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Flash/Butt Welding
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Flash/Butt Welding

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  1. Flash/Butt Welding

  2. Flash Butt Welding • Learning Activities • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • The flash and butt welding process for plain carbon steel • The weld parameters which must be controlled to get good welds • Typical flash/butt weld defects Keywords Flash Weld (AC), Butt Weld (DC), Flashing Current, Upset Current, Upset Force, Upset Velocity, Upset Distance, Forging Temperature, Linear Platen Motion, Parabolic Platen Motion, Continuous Acceleration Platen Motion, Flat Spots, Penetrators

  3. Introduction to Flash Welding [Reference: Welding Process Slides, The Welding Institute]

  4. Basic Steps in Flash Welding Electrodes (a) (c) (b) (d) Position and Clamp the Parts Flash Upset and Terminate Current Apply Flashing Voltage and Start Platen Motion [Reference: Welding Handbook, Volume 2, p.583, AWS]

  5. Equipment Example of Flash Welding [Reference: Welding Process Slides, The Welding Institute] Typical applications: (1) Butt welding of matching sections. (2) Chain links. (3) Railway lines. (4) Window frames. (5) Aero-engine rings. (6) Car wheel rims. (7) Metal strip in rolling mills.

  6. Advantages of Flash Welding • Flexible cross sectioned shapes • Flexible positioning for similar cross section parts • Impurities can be removed during upset acts • Faying surface preparation is not critical except for large parts • Can weld rings of various cross sections • Narrower heat-affected zones than those of upset welds

  7. Limitations of Flash Welding • Produce unbalance on three-phase primary power lines • The ejected molten metal particles present a fire hazard • Require special equipment for removal of flash metal • Difficult alignment for workpieces with small cross sections • Require almost identical cross section parts

  8. Common Types of Flash Welds Axially Aligned Weld Dies Cross Section After Welding Fixed Platen Movable Platen Transformer [Reference: Welding Handbook, Volume 2, p.589, AWS]

  9. Common Types of Flash Welds (CONT.) Miter Weld Movable Platen Fixed Platen Cross Section After Welding Transformer [Reference: Welding Handbook, Volume 2, p.589, AWS]

  10. Common Types of Flash Welds (CONT.) Ring Weld Shunt Current Movable Platen Fixed Platen Cross Section After Welding Transformer [Reference: Welding Handbook, Volume 2, p.589, AWS]

  11. Typical Mill Forms and Products of Upset Welding [Reference: Welding Handbook, Volume 2, p.600, AWS]

  12. Systems • Electrical • Force Application Savage, Flash Welding, Welding Journal March 1962

  13. Applications Wheel Truck Rims Ball Bearing Raceways Bar Welding Strip Welding During Continuous Processing Pipelines

  14. Schematic of Typical Flash Weld Cycle Savage, Flash Welding, Welding Journal March 1962

  15. 0 .05 .15 .10 Initial Flashing Partial Burn-off Stage 1 - Heat Soaking Increased Burn-off Stage 2 - Steady State Excessive Burn-off Stage 3 - Heat out

  16. Best Region For Upset Nippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951

  17. In Steady State, the Heat into the HAZ Equals the Heat Out Stage 3 Occurs When More Heat Flows Out than is Flowing In

  18. Upset in the Steady State - Stage 2 Region Forge Temp At Upset Short Time After Long Time After

  19. Nippes, Cooling Rates in Flash Welding, Welding Journal, July 1959

  20. At Moment Of Upset & Short Time Thereafter Temperature vs Time As a Function Of Distance From Interface At Moment of Upset

  21. Nippes, Cooling Rates in Flash Welding, Welding Journal, July 1959

  22. Factors Which Effect Extent of Stable Stage 2 • Material Electrical & Thermal Conductivity • Platen Motion During Flashing • Initial Clamping Distance • Preheat • Material Geometry

  23. Electrical & Thermal Conductivity HAZ High Resistance = More I2R Heating Low Thermal Conductivity = Less Heat Out • More Rapid Heating • Longer Stage 2 • Higher Temperature • Wider HAZ

  24. Wide HAZ Narrow HAZ Oxides Trapped At Interface Oxides Forced To Flashing

  25. Platen Motion Continuous Acceleration Linear Parabolic Continuous Acceleration lead to Stub Out

  26. Nippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951

  27. Linear Flashing - Effect of Increased Velocity Higher Velocity

  28. Parabolic Flashing Nippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951

  29. Temperature Comparison of Linear and Parabolic Flashing Nippes, Temp Dist During Flash Welding, Welding Journal, Dec 1951

  30. Initial Clamping Distance Closer Initial Clamping • Shorter Stage 2 • More Burnoff to Establish Steady State • Steeper Temperature Gradient

  31. Effect of Preheat Beneficial Larger HAZ

  32. Thicker Material Thicker Material is more of a Heat Sink

  33. Questions? • Turn to the person sitting next to you and discuss (1 min.): • OK, we went back to the faster platen motion and told the night shift guy to keep his hands off, but the weld still seems to be too cold. What would you suggest?

  34. DC Butt Welding

  35. Introduction to Upset Welding To Welding Transformer Clamping Die Clamping Die Heated Zone Upsetting Force Movable Part Stationary Part Finished Upset Weld [Reference: Welding Handbook, Volume 2, p.598, AWS]

  36. Schematic of Typical Butt Weld Cycle Medar Technical Literature

  37. Questions? • Turn to the person sitting next to you and discuss (1 min.): • Because the part are first touching as DC current is applied in butt welding, large current levels occur immediately. How would welding steels containing large manganese sulfide inclusions be effected by this?

  38. FLASH/BUTT WELD DISCONTINUITIES • MECHNICAL • Misalignment • Poor Scarfing • Die Burns • HEAT AFFECTED ZONE • Turned Up Fibers (Hook Cracks) • HAZ Softening • CENTERLINE • Cold Weld • Flat Spots / Penetrators • Pinholes • Porosity • Cracking

  39. Misalignment Notch: Stress Riser

  40. Poor Scarfing Notch Thin Section

  41. Die Burns Arcing Crack Martensite

  42. Turned Up Fibers - Hook Cracks

  43. Hook Cracks

  44. Hardness Loss

  45. Cold Weld Cold Weld

  46. Flat Spots & Penetrators in Flash Welds