Computer numerical control ( CNC )

CONTENT
 INTRODUCTION
 HISTORY
 ELEMENTS OF CNC MACHINE
 MACHINE CONTROL UNIT (MCU)
 OPEN LOOP AND CLOSE LOOP CONTROL
 HOW CNC WORKS ?
 FEATURES OF CNC MACHINERY
 CNC PROGRAMING BASIC
 PROGRAMING KEY LETTERS
 ADVANTAGES OF CNC MACHINE
 CHALLAGE OF CNC MACHINE
 APPLICATION OF CNC MACHINE
 CONCLUSION
 REFRANCE

INTRODUCTION
 CNC is the acronym for computer numerical control.
 It is an outgrowth of the older term "NC", which
stands for just "numerical control".
 Numeric control is a programmable automation in
which process is controlled by numbers, letters and
symbols. (Computer + NC=CNC)
 CNC refers to the idea of controlling machine tools
programmatically via computer. With the older "NC"
term, A computer need not be involved

INTRODUCTION
 This means a computer converts the design produced
by Computer Aided Design Software (CAD), into
numbers. The numbers can be considered to be the
coordinates of a graph and they control the movement
of the cutter. In this way the computer controls the
cutting and shaping of the material.
 CNC can control the motions of the work piece or
tool, the input parameters such as feed, Depth of cut,
speed, and the functions such as turning spindle
on/off, turning

HISTORY
 The first NC machines were built in the 1940s and 1950s by Prof. John T Parson.
 Conceived method of using punched cards containing coordinate position data to
control the machine tool.
 In 1948, Parson demonstrated his concept to U.S Air Force
 CNC machine came to existence after evolution of computer around 1980.
 Modern CNC Machine are improving further as the technology is changing with
variety of functions according to applications.

ELEMENTS OF CNC MACHINE
 A CNC machine consists of following 6 major
elements:
• Input device
• Machine control unit
• Machine tool
• Driving system
• Feedback devices
• Display unit

MACHINE CONTROL UNIT (MCU)
 the machine control unit is the heart CNC system.
There are two sub-units in the machine control unit:
 Data Processing Unit(DPU)
 Control Loop Unit(CLU)

OPEN LOOP AND CLOSED LOOP
CONTROLS
 In open loop systems the slide may overshoot or may not reach desired position because
of inertia, wear and tear and friction, hence inaccurate machining.
 In closed loop systems the position sensors are used to correct slide movements and
achieve higher accuracy and repeatability

HOW CNC WORKS ?
 Controlled by G and M codes.
 These are number values and co-ordinates.
 Each number or code is assigned to a particular
operation.
 Typed in manually to CAD by machine operators.
 G & M codes are automatically generated by the
computer software.

FEATURES OF CNC MACHINERY
 The tool or material moves automatically.
 Tools can operate in 1-5 axes.
 Larger machines have a machine control unit (MCU)
which manages operations.
 Movement is controlled by motors (actuators).
 Feedback is provided by sensors (transducers)
 Tool magazines are used to change tools
automatically.

CNC PROGRAMMING BASICS
 CNC instructions are called part program commands.
 When running, a part program is interpreted one
command line at a time until all lines are completed.
 Commands, which are also referred to as blocks, are
made up of words which each begin with a letter
address and end with a numerical value.

PROGRAMMING KEY LETTERS
 O - Program number (Used for program identification)
 N - Sequence number (Used for line identification)
 G - Preparatory function
 X - X axis designation
 Y - Y axis designation
 Z - Z axis designation
 R - Radius designation
 F – Feed rate designation
 S - Spindle speed designation
 H - Tool length offset designation
 D - Tool radius offset designation
 T - Tool Designation
 M - Miscellaneous function

Advantages of CNC
• Easier to program;
• Easy storage of existing programs;
• Easy to change a program
• Avoids human errors
• CNC machines are safe to operate
• Complex geometry is produced as cheaply as simple
ones
• Usually generates closer tolerances than manual
machines

CHALLENGES
 COSTLY SETUP, SKILLED OPERATORS.
 COMPUTERS, PROGRAMMING KNOWLEDGE
REQUIRED.
 MAINTENANCE IS DIFFICULT.

APPLICATIONS
 The applications of CNC include both for machine tool as well as non-
machine tool areas. Some are as follows:
 lathe,
 drill press,
 milling machine,
 Grinding unit,
 laser,
 sheet-metal press working machine,
 tube bending machine etc.
 welding machines (arc and resistance),
 Measuring machine,
 electronic assembly,
 tape laying and
 filament winding machines for Composites etc.
 This Technology is applied to Prosthetics and Orthotics field as well.

CONCLUSION
 The advantage of a CNC system are that the operation of
a conventional machine is removed and the part
production is made automatic.
 It reduces the labor work and hence highly efficient in
the manufacturing process.
 BHEL generally uses CNC machines to achieve its
manufacturing targets. For manufacturing works of large
scale it is very difficult to work with manual machines as
they are time consuming. CNC machines have their wide
scope because they are easy to handle, the work becomes
easier and jobs are done with perfection

REFERENCES
 Manual of CNC from BHEL Jhansi
 http://en.wikipedia.org/wiki/computer_numerical_co
ntrol
 http://www.motioncontrol.com/articles/gearheads-
modularspindle-drives
 http://www.seminarprojects.com/cnc

Computer numerical control ( CNC )

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