MACHINING NEW MATERIALS
adheres to the tool cutting edge—leading to poor surface fi nish and shorter tool life. Build-up on the tool can also be deposited onto the workpiece, and when build-up is released from the cutting edge, it can take particles of the cutting tool with it, leading to premature tool failure.
Because of the potential for BUE, Seco Tools recom- mends solid-carbide tools with positive angles, sharp to light edge hone, and smooth, high-polish coatings for high-silicon aluminums. “The positive angles allow us to cut the soft material rather than pushing, or smearing it, which sometimes happens when using negative inserts,” said Eller. “The smooth, high-polish coatings add lubricity, allowing the cut material to fl ow away from the cutting edge. The edge hone gives us the added edge toughness needed to combat the abrasiveness of the material.” Eller noted that polycrystalline diamond (PCD) tools have sharp edge preps and are polished uncoated in order to keep as sharp an edge as possible. Utilizing PCD grades with a submicron grain structure in these applications can also be affective against BUE. BIG Kaiser’s Cetkovic noted that, as in machining
A jet wing rib machined from Airware alloy produced by Constellium.
TiAl, new coatings are enhancing the machinability of high-silicon aluminums. “We’re taking our standard Sphinx cutting tools for aluminum and applying new, innovative coatings, which lead to increases in both performance and tool life.” Compared to uncoated tools, which can produce as few
as fi ve parts per tool, tools with new coatings can produce as many as 250 parts per tool. Again, a hard undercoating is followed by a smooth outer coating that enhances chip evacuation and helps prevents BUE. “For aluminums, we have a series of straight-fl uted
micrograin carbide drills that enhance chip evacuation at extremely high operating speeds and feeds; they reduce the length the chip must travel to exit the tool,” he said. “We’re usually in the ball park of tens of thousands of parts per tool.” One high-silicon aluminum automotive application was as high as 72,000 parts using a drill with an aspect ratio of 40 to 1 (length-to-diameter ratio). “While tools like these are expensive, shops using them un- derstand they are not buying a drill, they are buying holes,” said Cetkovic. “Four hundred dollars for each tool may seem like a lot of money, but if it gives you 72,000 holes, it’s really not.”
Aluminum-Lithium Alloys In the global aerospace market, new aluminum-lithium
alloys are gaining traction. The low-density alloy combines weight reduction with lower assembly and maintenance costs, and, with advanced welding practices such as friction welding as well as aerostructure redesign, offers up to 25% weight reduction. The lower alloy density and
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AdvancedManufacturing.org | January 2017
Photo courtesy Constellium
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