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NUMERICAL CONTROL
CHAPTER 1
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What Is Numerical Control?
An automated manufacturing process inwhich a machine tool is controlled;
In an ordered sequenceAlong a predetermined path
To require dimensions
At a specific feed and speed rateDone through a group of alphanumeric
instructions
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A Definition:
Numerical Control is a system in which
actions are controlled by the direct insertion
ofnumerical data at some point. Thesystem must automatically interpret at leastsome portion of the data
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Numerically Controlled Machine Tools
Functionally the same as a conventional machinetool. The difference is in the way in which thevariousmachine functions and slide movements are controlled.
The functions and motions such as;
turning the spindle on and offsetting cutting speeds
setting feed rate
turning coolant on and off
moving tool with respect to work part
are performed by Machine Control Unit (MCU) inNC machine tools.
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MACHINE UNIT
NUMERICAL
CONTROLLER
NUMERICAL
DATA
(NC CODE)
MANUFACTURING
OPERATOR
PROCESSEDPART
Drive Control
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Objectives
1. Increased production
2. Reduced labor costs
3. Make production more economical
4. Make production jobs easier
5. Do production jobs that are impossiblewithout numeric control
6. Increased accuracy on duplicate parts
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Brief History of Machine Tool
Basic machining, as early as 700 B.C.
15th century - Metal machining,
18th century - industrialization, production-type machine tools.
early 20th century - Invention of high speed steel,
First two decades of 20th century - Automated machine controlled bymechanical devices,
Screw machines
Transfer lines
Assembly lines
using cams and preset stops
1955 - John Parsons and US Air Force define a need to develop amachine tool capable of machining complex and close toleranceaircraft parts with the same quality time after time (repeatability).MIT is the subcontractor and builds the machine for the project.
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1959 - MIT announces Automatic Programmed Tools (APT)programming language
1960 - Direct Numerical Control (DNC). This eliminates paper tapepunch programs and allows programmers to send files directly to
machine tools 1968 - Kearney & Trecker machine tool builders market firstmachining center
1970s - CNC machine tools & Distributed Numerical Control
1980s - Graphics based CAM systems introduced. Unix and PCbased systems available
1990s - Price drop in CNC technology
1997 - PC- Windows/NT based Open Modular Architecture Control(OMAC) systems introduced to replace firmware controllers.
Brief History of Machine Tool
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Types of Numerical Control
Conventional Numerical Control (NC)
Direct Numerical Control (DNC) Computer Numerical Control (CNC)
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Conventional Numerical
Control (NC)
Data is sent to the machine tool by means of
punch cards or tapes. The reader at themachine performs no calculations orinterpolations.
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The part cannot produce without a tape being run
through the m/c
The tape has to be run repeatedly depending onthe number of components to be produced.
The modification in the design of components is
not possible, the tape is discarded and new tapewith changed program has to be produced.
Features of NC system
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The control system does not provide the
opportunity to make the changes in speeds and
feeds.
There are always chances of part programming
mistakes on the running tape.
The storage of these input media is also oneproblem.
Features of NC system
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Computer Numerical Control (CNC)
The idea of computer numerical control is to
position a computer right at the machine tool.Most, if not all machine tools that are
numericaly controlled are CNC machine tools.
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Basic Elements of a CNC System
DEFINE GEOMETRY
CREATE TOOL PATH
POST PROCESS TO
CREATE CODE
READ CODE TO
CONTROLLER
INTERPOLATE CODEINTO DRIVE
FINISHED PART
COMPUTER
MACHINE
TOOL
MACHINECONTROL UNIT
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Some ofadditional features available in CNC machine tools are
given below:
1.The part program can be input to controller unit through keyboard
or the tape reader in the control unit can read the paper tape.
2.The part program once entered into the computer memory can be
used again and again.
3.The part program can be edited and optimized at the machine toolitself.
4.The part program can be changed according to the designrequirements of the component produced on the machine tool.
Additional features available inCNC machine
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5. The input information can be reduced to a great extent with the
use of special sub-programs developed for repetitive machining
operations.
6. The CNC systems have facility for providing the part programwithout actually running it on the machine tool.
7. The CNC control unit allows compensation fro any changes in
the dimensions of the cutting tool.
8. The CNC system also provides the facility to obtain informationon machine utilisation, which is useful to the management.
Additional features availablein CNC machine
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Computer Numerical Control (CNC)
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Direct Numeric Control
Is a method where a single computer controlsmany numerical control machine tools. Thesemachine tools may or may not be of a similar nature
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The central computerdownloads complete
programs to the CNC
machines, which can be
workstations or PCs, and
can get the information for
the machine operations.
The speed of the system
is increased, large files can
be handled and the number
of machine tools used is
expanded.
Distributed Numerical Control (DNC)
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Distributive Numerical Control
Because CNC machine tools have the ability to run
multiple programs without being attached to a
centralized computer this enables a centralized
computer to perform many different tasks.Line balancing
Scheduling
Monitoring
Quality
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Execute Machine Control Unit(MCU) or ConsoleSetups
Start and Stop Machines
Load and Unload Workpieces
Maintain High- Level Machine Tool PerformanceStandards
Change NC Inputs as Necessary (As Per Engineering)
Feedback Information to Programmer/Engineer
Role of the Operator
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Advantages
The various Advantages of CNC system are:o Reduces time for delivery of part
o Reduces scrap rate of material
o Reduces tooling costs
o Reduces layout time
o Increases machine and tool life
o Reduces storage problems
o Less setup time
o Reduces actual machining time Allows rapid design
changes in part Less jigs and fixtures are needed
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Advantages of Numerical Control
o Greater operator safety
o Reduced lead time for production
o Fewer chances for human error
o Maximal accuracy andinterchangeability of parts
o Increased productivity
o Minimal spare parts inventory
o Greater machine tool safety
o Fewer man hours for inspection
o Greater machine utilization
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Limitations
o High initial investmentMachine tools cost $30,000 - $1,500,000
o High maintenance requirements
Maintenance personnel must have both mechanicaland electronics expertise
o Not cost-effective for low-level production onsimple parts
As geometric complexity or volume increases CNCbecomes more economical
o Retraining and recruitment of staff
o Newsupport facilities
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Industries Most Affected by
Numerical Controlo Aerospace
o Machinery
o Electricalo Fabrication
o Automotive
o Instrumentationo Mold making
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Chip producing machines:
Drills, Mills, Lathes, Bores, Saws, Etc.
Chipless machining:Flame Cutting, Punches, Wire EDM, Welding,
Non machining:
Paint Spraying, Tube Bending, Assembly, Etc.
APPLICATIONS OF NC MACHINES
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CNC TURNING
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CNC MILLING
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CNC LASER CUTTING
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CNC PLASMA CUTTING
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CNC PRESS
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CNC RAPID PROTOTYPING
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Mass production quantities
Complex geometries
Tight tolerances
Replacement parts
Parts subject to modification
Circumstances best suited to NC
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SAMPLE PRODUCTS
OFCNC MANUFACTURING
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AUTOMOTIVE INDUSTRY
Engine Block
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AUTOMOTIVE INDUSTRY(Contd)
Different Products
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AEROSPACE INDUSTRY
Aircraft Turbine Machined by
5-Axis CNC Milling Machine
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CNC MOLD MAKING
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ELECTRONIC INDUSTRY
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RAPID PROTOTYPING
PRODUCTS
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