The accuracy of machined workpieces, especially those that are delicate or of thin-wall construction, can be adversely affected if clamping pressure is too high. If the grip is too weak, however, there is a possibility of the part becoming dislodged during machining, risking operator injury, machine damage, tool breakage and scrap.

During automated hydraulic clamping, oil pressure is easy to measure, but other variables can also influence the clamping force. In manual clamping systems, straightforward torque measurement is often used, but the relationship between torque and actual clamping force can be inaccurate. The approach that OK-Vise has taken is to integrate clamping force measurement directly into the company’s modular Multi-Rail RM fixturing system.

An on-screen digital readout of clamping pressure from a Digiforce device enables the operator to verify that a hydraulically secured component is held correctly. An optional SCADA (supervisory control and data acquisition) system can collect information from several Digiforce displays over a standard Modbus connection, so that historical data can be viewed and adjustments made as necessary.

Digiforce provides confirmation of holding force

A second device, Dotforce, allows the holding force of manually secured workpieces to be checked. It also forms part of the Multi-Rail RM workholding system and utilises a visual red dot in a clamp module. The dot gradually fades to grey as a spanner is turned, showing when the holding force is correct. Various modules are available for different clamping pressures.