Spot Weldability

1
Spot Weldability Quality and Performance
2
Spot Weldability

• Learning Activities
• View Slides
• Read Notes,
• Listen to lecture
• Do on-line workbook
• Do Homework

• Lesson Objectives
• When you finish this lesson you will understand
• visual identification of discontinuities
• how to develop use lobe curves
• electrode life
• peel test failure modes

Keywords Current level Current Range Lobe
Curve Electrode life Nugget Dia Button Dia. Peel
Test Tensile Shear Cross tension Shunt current
3
Process Requirements

• Electrode Materials
• Electrode Geometry
• Welding Force
• Welding Cycle
• Squeeze time
• Welding time
• Hold time
• Welding Current

How Do We Know These Are All Correct
4
Visual Inspection of Quality
b
a
d
c
W. Stanley, Resistance Welding McGraw-Hill, 1950
5
Visual Inspection of Quality
a
b
d
c
e
W. Stanley, Resistance Welding McGraw-Hill, 1950
6
Process Characteristics as a Measure of
Weldability

• Current Level
• Current Range Weldability Lobe
• Process Deterioration
• Characterization of the loss in weld size at
  constant welding conditions
• Characterization of the variation in process
  requirements for maintaining welds of an adequate
  quality

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Current Level
Simple Current Levels for a Range of 0.8 mm Sheet
Steels
Material Welding Current (kA)
Uncoated Steel 9 Hot-Dipped
Galvanized 13 Electro Galvanized 12 Galvanne
aled 10 Fe-Zn Electro Coated 10
(6.1 mm Electrodes 12-14 Cycles of Welding Time)
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Current Range Weldability Lobe
Expulsion
Acceptable Nuggets
Nugget Diameter
Minimum Nugget Diameter
Time A
Small Nuggets
Weld Current
Lobe Curve
Time A
Weld Time
Smaller Brittle Nuggets
Expulsion Level
Acceptable Nuggets
Weld Current
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Effect of Weld Time on Current Range (Weld Lobe)
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Effect of Hold Time on Lobe Curve
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Effect of Electrode Force on Lobe Curve
Lobe moves to Higher Current Longer Times
Very High Force
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Effect of Electrode Misalignment on Lobe Curve
Karagoulis, Process Control in Mfg, AWS Sheet
Metal Conf V, 1992
13
Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)

14
Pareto Charts Relate Importance of Process
Parameters
Standard Approach
Graeco-Latin Approach

• Current Density
• Weld Force
• Weld Time

• Current Density
• Weld Force
• Weld Time
• Weld Spacing
• Surface Conditions

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What is a Pareto Chart ?

• In our case, A Pareto Chart is a graphical
  comparison of process variables vs. weld quality.
  In other words it ranks the process variables in
  the order of their potency (amount they change
  weld quality).

Scharfy Kuhnash Pareto Chart Development for
Resistance Welding Senior Capstone, OSU, 2000
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Defining Window Size

• Develop weld windows for each process parameter
• Determine the affect of changing the parameter
  has on the weld window

Window Size expulsion - initiation
Scharfy Kuhnash Pareto Chart Development for
Resistance Welding Senior Capstone, OSU, 2000
17
Weld Force Windows
Scharfy Kuhnash Pareto Chart Development for
Resistance Welding Senior Capstone, OSU, 2000
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Weld Time Windows
Scharfy Kuhnash Pareto Chart Development for
Resistance Welding Senior Capstone, OSU, 2000
19
Window Size Pareto Chart
Negative Change
Scharfy Kuhnash Pareto Chart Development for
Resistance Welding Senior Capstone, OSU, 2000
20
Current Median Pareto Chart
Scharfy Kuhnash Pareto Chart Development for
Resistance Welding Senior Capstone, OSU, 2000
21
Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)

22
Process Characteristics as a Measure of
Weldability

• Current Level
• Current Range Weldability Lobe
• Process Deterioration
• Characterization of the loss in weld size at
  constant welding conditions
• Characterization of the variation in process
  requirements for maintaining welds of an adequate
  quality

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Process Deterioration
Minimum Acceptable Diameter
Weld Diameter
Number of Welds
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Low Electrode Force
Surface Expulsion
Hirsch, R Leibovitz, R, Improved Weld Quality
and Electrode Life in Resistance Welding
Practical Welding Today, Nov-Dec, 1997
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Low Electrode Force
Hirsch, R Leibovitz, R, Improved Weld Quality
and Electrode Life in Resistance Welding
Practical Welding Today, Nov-Dec, 1997
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Mechanical Properties as a Measure of Weldability

• Button Size as a Measure of Weld Quality
• Simulative Mechanical Tests
• Tensile shear loads
• Peel loads
• Cross tension
• Modes of Failure in Spot Welds
• Full button
• Irregular button
• Interfacial failure

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Button Size as a Measure of Weld Quality
Button Diameter
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Simulative Mechanical Tests
Peel
Tensile Shear
Cross Tension
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Introduction to Peel Testing Technique
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Geometric Effects on The Qualified Peel Test
W
450 350 250 150
x
Max. Load, lbs
W 1
Load
W 1.5 W 2
0 1/4 1/2 3/4
1 1-1/4
Distance x, in
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Modes of Failure in Spot Welds
Full Button Irregular Button
Interfacial Failure
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Microstructural Measures of Weldability

• Weld Geometry
• Degree of weld penetration
• Actual diameter of weld
• Weld Structural Integrity
• Weld Hardness

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Weld Geometry
Weld Diameter
Weld Penetration
Full Size Weld Sub-Size Weld
Weld Diameter
Weld Penetration
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Weld Structural Integrity
Fine Weld Porosity
Residual Dendritic Structure
Workpieces
Weld Nugget
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Weld Hardness
Hardness
(a) Weld Morphology (25X)
Distance (mm)
(B) Variation in Weld Hardness
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Questions?

• Turn to the person sitting next to you and
  discuss (1 min.)

37
Other Factors Effecting Weld Geometry

• Shunt Current
• Electrode Radius

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Effect of Shunt Current on Spot Weld Quality

• International Recommendations
• Spot Spacing 16 (sheet thickness)
• Spot Spacing 3 (recommended electrode face
  dia.)

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Shunting Currents
Howe, Spot Spacing Effect on Buton Size AWS
Sheet Metal Conf. VI, 1994
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International 16 t Formula
Conclusion Above the internationally recommended
spot spacing, there is little effect on button
size
Howe, Spot Spacing Effect on Buton Size AWS
Sheet Metal Conf. VI, 1994
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Effect of Electrode Radius
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RSW Certification Training Class, Boeing
43
RSW Certification Training Class, Boeing
44
RSW Certification Training Class, Boeing
45
Homework
Assignment 2
Spot Weldability