It is not difficult to understand why automotive, medical, chemical, micro-component and, especially, aerospace designers love titanium. Its density is only about half of steel, so titanium parts weigh roughly half as much as steel parts. But its high strength — 80,000 psi for pure titanium and 180,000 psi-plus for its alloys — is far greater than the strength of many alloy steels giving it an extremely high strength-to-weight ratio. Titanium has twice the elasticity of steel, making it an ideal choice for applications that require flexible materials that don’t crack or rupture. Also, titanium alloys resist corrosion and oxidation better than stainless steels.
| Because of its high strength and light weight, titanium is a favorite with aircraft engine designers. (Photo courtesy Pratt & Whitney.) |
Many of the same qualities that enhance titanium’s appeal for most applications also contribute to its being one of the most difficult to machine materials.
However, shops that understand this material’s peculiarities can machine them successfully and cost-effectively.
Most titanium alloys are poor thermal conductors. Heat generated during cutting doesn’t dissipate through the part and machine structure, but concentrates in the cutting area. The high temperatures that can be reached — 2,000°F in some cases — can lead to cutting edge chipping and deformation, and dull edges on tools generate even more heat and further reduce tool life. Cutting temperatures can get so high that titanium chips sometimes burst into flames.
The high temperature generated during the cutting process also causes a work hardening phenomenon that affects the surface integrity of titanium, and could lead to geometric inaccuracies in the part and severe reduction in its fatigue strength.