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machines & automation


Solid-Diamond vs. Coated One of the arguments in composite machining is whether to use solid-diamond or diamond-coated tools. Some parts makers say that diamond coating is superior while others ar- gue that PCD (solid diamond) is better than diamond coating. “It’s true that a PCD tool can have sharper cutting edges than one with diamond coating,” said MacArthur. “But we’ll have applications where diamond coating will absolutely outperform PCD and applications where PCD will outperform diamond coated. It all depends on the material, what the composite lay- ers look like, and how the customer is cutting it.” PCD tools carry a much higher price tag than diamond- coated tools. For example, the cost of a diamond-coated drill might range from $100 to $200 while a similar PCD drill might cost $500. “However, one of our customers is using a PCD drill and getting 8000 holes with zero delamination and no uncut fi bers,” said MacArthur. “They drill a hole and never have to perform a secondary operation. The thou- sands of holes they do with zero problems makes the PCD drill cost effective.”


Taking on Honeycomb


While the use of solid-carbide and HSS tools in compos- ite machining is somewhat limited, there are applications where they are preferred, according to Ball of Seco Tools. “Typically, when people think of composites they think of CFRP, but there are also a lot of compos- ite honeycomb-type products that are made out of Kevlar or paper, and also stacked composites that include CFRP and metals,” he said. “With those type of materials, you’re typically applying a uncoated solid- carbide tool that’s extremely sharp to cut and shear the material.” Ball noted that there are some


aerospace composite applications for uncoated high-speed steel because it can be made sharper than solid carbide. “HSS doesn’t have the tool life, but then again you’re machining material that might not be as abrasive as a CFRP composite,” he said.


Specialized Machines


Like the cutting tools used in them, the machines used in composite part making are specialized to accommodate the unique nature of the work material. For example, Mitsui Seiki USA Inc. (Franklin Lakes, NJ) builds machines for CFAN Co. (San Marcos, TX), which, among other projects, makes CFRP turbine blades for the GE90 engine used in the Boeing 777. CFAN is a joint-venture between two aerospace companies, GE Aircraft Engines and SNECMA.


The CFRP blades include leading and trailing titanium edges. The fi ve-axis Mitsui Seiki HU100-TS HMCs, with the TS standing for tilt spindle, are used to trim the composite blade body and root section. “They are high-speed [15,000 rpm], 50-taper machines, and the challenge is they have to use only water as coolant because any additives to the coolant would cause delamination between the titanium and the carbon fi ber,” said Walker. “Everything on the machine, including pallets, has to be stainless or nickel-plated to avoid rust.” Walker noted that, unlike the HU100-TS, most machine tools used in composite machining are gantry, or bridge style, machines with articulating heads and CAT 20 tapers or HSK63-style tapers offering spindle speeds up to 50,000


A potted fi berglass honeycomb workpiece is shown being shaped with an Onsrud honeycomb hogger with an integrated blade.


94 — Aerospace & Defense Manufacturing 2016


Photo courtesy Royal Engineered Composites


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