CNC part program contains a combination of machine tool code and machine-specific instructions. It consists of:

(a) Information about part geometry

(b) Motion statements to move the cutting tool

(c) Cutting speed

(d) Feed

(e) Auxiliary functions such as coolant on and off, spindle direction

In this lecture, first we will understand the coordinate systems of the machine tools and how they work.

1. CNC Machine Tool

Figure 7.1.1 Schematic of a CNC machine Tool

Figure 7.1.1 shows a schematic of a machine tool controlled by a computer. It consists of a Machine Control Unit (MCU) and machine tool itself. MCU, a computer is the brain of a CNC machine tool. It reads the part programs and controls the machine tools operations. Then it decodes the part program to provide commands and instructions to the various control loops of the machine axes of motion. The details regarding the construction and working of mechatronics based system have already been studied in last lectures.

CNC systems have a limitation. If the same NC program is used on various machine tools, then it has to be loaded separately into each machine. This is time consuming and involves repetitive tasks. For this purpose direct numerical control (DNC) system is developed. Figure 7.1.2 shows the schematic of a DNC system. It consists of a central computer to which a group of CNC machine tools are connected via a communication network. The communication is usually carried out using a standard protocol such as TCP/IP or MAP. DNC system can be centrally monitored which is helpful when dealing with different operators, in different shifts, working on different machines.

 

Figure 7.1.2 Direct numerical control (DNC) system