Machining Titanium

The metallurgical properties of titanium make it a bit more difficult to machine than steels of the same hardness. Typically commercial grades of titanium are easier to machine than aircraft alloys. The included challenges of machining titanium are damages resulting in the form of micro-cracks, built-up edge, plasmatic deformation, heat-affected zones, and tensile residual stresses which can lead to degraded fatigue strength and stress corrosion resistance.

Breakthroughs of new tooling materials have improved the machinability of titanium. Titanium's physical, chemical and mechanical properties are part of what makes it a challenging material to machine:

Titanium is a poor conductor of heat which tends to concentrate most of the heat on the material cutting edge and tool face.
Tooling operating temperatures can have an impact on an alloying tendency (chemical reactivity) between the titanium being machined and the material composition of the tools used
Unless heavy cuts are maintained or proper backup is employed, titanium's low modulus of elasticity tends to cause thin material to deflect under tool pressures resulting in chatter, tool rubbing and tolerance problems.
Rapid tool break-down is often experienced due to titanium's work-hardening characteristics. There is no presence of a stationary mass of metal ahead of the cutting tool (absence of a built-up edge) which results in a high shearing angle and causes high bearing loads per unit area on the tool face. This combined with the mechanical reactions of material cutting (chip formation, attaches to tool face) increases heat in a localized portion of the cutting tool.
Surface integrity is greatly challenged during the grinding of titanium. Losses of mechanical behavior resulting in fatigue are the results of not using proper techniques and conventional parameters.

For these reasons proper speeds, feeds, cutting tools, fluids and techniques combined with a working knowledge of your application and titanium grade or alloy are paramount. Be sure to consult with your tooling provider and published information for the right approach to your machining needs.