Forecasting Initial Exit Point and Attributes of Burr Formation in Drilling of Free-Form Surfaces

The initial exit point (IEP) denotes the first location where the tool emerges from the underside of the workpiece during drilling and has a substantial influence on burr formation. This effect becomes particularly pronounced when the underside of the workpiece is not flat. In such cases, unfavorable IEP positioning may lead to increased burr height, unstable material separation, and non-uniform exit deformation, thereby deteriorating surface quality and increasing the need for secondary deburring operations. The IEP, together with the tool initial position (TIP), is governed by the tool’s starting placement, workpiece thickness, feed rate, and spindle speed, all of which are highly adjustable parameters. In this study, burr formation during the drilling of a B-spline free-form surface was investigated by mathematically modeling the tool cutting edge tip with respect to the IEP. The proposed model was developed in the MATLAB environment and experimentally validated on a workpiece containing a B-spline surface. The results demonstrate that accurate prediction and control of the IEP enable effective regulation of burr formation on free-form surfaces. By optimizing drilling parameters, burr height was significantly reduced, achieving an average decrease of 27.8% when the exit occurred near the tool tip region compared to exits between the tip and diameter edge. These findings highlight both the critical role of the IEP in burr generation and the necessity of its careful control in drilling operations on non-flat surfaces.