Dynamic forces and hole quality in drilling process

Abstract

Drilling is one of the most commonly used machining processes in various industries such as automotive, aircraft and aerospace, dies/molds, home appliance, medical and electronic equipment industries. Due to the increasing competitiveness in the market, cycle times of the drilling processes must be decreased. Moreover, tight geometric tolerance requirements in designs, drilled hole precisions must be increased in production. On the other hand, process engineers have to be conservative when selecting machining conditions with respect to metal removal rate in order to avoid undesirable cases such as drill breakage, excessive cutter deflection and undesirable hole profile problems. In this research, a new mathematical model based on the mechanics and dynamics of the drilling process is developed for the predictions of cutting forces and hole qualities in advance. A new method is also proposed in order to obtain cutting coefficients directly from a set of relatively simple calibration tests. The model is able simulate the cutting forces for various cutting conditions in the process planning stage. In structural dynamics module, measured frequency response functions of the spindle and tool system are integrated into the model in order to obtain drilled hole profiles. Therefore, in addition to predicting the forces, the new model allows to determine and visualize drilled hole profiles in 3D and to select parameters properly under the manufacturing and tolerance constraints. Extensive number of experiments is performed to validate the theoretical model outputs with the measured forces and CMM hole profiles. It is observed that model predictions agree well with the force and CMM measurements. Some of the typical calibration and validation results are presented in this paper.