1. Lätt UHS Repair spot welding Anna de Try och Arne Melander Swerea KIMAB

2. Aim: To determine how different conditions typical to a repair work shop influence spot welding of UHSS. To produce corresponding welding diagrams

3. Five different conditions were investigated in this project: The effect of shunt spots The effect of grinding of the surface of electro coated steel sheets The effect of epoxy and rubber-based adhesives The effect of different misalignments between two sheet material combinations. The effect of different electrode forces

4. Equipment used MFDC Current 0-13kA Force 0-5.5kN

5. Shunt spot effecs Study with one, two and three spots with different distance between spots: (10*t= 15, 20*t=30, 30*t=45, t=1,5mm). DP1000 Z100 1,5mm DX54 Z100 1,5mm

6. Influence of distance between the three spots

8. Weld current Number of weld spots Effect plot of weld current: Dogal 1000

9. Number of weld spots Weld current Distance between weld spots current* Distance Effect plot of weld current: DX54

10. Compensation for shunts UHSS less sensitive to shunt effects than mild steel Compensation must however be made when going from data without shunt to data with shunt Compensation by increasing current

11. Effect of ED coat on outside surfaces on spot welds Two sheets of Dogal 1000DPX Z100 fully ED coated The contacting surfaces between sheets contain ED coat The outside surfaces towards electrodes are in three conditions: Moderately ground Well ground

12. MGNG MG -NG - - MG 1

13. ED coat condition

14. It is possible to weld with ground outer surface and ED beween sheets but Spatter observed originating between sheets in all cases. This is main cause of scatter and difficulty to reach large spot size.

15. Two cases Case I –TDPX1000Z100(1,5mm)- DPX1000Z100(1,5mm) –Welding through cured and non cured adhesive (one shunt) Case II –DPX1000Z100(1,5mm)- DPX1000Z100(1,5mm)- DX54(0,8mm) –Welding through cured adhesive ( two shunts) Effects of epoxy adhesives for DP1000

17. Elektrode force = 2,4kN Elektrode force = 5,0kN 6,8kA/200ms/450ms D=3mm, Interfacial, ss 6,8kA/200ms/450ms D=6,0mm, Interfacial, s 8kA/200ms/450ms+6,8kA/ 200ms/450ms D=6,9mm, Interfacial, s 8kA/200ms/450ms+6,8kA/ 200ms/450ms D=7,8mm, Interfacial, ss

18. Adhesive – DP1000 Epoxy It is possible to weld through adhesive ( cured and non cured) if shunt exist Non cured adhesive usually no problem Problems with spatter for cured adhesive Larger electrode force -> less risk of spatter Interfacial failure frequent. Pre pulse with large current to ”evaporate” cured adhesive or is often required

20. Epoxy adhesive – 2*DP1000(1,5mm) + DX54(0,8mm) Weld data Electrode force: 2,4kN Upslope: 200ms Weld pulse: 700ms Hold: 400ms Current: 6,8 – 8,2kA DX54 0,8mm DP 1000 Z100 med härdat epoxy lim + två shuntpunkter Svetsat utan lim Svetsat i ohärdat lim Svetsat i härdat lim, treplåts komb.

21. Spatter avoided at weld time 700ms

22. Tripple sheet with epoxy between UHSS Possible to weld through cured epoxy with long weld time

23. Misalignment DPX 1000 Z100 1,5mm

24. Misalignment gives spatter which gives scatter in weld size

25. Misalignment Misalignment gives problems with spatter which can produce scatter in weld size due to loss of weld size Increase electrode force might be solution

26. Magnitude of electrode force DPX 1000 Z100 1,5mm

27. High electrode force gives small weld size

28. Electrode force Higher electrode force is not always solution to good results since contact resistance is reduced with smaller weld size as result Higher electrode force can however be solution to reduce misalignment or reduce spatter from obstacles between sheets such as ED or cured adhesive

29. Conclusions Dogal 1000DPX not sensitive to number (1 or more) or distance between shunt spots DX54 more sentitive to shunt effect than Dogal 1000DPX It is possible to weld through ED coat on inside. No large effect of quality of grinding on outside for Dogal 1000DPX. Large risk of spatter with loss of weld size. It is possible to weld through cured and non cured epoxy adhesive if shunt spot is present. Pre pulse or long weld pulse can be needed for cured adhesive. Large risk of spatter Misalignment produces problems with spatter Difficult to obtain large spot sizes with high electrode force only