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Coated Steel Weldability PowerPoint Presentation
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Coated Steel Weldability

Coated Steel Weldability

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Coated Steel Weldability

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  1. Coated Steel Weldability

  2. Coated Steel Weldability • Electrode Factors • Coating Factors • Welding Equipment Parameters

  3. Electrode Life • Electrode Material • Electrode Design Electrode Cap Diameter For Coated Steel Weld Button Diameter For Coated Steel Weld Button Diameter Uncoated Steel

  4. Electrode Life • Electrode Material • Current History • Electrode Design Copper Alloy Electrode Molten Zinc brass Solid Zinc Coating Steel

  5. ~45% ~60% ~85% Cu Zn

  6. Electrode Alloying during Resistance Welding on Galvanized Steel HV15 Cu Zn Al Fe 8 59 33 17 44 32 7 55 45 360 130 100 10 mm

  7. Uncoated Hot Dipped Galvanized

  8. Electrode Material Standard Electrodes Brazed Tip Electrodes Mo - called TZM Electrode W - results scattered Flame Sprayed or Coated Electrodes Mo, W, MoC, WC, Ag, Au, Al2O3

  9. Copper-Chromium-Zirconium (Cu-Cr-Zr) Material Higher hardness and softening temperature Its conductivity is about the same as Cu-Cr material Alloy addition: 0.7 wt% Cr + 0.1 wt% Zr Copper-Zirconium (Cu-Zr) Material Lower hardness than Cu-Cr material Higher electrical conductivity (up to 93% IACS) Alloy addition: 0.15 wt% Zr Electrode Materials for Spot Welding Coated Steel • Traditional (Class 2) Copper-Chromium (Cu-Cr) Material • High hardness • Moderate electrical conductivity (about 80% IACS) • Alloy addition: 0.8 wt% Cr • Dispersion-Strengthened Copper (DSC) Material • Higher electrical conductivity (98% IACS) • A powder metallurgy product

  10. Electrode Material Class 1 Class 2 Cu-Cr Cu-Zr Al2O3 Flame Spray Al2O3 Dispersion (Variation in Results) TZM (Mo Alloy Brazed Cap)

  11. Comparison of Electrodes High Current on HDG Steel Nugget Size (inch) Weld Number (Thousands) Surprising since high hot hardness Z-Trode Cu-Cr Al2O3 DSC Cu-Zr

  12. Excursions Above Expulsion Effect DSC History of Current Excursions Gugel, Comparison of Electrode Wear, SMWC V, AWS, 1992

  13. Deterioration Model History of Current Excursions In The Harder DSC There Is No Self Healing. Excursions Above Expulsion Where Electrodes Are Hotter Allow Some Healing. The Lower Hot Hardness of Cu-Cr & Cu-Zr Allow Some Healing of the Pits Gugel, Comparison of Electrode Wear, SMWC V, AWS, 1992

  14. Electrode Design Electrode-Wear Pattern for Flat Electrodes Flat Electrode Edges Broken Creating Natural Dome Craters Forming Self-Heating + Build-up along Sides Large Central Cavity [Reference: Welding in the Automotive Industry, p.174, D. W. Dickinson]

  15. Electrode Design Dome Electrode Flattening Zinc Buildup Reduced Current Density Poor Welds

  16. Electrode Design Electrode Geometry for Galvanized Steel 1/4” Flat Face x 45° 1/4” Flat Face x 20° 1” Radius Face 3” Radius Face 3” 1” 20° 45° 1/32” Wear 7/8” 1/2” 1/32” Wear 1/32” Wear 27/64” 1/32” Wear 5/16” 63% Increase in Area 185% Increase in Area 300% Increase in Area 1100% Increase in Area Recommended for sheet up to 1/16” thick Recommended for sheet over 1/16” thick Satisfactory only when alignment is a serious problem Unsatisfactory

  17. Electrode Design Effect of Cone Angle Heat Sink Because of Higher Temp More Copper From Electrode Sticking To Part Ikeda et al, Effect of Electrode Configuration…, Adv Tech & Proc, IBEC’94, 1995

  18. Electrode Design Effect of Cone Angle Higher Electrode Temp Faster Face Enlargement Lower Current Density Best Range Ikeda et al, Effect of Electrode Configuration…, Adv Tech & Proc, IBEC’94, 1995

  19. Electrode Design Electrode Cooling Poor Cooling Good Cooling Poor Cooling (a) (b) (c)

  20. Process Parameters: Weld Current(Heat Generation) Weld Time Hold Time Electrode Force Electrodes Coating Parameters: Coating Thickness Coating Types Process Variables

  21. Zn has lower R & is soft = good Contact

  22. Weld Diameter vs. Current for Various Coatings 0.25 27% Ni-Zn 30% Fe-Zn 20% Ni-Zn Nominal Current Level 0.20 Uncoated Steel 0.15 Weld Diameter, inches Current Range Uncoated 0.10 23% Fe-Zn Current Range Coated 9% Fe-Zn Zinc Only 0.05 6 8 10 12 14 Weld Current, kA [Reference: Welding in the Automotive Industry, p.179, D. W. Dickinson]

  23. Comparison of Current Level Simple Current Levels for 0.8 mm Sheet Steels Material Current Level (kA) Uncoated Steel 9 Fe-Zn Electro Coated 10 Galvannealed 10 Electro Galvanized 12 Hot Dipped Galvanized 13 (6.1 mm Electrodes & 12-14 Cycles of Welding Time)

  24. Lobe Curves Hot-Dip Galvanized Uncoated Zinc Melting Weld Time Weld Time Steel Melting Weld Current Weld Current

  25. Weld Current vs. Tensile-Shear Strength Tensile-Shear Strength (lbs) [Reference: Welding in the Automotive Industry, p.203, D. W. Dickinson] Welding Current (Amps, x 103)

  26. Electrode Sticking Test 28 As the number of welds & Electrode deterioration increase the current to get a nominal size weld (or expulsion or sticking) increases 24 Stick 20 Welding Current (kA) Expulsion 16 Nominal 12 8 0 550 1100 1850 2200 Number of Welds

  27. Shunting during Series Welding The extra current required to compensate for the shunting causes electrodes to run hotter and results in electrode wear. AWS Welding Handbook

  28. Process Parameters: Weld Current (Heat Generation) Weld Time Hold Time Electrode Force Coating Parameters: Coating Thickness Coating Types Process Variables

  29. Nugget Development during Weld Time Interval 0.041” Bare & Galvanized Steel Nugget Diameter, inches [Reference: Welding in the Automotive Industry, p.175, D. W. Dickinson ] Weld Time, cycles

  30. Weld Time vs. Nugget Development Nugget Diameter at Expulsion Nugget Growth Surface Breakdown Nugget Diameter Uncoated Coated Steel Surface Breakdown Nugget Growth Zinc Melts Weld Time

  31. Average Button Size at Expulsion as a Function of Weld Time for Each Materials Ave Button Size at Expulsion (inch) Welding Time (Cycles) [Reference: EWI Research Paper: MR8802, p.46, Gould & Peterson]

  32. Nugget Dimension Vs. Weld Time Effect of Coating Type Uncoated Nugget Width (mm) Fe-Zn Electro Electro-Galvanized Hot Dipped Galvanized Galvannealed Weld Time (Cycles) [Reference: EWI Research Paper: MR8814, p.29, Gould & Peterson]

  33. Mechanism of Heat Generation 7 Cycles 9 Cycles 10 Cycles 2 Cycles 4 Cycles 5 Cycles 6 Cycles Step I Step III Step II Step IV

  34. Nugget Development of Hot-Dipped Galvanized Steel 3 Cycles 7 Cycles 4 Cycles 9 Cycles 12 Cycles 6 Cycles [Reference: EWI Research Paper: MR8814, p.21, Gould & Peterson]

  35. Effect of Weld Time on Current Range for Hot-Dip Galvanized Steel Minimum Nominal Expulsion Welding Time (Cycles) Welding Current ( kA) [Reference: EWI Research Paper: MR8802, p.19, Gould & Peterson]

  36. Effect of Weld Time on Electrode Life Current Short Time High Current and Overheating Electrode Life Longer Time Greater Alloying Weld Time

  37. Electrode Life Vs. Welding Time Electrode Diameter: 0.19” Electrode Diameter: 0.25” Electrode Diameter: 0.28” 3200 2400 Electrode Life (Number of Welds) 1600 800 0 5 9 13 17 21 25 29 Welding Time (Cycles)

  38. Process Parameters: Weld Current (Heat Generation) Weld Time Hold Time Electrode Force Coating Parameters: Coating Thickness Coating Types Process Variables

  39. No Data Could be Found On the Effect of Hold Time Related to Coating other than That already discussed for Uncoated High Carbon Steels This might be an area for research

  40. Process Parameters: Weld Current (Heat Generation) Weld Time Hold Time Electrode Force Coating Parameters: Coating Thickness Coating Types Process Variables

  41. Effect of Electrode Force on Electrode Deterioration Zinc Layer Electrode Tip Diameter Diameter Steel Nugget Diameter Number of Welds

  42. Dual Force Technique Electrodes Seat, Zn Forced Out Before High Pressure, Less Mushrooming Low Pressure Upslope Helps Zn Flow From Under Electrode

  43. Process Parameters: Weld Current (Heat Generation) Weld Time Hold Time Electrode Force Coating Parameters: Coating Thickness Coating Types Process Variables

  44. Weldability Lobe Vs. Coating Weight(Up To G90 Weight) G40 Weldability Lobe G60 Weldability Lobe Coating Thickness Only Minimal Effect on Position or Width Weld Time (Cycles) Weld Time (Cycles) G90 Weldability Lobe Current (kA) Current (kA) Thicker Coating more Erratic Weld Time (Cycles) Current (kA)

  45. Coating Weight Above G90 G90 Improved Electrode Life Welding Parameters Needed to get 0.20” Diameter Weld

  46. Substrate/Coating Thickness Effects 0.037 inch sheet thickness 0.020 inch thick Electrode Face Closer to Hot Weld Nugget

  47. Process Parameters: Weld Current (Heat Generation) Weld Time Hold Time Electrode Force Process Variables

  48. Coating Thickness Coating Types Coating Parameters: