Investigation of the burr formation during the drilling of free-form surfaces in al 7075 alloy

The use of free-form shapes has become widespread to design complex products that have to fulfil engineering requirements as well as aesthetic criteria. Conventional drilling with twist drilling still remains one of the most economical and efficient machining processes for hole making as well as for riveting and fastening structural assemblies in the aerospace and automotive industries. In drilling, one of the major issues of the process pertains to burrs formation, which affects the quality of the final product and, thus, the capability to meet the part desired functionality. Though it is noted that drilling operations produce burrs on the machined parts, burrs removal on free form surface is more difficult, producing an increase of both the time and cost for deburring. In this study, the effects of drilling parameters on the formation of burrs during the drilling of free-form surfaces were examined. A free-form surface manufactured from Al7075 was drilled using different exit surface angle, spindle speed and feed rate parameters. The drilled workpiece was then scanned using a 3D scanner to obtain data related to burr formation and burr height. By evaluating these data via the TAGUCHI, ANOVA and NLR statistical methods, optimum drilling parameters for minimum burr height were determined. In addition, a mathematical model for predicting burr height was developed, with first fracture points, hole morphology and the burr formation process investigated based on images taken during and after drilling. The lowest burr height was measured 15° exit surface angle, 2300 rpm spindle speed and 0.1 mm/rev feed rate. In addition, a mathematical model was developed using NLR analysis which estimate actual results by 90.26%.