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Technology update
High speed machining for the aerospace industry
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Advances in numerical-control systems have allowed the aerospace industry to benefit from the use of high-speed machining. With a high-speed spindle and suitable structure, high-speed machining systems facilitate an increase in the rotational speed of cutting tools by a factor of 10 or more, and show very significant productivity gains for operations involving the removal of swarf. Machining at high speed is particularly suitable for light alloys and composites, stated Francois Lhuillier, Technical Manager of the French company, Realmeca: "The energy released by high-speed machining is 95% dissipated in the swarf with little heating of the part. The milling tool literally cuts the metal without subjecting it to internal stresses. That is why the result is better than with conventional machining."
At Dassault Aviation, Research and Development Engineer Daniel Marchand, stated: "The milling of our large dimension parts can take dozens of hours. To shorten this time we examine all possible methods to accelerate the machining."
Dassault has been testing high-speed machining techniques since the early 1980s, but at that time, the company found that numerical control and axes of displacement with the ability to track tools at very high rpm were not available. However, with technology advances, Dassault now uses machines fitted with high-speed spindles, the most recent a gantry system with a worktable 36 ft long and a
high-speed spindle capable of operating at 30,000 rpm. The machine carried out milling of structural parts of up to 14.8 ft. The manufacturer of the machine is Forest-Line, which designs and produces large-dimension gantry-machining equipment for many aerospace companies. This year, Forest-Line introduced a vertical milling machine equipped with linear motors. The motors replace traditional ball screws and provide displacements of the high-speed spindle with very high accelerations. Displacements are said to reach speeds three to five times higher than those using ball screws. Linear motors reduce maintenance because they have fewer working parts and they are also quieter in operation.
Stuart Birch
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