To describe desired work part program is used. The part program is given in a sequence of instructions read by computers using numerical control computer programs. In part programming drawing sheet is converted into part programming. Data required by the control system is converted into a format that is acceptable by the numerical control system.
Programs are used to compile the data contained in the numerical control system and convert it into a format that is acceptable by the control system. The data that is acceptable by the control system consists of process classification, start-up point of the tool, depth of cutting, the path of the tool, etc. data also describes the speed of the spindle, rate of feeding, coolant conditions, and conditions under which cutting will be done. The data also consists of conditions under which cutting tolls will be selected.
The part program is developed using information about what amount of dimensional data will be extracted from the part drawings and information related to level surface quality to be achieved. The part program also provides selection criteria of tools and what should be the appropriate offset of the tool.
The part program also describes the zero position that should be used for a particular workspace. The part also has instructions that should be used to set the speed and rotation required for the spindle. The part program contains information related to the motion of the tools required to develop a particular profile. The part program sets the cutting tool at the desired location when the required work is completed. When the work is completed part program stops the spindle and coolant.
The part program works according to the X, Y, and Z coordinates to set the path of the tool. The pat program contains information related to feed and speed. The information used by the part program to accomplish a particular task is known as the NC word. When these NC words are combined together it is known as NC instructions and these NC instructions are combined together to form blocks.
Part programming is accomplished using two types of methods and these methods depend on two types of techniques. This technique includes Manual part programming and Computer-aided part programming.
In Manual part programming, the manuscript is developed in a particular standard format. The manuscript of the program is written using a flexo writer. The flexo writer is also used to write programming instructions. When the program is completed the flex writer prepares punch tape. The more complex is the shape of the component the more complex is the calculation required to attain that shape. Part programming is more suitable for machine parts that are simple and these parts are developed using machinery that is point-to-point.
Manual part programs can also be developed if information related to the manufacturing process and information related to machines is known, if it is known what amount of information is to perform for a particular component, if parameters of cutting are known, and if it is known what type of codes and functions to used in the part programs.
If the shape of the component is complex and requires heavy calculations then Computer-Aided Part programming is used. Programmers can use programming languages to make communication with the system, the programming language used are ADAPT, APT, 2CL SPLIT etc. These languages are used to develop computer-aided part programs.
The programmers of part programming define the geometry of the work part, define the work that requires repetitions, and gives the sequence of operations. The programmers also consider the dimensions to be used by the system, the number of axes to be used, the path of the machine tool is also considered to decide whether the path is continuous or point-to-point. The programmer also considers the NC words. One NC word corresponds to one NC instruction.
NC instructions are given in word blocks. Machine Control Unit is able to read a block consisting of 5 words, if the block does not contain 5 words then it omits that block. Each word in the block consist of a code and each code has its own function associated with it.
Some of the codes that are common in part programming include – G-codes that are related to preparatory functions and M codes that are related to miscellaneous functions. In the same wary F, code is used for feed, S is used for speed, D is used to denote offset of diameter cutter, T is used to denote the tool number.
M code is miscellaneous code and is used to denote ON and OFF conditions of functions. M codes are responsible to handle machine operations. To stop a program M00 code is used, to end a program M02 code is used, to start the spindle M03 code is used, to stop the spindle M05 code is used, to change tool M06 code is used, to turn on coolant M08 code is used and to turn off coolant M09 code is used.
Three types of formats are used to compile NC data. These formats include Word Address Format, Tab Sequential Format, and Fixed Block format.
Word address format use alphabet. These alphabets are known as addresses. This format is most compatible with the NC machines or it can be said that this format is compatible with variable blocks.
Tab sequential format uses tab codes. These tab codes separate two words. The Machine Control Units control these tab codes.
Fixed block formats do not use Tab code letter addresses and fixed block format can not omit words. The fixed block format can read the whole block at once instead of fetching characters one at a time.
The Zero point of the machine can be set manually using zero shift and by using coordinates. When the zero points are set manually Machine Control Unit moves the spindle to the desired part zero and then fixes the X and Y coordinate registers to the desired part.
The absolute zero shift uses the CNC program command to set the coordinates. The program manages the movement of the spindle. Using the program command spindle can be moved from the home location denoted by zero to the desired location denoted by coordinates.
To specify the distance up to which the tool has to be moved coordinate words are used. The word specifies the address to which the tool has to be moved and the word also specifies the value and the desired direction towards which the movement has to be done.
S address is used to command the spindle speed, and the spindle speed is measured in revolution per minute. Spindle speed is the ratio of the speed at which the surface is cut to the diameter cutter multiplied by the pie value.
Spindle Speed = Surface cutting speed in m/min * 1000 / 3.14* Diameter Cutter in mm
The tool is selected using the T address. For example, if the programmer wants to select tool 4 then it is represented by T04.