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

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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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Presentation Transcript
slide1

Capacitor Discharge Welding

Percussion Welding

Magnetic Force (AC)

Stud Welding

slide2

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

slide3

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.

slide5

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)
slide7

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

slide8

Low Voltage

Hand Held

Unit

AWS Welding Handbook

slide9

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

slide11

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
slide13

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
slide14

Mechanical Properties vs Weld Time

Weld Time

Bakshas, “The quality of capacitor deischarge…< Automatic Welding, Mar., 1981

slide15

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
slide16

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

slide17

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.

slide18

Gravity Unit

Thompson, “Attachment of Thermocouple Instrumetation…”,

Welding Journal, June 1982

slide19

Spring Loaded Unit

Thompson, “Attachment of Thermocouple Instrumetation…”,

Welding Journal, June 1982

slide20

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.
slide21

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
slide22

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)
slide23

Air Cylinder applies

initial force to bring

contact to nib

Electromagnetic

Force applied during

Welding

Metals Handbook, ASM, 1983

slide24

Schlegel, “All About Percussion Welds”,

Welding Design & Fabrication, Oct. 1990

slide28

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
slide29

Acceleration of the moveable head:

  • Directly proportional to the magnetic force applied
  • Inversely proportional to the mass