Page 38 - machining_titanium_05_2019

MILLING TITANIUM In view of this, the up-to-date machining centers, which MTB companies offer to producers

of titanium components, are suitable for HPC supply. As practice shows, machining with HPC
can even double cutting speed in comparison with classical As shown in practice, Accurate
value for increasing cutting speed depends on specific factors. To estimate initial cutting
speed in milling with HPC VHP, it is recommended to use the following equation (8):
VHP=(1.2…1.3)×Vc,
(8)
where Vc – Initial cutting speed, given by equation (1), or determined with the use of (Table 6).
By assuming that the increase in VHP is 25% in average, this equation
after substituting the terms of equation (1) will look as follows:
VHP=1.25×Vo×Km×Ke×Ks (8a)

As in case of finding starting speed in milling in general, basic cutting speed Vo, factors: Km
(machinability), Ke (engagement) and Ks (stability) are (also) found in Tables 7-10. Stability factor
Ks is assumed as 1 for normal stability, and 0.7…0.8 for milling in unstable conditions.

Example
Find initial cutting data for rough milling deep square shoulder in a workpiece from titanium Ti-
6Al-4V ELI. The applied tool is ISCAR’s 80 mm (3 in) dia. indexable extended cutter carrying
inserts made from carbide grade IC5820. The cutting parameters are as below:
depth of cut ap=85 mm (3.35 in), width of cut ae=20 mm (0.79 in).
The machine intended for the milling operation is a vertical machining center with HPC option, and the
cutter has inner channels for high pressure coolant supply. Operational stability can be estimated as high.

Vo=43 m/min (141 sfm). (Table 7, hard type of machining)
Km=1.1 (Table 9).
Ke=1.2 (Table 10).
Ks=1.
Vc=43×1.1×1.2×1=52 (m/min) or 170 sfm.
Hence, VHP=(1.2…1.3) ×Vc ≈ 65 m/min=
213 sfm.
From Table 15 for ae/d=0.25 fzo=0.14 mm/tooth (0.0055 ipt) and
fz=fzo×Ks=0.14×1=0.14 (mm/tooth)
or 0.0055 ipt.

There are different factors that influence HPC supply through the body of a milling cutter,
which tool engineers take into account when designing the cutter. In indexable milling, from
the application point of view, attention should be drawn to the coolant outlets. They are
formed by nozzles, screwed in appropriate holes that open into chip gullets (Fig. 17, 18).

Fig. 17 A T490 extended flute cutter Fig. 18 A nozzle mounted in a coolant
Intended for HPC. The cutter design supply hole near a T490 extended
Enables nozzles to be mounted in the flute cutter face-cutting insert
Coolant supply hole outlets

36 ISCAR