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

Lätt UHS Repair spot welding Anna de Try och Arne Melander Swerea KIMAB. Aim:. To determine how different conditions typical to a repair work shop influence spot welding of UHSS. To produce corresponding welding diagrams. Five different conditions were investigated in this project:.

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

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  1. Lätt UHS Repair spot welding Anna de Try och Arne MelanderSwerea 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

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

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

  9. 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

  10. 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

  11. 1

  12. ED coat condition

  13. 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.

  14. Effects of epoxy adhesives for DP1000 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)

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

  16. 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

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

  18. Spatter avoided at weld time 700ms

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

  20. Misalignment DPX 1000 Z100 1,5mm

  21. Misalignment gives spatter which gives scatter in weld size

  22. 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

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

  24. High electrode force gives small weld size

  25. 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

  26. 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

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