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Capacitor Discharge Welding Percussion Welding Magnetic Force (AC) Stud Welding

Capacitor Discharge Welding Percussion Welding Magnetic Force (AC) Stud Welding. Capacitive Discharge Welding. Learning Activities View Slides; Read Notes, Listen to lecture Do on-line workbook. Lesson Objectives When you finish this lesson you will understand:

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Capacitor Discharge Welding Percussion Welding Magnetic Force (AC) Stud Welding

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  1. Capacitor Discharge Welding Percussion Welding Magnetic Force (AC) Stud Welding

  2. Capacitive Discharge 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 mechanism of percussion welding and magnetic force welding • Applications of use of these methods Keywords Percussion Weld, Capacitor Discharge, Nib, Magnetic Force Weld

  3. Percussion Welding (PEW): A resistance welding process which produces coalescence of the abutting members using heat from an arc produced by a rapid discharge of electrical energy. Pressure is applied percussively during or immediately following the electrical discharge. Cueman, “Process Model for Percussion Welding”, Welding Journal, Sept, 1989 Applications: can be used to join like and unlike metals that cannot usually be flash or stud welded. It is used for fine wire leads to filaments such as in lamps and electrical components.

  4. AWS Welding Handbook

  5. Variations of Percussion Welding • Capacitor Discharge, Low V, Nib Start • Capacitor Discharge, Low V, High Frequency Start • Capacitor Discharge, High V • Magnetic Force Method (AC)

  6. Metals Handbook, ASM, 1983

  7. Low Voltage: Hand held & bench type welders High Voltage: More uniform arc, No Nib start , More control Transformer: for Magnetic-force, weld made during first 1/2 cycle Metals Handbook, ASM, 1983

  8. Low Voltage Hand Held Unit AWS Welding Handbook

  9. Metals Joined Welded to Copper Gold Silver Copper-tungsten Silver-tungsten Silver-cadmium oxide Molybdenum Like Metals Tantalum Alloys Copper Alloys Aluminum Alloys Nickel Alloys Low-carbon steel Medium-carbon steel Stainless Steels Diffusion during prolonged high temperature exposure may produce weak or embrittled structures.Transition joints of a compatible third material may help. Other Dissimilar Wires Thermocouple Wires Molybdenum Wires Nb-1Zr 85Zr-15Nb Tantalum

  10. Metals Handbook, ASM, 1983

  11. Welding Energy E = energy in watt-seconds (joules) C = capacitance in farads V = voltage • Amount of Energy Needed to Make Joint Depends on: • Cross-sectional area of joint • Properties of work metal or metals • Depth to which metal is melted on workpieces

  12. Metals Handbook, ASM, 1983

  13. Arc Time (Arc Duration) Interval that begins when arc is initiated and ends when workpieces touch Generally, the shortest weld time allowing some penetration into each part while minimizing heating is recommended • Factors Affecting Arc Time • Work Metal or Combination • Mass of Moving Workpiece • Nib Dimensions • Welding Voltage • Welding Current • Welding Force • Synchronization of Machine Functions

  14. Mechanical Properties vs Weld Time Weld Time Bakshas, “The quality of capacitor deischarge…< Automatic Welding, Mar., 1981

  15. Heat Affected Zone (Very Narrow) Lower Melting Temp Only a few Millionths Inch to 0.025 Higher Melting Temp • Because HAZ is so small • Heat treated metals can be welded without softening • Heat sensitive components near weld unaffected

  16. Welding Current • Polarity: • No Effect for Like materials • Positive polarity for: • Large Cross Section • Higher Melting Point • Higher Thermal Conductivity Peak Current Density =300,000 A/in2

  17. Welding Force • Force Supplied By: • Electromagnet • Gravity • Cam-activated Direct Drive • Spring • Pneumatic Force must be strong enough to accelerate moving part over short gap. Peak loads = 15 - 30 ksi Wire SizeImpact Velocity 5 mils 10-60 in/s 0.01 80-150 in/s Because the force applying unit may rebound and put a tensile loading on welded part, a means of damping must be provided.

  18. Gravity Unit Thompson, “Attachment of Thermocouple Instrumetation…”, Welding Journal, June 1982

  19. Spring Loaded Unit Thompson, “Attachment of Thermocouple Instrumetation…”, Welding Journal, June 1982

  20. Advantages of Percussion Welding • Brevity of arc limits melting and heating. Heat-treated and cold worked materials can be welded without annealing. • No Filler Metal required, No cast structure at interface. • Charging rate is low and controlled, Line power line demand • Can tolerate some contamination on faying surface.

  21. Limitations of Percussion Welding • Limited to butt joints • Total area limited • Similar metals can usually be joined more economically by other processes. • Usually confined to joining of dissimilar metals not normally considered weldable

  22. Variations of Percussion Welding • Capacitor Discharge, Low V, Nib Start • Capacitor Discharge, Low V, High Frequency Start • Capacitor Discharge, High V • Magnetic Force Method (AC)

  23. Air Cylinder applies initial force to bring contact to nib Electromagnetic Force applied during Welding Metals Handbook, ASM, 1983

  24. Schlegel, “All About Percussion Welds”, Welding Design & Fabrication, Oct. 1990

  25. AWS Welding Handbook

  26. AWS Welding Handbook

  27. AWS Welding Handbook

  28. Arc Time is a Function of: • Magnitude of magnetic force • Timing of the magnetic force with relation to welding current • Inertia or mass of the moving parts in the force system • Magnitude of the welding current and the diameter of the projection

  29. Acceleration of the moveable head: • Directly proportional to the magnetic force applied • Inversely proportional to the mass

  30. Section through a Silver Contact (Top) to a Brass Terminal AWS Welding Handbook

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