Page 18 - machining_titanium_05_2019

MILLING TITANIUM Initial Cutting Data In Milling

Generally, cutting data relates to finding depth and width of cut (ap and ae correspondingly),
cutting speed Vc and feed per tooth fz. Defining ap and ae is strongly dependent not only on
a chosen milling method and process planning but also on tool design characteristics such as
diameter and maximal cutting length. This section of the guide considers Vc and fz estimation.

Cutting Speed
Vc varies within a broad range, depending on the type of machining and machinability
of a specific titanium grade. Typical Vc values are shown in Table 6.

Table 6 Typical Cutting Speed Vc When Milling Titanium

Type of Machining Examples Cutting speed Vc, m/min (sfm)
Heavy-duty roughing, milling in 25-60
Hard (H)
unfavorable conditions (80-200)
Medium-duty roughing, 40-80
Medium (M)
semifinish milling (130-260)
Finish milling, 70-120
Light (L)
light-duty cutting (230-400)
A more accurate estimation of starting speed Vc requires a
simple calculation in accordance with equation (1).
Vc=Vo×Km×Ke×Ks (1)
Where: Vo – basic cutting speed
Km – machinability factor
Ke – engagement factor
Ks – stability factor

Basic Cutting Speed Vo

Basic cutting speed Vo depends on a tool material. Table 7 gives Vo values for the
carbide grades that are used in indexable milling cutters, and Table 8 gives Vo values
for the carbide grades intended for SCEM and MULTI-MASTER heads.

Machinability Factor Km
Machinability factor Km reflects the difference in machinability for titanium grades. It is
a derived value of machinability rating (Table 3, Fig. 2). Km is shown in Table 9.

Engagement Factor Ke

Reducing the angle of engagement AE (i.e. width of cut ae) allows increasing the
cutting speed Vc (Fig. 8). Table 10 gives appropriate values Ke for correction.

Stability Factor Ks

Stability factor Ks is defined by the estimate below of milling operation stability:
• Ks=1 for normal stability
• Ks=0.7-0.8 for unstable operations (high overhang, poor tool- or workholding,
milling thin walls, etc.) and milling in unfavorable conditions.

16 ISCAR