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On CNC Machines, drilling holes under perfect condition is possible. For drilling holes into titanium, composite and aluminum stacked materials the specific cutting condition can be selected. Furthermore surrounding conditions such as peck cycle, MQL and force and torque monitoring can be easily adapted. When drilling holes in the final assembly, CNC machine tools cannot be employed due to sizes and accessibility. Power Feed Units or Automated Drill Units ADUs are very handy, flexible and depending upon the jig extremely rigid. Whenever a machine tool does not fit, ADUs are highly recommended. In comparison to machine tools, conventional pneumatic ADUs can be used with one fixed set of feed, speed and micro peck only. Due to that a compromise in cutting condition has to be chosen in drilling stacked material with different layers.

The present paper characterizes the difference between metals and composite repairs in aerospace application. The main difference, focus on 5 axis scarfing instead of 2 axis sheet metal cutting, using a ball nose tool in comparison to a Torus type end mil. Even high feed / low speed strategy comes out to a better surface finish and longer tool life. Using the higher step over on special typed end mills, this increases the tool life and consequently, lowers the cost per part. The new strategy and process understanding leads to more economic in onsite and out site repair solutions.

Up to now, the reliability achieved by COTS components was largely sufficient for avionics, in terms of failure rate as well as time to failure. With the implementation of new and more integrated technologies (90 nm node, 65 nm and below), the question has arisen of the impact of the new technologies on reliability. It has been stated that the lifetime of these new technologies might decrease. The drift is expected to be technology dependent: integration, technology node, materials, elementary structure choices and process pay a key role. Figures have been published, which gives smaller lifetime than the 30 years generally required for avionics. This would of course impact not only the reliability, but also the maintenance of COTS-based avionics. Hence a new policy should be defined for the whole COTS supply chain. Faced with these impending risks, different methodologies have been developed.

This article describes the physical background and the experience in the drilling of carbon fiber and aluminum-carbon fiber stacks. Low temperatures and intelligent chip removal technologies are the most important requirements for dry drilling or to avoid the MQL (minimum quantity lubrication). The drilling in one shot and in IT8 quality is mandatory. In case of machining metal, like aluminum or titanium, a lot of heat is generated by the tools and the cutting process. Machining of composites, the material and the tool should remain as cold as possible even by drilling without external or internal coolant. A new drill design is now developed, qualified and patented by MAPAL that allows the dry drilling of metals at very low temperatures also. We are now able to drill, all batches (composite / aluminum) without MMS. The high drilling feed and due to that, the shorter contact length between the tool and the material stack also gives us approximately twice the tool life.

Drilling holes into metal with MQL (Minimal Quantity Lubrication) is a normal procedure, because the drill is designed for drilling metal and the malleable capability of the metal compensates for the insufficient cutting capability of a worn out drill. Drilling composite materials using the same drill (designed for drilling metal) is a different procedure, because composite fibers are not malleable like metal at all. Due to this fact the tools become very hot trying to forge composite fibers like metal. The elastic behavior of the composite and the delamination inside the hole makes the tool temporary smaller than the diameter of the drill. The hole in the metal part of the stack remains slightly larger due to the heat and the thermal expansion rate. This paper shows how to drill metal and composite with the same diameter, so that achieving H8 quality is no longer a dream.