2. i
DECLARATION
We hereby declare that the work in this project is our own except for quotations and summaries
which have been duly acknowledged.
Date: july/2019
Name Registartion number Contact:
Abdirahman Said Dhore B1EN27 Abdirahmansaciid04@gmail.com
Abdullahi Abubakar Ahmed B1EN34 Engdalmar74@gmail.com
Abdullahi Hashi Salad B1EN44 Raagehashi@gmail.com
3. ii
ACKNOWLEDGMENTS
First and foremost, we would like to thank Allah (Subhanahu Wa Ta'ala) for giving us faith,
health, strength, ability and patience to finish this humble effort. We hope that this project will
contribute to the university research in this field.
We would like to extend our sincere thanks to the lecturer of our class, Eng. Ahmed Ali
Abdi, for his help, suggestions, corrections, long-term guidance in support, the tremendous
teaching, warm encouragement and considerate understanding throughout the course of our study.
We are truly grateful for all his support and encouragement.
We would like to express our appreciation to our colleagues, friends, lecturers, academic
and general staff of Somali National University. And we wish to extend our grateful appreciation
to all those who had contributed directly and indirectly to the preparation of this project.
We would like to thank our beloved family for all support, patience, understanding, and
being helpful throughout our study. Especially, we give our deepest gratitude and sincerest love to
our parents for their love, support, encouragement, patience, and assistance through our entire life.
We are forever indebted to our parents, who always keep us in their prayers, encourage us to pursue
higher goals and cheer us up in the difficult moments.
4. iii
ABSTRACT
This paper discussed of literature review of different author who have tried to build the
smaller CNC machines. Today CNC technology has major contribution in industries. CNC
machines are main platform in the contribution of good quality products in industries. Basically
CNC machines are automated operating machines which are based on code letters (NC etc.),
numbers and special characters. The numerical data required for manufacturing a part provided by
machine is called CNC (Computer Numerical Controlled).
5. iv
TABLE OF CONTENTS Page
DECLARATION……………………………………………………………….. i
ACKNOWLEDGEMENT……………………………………………………... ii
ABSTRACT…………………………………………………………………….. iii
TABLE OF CONTENTS………………………………………………………. iv
CHAPTER I INTRODUCTION
1.1 Introduction………………………………………………... 1
1.2 History of CNC……………………………………………. 2
1.3 Types of CNC machines…………………………………... 3
1.3.1 CNC Router............................................................... 3
1.3.2 Milling Machine....................................................... 3
1.3.3 CNC Plasma Cutter……………………………….. 4
1.3.4 CNC Laser Cutter…………………………………. 4
1.3.5 CNC 3D Printer…………………………………… 4
1.3.6 Pick and Place Machine.......................................... 5
1.3.7 CNC lathe……………………….......................... 5
1.4 Why is CNC machining necessary? ..................................... 6
1.5 Major elements of CNC machine tools………………….. 6
1.5.1 Program……………………………………………. 6
1.5.2 Program input device……………………………… 7
1.5.3 Machine Control Unit……………………………… 7
1.5.4 Machine Tool………………………………………. 8
6. 1
CHAPTER 01
Introduction
1.1 Introduction
The present day computer can be considered as a direct consequence of the progress in the
field of numerical control of machine tools. A real breakthrough was achieved around 1965 when
numerical control machines were fitted with minicomputers which introduced the name Computer
Numerical Control. The first step in the process of implementing automation in any industry is to
manufacture parts or components through automation using machines and machine tools with little
human intervention. In order to meet the increasing demand to manufacture complicated
components of high accuracy in large quantities, sophisticated technological equipment and
machinery have been developed. Production of these components calls for machine tools which
can be set up fairly rapidly without much attention. The design and construction of Computer
Numerically Controlled (CNC) machines differs greatly from that of conventional machine tools.
This difference arises from the requirements of higher performance levels. The CNC machines can
be operated automatically using computers. A CNC is specifically defined as “The numerical
control system where a dedicated, stored program computer is used to perform some or all of the
basic numerical control functions in accordance with control programs stored in read & write
memory of the computer” by Electronic Industries Association (EIA). (1)
CNC is a microprocessor based control system that accepts a set of program instructions,
processes and sends output control information to a machine tool, accepts feedback information
acquired from a transducer placed on the machine tool and based on the instructions and feedback,
assures that proper motion, speed and operation occur. Computer Numerically Control can be
applied to milling machines, Lathe machines, Grinding machines, Boring machines, Flame cutters,
Drilling machines etc. (2)
7. 2
1.2 History of CNC
Computer Numerical Control or CNC machinery has been with us for a period of about seven
decades. The earliest forms of CNC machines were introduced to the workplace just after World
War II. The early technology, known then as simply numerical control, provided manufacturing
with a way to replicate precise parts, especially those required for such industries as the growing
aircraft industry.
The pioneer of numerical control (which would develop into CNC technology) was a man by
the name of John T. Parsons. Parsons, an inventor, worked for his father’s company in Traverse
City, Michigan. Working with an engineer he hired named Frank Stullen, together they developed
a process using an IBM punch card reader to calculate accurately the curvature of helicopter rotary
blades, needed by the newly formed U.S. Air Force. Their work, which was revolutionary for the
time, led to the creation of the numerical control processes that served as the forerunner of CNC
machinery.
Parsons and Stullen worked with MIT’s Servomechanisms Laboratory in 1949 in pursuit of
the development of a machine that can replicate the production of precise machine parts. Their
work at MIT the early 1950s led to the unveiling of a machine that could perform such work in
September of 1952. Unfortunately, given the cost prohibition of the machine (upwards of $2
million in today’s dollars), the Air Force halted funding for the project and Parsons would be out
of a job as head of his own engineering company.
Fortunately, a small machine tool company located in Fond du Lac, WI named Giddings &
Lewis stepped in and developed a machine using magnetic tape readers (in place of the punch card
readers). The machine developed by Giddings & Lewis reduced costs and improved both quality
and efficiency. This advancement led to the development in 1957 to a fully computer controlled
numerical control machine. These new CNC machines have since become the standard tool for
making precision machined parts used in a wide variety of industries. (3)
8. 3
1.3 Types of CNC Machines
When CNC was first invented it was a technology that was adapted to fit existing machines.
Today CNC technology is still being retrofitted to various machine tools but there are also many
machines which are created for the sole purpose of being CNC machines. (4)
1.3.1 CNC Router
CNC Routers are a very common piece of machinery you will see a lot when learning about
CNC. These are machines built exclusively to be operated by CNC technology and typically have
no human interface other than through the computer. Routers are generally for producing larger
dimension parts and more commonly built with the idea of cutting wood, plastics and sheet metal
in mind. Routers also are most commonly found in a 3 axis Cartesian coordinate setup (X, Y and
Z). A 3 axis set up will allow cutting of profiles, pocketing and 3 dimensional relief machining.
There are also CNC routers which are 4, 5 or even 6 axis (the additional axes are rotary and used
to rotate the tool around the work piece or vice versa), these machines are more suited towards
cutting more complex shapes or prototype models.
1.3.2 Milling Machine
There are many milling machines today which were built specifically for CNC as
opposed to being retrofitted at a later stage. Some of these machines are absolutely massive, have
built in tool changers, auto-feed mechanisms for loading in material and various electrical
sensors for safe monitored machining.
Figure 1.1: basic CNC Router
Figure 1.2: basic milling machine
9. 4
1.3.3 CNC Plasma Cutter
CNC plasma cutters are very similar to CNC routers in size and setup. However plasma
cutters don’t require as much of a powerful set up because as opposed to dragging around a
spinning tool in material they fly above the table with a plasma torch. Plasma cutters are made for
cutting 2 dimensional profile shapes into sheet metal.
1.3.4 CNC Laser Cutter
CNC laser cutters follow the same principle as the plasma cutter, except they use a powerful
laser to do the cutting. Laser cutters are often good for cutting wood, plastic and metal; each will
need a different strength of laser suited for the material depending on the hardness and thickness.
1.3.5 CNC 3D Printer
A 3D printer uses a similar set up as a CNC router or laser cutter, but unlike those machines
it does additive machine as opposed to subtractive machining. Instead of starting with a solid piece
of material and removing bits of that material to end up with the desired part, the 3D printer starts
with a blank canvas and builds a part up layer-by-layer. The 3D printer does this either by using
an extruder that pushes a material (typically plastic) out from a tiny nozzle, or by using a laser that
quickly solidifies a powder or liquid.
Figure 1.3: basic CNC Plasma Cutter
Figure 1.4: basic CNC 3D Printer
10. 5
1.3.6 Pick and Place Machine
A pick and place machine again uses a similar set up as a CNC router or laser cutter. This
time instead of a tool used for cutting a material, there are multiple small nozzles that pick up
electrical components using a vacuum. The machine then moves to a desired location and places
that electrical component down on the printed circuit board (hence the name pick and place). Pick
and place machines move very quickly and are used to place the many hundreds or even thousands
of electrical components that make up devices such as computer motherboards, phones / tablets,
and pretty much everything else that has a printed circuit board.
1.3.7 CNC lathe machine
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. However, a programmer can manually design a
part or tool path as well. The resulting coded computer file is then uploaded to the CNC machine,
and the machine will then automatically produce the desired parts for which it was programmed
to design
1.4 Why CNC machining is necessary?
a) To manufacture complex curved geometries in 2D or 3D was extremely expensive by
mechanical means (which usually would require complex jigs to control the cutter motions)
b) Machining components with high Repeatability and Precision
c) Unmanned machining operations
Figure 1.5: basic CNC lathe machine
11. 6
d) To improve production planning and to increase productivity
e) To survive in global market CNC machines are must to achieve close tolerances.
1.5 major elements of CNC machine tools
Any CNC machine tool essentially consists of the following elements: (5)
1.5.1 Program
A series of coded instructions required to produce apart which 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.
1.5.2 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 communication.
1.5.3 Machine Control Unit
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.
12. 7
1.5.4 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.
Figure 1.6: Machine Control Unit
Figure 1.7: Machine tools
13. 8
1.5.5 Feed Back 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.
1.5.6 Drive System
Drives are used to provide controlled motion to CNC elements; 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.
1.5.7 POWER DRIVES
Figure 1.9: Drive System
Figure 1.8: Feed Back System
14. 9
In machine tools, power is generally required for driving the main spindle, saddles and
carriages and to some auxiliary units. The motors used for CNC system are of two kinds Electrical-
AC, DC also known as Stepper motors or Fluid-Hydraulic or Pneumatic. In CNC, usually stepper
and servo electrical drives are used because they exhibit favourable torque-speed characteristics
and are relatively inexpensive.
1.6 advantages of CNC machines
a) High Repeatability and Precision, e.g. Aircraft parts.
b) Volume of production is very high.
c) Flexibility in job change, automatic tool settings, less scrap.
d) Safer, higher productivity, better quality.
e) Less paper work, faster prototype production, reduction in lead times.
f) Easy storage of existing programs.
g) Avoids human errors.
h) Usually generates closer tolerances than manual machines.
i) Control systems upgrades possible.
j) Option -resident CAM system at machine tool. (6)
1.7 disadvantages of CNC machines
a) Costly setup, skilled operators.
b) Computers, programming knowledge required.
c) Maintenance is difficult.
d) Machines have to be installed in air conditioned places. (6)
Figure 1.10: POWER DRIVES
15. 10
1.8 applications of CNC machines
The following parts are usually made in practice on the CNC Machines: (6)
a) Aerospace equipment.
b) Automobile Parts.
c) Electronic industry uses CNC e.g. Printed circuit board.
d) Where much metal needs to be removed.
e) When the part geometry is so complex.
f) The operations are very complex.
1.9 Environmental control for CNC machines
There are various factors, which are very much important to maintain proper environmental
conditions. CNC machines are very costly and complex in design, so great care is necessary for
these machines in handling as well as up keeping. For proper working of these machines, the
following environmental conditions are to be maintained (6)
a) Well air circulation.
b) Electrical power supply should be regulated.
c) The machine should be protected from the moisture.
d) Dust free floor space and environment.
e) Trained person should operate the machine.
f) Proper lighting to the system.
g) Sufficient supply of coolant required during machining.
h) There should not be presence of vibrating source near to the machine.
i) There should be proper disposal point for scrap.
16. 11
CHAPTER 02
LITERATURE REVIEW
Dr.B.Jayachandraiah, O.Vamsi Krishna, P.Abdullah Khan, R.Ananda Reddy’ have studied
that rapid growth of technology increases the demand for CNC which are expensive. So they
suggested the development of low cost CNC Router. They also stated that lower cost can be
achieved by combining the features of standard PC interface with microcontroller based CNC
system in an Arduino based embedded system. ‘Low Cost CNC Using Open Source Software and
Hardware’ by ‘Muhammad Yaqoob Javed, Syed Hussain Rizvi, M.Amer Saeed, Kamran Abid,
Osama Bin Naeem, Adeel Ahmad, Kamal Shahid’ presents a low cost serial communication based
CNC machine based on open source software and hardware. In their research they have used
Universal Serial Bus (USB) CNC controller with open source software (G Code & GRBL) and
hardware (Arduino & GRBL shield) which are easily available and at low price as compared to
other controllers (7)
Ahmed A.D.Sarhan et al. (2015) in this paper, an initial CNC gantry milling machine
structure with the potential to produce high surface finish has been designed and analyzed. The
target of the author is to achieve lowest natural frequency of 202Hz corresponding to 12000 rpm
at all motion amplitudes with a full range of suitable frequency responses. Modal analysis of the
initial gantry structure design was performed and its natural frequency was 102.36HZ. (8)
Ahmed A.D.Sarhan et al. (2014) present a knowledge-centric process management
framework for the CNC machine tool design and development (D&D) with the integration of
process and knowledge. Requirements for the framework are generated based primarily on the
nature of the machine tool design practice. The proposed framework consists of process integration
model, process simulation, process execution and knowledge objects management modules. Each
of these modules is elaborated to support the knowledge-centric machine tool development process
management. (8)
D.Dimitrov et al. had given comparison between 3-axis machining and 5-axis cutting
machining with CAD/CAM system in various case study like Hermle C40U dynamic HSC milling
17. 12
centre was used with the CAM programming with the help of utilizing Delcam’s Power mill, found
that Using 5-axis machining the routing fixture could be machined in a single setup, with the help
of this minimize processing and lead time. This study shows comparison of the 3axis and 5 axes
machining with different parameters.
Ahmed A.D.Sarhan et al. developed an intelligent and very useful scheme to control the
CNC machine under sudden breakdown condition. The work comprises to develop and program
of a fuzzy controller for a closed loop speed control where the manipulated variable is the speed
relation and, therefore, the slip value. The sudden power failure occurs at 0.5 second can be
immediately recovered by the fuzzy controller at 1 second. The actual environment is immediately
build up in the Makino A77 CNC machine which minimizes breakdown. This will help in
minimizing the breakdown and controlled sudden breakdown, results in the enhancement of
productivity. (8)
After analysing and carefully reading of the above researches we found that CNC machines
are extremely versatile this day for having the capability of a wide range of functions including
cutting, drilling, routing and milling.
18. 13
CHAPTER 03
CNC MACHINE TOOLS STRUCTURE
3.1 Introduction
the important parts of CNC machines are Machine structure, guide ways, feed drives,
spindle and Spindle bearings, measuring systems, controls, software and operator interface,
gauging, tool monitoring. The information stored in the computer can be read by automatic means
and converted into electrical signals, which operate the electrically controlled servo systems.
Electrically controlled servo systems permits the slides of a machine tool to be driven
simultaneously and at the appropriate feeds and direction so that complex shapes can be cut, often
with a single operation and without the need to reorient the work piece (6)
3.2 CNC system basic components
A CNC system basically consists of the following:
3.2.1 Central Processing Unit (CPU)
The CPU is the heart of a CNC system. It accepts the information stored in the memory as
part program. This data is decoded and transformed into specific position control and velocity
signals. It also oversees the movement of the control axis or spindle and whenever this does not
match with the programmed values, a corrective action was taken. All the compensation required
for machine acquires (like lead screw pitch error, tool wear out, backlashes.) are calculated by
CPU depending upon the corresponding inputs made available to the system. The same will be
taken care of during the generation of control signals for the axis movement. Also, some basic
safety checks are built into the system through this unit and continuous necessary corrective
Figure 3.1: Computer Numerical Control (CNC) System
19. 14
actions will be provided by CPU unit. Whenever the situation goes beyond control of the CPU, it
takes the final action of shutting down the system and in turn the machine.
3.2.2 Servo Control Unit
The decoded position and velocity control signals, generated by the CPU for the axis
movement forms the input to the servo control unit. This unit in turn generates suitable signals as
command values. The command values are converted by the servo drive units which are interfaced
with the axes and the spindle motors. The servo control unit receives the position feedback signals
for the actual movement of the machine tool axes from the feedback devices (like linear scales,
rotary encoders, revolvers, etc.)
3.2.3 Operator Control Panel
The Operator Control Panel provides control panel provides the user interface to facilitate
a two way communication between the user, CNC system and the machine tool. This consists of
two parts are Video display unit and Keyboard.
3.2.4 Machine Control Panel
It is the direct interface between the operator and the NC system, enabling the operation of
the machine through the CNC system. During program execution, the CNC controls the axis the
motion, spindle function or tool function on a machine tool, depending upon the part program
stored in the memory. Prior to the starting of the machining process, machine should first be
prepared with some specific takes like, establishing a correct reference point, loading the system
memory with the required part program, loading and checking of tool offsets, zero offsets, etc.
3.2.5 Programmable Logic Controller (PLC)
A PLC matches the NC to the machine. PLC’s were basically as replacement for hard wired
relay control panels. They were basically introduced as replacement for hard wired relay panels.
20. 15
They developed to be re-programmed without hardware changes when requirements were altered
and thus are re-usable. PLC’s are now available with increased functions, more memory and larger
input/output capabilities. In the CPU, all the decisions are made relative to controlling a machine
or a process. The CPU receives input data, performs logical decisions based upon stored programs
and drives the output connection to a computer for hierarchical control are done through CPU.
3.2.6 Other Peripheral Devices
These include sensor interface, provision for communication equipment, programming
units, printer, tape reader interface, etc.
3.2.7 Hardware
Hardware includes the microprocessors that effect control system functions and peripheral
devices for data communication, machine tool interfacing and machine tool status monitoring.
3.2.8 Software
Software includes the programs that are executed by the system microprocessors and
various types of software associated with CNC.
3.2.9 Information
Information regarding the dynamic characteristics of the machine and many other
information pertaining to the process. When any of these unreliable components fails, the
diagnostics subsystem would automatically disconnect the faulty component from the system and
activate the redundant component in place of faulty one so that newly installed component can
perform its function. These three last points also known as CNC concept terms
21. 16
CHAPTER 04
CONCLUSION
After reviewing above papers we can say that, CNC machine tools must be better designed
and constructed, and must be more accurate than conventional machine tools. It is necessary to
minimize all non-cutting machine time, by fast tool changing methods, and minimize idle motions
by increasing the rapid traverse velocities to make the use of the machine tool more efficient.
Digital control techniques and computers have undoubtedly contributed to better accuracy and
higher productivity. However, it should be noted that it is the combined characteristics of the
electric control as well as the mechanical design of the machine tool itself that determine the final
accuracy and productivity of the CNC machine tool system. High productivity and accuracy might
be contradictory. Because high productivity requires higher feed, speed and depth of cut, which
increases the heat and cutting forces in the system. This will lead to higher deflections, thermal
deformations and vibration of the machine, which results in accuracy deterioration. Better accuracy
is obtained in CNC machines by using low-friction moving parts, avoiding lost motions and
isolating thermal sources. Regular sliding guides have higher static friction than the sliding
friction. The force used to overcome the static friction grows too large when the guide starts to
move. Due to inertia of the slide the position goes beyond the controlled position, adding overshoot
and phase lag to the system response, and affects the accuracy and surface finish of the part. This
can be avoided by using slides and ball screws in which the static friction is lower than the sliding
friction for example, rolling type parts such as ball-bearing ball screw and recirculating linear
slides can be used.
22. 17
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