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Spot Weld Mechanical Properties 2

Spot Weld Mechanical Properties 2. Cross Tension Ductility Ratio Torsion Test. Mechanical Properties 2. 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:

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Spot Weld Mechanical Properties 2

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  1. Spot Weld Mechanical Properties 2 Cross Tension Ductility Ratio Torsion Test

  2. Mechanical Properties 2 • 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: • Cross Tensile and Torsion Mechanical testing techniques • Factors which effect performance in these mechanical tests • The importance of these test for part design Keywords Cross Tensile Test, Ductility Ratio, Torsion Test, Twist Angle

  3. Mechanical Properties of Spot Welds • Peel Tests • Chisel Test • Tensile Test – Tensile Shear • Tensile Test - Cross Tension • Tensile Shear Ratios • Torsion Test • Impact Tests • Fatigue Test

  4. Direct Tension Testing Dickinson, “Welding in Auto Industry, AISI, 1981

  5. Material Thickness on Direct Tension Tensile Shear Higher Carbon Material lower Strength Because Brittle Nuggets Heuschkel, “Some Metallurgical Aspects…” Welding Journal, Oct 1947

  6. Tensile Shear Effect of Weld Current (Sheet Thickness) On Cross Tension Pollard, “Spot Welding Characteristics…” Welding Journal, Aug 1974

  7. Effect of Nugget Size (Current) Strength Determined By Nugget Size Strength Determined By Weld Ductility Above Expulsion Erratic Behavior Small Nugget Interfacial Tearing

  8. Effect of Weld Time High Currents = increase heat input to HAZ reducing cooling rate so that less hard martensite present High Current Thus peak may be chemistry dependent Intermediate Current Increase in time = larger nuggets thus higher direct tensile strength Low Current

  9. Effect of Hold Time - Direct Tension Tensile Shear The More the Interfacial Mode The lower the Direct Tensile Strength Note Difference between Tensile Shear and Direct Tensile Sawhill, “Spot weldability for High Strength Steels”, SAE 810352, Feb 1981

  10. Effect of Carbon Content Tensile Shear Note Difference between Tensile Shear and Direct Tension Heuschkel, “The Expression of Spot Weld Properties”, Weldign Journal, Oct 1952

  11. Effect of Steel Cleanliness Strength Determined By Nugget Size Strength Determined By Weld Ductility Above Expulsion Erratic Behavior Small Nugget Interfacial Tearing 50% lower Lamellar Type Tears

  12. Effect of Base Metal Strength Slightly Raises Cross Tension Strength Strength Determined By Nugget Size Yamauchi, “Spot Weldability of High …” IIW III-644-80, 1980 Strength Determined By Weld Ductility Above Expulsion Erratic Behavior Small Nugget Interfacial Tearing 50% lower Lamellar Type Tears

  13. Effect of Post Weld Temper

  14. Upslope/Downslope, Hold Time, & Temper Electrode Pressure Weld Current Current Temper Current Upslope Downslope Temper Squeeze Time Weld Time Off Time Hold Time

  15. Degradation Temper Improvement

  16. Analytical Approach Heuschkel, J. “The Expression of Spot Weld Properties”, Welding Journal, Oct. 1952

  17. Mechanical Properties of Spot Welds • Peel Tests • Chisel Test • Tensile Test • Tensile Shear Ratios • Torsion Test • Impact Tests • Fatigue Test

  18. Dickinson, “Welding in the Automotive …” AISI, !981

  19. Angle taken as Failure Angle Dickinson, “Welding in the Automotive …” AISI, !981

  20. Torsion Test • Factors Affecting Angle of Twist (Ductility) • Sheet Thickness • Material Strength • Carbon Content & Chemistry • Post Weld Heat • Factors Affecting Torque • Sheet Thickness • Material Strength • Post Weld Temper • Hold Time

  21. Effect of Sheet Thickness & Material Strength Sheet Buckling • Twist Angle Reduces With • Increased Thickness • Stronger Material Bibber, “Spot Weldability of Low Carbon….” Welding Journal, Dec 1943

  22. Effect of Hold Time, Carbon Content, Post Weld Temper Nugget Defects At Short Hold Martensite Harder Martensite Joumat, P. “Assessment of Spot Quality…” British Welding Journal, May 1955

  23. Effect of Chemistry Heuschkel “The Expression of Spot Weld Prop..” Welding Journal, Oct 1952

  24. Effect of Post Weld Heat on • Twist Angle • Torque Joumat, P. “Assessment of Spot Quality…” British Welding Journal, May 1955

  25. Effect of Hold Time on Torque Sawhill, “Spot Weldability for HS Steels” SAE Paper 810352, Feb, 1981

  26. Effect of Steel Type on Angle and Torque French “A Comparison of Methods of Assessing….” British Welding Journal, Nov 1957

  27. Homework Assignment 3 High Tensile Loaded Joint

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