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Machine tool spindle condition monitoring

The machine tool spindle is the key element of the machine not only in terms of function but also in terms of required machine accuracy. Spindle diagnostics must, therefore, be able detect more than just usual operational problems of rotating machines such as imbalance, misalignment or resonance of the machine. It is also important to monitor the effects caused by the wear of operating tools, the machining process or crash of the tool during machining, the wear of bearings and spindle clamping parts. Condition-based monitoring enables early detection of arising machine damage. So, maintenance can be planned and the residual life of important components can be ideally used.

Spindle diagnostics meeting the requirements described above needs a permanent installation of the measuring system and online monitoring throughout the machine's operating cycles. The following operating modes can be distinguished by different machining processes and possible malfunctions:

Run without load (Idle) - Allows you to check machine geometry and component wear, including bearings. These include common failures such as imbalance, misalignment, and failures with occurrence on high frequencies, which are typical for arising bearing wear.

Start up and the tool affect - the machine to vibrate significantly, indicating a possible tool release or damage. The tool which is loosely or incorrectly fixed can cause considerable damage.

Beginning of machining process - inappropriately selected tool or a sharp shift when you start cutting (crash) they causes considerable dynamic forces. The early detection of a dynamic increase in power leads to a switch-off of the energy in the machining process.

Diagnostics of Spindle Bearing Wear - the condition of spindle bearings cannot be monitored during machining. Gradual increase of higher frequency vibrations at the time of the reference machine run (without load) is a measure of wearing of spindle bearings

Monitoring during machining - changes in the cutting forces such as caused by blunt drilling machines or swarf jam are detected on the basis of the changed vibration characteristics. Individual setting of limits for each tool is prevention for damage to the workpiece.

Total wear of the machine - the detection of excessive dynamic load and the sum of times its duration is useful to estimate the total wear of the machine tool

Suitable design of the diagnostic system of the spindle is represent as a combination using of the measuring system capable of measuring a wide frequency range with high dynamics of the signal, and the possibility for connection to the control system of the machine tool (PLC). The control system provides information on the operating modes of the machine and its program allows the evaluation and storage of the monitored manifestations and their processing in terms of the frequency of the failures and their overall duration. Combination of Vibration Diagnostics system and PLC provides a relatively simple and cost-effective comprehensive spindle diagnostics system.

The VKS 01 kit containing electronics and miniature piezoelectric sensors of the SVE 100 or SVE 200 type is now available from own R@D of AURA a.s. Dimensions of sensors allows for a trouble-free direct assembly on the spindle with corresponding contact with both the spindle surface and the bearing surface too. VKS 01 electronics provide signal processing from the sensor across a wide range of frequencies and the dynamics needed to detect fault manifestations in all mentioned operating modes. Design solutions VKS 01 respects the difficult industry conditions, including the effects of temperatures, vibration, electromagnetic fields and electrical interference (EMC). In combination with the machine control system (PLC) represents VKS01 comprehensive diagnostic system of machine, easy to access. Other variants of the system replacing the PLC control system - separate system for the processing and recording of diagnostic data are already being prepared in AURA a.s.

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