Burr and Cap Formation by Orbital Drilling of Aluminum

In orbital drilling the tool (special end mill) moves relative to the workpiece on a helical course. Because of the three dimensional tool path and the superimposed rotary cutting motion a complex machining motion results which determines the contact conditions of the tool. In the aircraft industry this process is used for cutting composite materials (CFRP/Aluminum) with automated drill and rivet machines, for example in the manufacturing of flap tracks and vertical tail planes. A key problem in the industrial manufacturing of closed structures is the cap and the burr formation on the bore exit side. All caps and chips must be able to remove by vacuum, in addition a minimum burr height is required. The objective of this study is to describe the effects of orbital drilling on cap and burr formation in the exit composite material, primed clad aluminum 2024. The influence on cap and burr formation with different tool geometries, different coatings, different cutting parameters, tool wear and minimum quantity lubrication were examined.