Spot weldability

Lesson ObjectivesWhen you finish this lesson you will understand:• Concept of Spot Weldability• Electrode arrangements

Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line

workbook

Keywords: Current Level, Current Range, Lobe Curve, Electrode Life, Peel Test, Nugget Size, Button Size, Interfacial Failure, Shunting Effect, Multiple Direct Electrodes, Series Electrodes, Electrode Tooling

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

Peel Test Used As MeasurePeel Test Used As Measure

Button Size as a Measure of Weld Quality

ButtonDiameter

Modes of Failure in Spot Welds

Full Button Irregular Button

Interfacial Failure

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

Peel Test Used As MeasurePeel Test Used As Measure

Nugget Diameter vs. Weld Current

Expulsion

SmallNuggets

AcceptableNuggets

Minimum Nugget Diameter

Weld Current

Nug

get D

iam

eter

Nominal Current

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

Peel Test Used As MeasurePeel Test Used As Measure

Current Range & Weldability Lobe

ExpulsionAcceptableNuggets

Small Nuggets

Minimum Nugget Diameter

Weld Current

Weld Current

ExpulsionLevel

TimeA Smaller

“Brittle” Nuggets

AcceptableNuggets

LobeCurve

Nug

get D

iam

eter

Wel

d Ti

me

Time A

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

Peel Test Used As MeasurePeel Test Used As Measure

Process DeteriorationMinimumAcceptableDiameter

Number of Welds

Wel

d D

iam

eter

Shunting Effect

AB

IB

IA

Itotal = IA + IB

IARA = IBRB

IB/Itotal = 1 - RB/(RA + RB)[Reference: Resistance Welding Manual, p.1-7, RWMA]

Multiple Direct Electrodes

Series Electrode

Tooling for Multiple Welding

Stud and Jam NutsEqualizing Bar

Split and Clampedto Electrode

Flexible ConductorsSlip-Fit

Lower Electrode

Welding PressureAdjustment Screw

Compression Spring

FlexibleConductors

Slip-Fit

Workpiece

(a) (b)[Reference: Resistance Welding Manual, p.17-8, RWMA]