New Machining Algorithms
Nowadays mechanical technology has been developed to the point where what was previously considered an insurmountable limit in terms of processing speed and sustainable acceleration has become almost a standard in the world of machine tools. It is now common to talk about high speed machines with speeds over 100m/min and acceleration of 1g or higher. A typical application of these machines is high speed milling of CAD generated surfaces.
The traditional solution offered by CNC, i.e. profiling as a sequence of linear micro interpolations, is no longer applicable. The mechanics have evolved steadily so that it is now possible to follow accurately the continuous changes of direction which can cause unwanted effects on the surface finish.
The OSAI approach to this problem is particularly innovative: the well-known and tested mathematical concept (spline), usually only applied to tool path geometry, has been extended and applied to the dynamic motion in order to achieve high speed cutting with a finish closer to the mathematical model.
The solution developed for Series 10 CNC consists of the following phases:
Geometric phase: where programmed I/O points are regarded as elements of a three dimensional polynomial curve. Information concerning rotation axes are supplied as vectors referred to tool position with respect to the work-piece which is therefore independent of machine and tool geometry.
Technological phase: where tool geometry is used to go from the work-piece reference system to tool reference by means of geometric transformations applied to polynomial curves which have been calculated during the geometric phase.
Kinematic phase: where machine geometry, i.e. kinematic motion of rotary axes is applied to the data processed during the technological phase thus automatically generating the polynomial curve pertaining to the rotary axes (if fitted).
Dynamic phase: an additional polynomial curve (time-function) stating the progression of machining speed is calculated depending on the dynamic specifications of each axis and programmed working speed.
Polynomial interpolation: movement interpolation is carried out directly from polynomial functions thus avoiding typical chordal errors due to approximation of curves as straight line segments. Acceleration is calculated according to tool path, machine geometry and axes dynamics in order to maximise machining speed and reduce mechanical stress on the machine tool.
A programming level suitable for these phases can be selected to take the maximum advantage of CAD potential. It is possible to program directly any position of tool head or to input angles of rotation axes. Polynomial format programming is also possible at CAD level if already available.