New Flexium Function – Adaptive Grinding

AC Grinding – Fully integrated, adaptive feed control

The major benefits of this new feature include improving the quality of tool surfaces as well as reducing the production times of various tools. This is achieved by constantly measuring and monitoring the torque of the grinding spindle as well as automatically regulating the optimal feed rate. NUM’s new purely software-based “adaptive grinding” feature can be integrated in all Flexium and Flexium+-based systems without additional hardware. To carry out a relevant spindle current measurement, a synchronous motor combined with a drive amplifier from the NUMDrive X or MDLU3 series are required.

How does AC grinding work?

The machine operator grinds a reference workpiece with a defined feed rate, during which the spindle current is evaluated. This spindle reference current value is then entered in the NUMROTO user interface. All subsequent workpieces are then grinded with identical reference currents. Thanks to the adaptive feed control, there is a constant grinding pressure during machining, which achieves uniform surfaces. The reference current value can also be called up and used on any machine for the corresponding workpiece and grinding wheel regardless of location.

The „AC grinding“ software package provides a recording function (monitoring tool), which records the current characteristic for the evaluation of the spindle current. The application offers various setting options, which can be set in the NUMROTO user interface in a user-friendly manner. During the AC grinding process, the machine operator master remains the master of the potentiometer and can intervene in the machining process at any time.

Shorter processing times

AC grinding can increase the feed to a defined maximum in „air grinding”. When penetrating into the material, the feed is reduced back to the reference current in accordance with the processing force. Time is saved by accelerating in areas with little or no ablation volume. Test runs have shown that production times can be reduced by 10% to 30%. 

Protection against excessive processing pressure

Since the grinding pressure is controlled during AC grinding, parts can be protected from processing pressure which is (much) too high. In extreme cases, for example, blanks broken off by a worn tool can be avoided, which reduces waste.

Advantages at a glance

  • Shorter production times for a large number of tools due to
  • higher feed rate in areas of lower removal rate
  • higher feed rate during air grinding (defined by the operator)
  • Smooth, even surfaces thanks to constant, controlled grinding pressure
  • AC grinding can protect workpieces from excessive grinding pressure, which in turn helps prevent workpiece breakage and overloading of the grinding wheel
  • Even wear of the grinding wheel during the process
  • Permanent spindle current monitoring
  • Collision detection as monitoring function
  • Avoidance of consequential damage due to overload
  • Feed controller offers individual marker functions
  • Reset after each tooth: The controller always starts with the preset potentiometer value
  • With marker: The feed controller starts at the next tooth with the old potentiometer value
  • Feed controller parameter adjustable (optimization of controller behavior)
  • Monitoring tool
  • Representation of the latest current flow during the respective grinding process
  • The recording function is used to evaluate the spindle current
  • Logging and storage of measured data for subsequent evaluation possible
  • Detection of the condition of the grinding wheel used
  • Feed speed drops when the grinding wheel wears out („closes“)
  • The necessary dressing or changing of the grinding wheel used can be controlled with this information
  • Various settings can be set via the NUMROTO interface in a user-friendly manner
  • Flexible definition of various monitoring and overload reactions (in the PLC)
  • User-friendly handling of the potentiometer (the operator is always the master)
  • The feed rate can be increased as well as reduced (depending on the defined pre-settings and current state of the grinding wheel)


AC grinding also provides monitoring functions for the spindle. Collision monitoring with a detection time of 2 ms immediately stops the machine when a configurable maximum current is exceeded and transmits a corresponding message to the PLC.

The wear of the grinding wheel can also be monitored. If the removal performance of the grinding wheel is reduced, the feed is automatically reduced by the control. If a predetermined minimum feed is fallen below, AC grinding sends a message to the PLC, which allows an individual reaction to the status. In this way, an automatic dressing of the wheel can be triggered among others.

Requirements and installation

As already mentioned, a synchronous motor and a drive amplifier of type NUMDrive X or MDLU3 are required for the spindle current measurement. But asynchronous motors can also be operated vectorially (with encoder). The use of other frequency converters can be checked individually.

Being a fully integrated solution between the CNC system and the NUMROTO software, installation is straightforward and easy with a software upgrade to existing machines.

The connection to Industry 4.0 is possible for effective and intelligent factory production.


The “AC grinding” package is available from NUMROTO Version 4.1.0 (around the third quarter of 2018).

Adaptive control not only for grinding

The basic function of AC grinding is the adaptive feed control, which reacts in dependence on the spindle load. The system can therefore also be adapted to various other applications.


Please contact us for further information:

Battenhusstrasse 16
CH - 9053 Teufen

Phone: +41 71 335 04 11