Modelling kinematics and cutting forces in vibration assisted drilling

One of the main drawbacks of the traditional drilling process is the formation of long chips when cutting metallic parts. Usually, peck drilling cycles are used to break and evacuate the chips through the flutes of the drill. However, this solution increases the operation time and therefore decreases the productivity. To solve this problem, vibration assisted drilling has been developed to meet industrial needs in terms of productivity. Forced vibrations impose a variation of the chip thickness in order to obtain its fragmentation. This process has been recently developed and optimal cutting conditions have yet to be determined to improve it furthermore. This paper presents, on the first hand, an experimental study of the kinematics of vibration assisted drilling. It showed a strong reduction of the amplitude of vibration during drilling, in the configuration of the tests. In addition, tests were conducted to show the apparition of interference phenomena at the centre of the tool. Interferences are difficult to separate from the cutting phenomenon, making the modelling of cutting forces difficult. From the kinematic model, chip height can be simulated in order to model the cutting forces. A thrust force and a torque model applied to vibration assisted drilling are presented in this paper. The thrust force model is based on a representation of the tool by several zones corresponding to each cutting mechanism: indentation at the centre of the tool, cutting along the cutting edges and bad cutting conditions in an intermediary zone. The periodically variable feed speed modifies the size of each zone and the thrust force they generate. The model presented in this paper formulates the interaction of several zones of the tool with the material and explains the particular shape of the thrust force observed. The models are identified and validated through an application on aluminium alloy 7010