1. Spot Weld Al Equipment

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. Various Types of Equipment Single-Phase AC Machines –Without slope control –With Slope control Polyphase Direct- Energy Machines –Frequency Converter –Rectifier Type Stored-Energy Machines Electromagnetic Type Electrostatic Type Electrochemical Type Home-Polar Type Single-Phase DC Machines - Rectified DC - Medium Frequency DC

4. Typical Current-Force Diagram for Single- Phase AC Type Machines Weld Time Weld Heat Time Postheat Time Hold Time Forge Force Forge-Delay Time Upslope Time Downslope Time Weld Force Postheat Current Welding Current Initial Current Time Squeeze Time [Reference: Resistance Welding Manual, p.11-21, RWMA]

5. Machine Settings for Spot Welding Aluminum Alloys on Single-Phase Machines [Reference: Resistance Welding Manual, p.11-14, RWMA] (Recommendations without Slope Control)

6. Recommended Weld Current with a Single-Phase AC Supply 1 23 Material Thickness, mm 70 60 50 40 30 20 Weld Current, kA

7. Recommended Electrode Force with a Single-Phase AC Supply Material Thickness, mm Electrode Force, kN

8. Effect of AC Conduction Angle on Electrode Life Longer Conduction Periods Allow more Uniform Heating & (Lower Peak Current) Without Long Cool Periods Between Half-cycles Increasing Electrode Life 4.6 msec 4.6 DC Lower Peak Currents Longer Conduction Period Increase Electrode Life Spinella, D, “Implications for Aluminum Resistance Spot Welding Using Alternating Current”, Materials & Body Testing, IBEC, 1995 Partial Nuggets Weld Cracking No Weld Cracking

9. Various Types of Equipment Single-Phase AC Machines –Without slope control –With Slope control Polyphase Direct- Energy Machines –Frequency Converter –Rectifier Type Stored-Energy Machines Electromagnetic Type Electrostatic Type Electrochemical Type Home-Polar Type Single-Phase DC Machines - Rectified DC - Medium Frequency DC

11. Spot Welding Schedule of Single- Phase Direct Current Machines [Reference: Resistance Welding Manual, p.11-23, RWMA]

12. Material Thickness, mm Weld Current, kA Weld Time, cycles Electrode Force, kN Recommended Welding Conditions with a Single- Phase DC Supply

13. Effect of DC Current on Electrode Life DC Results in Off Center Weld More Wear on One Electrode Kumagai, M, High Performance Electrode Material… IBEC’95, Material & Body Testing, 1995 Electrode Face with Higher Operating Temperature

14. Various Types of Equipment Single-Phase AC Machines –Without slope control –With Slope control Polyphase Direct- Energy Machines –Frequency Converter –Rectifier Type Stored-Energy Machines Electromagnetic Type Electrostatic Type Electrochemical Type Home-Polar Type Single-Phase DC Machines - Rectified DC - Medium Frequency DC

15. Newton, et al, Fund of RW Aluminum, AWS, SMWC VI Oct 1994

16. Comparison of 50-Hz AC and MFDC Waveforms MFDC AC 50 HZ Time (sec) Current (kA)

17. ACMid-Frequency DC 61114-T4 Aluminum Michaud, E, A Comparison of AC & MFDC SMWC VII, AWS, 1996 Reduced Expulsion

18. AC MF DC

19. Increase Force As Increase Gage, Lobe Moves Effect of Force and Gage on Lobe for MF DC Browne, D., Model to Predict, IBEC’95, Adv Tech & Processes, 1995

20. Browne, D., Model to Predict, IBEC’95, Adv Tech & Processes, 1995 Effect of Electrode Tip Diameters on MFDC

21. Browne, D., Model to Predict, IBEC’95, Adv Tech & Processes, 1995 Effect of Weld Spacing in MFDC

22. Browne, D., Model to Predict, IBEC’95, Adv Tech & Processes, 1995 Effect of Deteriorated Tips with MFDC

23. Various Types of Equipment Single-Phase AC Machines –Without slope control –With Slope control Polyphase Direct- Energy Machines –Frequency Converter –Rectifier Type Stored-Energy Machines Electromagnetic Type Electrostatic Type Electrochemical Type Home-Polar Type Single-Phase DC Machines - Rectified DC - Medium Frequency DC

24. Typical Current-Force Diagram for Electrostatic Stored Energy Type Machines Squeeze Time Weld Time Hold Time Current Forge Force Forge-Delay Time Weld Force [Reference: Resistance Welding Manual, p.11-21, RWMA]

25. Spot Welding Schedule of Electrostatic Stored Energy Machines [Reference: Resistance Welding Manual, p.11-23, RWMA]

26. Various Types of Equipment Single-Phase AC Machines –Without slope control –With Slope control Polyphase Direct- Energy Machines –Frequency Converter –Rectifier Type Stored-Energy Machines Electromagnetic Type Electrostatic Type Electrochemical Type Home-Polar Type Single-Phase DC Machines - Rectified DC - Medium Frequency DC

27. Insert diagram of Frequency Converter waveform

28. Spot Welding Schedule of Typical Three-Phase Frequency Converter [Reference: Resistance Welding Manual, p.11-22, RWMA]

29. Various Types of Equipment Single-Phase AC Machines –Without slope control –With Slope control Polyphase Direct- Energy Machines –Frequency Converter –Rectifier Type Stored-Energy Machines Electromagnetic Type Electrostatic Type Electrochemical Type Home-Polar Type Single-Phase DC Machines - Rectified DC - Medium Frequency DC

30. Typical Current-Force Diagram for Three- Phase Rectifier Type Machines [Reference: Resistance Welding Manual, p.11-20, RWMA] Final Force Hold Time Total Weld Time Postheat Current Initial Force Welding Current Weld Time Forge-Delay Time Squeeze Time Postheat Time

31. Spot Welding Schedule of Typical Three-Phase Direct Current Rectifier [Reference: Resistance Welding Manual, p.11-22, RWMA]

33. Process Parameters Weld Current –High current levels are required to break down the surface oxide and generate the heat necessary for developing an acceptable weld nugget –Weld Time –Require short weld time due to high current levels Upslope/Downslope –Generally not recommended for welding aluminum alloys Electrode Design/Material –Due to the required higher current levels, electrodes with high current capacity, such as Class 1 and Class 2, are commonly used –Electrode designs have mainly been dome-shaped –Electrode tips must also be dressed frequently Forging –Forging cycles are commonly used to prevent weld cracking in aluminum alloys

34. Weld Defects Surface Burning and Tip Pickup Cracks Excessive Indentation Sheet Separation Porosity Weld Metal Expulsion Unsymmetrical Weld Nugget Inclusion of Unwelded

35. Surface Burning and Tip Pickup [Cause] Surface burning is caused by excessive heat on the metal surface under the electrode and is indicated by burned, pitted and discolored welds. Excessive electrode pickup is caused primarily by the same factors. [Remedy Those Conditions] Improper surface conditions Electrode skidding Improper Electrode Material - conductivity too low Dirty or improper cleaned electrodes Excessive “weld time” Excessive welding current Inadequate welding force

36. Cracks [Cause] Internal and external cracks in welds, generally caused by improper thermal and pressure conditions, are observed in the weld structure and surface, respectively. [Remedy Those Conditions] Excessive penetration Insufficient force Improper rate of current rise Improper electrode cooling Improper electrode contour Delayed application of forging force Electrode skidding

37. Excessive Indentation [Cause] Excessive indentation, generally caused by improper force application, is indicated by depression on the weld surface. [Remedy Those Conditions] Excessive force Weld metal expulsion Improper electrode contour Excessive surface heating Improper forging cycle Excessive Welding Current

38. Sheet Separation [Cause] Excessive sheet separation, generally caused by poor fitup of parts and excessive surface deformation, is indicated by a wide separation of the base metal adjacent to the weld. [Remedy Those Conditions] Excessive force Improper fitup of parts Weld metal expulsion Incorrect electrode contour Excessive welding current Tip misalignment Excessive “weld time”

39. Porosity [Cause] A porous weld structure, generally caused by improper application of heat and force, is observed by sectioning and etching the weld. [Remedy Those Conditions] Insufficient “weld time” Improper rate of current rise Improper electrode contour Incorrect sequencing of weld and forging force Insufficient force

40. Weld Metal Expulsion [Cause] Weld expulsion, generally caused by extreme heat and improper force, is indicated by expelled metal from the weld. [Remedy Those Conditions] Insufficient force Tip misalignment Erratic contact resistance Foreign substance at faying surface Electrode skidding Excessive welding current Excessive “weld time”

41. Unsymmetrical Weld Nugget [Cause] Unsymmetrical welds, generally caused by unsymmetrical gauge combination, improper electrode contour, poor fitting workpiece or surface preparation, may be observed by sectioning the weld. [Remedy Those Conditions] Improper electrode contour Inadequate surface preparation Improper fitup of workpieces Electrode misalignment Electrode skidding