An experimental investigation on hole exit geometric error in orbital drilling process

As an alternative to conventional drilling, orbital drilling has been applied to drilling difficult-to-machine materials, while unfavorable geometric error usually occurs at hole exit in orbital drilling of small-diameter holes. This drawback has prevented the wide application of this novelty process for drilling small-diameter holes. In order to minimize the geometric error in orbital drilling, this paper experimentally studied the geometric error by Taguchi and response surface methodologies. The formation mechanism of the geometric error was firstly revealed theoretically. Moreover, the influence of process parameters (tool slenderness index, spindle speed, tangential feed per tooth and axial feed per tooth) on the geometric error in orbital drilling of aluminum alloy was investigated by Taguchi methodology. The ANOVA analysis led to the following optimal combination of drilling parameters: tool slenderness index (50), spindle speed (8000 rpm), tangential feed per tooth (120 μm/rev) and axial feed per tooth (3 μm/rev). In addition, a second-order response model for the geometric error with respect to the drilling parameters was developed by the response surface methodology. Conformation tests were conducted and the results showed that the established model can be used for prediction of the hole exit geometric error in orbital drilling process.