The document discusses resistance spot welding processes. It covers heat generation and nugget growth during welding, different weld cycles including basic, enhanced and pulsed cycles, advantages and limitations of spot welding, and a basic model of expulsion. Key terms defined include spot weld, contact resistance, expulsion, heat flow, and weld cycle. Diagrams show the welding process and different stages of a welding cycle.

1. 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 View Slides; Read Notes, Listen to lecture View Demos Do on-line workbook Do Homework Keywords Spot weld contact resistance expulsion heat flow Weld cycle bulk resistance pulsing electrode

3. Electrodes or Welding Tips Electrodes or Welding Wheels Electrodes or Dies Projection Welds Electrodes or Dies Spot Weld Seam Weld Projection Weld Upset Weld Flash Weld After Welding After Welding [Reference: Resistance Welding Manual, RWMA, p.1-3]

4. Top Electrode Water Weld Nugget Bottom Electrode Resistance Distance

5. (a) (b) [Reference: Welding Process Slides, The Welding Institute]

6. [Reference: Welding Process Slides, The Welding Institute]

7. Adaptability for Automation in High-Rate Production of Sheet Metal Assemblies High Speed Economical Dimensional Accuracy

8. 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

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

10. Preheat Time Upslope Time Cool Time Weld Time Cool Time Preweld Interval Welding Cycle Weld Interval Postweld 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 Area Electrode Force Electrode Force Small Current R ec R ec R sc R v R v R ec 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. 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. Questions? 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. 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]

15. Link to spot weld nugget growth video Link to nugget growth demonstration

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

17. (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. 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. Cool Time Pulse 1 Pulse 2 Pulse 3 Pulse Time

24. Without Pulsing With Pulsing