2017cnc10-11

48 www.CNC-West.com CNC WEST October/November 2017 T he 3D-ToolComp option of HEIDENHAIN controls compensates for deviations from an ideal circular shape on radius milling cutters. Together with the probing cycle 444 of the TNC controls, however, it also im- proves the accuracy of a touch probe during use. Both features ensure high-accuracy free-form surfaces. In spite of state-of-the-art accuracy in tool manufacturing methods: spherical cutters in particular do not have uniform geometry, and the radius of each tool usually deviates individu- ally from the ideal circular interpolation. This is a problem for high-accuracy machining. The contact point of the milling ra- dius with the workpiece as calculated by the control does not match the actual radius, and this is the case with each individ- ual milling cutter. The same applies to the use of workpiece touch probes. Each device has its individual switching behavior. Depending on the touch probe used and the length of the stylus, it causes error in the range of up to one hundredth of a millimeter. The measur- ing error might then be correspondingly large if you measure without prior calibration. MACHINING WITH REAL CUTTER RADII A CNC control with special compensation can handle these errors. Such is the case, for example, with the 3D-ToolComp option that enables HEIDENHAIN TNC controls to perform powerful, three-dimensional tool radius compensation. A com- pensation-value table is used to define angle-dependent delta values that describe the tool deviation from the ideal circular form. The TNC then corrects the radius value defined for the tool’s current point of contact with the workpiece. In order to determine the point of contact exactly, the NC program must have been created with surface-normal blocks (LN blocks) by a CAM system. In addition to the position of the tool tip, the vector sets include a vector that points from the point of con- tact on the workpiece to the center point of the radius cutter, the so-called surface normal. Moreover, such vector sets can also define the orientation of the tool relative to the workpiece. The TNC-controlled machine tool compensates the tool er- ror automatically. Also, the shape of the tool is measured using a laser system and a special cycle. The TNC control can use this data directly and document it in a compensation table. The user does not have to enter the tool compensation again in the NC program. The TNC control handles the variable influences Article Supplied by HEIDENHAIN GUARANTEED HIGH-PRECISION FREE-FORM SURFACES Process reliability thanks to 3D-ToolComp: A tool change does not result in unexpected surface changes.