This document discusses the effect of welding fixtures on welding distortions. It begins by defining distortion as any unwanted physical change in a fabricated structure due to welding. The main causes of distortion are identified as non-uniform expansion/contraction during heating/cooling and internal stresses from fixed surrounding components. Material properties like coefficient of thermal expansion, thermal conductivity, yield strength, and modulus of elasticity affect the extent of distortion. Different types of distortions are described like longitudinal, transverse, angular, bowing, rotational, buckling and twisting. Methods to measure, control, and correct for distortions are provided. A case study example of determining locating surfaces and possible distortion points for a fixture design is presented.

1. The effect of welding fixtures
on welding distortions
1
SUBMITTED TO SUBMITTED BY
DR. B S PABLA DEVI LAL
PROFESSOR, MECHANICAL ROLL NO 152208
ENGINEERING DEPARTMENT ME (MT)

2. CONTENTS
 Introduction: Distortion in Welding
 Significance of Material Properties
 Types of Welding Distortions
 Welding Suitability Index based on Distortion
 Measurement of Distortion
 Control of Distortion in Weld elements
 Correction of Distorted Weld elements
 Case study
 References
2

3. Introduction: Distortion in
Welding
Q. What is Distortion?
 Any unwanted physical change or departure from
specifications in a fabricated structure or component, as
a consequence of welding
Figure: Distortion in Sheet due to Welding Figure: Simulation for T-Joint Welding
3

4. Introduction: Distortion in
Welding
 Main Causes of Distortion
 Non-uniform Expansion and Contraction, i.e. Shrinkage
due to plastic thermal strain, of the weld metal and base
metal during the heating and cooling cycle
 Internal stresses formed in base metal due to removing
restraints given to welds by fixed components surrounding
it
So, both Welding processes & procedures and Material
properties
affect the extent of distortion
 Effects of Distortion:
 Complicate further fabrication
 Reduced application of the structure
4

5. Significance of Material
Properties5
Properties of Materials Effects
(Requirements for Less
Distortion)
Coefficient of Thermal
Expansion (α)
Lower coefficient of thermal expansion
Thermal Conductivity (K) High Thermal Conductivity leads to low
thermal gradients
Yield Strength (ơy) Lower the yield strength of the parent
material, lower the residual stresses causing
distortions
Modulus of Elasticity (E) Higher the Modulus of Elasticity (stiffness) of
the parent material

6. 6
TYPES OF
WELDING
DISTORTIO
NS
Longitudin
al
Shrinkage
Transverse
Shrinkage
Angular
Distortion
Longitudin
al
Distortions/
Bowing or
Bending
Rotational
Distortion
Buckling
and
Twisting

7. 7
Schematic View of Distortions in
Welding

8. Longitudinal Shrinkage
8
 Shrinkage in the direction of the weld axis
 Cause:
 Preheat or fast cooling problem
 Shrinkage stresses in high constraint areas
 Prevention:
 Weld toward areas of less constraint
 Weld short length
 Also, preheat to even out the cooling rates
 Straightening press, jacks, clamps should be
used
Figure: Longitudinal
Shrinkage

9. Longitudinal Shrinkage
9
 Butt Welds
• ẟL= longitudinal shrinkage, mm
• I = welding current, amps
• T = length of the weld, mm
• t=plate thickness, mm
 Fillet Welds
• ẟL = longitudinal Shrinkage
• Aw = Cross-sectional area of the weld metal
• Ap = Cross-sectional area of the resisting structure
Figure: Butt Joint
Figure: T-joint with two fillet
welds

10. Angular Distortion
10
 Weld tends to be wider at the top than
the bottom, causing more solidification
shrinkage and thermal contraction
 For Double-V Edge Butt weld-joint, it
depends upon root face and root gap
 Fillet welds-joints, it depends upon the
flange width, weld leg length and
flange thickness
 Depends Upon:
 Width and depth of fusion zone relative
to plate thickness
 Type of joint
 Weld pass sequence
 Thermo-mechanical material properties
 Heat input per unit length of weld,
Figure: Angular Distortion in Butt Weld-
joint
Figure: Angular Distortion in Fillet Weld-
Joint

11. Angular Distortion
11
 Occurs at butt, lap, T, corner joints due to single-sided as well as
asymmetrical double-sided welding
 Prevention:
 Reducing the volume of weld metal
 Using double-V joint and alternate welding
 Placing welds around neutral axis
 Presenting: By compensating the amount of distortion to occur in
welding
 Elastic pre-springing can reduce angular changes after restraint
is removed.
 Preheating and post weld treatment

12. Welding Suitability Index
12
 Welding Suitability Index based on Distortion
(λƐ)
where,
Tm, a, α, E, ơy, refers to material under consideration
Tm*, a*, α*, E*, ơy
* refers to those of reference material
Tm: Melting Temperature, (°C)
a : Thermal Diffusivity, (mm2 / sec)
α : Thermal Expansion, (1/°C) *10-6
E : Elastic Modulus, (kN/mm2)
ơ : Yield Limit, (N/mm2)

13. 13
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6 7 8
Welding Suitability Indices in
Distortion
Welding Suitability
Indices in Distortion
Base Metal
Melting
Temperature,
Tm (°C)
Thermal
Diffusivity, a
(mm2 / sec)
Thermal
Expansion, α
(1/°C) *10-6
Elastic
Modulus, E
(kN/mm2)
Yield Limit,
ơy, (N/mm2)
Welding
Suitability
Indices in
Distortion
Low Alloy Steel 1520 7.5-9.5 11 210 200-700 1
High Alloy Steel 1400 5.0-7.5 16 200 250-550 0.86
Aluminium Alloy 600 75-100 24 65 80-280 0.01
Titanium Alloy 1800 6 8.5 110 500-700 1.08
Copper Alloy 1080 120 18 130 30-420 0.02
Nickel Alloy 1435 15 13 215 120-630 0.43

14. Measurement of Distortion
14
 Distortion in the post weld cooled state is determined by
applying length and angular measuring techniques
 Transverse and Longitudinal Shrinkage are determined by
Measuring Tape
 Angular Shrinkage is measured on a measuring plate by
means of straight edge set against the component (as shown
in below figure)
Figure: Measuring Longitudinal
& Transverse Shrinkage
Figure: Measuring Angular Distortions

15. Measurement of Distortion
15
 Measuring Bending or Angular Distortion
Figure: Measuring Angular Distortions or
Bending
Figure: Measuring Angular Distortions
Figure: Measuring Bending

16. Measurement of Distortion
16
 Circumferential
measurements on spherical
and cylindrical shells are
performed by string wrapped
around the structure
 Vertically extended
components, e.g. Pillars,
supports and tank walls,
inclinations and deflections
are measured by means of
strings hanging exactly
vertically and tensioning
weight immersing in water
Figure: Distortions in Circumferential Figure: Distortions in vertically Extended

17. Control of Distortion in
Weldments17
 Welding Residual stresses and Welding Distortion behave in
a contrary way
 Least root gap:
 As small as possible, but sufficient for good penetration
 Excessive gaps should be avoided
 Included angle should not exceed 60°
 For heavy sections, double-V preparation should be preferred

18. Control of Distortion in
Weldments18
 Tack Welding
 Sufficiently long tack welds
transmit shrinkage forces
 Tack weld length should be
two-three times the plate
thickness
 Preheating, slag removal and
further defect removal
methods are employed to
counter undesired
phenomenon due to tack weld
 Narrow Groove Section in
Welding
 Least as possible to produce least
heat concentration
 U shape groove is preferable than
Vee shape
 Symmetrical weld groove reduces
angular shrinkage, but residual
stresses are increased
 Double-sided fillet weld is selected
over single-sided fillet weld

19. Control of Distortion in
Weldments19
 Counter or Opposing Set-up
Figure: War page in a T-beam and
Suggested Counter setup
Figure: Counter Set-up for Angular Distortion

20. Correction of Distorted
Weldments20
 If a weldment warps despite the precautions taken, there are
ways and means of correcting the defect using one of the
following two methods:
Methods for Correction of
Distorted Weldments
Mechanical
Methods
Presses, Jack Screws
, Straightening Rolls,
Sledges, Special
Fixtures
Thermal
Methods
Oxy-
acetylen
e torch
Carbon
Arc
Powerful
oil or
gas
burners

21. Case study
21

22. Determined locating surfaces ,pressure force
and find possible distortion points are
shown.22

23. Completed fixture is shown in
Figure23

24. References
24
 Journal of Achievements in Materials and Manufacturing
Engineering VOLUME 20 ISSUES 1-2 January-February
2007
 R. S. Parmar, Welding Engineering and Technology, Khanna
Publishers, 2010
 Zhili Fen, Processes and mechanisms of welding residual
stress and distortion, 2005, Pg 209-216
 airproducts.com

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