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The goal of aircraft weight reduction is driving the current increased use of advanced exotic materials such as composites, titanium’s and Inconels in the aerospace industry. While materials such as these are lighter, yet stronger than those typically used, they each present their own sets of challenges when it comes to machining, more specifically drilling.
For drilling operations, aerospace manufacturers often use solid carbide and/or solid high-speed-steel tools.
During those machining operations, these manufacturers must achieve the highest levels of quality possible – often accomplished through carefully monitored and maintained process security. There are concerns about cost per part, but in most instances, producing perfect parts is a much higher priority, and increasing productivity tends to be secondary.
Aerospace manufacturers strive for process security and consistency through predictable performance of machines and tooling. In the case of tooling, these manufacturers must have milling cutters and drills that deliver practically the same exact amounts of tool life from one tool to the next.And even when they do know precisely how long a tool will last, aerospace manufactures often schedule machines to exchange tools well before they are completely worn.
Thanks to machine and cutting tool technologies, materials such as composites, titanium’s and Inconels have advanced from a stage of being almost impossible to machine to a point today where aerospace manufacturers machine them with confidence and efficiency. One tooling technology that gives better process control and consistency is advanced specialized solid rotary drills. These tools have been developed specifically for overcoming the machining challenges presented by these materials. Through the incorporation of various innovative coatings and geometries used in tandem with advanced machining techniques and strategies, these specialized tools will not only provide process security, but will also increase production speed and output.
Drilling
Drilled holes in composites must be perfectly clean and without ragged or frayed fibres that can interfere with and compromise subsequent assembly operations.
Two common challenges of drilling composites are delamination and uncut fibres, especially on the backside or drill exit side of workpieces. When drilling, tool forces push down on the material and as the drill nears the exit side, excessive force can cause the drill to push through, as opposed to cut through, the last portion of the hole. The result is composite fibres that are ripped and ragged instead of cleanly cut, causing material delamination.
To overcome these challenges, tooling companies strive to decrease drill feed forces against the material through the use of different point angles and helix angles on drills. It should be noted that some drill geometries generate lower feed forces and perform better than others.
For example, a 140-degree point angle – the most common for solid carbide drills – will work quite well for several holes when drilling composites. Unfortunately, as soon as the tool dulls at all, it loses its effectiveness. With C1 diamond coated solid carbide drill for composites, Seco imparts geometry with two point angles – a 130-degree angle in the centre and 60-degree angle on the chamfer of the drill. In operation, the drill’s centre point exits the end of the hole first, cutting away some of the hole’s material. So when the 60-degree portion exits, the feed forces of the drill through the material are drastically reduced. Thus, there is less delamination and fewer, if any, uncut fibres.
