Three methods can be used to control machines. The first is manually (mechanically) through pure physical manpower. The second is semi–automatically through automated mechanical drives combined with manpower. The third is automatically via programmed systems. Such an automatic process is the use of numerical control machine programs. NC refers to the control of manufacturing process by use of direct coded numerical instructions that are input to the machine tool. Numerical control is simply defined as a process that is run through the use of alphanumeric symbols or characters (Bone, 1986).
NC machine tool refers to the original numerically controlled machines that had a hardwired control. Control was done by the use of punched plastic cards that could easily wear or get dirty. These were problematic in that one had to reload the tapes for every new part, and the program could not be edited.
CNC machine tool was a development of the NC tool. This had included a computer to store all the numerical data required. Other storage means such as hard disks and magnetic tapes could be used in these computers. It became easier to execute and store large data well as allow programs to be edited easily.
After many years of the redevelopment of CNC, the Distributed Numerical control (DNC) was released. Unlike the CNC, a host (remote) computer is used to control a line of machines in DNC (Necsulescu, 2009). The programs used to run the machine tool are stored in a mainframe computer that is off the site. The programs downloaded from the host are fed into the local controller that in turn feeds the instructions to NC machine tool. A local network is used in communication between the computers.
2) CLDATA (cutter location data) designates the position which the CNC machine is instructed to hold the tool as instructed in the program. The files are generated from the paths specified in the manufacturing CNC sequence. The generated files are them passed to the machine specific processors for efficient communication.
APT is a high-level language that allows not only arithmetic operations, macros, and subroutines but also a parametric representation of single space to complex 3-d surfaces. It involves the use of four primary statements; motion, geometry, post processor and auxiliary.
Post processor refers to statements that are used in specific control systems and machine tools. They specify speeds, feeds and other features of the machine tool.
Circular interpolation- sometimes the NC does not have built-in functions for geometries that are complex in nature like parabolas and circles. Computer-assisted languages contain subroutines that can be used for calculating these points automatically. Circular interpolation is one of the subroutines used to generate circular clockwise or counterclockwise profiles (Leslie, 1978).
G and M codes are sets of codes used in CNC programming system. The G codes are preparatory functions that represent the specific movement of the tool geometry and axes. M codes, on the other hand, represent miscellaneous functions used to operate controls in the CNC system. Such controls include tool change, stopping tool rotation and coolant supply.
3) N represents the sequence number used for identification
G represents the preparatory function that describes the geometry or axes movement.
M represents auxiliary functions for operation control purposes.
S refers to the spindle speed
F designates the federate and.'
T designates the tool (Leondes, 2003).
References
Necsulescu, D. (2009). Advanced mechatronics. Singapore: World Scientific.
Leslie, W. (1978). Numerical control and computer-aided manufacture. Computer-Aided Design, 10(1), p.88.
Leondes, C. (2003). Computer aided and integrated manufacturing systems. Singapore: World Scientific.
Bone, J. (1986). Opportunities in computer-aided design and manufacturing. Lincolnwood, Ill., U.S.A.
