PART PROGRAMMING FOR CNC
The transfer of an engineering blueprint of a product to a part program can be performed
manually using a calculator or with the assistance of a computer language. A part programmer
must have an extensive knowledge of the machining processes and the capabilities of the
machine tools . In this section, we describe how the part programmers execute manually the
part programs.
First, the machining parameters are determined . Second, the optimal sequence of operations
is evaluated . Third, the tool path is calculated . Fourth, a program is written. Each line of the
program, referred to as a block, contains the required data for transfer from one point to the
next.
A typical line for a program is given below.
N100 G91 X -5.0 Y7 .0 F100 S200 T01 M03 (EOB)
The significance of each term is explained below.
Sequence Number : N
Consisting of typically three digits, its purpose is to identify the specific machining operation
through the block number particularly when testing a part program.
Preparatory Function, G
It prepares the MCU circuits to perform a specific operation . The G-codes (some) are shown
in Table 1 . G91 implies incremental mode of operation.
Dimension Words
1 . Distance dimension words, X,Y,Z
2 . Circular dimension words, I,J,K for distances to the arc center
3 . Angular dimensions, A,B.C
PART PROGRAMMING FOR CNC
While (1) and (3) are expressed either by incremental or absolute mode, (2) is always in given
in incremental mode. All angular dimensions are specified in revolutions or degrees.
In the above block, X moves a distance of 5 in. in the negative direction while Y moves a
distance of 7 in. in the positive direction. Other axes remain stationary. In some systems,
actual distances are used. In others, the dimension words are programmed in BLUs.
Feed rate: F
It is expressed in in/min or mm/min and, is used in contouring or point-to-point or straight-cut
systems. For example, a feed rate of F100 implies 100 in/min or 100 mm/min. Feed rates are
independent of spindle speed.
F = [(part contour radius ± tool radius)/part contour radius] (required feed rate)
In linear motions, the feed rate of the cutting tool is not corrected for the cutter radius . But
in circular motions, the feed rate should be corrected for the tool radius as follows :
For cutting around the outside of a circle, the plus sign in the above equation is used, and the
feed rate is increased. For cutting around the inside of a circle, the minus sign is used, and the
feed rate is decreased .
Spindle speed: S
Programmed in rev/min, it is expressed as RPM or by a three-digit code number that is
related to the RPM.
Tool word:T
Consisting of a maximum of five digits, each cutting tool has a different code number. The
tool is automatically selected by the automatic tool changer when the code number is
programmed in a block.
Miscellaneous Function:M
Consisting of two digits, this word relates to the movement of the machine in terms of spindle
on/off, coolant on/off etc shown in Table 2.
EOB(End of Block):
The EOB character is used at the end of each block to complete a line.
manually using a calculator or with the assistance of a computer language. A part programmer
must have an extensive knowledge of the machining processes and the capabilities of the
machine tools . In this section, we describe how the part programmers execute manually the
part programs.
First, the machining parameters are determined . Second, the optimal sequence of operations
is evaluated . Third, the tool path is calculated . Fourth, a program is written. Each line of the
program, referred to as a block, contains the required data for transfer from one point to the
next.
A typical line for a program is given below.
N100 G91 X -5.0 Y7 .0 F100 S200 T01 M03 (EOB)
The significance of each term is explained below.
Sequence Number : N
Consisting of typically three digits, its purpose is to identify the specific machining operation
through the block number particularly when testing a part program.
Preparatory Function, G
It prepares the MCU circuits to perform a specific operation . The G-codes (some) are shown
in Table 1 . G91 implies incremental mode of operation.
Dimension Words
1 . Distance dimension words, X,Y,Z
2 . Circular dimension words, I,J,K for distances to the arc center
3 . Angular dimensions, A,B.C
PART PROGRAMMING FOR CNC
While (1) and (3) are expressed either by incremental or absolute mode, (2) is always in given
in incremental mode. All angular dimensions are specified in revolutions or degrees.
In the above block, X moves a distance of 5 in. in the negative direction while Y moves a
distance of 7 in. in the positive direction. Other axes remain stationary. In some systems,
actual distances are used. In others, the dimension words are programmed in BLUs.
Feed rate: F
It is expressed in in/min or mm/min and, is used in contouring or point-to-point or straight-cut
systems. For example, a feed rate of F100 implies 100 in/min or 100 mm/min. Feed rates are
independent of spindle speed.
F = [(part contour radius ± tool radius)/part contour radius] (required feed rate)
In linear motions, the feed rate of the cutting tool is not corrected for the cutter radius . But
in circular motions, the feed rate should be corrected for the tool radius as follows :
For cutting around the outside of a circle, the plus sign in the above equation is used, and the
feed rate is increased. For cutting around the inside of a circle, the minus sign is used, and the
feed rate is decreased .
Spindle speed: S
Programmed in rev/min, it is expressed as RPM or by a three-digit code number that is
related to the RPM.
Tool word:T
Consisting of a maximum of five digits, each cutting tool has a different code number. The
tool is automatically selected by the automatic tool changer when the code number is
programmed in a block.
Miscellaneous Function:M
Consisting of two digits, this word relates to the movement of the machine in terms of spindle
on/off, coolant on/off etc shown in Table 2.
EOB(End of Block):
The EOB character is used at the end of each block to complete a line.
Comments
Post a Comment