Titanium has properties like high strength, good corrosion resistance, low electrical conductivity, and a very good strength-to-weight ratio. It is widely used in aerospace, medical, automotive, and many more industries.
On other hand, it is easy to be welded to the cutter, likely to work hardening, and with high cutting pressures during the machining process, so titanium is also one of the most difficult materials to machine.
What causes the machining difficulty, two of reasons are listed below, let us dive in.
1. High heat generated during machining.
Most titanium alloys have very low thermal conductivity, which is only 1/4 that of steel and 1/13 that of aluminum. It conducts heat very poorly, and the heat generated in the cutting process is quite difficult to be carried away.
If the heat is not controlled well enough, it will concentrate in the cutting area, making the temperature to be more than 1 000℃, then the cutting edge of the tool will wear rapidly, cracking or forming the built-up edge.
While the rapidly worn cutting edge results in generating more heat in the cutting area, thus, it shortens the life of the tool further. Meanwhile, the high temperature will trigger work hardening, which reduces the fatigue strength of the parts.
2. Low modulus of elasticity property.
The modulus of elasticity is a measure of the ability of an object to resist elastic deformation. Generally speaking, it is the stiffness of the material.
Titanium alloys have a low Modulus of elasticity, which is only 1/2 that of steel, which means it will suffer more from spring back than steel or other materials during the machining process.
This also leads to more friction between the cutting tool and workpiece, generates more heat, and impacts the surface quality of the part.
By understanding the above reasons, you may want to know what is the solution for machining the titanium alloy parts, here we will share some tips as follows.
1. Adopt a positive angle cutting tool, to reduce cutting force, cutting heat, and workpiece deformation.
2. Use proper feeds and speeds. Lower the radial engagement is important to control heat and avoid work hardening.
3. Use High-Pressure Coolant and increase coolant concentration. It will help to conduct the heat generated during the Titanium machining process, then avoid workpiece deformation and cutting tool damage due to the high temperature.
4. Keep the cutting edge sharp, blunt tool is one of the reasons for heat concentration and cutting edge wearing,potentially cause premature tool failure.
5. To Avoid machining the Titanium after hardening, heat treatment increases the part hardness, makes it much more difficult to cut, also accelerates the wear of the cutting tool.
6. Using the Arc-in tool path strategy will reduce the shock when the tool enters the material for the first time. If you feed straight in, the tool will chip from the shock.
7. Adopt climb milling. In the milling process, the chips are from thick to thin, and the initial thick portion of the chip will get rid of more heat, thus less heat will stay in the tool. the thin end of the chip is less likely to create the built-up edge.
8. Use the special milling cutter on the market to machine titanium alloy parts, the kind of milling cutter is with unique structures, during machining, it sprays a large amount of high-pressure coolant to the cutting edge, to get the heat out of the work zone rapidly.
