B–63522EN/02
3. INTERPOLATION FUNCTIONS
NC FUNCTION
67
Many computer–aided design (CAD) systems used to design metal dies
for automobiles and airplanes utilize non–uniform rational B–spline
(NURBS) to express a sculptured surface or curve for the metal dies.
This function enables NURBS curve expression to be directly specified
to the CNC. This eliminates the need for approximating the NURBS
curve with minute line segments. This offers the following advantages:
1. No error due to approximation of a NURBS curve by small line
segments
2. Short part program
3. No break between blocks when small blocks are executed at high
speed
4. No need for high–speed transfer from the host computer to the CNC
When this function is used, a computer–aided machining (CAM) system
creates a NURBS curve according to the NURBS expression output from
the CAD system, after compensating for the length of the tool holder, tool
diameter, and other tool elements. The NURBS curve is programmed in
the NC format by using these three defining parameters: control point,
weight, and knot.
CAD (Designing a metal die)
Generating a metal die surface
(NURBS surface or curve)
CAM (Creating an NC part program)
Studying the machining
method and others
Tool compensation file
NC part program after tool compensation
(NURBS curve)
NURBS curve (control point, weight, knot)
CNC equipment
Machine tool
Fig. 3.15 NC part program for machining a metal die according to a
NURBS curve
3.15
NURBS
INTERPOLATION
(G06.2)