1. Resistance Welding

2. Based on principle: 1. elect (AC) current passed through metal
decrease in Amps
increase in volts
2. resistance of metal to electric flow
3. heats metal at contact until molten
4. pressure
5. cooling

3. Rougher metal = more resistance

4. Adv: fast little warpage accurately controlled
well suited for production

5. 10 Processes

6. (1) Spot - most common

7. two pieces fused with small nugget

8. lapping metal together
clamp between two electrodes - current passes with pressure - solidifies
can make up to 2000 spot welds on mild steel before redressing electrode

9. 5 variables 1. time - Squeeze, Weld, Hold, Off 2. current
3. force - mechanical, elect, pneumatic, hydraulic

10. 4. machine selection

11. rocker

12. press

13. portable

14. 5. electrode contact area - weld size should equal tip diameter - proper current

15. Defects
expulsion - molten metal squirts out from weld - current too high

16. blow holes - caused by excessive heat or too little pressure

17. large indentions - caused by improper electrode alignment - excessive pressure

18. (2) Projection

19. form projections with dies

20. pieces are pressed together

21. current passes through two pieces and is concentrated at bumps

22. forms a spot weld

23. adv: several spots welded at once and welds are concentrated at bumps

24. disadv: not cost effective for short runs

25. (3) Seam

26. two wheeled electrodes travel over metal - current passes through them

27. can produce continuous seam

28. can produce intermittent seam of overlapping spots for leak proofing

29. Seam welding I-Beams

30. (4) Butt Seam
another form of seam

31. Weld longitudinal pipe seam
elect current heats pipe to molten state before passing through rollers