Dynamic modelling in micromachining

Yılmaz, Emre Ersoy
Micro milling applications are rapidly growing in various industries such as micro machines, medical, electro-mechanical component production etc. Due to very high precision requirements, dimensional accuracy and surface quality of micro milled components are very critical. As commonly known chatter vibrations arising due to instability in cutting yield poor surface finish and reduced tool life with potential damage to cutting edges and machine tool. Chatter vibrations are even more critical for micro milling tools due to their very flexible and weak bodies which may easily be damaged or broken under unstable chatter vibrations. Therefore, prediction of chatter stability limits is of utmost importance in order to achieve desired outcome in micro milling operations. The main problem in prediction of stability diagrams in micro milling has been the determination of micro mill frequency response function (FRF). Measurement of FRF is usually performed using impact testing in conventional machining which is almost impossible in micromachining due to small tool size. In this thesis, analytical modeling for obtaining tool point FRF for micro end mills by using chatter tests is presented. First of all, Timoshenko beam model with gyroscopic effects is utilized to obtain point FRF at tool tip. Then, chatter detection in micro machining is investigated using three different sensors which are accelerometer, acoustic emission sensor and microphone. Next, chatter tests are performed with micro end mills and chatter frequencies are experimentally obtained. An inverse stability analysis is performed to obtain the modal parameters of the micro mill using the data obtained from chatter tests. These modal parameters are used to predict the stability diagram. Then, the predicted stability diagram is verified by using further chatter experiments. Afterwards, modal parameters are used to generate the point FRF of the micro end mill. This FRF is compared with the previously obtained theoretical FRF, and thus the theoretical model is updated to better represent the dynamics at the micro end mill which can be used to obtain stability diagram under different conditions. The results of this study will enable accurate prediction of the stability diagram for micro-milling operations and thus increase production rate.
Citation Formats
E. E. Yılmaz, “Dynamic modelling in micromachining,” M.S. - Master of Science, Middle East Technical University, 2015.