Understanding how data is processed helps to select the appropriate CNC control for a five-axis machine to optimize machining time, surface finish quality and workpiece accuracy. Here are five basic requirements a CNC control should meet:

  1. Effective monitoring of contour tolerances. The NC will control the axis movements to follow the 3D surfaces within a predefined tolerance band that are usually created with a CAM system and consist of simple line segments. The CNC should be able to automatically smooth the block transitions while the tool moves continuously on the workpiece surface. An internal function that monitors the contour deviations controls that automatic smoothing. This function enables the user to define the maximum-allowed contour deviation. The default value is defined by the machine tool builder in a machine parameter of the control (typically 0.01 to 0.02 millimeter).  The tolerance also affects the traverse paths on programmed circular motions. This is particularly important if the core or cavity has cylindrical details, which a user machines with either an interpolation milling or a mill-turn function. The latter requires a specific configured machine tool. This newer type of five-axis technology minimizes setup time, improves part detail accuracy and eliminates secondary part setup in a lathe or jig grinding machine.
  2. Exact reproduction of adjacent paths after cutting direction reversal. The CNC control should be able to interface with a linear encoder system, ensuring that all machine axes follow the exact path when moving from X-plus to X-minus and then moving from X-minus to X-plus after a step over .
  3. Elimination of vibration from highly dynamic movements. A machine axis moving very fast and changing direction on a point or a using a higher-than-permitted feed rate for the cutting tool can generate vibration in the axis, which will impact part quality. The CNC control should be able to monitor any type of tool vibration caused by either high dynamic movements or higher-than-permitted feed rates, and then adjust feeds and speeds to avoid chatter marks on the final part.
  4. Flexibility. The CNC control should allow the operator or programmer to verify and optimize the program on-the-fly. Consider, for example, several different mold components made on the same machine. Each part has different accuracy, surface finish and leadtime requirements. Here, the CNC interface should allow the operator to optimize the machine dynamics based on each part’s feature priorities.
  5. Automatic feed and speed adjustment. Milling through mold cores or cavities with variable workpiece thicknesses is another machining challenge. A solution is a CNC that can detect how much material is currently cut, so the feeds and speeds can be automatically adjusted without operator intervention. This is accomplished with sensors connected to the CNC that measure spindle load and vibration, and then identify and adjust speeds and feeds within milliseconds. This technology ensures that the machine maximizes chip removal rate, based on workpiece cutting tool engagement, and cutter and spindle life.
  6. Five-sided machining in one setup. Not all parts require a full five-axis simultaneous motion. Many mold cores or bases require five-sided machining in one setup. This technique ensures positioning accuracy of features on all five sides of the part, eliminating several setups, and consequently improving the finished part quality. Specifically, this technique improves the tolerances between features on each side of the part. To accomplish this, the machinist wants to program each side of the part in an X-Y-Z plane without changing the CAM program. The CNC should have a spatial plane function that allows the machinist to set the plane that is machined on each side of the part.