This document provides an overview of resistance welding, including resistance spot welding, projection welding, and seam welding. It discusses key factors that affect heat generation in resistance welding such as welding time, current, and resistance. The document also examines electrode materials and geometry, welding problems such as expulsion and shunting effects, and mechanical testing of resistance spot welds.

1. Resistance WeldingResistance Welding
By:
Majid Pouranvari
Materials Science and Engineering Department,
Sharif University of Technology
Fall, 2014
A little about me…
Education
Authorship
Reviewership
Faculty
PhD, Materials Engineering, Major in Welding,
Sharif University of Technology, 2013
Sharif University of Technology
55 ISI-WoS Papers
22 National & Inter. Papers in Scientific Journals
40 Papers in conferences
Reviewer for MSEA, STWJ, JALC, JMAD, JMPT,
JMEP, …

2. Resistance Welding
Table of ContentTable of Content
(1) Resistance Spot Welding
(2) Resistance Projection Welding
(3) Resistance Seam Welding
(4) Resistance Butt Welding

3. Definition of Resistance
Welding
 Resistance welding is a fusion
welding process in which
coalescence of metals is
produced at the faying surfaces
by the heat generated at the
joint by the resistance of the
work to the flow of electricity.
 Force is applied before, during,
and after the application of
current to prevent arcing at the
work piece.
 Melting occurs at the faying
surfaces during welding.
Resistance Welding
 Heat generation is expressed as
Q = I2R T,
Q = Heat generated.
 Resistance welding depends on
three factors:
Time of current flow (T).
Resistance of the conductor (R)
Amperage (I).

4. Principal Types of Resistance Welds
Electrodes
or Welding
Tips
Electrodes
or Welding
Wheels
Electrodes
or Dies
Projection
Welds
Electrodes or Dies
Spot Weld Seam Weld Projection Weld
Upset Weld Flash Weld
After Welding After Welding
[Reference: Resistance Welding Manual, RWMA, p.1-3]
The dominant process for welding of automotive
sheets
Resistance Spot Welding

5. Resistance Spot Welding
Professor T. W. Eagar, MIT
“ The more one studies the resistance welding process, the more
one appreciates how complex the process is ”

6. RSW
Equipments

9. Heat Generation in Resistance Spot Welding

10. Block Diagram of Single-Phase
Spot Welder
Spot Weld
Main Power Line
Contactor
N = np /ns
V s= V p /N
Is = Ip N
Typically, the turns ratio in resistance welding
transformers is about 100 to 1. Therefore, if 480 V, 200
A power is available at the primary, 4.8 V at 20kA will
be available at the secondary (neglecting losses).

11. Temperature Readings of A Spot Welding Process
Workpiece
This illustration was taken
about 4/60th of a second
after the welding current
starts.
(Note: Temp at Electrode Sheet Interface Higher than Bulk)
After 20%
welding time
At the end of
welding time
Temperature
ElectrodeElectrode
Workpiece
Temperature
distribution at
various
location
during
welding.
Temperature Distribution

12. Welding Cycle
Upslope/Downslope, Hold Time,
& Temper
Weld Current
Temper Current
Electrode
Pressure
Current
Squeeze Time Weld Time Off Time Hold Time
Upslope Downslope Temper

13. Enhanced Welding Cycle
Preheat
Time
Upslope
Time
CoolTime
Weld
Time
CoolTime
Preweld
Interval
Welding Cycle
Weld Interval Postweld Interval
Downslope
Time
Quench
Time
Temper
Time
Hold
Time
Pulse
Impulse
Tempering
Current
Welding Current
Electrode
Force
Forge Delay Time
Forge Force
[Reference: Welding Handbook, Volume 2,
AWS, p.539]
Squeeze time
Advantages of Resistance Spot Welding
 Excellent for sheet metal applications, < ¼-
inch
 High speed, < 0.1 seconds in automotive
spot welds
 Adaptability for Automation in High-Rate
Production of Sheet Metal Assemblies
 No filler metal
 Economical
 Dimensional Accuracy

14. Process Disadvantages and Limitations
 Higher equipment costs
than arc welding
 Power line demands
 Nondestructive testing
 Low tensile and fatigue
strength
 Not portable
 Electrode wear
 Lap joint requires additional
metal
 Difficulty for repair
Macrostructural Features of a RSW

15. Weld Size Requirements
Weld Penetration Requirements
In general, a large penetration
is acceptable if it does not
create a large indentation. The
requirements on penetration
are often applied together with
those on weld size.

16. Factors Affecting Heat Generation (Q):
 Welding time
 Welding Current
Welding current is most effective in
heat generation compared to welding time
Q = I2Rt

17. Factors Affecting Heat Generation (Q):
 Resistance
Bulk Resistance vs. Contact Resistance
R=f (Materials Properties and Pressure)

18. Factors Affecting Heat Generation (Q):
 Resistance
Surface Condition
Steel
Steel
Steel
Steel
Oils/Dirt
Oxide
Oxide
Oils/Dirt
(a) Pickled Conditions
(b) Rusted Conditions
Rusty
Pickled
Polished
Electrode Force
Resistivity

19. Resistance Varies with
Pressure
Low Pressure Medium Pressure High Pressure
(a) (b) (c)

20. Expulsion: A common Phenomena in
Resistance Welding
Expulsion: A common Phenomena in
Resistance Welding

21. Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”,
AWS Sheet Metal Conf VIII, 1998
Effect of Welding Parameters on Expulsion
 Welding Current
 Welding time
 Electrode force
Effect of Expulsion
 Void
 Excessive electrode indentation

22. Operating Window - Lobe Curve
Current (1000’s of amperes)
Time(cyclesofcurrent)
ExpulsionNugget
too small
Acceptable
nugget
size
Constant electrode
force
Effect of Process variable on
Operating Window - Lobe Curve
Materials properties

23. Some welding problems
Some welding problems

24. Some welding problems
Some welding problems

25. Some welding problems
Some welding problems

26. Some welding problems
Some welding problems

27. Heat Balance
In RSW, heat balance can be defined as a condition
in which the fusion zones in both pieces being joined
undergo approximately the same degree of heating
and applied pressure. It describes the ideal situation
when a symmetric weld (with equal depth of nugget
penetration) is made.
Heat balance is influenced by the relative thermal
and electrical conductivities of the materials to be
joined, the geometry of the weldment, and the
geometry of the electrodes.
Dissimilar Thickness Welding
In the case of dissimilar thickness, bulk resistance of
thicker sheet is lager than that of the thinner sheet. This
leads to an asymmetric weld nugget (i. e. penetration of the
weld nugget into the thicker sheet is larger than that of the
thinner sheet).

28. Dissimilar Thickness Welding
Solution for Heat Unbalance in
dissimilar Thickness Welding
This can be overcome by using electrodes of two different
diameters or by inserting a high-resistivity tip in one electrode.
The smaller electrode or the one with high-resistivity insert
should be placed against the thinner of the two sheets

29. Dissimilar Metal Welding
Shunting Effect
Previously made welds may affect the subsequent welding if the welds
are spaced close to each other due to electric current shunting.
The welding current may be diverted from the intended path by the
previously made welds. As a result, the current or current density
may not be sufficient to produce a quality weld.

30. Shunting Effect
Shunting Effect

31. Shunting Effect
Shunting Effect
The shunting effect is a strong function of the bulk resistivity of the
sheet material. A high conductive metal, such as aluminum, requires a
large space between the welds.
This should be taken into account when welds are designed into
structures, as putting too many welds close to each other may not
provide the intended strength.

32. electrode
electrode
Electrodes
Electrode Functions
 Conduct the welding current to the work
 Transmit the proper electrode pressure or
force to the work in order to produce a
satisfactory weld
 Help dissipate heat from the weld zone

33. Material Requirements for
Electrode in Resistance Welding
 High electrical conductivity
 High Thermal conductivity
 High temperature mechanical strenght
Effect of Strengthening Mechanism on the
Electrical Resistivity?
RWMA Electrode Material Standards
 Group A - Copper
Base Alloys
 RWMA Class 1
 Zirconium Copper
 Cadmium Copper
 Chromium Copper
 RWMA Class 2
 Chromium-Zirconium
Copper
 Chromium Copper
 RWMA Class 3
 Cobalt-Beryllium
Copper
 Nickel-Beryllium
Copper
 Beryllium-Free Copper
 RWMA Class 4
 Beryllium Copper
 RWMA Class 5
 Aluminum Copper

34. RWMA Electrode Material
Standards (CONT.)
 Group B - Refractory
Metals and Refractory
Metal Composites
 RWMA Class 10
 Copper Tungsten
 RWMA Class 11
 Copper Tungsten
 RWMA Class 12
 Copper Tungsten
 RWMA Class 13
 Tungsten
 RWMA Class 14
 Molybdenum
 Group C - Specialty
Material
 RWMA Class 20
 Dispersion-
Strengthened Copper
Electrode Materials
RWMA
Class #
Electrical
Conductivity
Composition
(%)
Ultimate
Strength
(ksi)
Annealing
Temperature
(°C)
Thermal
Conductivity
(Cal/cm-sec-°C)
-
1
2
3
4
5
Cu
99-Cu,
1-Cd
99.2-Cu,
0.8-Cr
97-Cu, 2.5-
Co, 0.5-Be
Cu & Be
Cu & Al
90
92
80 (C)
82 (F)
48 (C)
52 (F)
20 (C)
23 (F)
18 70 - 0.16
30 - -
60 (F)
30 (C)
62 (F)
95 (C)
105 (F)
110 (C)
170 (F)
660 0.82
710
0.77 (C)
0.75 (F)
0.43 (C)
0.45 (F)
0.18 (C)
0.19 (F)
930 (C)
900 (F)
1020 (C)
900 (F)
* C = Cast, F = Forging

35. Typical Electrode Hardness-Temperature Curves
[Reference: Resistance Welding
Manual, p.18-2, RWMA]
Electrode Geometry
“A” “A” “A” “A”
6° 20°
45°
3
1
4
1
4
1
4
1
4
45°20°
Pointed
Dome
Truncated
Cone
Truncated
Cone
[Reference: Welding in the Automotive Industry, p.135, D. W. Dickinson]

36. Electrode Size
Net Electrode Force (lb x 102)
Electrode Face Diameters (inch)
Electrode Body Diameters (inch)
[Reference: Resistance Welding Manual, p.18-14, RWMA]
W. Stanley, Resistance Welding
McGraw-Hill, 1950

37. Electrode Life
Number of Welds
Diameter
Electrode Cap Diameter
For Coated Steel
Weld Button Diameter
For Coated Steel
Weld Button Diameter
Uncoated Steel
Electrode Degradation
(1) Mechanical Degradation
(2) Metallurgical Degradation

38. Electrode Life
Steel
Solid Zinc Coating
Molten Zinc
Copper Alloy Electrode
brass
MeltingPoint (F)
Copper 1980
Brass Downto1710
Zinc 787
Measured
ElectrodeFaceTemp(F)
Bare 1000-1200
Galvanized 1500-1700
Cu Zn
~45% ~60% ~85%

39. Uncoated
Hot Dipped Galvanized
Spot Weld Mechanical Properties

40. Interfacial Mode
Pullout Mode

41. Weld With Expulsion Failed in Pullout Mode
Dickinson, “Welding in Auto Industry,
AISI, 1981
Workshop Tests

42. AWS Spec D8.9-97, 1997
Advantages of Peel Test
• Ease of Performance
• Low Cost
• Ability to use on Shop Floor as quality control test
Disadvantages of Peel Test
• A qualitative rather than a quantitative

43. Dickinson, “Welding in Auto Industry,
AISI, 1981
Chisel Test
Turn to the person sitting next to you and discuss (1 min.):
• Why do automotive manufactures prefer the chisel test on
the production line over the peel test?

44. Mechanical Properties of RSW
Mechanical Properties of RSW
Tensile-Shear Test

45. Mechanical Properties of RSW
Coach-Peel Test
Mechanical Properties of RSW
Cross-Tension Test

46. Mechanical Properties of RSW
Tensile-Shear Test
Strength Requirements for Steels

47. Strength Requirement for Mg & Al

48. Heuschkel, “Expression of Spot Weld Properties”,
Weldign Journal Oct 1952
FTS=Dt[-(C+0.05Mn)] BM

49. Failure Mode of Spot Welds

50. ‫اي‬ ‫ﻧﻘﻄﻪ‬ ‫ﻣﻘﺎوﻣﺘﯽ‬ ‫ﺟﻮﺷﻬﺎي‬ ‫ﺷﮑﺴﺖ‬ ‫ﻣﻮد‬
‫در‬ ‫ﮐﻪ‬ ‫دارد‬ ‫وﺟﻮد‬ ‫ﺑﺤﺮاﻧﯽ‬ ‫دﮐﻤﻪ‬ ‫ﻗﻄﺮ‬ ‫ﯾﮏ‬
‫ﻣﺸﺘﺮﮐﯽ‬ ‫ﻓﺼﻞ‬ ‫ﺷﮑﺴﺖ‬ ،‫آن‬ ‫از‬ ‫ﺗﺮ‬ ‫ﭘﺎﯾﯿﻦ‬ ‫ﻣﻘﺎدﯾﺮ‬
‫اﺳﺖ‬ ‫ﺣﺎﮐﻢ‬.
AWS: D=4t0.5
DVS/JIS: D=5t0.5
‫درﺟﺎ‬ ‫ﺗﻤﭙﺮ‬ ‫ﻃﺮﯾﻖ‬ ‫از‬ ‫ﺷﮑﺴﺖ‬ ‫رﻓﺘﺎر‬ ‫ﺑﻬﺒﻮد‬

51. Introduction to Projection
Welding
(a) (b) (c) (d)
[Reference: Welding Handbook, Volume 2, p.566, AWS]
Examples of Various Projection Designs
(c) (d)
[Reference: Welding Handbook, Volume 2, p.562, AWS]
(b)
(a)

52. Examples of Various Projection Designs
(CONT.)
(e) (f) (g)
[Reference: Welding Handbook, Volume 2, p.562, AWS]
Projection Types for Sheet and
Solid Applications
[Reference: Metals Handbook, Volume 6 (Welding, Brazing and
Soldering), p.503-524, ASM]
Spherical Projections
Elongated Projections

53. Cross-wire welding
Projection in Nuts

54. Advantages of Projection
Welding
 Ease of obtaining satisfactory heat balance for welding
difficult combinations
 More uniform results in many applications
 Increased output per machine because several welds
are being made simultaneously
 Longer electrode life

55. Advantages of Projection
Welding (CONT.)
 Welds may be placed more closely together
 Finish, or surface appearance, is often improved
 Parts may be projection welded that could not be
otherwise resistance welded
Limitations of Projection
Welding
 Requires an additional operation to form projections
 Requires accurate control of projection height and
precise alignment of the welding dies with multiple welds
 Requires thickness limitation for sheet metals
 Requires higher power capacity equipment than spot
welding

56. Projection Weld Formation
[Reference: Resistance Welding Manual, p.3-9, RWMA]
Stage 1 Stage 3
Stage 2 Stage 4
Projection Weld Formation
(CONT.)
[Reference: Resistance Welding Manual, p.3-9, RWMA]
Stage 5 Stage 7
Stage 6 Stage 8

57. Basic Projection Design in Steel
Sheet
[Reference: Welding Handbook, Volume 2, p.563, AWS]
Spherical
Radius
Projection
Wall
Thickness Should
Be at Least 70%
of Sheet Thickness
Punch Die
Point Radius
“R”Projection Should Blend
into Stock Surface without
Shouldering
D
T
H
A
D
B
45°
15°
Effect of H?
Recommended Projection
Designs
[Reference: Recommended practice for resistance welding, AWS
Document C1.1-66, AWS, 1966]
T(in.) D(in.) H(in.) L(in.)
0.010-0.014 0.055 0.015 1/8
0.016-0.020 0.067 0.017 5/32
0.025 0.081 0.020 3/16
0.031-0.034 0.094 0.022 7/32
0.044-0.050 0.119 0.028 9/32
0.062-0.070 0.156 0.035 3/8
0.078 0.187 0.041 7/16
0.094 0.218 0.048 1/2
0.109 0.250 0.054 5/8
0.125 0.281 0.060 11/16
0.140 0.312 0.066 3/4
0.156 0.343 0.072 13/16
0.171 0.375 0.078 7/8
0.187 0.406 0.085 15/16
0.203 0.437 0.091 1
0.250 0.531 0.110 1-1/4
H
T
D
T: Thickness of thinnest outside piece
D: Diameter of projection
H: Height of projection
L: Minimum contacting overlap
L

58. [Reference: Resistance Welding Manual, p.3-13, RWMA]
Projection Welding of Low Carbon Steel (Two Equal Thicknesses)
Resistance Seam Welding

59. Resistance Seam Welding
Upper Electrode Wheel
Workpiece
Lower Electrode Wheel
Throat
Knurl or Friction
Drive Wheel
Roll Spot Weld
Overlapping Seam
Weld
Continuous Seam
Weld
[Reference: Welding Handbook,
Volume 2, p.553, AWS]
Lap Seam Weld
Electrodes Overlapping
Weld
Nuggets
Travel
Front view Side View
[Reference: Welding Handbook, Volume 2, p.554, AWS]

60. ASM Handbook Vol6, 1993
ASM Handbook Vol6, 1993
Schematic of seam weld.
Length of electrode footprint holds 3 welds

61. RSW Certification Training Class, Boeing
Effect of Cool Time (Heat %) on Nugget Properties
Resistance Welder Manufacturers Association Bulletin # 23
@ 6 Cycle Heat

62. Welding Speed
Resistance Welder Manufacturers Association Bulletin # 23
Tensile Tests
Pillow Tests
Seam Weld
Quality Tests
Resistance Welder Manufacturers
Association Bulletin # 21

63. 6 x 6 inch Pillow
6 x 10 inch Pillow
Typical data from Pillow Testing
Resistance Upset Welding

64. Upset Welding
Finished Upset Weld
Heated Zone
To Welding Transformer
Clamping Die
Upsetting
Force
Movable Part
Clamping Die
Stationary Part
[Reference: Welding Handbook, Volume 2, p.598, AWS]
Schematic of Typical Butt Weld Cycle
Medar Technical Literature

65. Mechanism
Stage 1: Resistance (Joule) Heating help ease of hot
plastic deformation
Stage 2: Application of extra upsetting pressure causes
material extrudes out-wards forming an upset.
Upset Resistance Welding

66. Upsetting
 The main mechanism to remove the
contaminants is the formation of the upset.
 By changing the welding conditions to generate
more upset the amount of contaminants will be
reduced, although more material will be lost and
more energy will be consumed.
Wheel rim production