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Spot Weldability Quality and Performance

Spot Weldability Quality and Performance . Spot Weldability. Learning Activities View Slides; Read Notes, Listen to lecture Do on-line workbook Do Homework. Lesson Objectives When you finish this lesson you will understand: visual identification of discontinuities

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Spot Weldability Quality and Performance

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  1. Spot Weldability Quality and Performance

  2. Spot Weldability • Learning Activities • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Do Homework • Lesson Objectives • When you finish this lesson you will understand: • visual identification of discontinuities • how to develop & use lobe curves • electrode life • peel test & failure modes Keywords Current level Current Range Lobe Curve Electrode life Nugget Dia Button Dia. Peel Test Tensile Shear Cross tension Shunt current

  3. Process Requirements • Electrode Materials • Electrode Geometry • Welding Force • Welding Cycle • Squeeze time • Welding time • Hold time • Welding Current How Do We Know These Are All Correct

  4. Visual Inspection of Quality b a d c W. Stanley, Resistance Welding McGraw-Hill, 1950

  5. Visual Inspection of Quality a b d c e W. Stanley, Resistance Welding McGraw-Hill, 1950

  6. Process Characteristics as a Measure of Weldability • Current Level • Current Range & Weldability Lobe • Process Deterioration • Characterization of the loss in weld size at constant welding conditions • Characterization of the variation in process requirements for maintaining welds of an adequate quality

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

  8. Current Range & Weldability Lobe Expulsion Acceptable Nuggets Nugget Diameter Minimum Nugget Diameter Time A Small Nuggets Weld Current Lobe Curve Time A Weld Time Smaller “Brittle” Nuggets Expulsion Level Acceptable Nuggets Weld Current

  9. Effect of Weld Time on Current Range (Weld Lobe)

  10. Effect of Hold Time on Lobe Curve

  11. Effect of Electrode Force on Lobe Curve Lobe moves to Higher Current Longer Times Very High Force

  12. Effect of Electrode Misalignment on Lobe Curve Karagoulis, “Process Control in Mfg”, AWS Sheet Metal Conf V, 1992

  13. Questions? • Turn to the person sitting next to you and discuss (1 min.):

  14. Current Density Weld Force Weld Time Current Density Weld Force Weld Time Weld Spacing Surface Conditions Pareto Charts Relate Importance of Process Parameters Standard Approach Graeco-Latin Approach

  15. Potency of a process parameter in influencing weld quality A B C D E F G Process Parameter What is a Pareto Chart ? • In our case, A Pareto Chart is a graphical comparison of process variables vs. weld quality. In other words it ranks the process variables in the order of their potency (amount they change weld quality). Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

  16. Stable slope Expulsion Weld Nugget Initiation Average Steep slope Process parameter Defining Window Size • Develop weld windows for each process parameter • Determine the affect of changing the parameter has on the weld window Window Size = expulsion - initiation Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

  17. Weld Force Windows Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

  18. Weld Time Windows Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

  19. Window Size Pareto Chart Negative % Change Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

  20. Current Median Pareto Chart Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

  21. Questions? • Turn to the person sitting next to you and discuss (1 min.):

  22. Process Characteristics as a Measure of Weldability • Current Level • Current Range & Weldability Lobe • Process Deterioration • Characterization of the loss in weld size at constant welding conditions • Characterization of the variation in process requirements for maintaining welds of an adequate quality

  23. Process Deterioration Minimum Acceptable Diameter Weld Diameter Number of Welds

  24. Low Electrode Force Surface Expulsion Hirsch, R & Leibovitz, R, “Improved Weld Quality and Electrode Life in Resistance Welding” Practical Welding Today, Nov-Dec, 1997

  25. Low Electrode Force Hirsch, R & Leibovitz, R, “Improved Weld Quality and Electrode Life in Resistance Welding” Practical Welding Today, Nov-Dec, 1997

  26. Mechanical Properties as a Measure of Weldability • Button Size as a Measure of Weld Quality • Simulative Mechanical Tests • Tensile shear loads • Peel loads • Cross tension • Modes of Failure in Spot Welds • Full button • Irregular button • Interfacial failure

  27. Button Size as a Measure of Weld Quality Button Diameter

  28. Simulative Mechanical Tests Peel Tensile Shear Cross Tension

  29. Introduction to Peel Testing Technique

  30. Geometric Effects on The Qualified Peel Test W 450 350 250 150 x Max. Load, lbs W = 1” Load W = 1.5” W = 2” 0 1/4 1/2 3/4 1 1-1/4 Distance x, in

  31. Modes of Failure in Spot Welds Full Button Irregular Button Interfacial Failure

  32. Microstructural Measures of Weldability • Weld Geometry • Degree of weld penetration • Actual diameter of weld • Weld Structural Integrity • Weld Hardness

  33. Weld Geometry Weld Diameter Weld Penetration Full Size Weld Sub-Size Weld Weld Diameter Weld Penetration

  34. Weld Structural Integrity Fine Weld Porosity Residual Dendritic Structure Workpieces Weld Nugget

  35. Weld Hardness Hardness (a) Weld Morphology (25X) Distance (mm) (B) Variation in Weld Hardness

  36. Questions? • Turn to the person sitting next to you and discuss (1 min.):

  37. Other Factors Effecting Weld Geometry • Shunt Current • Electrode Radius

  38. Effect of Shunt Current on Spot Weld Quality • International Recommendations • Spot Spacing = 16 (sheet thickness) • Spot Spacing = 3 (recommended electrode face dia.)

  39. Shunting Currents Howe, Spot Spacing Effect on Buton Size” AWS Sheet Metal Conf. VI, 1994

  40. International 16 t Formula Conclusion: Above the internationally recommended spot spacing, there is little effect on button size Howe, Spot Spacing Effect on Buton Size” AWS Sheet Metal Conf. VI, 1994

  41. Effect of Electrode Radius

  42. RSW Certification Training Class, Boeing

  43. RSW Certification Training Class, Boeing

  44. RSW Certification Training Class, Boeing

  45. Homework Assignment 2 Spot Weldability

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