Detail english 2015-11-12

602 Metal Monocoques – Moving Buildings Welded like Ships 2015 ¥ 6 ∂
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a 3D model depicting the geometry of the
end product and to project this on to twodimensional
surfaces. Throughout the production
chain, thick steel sheeting in particular
is subject to dimensional changes, and
this has a far-reaching effect on the accuracy
of the parts. Deformation specific to the
material and occurring in the later stages of
production as a result of plasma-cutting,
bending or welding has to be coordinated
with the specific metal from the outset and
must be taken into account in the dimensions
of the flat constructional members.
Only cold-forming can guarantee dimensional
accuracy. Metal subject to heating in
the shaping process undergoes subsequent
dimensional changes.
The standard dimensions of steel sheeting
from supply firms are 3 ≈ 12 m, whereas
aluminium sheets are 2 ≈ 6 m as a rule.
The workpieces are distributed by a computer
program over the unprocessed semi-
finished products in such a way that as little
loss of material as possible occurs through
cutting. This process is known as “nesting”.
All cross-members that have to be subsequently
welded to other elements should
now be marked with precise details of the
quality of the welding seams. A fully automatic
plasma-cutter separates the sheets
from the raw material (ill. 10). The technology
behind high-definition dry plasma-cutting
does not achieve the precision of lasers, but
that is not necessary in view of the thick
welding seams. Plasma-cutting, on the other
hand, is fast and can cope with metal thicknesses
of up to 30 mm. Metal sheeting up to
120 mm thick can be cut in an oxyacetylene
process. The greatest thickness of sheeting
ever worked by CIG – part of a sculpture by
Anish Kapoor – was 80 mm.
For the creation of monocoques, it is necessary
to work linear sections for the struts as
well as sheets for cross-struts and the outer
skin, shaping them freely in two directions.
The Dutch shipbuilding concern developed
the machinery itself that it required for working
both types of raw material, repeatedly
optimizing it. Computer controlled in this
way and laser monitored, even large
Å-girders can be curved or turned to virtually
any form. More spectacular still is the fully
automatic two-directional shaping of thick
steel plates: crane claws fixed to chains
hold the plate at the ends and slide it between
a high-performance press and die.
While the steel is processed with a pressure
of up to 6,000 kN by a repeated up-anddown
movement like that of an automatic
sledgehammer, but in a much more controlled
form, the claws move the metal element
synchronously along the programmed
route (ill. 6). It is important in this respect to
unhook the sheets in order to relax the material.
The problem here lies not in the large
dimensions. Limitations exist only in the
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6 Computer-controlled shaping of thick
steel sheets with high-performance
presses.
The three crane claws move the sheet
synchronously. The press, with interchangeable
stamps, is fixed in position.
The curvature is subsequently checked
against the wooden templates by
technicians
7, 8 Steel monocoque with high-gloss painted
finish: elevated seminar space with
viewing platform above in the atrium of
Southampton Solent University;
architect: Scott Brownrigg
7 Mock-up with high-gloss painted surface
and artificial joint
9,10 Principle of monocoque shell, consisting
of load-bearing grid and sheet-metal
covering as a single structural entity:
Porsche Pavilion, Autostadt Wolfsburg,
2012;
architects: Henn Architects
9 Individually shaped frame members and
25 mm stainless-steel covering sheets are
automatically laid out in a cutting
optimization program (nesting) and
removed with computer-controlled
plasma-cutters. Individual frame
members are also cut from composite
wood boarding as templates.
11 Steel monocoque with prefabricated
columns prior to welding on the covering
sheets to form the roof skin:
Münchner Freiheit tram station,
Munich, 2009;
architects: RPM.