Study of vibration severity assessment for Machine Tool spindles within Condition Monitoring

Sammanfattning: Today, machine tools are indispensable for production of manufactured goods. Several industries rely in this equipment to manufacture finished products by removing material through different cutting operations. Automobile, military and aerospace are just examples of industries where machine tools are used intensively. Today these industries strive for higher precision, narrower tolerances and more productivity in order to develop higher quality products using lesser resources and minimizing the impact on the environment.Condition Based Maintenance CBM program has been proved as an effective preventive maintenance strategy to face these challenges. Reduction in downtimes, operation losses and maintenance costs are some of the benefits of adopting a CBM approach. The core of a CBM is Condition Monitoring CM, which refers to the surveillance of a suitable parameter for assessing the need of maintenance tasks in the equipment. These parameters are later compared with reference values to obtain a machine health assessment.In machine tools, vibration level in the spindle units is considered a critical parameter to evaluate machine health during their operational life. This parameter is often associated with bearing damage, imbalance or malfunction of the spindle. Despite the importance of vibration levels there is not ISO standard to evaluated spindle health. This fact obstructs in some extend the planning of maintenance task for these high precision assemblies.In the first part of this work, spindle components are studied and their function explained. Besides the main sources of vibration are listed, putting emphasis in three due to is importance when measuring vibration within condition monitoring of spindles. These are imbalance, bearing damage and critical speed. Later relevant concepts of vibration technology and signal analysis are introduced.In the experimental part of the present study, controlled experiments were carried with the purpose of understanding which factors affect vibration measurements on the spindle housing. Control variables as spindle speed, accelerometer’s angular location, and spindle position were studied. Finally, a contactless excitation device CERS and its potential for industry in detecting bearing damage, is evaluated with two experimental setups.The results indicate that vibration levels measured spindle housing depends on great extent on the angular mounting position of the accelerometers. Results also show that some vibrations severity indicators vary considerably along spindle speed range. It was also found that CERS could be potentially used on condition monitoring of machine tool spindles for detecting onset damage on bearings. However further research is considered necessary for this purpose.