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Mapal Combination tool for dry machining of Al/Al stacks

Aircraft manufacturers frequently employ stacks of different aluminium alloys for the aircraft fuselage. During final assembly of the aircraft, drill feed units are used to drill bores for riveted joints in these two aluminium alloys that form the ribs and outer skin of the aircraft. Until now minimum quantity lubrication (MQL) has been used to cool the drilling and countersinking tools. However, the cooling medium then got inside the aircraft where further assembly steps were taking place at the same time. This type of cooling also requires extensive cleaning. As a result, the demand arose for a tool for dry machining of the Al-Al stacks.

Not only the dry machining made demands on the tool, but also the varying properties of the two different aluminium alloys. The machining operation must not produce a burr, either at the bore exit or between the two layers.

MAPAL has taken up this challenge and developed a new drill with countersink step in order to be able to drill the bores for the riveted joints dry. The twin cutting edged carbide tool has an extremely positive cutting edge and a double point angle. This minimises burr formation and achieves better centring. The coating of the drill prevents material adhesion to the cutting edge. A leading stage provides for an optimum bore quality. Specially formed chip flutes ensure optimum chip removal. Air is used for cooling, preventing overheating of both the tool blade and the aluminium and hence burr formation. The compressed air is also used to blow out the chips.

At one aircraft manufacturer the new drill is used i.a. for the bores on the longitudinal seam in the rear main span. A spindle speed of 2,959 rpm and a feed rate of 0.154 mm are used here. The drill with its diameter of 4.748 mm and a 100° countersink step reliably produces 1500 bores before the bores no longer lie within the demanded tolerance of 4.73-4.805 mm.

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