hpt 2022 #4

cover story
figure 1
Titanium: “Like drilling into rubber”
“It’s like drilling into rubber”, says Alberto Gotti, head of R&D
at Mikron Tool. “Drilling titanium is much more challenging
than milling; and it is even more difficult when the diameter-drilling
depth ratio increases”. It becomes problematic
above 3 x d. Titanium’s viscoelastic properties cause the drill
to jam, which increases the pressure on the cutting edges.
Material build-up on the cutting edges and margins increases
the cutting forces which, in turn, can cause cutting edge
breakout. Once the surface is compromised, even more material
will build up and lead to higher friction. Also, the chip
shape becomes problematic because the titanium chips tend
to accumulate in the tip area and prevent smooth flowing of
chips. In turn, this often leads to uncontrolled drill breakage.
A further compounding factor are the high temperatures to
which edges are exposed. From a temperature of 600 ° Celsius
the cobalt binding matrix in the carbide substrate becomes
‘soft’ and is no longer able to bind the hard tungsten carbide
optimally. That leads to plastic deformation and micro-wear,
and ultimately cutting-edge breakouts.
Material-specific tools are the solution
One remedy are cutting edges which need to be very sharp
and very stable at the same time – a contradiction in itself.
Mikron Tool has developed an ingenious specific cutting
geometry that manages this balancing act and, as a result,
cutting pressures can be reduced significantly. As described
above, the heat needs to be moved from the machining area.
The solution: two cooling channels with very large crosssections
deliver large quantities of coolant through to the
drill tip to guarantee constant cooling, including lubrication
of the cutting edges. At the same time, the solid coolant
jet flushes the chips through the polished flutes and prevents
jamming chip backup. (figure 1)
There is nothing new here, but: the patented special design
of the cooling channels by Mikron Tool allows four times
the amount of coolant quantity to be shot into the tool with
constant pressure. This is a further key to success and stands
for innovation in the thermal dissipation and chip removal
technology.
Three years of meticulous development work has gone into the sensational ‘divine’ drills for titanium by Mikron Tool
no. 4, November 2022
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