How to Grind Titanium Alloys: Wheels, Fluids, and Parameters

1. Why Titanium Is Difficult to Grind

2. Selecting a Grinding Wheel

3. Grinding-Fluid Selection

1. The fluid must cool, lubricate, and flush the grinding zone.
2. It should suppress adhesion and chemical reaction between titanium and the abrasive.
3. Supply at least 0.5 L/min for each millimeter of wheel width, increasing flow with wheel speed. Tank capacity should be about 1.5-3 times the flow rate to keep the fluid cool.
4. Titanium chips are flammable; take fire precautions when using oil-based fluids.
5. Suggested fluids include potassium nitrite solution; potassium nitrite plus sodium formate; sodium nitrite solution; sodium nitrite plus sodium formate; amine nitrite solution; or highly chlorinated oil.
6. For creep-feed grinding, one source formula by mass is 1% sodium nitrite, 0.5% sodium benzoate, 0.5% glycerol, 0.4% triethanolamine, and balance water.

4. General Grinding Parameters

The GC60JV (TL60R₃A) wheel in this table is for wet grinding; use a softer wheel for dry grinding. If roughing and finishing use separate setups, use a harder wheel for roughing and one grade softer for finishing. For surface or external grinding with wheels above 350 mm diameter, use one grade softer. Internal-wheel width should not exceed 1.5 times wheel diameter, and the stated data apply to wet-grinding 20-50 mm holes whose length is 2.5 times diameter.

5. Creep-Feed Grinding

Creep-feed grinding, also called deep-cut creep-feed grinding, uses depths up to 30 mm, about 100-1000 times those in conventional grinding, with work feeds of 5-300 mm/min. One or several passes can produce final dimensions and form. Reported accuracy is 2-5 μm, surface roughness R_a is 0.16-0.63 μm, and productivity is one to five times that of conventional grinding. It is mainly used for form grinding and deep slots.

Use a harder wheel when a lower roughness value is required. Diamond or steel rolls may dress the wheel for form grinding.

6. Low-Stress Grinding

Low-stress grinding removes a small allowance to reduce residual stress and avoid burn, deformation, and cracking on highly stressed titanium parts. It uses a softer, frequently dressed wheel, reduced radial infeed and speed, and abundant suitable fluid, but productivity is low.

For the final 0.25 mm allowance, remove 0.20 mm using 0.013 mm/stroke, then remove the final 0.05 mm using 0.005 mm/stroke.

Other Developing Titanium Machining Methods

1. Cryogenic cutting: Liquid nitrogen at -180°C or low-temperature fluid at -76°C controls the cutting environment and limits heat-driven tool wear.
2. Vacuum cutting: Excluding air prevents reactions between titanium and atmospheric contaminants that shorten tool life.
3. Inert-gas cutting: A local inert environment isolates the surface with simpler implementation than full vacuum cutting.
4. Electrostatic cold dry cutting: Ionized compressed air absorbs heat during recombination and forms a lubricating oxide film at tool-chip and tool-workpiece contacts.
5. Ultrasonic vibration drilling: Small-amplitude vibration can reduce deformation-zone size and cutting force, suppress built-up edge, improve dynamic stability, and improve fluid penetration, although alternating load may reduce tool life.

Other methods include laser, electrochemical, electromagnetic, heated, abrasive-liquid-jet, and special heat-treatment-assisted cutting.