Post on 07-Apr-2018
transcript
8/4/2019 Introduction to NC2
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Introduction to NC/CNC
8/4/2019 Introduction to NC2
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Definitions of NC/CNC
• Numerical Control (NC) is the term used to
describe the control of machine movements
and various other functions by instructions
expressed as a series of numbers and initiated
via an electronic control system.
Consequently, Computer Numerical Control
(CNC) is the term used when the electroniccontrol system is influenced by a computer. [1]
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Definitions of NC/CNC cont.
• Numerical Control (NC) is the operation of a machine tool by a
series of coded instructions consisting of numbers, letters of
the alphabet and symbols that the machine control unit
(MCU) can understand. These instructions are converted into
electrical pulses of current that the machine’s motors and
controls follow to carry out machining operations on a
workpiece. The numbers, letters and symbols are coded
instructions that refer to specific distances, positions,
functions or motions which the machine tool can understandas it machines the workpiece. [2]
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Definitions of NC/CNC cont.
• Computer Numerical Control is the control of
a machine tool using numbers and letters. It is
a system in which programmed numerical
values are directly inserted and stored on
some form of input medium and automatically
read and decode to cause a corresponding
movement in the machine which it iscontrolling.[4]
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Definitions of NC/CNC cont.
• CNC is the process of manufacturing
machined parts using a computerizedcontroller to command motors which
drive each machine axis
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Effect of NC/CNC in
Manufacturing
• NC and CNC have changed the manufacturing industry more
specifically the metalworking industry.[2]
• Machines that are combined with NC or CNC can produce and
fabricate parts with an accuracy that is nearly impossible to
achieve by human operators. [2]
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Effect of NC/CNC in
Manufacturing cont.
• Furthermore, these parts can be replicated
many times over given that the NC or CNC
controls and commands allow it.[2]
• The operating commands that control the
machine tool are executed automatically with
amazing speed, accuracy, efficiency and
repeatability. [2]
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Effect of NC/CNC in
Manufacturing cont.
Reasons for using CNC/NC [3]:
• Increase production throughput
•
Improve the quality and accuracy of manufactured parts
• Stabilize manufacturing costs
•
Manufacture complex or otherwise impossible jobs – 2D and 3D contours
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Getting to Know the CNC
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CNC Manufacturing Process
Machine Tool Control
SlideMovement
SpindleRotation
ToolingWork
HoldingSupporting
Function
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CNC Manufacturing Process cont.
Spindle Rotation
- Control of machine spindles are driven directly
or indirectly by electric motors.
- The speed of the spindle is often infinitely
variable and will automatically changes as
cutting is taking place to maintain a
programmed surface speed.
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CNC Manufacturing Process cont.
Tooling
- may incorporate turrets or magazines which
hold a number of cutting tools.
- The machine controller can be programmed to
cause indexing of the turret or magazine to
present a new cutting tool to the work or to
facilitate tool removal and replacement where
automatic tool-changing devices are involved.
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CNC Manufacturing Process cont.
Work holding
- can be fairly conventional: vices, chucks,
collets and fixtures are all used.
- The NC can extend to loading the workpiece
by the use of robots and securely clamping it
by activating hydraulic or pneumatic clamping
systems.
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CNC Manufacturing Process cont.
Supporting functions
- supplementary functions that are done during
machining which might be vital to the success
of the operation.
- Tool monitoring might also fall under this
category.
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Machining Process
• Roughing
•
Semi Roughing
• Semi Finishing
• Finishing
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History of NC/CNC
• 1947 Developed a control system that
directed a spindle to many points in
succession
• 1951 Added computer to Parson’s system
• 1952 Cincinnati Milicron Hydro-Tel Vertical
Spindle Milling Machine
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History of NC/CNC cont.
• 1954 NC was announced in public
•
1957 First production NC machines weredelivered and installed
•
1960 NC machine tool commonly available
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Advantages of NC/CNC
• Flexibility of operation is improved, as is the
ability to produce complex shapes with good
dimensional accuracy, repeatability, reduced
scrap loss, and high production rates,productivity and product quality
• Tooling costs are reduced, since templates and
other fixtures are not required.
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Advantages of NC/CNC cont.
• Machine adjustments are easy to make with
microcomputers and digital readouts
• Simplified inspection. Once the first piece has
passed inspection, minimal inspection is
required on subsequent parts
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Advantages of NC/CNC cont.
• Faster prototype production is possible.
•
Required operator skill is less than that for aqualified machinist, and the operator has
more time to attend to other tasks in the work
area.
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Limitations of NC/CNC
• Relatively high initial cost of the equipment.
•
The need and cost for programming andcomputer time.
•
Special maintenance with trained personnel.
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Limitations of NC/CNC cont.
• High preventative maintenance since
breakdowns is costly.
• Tools on NC machines do not cut metal any
faster than conventional machines
• NC does not eliminate the need for expensive
tools.
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Limitations of NC/CNC cont.
• NC will not totally eliminate errors. Operators
can still fail to push the correct buttons, make
incorrect alignments and fail to locate parts
properly in a fixture.
• Physical limitations
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Thank You