Transcript Numerical Control I - Department of Engineering Technology

Numerical Control I
NC - Numerical Control - Software control of manufacturing processes.
Based on a code of letters, numbers & special characters called a program.
CNC- Computerized Numerical Control – NC machine with the addition of an on-board
computer referred to as a machine control unit or MCU
NC History
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1725-Knitting machine controlled by sheets of punched cardboard
1863-Player piano introduced
1947-John Parsons of Parsons Corp. in Traverse City, Michigan coupled a computer
to a jig borer
1952-MIT coins phrase “Numerical Control” & demonstrates vertical mill with
special control unit
1955-National Machine Tool Show, commercially available NC machines were
displayed
Improvements in electronics & solid-state devices reduced size of
control units and increased capabilities
Numerical Control I
Applications of NC
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.
NC used to
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Position cutter (move table)
Change tooling
Adjust coolant flow (flood/mist-on/off)
Adjust spindle speeds
Perform operations at a point (plunge, tap, bore, etc.)
Numerical Control I
STEPS INVOLVED ON GENERAL PURPOSE MACHINE:
Operation
Off Machine
Plan operation sequence
X
Select tools
X
Set and change tools
Select feeds and speeds
X
Set feeds and speeds
Position work
Start and stop machine operations
Control path between work & tool
during cutting
Rapid position tool for next cut or
part unloading
* Performed via Numerical Control software
On Machine
X
X*
X
X*
X
X
Numerical Control I
Circumstances best suited to NC
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Mass production quantities
Complex geometries
Tight tolerances
Replacement parts
Parts subject to modification
Numerical Control I
Advantages of Numerical Control
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Greater operator efficiency
Greater operator safety
Reduction of scrap
Reduced lead time for production
Fewer chances for human error
Maximal accuracy and interchangeability of parts
Lower tooling costs
Increased productivity
Minimal spare parts inventory
Greater machine tool safety
Fewer man hours for inspection
Greater machine utilization
Numerical Control I
Role of the Operator
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Execute Machine Control Unit (MCU) or Console Setups
Start and Stop Machines
Load and Unload Workpieces
Maintain High- Level Machine Tool Performance Standards
Change NC Inputs as Necessary (Per Engineering)
“Feedback” Information to Programmer/Engineer
Numerical Control I
Programming methods for NC
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MANUAL (#4)
COMPUTER ASSISTED
A) Language (#5A)
B) Graphic (#5B)
Numerical Control I
Two ways information is fed into an NC machine.
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Auxiliary Operations:
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Geometrical Machine Movements:
Tool change, spindle reversal, tool on/off, coolant on/off,
spindle speeds (RPM), spindle feeds (IPM)
a) Translation – X , Y , Z
b) Rotation – about X , Y , Z axis
Numerical Control I
Any movement under control of NC input is called an axis. (ie)
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2
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axis
axis
axis
axis
machine:
machine:
machine:
machine:
X,Y control (usually lathe)
X,Y,Z control
X,Y,Z, one rotational control
X,Y,Z, two rotational control
*often called machining centers and include tool changes…
Toshiba – 9 axis mill for sub propellers
Numerical Control I
To specify coordinate points to a machine tool, there are two
positioning point reference systems. (#7)
 Absolute:
all measurements are taken from a fixed origin (X=0,Y=0,Z=0)
*helpful to have part prints with baseline dimensioning*
 Incremental:
all measurements for the next position are made from the last
or previous position