With coated hard metal tools machining at cutting speed around 200 m/min is currently common, against the 40 m/min applied 8 years ago. Thus, it is not truly a high speed machining but a much ‘quicker machining’. Diameters of tools used are between 4 and 20 mm, therefore the milling machines do not require spindles over 6000 rpm.
Titanium alloys present several problems:
- They have very low thermal conductivity, and therefore heat concentrates in the cutting area.
- High temperatures in the contact area between tool/chip and the high chemical reactivity of the titanium alloys with most tool materials, are the main causes for the rapid crater wear.
- The low elasticity module of these alloys causes flexions in the part, particularly on thin walled parts. This causes large inaccuracies on the finish and enables machining instability
Fig.11 Aeronautic engine components (photo courtesy of Volvo Aero).
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