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Machining Nitinol

Machining parameters must be chosen carefully in order to successfully machine Nitinol. Nitinol work hardens very rapidly. It has a low modulus and low thermal conductivity. These factors make machining difficult and reduce tool life. Cutting speed, feed rate, tool type, tool geometry and lubrication must be selected carefully.

Carbide tools are preferred for machining Nitinol. Cutting speeds are slower than for other nickel-based alloys in order to prevent excessive tool wear. Feed rate, tool geometry and cutting fluid are adjusted to maintain reasonable tool life.

Stranded wire from 1 x 7 x 0.076 mm (0.003") to 1 x 7 x 0.2 mm (0.008") diameter, as drawn or straight superelastic.

Grinding is often used for metal removal. However grinding too fast can be abusive and cause surface defects.

The following are excerpts from "Machinability of Nickel - Titanium Alloys:

  1. Nitinol alloys are turned 10 to 20 times faster with carbide tools compared to high speed steel tools.
  2. Feeds of 0.003 to 0.005 inches per revolution are used in turning.
  3. The optimum tool geometry for face milling is 0 degree axial rake and 0 degree radial rake.
  4. A feed of 0.005 inches per tooth is used in face milling. At higher and lower feeds, tool life decreases rapidly.
  5. Drilling speeds of Nitinol was 5 to 10 times faster with carbide drills versus high speed steel tools.
  6. Drilling speed is critical. A deviation of 5 feet per minute from the optimum will decrease tool life over 50 percent.
  7. Light feeds are used in drilling Nitinol. Feeds over 0.002 inches per revolution will result in very short tool life.

The Machining Data Handbook published by TechSolve (www. TechSolve.org) details parameters for many machining configurations such as turning, milling, threading, drilling, reaming, boring, grinding and centerless grinding of Nitinol.

References:
1. D. E. Hodgson, "Fabrication, Heat Treatment and Joining of Nitinol Components" in SMST-2000, Proceedings of the [Third] International Conference on Shape Memory and Superelastic Technologies, edited by Russell and Pelton, Pacific Grove, CA, April, 2000, pp 11 - 24.
2. J. V. Gould, "Machinability of Nickel - Titanium Alloys" AD 419-009, Metcut Research Associates, June, 1963.