tooling
New applications and materials are driving coating
developments in tandem with the holy grails of
faster cycle time and extended tool life.
By Steed Webzell
Cut your coat
according to
your cloth
Seco’s Duratomic CVD
process delivers
extreme levels of both
toughness and wear
resistance
Sumitomo has
developed super fine
levels of coatings through
the application of nano
technology principles
‘UNCOATED cutting tools are set to disappear as
there is now no real need for them,’ said Jacob Harpaz,
the president of the influential IMC Group, which
includes TaeguTec, Iscar and Ingersoll Cutting Tools.
He was speaking at a TaeguTec marketing seminar in
late 2006 and, less than 18 months later, his words of
wisdom nudge ever closer to becoming reality.
However, to predict the future we must first assess
the present. So what do we already know about cutting
tool coatings? Well, it seems that the majority of the
newest depositions are based largely on an established
selection of formulae. Guhring provides the following
guide. TiN (titanium nitride, Guhring S-coat) is a well
proven, cost efficient, all-round coating, while TiCN
(titanium carbon nitride, Guhring C-coat) brings
considerable advantages in steel machining operations,
interrupted cutting in difficult-to-machine materials
or whenever demands as to hardness and toughness are
above average. TiAlN (titanium aluminium nitride,
Guhring A-coat) is for machining abrasive materials
such as cast iron and/or for working at high
temperatures, such as dry machining or in deep or
small diameter holes. AlTiN (aluminium titanium
nitride, Guhring Super A-coat) gives good high
temperature (red) hardness and oxidisation resistance. It
is used for difficult-to-machine materials such as
titanium alloys, Inconel and hardened steels above
52HRc, as well as for high speed machining. AlCrN
(aluminium chromium nitride, Guhring P-coat) gives
high oxidation resistance and red hardness for
enhanced wear resistance and productivity.
Coatings certainly play an essential role in delivering
Sandvik Coromant’s new generations of inserts and
grades. The company says that typically it is a
combination of more than one coating, PVD or CVDapplied,
that delivers the greatest steps forward. For
example, one of the latest coated grades is GC4215,
which is designed for increased steel turning
productivity primarily in the P15 area, although it also
offers improved cutting data across P10 to P20
applications. It features a CVD-deposited TiCN coating
78 MWP march 2008
that demonstrates enhanced adhesion to the substrate
and increased resistance to mechanical and flank wear.
However, a further coating of thicker, low stress Al2O3
(aluminium oxide) provides high thermal and
chemical protection to resist crater and other forms of
wear.
Another technological breakthrough in coating and
substrate technologies has enabled Sandvik Coromant
to improve wear resistance, security and higher cutting
speeds in the parting, grooving and profiling
application area. PVD of TiAIN layers and a new, finegrained
substrate optimised for steels and stainless steels
deliver improved hardness. Sandvik says the GC1125
grade excels when machining cast iron and heatresistant
superalloys. For the latest Sandvik milling
grade, GC4220, new coatings and substrate deliver
between 20 and 30% greater productivity than the
previous grade. A thin top coating is applied over a
TiCN coating, both applied by MT-CVD, on an
optimised substrate to achieve this improvement. The
top coating ensures better edge line toughness and no
flaking with enhanced surface finish. A new Sandvik
treatment of this top coating has also reduced the risk
of workpiece adhesion.
Oerlikon Balzers is another believer in multi-layer
coatings, having just introduced a dual-layer PVD
coating that allows the cost-effective hard milling
(above 60HRc) of moulds and dies by preventing the
cutting heat from penetrating the tool, instead
confining it to the chip. An adapted TiAlN base coating
ensures good adhesion and mechanical strength, while
a nanocrystalline AlCrN-based coating system applied
over the top features high hot hardness, resistance to
oxidation and thermal insulation properties.
According to Sumitomo Electric Hardmetal, more
than 80% of turning operations and 50% of milling
applications are performed with coated carbide, cermet
and CBN tools, a fact that has prompted the company to
develop super fine levels of coatings through the
application of nano technology principles. Sumitomo
first introduced 10 years ago the Sumitomo ZX
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