Page 25 - machining_titanium_05_2019

Example

According to a manufacturing method, a 90° face mill of 100 mm (4 in) diameter is planned
to machine the open plane surface of a part. The surface width is 75 mm (3 in). What is the
value of feed per tooth that should be set to ensure average chip thickness 0.1 mm (.004”)? MILLING TITANIUM

Referring to Table 12 and Fig. 13, case a), hm=fz×sin(AE/2) fz=hm/sin(AE/2).
Angle of engagement AE=90°+arcsin((ae-r)/r) where r=d/2 – the radius of the face mill.
AE=90°+arcsin((75-50)/50)=120°, AE/2=60° and fz=0.1/sin60°=0.11 (mm/tooth).

For a 4 in. dia. cutter: AE=90°+arcsin((3-2)/2)=120°, fz=.004/sin60°=.0046 (ipt).

Example

A deep square shoulder in a titanium part is roughly machined by an 80 mm (3 in)
diameter indexable extended flute cutter that is operated with the following data:
ae=20 mm (.75 in),
fz=0.2 mm/tooth (.008 ipt).
Find the chip parameters.

With the use of Table 11 and Fig. 11:
- average chip thickness
hm=fz×√(ae/d)=0.2×√(20/80)=0.1 (mm),
- maximum chip thickness
hmax=2×fz×√(d×ae-ae )/d=2×0.2×√(80×20-20 )/80=0.17 (mm).
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Accordingly, for the inch-size cutter:
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hm=.008×√(.75/3)=.004 (in),- hmax=2×.008×√(3×.75-.75 )/3=.007 (in).

Radial chip thinning
The given examples show that the calculated values of both average hm and maximum chip
thickness hmax are lower than feed per tooth (chip load) fz. The examples illustrate one conclusion
that can be made when examining Tables 11 and 12: if width (radial depth) of cut ae in peripheral
milling and face milling (cases a) and d)) is less than the radius of a milling cutter, hmax becomes
lower than fz. Reducing ae leads to decreasing hmax and, accordingly, hm. This effect is
known as “radial chip thinning”, and taking it into account is very important, especially in milling
titanium which features intensive heat generation. Produced chips transfer most of the heat
and, therefore, they should be thick and massive enough to retain the heat and carry it away.
Maintaining the feed per tooth should ensure the required chip thickness and avoid critical
chip thinning. Understanding this effect is a key element for correctly programmed fz.

Tables 13 and 14 give auxiliary data that can help in quickly calculating
chip thickness for more common cases of milling:
- Table 13 for peripheral milling when AE<90° (or ae<d/2),
- Table 14 for face and peripheral milling when AE>90° (ae>d/2).
The following formulas may be useful for estimating AE in peripheral milling with ae<d/2:

AE=arcsin (2×√c-c ) (3)
2
and
AE=arccos (1-2×c ) (3a)
where c=ae/d – ratio of width of cut ae to nominal tool diameter d.

Table 13 Auxiliary Data for Peripheral Milling When AE<90°
Ae/d 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
√ae/d 0.224 0.316 0.387 0.447 0.5 0.547 0.591 0.632 0.67
SinAE 0.436 0.6 0.714 0.8 0.866 0.916 0.954 0.98 0.995
AE 25.8° 36° 45.6° 53° 60° 66.4° 72.5° 78.5° 84.3°

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