**5.5 Simulation of the machining in the CAM software**

The phase of simulation can possess different objectives:

a. **Verify undesired tool invasions into the part (gouge)**. These invasions can occur either due to error during tool path calculation (software) or by misconceptions of the user, in the definitions of the movements and specific settings.

Advanced Free Form Manufacturing by Computer Aided Systems – Cax 571

the program CNC that will go for the machine. The program CNC is created starting from the paths, in a phase named post-processing, detailed it follow. Mainly in the machining 5 axes, errors can occur in the post-processing. A simulation carried out in the CAM cannot correspond with some movements of the machine, being able to cause collisions. Specific software for simulation exists of the program CNC and of the machine. This simulation

The calculation of the tool path is the main function of the software CAM. The result of the final part is straightly related with the quality of the tool path, implying in the quality of the surface machined, dimensional errors and times of path calculation and real machining. The algorithms and the methodologies for tool path calculation are developed by each software

In the current procedure used for most commercial CAM codes to generate free form tool paths, the system first calculates the cutter-contact points (CC) over the 3D CAD geometry. Then the tool offset is included resulting in the cutter-location (CL) points, which are used to generate the NC program blocks; using the traditional method to create a free-form tool path, i.e., the linear interpolation of straight-line segments, with continuity C0. These CL points are easily transformed into the ordinary G01 CNC code, according to DIN 66025.

Points of the CNC

program

The length of these segments is related with the tolerances of calculation in the CAM and the degree of curvature of the surface. The CAM software adjusts the tool path segment lengths to fit inside a tolerance band defined by the user, known as "chord error". The smaller the tolerance band, the closer the tool path will be it to you the original CAD 3D model. The smaller the tolerance band, the closer the tool path will be to the original CAD 3D model. Thus linear segments are generated by such a procedure and, for highly curved paths, the number of segments increases dramatically, along with the CNC program size. The Figure 16 shows the influence of the curvature of the surface in the length of the segments of straight lines of a program CNC, calculated inside a same band of tolerance.

Some CAM systems allow to establish through a band of variation, limits of tolerances with the possibility of deviation from the path inward and/or for outward of the geometry. The

**5.6 An introduction to tool path calculation for free form geometries** 

confers bigger security to the trial.

house, and represent industrial secrets.

Fig. 15. Points that describe a complex tool path for milling


Advanced CAM, beyond identify the areas of possible collisions, the software can identifies the maximum depth that the system tool/tool holder can reach without collisions; divides the path in a first one breaks (that will be the first program CNC), as far as the system can achieve, and for the near depth (second program CNC), the CAM identifies the length of necessary. In this way, the initial path, with a smaller length should be more stable, as regards vibrations, and by that, can be quicker. Already in the second programs the user should have bigger caution in the machining. This can be an important aid in the CNC programming by the software CAM.


Fig. 14. Simulation of CNC machining considering the machine

Due to complexity of the milling 5 axes, the simulation CAM can take a significant time in this manufacturing process.

It is important to note that in all these simulation steps presented above are used to simulate the tool paths in the computational format of the software CAM. These paths do not be still

b. **Verify tool path adequacy after calculation**. Due to the big cut strategies range, associated to the diversity of geometrical forms, even for experienced users, in many cases, barely is possible estimate the quality and adaptation of the path calculated,

c. **Verify tool path collisions according to tool holder geometry**. The software should consider the tool balancing length, his diameter and the geometrical characteristics of

d. **Simulate collisions with the fixation of the piece on the table of the machine**. Diverse CAM systems are going to attribute geometrical forms, many times modelled in the CAD, for represent the systems of fixation of the piece on the table of the machine, when necessary. With that, the CAM passes it calculates the paths avoiding of the

e. **Simulation of machining 5 axes**. Due to the complexity of movements, with 5 ranks of liberty, the simulation of 5-axis machining is of vital importance for movable and fixed parts of the machine does not collide. In that case, is very important the CAM carry out the simulation employing all the geometry of the machine, limits of movement, and

Due to complexity of the milling 5 axes, the simulation CAM can take a significant time in

It is important to note that in all these simulation steps presented above are used to simulate the tool paths in the computational format of the software CAM. These paths do not be still

important aid in the CNC programming by the software CAM.

fixations of the piece. The Figure 14 illustrates a machining 5 axes.

Fig. 14. Simulation of CNC machining considering the machine

Advanced CAM, beyond identify the areas of possible collisions, the software can identifies the maximum depth that the system tool/tool holder can reach without collisions; divides the path in a first one breaks (that will be the first program CNC), as far as the system can achieve, and for the near depth (second program CNC), the CAM identifies the length of necessary. In this way, the initial path, with a smaller length should be more stable, as regards vibrations, and by that, can be quicker. Already in the second programs the user should have bigger caution in the machining. This can be an

through the simulation.

geometries of fixation.

this manufacturing process.

the tool holder.

the program CNC that will go for the machine. The program CNC is created starting from the paths, in a phase named post-processing, detailed it follow. Mainly in the machining 5 axes, errors can occur in the post-processing. A simulation carried out in the CAM cannot correspond with some movements of the machine, being able to cause collisions. Specific software for simulation exists of the program CNC and of the machine. This simulation confers bigger security to the trial.
