Mastering CNC Programming: G-Code & M-Code Essentials

CNC programming is alphanumeric formatting data (G and M codes) on geometry and technology of parts, which needs to be processed on such a machine, but also another programming, which they usually perform machine manufacturers.

Programming CNC machines using G code is mostly sentence-based, which can be seen in previous examples where the explanation of G functions was done as interpreting the sentences of a program written in G code. There are several methods of CNC programming, i.e. generating G and M codes:

1. Manual programming,
2. Programming in operation and
3. Programming using CAD (Computer-Aided Design)/ CAM (Computer-Aided Manufacturing) systems.

Manual Programming

With manual CNC programming, a programmer based on his own knowledge and experience as well available information on machines, tools, machine accessories, processing modes, applying programming instructions, manually writes geometric and technological information required to complete the alphanumeric program. Manual programming can be organized as the following basic activities:

• Defining processing, basing, and tooling plans,
• Translating geometric information with workshop drawing, for route planning purposes
• Tools, and arranging them into blocks according to processing order,
• Writing and completing programs in the form program sheet (G code) and
• Transfer of information from the program sheet to control unit memory

Programming in operation

In order to constantly improve the method of CNC programming, as well as the desire to put the programming on the machine itself, in order to still larger and easier applications of CNC, some manufacturers have offered control units that they support programming directly on the machine itself. Although from the very beginning of the application of CNC there was the possibility of immediate programming on the machine in the so-called MDI (Manual Data Input) mode, programming in operation represents a completely new method of programming.

With this method, the Control Unit, which supports it, has integrated additional functions that are avoided classical programming using G code. Programming here comes down to interactive dialogue between the operator and the control unit, via keyboard and graphical user interface, which can generate simple processing contours as well as typed cycles for processing. Control unit based on entered queries, performs the necessary tool path calculations, and automatically generates a G code.

Programming using CAD/CAM systems

The geometry of the parts, used for example in the aerospace, military, and other industries, is very complex with second-order surfaces, which require multi-axis machining (3-axis, 4-axis, and 5-axis CNC machining). Complex programs for processing such surfaces require several thousand blocks (sentences) whose handwriting is very hard and time-consuming. Therefore, it was necessary to use computers for technological preparation, i.e. programming of CNC machines for machining the above-mentioned parts on the basis of G code and M code.

CAD / CAM programming can be classified as computer CNC programming. The integration of CAD and CAM has led to improvements in NC programming, especially in terms of programming simplification. Now the programmer doesn’t have to think about defining geometry, that’s what CAD / CAM software does. What remains for the programmer is that through active interaction with the system in the program, he adds other technical information such as grips, basing, clamping, cutting tools, and processing modes. It should be emphasized that there is an integration of CAD / CAM and CAPP (Computer Aided Process Planning), which develops a solution for these requirements as well.

This is what the Procedure for programming a machine in a CAD / CAM environment looks like:

1. Modeling of CAD models,
2. Processing planning using available CAM strategies for processing and calculating tool paths and obtaining CL (Cutter Location) file,
3. Tool path simulation and material removal simulation for program verification and detection of possible errors and collisions,
4. Post processing the CL file and obtaining the G code using the postprocessor for the selected machine,
5. Transfer the G code to the control unit. Preparation of tools and workpieces. Base the workpiece on the machine,
6. Check processing conditions and modes, check speeds and accelerations, which can significantly affect the quality of processing and
7. Machining of a workpiece on a machine.