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.

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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

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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.

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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.

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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.

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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

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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.

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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”