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High Speed Milling Titanium

High Speed Milling (HSM) Can Refer To Several Operations:
• high cutting speed milling,
• high spindle speed milling, MILLING TITANIUM
• high feed speed milling.
All the mentioned speeds are interrelated. Increasing spindle speed n automatically results in
increasing feed speed Vf as well, and likewise more cutting speed Vc requires more spindle speed
n to the same extent. As cutting speed varies in direct proportion to the diameter of a rotating
tool, ensuring the same Vc for mills of different diameters demands different spindle speeds.
In the context of the guide, more correct understanding of HSM relates to high spindle speed.
In milling titanium, cutting speeds are significantly lower than in milling steel.
Although advanced tool materials and new machining techniques have led
to growing a growth in averaged cutting speeds set for milling titanium, high
Vc and n values for titanium may look like “normal” values for steel.

There are several factors that result in high spindle speed n:
• small tool diameter,
• small effective diameter,
• trochoidal milling as the machining strategy.

The small effective diameter de relates to milling by profiling tools (especially ball
nose or lens type) at shallow depth of cut. Table 28 and Fig. 23 show possible
cases for calculating the effective diameter for ball nose milling cutters.

Example
An 8 mm (0.315 in) solid carbide ball nose endmill machines the inclined
surface of a titanium workpiece by ramp-up milling. Ramping angle α=12°,
machining allowance per pass a=0.1 mm. The workpiece material is annealed
Ti-6Al-4V, the endmill carbide grade – IC908. Find spindle speed n.

From Table 28 effective diameter
de=(8-2×0.1)×sin12°+2×√((8×0.1-0.1 )×cos12°=3.36 (mm) (0.132 in).
2
Basic cutting speed V0=65 m/min (213 sfm), Table 8.
For simplicity assume that cutting speed is the same (Vc=V0).
Spindle speed n=(1000×65)/(π×3.36)=6158 (rpm).

Effective diameter
A profile milling tool (ball nose cutter, toroidal mill etc.) features a shaped, non-straight cutting profile
and the cutting diameter is a function of a depth of cut. In profile milling, the effective diameter is the
largest true cutting diameter.
Generally, it corresponds to the diameter, measured at the axial depth of cut.

A necessary cutting speed should be calculated with respect to the effective diameter.
Ignoring it can cause essential errors in cutting data and result in poor performance.

Note. For the equal cutting speed, which corresponds to nominal tool diameter d=8 mm (0.315
in), spindle speed will be 2586 rpm. For the nominal diameter, the found spindle speed provides
the cutting speed 154.8 m/min (507.8 sfm). Using this virtual speed as a characteristic of the
considered operation is misleading because the real cutting speed is much lower.

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