Since CNC machine tools are capable of producing more complex workpieces than conventional ones, tool path generation for CNC machine tools has become important. Tool path generation for sophisticated parts is complicated; therefore special software programs are needed to achieve this task.

The software that are developed for this purpose are called Computer Aided Manufacturing (CAM) software . By means of these CAM software, complex parts can be machined more easily.

Today there are many commercially available CAM software in the market. Some of these programs are standalone CAM software and some of them are integrated with a CAD software. The workpiece model, which is prepared using CAD software , is transferred to CAM software in a suitable data transfer format. After that, the raw material, which the workpiece will be machined from, is defined. The initial raw material can be in various forms. It can be a forged, cast or a block material having any geometry.

All the necessary parameters are input to the CAM software. These parameters are; the selection of suitable tool and tool diameter, the depth and width of cut for each cuts, the selected surfaces to be machined for finishing operations and the cutting feed of the tool. In addition to this basic information, CAM software also allows user to specify some other specific information for advanced applications. For instance, with a conventional milling machine tool, it depends on the operators ability to adjust tool and workpiece first touch conditions; the plunge feed, the approach distance, the approach type and approach angle of the tool to the workpiece. This is almost impossible to adjust properly in a conventional milling machine. However, CNC machine tools are capable of adjusting these parameters with proper selections in CAM software. While creating the tool path for machining, the CAM software user can easily specify this information.

Tool path generation is much more complicated for five-axis milling operations because of the nature of the five-axis milling processes. In a three-axis machine tool, the cutting tool always orients along Z-Axis with respect to the machine coordinate system. However, in a multi-axis machine tool while performing advanced finishing operations, the cutting tool can be in any orientation with respect to the workpiece. The tool can be positioned perpendicular or in any desired orientation to the workpiece surfaces.

In multi-axis milling CAM operations , the user can adjust the position of the cutting tool in any desired orientation. And several different combinations of different milling strategies with different cutting tool orientations are in use in industry for various purposes like increasing tool life or increasing surface quality.

By means of CAM programs, the user can create the required tool path for machining operation. The generated tool path is in the APTSoruce or CL (Cutter Location) Data Format (note: in some CAM programs generating CL files is not possible, instead you directly generate G-code) All the cutting information is stored in CL-Data file. The spindle speed, the cutting, plunge and retract feedrates, the coolant condition and most importantly the motions that will be performed are all included in CL-Data file.

The APTSource and CL-Data file created using any CAM program includes the machining information, however, this format is not suitable to use in any machine tools directly. The CNC Machine tools recognize NC-Code (a.k.a. G-Code) format for machining. Therefore CL-Data has to be converted to G-Code with an operation named postprocessing. Postprocessing is a step that converts the CL-Data format into G-Code format. The G-Code created will directly be used for machining. The G-Code is the recommended standard (EIA RS 274 D) for numerically controlled machines developed by the Electronic Industry Association (EIA).

Some other important issues must be performed while performing postprocessing. In the CL-Data format, machine tool parameters are not specified. Some of these machine tool parameters are; machine tool motion axes, travel limits of these motion axes and positions of rotating axes. These parameters are very important for postprocessing. For instance, when a five-axis CNC machine tool is considered which has a rotating and tilting table, the travel limits on rotational axes may cause changing of the required machining code (i.e. G-Code) extensively. For the same job, a machine tool with A-Axis limits of -90º and 0º will need a different G-Code and a machine tool with A-Axis limits of -30º, +90º will need a completely different G-Code. If the same G-Codes is used in different machine tools without considering the machine parameters, the result will be a fatal error, which can cause a collision between spindle, cutting tool, table or workpiece. The broken cutting tools, deformed workpieces and most importantly damaged machine tool components will cause high costs and big losses in productivity. Therefore, these machine parameters must be taken into account while creating a proper postprocessor for multi-axis milling operations.

The machine parameters are specific for each five-axis CNC machine tool. Even for machine tools with similar configurations, these machine parameters vary reasonably. Furthermore, today there are many five-axis machine tools, which have completely different configurations, on the market and these machine tools have totally different machine parameters. This means that any machining code that will be prepared have to be specific for the particular machine tool whether the created tool paths are the same or not. These circumstances make five-axis machining works more sophisticated and troublesome and make the postprocessing an important machine code preparation step and it is obvious that without a proper postprocessor, it is almost impossible to operate five-axis CNC machine tools.

Some CAM programs have also modules for postprocessing. These are interactive programs where the user can define technical specifications of the machine tool, and the package program creates the required postprocessor.

Postprocessor preparation capabilities of these programs are generally sufficient when postprocessors have to be designed for three-axis CNC milling machine tools or two-axis CNC lathes. However, their capabilities are limited and they are insufficient for complex multi-axis postprocessor design.