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1
LASER WELDING DISTORTIONS ON THIN PLATES
Valter S. Carrolo Technical University of Lisbon, Instituto Superior Técnico
Department of Mechanical Engineering – STM
Abstract - Over the years, laser welding machines have
developed and increased its use through the industry. Laser
beam (LBW) technology with its high production capacity,
precision and low heat delivery, was the solution to many
welding problems. Such evolution only lead to more
complex problems, by allowing faster welding processes
and stronger welds on thinners components. Since welding
processes exposes the work piece to high temperatures,
weld-induced distortions is always present. In this work it
will be investigated how distortion affects the weld quality
and present several methods to reduce its negative effects.
These methods are often simple, but without them the
plates could not be welded within its conformity.
This thesis focuses on the processes and procedures
involved in a water jacket production at Carr’s Welding
Technologies. The water jacket is essencially composed by
two plates made of AISI 304. The preliminary work had
low weld quality, geometrical tolerance faults and aesthetic,
it is in this context that this thesis appears. The final result
is to allow its production with repeatable quality and a
competitive cost.
After analyzing the prototypes, it was clear that the
problem in the welding process was the heat distortions.
The plates were moving defocusing the laser (warping) and
were separating; consequently the welds were not reaching
the penetration necessary to resist the insufflation process.
In this work is was determined the best welding conditions:
focus (+1 mm), focus lens (150mm) and welding speed (v =
0.008 m / s), to control the adverse effects of thermal
distortion, was overcome by applying distortion control
techniques such as pre-bending and clamping. Finally, as a
request of CWT, it was studied the welding pattern. It was
concluded that the current pattern was too conservative
therefore other patterns could be used, more sparse,
without compromising the integrity of the final structure.
I. Introduction
Weld induced residual stress and distortion is among
the most studied subjects in welded structures. The
localized heating and non-uniform cooling during
welding results in a complex distribution of the residual
stress in the joint region, as well as the often undesirable
deformation and/or distortion of the welded structure. As
residual stress and distortion can significantly impair the
performance and reliability of the welded structure; they
must be properly dealt with during design, fabrication
and in-service use of the welded structures.
All studies compiled on this subject along the years
agree on one fact: it is impossible to avoid residual stress
and heat distortion therefore this thesis is going to focus
in controlling techniques.
A review of the literature shows a significative number
of articles and patents related to theme, however the
author had to concentrate in the ones that could be
applied in specific production environment at Carr’s
Welding Technology and had to consider their
applicability due to the plates’ dimensions.Since the
early 1990s, considerable progress has been made on
residual stress and distortion control, measurement
techniques have improved significantly and, more
importantly, the development and application of
computational welding mechanics methods have been
remarkable due to the explosive growth in computer
capability and to the equally rapid development of
numerical methods, therefore in this study FEM analysis
was used to corroborate the trials results since the
information that could be extracted was limited.
The component under analysis is a water jacket
used in the production of cheese. Figure 1 is the
technical drawing of the product to be manufactured.
The manufacturing processs starts by welding two metal
sheets, with 525 circular shaped welds and straight line
welds along the edges. The plates are made of stainless
steel AISI 304. After welding the plates, they are bent
into the position shown in Figure 1.
The last step is the insufflation, it is applied a pressure of
25 bar apart to induce permanent deformation. It is in
this step that, possible defected welds are detected.
Figure 1 – Technical drawing of the water jacket
It was registered problems in the first prototypes.
An analysis of the prototypes, revealled a problem in the
welding process, due to the weld induced distortion the
welds were notreaching the target penetration, therefore
did not have the enougth strength to withstand the
insufflation process. It was detected mainly three types
of movement , the plates were moving upwards
defocusing the laser (out-of-plane displacement), were
separating and uosetting in the edges.
This paper is organized in the order that follows:
The second chapter is Residual stress and distortion
mechanism; the third chapter gives the experimental
method and the results obtained with the trials; the fourth
chapter shows the results obtained with the finite
elements analysis. In fifth chapter the conclusion are
summarized. The sisth chapter is intended for references.
2
II. Residual Stress and Distortion
The residual stresses in a component or structure are
stresses caused by incompatible internal permanent
strains. They may be generated or modified at every
stage in the component life cycle, from original material
production to final disposal. Welding is one of the most
significant causes of residual stresses. It typically
produces large tensile stresses whose maximum value is
approximately equal to the yield strength of the materials
being joined, and balanced by lower compressive
residual stresses elsewhere in the component.
The distortion causes the degradation of the product
performance, poor fit-up of the product and the increase
of the manufacturing cost, so that it need be eliminated
or minimized below a critical level.
Residual stresses may be measured by non-
destructive techniques, such as X-ray diffraction, neutron
diffraction and optic magnetic and ultrasonic methods; or
by locally destructive techniques, including hole drilling
and the ring core and deep hole methods; and by
sectioning methods including block removal, splitting,
slicing, layering and the contour method. The selection
of the measurement technique should take account of
volumetric resolution, material, geometry, accessibility
and if the component needs to be used after the testing
(NDT has to be used) or not.
A. Residual stress and distortion Mechanism
Four types of distortion induced by welding were
discovered. The first two are longitudinal shrinkage and
transverse shrinkage that occur in plane. The other two
are angular distortion and longitudinal distortion
(bowing), which appear out of plane. The angular
distortion is mainly caused by the non-uniform extension
and contraction through thickness direction due to the
temperature gradient. The longitudinal distortion (also
called buckling distortion) is generated by the
longitudinal tensile residual stress.
Heat distortions have origin in fast temperature
variation that generates non-uniform dilation and
contractions. The localized heating and non-uniform
cooling during welding results in a complex distribution
of the residual stress in the joint region, as well as the
often undesirable deformation or distortion of the welded
structure. A number of factors influence the residual
stress and distortion of a welded structure. They are
related to the solidification shrinkage of the weld metal,
non-uniform thermal expansion and contraction of the
parent metal, the internal constraints of the structure
being welded, and the external structural restraints of
fixtures used in a welding operation. For many
engineering materials, a transient welding thermal cycle
also results in micro structural changes in the joint
region, which can further complicate the formation of the
residual stress field.
The effect of coupling between metallic structures,
including the molten state, temperature, and stress or/and
strain occurring in processes accompanied by phase
transformation, sometimes play an important role in
industrial processes like welding. Figure 2 represents the
schematic features of the effect of metallurgy, thermal
and mechanical coupling in heat distortions phenomena.
Austenitic stainless steel does not have phase
transformation therefeore, thies phenomenon does not
need to be considered. Still local dilatation due high
temperature creates stress and interrupts the stress or
strain field in the body.
∆� = ���(�� − �)
Figure 2- Diagram of residual stress mechanism [3]
A. Residual stress and distortion parameters
There are several factors that influence distortion
control strategy, they may be categorized into:
- Design-related and process-related variables, that
includes weld joint details, plate thickness and
thickness transition if the joint consists of plates of
different thickness, stiffener spacing and number of
attachments, corrugated construction, mechanical
restraint conditions, assembly sequence and overall
construction planning.
- Welding process, there are important variables
related to the technology used such as heat input,
heat delivery method, travel speed and welding
sequence.
The implementation of distortion mitigation techniques
can be applied before, during and after the welding and
their objective is to counteract the effects of shrinkage
during cooling, which distorts the fabricated structure.
They do that by balancing weld shrinkage forces as they
prevent the typical component distortion.
Once the parameters that affect the heat distortion are
identified, theoretically they can be controlled, with a
better knowledge of mechanism, less conservative
decisions regarding weld are considered, because in
general all measures that can be taken to prevent
distortion, add cost to the process. This cost can be either
by the usage of more material, or more energy
consumption.
One common problem associated with welding, which
has been realized and documented for many years, is the
dimensional tolerance and stability of the finished
products.
The pictures below synthesize the typical temperature
variation, stress induced and behavior of th
welding process and the stresses introduced by the
welding process.
Figure 3 - Thermal stress distribution before, during
and after the welding [3]
Figure 4 - Thermal stress after the
B. Heat distortions in the water jacket
In the component in analysis the heat distortions are
critical because they affect the welding quality by
inducing the separation of the plates, therefore,
normal production procedures have to be broken
time-consuming and costly distortion removal
Welding-induced buckling differs from bending
distortion by its much greater out-of-plane deflections
and several stable patterns. Buckling patterns depend
much more on the element’s geometry, and ty
joint especially dependent on the thickness of sheet
materials under certain conditions, it also depends on
rigidity of elements to be welded and welding heat
inputs. It has been identifiesd the problem of buckling
3
by the usage of more material, or more energy
roblem associated with welding, which
has been realized and documented for many years, is the
dimensional tolerance and stability of the finished
The pictures below synthesize the typical temperature
variation, stress induced and behavior of the material in a
welding process and the stresses introduced by the
Thermal stress distribution before, during
Thermal stress after the welding [3]
eat distortions in the water jacket
In the component in analysis the heat distortions are
critical because they affect the welding quality by
of the plates, therefore, the
procedures have to be broken for
distortion removal tasks.
induced buckling differs from bending
plane deflections
and several stable patterns. Buckling patterns depend
much more on the element’s geometry, and types of weld
joint especially dependent on the thickness of sheet
materials under certain conditions, it also depends on
rigidity of elements to be welded and welding heat
It has been identifiesd the problem of buckling
distortions in plates with less than 4mm, due to their
lower critical compreensive stress.
Buckling distortions caused by circular welds in the
plates are mainly determined by transverse shrinkage of
welds in the radial direction, whereby compressive
stresses are produced in the tangential direction.
circular welds the bending direction changes along the
path, due to the adjacent bending effect which is induced
by moving heat source, and also due to the direction
change of the major inherent mechanical constraint.
Figure 5 - Loss of stability of (left) the plate (center)
inner circle (right) Outer contour [3]
It is also important to highlight the upsetting
phenomenon that occurs on the plates and that plays a
major role on the welds ‘quality that are
the edges of the plate. Before it is heated the metal sheets
are square and flat. As the welds on the center are done,
the uneven heating of the plate, the restraint offered by
the weld already made and the cooler areas cause
dimensional change called upsetting. The upsetting
configuration is shown on figure 19.
Figure 6 - Effect of upsetting in a sheet plate
C. Distortioncontrol techniques
Distortion control methods increas
costs due to requirements for more energy,
consumed in non-adding value activities, increase of
labor and potentially high-cost capital equipment,
howeger without them some welds simply could not be
done. Some methods may not b
LBW due to interruption from fixtures or stiffener
arrangements. Understanding their capability and
limitations of all these distortion control methods is
critical to a successful welding fabrication project.
less than 4mm, due to their
lower critical compreensive stress.
Buckling distortions caused by circular welds in the
plates are mainly determined by transverse shrinkage of
welds in the radial direction, whereby compressive
ngential direction. On
circular welds the bending direction changes along the
path, due to the adjacent bending effect which is induced
by moving heat source, and also due to the direction
change of the major inherent mechanical constraint.
Loss of stability of (left) the plate (center)
inner circle (right) Outer contour [3]
It is also important to highlight the upsetting
phenomenon that occurs on the plates and that plays a
major role on the welds ‘quality that are made later on
the edges of the plate. Before it is heated the metal sheets
are square and flat. As the welds on the center are done,
the uneven heating of the plate, the restraint offered by
the weld already made and the cooler areas cause
ge called upsetting. The upsetting
configuration is shown on figure 19.
Effect of upsetting in a sheet plate
Distortioncontrol techniques analized
istortion control methods increase manufactures
costs due to requirements for more energy, more time
adding value activities, increase of
cost capital equipment,
howeger without them some welds simply could not be
Some methods may not be suitable for automated
ue to interruption from fixtures or stiffener
arrangements. Understanding their capability and
of all these distortion control methods is
critical to a successful welding fabrication project.
4
Recent progress in eliminating distortions, has
resulted in trends from the adoption of passive
technological measures to the creation of active in-
process control of inherent (incompatible residual
plastic) strains during welding without having to
undertake costly reworking operations after welding.
The control methods listed below are some of the more
popular weld manufacturing methods to control residual
stresses and distortions. This is not an exaustive list and
new techniques are being developed. There is not a
technique superior to all, each case has to be analyzed
carefully, parameters such as the geometry of the
component and the weld are a important when choosing
DCT, furthermore the geometrical tolerance (precision)
and cost, also influences the choice of the distortion
control techniques. DCTs can also be combined, to
achieve better results.
Weld technique
Each situation must be analyzed carefully; the wrong
technique will lead to a more expensive and harder job.
In extreme situations it may even be impossible at all.
Fusion welds often lead to the largest distortions while
laser, electron beam welding and friction stir welding
result in lower distortions.
However, friction stir welding can impart large plastic
strains to the structure even though the residual stresses
may be low. These large strains, which locally strain
harden the material, can influence the fracture response
of the structure.
Weld parameter optimization Weld parameters of the technique applied must be tuned
to obtain better results. The most important parameters
are travel speed, power input, weld groove geometry, and
weld size.
Weld sequencing Weld sequence simply means the order in which the
welds are deposited. Sequencing is more important for
distortion control although it can affect weld residual
stresses as well. For some fabrications, weld sequencing
is not sufficient for distortion control and it is used in
conjunction with some of the other.
Fixture design Fixtures control residual stresses and displacements by
forcing the displacements and rotations of some portions
of the welded component to be zero. The ‘zero points’
should be carefully designed to achieve the distortion
control goals.
Pre-cambering Pre-cambering consists of elastically (or plastically)
bending some of the components (usually in a specially
designed fixture) in a predefined manner and then
welding. After welding, the pre-camber is released and
the fabricated structure ‘springs back’ to a minimally
distorted shape. The pre-camber pattern must be
carefully designed. Pre-camber also affects weld residual
stresses.
Pre-bending
Pre-bending consists of plastically bending some of the
components before welding and possibly before placing
them in a fixture. The welding is performed with or
without a fixture.
Hammer peening
Hammer peening is used to introduce
compressive residual stresses at the weld. It counteracts
the shrinkage forces of a weld bead as it cools. Peening
consists in slightly reshaping the weld bead, its stretches
and makes it thinner, thus relieving (by plastic
deformation) the stresses induced by contraction as the
metal cools. This method must be used with care.
Generally, peening is not permitted on the final pass,
because of the possibility of covering a crack and
interfering with inspection, and because of the
undesirable work-hardening effect. Thus, the utility of
the technique is limited, even though there have been
instances where between-pass peening proved to be the
only solution for a distortion or cracking problem. This
method can be helpful but on the skill of the welder.
D. Advantages of prediction weld distortion and
residual stress
Two tremendous advantages are obtained by
developing fabrication solutions via the computer. First,
designing the fabrication to minimize or control
distortions can significantly reduce fabrication costs.
Second, controlling the fabrication-induced residual
stress state can significantly enhance the structure service
life.
For distortion control, fabrication design via modeling
can achieve the following;
• It can eliminate the need for expensive distortion
corrections.
• It can reduce machining requirements.
• it can minimize capital equipment costs.
• It can improve quality.
• It can permit pre-machining concepts to be used.
Residual stress control via modeling has the following
results;
• It can reduce weight.
• It can maximize fatigue performance.
• It can lead to quality enhancements.
• It can minimize costly service problems.
• It can improve damage resistance during attack (e.g.
naval structures).
It is important to note that fabrication modeling tools can
be used to develop new control methods or test methods
that, at the time, are not avaiable, since the methods can
be first attempted on the computer. Some of these
methods will be considered in the examples discussed
later.
5
III. Experimental Method
The trials were composed by four sections.
Distortion analysis were it analyzed the weld sequence
and the DCT. Welding procedures optimization where it
was analyzed the lens, the collimation and speed. In third
it was the tensile test, that was used to verify the results
obtained previously and quantify the strength of the
welds. The last was the quality test to ensure the quality
of the welds.
A. Distortion analysis
Objective: : Test the influence of heat distortions in weld
quality and analyze the available techniques in reducing
thermal distortion
Material: 1000x350x1.5, these plates were used in the
distortion test. The size of these metal sheets is around
one third of the real size. It was important to use big
sheets since the residual stress and distortions have a
cumulative effect. It was engraved small cycles to
measure local strains.
Figure 7- Plates used in distortion test
Procedure
1- Were performed rows of four circles (7mm
radius) along the plate’s width with the 70x80 pattern. In
each plate different distortions controlling techniques
were applied.
2- Measure distortion caused by welding, with and
without DCT. Measure out-of-plane displacement and
plate separation with pachymeter.
The target penetration was 3mm. It was used a 0mm
collimation, 150mm Focal lens and V=0,008m/s welding
speed.
Figure 8- Distortion analysis test set up
B. Welding Procedures optimization
Objective: Determine parameters that produced the
strongest weld possible, without undesirable distortions
and minimize the residual stress
Material: 2 plates with 150x120x1.5mm were used to test
the welding conditions in order to optimize parameters
such as velocity, collimation and lens.
Figure 9 - Plates used in the welding procedures
optimization test
Procedure
1- Were performed straight lines welds across the
plates as sown in Figure 11 with different combinations
of collimation, Focal lens and speed.
2- After was analyzed weld quality, trough visual
inspection method and macro graphic analysis:
Aspects analyzed:
- Weld defects such as, porosity or cracks
- Width and penetration of the weld
Figure 10 - welding procedures optimization set up
C. Peel test
Objective: : Verify quality and determinate strength of
the previous tests best welds.
Material: It was used a plate with 100x30x1,5mm and a
plate with 100x30x4mm.
Figure 11 - Plates used in the Tensile test
Procedure
1- Weld the plates as shown on the figure 13, with
the best conditions combinations, determined in the
previous tests.
2- The test pieces were sent to NDT, where the
tensile test was performed.
6
IV. Trials Results Presentation and Analysis
A. Distortion analysis
A.1. Weld Sequence Test
As shown in figure 14, it is ckear the lack of
penetratration on row sequence (A). The distortion
results cverify that fact. The maximum out-of-plane
distortion registered in (A) is 14mm while in collumn
sequence (B) was 13,08mm. The plate separaration
measured in (A) was 6,31 and in (B) was 4,5mm.
Figure 12 – Weld sequence test
A.2. DCT Test
In this test it was tested hamer-peening, clamping, pre-
bending, pre-cambering and pre-bending combined with
clamping.
Distortion could be decreased by hammering, at all.
Clamping was good in the clamped area, however in the
area that was not clamped, the upsetting values, out-of-
plane distortion were high, up to 10,79mm, the
maximum plate separation was 2,82mm.
Plate separation in pre-bending was 0,87mm and the out-
of-plane distortion was 11,02mm.
When pre-bending is applied clampnig has little weight
in the distortions reduction, plate separation and
upsetting, however it improves a the out-of-plane
distortion. The results combining pre-bending and
clamping were 0,38 in plate separation and 10,17 of out-
of-plane distortion.
B. Welding Procedures Optimization
B.1. Lens test
Several straight line welds were performed to test the the
lens the results are shown in the table bellow.
B.2. Collimatin test
Several straight line welds were performed to test the
the lens the results are shown in the table bellow.
C. Tensile Test
It was performed an tensile test on the welds
with the best conditions combinations from the previous
tests. The results are shown in the table bellow.
Tensile test
number Parameters
Force applied
to rupture
[KN]
#1 V=0.06 C=0 25,21
#2 V=0.08 C=0 24,41
#3 V=0.1 C=0 8,43
#4 V=0.06 C=1 28,07
#5 V=0.08 C=1 26,64
#6 V=0.1 C=1 16,52
Table 3 – Tensile test results
D. Quality test
There were no record of problems during the insufflation
process. The plates were approved by the client.
IV. Finite Element Analysis A. Pattern Analysis
The welds’ pattern, is defined by the gap between the
center of circle welds, and the distance from the plate’s
edge to the center of the circle welds. The optimum
pattern is a result from compromise of productivity and
strutural resistance.
The client recommends CWT to use the folowing
pattern: A=70mm B=80mm C=70mm D=80.
weld properties
width penetration energy loss
Fc=100mm 1mm Full-penetration 40%
Fc=150mm 2mm Full-penetration 5%
Fc=200mm 2,5/3mm insuficient 0%
Table 1 – Weld bead analysis results resume
Collimation
Test Observations
Velocity [m/s] 0,008
Lens [m] 150
Collimation
[mm] -2 -1,5 -1 0,5 0 0,5 1 1,5 2
Penetration
[mm] 1,8 2,1 2,5 2,7 2.9 3.2 3.3 3.2 3
Table 2 – Collimation test results resume
7
The objective of this analysis is to discover why
this pattern has been choosen and to verify if it is
possible to use a wider pattern in order to improve
productivity, within the standard level of safety.
Boundary conditions
• Fixtures: The 1.25mm plate is going to be
welded to one with with 4mm, so it is assumed that it
will be the 1.25 thick plate that will deform and will fail,
therefore it was not considered to be necessary to
simulate the second plate.
The circle welds and the side welds do not move, as they
are attached to the 4mm plate that is considered to be a
rigid body. The displacement constragiments in the
welds are signalled with green arrows in figure 36.
• Pressure applied: On the bottom of the plate it is
applied a pressure of 2.5Mpa (25 Bar)
The results obtained of the simulation are the following:
The minimum necessary pressure deform the
plate is 18,5bar.
Area Pressured [mm2] 3,67x106
Total Force [N] 9,17x106
Total Length of weld [mm] 31,6 x103
Force Weld [N/mm] 296
Table 4 - Weld’s strength calculations data
The maximum displacement is3,2mm.
Figure 13 - Displacementon on the plate
The maximum stress registered was 254MPa.
Figure 14 –Plate stress
The safety factor of the plate in insufflation is
2,03. Since the safety factor is high it was tested further
weld patterns to see the evolution of the stress in the
plates and their production time..
The results are summarized in the table bellow.
AxB
CxD
Num
ber of
welds
Force
per mm
of weld
[N/mm]
Maxi
mum
disp.
[mm]
Max.
plate’s
stress
[MPa]
Safe
ty
Fact
or
75x75
70x70 532 287 3,1 242 2,13
70x80
70x80 525 290 3,2 254 2,03
75x80
70x70 490 305 3,4 262 1,97
80x80
70x70 455 322 3,6 265 1,95
80x85
70x70 429 336 3,8 271 1,90
90x90
80x80 372 371 4,4 305 1,69
100x1
00
100x1
00
280 445 5,2 327 1,58
Table 4 - Parametres influenced by th welding pattern
B. Welding distortion analysis
The objective of this analysis was to test the efficiency of
the distortion control techniques used in order to validete
the results obtained in the trials.
To analyze such a complex situation it is necessary a
sequentially coupled physics analysis. This analysis will
simulate a core hole drilling and strain gage technique.
Each physic enviroment (thermal and structural) was
contructed separatly, but only one geometry exists, only
one set of nodes and elements type is used for the entire
analysis.
First the geometry, and element type were defined, then
material properties, boundary conditions and load steps
of each enviroment. The Thermal Environment is where
the laser heat is applied. On the Structural Environment,
different types of constrains were applied and then
displacement and stress were calculated based on the
previous thermal analysis.
8
Figure 15 - Input-Output flow tree
The thermal analysis shows the heat distribution durong
the welding process.
Figure 16 - Temperature distribution in the plate
during the weldng process
The maximum temperature registered is
1732°C.
The temperature near the oouter walls remains close to
25°C during the welding process.
Figure 17 - Displacement of the model with
displacement constraints
The maximum weld induced stress registered is 243MPa,
therefore the maximum residual stress is 38MPa.
The table below shows the values of the displacments
calclulated using diferent DCT’s methods.
No DCT Pre-
bending
Pre-
cambering
Uniform Pre-
stress 200MPa
Uniform Pre-
stress 243MPa
Pre-stress
longitudinal
200MPa
Pre-stress
longitudinal
243MPa
Disp. Sum 0,157 0,103 0,0742 0,12 0,0511 0,237 0,185
Z Disp 0,0252 0,0181 0,0154 0,0209 0,0145 0,0303 0,0264
Table 5 - Simulation result’s resume
V. Conclusions
The best conditions are the following C=+1mm
V=0,008m/s Fc=150mm Power=1KW. These conditions
generate a weld bead with a tensile strength of 440MPa.
These calculations were based on the strength
determined on the tensile test perform by NDT as seen on
Table 3.
Sequence B (columns) presented better results and has
less Non-added value time per plate. However due to the
size of the water-jacket, clamping is impossible and the
bending is harder to be applied.
Sequence B (columns) presented better results and has
less Non-added value time per plate. However due to the
size of the water-jacket, clamping is impossible and the
bending is harder to be applied.
9
Hammering did not produce any measurable results.
Clamping alone is not very effective. In the clamped area
the distortions were minimized however, it could not
control the upsetting on the edges of the plates.
Pre-bending is effective in reducing weld induced
distortions. From the distortion resistance point of view,
the moment of inertia of the cross-section of the entire
panel structure increases as the structure is bent. Since
the weld shrinkage force remains unchanged, the
magnitude of global bending of the panel structure is
reduced by the increasing cross-sectional rigidity. This
method was particularly good in avoiding plate
separation since the process of bending the plates pushes
them against each other, and once the welds are done
correctly they will act as clamp keeping them together.
It is also very good in controlling the upsetting on the
plates edges however, it slightly bents the plate which
explains the high out-of-plane displacements it presents.
The best results were obtained combining Pre-bending
and clamping. The results showed that the clamp
pressure does not need to be high since its main function
is to the out-of-plane distortion that the bending induces.
The client proposerd the weld pattern of 70x80-70x80
because this patterns has a safety factor in the insuflation
setp of two. The finite element analysis shows that a
wider patterns could be used, still within the standard
safetu. This would decrease the production time.
The analysis distortions tests simulated in Ansys were
coherent with the results obtained in the trials.
It also showed that the DCT’s applied in the plastic
regime produce better results than the ones i the elastic
regime. This happens because they do cancel the residual
stress introduced by the welding process.
Finnaly the simualtions point out that it might be
nteresting to study in the laborator the pre-tension
technique since it was the one wit better results.
The initial difficulties that this work presented, with low
weld quality in the preliminary attempts, indicated that
this was not the ideal technology to be used in this job.
However this study shows that using the conditions and
the DCT suggested, this work can be accomplished.
Further to this study, with laser beam welding inherent
capacities, water jackets can the produced at a
competitive cost. Finally useful data is provided that
allow smaller production time
VI. References
[1] Feng, Zihli – “Processes and mechanism of welding
residual stress and distortion” – Woodhead Publishing
limited, 1st Ed, Cambridge, England, 2005, Chap. 1-3, 5-
9.
[2] C. L. TSAI, S. C. PARK AND W. T. CHENG –
“Welding Distortion of a Thin-Plate Panel Structure” –
People’s Republic of China, May, 1999
[3] Tiago Carlos Pereira e Rosa – “Modelação Térmica e
de Tensões Residuais de Soldadura de Metais Duros” –
Dissertação de mestrado em Engenharia Mecânica,
Faculdade de Ciências e Tecnlogia da Universidade
Nova de Lisboa, 2008
[4] DT.D Huang, P.E,P. Keene and L. Kvidahl –
“Distortion Mitigation Technique for Lightweight
Structure Fabrication”, University of New Orleans
[5] P. Michaleris and A. DeBiccari – “Prediction of
Welding Distortion”, Edison elding Institute, Colombus
University
[6] Trumpf User’s manual guide
[7 ]P. J. Withers and H. K. D. H. Bhadeshia - “Residual
stress Part 1 – Measurement techniques” University of
Manchester, University of Cambridge, England, March
2000
[8] F. W. Brust, Paul Scott – “Weld Distortion Control
Methods and Applications of Weld Modeling” - SMiRT
19, Toronto, August 2007
[9] Michaleris, P. and DeBiccari, A., 1997, “Prediction
of Welding Distortion” Welding Journal, Welding
Research Supplement, 76 (4), p 172s-181s
[10] Erdogan Madenci, Ibrahim Guven – “The Finite
Element Method and Applications in Engineering using
ANSYS®” – Springer – Verlag, 3ª Ed, London, England
, 2006
[11] University of Alberta ANSYS Tutorials – “Coupled
and Structural analysis”