Numerical and experimental modal analysis of machine tool spindles accounting for system decay and its application to chatter avoidance.
thesisposted on 24.05.2021, 12:04 by Omar Gaber
Cycle time, which is the time it takes to machine a certain part, has undergone a great deal of scrutiny as it is directly related to a company's profitability. When trying to machine a part as quickly as possible, selecting the wrong cutting parameters will cause chatter. Tight surface finish and thickness tolerances are usually required by customers. Money lost due to rework and scrap from the destructive nature of chatter has driven a significant number of research studies. It is well established that chatter is directly linked to the natural frequency of the cutting system. As the spindle ages, the vibrational characteristics of the system change. The wear in the spindle bearings causes the system stiffness to decline which results in the changing of natural frequency changing. This change causes the stability lobes to shift. This shift could render a usually stable cut unstable, causing poor surface finish. Excessive chatter can also damage the spindle and shorten its usable life. The objective of this study is to predict the vibrational behaviour of a spindle as it ages. This will be done for spindles utilized under different production constraints. A model of the spindle is also developed by exploiting its Dynamic Stiffness Matrix (DSM) and applying the proper boundary conditions. These results will then be compared to the experimental results obtained from tap testing different spindles to validate and tune the model. Once the static (non-spinning) results are confirmed and the spindle model tuned to represent the real system, the DSM formulation will then be extended to include varying rotational speeds and relevant boundary condition for further modelling purposes. Ultimately, the goal of this research is to develop a procedure to be able to select the correct cutting parameters over the life cycle of the spindle while minimizing the number of tap tests done on the spindle.