AFRICAN FUSION—MARCH2014
14
Sustainability through automation
S
ustainableaction is theconsciousandcareful handling
of available resources.Sustainability inwelding technol-
ogy requires, not only the savingof energy, rawmateri-
alsandemissions,but alsoofwelding timeand,with it, costs.
Thesesavingscanbeachievedusinghighlydynamic, energy-
saving power sources and innovative welding processes. In
an industrial environment, quality and economic efficiency
have toppriority. Toenablesustainability, economicefficiency
andqualitymust complement eachother in thebest possible
way, and precise knowledge of all interrelationships and the
interaction of the different components is fundamental.
Using the example of an automated surface welding
process on an actual welding task, these three interrelation-
ships and their relevance from an overall perspective are
clarified below.
Surface coating
The productivity of machines and plants is determined, to a
large degree, by theway they deal with demands that arise.
For certain applications, the corrosion and wear properties
or their tribological behaviour are the significant factors in
designing components. Special surface-coating processes
have been developed to improve the surface properties of
components. These techniques permit the economic and
resource-efficient use of materials. In the field of thermal
coatingprocesses, ageneral distinction ismadebetween the
surfacing processes of cladding, hardfacing and buffer-layer
welding. Cladding is primarily used for corrosion protection
of the parent metal, whereas hardfacing is used for wear
protection. Buffer layers are applied to the parent metal as
intermediate passes for dissimilar surface coatings [1; 2].
In thermal surfacing, a wear- or corrosion-resistant
surface material is applied to a dissimilar, often unalloyed,
steel using arc processes, in order to improve the properties
At the 66
th
IIW Annual Assembly and International Conference in Essen, Germany
in September 2013, ABurt, C Fink andDMündersbach presentedwork on surface
overlay cladding using a dc TIG process with ac hotwire, while their colleague,
PKuebler fromRocklea, Queensland, presented some examples of sustainable,
innovative and automatedwelding and cutting applications from Australia.
Sustainability through innovativewelding
processes in automated applications
of the surface in line with respective demands. The firmly
bonded connectionbetweena sufficiently elastic component
and its functional surface and the associated high thermal
conductivity, geometry independent anddensesurface layers,
offer surfacing significant advantages over thermal spraying
processes.
Thepropertiesof the functional coatingdependverymuch
on thedilution, ie, the ratioof fusedparentmetal to theentire
fused volume. The degree of dilution of the functional layer
can be determined by means of polished cross-sections or
via ratios of the chemical analyses of the different layers.
Depending on the welding task, material, surface layer and
degree of automation, dilutions of between 5 and 30% can
be achieved at deposition rates of up to 40 kg/h [3]. Using
TIG surfacing in practice, dilutions of less than 10% can be
achieved at deposition rates of up to 4,0 kg/h.
Alternative dc TIG process with ac hotwire
TheTIG-dcwithachotwireweldingprocess isanewlydevel-
opedalternativeprocess inwhich thearc isproducedbetween
a non-consumable tungsten electrode and the workpiece
using direct current. The filler material is fed mechanically
andpreheatedby an ac current of between30 and170A at
voltagesofbetweenapproximately2,0V to8,0V (ie,between
60W and 1,4 kW). The combination offers the advantage
of achieving a continuous and reproducible process with a
considerably higher deposition rate compared to amanually
fedwelding rod.Here, the fedweldingwireelectrode isheated
with alternating current instead of direct current. Electrical
engineering has shown that a magnetic field arises around
energised wires and that its direction of action changes de-
pending on the direction of energy flowwithin them.
Themagnetic field formeddue toahotwirewithalternat-
ing current flowing through it and themagnetic field formed
by theenergiseddcarc interactwithoneanotherby reciprocal
attraction and repulsion of the arc column. For this reason,
the arc can easily be deflected by amagnetic field owing to
the highly flexible plasma column.
Normally, deflectionof theplasma column isundesirable
for arc processes, but this property gives dc TIGwith an ac
hotwireaprocessadvantage.Byapplyingalternatingcurrent
to the fillermaterial, a constantly changingmagnetic field is
created, since themagnetic fieldof anenergisedwire reverses
depending on the direction of the current. Because of this
effect, the arc is constantly being deflected at the frequency
of the alternating current, ie, attracted or repulsed.
Figure 1:Weaving of the arc due to the alternatingmagnetic
field in the hot welding wire.
