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Technology
Hydrogen-Free DLC Coatings
Make Tools Hard and Smooth
A PVD coating technology with high potential in toolmaking is transferred from
the automotive field.
In the development of physicalvapour-deposition
(PVD) coatings,
market cross-fertilization has
been important. For example, the
forming- and cutting-tool market
can take advantage of coatings
developed for use on
automotive engine components.
The Dutch PVD coating
expert Hauzer Techno
Coating B.V. has transferred
its diamond-like-carbon
(DLC) tribological coating
technology to the tool market
with excellent results.
Coating hardness and
adhesion are key in many
tool applications, but other
features of coatings also can
be hugely advantageous. Nonsticking
performance, for instance,
is essential in the machining of
soft materials such as aluminium
and plastics, enhancing both tool
life and productivity. Smoothness,
on another hand, is very desirable
in forming tools. This property
can eliminate the need for
a posttreatment processing step.
All of these coating characteristics
have been studied in automotive
coating applications, and coatings
have been optimized.
Figure 2
Figure 1
DLC coatings are common in
automotive applications because
of their excellent tribological properties.
Their coefficient of friction
is low and they display nonsticking
behaviour. Depending on how
the coating is deposited (sputtering,
plasma-assisted chemical
vapour deposition or arc evaporation),
properties can be adapted
to the purpose. DLC is suitable for
coating drills, inserts, end mills,
saw blades, taps, punches, plastics
moulds, and dies. Applications
for DLC-coated tools include the
machining of aluminium, other
nonferrous metals, and plastics.
Another example of technology
transferred from one market to
another is hydrogen-free DLC, or
ta-C. During the European Nanocoat
project in which Hauzer took
part, tests were performed on several
DLC coatings used on auto-
motive engine components at the
Fiat Research Centre in Turin. The
researchers concluded that
ta-C coatings were unsurpassed
in their combination
of high hardness and low
friction coefficient. Hauzer
applied knowledge gained
from this project to solve
adhesion issues involving
ta-C. The result is a range of
ta-C coatings that have good
adhesion and hardness values
(40–70 GPa and DB 1–2)
and can be used industrially.
Hauzer has coated end mills
with ta-C (Figure 1).
Measurements of impact
effect taken by an engine manufacturer
showed that the ta-C
coating was still intact following
an impact load of 2 kN; only
small cracks were visible. Such
an impact load had previously
removed a benchmark coating. A
Rockwell indent reveals the ta-C
coating’s good adhesion (Figure 2).
Hydrogen-free ta-C coatings
are produced by means of arc
technology (circular arc or laser
arc) and possess a diamond-like
structure. They can achieve a typical
hardness between 3,000 and
7,000 HV. Their typical coefficient
of friction falls between 0.02 and
0.1. The advantageous features of
ta-C, taken together with Hauzer’s
solution of the adhesion issues,
make this coating promising for
the future of precision tooling.
» Hauzer Techno Coating B.V.
Venlo, Netherlands
www.hauzertechnocoating.com
European Tool & Mould Making | May 2011 | www.etmm-online.com