18-01-2013, 02:40 PM
FUNDAMENTALS OF PART PROGRAMMING
FUNDAMENTALS.pdf (Size: 500.74 KB / Downloads: 307)
INTRODUCTION
Types of part programming, Computer aided part programming, Part programming manual, Part programme using sub routines, do loops and fixed cycles are described in this Unit.
TYPES OF PART PROGRAMMING
The part program is a sequence of instructions, which describe the work, which has to be done on a part, in the form required by a computer under the control of a numerical control computer program. It is the task of preparing a program sheet from a drawing sheet. All data is fed into the numerical control system using a standardized format. Programming is where all the machining data are compiled and where the data are translated into a language which can be understood by the control system of the machine tool. The machining data is as follows :
(a) Machining sequence classification of process, tool start up point, cutting depth, tool path, etc.
(b) Cutting conditions, spindle speed, feed rate, coolant, etc.
© Selection of cutting tools.
While preparing a part program, need to perform the following steps :
(a) Determine the startup procedure, which includes the extraction of dimensional data from part drawings and data regarding surface quality requirements on the machined component.
(b) Select the tool and determine the tool offset.
© Set up the zero position for the workpiece.
(d) Select the speed and rotation of the spindle.
(e) Set up the tool motions according to the profile required.
(f) Return the cutting tool to the reference point after completion of work.
(g) End the program by stopping the spindle and coolant.
The part programming contains the list of coordinate values along the X, Y and Z directions of the entire tool path to finish the component. The program should also contain information, such as feed and speed. Each of the necessary instructions for a particular operation given in the part program is known as an NC word. A group of such NC words constitutes a complete NC instruction, known as block. The commonly used words are N, G, F, S, T, and M. The same is explained later on through examples.
Manual Part Programming
The programmer first prepares the program manuscript in a standard format. Manuscripts are typed with a device known as flexo writer, which is also used to type the program instructions. After the program is typed, the punched tape is prepared on the flexo writer. Complex shaped components require tedious calculations. This type of programming is carried out for simple machining parts produced on point-to-point machine tool.
To be able to create a part program manually, need the following information :
(a) Knowledge about various manufacturing processes and machines.
(b) Sequence of operations to be performed for a given component.
© Knowledge of the selection of cutting parameters.
(d) Editing the part program according to the design changes.
(e) Knowledge about the codes and functions used in part programs.
Computer Aided Part Programming
If the complex-shaped component requires calculations to produce the component are done by the programming software contained in the computer. The programmer communicates with this system through the system language, which is based on words. There are various programming languages developed in the recent past, such as APT (Automatically Programmed Tools), ADAPT, AUTOSPOT, COMPAT-II, 2CL, ROMANCE, SPLIT is used for writing a computer programme, which has English like statements. A translator known as compiler program is used to translate it in a form acceptable to MCU.
Standard G and M Codes
The most common codes used when programming NC machines tools are G-codes (preparatory functions), and M codes (miscellaneous functions). Other codes such as F, S, D, and T are used for machine functions such as feed, speed, cutter diameter offset, tool number, etc. G-codes are sometimes called cycle codes because they refer to some action occurring on the X, Y, and/or Z-axis of a machine tool. The G-codes are grouped into categories such as Group 01, containing codes G00, G01, G02, G03, which cause some movement of the machine table or head. Group 03 includes either absolute or incremental programming. A G00 code rapidly positions the cutting tool while it is above the workpiece from one point to another point on a job. During the rapid traverse movement, either the X or Y-axis can be moved individually or both axes can be moved at the same time. The rate of rapid travel varies from machine to machine.