2 - ALU-WEB.DE

10 MACHINING 4 | 12-2009 APT ALUMINIUM NEWS
Sophisticated aluminium supporting structure for gigantic jewel
Industrial service provider
turns architectural vision into reality
It is often a long and thorny
journey from a design on a
computer screen to its actual
realisation. This applies
all the more the greater the
dimensions. There is a need
for service providers who
take overall responsibility
for the implementation
and deal with every aspect
from material procurement
through to the supply
of components ready for
installation.
“The Makkah Clock
adds the crowning finish to
an extremely sophisticated
skyscraper project in Islam’s
most important place of pilgrimage,”
explains Martin
Meenen, CEO of Aquatec
GmbH based in Emmerich,
Germany. The company
started life as a job shop specialising
in the waterjet cutting
of large format parts.
It now operates two of the
largest waterjet cutting units
in Europe, with table sizes
of 16,000 x 4,000 mm, and
has developed uncompromisingly
into an all-round
Graphics: Aquatec
The ‘Jewel’ located on top
of the Makkah Clock at a
height of about 500 m is
a sophisticated structure
made of glass and aluminium
service provider, offering
its clients practically every
desirable additional service
– from the procurement of
material via the selection
of suitable processing steps
through to implementation
and supply of ready-to-install
parts as a complete package.
A current example of this is
the company’s contribution
to the ‘jewel’ above the clock
at the top of the 500 m high
building that together with
four other skyscrapers will
dominate the skyline of this
Saudi Arabian city. The top
part, the design of which is
based on a precious stone, is
29 m high and consists of a
total of eight aluminium and
glass segments each up to 10
m wide. The desired faceting
As a specialist for large-format waterjet cutting, Aquatec has two of Europe’s largest waterjet
cutting machines with table sizes of 16,000 x 4,000 mm
of the exterior is achieved via
a complex, intricate, threedimensional
latticework of
aluminium nodes and crosspieces
to which the massive
panes of glass, almost 80 mm
thick, are bonded directly.
This thickness is required in
order to withstand the enormous
wind loading: at this
height, the desert wind often
Each of the numerous
triangular surfaces is bordered
by up to 6 m long
aluminium mullions that
are joined together (lower
left) with the help of complex
node elements
reaches hurricane force. Nevertheless,
the widths of the
webs between the huge plates
of glass that are visible from
the outside are only about 20
mm wide so as not to impair
the overall aesthetic appearance.
Even the material
requirements are
extremely demanding
…
“The vision is always to the
fore in such projects,” explains
Mr Meenen. “It is essential
to create something distinctive
that has never been built
before. The demands are correspondingly
high.” This forces
both architects and their
engineering teams to take
their conceptual designs into
areas where others have previously
not dared to tread. This
pressure is in turn passed on to
the service providers carrying
out the work, who then have
to go searching for materials,
production processes and
special solutions that are not
available on the market, or at
least not in the required form.
This starts with material procurement
because as a result
of the extremely high loading
the combinations of material
and strength required for the
nodes and crosspieces, which
were hitherto not available
from any manufacturer. For
example, the AlSi1MgMn T6
blanks for the massive nodes
were cut from round stock
with diameters between 400-
650 mm and had to have a
proof strength of 230 MPa in
the interior even though the
manufacturers of such material
thicknesses usually only
guarantee 180-200 MPa. It
was not possible to revert to
another material, in part for
technical reasons such as corrosion
resistance, anodisability
and the like, and in part
for cost reasons. The search
for a producer who was willing
to guarantee the specified
requirements proved to be
complex and required intensive
negotiations.
The procurement of the
raw material for the crosspieces
proved to be equally
problematic; these were made
Martin Meenen: “Our job
is to turn our customer’s
concept into reality. We
take overall responsibility
for that.”
from rolled plate of the naturally
ageing alloy AlMg4.5Mn
with a wall thickness of 82 mm
and had to have a minimum
proof strength of 155 MPa.
Here, too, it was only after
a long search that one was
able to find a producer who
could guarantee this value
instead of the usual 115-125
MPa – thanks to a specially
designed thermo-mechanical
treatment.
Machining: extremely
demanding, exceedingly
long
“Having solved the material
procurement problem we
were still far from solving all
the problems because to some
The 82-mm thick AlMg4.5 Mn rolled plate for the mullions.
A special thermo-mechanical treatment was devised in order
to guarantee a proof strength of 155 MPa
all Photos: Klaus Vollrath
The production-related challenges included milling of deep
pockets with a tool that was 250 mm long but could only
have a maximum diameter of 16 mm
extent we had to break new
ground in the processing,” Mr
Meenen recalls. This began
with the minimal machining
tolerances of only 2 mm all
around the mullions, and this
despite the fact that they were
up to 6,000 mm long. One of
the reasons for choosing these
exceptionally low values was
that the wall thickness was a
critical factor in ensuring the
necessary mechanical properties.
The consequence was
extremely tight tolerances for
distortion of the blanks to be
processed. This proved to be a
challenge even when it came to
choosing a suitable machine
for the five-axis processing of
these parts and the necessary
special milling cutters. In the
end, this was only made possible
by special modification
of a Chiron machine tool by
lowering the machine bed.
The machine was equipped
with two identical swivelling
tables that could be synchronised
in such a way using the
machine controls that it was
possible to machine individual
workpieces having excess
length. With shorter components,
the two tables could be
used for different jobs independently
of each other. As
an alternative for future use,
the machine can be optionally
equipped with a loading
door on the side thus making
it capable of accommodating
workpieces up to 13,000 m
long. An added challenge was
the development of suitable
technologies for machining
the cut-outs, which in some
cases were extremely deep,
especially in the area of the
locking devices at the end of
the crosspieces. Here, tools
and machining strategies
had to be found that enabled
the machining tolerances
to be adhered to even using
extremely thin and long milling
cutters. The required radii
of only 8 mm limited the
diameter of the milling tool to
a maximum of 16 mm – and
that at immersion depths of
up to 250 mm.
Waterjet cutting as
core competence
“The benefits of using a
waterjet manifested themselves
fully even as soon as we
cut the individual mullions
out of the rolled slab,” explains
Mr Meenen. With a thermal
process, such as laser-beam
cutting, large machining
allowances would have had
to have been used in order
to eliminate microstructural
damage by completely removing
the heat-affected zone,
which would have resulted
in correspondingly higher
costs. In addition, the kerf in
waterjet cutting is significantly
narrower than with a saw
cut, which allows more blanks
AlSi1MgMn T6 blanks with diameters from 400-650 mm,
which also had to have a proof strength of 230 MPa in the
interior, were used for the nodes