3-D ToolComp: work with the actual cutter radius

Despite all of the precision that goes into tool manufacturing, radius cutters, in particular, lack a uniform geometry. The actual radius of every single tool typically exhibits distinct deviations from an ideal circular form. Research has shown that deviations of up to 0.015 mm can be expected for a standard tool. Even expensive, high-end precision cutters can have deviations in the micron range.

The 3D-ToolComp option provides powerful three-dimensional tool radius compensation that can account for these deviations. Workpiece accuracy is thereby significantly increased, especially when free-form surfaces are involved.

Compensation of tool form errors

In high-precision machining, deviations between the actual cutter radius and its ideal form are a hindrance. This is because the cutter’s contact point with the workpiece, as calculated by the control, does not agree with the actual radius—and this is true of every newly loaded cutter.

A compensation table enables the specification of angle-dependent delta values that describe the tool’s deviations from an ideal circular form. The TNC control then compensates for the radius value defined at the current tool contact point on the workpiece.

For the contact point to be determined with precision, the NC program must be generated with surface-normal blocks (LN blocks) by the CAM system. These surface-normal blocks define the tool position and the contact point on the workpiece, and optionally specify the tool orientation relative to the workpiece surface. The TNC-controlled machine tool automatically performs the compensation.

Two approaches to the same goal: perfect contours

Variant 1: Measurement of 3-D geometries

The example of an aspheric lens illustrates the effects of 3D-ToolComp: the left image shows the form errors after the initial test cut, as determined by probing cycle 444. The right image shows the machined lens after compensation of the radius deviations with 3D-ToolComp.

The procedure is as follows:

1. Use the tool to perform a milling operation on a test workpiece.

2. Then measure the resulting contour using a touch probe in combination with Cycle 444 PROBING IN 3-D.

The discrepancies between the milled contour and the desired contour are used to derive the tool radius deviations, which can be entered directly into a compensation table.

Tip: Before probing the workpiece surface, use 3D-ToolComp to perform a 3-D calibration of the touch probe.

Variant 2: Measurement of the tools

You can measure the tool form fully automatically using a laser system and a special cycle, so that the TNC control can directly use these data and record them in a compensation table. After doing so, you no longer need to perform tool compensation in the NC program.

Tip: With this method, the TNC control automatically handles the variable effects of tool form errors and thereby meets an important criterion for reliable machining processes in conformity with medical technology requirements.

Perform highly accurate in-process quality inspection

By the way, 3D-ToolComp can do more than compensate for radius deviations on cutters and optimize your machining results. This option also assists you with the high-accuracy quality inspection of workpieces featuring free-form surfaces inside the machine’s work envelope. To receive highly accurate measurement results, use 3D-ToolComp to perform a 3-D calibration of the touch probe before utilizing Cycle 444 PROBING IN 3-D. The cycle then compensates for the distinct switching behavior of the touch probe in any direction.

Cycle 444 is used for the automatic measurement of points on free-form surfaces. To do this, simply enter the given measuring point with its coordinates and the associated normal vector into the cycle.

After probing, the TNC control automatically determines whether the measured point lies within a defined tolerance.
Cycle 444 also automatically generates a convenient calibration chart in HTML format.
In addition, you can request the results via system parameters in order to initiate rework under program control, trigger a program stop, or issue a notification, for example.