tooling
Development of an abrasion and heat resistant coating for indexable inserts overcomes
traditional performance barriers presented by intense cutting conditions
Going with the grain
Steeltec LC240F insert
showing Nanolock
coating
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TITANIUM carbonitride (TiCN) coatings have
been widely used to prevent wear on indexable cutting
inserts and tools, but insert development has been
hampered by an inability to reduce the grain (crystal)
size of the coating. Now, in what could be regarded as
a nanotechnology breakthrough, LMT’s Boehlerit
division has with Nanolock created a coating which is
both extremely hard and tough, and which can protect
the insert from excessive wear under high
productivity cutting conditions.
TiCN coatings are applied by either Chemical
Vapour Deposition (CVD) or Physical Vapour
Disposition (PVD); over 90% of all CVD coated inserts
use at least one layer of TiCN to bond the ceramic
layer (such as aluminium oxide) to the carbide insert
or cutting edge. The CVD process creates a hard
surface and achieves very strong adhesive properties,
but the end result lacks toughness. So, multi-layer
coatings are customarily regarded as the best available
solution for protecting tools against wear, as well as
from mechanical and thermal stresses. However they,
too, tend to be either extremely hard or tough,
according to the application - to date it has been
impossible to obtain both. CVD-applied layers are
thick compared to PVD coatings, and although not as
tough they last longer before becoming brittle;
however, coating layers can separate when higher
machining speeds are being pursued.
LMT Boehlerit, via a two-year development
programme using CVD, has found a way to reduce the
grain size of the coating and thereby improve the
bonding of the different materials. Says Reinhard
Pitonak, Head of Coating Development: ‘We are on
the threshold of a major new development in hard
coatings for heavy duty applications such as milling,
bar peeling and cam and crankshaft type machining.’
LMT Steeltec LC215K indexable inserts, the first
fruits of this development, are already running on
steel at cutting speeds of over 300m/min, registering a
cutting life 50% higher than the conventional inserts
they replaced. The Steeltec inserts also incorporate a
special combination layer producing a yellow ceramic
top coating surface, giving visual advanced warning of
wear that could lead to insert failure. Trials have
demonstrated the Nanolock layer development is
extremely hard, and only marginally influenced by
abrasion; it combines the abrasion resistant properties
of the titanium carbonitride with the heat-resistance
of aluminium oxide. And while the higher operating
temperatures under cutting conditions could cause
wear on the open spaces of the insert through plastic
deformation at the corners, layers such as aluminium
46 MWP january 2008
Cam shaft whirling using Nanolock inserts
oxide function as a protective thermal shield.
Once Pitonak saw the practical benefits of the new
insert he approached Vienna Technical University to
investigate the structure using electron microscopy -
and discovered that the company had created the first
‘nanocrystalline’ coating. ‘According to all the
textbooks our Nanolock coating should never exist,’ he
says when reflecting how the Boehlerit team
experimented with the use of higher temperatures on
the company’s latest CVD coating furnaces (working
at 900-1100 oC rather than the normal 700-900 oC) to
develop a harder TiCN coating.
‘At the University, the unusual microstructure we
had created was clearly discernible under the
microscope at 1,000x magnification.’ He adds that,
instead of being presented in a uniform colour, under
magnification the Nanolock layer had dark orange to
red areas, very rich in carbon and were laid out side by
side. ‘This proved we had achieved what pundits
claimed was impossible. We had been able to mix the
elements of carbon and nitrogen present in the TiCN
layer at both micro and nanostructure levels.’
He maintains his team had been working
nanotechnologically without even realising what they
were doing. They had developed a new layer with grain
size roughly three times finer than previously achieved
(just 25 nanometres) and created a so-called ‘composite
character’ - two different grain structures that are
simultaneously present and adjacent to one another.
More critical to the application of cutting inserts is that
the Nanolock coating has extremely fine, needle-like
surface that intensifies the adhesion to the adjoining
layer.
www.LMT-tools.com
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