All metals are not created equal. Therefore, neither are the machine tools for cutting them. Parts for extreme aerospace applications, such as in engines, landing gear and flap tracks, must be made of a heat- and corrosion-resistant metal, which typically has a high Young's modulus of elasticity and is difficult to machine. These include titanium, stainless steel and high-nickel alloys.\r\nThe “hard metal†machines that process the parts must be stiff, typically requiring a large mass, and have a large servomotor to create lots of thrust. They also need a high-torque spindle to effectively move the cutter through the material and a high thrust load on the axes of the ballscrews, which often have a low 8mm pitch, to offer an effective mechanical advantage, according to Scott Walker, president of machine tool builder Mitsui Seiki USA Inc., Franklin Lakes, N.J. He explained that the machines are built that way because aerospace customers typically run them slower than 600 rpm, require around 2,000 ft.-lbs. of torque and take maximum chip loads from 0.002 to 0.006 ipt. “So you build this big, rugged machine,†Walker said.
