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WE 602Resistance Welding Processes
Review&
Physics of Spot WeldingReference Web Site for Review:
www-iwse.eng.ohio-state.edu/we601
Resistance Welding Process Review
Lesson ObjectivesWhen you finish this lesson you should understand:• Heat generation & nugget growth in resistance spot welding• Basic, enhanced and pulsed weld cycles• Advantages and limitations of spot welding• A basic model of expulsion
Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. View Demos5. Do on-line
workbook6. Do Homework
KeywordsSpot weld contact resistance expulsion heat flowWeld cycle bulk resistance pulsing electrode
Principal Types of Resistance Welds
Electrodesor WeldingTips
Electrodesor WeldingWheels
Electrodesor Dies
ProjectionWelds
Electrodes or DiesSpot Weld Seam Weld Projection Weld
Upset Weld Flash Weld
After Welding After Welding[Reference: Resistance Welding Manual, RWMA, p.1-3]
Introduction to Resistance Spot Welding
Top ElectrodeWater
WeldNugget
Bottom Electrode
Resistance
Dis
tan
ce
Typical Equipment of Resistance Spot Welding
(a) (b)[Reference: Welding Process Slides, The Welding Institute]
Process Operation of Resistance Spot Welding
[Reference: Welding Process Slides, The Welding Institute]
Advantages of Resistance Spot Welding
Adaptability for Automation in High-Rate
Production of Sheet Metal Assemblies
High Speed
Economical
Dimensional Accuracy
Limitations of Resistance Spot Welding
Difficulty for maintenance or repair Adds weight and material cost to the product, compared with
a butt joint
Generally have higher cost than most arc welding equipments
Produces unfavorable line power demands
Low tensile and fatigue strength The full strength of the sheet cannot prevail across a spot
welded joint
Eccentric loading condition
Basic Single Impulse Welding Cycle
Electrode Force
Welding Current
Welding Cycle
Squeeze Time Weld Time HoldTime
OffTime
[Reference: Welding Handbook, Volume 2, AWS, p.538]
Enhanced Welding Cycle
Pre
heat
Tim
e
Ups
lope
Tim
e
Coo
l Tim
e
WeldTime
Coo
l Tim
e
PreweldInterval
Welding Cycle
Weld Interval Postweld Interval
Dow
nslo
peT
ime
Que
nch
Tim
e
Tem
per
Tim
e
Hol
dT
ime
PulseImpulse
TemperingCurrent
Welding CurrentElectrodeForce
Forge Delay Time
Forge Force
[Reference: Welding Handbook, Volume 2,AWS, p.539]
Squeeze time
Contact-Resistance Measurement
ContactArea
Electrode Force
Electrode Force
Small Current
Rec
Rec
Rsc
Rv
Rv
Rec
Rec
Rtotal
Rec = contact resistance between electrode and sheet surface
Rsc = contact resistance at the faying surface
Rv = volume resistance of the sheets
Resistivity as A Function of Temperature
100 200 300 400 500 600 700 800
102030405060708090
100110120130
HSLA
Low Carbon
Temperature, °C
Res
istiv
ity,
-cm
[Reference: Welding in the Automotive Industry, D.W. Dickinson, p.125]
Turn to the person sitting next to you and discuss (1 min.):• The total resistance across the spot weld for plain carbon steel usually starts high because of interfacial surface asperities and oxides and surface contaminants. But the total resistance changes as current passes. What would be the value of resistance as time increases (dynamic resistance)? Draw a curve.
Num ber of Cycles
Resis
tan
ce
Temperature Gradient of A Spot Weld
End of“Weld Time”
20% of “Weld Time”
Water Temperature
Water
Water
Electrode
Electrode
Work
Welding Temperature
[Reference: Resistance Welding Manual, RWMA, p.1-4]
Nugget Growth
(a) (b)
Point 1
Point 2
Point 3
Nugget Growth (CONT.)
(a) (b)
Expulsion at Interfacial Surface
Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998
Temperature Readings of A Spot Welding Process
This illustration was taken about 4/60th of a secondafter the welding currentstarts.
Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998
Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998
Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998
Pulsing
Cool Time
Pulse 1 Pulse 2 Pulse 3
PulseTime
Without Pulsing With Pulsing
Turn to the person sitting next to you and discuss (1 min.):• We have seen the nugget growth with AC current to grow when the peak in current is reached and shrink slightly as the current goes to zero each half cycle. What might occur when DC current is used?
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