Modeling of Weld Penetration in High Productivity GTAW
Asymptotic and regression analysis of a a large number of welds resulted in a general, accurate model
Üstün Duman1, Patricio F. Mendez2
1:
Ph.D., Center for Welding, Joining, and Coatings Research (CWJCR) – Colorado School of Mines, Golden, CO – (Currently at Novelis Corporation, Greensboro, GA 30677)
2:
Weldco/Industry Chair, University of Alberta, Department of Chemical and Materials Engineering, Edmonton, Canada
→ Research Motivation
→ Methodology
• The goal of this study is to model weld penetration depth when
there is a gouging region.
• The welds were carried out bead on-plate with Miller® Dynasty 700
• D.C. was used with a high frequency start of 60 Hertz
• Welding currents varied 225-700 A and travel speeds between 2 – 17 mm/s
depending on material type.
• Industrial purity argon was used with a constant flow rate of 30 ft3/h.
• The electrodes were 2% thoriated tungsten at a fixed tip angle of 45° and at
diameters of 1/8 and 5/32 inch (3.175 and 3.96 mm).
• The torch angle was always 90° to the plate surface.
• The electrode to work piece distance (arc gap) was kept constant at ¼ inch
(6.35 mm).
• Electrode tip to nozzle tip distance was ½ inch (12.7 mm).
• Filler metal was decoupled from the torch.
• Spot welds were performed on the same type of material prior to each weld
• Materials welded are; ASTM A36 structural steel, AISI304 stainless steel,
AA1020 and AA5083 Aluminum alloys and CP Titanium Grade 3
• Plates were 12 in long, 2 in wide, 1 and ½ inch thick.
• This study involves mathematical and experimental studies of
weld penetration mechanism during high productivity GTAW
and validation of the weld penetration model.
• Understanding the penetration mechanism under high
productivity arc welding condition is critical for welding heavy
and thick sectioned materials
→ Background
• Weld penetration mechanism was explained with
recirculating flow mechanism at relatively low
welding currents and travel speeds in arc welding.
• Under high welding current the arc pressure
depresses the molten metal generating a gouging
region under the arc, as displayed in Figure B.
AISI304 at 100A – 1.2 mm/s
CP Ti at 500A – 5.3 mm/s
• Coupling of depression with high travel speeds causes the molten metal in the weld
pool to be pushed to the back and sides of the gouging region resembling a key hole in
front of the weld pool.
• There are no relevant gouging penetration estimation work preformed before, to the
best of authors knowledge, however there can be found many studies explaining the
recirculating flow penetration mechanism and estimation in literature.
→ Results
Experimental setup of the GTA welds in CWJCR welding laboratory at Colorado School of Mines
• A fast moving heat source is assumed
• The model was constructed depending on
(Condition 1).
to the scaling analysis of the 1-D heat
• The preheating effect of the torch and the
transfer in gouging region using governing
thickness of the thin liquid film in the
heat transfer equations.
gouging region are neglected (Condition 2).
• The experimental studies are performed
• The thin film layer between gouging
for the verification of the gouging
region and base metal is neglected
penetration depth model.
(Condition 3).
Coordinates and schematic view of the gouging region.
• The arc width and penetration depth
relationship is accounted by Condition 4.
• The model was constructed depending on to the scaling analysis
of the 1-D heat transfer in gouging region using governing heat
transfer equations.
• The experimental studies are performed for the verification of
the gouging penetration depth model.
GTA weld on CP Titanium
300 A – 7 mm/s
Table below displays thermo-physical properties of materials
Parallel cross-section, top view and transverse cross-section of gouging penetration depths
• The dependence of the model
on the simplifications is shown
in Figures on the left.
• Depending on the trend
observed in condition 2, a
correction function is developed
to improve the normalized
observation of the penetration
depths.
Normalized observations of the penetration depths against condition 1.
Normalized observations of the penetration depths against condition 2.
Normalized observations of the penetration depths against condition 3.
Normalized observations of the penetration depths against condition 4.
The weld penetration model is constructed by relying on the mathematical analysis of the physics of the process and its range of validity is tested in a variety of materials using D.C.
GTAW. The limits are specified where the gouging region is observed visually and within the range of the machinery limits.
→ Conclusions
→ Future Work
• Gouging region is generated by the plasma shear stress at high welding currents and
travel speeds (Currents >140A and travel speeds >4mm/s depending on material type)
• The weld penetration at high productivity GTA welding is generated by the direct
action of the arc in gouging regime.
• The gouging penetration modeling provided a reliable scaling law.
• The formulation is valid, when the simplifications of the model are full-filled.
• The estimation of penetration depth is proven to be valid for five different materials.
• Understanding the physics of the
gouging penetration depth will help to
reveal the occurrence of some welding
discontinuities such as humping,
undercutting and tunnel porosity in arc
welding.
• Understanding the force balance at the
transition line of the trailing region and
gouging region.
• Coupling of wire addition to the GTA
torch and modeling weld penetration.
Gouging penetration depth:
The corrected penetration depth estimations (Dˆ+) vs. he measured penetration depths (D)
Acknowledgements:
C1, C2 and C3 stands for constants of the corrective function that were estimated through linear regression analysis
• Miller, Inc. for providing TIG Dynasty 700 welding machine and parts
• TiMet for providing CP Ti Grade 3 plates
• Novelis for providing CP Aluminum alloy
• Alcoa for providing AA5083 aluminum alloy
• Center for Welding, Joining and Coatings Research (CWJCR) fellow students
• NSF CAREER Award
• Dr. Stephen Liu, Dr. Gerard J. Martins, Dr. Chester J. Van Tyne at CSM
• Special thanks to Yasemin Duman