Siemens SINUMERIK 840D sl Function Manual page 713

Figure 19-15 Change in the machining point on the tool surface close to a point in which surface normal
The problem is basically solved as follows: If the angle d between the surface normal vector
n and tool orientation w is smaller than a limit value (machine data) δ
F
y on tools with a flat end face (e.g. torus cutter or cylindrical mill) must be 0. This restriction
does not apply to tool types with a spherical end face (e.g. ball end mill, die sinker) since
angular changes close to the singular point do not lead to abrupt changes in the machining
point on the surface of such tools. If δ now becomes 0, i.e. the sign of lead angle b changes,
the machining point moves from its current position to the opposite side of the tool. This
movement is executed in an inserted linear block.
The machining operation is aborted with an alarm if an attempt is made to machine within the
illegal angular range for the side angle y (i.e. δ < δ
The insertion of linear blocks makes it necessary to split the original blocks at the singular
points. The partial blocks created in this way are treated as if they were original, which
means, for example, that a concave path containing a singularity is treated like an inside
corner, i.e. there is no contour violation. Each new partial block must contain at least one tool
contact point since this is always calculated on the basis of adjacent traversing blocks.
Singularities do not just occur at isolated points, but along whole curves. This is the case, for
example, if the curve to be interpolated is a plane curve (i.e. a curve with a constant
osculating plane) and the tool is constantly aligned in parallel to the binormal vector, i.e.
perpendicular to the osculating plane. A simple example is a circular arc in the x-y plane that
is machined by a tool aligned in parallel to the z axis. On paths of this type, the tool offset is
reduced to a tool length compensation, i.e. the tool is moved so that its tip FS is positioned on
the programmed path.
On transition between singular and non-singular curves, linear blocks must be inserted in the
same way as for isolated singular points so that the machining point on the tool can move
from the tool tip FS to the periphery (on outside corners and convex surfaces) or the paths
must be shortened to avoid contour violations (on inside corners and concave surfaces).
Special Functions
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
vector and tool orientation are parallel
W5: 3D tool radius compensation
, then the side angle
min
and γ , 0).
min
19.3 Face milling
713