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June 2017
AFRICAN FUSION
13
Welding process % Fe in Layer 1 % Fe in Layer 2 Deposition rate kg/h]
GMAW Pulse
18.48
3.40
3.17
CMT
2.38
0.37
4.61
Time Twin
15.69
3.60
10.73
CMT Twin
2.78
0.31
7.50
GTAW Cold wire
12.74
2.26
0.75
GTAW Hotwire
7.37
1.34
1.62
Laser Cladding
16.37
3.96
5.19
Table 2: Fe content in layers 1 and 2.
pends on two factors: hot wire current,
which is adjusted in the hot wire power
source; and the electrical resistance of
the filler material itself. The positive ef-
fect of the preheating compared to cold
wire welding is shown in Figure 3. This
effect can be also applied to welding
processes other than TIG.
Other cladding process variants
In [5], claddingwith Inconel 625 for vari-
ous welding processes is investigated.
Measurements of the iron content in
the clad layers were taken with EDX
line scans.
Energy-dispersive X-ray spectros-
copy (EDS, EDX, or XEDS) – sometimes
called energy dispersive X-ray analysis
(EDXA) or energy dispersive X-ray mi-
croanalysis (EDXMA) – is an analytical
technique used for element analysis or
characterisation of a sample. It relies on
an interaction of some source of X-ray
excitation and a sample.
The iron content was measured in
steps of 0.5mmstarting fromthe surface
of theweld overlay to the basematerial.
As a reference value for the dilution of
the basemetal, the Fe content was used.
Welding processes with high energy
density or ones with low welding speed
(GTAWwith coldwire and laser cladding)
exceed the dilution rate of 5.0% iron con-
tent, whilewelding processeswith lower
heat input were shown to maintain the
Fe content below 5.0%.
All samples have in common a steep
rise of the iron content when approach-
ing the basematerial. Table 2 shows the
iron content for the two layers, and the
deposition rate. The comparison shows
that a process that provides a low heat
input and therefore a lowFe percentage
cannot achieve high deposition rates.
On the other hand, high deposition pro-
cesses produce the highest percentages
of Fe content.
GMAW with hot wire
The use of the GMAW pulsed welding
for cladding was presented in Table 2.
The main disadvantage of the process
is a high % Fe content in the clad layer.
Combined with the limited maximum
arc power and associated limited pro-
ductivity in terms of deposition rate,
GMAWpulsedwelding is applicable only
in a few cases.
The addition of filler material from
outside the GMAW process could offer a
significant improvement inproductivity.
In addition, the deposition of more filler
material with a proportionally small
increase in the welding power would
have a positive effect on the dilution
and, therefore, on the Fe content in the
clad layers. The process setup is shown
in Figures 4 and 5. The possible deposi-
tion rates are comparable with most
twin wire GMAW processes.
Application
The application of the GMAW hot wire
process is easy to setup, adjust and
maintain. Highest travel speeds and
highest deposition rates can be reached
when the process is applied with the
help of mechanised manipulators.
The welding system is put together
using standard components: GMAW
welding system Phoenix 551 Progress
Puls (Figure 6); and an additional wire
feed systemwith an integratedTigspeed
drive 45 hotwire power source (Figure 7).
Figure 1: The surface of an Inconel 625-clad layer after a high-temperature corrosion test [3]:
a) Fe content of 2,5%: b) Fe content of 10%.
Figure 2: A welding process diagram for TIG hot wire
welding.
Figure 3: Deposition rates of cold wire and hot wire
welding as a function of arc energy [4].
Figure 4: A process diagram for GMAW hot wire
welding.
Figure 5: A photograph of the GMAW arc and the hot
wire entering the weld pool.