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Spot Weld Mechanical Properties

Spot Weld Mechanical Properties. Mechanical Properties. Learning Activities View Slides; Read Notes, Listen to lecture Do on-line workbook. Lesson Objectives When you finish this lesson you will understand: Peel Chisel and Tensile Mechanical testing techniques

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Spot Weld Mechanical Properties

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  1. Spot Weld Mechanical Properties

  2. Mechanical Properties • Learning Activities • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • Peel Chisel and Tensile Mechanical testing techniques • Factors which effect performance in these mechanical tests • The importance of these test for part design Keywords Peel Test, Chisel Test, Tensile Shear Test, Multiple Nugget Test, Weld Bond Tensile Test, Coupon Dimensions, Weld Spacing, Electrode Conditioning, Button Shape, Plastic Hinge

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

  4. AWS Spec D8.9-97, 1997

  5. AWS Spec D8.9-97, 1997

  6. AWS Spec D8.9-97, 1997

  7. AWS Spec D8.9-97, 1997

  8. AWS Spec D8.9-97, 1997

  9. AWS Spec D8.9-97, 1997

  10. Dickinson, “Welding in Auto Industry, AISI, 1981

  11. AWS Spec D8.9-97, 1997

  12. AWS Spec D8.9-97, 1997

  13. Advantages of Peel Test • Ease of Performance • Low Cost • Ability to use on Shop Floor as quality control test • Disadvantages of Peel Test • Only in restricted cases are quantitative values relating to the strength of the weld nugget or its performance in service obtained • Nugget fracture appearance is not a reliable predictor of load-carrying capacity or impact resistance

  14. Geometric Effects on the Peel Test Distance “x” can cause a wide variation in load results, thus peel test can NOT be used with confidence to develop mechanical property data Orts, Armco Steel, Private Communication, Nov 1980

  15. Instrumented Peel Test Area = Energy “Static Toughness” Sawhill, Spot Weldability of High Strength Sheet Steel”, Welding Journal, Jan 1980

  16. Sawhill, Spot Weldability of High Strength Sheet Steel”, Welding Journal, Jan 1980

  17. Peel Tested When Cold Peel Tested While Still Warm Promotes Partial Nugget Failure Promotes Full Nugget Pull-Out

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

  19. Dickinson, “Welding in Auto Industry, AISI, 1981

  20. Min. Nugget With Peel Test Min. Nugget With Chisel Test Chisel Test Tends to Expose Nugget Closer to Fusion Line

  21. Questions? • Turn to the person sitting next to you and discuss (1 min.): • Why do automotive manufactures prefer the chisel test on the production line over the peel test?

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

  23. Dickinson, “Welding in Auto Industry, AISI, 1981

  24. AWS Spec D8.9-97, 1997

  25. Kraus, “A Practical Design approach…” Welding Journal, Oct 1961

  26. Dickinson, “Welding in Auto Industry, AISI, 1981

  27. Vanden Bossche, “Ultimate Strength and Failure Mode..”, SAE paper 770214, Feb 1977

  28. Dickinson, Republic Steel Corp Internal Document, 1978

  29. Tensile Shear Test • Single Nugget Test – Tensile Shear • Material Thickness • Nugget Size (Current & Time) • BM Strength • Carbon Content • BM Structure • Coatings • Hold Time • Post Weld Furnace Treatment • Test Temperature • Test Cross Head Speed • Multiple Nugget Test – Tensile Shear • Weld Bonding (Nugget plus Adhesive)

  30. Material Thickness – Tensile Shear In the thinner gages, the lower C Steels tend to have higher strength because the higher carbon materials develop hard brittle interfacial failures. Heuschkel, “Some metalurgical aspects of carbon steel spot welding”, Welding Journal, Oct 1947

  31. Nugget Diameter – Tensile Shear • Increased Tensile Shear • Nugget Diameter • Sheet Thickness • BM Strength Pollard, Spot Welding Characteristics of HSLA”, Welding Journal, Aug 1974

  32. Nugget Diameter (Current & Time & BM Strength) – Tensile Shear Nugget Pullout Increase BM Strength Interfacial Failure • Increased Weld Current • Greatly Increased Nugget • Greatly Increased Tensile Shear Strength • Increased Weld Time • Slightly Increased Nugget • Greatly Increased Tensile Shear Strength • Increased BM Strength • Increased Tensile Shear Pollard, Spot Welding Characteristics of HSLA”, Welding Journal, Aug 1974

  33. Is it Current, or Effect of Current on Nugget Diameter? Combinations of Current and Electrode Face Diameter gives Constant Nugget Diameter Relationship between Nugget Dia and Strength Not Current/Strength

  34. Questions? • Turn to the person sitting next to you and discuss (1 min.): • What criteria do you suppose automotive and appliance designers use when selecting the type of weld joint they will recommend for their products? Think about the joint designs in cars and appliances.

  35. Base Metal Strength • Solid Solution Strengthening • Grain Refinement Through Special Processing • Precipitation Strengthening • Cold-work Strengthening • Heat Treatment Strengthening (Hardening)

  36. Effect of Carbon Content Hard Brittle Martensite Interfacial Failures Heuschkel, “Some Metallurgical Aspects….” Welding Journal, Oct 1947

  37. Effect of Base Metal Strength Grain Refinement Precipitation 10o The Stronger Materials have less sample rotation thus they carry greater tensile shear load than expected 30o Pollard, “Spot Weldability of HSLA Steels”, ASM/ADDRG Seminar, Nov 12&13, 1971

  38. Effect of Structure • Tensile Shear Strength Increases when a material is giving the following • Annealed • Bainitic (Heat Treated) • Martensitic (Heat Treated) • Cold-rolled (Lower at higher currents due to HAZ softening) Chandel, “Mech & Metallurgical Aspects…” Metals Technology, Sept 1974

  39. Defourney, “Spot Welding of HSS, IIW 646-80, 1980 Sawhill, “Spot Weldability of HSS”, Welding Journal, Jan 1980 Heuschkel, “Expression of Spot Weld Properties”, Weldign Journal Oct 1952

  40. Critical Diameter to Thickness Ratio Thus, higher strength materials should have larger nuggets (electrode) d = nugget diameter t = sheet thickness ysbm= yield strength base metal yswm = yield strength weld metal Vanden Bossche, “Ultimate Strength and Failure Modes…” SAE 770214, Feb 1977

  41. Effect of Coating When only Zn-Zn Bonds lower strength than bare seel. When steel-steel bonds strength equal to or greater Armco Steel Fabrication Data, 1981

  42. Questions? • Turn to the person sitting next to you and discuss (1 min.): • We have looked at some factors which effect tensile shear strength. And some people have developed empirical equations to calculate tensile shear strength. How reliable are these equations? What factors might lead to inaccuracies?

  43. Hold Time – Tensile Shear Hold Time Sensitive Material in Peel Test Not Hold Time Sensitive in Tensile Shear Hold time appears to have no effect Sawhill, “Spot weldability for High Strength Steels”, SAE 810352, Feb 1981

  44. Effect of Post Weld Furnace Treatment >0.2% C Steels Slight loss in strength No benefit + Expensive In Machine Q&T > 0.2 % C Steels Up to 300% benefit Must be done correct <0.2% Carbon No Benefit Balasubramanian et al, “Improvement of Resistance Spot Weld Characteristics”, Welding Research Abroad, Nov 1978

  45. Effect of Test Temperature for Plain Carbon Steel Heuschkel, “The Expression of Spot Weld Properties”, Welding Journal, Oct 1952

  46. Effect of Cross Head Speed on Tensile Testing Machine Impact Chandel, “Mech Aspects pf Spot-WeldedJoints…”, Metals Technology, Jan 1977

  47. Tensile Test • Single Nugget Test – Tensile Shear • Multiple Nugget Test – Tensile Shear • Total Spot Weld Area • Sheet Thickness • Nugget Rotation (spot pattern) • Weld Bonding (Nugget plus Adhesive)

  48. Dickinson, “Welding in Auto…”, AISI, Aug 1981

  49. Effect of Total Nugget Area on Double Transverse Spot Welds Capelli, et al, “Fatigue Strength of Spot-welded Joints..” Welding of HSLA Steels, ASM, 1978

  50. Effect of Increasing Number of Welds Non-uniform loading on Outside welds causes deviation Hills, “Effect of number of welds in spot welded…”, Iron & Steelmaking, Vol 23, No 2, 1996

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