Before examining CNC requirements, let’s review how data processing can influence a mold’s accuracy and surface quality. Here are four key influencers of data processing on the results of five-axis mold machining:

  1. Non-Uniform Rational B-Splines (NURBS). The CAD-model geometry is transformed into tool paths. Typically, this means the workpiece contour is modeled with NURBS, which makes it possible to mathematically describe free-form surfaces.
  2. Computer-Aided Manufacturing (CAM). The tool path elements are calculated point by point under consideration of the milling strategy (what section to rough cut first, how much stock to leave for the finishing cut, etc.), as well as the tool compensation values from the CAD geometry. From there, the predefined model accuracy determines the distance between points.
  3. Computer Numerical Control (CNC). The numerical control (NC) program is converted into axis point-to-point movements (machine movements that the CNC control executes) and velocity profiles (speed rates based on part shape or contour). Then preset path tolerances are calculated. This tolerance window determines how close the machine has to move to the actual contour or geometry of the part .To obtain high-surface definition, the deviations between adjacent milling paths must remain significantly smaller than the defined path tolerances. Basically, the more accurate and consistent the axis movement follows and repeats (moving back and forth in different directions), the better the surface finish and accuracy will be.
  1. Mechatronics. The mechanics of the machine and the electronic components that move the mechanical machine components are essential to data processing. For example, the five-axis movements are available in a fixed-time scale (or specified feeds and speeds rates) as nominal, and actual movements are converted over the machine geometry into tool and workpiece movements. This means that you define your movement in the program, but the machine will deviate due to mechanical tolerances from these values. The resulting error of the feed axes, deviations from the machine’s nominal geometry, and machine frame and motor thermal influences and vibrations can reduce the workpiece accuracy.