With high-speed rough milling, correct programming can prevent exceeding the limit value of the radial cutting width and breaking the tool. In curves and transitions, however, the cutting width can temporarily increase, while this is not what is needed. A new method now automatically ensures that the cutting angle remains constant in all circumstances, which brings some interesting advantages.
Milling tools have a certain useful cutting length. In theory, they can be used without any problems, provided that a limit value for the radial cutting width is not exceeded during the machining operation. If this does happen, there is a good chance that sooner or later the cutting tool will break, with the known consequences. When programming a pocket rough milling operation within a CAM system, it is perfectly possible to enter a large axial cutting depth and a small radial cutting width, also known as high-speed roughing. On straight sections of the milling path, the tool will maintain these settings, but in curves or transitions to the next section, the cutting width may temporarily increase while this is not required. Many CAM systems do not yet support the functionality to limit the cutting width in these places. And that is why the cutting depth is must necessarily limited by the CAM programmer. The disadvantage of this is that the cutting edge is not fully utilised and the machining time is increased.
Vortex working principle
As mentioned above, the set and optimal cutting parameters are mainly realised on a straight section of the milling path. The intervention angle between tool and workpiece is constant at these locations (figure below on the left). As soon as the tool approaches an internal angle, or moves to a concentric trajectory outwards or inwards, the cutting width and thus the intervention angle will increase (figure below on the right).
Intervention angle on straight section Intervention angle in a bend
The load on the tool will also increase. A possible solution to reduce the cutting force is to temporarily reduce the feed speed and spindle rotation speed. Without custom software, this is an impossible task. Alternatively, the feed rate can be selected according to the location where the tool is most heavily loaded. The disadvantage is that the chosen feed rate is too low for many other locations, and therefore unnecessary time is lost. In the example of the following figure, the intervention angle is optimal (cyan) for 90 percent of the time. For 10 percent of the time, the intervention angle is greater. So a whole lot of time is lost by adjusting the feed rate to the red zones.
Top view conventional roughness strategy (source: Delcam)
In the Vortex method, developed by CAM supplier Delcam, the algorithm for high-speed roughing automatically ensures that the previously discussed intervention angle remains constant in all conditions, not only on straight sections, but also at transitions and in curved parts. In transitions and curves, the intervention angle can be kept constant by inserting a number of trochoidal movements. This is done automatically according to the imposed parameter settings (see figure below).
Top view Vortex roughness strategy (source: Delcam)
The Vortex method is particularly suitable for high-speed roughing of 2.5-pockets with a solid carbide roughing cutter.
- Reduction of machining time because higher feed rates can be programmed, and consequently an increase in machine capacity.
- Better use of the available cutting edge.
- Improved process reliability because the load on the cutting tool is constant (constant intervention angle).
- Improving process reliability is particularly suitable for unmanned operations.
As already mentioned, the Vortex algorithm will automatically add a number of trochoidal movements. The question that now arises is which is the optimal measure for the trochoid. Much depends on the dynamic behaviour of the milling machine on which the operations are carried out. In order to map the dynamic behaviour of the machine, Delcam has developed a new concept especially for the Vortex method, called 'Machine DNA'. The Machine DNA function generates a number of motion patterns for the machine in question, which must be carried out by the Vortex user. During the movements, dynamic aspects of the machine are logged. At the end of the program, the user receives information about optimal trochoid settings for his Vortex settings. In the example below the equation between theoretical time and real time is made for three trochoidal movements. The best match between theory and practice is realised in setting 3.
Different trochoid settings (source: Delcam)
To be able to use Vortex, the optional Machine DNA function is not a must, only an optimization.