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Diamond-coated carbide thickness and sharpness: (left) uncoated carbide; (center) 2-4 micron thick Crystallume ThunderBolt diamond coating; (right) 18-20 micron thick Crystallume Standard Premium diamond coating.


ites that are susceptible to delamination during trimming. In 2012, the company purchased a waterjet composite machin- ing center that has both a five-axis router and a five-axis abrasive waterjet with an envelope of 6.5 x 2.5 x 1 m from Flow International Corp. (Kent, WA). Royal transitioned most of its unidirectional jobs to that machine. As the name implies, threads in unidirectional composites run all in one direction, as opposed to woven materials with threads crossing each other at 90-degree angles. Unidirection- als are stronger than wovens and can be cross-laminated like plywood, said O’Dey. They’re often more expensive to process than multidirectional composites, but offer weight and strength optimization that can be crucial in many aerospace parts.


Practice Makes Perfect


Over the past few years, Royal has improved its machin- ing performance not only by using improved tools, but also by changing how they use them. “The more we use tools, the better we understand them,” said Macklin. “By balancing tools and using shrink-fit holders to minimize runout, we’ve been able to increase the life of our diamond-coated tools. The coatings are typically very thin, so virtually any amount of runout would substantially reduce tool life.”


Another key issue is achieving the right feeds and speeds,


a process that can sometimes be counterintuitive, according to Macklin. “Some of our tools like to be pushed harder than what we expected,” he said. “We started out with more of the conventional bonded diamond grit-type cutting tools. With these tools, you’re usually looking at low feed rates relative to your rpm, but some of these cutters and routers like high feed rates and high chip loads and will actually last longer if you push them harder.”


Tool Change The growth in use of solid-diamond and diamond-coated tools has led to a growing range of tool choices for aircraft


manufacturers. For example, RobbJack is offering variable thicknesses on many of its coated tools. MacArthur noted that thinner coatings—some in the 2–3 micron range—enable higher sharpness and cost less than thicker coatings, but are less wear resistant. Longer wearing coatings, with 15–20 micron thicknesses, make tools less sharp but longer lasting. Not satisfied with standard thicknesses, many aircraft manu- facturers are demanding custom coatings that better match specific applications. Ball of Seco Tools agreed that custom coating thick-


nesses are an important feature. He noted that Seco offers a standard range of tools with a 5 to 12 micron-thick CVD coating, but the company can vary the thickness depending on the application. As aerospace applications expand, the types of tool geometries are multiplying, which can be challenging for toolmakers. “We have 8–10 different kinds of drill tips and hundreds of different geometries for trimming and milling,” said MacArthur. As a result, about 60% of the tools RobbJack sells for composites are custom. “For example, we tend to match our drills to aircraft rivet sizes. One manufacturer may want rivets to sit a bit higher than the guy next door, who likes to be on the low size. They all end up having minor differences, such as in-hole diameter. The ability to be flexible and come up with engineered solutions for different customers is very important.” Another trend is the major change that has occurred in solid- diamond tools. Ten years ago, solid-diamond tools consisted of a flat sheet of diamond brazed into a flute, with limited geometry options, according to MacArthur. “Today, toolmakers can work with a solid slug of diamond that can be brazed onto a carbide tip, which is in turn brazed onto the tool shaft, so we’re actually brazing the carbide to carbide,” he said. “We use electrical discharge grinding machines with advanced software, probes and vision systems to flute the solid diamond as you would a solid-carbide tool, so any geometry is possible.”


93 — Aerospace & Defense Manufacturing 2016


Photo courtesy RobbJack/Crystallume


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