Investigation of interlayer burr formation in the drilling of stacked aluminum sheets
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During the drilling process, sharp edges of material called burrs are produced and protrude from the original surface. When a through-hole is drilled, burrs form on both the entry and exit surfaces around the hole, requiring expensive deburring operations to be performed in order to meet part specifications. A common hole producing operation in aircraft assembly is drilling holes through multiple sheet metal layers in order to fasten them together. However, at the interface between two layers, burrs form on both the exit of the first layer (termed "skin") and entry of the second layer (termed "frame"). Consequently, the layers frequently need to be taken apart, deburred, and put back together again before being fastened, resulting in additional costs and increased assembly time. The goal of this thesis was to understand the role of key factors such as drill geometry, drill wear and clamping conditions on burr formation at the interface of two thin sheets of 2024-T3 aluminum so that interlayer burr formation could be minimized. This problem was approached from three different angles. First, an experimental study was performed to find the drill geometry parameters for minimization of interlayer burrs and to ascertain the relationship between the average burr size and drill wear. Next, a new kind of clamping system for holding sheet metal layers together during drilling was designed, prototyped, and tested for its effectiveness. Finally, a preliminary analytical model of interlayer burr formation was created in order to better understand the burr formation process in stacked layers of sheet metal and to better understand the effect that each drilling parameter has on the resulting burr size.