1. WE 602 Resistance Welding Processes Review & Physics of Spot Welding Reference Web Site for Review: www-iwse.eng.ohio-state.edu/we601

2. Resistance Welding Process Review Lesson Objectives When 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 Activities 1.View Slides; 2.Read Notes, 3.Listen to lecture 4.View Demos 5.Do on-line workbook 6.Do Homework Keywords Spot weldcontact resistanceexpulsionheat flow Weld cyclebulk resistancepulsingelectrode

3. Principal Types of Resistance Welds Electrodes or Welding Tips Electrodes or Welding Wheels Electrodes or Dies Projection Welds Electrodes or Dies Spot WeldSeam Weld Projection Weld Upset WeldFlash WeldAfter Welding [Reference: Resistance Welding Manual, RWMA, p.1-3]

4. Introduction to Resistance Spot Welding Top Electrode Water Weld Nugget Bottom Electrode Resistance Distance

5. Typical Equipment of Resistance Spot Welding (a) (b) [Reference: Welding Process Slides, The Welding Institute]

6. Process Operation of Resistance Spot Welding [Reference: Welding Process Slides, The Welding Institute]

7. Advantages of Resistance Spot Welding l Adaptability for Automation in High-Rate Production of Sheet Metal Assemblies l High Speed l Economical l Dimensional Accuracy

8. Limitations of Resistance Spot Welding l Difficulty for maintenance or repair l Adds weight and material cost to the product, compared with a butt joint l Generally have higher cost than most arc welding equipments l Produces unfavorable line power demands l Low tensile and fatigue strength l The full strength of the sheet cannot prevail across a spot welded joint l Eccentric loading condition

9. Basic Single Impulse Welding Cycle Electrode Force Welding Current Welding Cycle Squeeze TimeWeld Time Hold Time Off Time [Reference: Welding Handbook, Volume 2, AWS, p.538]

10. Enhanced Welding Cycle Preheat Time Upslope Time Cool Time Weld Time Cool Time Preweld Interval Welding Cycle Weld IntervalPostweld 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

11. Contact-Resistance Measurement Contact Area Electrode Force Small Current R ec R sc RvRv RvRv R ec R total R ec = contact resistance between electrode and sheet surface R sc = contact resistance at the faying surface R v = volume resistance of the sheets

12. Resistivity as A Function of Temperature 100 200 300 400 500 600 700 800 10 20 30 40 50 60 70 80 90 100 110 120 130 HSLA Low Carbon Temperature, °C Resistivity,  -cm [Reference: Welding in the Automotive Industry, D.W. Dickinson, p.125]

13. 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.

14. Temperature Gradient of A Spot Weld End of “Weld Time” 20% of “Weld Time” Water Temperature Water Electrode Work Welding Temperature [Reference: Resistance Welding Manual, RWMA, p.1-4]

16. Nugget Growth (a) (b) Point 1 Point 2 Point 3

17. Nugget Growth (CONT.) (a) (b)

18. Expulsion at Interfacial Surface Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998

19. Temperature Readings of A Spot Welding Process This illustration was taken about 4/60th of a second after the welding current starts.

20. Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998

21. Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998

22. Zhang et al, “Expulsion Modeling in RSW of Steel and Al Alloys”, AWS Sheet Metal Conf VIII, 1998

23. Pulsing Cool Time Pulse 1Pulse 2Pulse 3 Pulse Time

24. Without PulsingWith Pulsing

25. 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?