New Tool for Dry Machining of CFRP-Aluminium Stacks
The fuselage, wings and flaps, as well as the horizontal and vertical stabilisers, of the latest generation of aircraft are produced out of CFRP-aluminium stacks. As the experts at Mapal know, assembling aircraft involves drilling innumerable bores including countersinking into these components to make the rivet joints. Drill feed units are used for machining in most cases. According to the tool specialists from Aalen, Germany, the dimensional accuracy of the bores is crucial when drilling. The bore must have exactly the same diameter in both materials. Drilling always takes place from the outside to the inside, which means the bore entrance and countersinking in CFRP and the bore outlet in aluminium.
Previously, minimum quantity lubrication (MQL) was applied for this manufacturing step. After machining, the components therefore had to be disassembled, cleaned and reassembled. In addition, machining was often carried out in several successive machining steps. Different tools were used for drilling, reaming to the final diameter, and countersinking. According to Mapal, the whole process was time-consuming and costly, and the required dimensions were often not reliably achieved. For example, the bore and countersinking often did not align on one axis.
Heat caused by machining not transferred to the component
The specialist tool manufacturer has now developed a new drill with countersinking for dry machining of CFRP-aluminium stacks. The particular geometry of this tool is designed to ensure that the heat resulting from machining is not delivered to the component and hence minimum quantity lubrication can be dispensed with.
The solid-carbide drill with two cutting edges is designed to combine the properties of a drill for machining aluminium with those of a drill for CFRP machining. A double point angle should also ensure good centring of the drill and minimum burr formation at the bore outlet. To avoid any delamination and fibre protrusion when countersinking in the CFRP, Mapal added a rake face correction at the countersink step. The drill is diamond-coated, meaning that the tool life is eight times that of an uncoated drill. The drill is applied with a speed of 5000 rpm and a feed of 0.1 mm. The drill is available with a diameter between 4.1 and 11.11 mm with the associated countersink step.