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This article characterizes the special features of machining composite in comparison to machining metal. Simplified theoretic models will demonstrate how CFRP should be machined without delamination, burn marks and cutting tool breakages. Different strategies can be chosen depending on the material removal rate. The paper will present, based on this analytical approach, how milling cutters should be designed for optimal trimming, and how a drill should be designed in order to avoid the entrance, inner and exit delamination. While entrance and exit delamination is well understood, the paper will focus more to the delamination inside the bore. The appearance and the avoidance of the so called "Volcano Effect" and the reason why holes in composite becomes smaller after a couple of days will be explained. The comparison between 4 different cutting tool technologies will prove and give a better understanding how to use this theoretical approach.

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.

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.

Ever since the advent of fiber reinforced polymer materials in the field of Aerospace, Metal-FRP stacks started to gain importance due to their superior fatigue performance, phenomenal low weight and good specific strength. However the machining, specially drilling these multi stack materials has always proved to be a challenge for the field of manufacturing and assembly. Drilling holes in only metal with a drill (metal drill), the material removal is through a process of clear shearing since the tool is much harder and sharper than the base material. The tools hence wears at a much slower and gradual rate, also the malleable properties of the machined metal compensate to the reduced cutting capability of the worn out drill. These properties of the machined metal act like a ‘FAIL SAFE’ mechanism during the machining process assuring a trouble free fail safe environment during the drilling process. However, drilling FRP composites is altogether a different story.

Industrial robot applications are going to reduce cost in capital investment and enhancing the capability. A new concept of drill technology is successfully running in composite trailing edge manufacturing for drilling 5/8\mi holes in Composite/Aluminum stacks in IT8 quality. This article characterizes the special features of drilling of CFRP/Titanium and Aluminum stacks. Simplified theoretic models will show how CFRP/Titanium stacks should be machined without scratches and burn marks contacting carbon. Low axial forces and smart chip removal technology are the main characteristics of the drilling tool technology, optimized to reach IT8 quality in one shot operation.

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.