14. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 24 M49 Disable Feed/Speed Overrides M98 Subprogram Call M99 Return from Subprogram / Rewind 4.2 G-CODES Table.4.2 G-CODES
  • 15. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 25 4.3 CNC Machine Start Procedure Fig.4.3 Steps involved in starting CNC machine.
  • 16. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 26 4.4 Method of inserting new program Fig.4.4 Steps for inserting new program to CNC machine
  • 17. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 27 5. TYPICAL SAMPLE PROGRAMS 5.1 Sample program on Milling Write a part program for milling operations being carried out on a CNC milling machine for the figure shown below. Fig.5.1 Milling sample Program: %1000 N1 G90 G54 G43 G17 G0 H1 Z50 N2 M03 S1500 N3 G0 X0 Y0 N4 G01 Z0 F500 N5 M98 P700 L15 N6 G0 G90 Z250 N7 M30 %700 N1 G92 Z-1 G0 F500 N2 G90 X0 Y25 N3 G03 X0 Y75 N4 G01 Y100 N5 X25 N6 G03 X75 Y100 R25 N7 G01 X100 N8 Y75
  • 18. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 28 N9 G03 X100 Y25 R25 N10 G01 Y0 N11 X75 N12 G03 X25 Y0 R25 N13 G0 X0 M99 5.2 SAMPLE PROGRAMME ON TURNING Write a part program for turning operations being carried out on a CNC turning center. Let us take an exercise: Figure shows the final profile to be generated on a bar stock by using a CNC turning center. After studying the required part geometry and features, the main program can be written as follows. Fig. 5.2 Turninig Sample N1 G21 G99 G40 N2 G28 U0W0 N3 T0101 M06 N4 G92 S1200 N5 G96 M04 S200 N6 G0 X75 Z2 N7 G71 U0.2 R1 N8 G71 P9 Q15 U0.2 W0.2 F0.1
  • 19. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 29 N9 G01 X0 Z0 G42 N10 G01 X20.0 Z-20.0 N11 X20.0 Z-45.0 N12 X40.0 Z-80.0 N13 X40.0 Z-105.0 N14 G03 X70.0 Z-120.0 R15.0 N15 G01 X70.0 Z-160 N16 G01 X100 Z2.0 N17 G28 UO WO N18 M06 T0202 N19 G92 S2500 N20 G96 M04 S200 N21 G70 P9 Q13 F0.01 N22 X100 G40 N23 M09 N24 M30
  • 20. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 30 6. ADVANTAGES, DISADVANTAGES AND APPLICATIONS OF CNC SYSTEMS 6.1 ADVANTAGES The manufacturing process can be simulated virtually and no need to make a prototype or a model. This saves time and money. Once programmed, these machines can be left and do not require any human intervention, except for work loading and unloading. These machines can manufacture several components to the required accuracy without any fatigue as in the case of manually operated machines. Savings in time that could be achieved with the CNC machines are quite significant. 6.2 DISADVANTAGES CNC machines are generally more expensive than manually operated machines. The CNC machine operator only needs basic training and skills, enough to supervise several machines. Increase in electrical maintenance, high initial investment and high per hour operating costs than the traditional systems. Fewer workers are required to operate CNC machines compared to manually operated machines. Investment in CNC machines can lead to unemployment. 6.3 APPLICATIONS CNC was initially applied to metal working machinery: Mills, Drills, boring machines, punch presses etchant now expanded to robotics, grinders, welding machinery, EDM's, flame cutters and also for inspection equipment etc. CNC electrical discharge machining (EDM). CNC fabrication machines (sheet metal punch press, bending machine, or press brake)
  • 21. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 31 I. NARRATION The internship started on 10th January 2018. In the first day of training all the students were asked to assemble and campus tour was held. Introduction about various machines present in the GTTC and their applications was taught. The next day, the students were divided into 2 batches and timings were decided. The batches were allotted a trainer. Mr. Kotrappa , our trainer, conducted classes for 4 hours from 9.30 am to 1.30 pm every day . Lectures were given on the theory of NC, mainly CNC machines during the first few days. Various preparatory functions (G codes) and miscellaneous functions (M codes) were taught. Basic programs on turning, milling using G codes and M codes were taught. The theory sessions were followed by laboratory sessions on simulation. After some days, we were given hands on training on CNC machines to perform basic turning and milling operations. Demo on wire EDM operations were also shown. The internship ended on 08th of February 2018 and the students were awarded with 4 weeks of internship certificate.
  • 22. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 32 II. SELF EVALUATION During 4 weeks of internship at GTTC Hassan, I was given training on CNC machines operations and their applications. I was eager to see the CNC operations as I was seeing it for the first time. It was a new experience for me to see such huge machines in working condition. The training started with some basic introduction to CNC machines. I could gain a decent knowledge about preparatory functions (G codes) and miscellaneous functions (M codes). I came to know about the differences between NC, CNC and DNC, and their operations, applications. Practical sessions were the most interesting ones. After 2 hours of theory sessions, we used to have practical sessions where I was allowed to have hands on experience on the machines. I also had laboratory sessions in the simulation lab which was comparatively a bit boring. Working in CNC machines was one of my most favourite parts. Our Trainer taught to write the programs really well which helped me to do well in the practical. Simulation lab was a bit boring since it was not that easy to understand. Even after trying for more than half an hour, I could not get the output. Another thing which was not satisfactory was complexities in programming for different types of machines. There are various types of machines such as SIEMENS, FANUC etc., for which we need to write different programs since the machines have differences in specifications. In spite of these drawbacks, it was a wonderful experience working as an intern in GTTC. Hence I have successfully studied about the CNC machine tool and their function. With their G & M codes and operation performed on these type of machine tool. The importance of lathes and milling machines even if they are conventional cannot be undetermined. These machines have played a vital role in bringing about industrial revolution and have laid the foundations. But the bringing about of the new technology in the present era is very important. The conventional machines are required in small quantities whereas the CNC machines must be increased to improve the quantity and quality of production.
  • 23. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 33 III. APPENDIX Samples of work: Milling samples Turning samples
  • 24. KMCT POLYTECHNIC COLLEGE KUTTIPPURAM INTERNSHIP REPORT DEPARTMENT OF MECHANICAL ENGINEERING 34 IV. REFERENCES http://en.wikipedia.org/wiki/computer_numerical_control. http://www.seminarprojects.com/cnc. http://www.slideshare.net