NC Part Programs:
Part Program is a set of
instructions proposed to get machined part starting with desired blank and NC
machine tool. Each line of instruction is capable of specifying dimension and
dimension data. Each line is written in specific format and is known as NC
block.
General Format:
n g x y z a b f s
t m eob
n= sequence number
g= preparatory function
x y z a b = dimension data
f = feed function
s= speed function
t= tool function
m= miscellaneous function
eob= end of block
Program to input media:
Program has to be converted into a medium acceptable to
machine control unit. Paper tape was used previously but nowadays computers are
used to directly feed the program into the machine tool. Information blocks of
program are converted into punched tape and hole patterns in the tape correspond
to various characters in program. Tape is usually 1" wide and punching is
done on a typewriter like machine (FlexowriterTM).
The codes, for punching holes in the tape, are
standardized by EIA, ISO &
ASCII. The codes, which are used for NC data mostly, represent the information
in two discrete positions, i.e binary system of representation.
A binary system takes the number 2 as base and there are two digits
0 and 1 which are used to represent various numbers.
1 can stand for ON PULSE HOLE PRESENT TRUE
0 can
stand for OFF
NO PULSE NO HOLE
ABSENT
FALSE
Machine
Control units can effectively process digital signals, i.e. Pulse (high Voltage)
and no pulse (low Voltage) using binary concept. Thus various characters can be
represented in terms of presence and absence of holes which in turn can be
represented electronically by presence /absence of pulse.
Pure
binary system is rarely used in NC machines. More sophisticated BCD (Binary
Coded Decimal) system is used.