Grade 2 titanium is generally considered moderately difficult to machine, falling between stainless steels and high-strength alloyed titanium grades (like Grade 5 Ti-6Al-4V). Its machinability characteristics are defined by the following key factors:
Low Thermal Conductivity: Titanium does not dissipate heat efficiently. During machining, heat concentrates at the cutting edge, leading to rapid tool wear, cratering, and potential workpiece burning.
High Chemical Reactivity:
At elevated cutting temperatures, titanium readily reacts with oxygen, nitrogen, and carbon from the atmosphere or tool coatings, forming a hardened surface layer (alpha case) that accelerates tool abrasion.
High Modulus of Elasticity & Springback:
Titanium has a lower modulus of elasticity than steel, causing the material to "spring back" away from the cutting tool. This can lead to chatter, poor surface finish, and dimensional inaccuracies if not accounted for.
Galling & Built-Up Edge (BUE):
The material tends to adhere to the cutting tool, forming a built-up edge. This degrades the surface finish and can cause premature tool failure.
Practical Machining Recommendations:
To machine Grade 2 effectively, the following practices are essential:
Tooling: Use rigid, sharp tools made of solid carbide or high-speed steel (HSS) with positive rake angles. Polycrystalline diamond (PCD) or cubic boron nitride (CBN) tools offer superior performance for high-volume production.
Cutting Parameters: Employ low cutting speeds (typically 30–60 m/min for turning, lower for drilling) and high feed rates to minimize heat generation and tool contact time.
Coolant: Use a high-pressure, high-flow rate coolant (preferably flood coolant with a high oil content or a synthetic ester-based fluid) to effectively cool the cutting zone and flush away chips.
Rigidity: Maximize the rigidity of the machine setup, workpiece fixturing, and tool holders to minimize vibration.
