Machining accuracy analysis for step multi-element varying-parameter vibration drilling of laminated composite materials

Laminated composite materials are being extensively used in various fields, and their micro-hole machining is difficult because of their layer structures and particular characteristics. To solve the problem effectively, a new method of step multi-element varying-parameter vibration drilling is proposed. Drilling laminated composite materials is a multi-zone operation which involves the entrance zone, the mid zones, the reciprocal zones and the exit zone. In each zone, optimum parameters including vibration frequency, amplitude and feed should be chosen so as to improve the machining accuracies of micro-holes. Based on the principle of multi-element orthogonal polynomial regression, parametric optimisation experiments of single materials are carried out, and optimum parameters for each zone are obtained. The proposed drilling method can be achieved by using these optimum values for each zone. Comparative experiments using the proposed method indicate that the deflection of the drill r, the error of the micro-hole diameter _D and the height of burrs H can be decreased compared to ordinary drilling, so machining accuracies can be improved.