Single Surface versus Multi Surface Machining in 5 Axis
Due to increased availability and lower pricing of 5 Axis Milling machines and recent developments from the controller side (Fanuc etc.), the need for information about 5 Axis machining has recently increased dramatically. This Help addresses tries to as easily and clear as possible address one frequent question about 5 Axis machining of multiple surfaces. There are more issues to explain, but due to the complexity of the subject it seems to be more reasonable to deal with one point of interest after the other step by step.
Single Surface 5 Axis Flow line Machining
CAD surfaces are generally built on customer-defined interpolation points. Surface XYZ-points in CAD/CAM-systems are afterwards usually defined by a 2-Parameter representation. These parameters are called U and V:
Each surface point’s X-, Y- and Z-coordinate can be calculated from a unique pair of U and V. Each surface point is associated with a surface normal that is always perpendicular to the surface at that point.
In 3 axis machining this surface normal for a ball end mill points to the cutter center. The cutter axis always comes from one direction and usually it is aligned with Z. In some rare cases the cutter is aligned with the Y axis.
In 5 Axis machining the surface normal may not only determine the cutter center but the cutter orientation as well (there are other ways to control the tool axis to achieve a 5 axis machining toolpath, but this will be discussed later):
A Flow line 5 Axis toolpath follows only the U-direction and V-direction of the surface. In the subsequent figure a 5 axis flow line toolpath is shown which is mainly calculated in u-direction. As soon as the surface edge is reached the tool steps in v and then continues movement in reversed u-direction to achieve a Zig-Zag (bidirectional) toolpath. During movement, the tool axis direction is changed in every single point of the toolpath according to the local surface normal. This kind of machining is called a single-surface 5 axis flow line toolpath.
On a real machine the machine has to move its axis to rotate the tool to the required direction as shown below.
Characteristics and Restrictions of Multi Surface Flow line Machining
Multi surface flow line machining requires all surfaces to have the same u- and v- parameter direction of the surfaces. The figure below shows a sample set of 3 surfaces, which have the same u- and v- direction and the resulting Multi Surface Flow line toolpath.
If surface number 2 does not have the same U- and V-Direction as in the sample shown below, a calculation of the toolpath based on the flow line of the surfaces is not reasonable any more:
Real Multi-Surface Machining
In this case a more sophisticated approach needs to be applied to solve the machining task. A solution has been developed which allows generate a smooth toolpath even on these arbitrary orientated surfaces:
The above is only one issue to address to generate an acceptable 5 axis toolpath. There are plenty of issues more like faulty surfaces or edge curves, collision avoidance, post processor output etc. All these small problems have been solved to be productive on 5 axis machining.