Manual Part Programming Formats

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Introduction

NC part programming consists of planning anddocumenting the sequence of processing steps tobe performed on an NC machine.

The documentation portion of part programminginvolves the input medium used to transmit theprogram of instructions to the NC machinecontrol unit.

Saturday, 06 July 2013 2Manual Part Programming Formats



Part programming can be accomplished using a variety of procedures ranging from highly manual to highly automated methods. Themethods are:

(1) Manual Part Programming(2) Computer-assisted Part Programming(3) Part Programming using CAD/CAM(4) Manual Data Input




Manual Part Programming

In manual part programming the codes are manually as per requirements followed by punching them onpaper tapes.

Part Program is the program required to machine a

specific part or component.

Require intimate knowledge about the processes.

NC part programmer should be a skill operator and

good part programmer for maximum utilization of machine capabilities and available resources like jigsand fixtures, cutting tools, without violating themachine constraints.




Fixed Sequential Format

The fixed sequential format requires thatspecific command data items be organizedtogether in a definite order to form a completestatement or block of information.

Every block must have exactly the samenumber of characters.

The significance of each character depends on

where it is located in the block.




The N/C controller has electronic pigeonholes called registers. Programinformation in the form of electronic pluses, minuses, and the digitszero (0) through nine (9) are placed into these registers.




The first register, the sequence number register,accepts four data characters, all numerals.

The second register, the preparatory functionregister, receives two numeral characters.

The third, fourth, and fifth registers, for the X-axis,

Y-axis, and Z-axis drives, respectively, receive sevencharacters each (the first of which must be a plus or a

minus sign ).

Registers six and seven are for feedrate and

miscellaneous commands. These registers receivefour and two characters each, respectively.




So with this particular fixed sequential

format structure, thirty-three charactersmust be entered into each and every blockand the seventh, fourteenth, and twenty-first characters must be a plus or minus sign

to indicate axis motion direction. A decimal is assumed (but not entered ) to

follow the ninth, sixteenth, twenty-third,and twenty-ninth character of each block.




Limitations :

No characters can be omitted and no extracharacters can be included because doing either will place other characters in the wrong register.

Blank spaces, called null characters, must be

used if no command data are to be given. Fixed sequential format requires that a fixed

number of data characters be entered in anexact sequence (No exceptions! ).

The specific number of characters, their order,and the assumed decimal placement can vary according to the make of controller.




Tab sequential format

The tab sequential format is just like the fixedsequential format except that null characters donot need to be placed into pigeon holes for whichthere are no data. Instead, a single character that

is produced by the “TAB” key on the data entry terminal is placed into all registers that aren't toreceive any data characters.

TAB tells the controller to "skip over" thoseregisters.




The nice thing about tab sequential formatting isthat program printouts are "columnized", making

the printout easier to read.

Otherwise, the tab sequential format is the sameas the fixed sequential format.

Both are obsolete (but still in use….)




Word address format

This format allowed the use of alphanumericcodes and the use of the special characters was also incorporated.

In this format not only can the sequence be

altered, one can also choose to skip theparameter that do not change from previousblock to the current block.

Eg: the value for speed, feed remainconstant for all the subsequent blocks untillaltered. Such functions are called MODALFUNCTIONS.




Coding Systems :

There are two standard coding systems currently

used in NC:(1) The Electronic Industry Association (EIA)

(2) The International Standards Organization (ISO).

The Electronics Industry Association system isknown as EIA RS-244-B.

The ISO code was originally developed as the American Standard Code for InformationInterchange (ASCII) and has been adopted by ISOas its NC standard.




NC words :

FEED RATE (F code):

This specifies the feed in machining operation. Units are

inches per minute ipm by convention.

PREPARATORY WORD (G code):This word is used to prepare the controller for instructions

that are to follow. For example, the word g02 is used to prepare

the NC controller unit for circular interpolation along an arc inthe clockwise direction. The preparatory word is needed so that

the controller can correctly interpret the data that follow it in the

block.




MISCELLANEOUS FUNCTION (M code):

The M code is used to specify certain miscellaneous or

auxiliary functions, which may be available on the machinetool. Of course, the machine must possess the function that is

being called. An example would be m03 to start the spindle

rotation. The miscellaneous function is the last word in the

block. To identify the end of the instruction, an end-of-block

EOB symbol is punched on the tape.

SEQUENCE NUMBER (N code):This is used to identify the block within an NC program

and provides a means by which NC commands may be rapidly

located.




CUTTING SPEED (S code):This specifies the cutting speed of the process, the rate at

which the spindle rotates.

TOOL SELECTION (T code):This code would be needed only for machines with a tool

turret or automatic tool changer. The t-word specifies whichtool is to be used in the operation.

COORDINATES (x-, y-, and z-words):These give the coordinate positions of the tool. In a two

axis system, only two of the words would be used. In a four- orfive-axis machine, additional a-words and/or b-words wouldspecify the angular positions.




The above figure shows all the codes used for NC manual part programming

using word address format




Example

Assume that a drilling operation is to be

programmed as:1. The tool is positioned at (25.4,12.5,0) by a rapid

movement.2. The tool is then advanced -10 mm in the zdirection at a feed rate of 500 mm/min., with theflood coolant on.

3. The is then retracted back 10 mm at the rapidfeed rate, and the coolant is turned off.




Program according to fixed sequential format

0010 00 +0025400 +0012500 +0000000 0000 000020 01 +0025400 +0012500 -0010000 0500 08

0030 00 +0025400 +0012500 +0000000 0000 09

Program according to tab sequential format

0010 TAB 00 TAB +0025400 TAB +0012500 TAB +0000000 TAB TAB0020 TAB 01 TAB TAB TAB -0010000 TAB 0500 TAB 08

0030 TAB 00 TAB TAB TAB -0000000 TAB 0000 TAB 09


Manual Part Programming Formats

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