The structure of the turning-broaching machine only permits the process force to be measured at the base on the revolver drive unit. Artis GmbH had the idea to install a measuring washer under an existing screw connection.

This resulted in a challenge:

• The screw connection needed to be tightened with the nominal pre-stress force to DIN 18800
• while relatively small process forces had to be reliably recorded at this high pre-stress force.

In practice, these are for example 110,000 N pre-stress with a standardized tightening torque of an M16 screw, quality 12.9, and machining forces of 500 – 1000 N.

Piezoelectric force washer and charge amplifier from HBM

“We discussed and compared possible measurement technology solutions based on piezo and SG systems with HBM and came to the conclusion that the CFW sensors in the Paceline series are predestined for this application. We were initially skeptical as we have in the past used piezoelectric sensors from other manufacturers without achieving satisfactory results”, remembered Hans Georg Conrady, managing director of Artis.

Indeed, sensors in this application are subject to particular challenges. These include, for example,

• cooling emulsion flowing around the sensors,
• hot metal chips falling onto sensors and cables,
• continuous shock and vibration loading of the sensors during crankshaft machining.

The technological advantage of the Paceline sensors – the sensitivity independent of measuring range – is particularly suitable here: The charge generated by the high pre-stress force of the screw connections is short-circuited by the CMD600 charge amplifier before measurement. In addition, the useful signal is optimally amplified and provided as a process parameter to the Artis process monitoring system CTM. The mechanical sturdiness of the measurement chain is also achieved by a metal-sheathed charge cable in order to meet the specified high requirements.

The crankshaft machining process is extremely complex and requires the highest of process safety.