**5.8 Post-process task**

572 Mechanical Engineering

lower the tolerance band, the closer will be the tool paths from the surface to be machined, however, smaller will be the followings segments of lines, CNC programs will possess greater volume of data, since more lines comprise the program and this characteristic will be able to limit the feed rate during machining, particularly in complex forms. The machine

The path of the tool calculated by a system CAM represents the central extremity of the tool, and by that, the path is not a simple offset of the surface it be machined. To develop the calculation, the software should identify two positions: a) Point of contact of the tool with the surface, known as CC - Cutter Contact and b) the point that represents the path of the

The lines of the programs CNC, referring the paths of the tool, contain the Cartesian information of each points CL. It must be noticed that the Cutter Contact is the point which should be inside this band of tolerance and not the path of the tool or the Cutter Location. Deferential ways exist to calculate both, the CC and CL. These algorithms are virtues of a CAM, therefore can have repercussions in the time of calculation, time of machining and quality of the surface machined. Initially, in a certain moment, and then it should calculate the final point the tool centre (CL) points that are linearly interpolated to generate the tool paths. An approach for calculate the CC in polynomial surfaces is the division of the own polygon of control of that describes the curve or surface. This subdivision can identify points about the curve or surfaces, which can be the CC. Others approaches are developed for such end. After it identified the CC, the CL must be calculated. The Figure 17 exemplifies a possibility to calculate the CL for two points of a path, considering that a previous algorithm already have found the CC. In this example, knowing to normal of the surface in the point desired (CC) and angle that this normal is found regarding the axis of the coordinates, is able to the

Due to the inconveniences of the traditional linear interpolation method for machining complex forms, an alternative is to use circular interpolation associated with linear

reduces the programmed feed rate, as studied by SOUZA & COELHO (2007).

Fig. 16. Tolerance to calculate the CNC programs

CL be found through the ray of the tool.

**5.7 Circular and linear tool path interpolation** 

tool (its central extremity), named of CL - Cutter Location.

After the CAM calculates and simulates the tool paths, there is the phase of post-processing, which is responsible for transforming these paths into CNC programs.

The initial calculation in the system CAM generates a generic file, without specifications. This file is known like Cutter Location File (CLF).

The post-processing has the function of encode the paths calculated by any software CAM in specific commands for a given configuration machine/CNC.

Therefore, two elements are necessary for create the program CNC:


For each equipment, machine/CNC should be developed a specific post-processor. The procedure for the creation of post-processors and development of programs CNC is presented in the Figure 18.

The information of the machine is related to its physical characteristics, as maxim movement of the axes, number of axes, speeds etc. Regarding the numerical control, there is a wide range of CNCs on the market today, ISO 66025 standardizes the main functions codes CNC. There are several distinctions among suppliers. The simplest cases involve, as example, the utilization of point or comma for separate decimal places; number of decimal places demanded; block end character need; command for beginning and end of program, among others.

Advanced Free Form Manufacturing by Computer Aided Systems – Cax 575

 The machining simulation stage was also costly. On some occasions the simulation does not detect collisions. Today, in addition to more accurate simulations are faster (gouge

 Great difficulty in limiting the work area when you wanted to perform machining in specific regions of a part, such as finishing or the use of a smaller diameter tool, for example. It was often necessary to use CAD to these limits (sometimes it is still convenient). These limits are known as borders or boundaries. Due to the difficulty in limiting areas of machining, the tool on many occasions it moved for a long time without removing material, to reach the region containing material to be removed.

 Software only for trajectories calculated for conventional geometries of the cutting tools. Currently, a range of tool geometries are available for calculating the trajectories. The variety of tool paths was extremely limited. There were few options for roughing and finishing. Today, the systems offer a wide variety of machining options, as the geometric shape. However, they still are not able to automatically identify the best

 The creation of a post-processor for a particular machine was not so simple. Today, although there are still challenges and specific problems, this step is already

Even with these difficulties, the use of CAM systems provided a significant evolution in the CNC programming process for the manufacture of moulds, dies and parts containing complex geometric shapes. After the mid-90s, industries requiring complex machining and

Today, CAM systems, 3-axis milling, are evolving at a level reaching its apex, the trajectories of the calculations and simulation. A market trend is the application of milling for 5 degrees of freedom. In this operation, apart from the machine and CNC, CAM system must also be

A CAD (Computer Aided Design/Drafting) has been developing to assist the design and part modelling through interaction with the computer which defines all geometric information necessary for manufacture. Currently there are a large number of systems

It should be aware that a CAD system may be more suitable for specific applications, and many of these systems should not be considered competitors. This is because there are CAD systems to meet product development activities and geometrical design which has powerful tools for modelling complex shapes, as well as CAD systems that supply more design functions properly. It is common to find companies working with 3D CAD systems

available in the market, ranging in a first classification between 2D and 3D systems.

Current systems allow the creation of boundaries very efficiently.

machining strategies. This work is based on the user experience.

did not have a platform CAD / CAM / CNC, were doomed to failure.

able to calculate trajectories and simulation.

**6. Application of CAD systems** 

inadequate to the tasks assigned.

to perform a specific machining.

free software).

consolidated.

preparations for the calculation, several programs with the variable set and other items, and end of the day, requesting the initiation of the calculations (Bach processing). The computer performed the calculations at night to use the CNC program the next day. Processing times are reduced, allowing even the possibility of studying different paths

In general, the post-processor is provided with the CAM software, and developed according to user requirements, and the CNC machine.

Fig. 18. Procedures required at this stage of post-processing generating CNC programs
