1. Coated Steel Weldability

2. Resistance Welding Lesson Objectives When you finish this lesson you will understand: Learning Activities 1.View Slides; 2.Read Notes, 3.Listen to lecture 4.Do on-line workbook Keywords

3. Coated Steel Weldability Electrode Factors Coating Factors Welding Equipment Parameters

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

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

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

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

8. Uncoated Hot Dipped Galvanized

9. 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, Al 2 O 3

10. Electrode Materials for Spot Welding Coated Steel 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 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

11. Class 1 Class 2 Cu-Cr Al 2 O 3 Flame Spray Al 2 O 3 Dispersion (Variation in Results) TZM (Mo Alloy Brazed Cap) Electrode Material Cu-Zr

12. Comparison of Electrodes Nugget Size (inch) Weld Number (Thousands) Z-Trode Cu-Cr Al 2 O 3 DSC High Current on HDG Steel Surprising since high hot hardness Cu-Zr

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

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

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

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

17. Electrode Geometry for Galvanized Steel 1/4” Flat Face x 45° 1/4” Flat Face x 20° 1” Radius Face 3” Radius Face 45° 1/32” Wear 5/16” 27/64” 1/32” Wear 20° 1/2” 1/32” Wear 7/8” 1/32” Wear 1” 3” 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 Electrode Design

18. 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 Electrode Design

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

20. Electrode Cooling Poor CoolingGood CoolingPoor Cooling (a)(b)(c) Electrode Design

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

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

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

25. Comparison of Current Level Material Current Level (kA) Uncoated Steel 9 Fe-Zn Electro Coated10 Galvannealed10 Electro Galvanized12 Hot Dipped Galvanized13 Simple Current Levels for 0.8 mm Sheet Steels (6.1 mm Electrodes & 12-14 Cycles of Welding Time)

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

27. Weld Current vs. Tensile-Shear Strength Welding Current (Amps, x 10 3 ) Tensile-Shear Strength (lbs) [Reference: Welding in the Automotive Industry, p.203, D. W. Dickinson]

28. Electrode Sticking Test 0 550 1100 18502200 28 24 20 16 12 8 Number of Welds Welding Current (kA) Stick Expulsion Nominal As the number of welds & Electrode deterioration increase the current to get a nominal size weld (or expulsion or sticking) increases

29. 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

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

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

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

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

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

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

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

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

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

39. Electrode Life Vs. Welding Time Electrode Life (Number of Welds) 3200 2400 1600 800 0 591317212529 Welding Time (Cycles) Electrode Diameter: 0.19” Electrode Diameter: 0.25” Electrode Diameter: 0.28”

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

41. 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

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

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

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

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

47. Weldability Lobe Vs. Coating Weight ( Up To G90 Weight) Current (kA) G40 Weldability LobeG60 Weldability Lobe G90 Weldability Lobe Weld Time (Cycles) Coating Thickness Only Minimal Effect on Position or Width Thicker Coating more Erratic

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

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

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

51. Coating Parameters: Coating Thickness Coating Types

52. IncompleteGalvannealed

53. Steel Aluminum Oxide Passive Layer Zinc Gamma 0.10.31.0 % Al in Bath Electrode Life Incomplete Oxide Layer Hot Dipped Galvanized High Si, Mn, Al in Steel Ties up Oxygen Also Causing Break in Passive Layer

54. Zeta Delta Gamma AlphaSteel Possible Phases in Galvannealed

55. Steel Gamma Delta Zeta Steel Gamma Zinc PartiallyGalvannealed Localized Hot Spots Zinc Alloying in Electrode Electrode Life Reduced Dross UncleanCoating

56. Steel Gamma Delta Zeta Pickett, Effect of Total Iron Content…. SMAW V, AWS, 1992

57. Seam Welding Galvanized Steel Usually not recommended Zinc Contamination of Wheel Electrodes Some outer surface of sheet cracking Wheels with continuous cleaning have helped Foil Butt Welding has also been effective (see next Slide)

58. Foil Butt Welding of Galvanized Steel AWS Welding Handbook

59. Projection Welding of Galvanized Steel AWS Welding Handbook

60. Projection Welding of Galvanized Steel Heat Loss to Electrode (Flat Face) Higher than Uncoated because Higher Thermal Conduction of Coating Contact Resistance at Faying Surface Only Slightly Lower than uncoated because soft zinc deformation Therefore: Somewhat lower electrode forces recommended

61. Projection Welding of Galvanized Steel On sheet thinner than 0.09 in. projection welding produces a forged bond rather than a fusion bond Increase in current causes burn off and expulsion of projection.