Küresel uçlu parmak frezeleme ile serbest formlu yüzey işlemenin dinamiği ile talaş genişliği ve kalibrasyon analizi

Thesis Title : Chip Load, Calibration Analysis and Dynamics of Ball-End Milling for Free-formSurface MachiningAuthor : Burak ÖztürkABSTRACTThe ball-end milling process is used extensively in machining of free-form surfaces in automobile,die/mold and aerospace industries. In planning machine operations, the process planner has to beconservative in selecting machining conditions with respect to metal removal rate in order to avoidunwanted results such as chipping, cutter breakage or overcut due to excessive cutter deflection. Theseproblems are particularly important for machining of free-form surfaces where axial and radial depthsof cuts are abruptly changing. For this reason it will be very critical to provide the process plannerwith guidance in selecting machining conditions. One solution to this problem is to consider thecutting force in the stage of selecting machining conditions. If the process planner can predict thecutting force for a certain machining condition, it would be very helpful in judging whether theselected condition is appropriate. In the prediction of cutting forces exact determination of engagementregions, calibration coefficients and force model play very important roles.Firstly, cutting force models for ball-end milling are based on the undeformed chip thickness.Undeformed chip load can be constructed from the boundaries of instantaneous engagement regionbetween the ball-end mill and workpiece. In order to predict the cutting forces accurately,determination of the varying engagement region is important. In the literature, there are two mainengagement region constructing methods; one is the Z-mapping and the other one is using a solidmodeler based on Boolean operation method. Both methods construct the engagement region withinaccuracy limits, on the other hand the computational time for these methods are long such that it is notpossible to calculate the forces at the same time of CL-point construction in a CAM package. Thiswork presents development of an analytical method for fast and accurate determination of theinstantaneous engagement regions in the 3D machining of monotonic free-form surfaces. Theanalytical tool is grid size independent, thus it is much faster than discretization and Boolean methods.In addition to that, there is no need for smaller grid sizes to have the exact engagement domain sincethe equations are analytical and thus give the exact engagement regions.Secondly, obtaining the calibration coefficients from calibration tests is a very influential processin the prediction of cutting forces. Accurately obtained calibration coefficients lead to better forcepredictions. In the literature the calibration coefficients are assumed to be independent of the changeof the start and exit angles within the engagement region, thus they are assumed to be identical for anyengagement region. Calibration coefficients are obtained from the horizontal slot cutting tests andthese tests are repeated for different depth of cuts. In this work, in order to achieve more precise forcepredictions in free-form machining simulations, a new modification algorithm for calibrationcoefficients is presented. In this research, with theoretical analysis and experimental force signals, it isshown that the inclination angle has a great importance in calibration and in force simulation of 3Dfree-form machining. CAD drawings are performed to validate the analytical engagement model withmeasured forces and extensive experiments are performed to validate both the analytical engagementregion and the modification model of calibration coefficients. Theoretical Dynamic analysis of ball-end milling is also studied.In addition to predicting the cutting forces, five-axis ball-end milling is also studied up to aninformative level for the future work. Experiments are performed in five-axis ball-end milling andeffect of lead/tilt angles on force signals is stated. Dynamics of ball-end milling is coupled withengagement model and an analytical method is presented which needs to be developed as a futurework.