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Spot Weldability Quality and Performance. Spot Weldability Lesson Objectives When you finish this lesson you will understand: visual identification of.

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Presentation on theme: "Spot Weldability Quality and Performance. Spot Weldability Lesson Objectives When you finish this lesson you will understand: visual identification of."— Presentation transcript:

1 Spot Weldability Quality and Performance

2 Spot Weldability 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 Learning Activities 1.View Slides; 2.Read Notes, 3.Listen to lecture 4.Do on-line workbook 5.Do Homework Keywords Current levelCurrent RangeLobe CurveElectrode life Nugget DiaButton Dia.Peel TestTensile Shear Cross tensionShunt current

3 Process Requirements Electrode Materials Electrode Geometry Welding Force Welding Cycle –Squeeze time –Welding time –Hold time Welding Current

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

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

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

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

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

10 Effect of Hold Time on Lobe Curve

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

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

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

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

15 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). A B C D E F G Process Parameter Potency of a process parameter in influencing weld quality Scharfy & Kuhnash “Pareto Chart Development for Resistance Welding” Senior Capstone, OSU, 2000

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

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

21 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 Number of Welds Weld Diameter

24 Surface Expulsion Low Electrode Force 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 Tensile Shear Peel Cross Tension

29 Introduction to Peel Testing Technique

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

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

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

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

36 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

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45 Spot Weldability Assignment 2


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