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Spot Weldability Quality and Performance . 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

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slide1

Spot Weldability

Quality and Performance

slide2

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

process requirements
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

slide4

Visual Inspection of Quality

b

a

d

c

W. Stanley, Resistance Welding

McGraw-Hill, 1950

slide5

Visual Inspection of Quality

a

b

d

c

e

W. Stanley, Resistance Welding

McGraw-Hill, 1950

process characteristics as a measure of weldability
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
current level
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

Galvannealed 10

Fe-Zn Electro Coated 10

(6.1 mm Electrodes & 12-14 Cycles of Welding Time)

current range weldability lobe
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

slide11

Effect of Electrode Force on Lobe Curve

Lobe moves to

Higher Current

Longer Times

Very High Force

slide12

Effect of Electrode Misalignment on Lobe Curve

Karagoulis, “Process Control in Mfg”,

AWS Sheet Metal Conf V, 1992

slide13

Questions?

  • Turn to the person sitting next to you and discuss (1 min.):
pareto charts relate importance of process parameters
Current Density

Weld Force

Weld Time

Current Density

Weld Force

Weld Time

Weld Spacing

Surface Conditions

Pareto Charts Relate Importance of Process Parameters

Standard Approach

Graeco-Latin Approach

what is a pareto chart

Potency of a process parameter in influencing weld quality

A B C D E F G

Process Parameter

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

defining window size

Stable slope

Expulsion

Weld

Nugget

Initiation

Average

Steep slope

Process parameter

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

weld force windows
Weld Force Windows

Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding”

Senior Capstone, OSU, 2000

weld time windows
Weld Time Windows

Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding”

Senior Capstone, OSU, 2000

window size pareto chart
Window Size Pareto Chart

Negative % Change

Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding”

Senior Capstone, OSU, 2000

current median pareto chart
Current Median Pareto Chart

Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding”

Senior Capstone, OSU, 2000

slide21

Questions?

  • Turn to the person sitting next to you and discuss (1 min.):
slide22

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
process deterioration
Process Deterioration

Minimum

Acceptable

Diameter

Weld Diameter

Number of Welds

slide24

Low Electrode Force

Surface

Expulsion

Hirsch, R & Leibovitz, R, “Improved Weld Quality and Electrode Life in Resistance Welding” Practical Welding Today, Nov-Dec, 1997

slide25

Low Electrode Force

Hirsch, R & Leibovitz, R, “Improved Weld Quality and Electrode Life in Resistance Welding” Practical Welding Today, Nov-Dec, 1997

mechanical properties as a measure of weldability
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
simulative mechanical tests
Simulative Mechanical Tests

Peel

Tensile Shear

Cross Tension

geometric effects on the qualified peel test
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

modes of failure in spot welds
Modes of Failure in Spot Welds

Full Button Irregular Button

Interfacial Failure

microstructural measures of weldability
Microstructural Measures of Weldability
  • Weld Geometry
    • Degree of weld penetration
    • Actual diameter of weld
  • Weld Structural Integrity
  • Weld Hardness
weld geometry
Weld Geometry

Weld Diameter

Weld Penetration

Full Size Weld

Sub-Size Weld

Weld Diameter

Weld Penetration

weld structural integrity
Weld Structural Integrity

Fine Weld Porosity

Residual Dendritic

Structure

Workpieces

Weld Nugget

weld hardness
Weld Hardness

Hardness

(a) Weld Morphology (25X)

Distance (mm)

(B) Variation in Weld Hardness

slide36

Questions?

  • Turn to the person sitting next to you and discuss (1 min.):
slide37

Other Factors Effecting Weld Geometry

  • Shunt Current
  • Electrode Radius
slide38

Effect of Shunt Current on Spot Weld Quality

  • International Recommendations
  • Spot Spacing = 16 (sheet thickness)
  • Spot Spacing = 3 (recommended electrode face dia.)
slide39

Shunting Currents

Howe, Spot Spacing Effect on Buton Size”

AWS Sheet Metal Conf. VI, 1994

slide40

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

slide45

Homework

Assignment 2

Spot Weldability