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UNIT 7
Computer Numerical
Control
CNC
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Evolution of Machine Tools
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Evolution of Machine Tools
First Milestone: Application ofPower
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Evolution of Machine Tools
Maudsleys Screw Cutting Machine is secondmilestone in machine
tools in which spindle andtool motion were synchronied
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Copying arrangement for Machining is thirdmilestone in
automation in which hardtemplates!masters were used to
machinecomponents"
Evolution of Machine Tools
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#n$process gauging is a fourth milestone
Evolution of Machine Tools
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Evolution of Machine Tools
CNC or Computer Numerical Control is a term derived from %Cor
%umerical Control.
NC refers to Control of a process or automatic operation of a
machine by using symbolic codes
consisting of characters and numbers.
NC was introduced in late 40s to control machine tools such as
!rilling and "illing machines. #ne of
the $rst applications of NC machine tool was in production of
helicopter rotor blades andship
propellers.
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CNC % Computer Numerical Control
Conventionally& an operator decides and ad'ustsvarious
machines parameters li(e feed & depth of cutetc depending on
type of 'ob & and controls the slidemovements by hand. In a CNC
"achine functions and
slide movements are controlled by motors usingcomputer
programs.
)art)rogram
"achineControl
Unit
"achine
Components #f a CNC *ystem
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CNC % Computer Numerical Control
)+,T ),#-,+"
*et of Instructions
ach instruction speci$es a particular operation to be
done
Can be written manually or automated
+ll instructions wor( towards achieving the $naldimension of the
wor(piece from its initial geometry
Instructions include% Tool motion& /eed rate&
*pindlespeed& tool change& coolant ono1 and many others
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Computer NumericalControl
)unched Tape
)+,T ),#-,+"
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CNC % Computer Numerical Control
"achine Control Unit 2"CU3
Converts instructions into electrical signals
*ends these signals to motors and other components toperform the
speci$ed function
-athers feed bac( signals from the machine tool
+d'usts machining parameters as per feed bac(
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Classi$cation of CNC *ystems
Type of Tool"otion
-)oint to )oint2)T)3-Continous
Coordinate*ystem
-Incremental-+bsolute
Type of /eed 5ac(
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#pen 6oop-Closed 6oop
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)oint to )oint *ystems
!rilling oles& Tapping& )robe based Inspection
usingC""& 8elding& )ic( and )lace operations&
,ivetting
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Continuous path system
*traight )ath Contour
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+bsolute Coordinatesystem
9
y
+. 29:;&y:& y:73
!. 29:?& y:=3
-#T# @:;&
A:&A:7-#T# @:?&
A:=
20&03
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Incremental Coordinatesystem
+. 29:;&y:& y:73
-#T# @:B&A :;
20&03 for )oint !
!. 29:?& y:=3
-#T# @: ;&A:B
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+bsolute and Incremental*ystems
In the +bsolute system& Interruptions caused by&
fore9ample& tool brea(age 2or tool change& or chec(ing
theparts3& would not a1ect the position at the
interruption.
asy change of dimensional data +bsolute *ystem
Incremental *ystem Useful for cycles and mirroring
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D igher Ee9ibilityD Increased productivity
D Improved Fuality
D ,educed scrap rateD ,eliable and *afe operation
D *maller footprint
+dvantages of CNC
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&ideo Time
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