Spot Weld Al Equipment

1
Spot Weld Al Equipment
2
Resistance Welding

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• Lesson Objectives
• When you finish this lesson you will understand

Keywords
3
Various Types of Equipment

• Single-Phase AC Machines
• Without slope control
• With Slope control

• Stored-Energy Machines
• Electromagnetic Type
• Electrostatic Type
• Electrochemical Type
• Home-Polar Type

• Single-Phase DC Machines
• - Rectified DC
• - Medium Frequency DC

• Polyphase Direct-Energy Machines
• Frequency Converter
• Rectifier Type

4
Typical Current-Force Diagram for Single-Phase AC
Type Machines
Weld Time
Postheat Time
Weld Heat Time
Hold Time
Downslope Time
Time
Forge-Delay Time
Upslope Time
Squeeze Time
Forge Force
Postheat Current
Initial Current
Weld Force
Welding Current
Reference Resistance Welding Manual, p.11-21,
RWMA
5
Machine Settings for Spot Welding Aluminum Alloys
on Single-Phase Machines
(Recommendations without Slope Control)
Reference Resistance Welding Manual, p.11-14,
RWMA
6
Recommended Weld Current with a Single-Phase AC
Supply
70
60
Weld Current, kA
50
40
30
20
1 2 3
Material Thickness, mm
7
Recommended Electrode Force with a Single-Phase
AC Supply
Electrode Force, kN
Material Thickness, mm
8
Effect of AC Conduction Angle on Electrode Life
Lower Peak Currents
4.6 msec
Longer Conduction Period
DC
4.6
Longer Conduction Periods Allow more Uniform
Heating (Lower Peak Current) Without Long Cool
Periods Between Half-cycles Increasing Electrode
Life
No Weld Cracking
Partial Nuggets Weld Cracking
Increase Electrode Life
4.6
Spinella, D, Implications for Aluminum
Resistance Spot Welding Using Alternating
Current, Materials Body Testing, IBEC , 1995
9
Various Types of Equipment

• Single-Phase AC Machines
• Without slope control
• With Slope control

• Stored-Energy Machines
• Electromagnetic Type
• Electrostatic Type
• Electrochemical Type
• Home-Polar Type

• Single-Phase DC Machines
• - Rectified DC
• - Medium Frequency DC

• Polyphase Direct-Energy Machines
• Frequency Converter
• Rectifier Type

10
(No Transcript)
11
Spot Welding Schedule of Single-Phase Direct
Current Machines
Reference Resistance Welding Manual, p.11-23,
RWMA
12
Recommended Welding Conditions with a
Single-Phase DC Supply
Electrode Force, kN
Weld Time, cycles
Weld Current, kA
Material Thickness, mm
13
Effect of DC Current on Electrode Life
DC Results in Off Center Weld More Wear on One
Electrode
Electrode Face with Higher Operating Temperature
Kumagai, M, High Performance Electrode
Material IBEC95, Material Body Testing, 1995
14
Various Types of Equipment

• Single-Phase AC Machines
• Without slope control
• With Slope control

• Stored-Energy Machines
• Electromagnetic Type
• Electrostatic Type
• Electrochemical Type
• Home-Polar Type

• Single-Phase DC Machines
• - Rectified DC
• - Medium Frequency DC

• Polyphase Direct-Energy Machines
• Frequency Converter
• Rectifier Type

15
Newton, et al, Fund of RW Aluminum, AWS, SMWC VI
Oct 1994
16
Comparison of 50-Hz AC and MFDC Waveforms
Current (kA)
MFDC AC 50 HZ
Time (sec)
17
AC
Mid-Frequency DC
Reduced Expulsion
61114-T4 Aluminum
Michaud, E, A Comparison of AC MFDC SMWC VII,
AWS, 1996
18
MF DC
AC
19
Increase Force
Effect of Force and Gage on Lobe for MF DC
As Increase Gage, Lobe Moves
Browne, D., Model to Predict, IBEC95, Adv Tech
Processes, 1995
20
Effect of Electrode Tip Diameters on MFDC
Browne, D., Model to Predict, IBEC95, Adv Tech
Processes, 1995
21
Effect of Weld Spacing in MFDC
Browne, D., Model to Predict, IBEC95, Adv Tech
Processes, 1995
22
Effect of Deteriorated Tips with MFDC
Browne, D., Model to Predict, IBEC95, Adv Tech
Processes, 1995
23
Various Types of Equipment

• Single-Phase AC Machines
• Without slope control
• With Slope control

• Stored-Energy Machines
• Electromagnetic Type
• Electrostatic Type
• Electrochemical Type
• Home-Polar Type

• Single-Phase DC Machines
• - Rectified DC
• - Medium Frequency DC

• Polyphase Direct-Energy Machines
• Frequency Converter
• Rectifier Type

24
Typical Current-Force Diagram for Electrostatic
Stored Energy Type Machines
Forge-Delay Time
Forge Force
Weld Force
Current
Squeeze Time
Hold Time
Weld Time
Reference Resistance Welding Manual, p.11-21,
RWMA
25
Spot Welding Schedule of Electrostatic Stored
Energy Machines
Reference Resistance Welding Manual, p.11-23,
RWMA
26
Various Types of Equipment

• Single-Phase AC Machines
• Without slope control
• With Slope control

• Stored-Energy Machines
• Electromagnetic Type
• Electrostatic Type
• Electrochemical Type
• Home-Polar Type

• Single-Phase DC Machines
• - Rectified DC
• - Medium Frequency DC

• Polyphase Direct-Energy Machines
• Frequency Converter
• Rectifier Type

27
Insert diagram of Frequency Converter waveform
28
Spot Welding Schedule of Typical Three-Phase
Frequency Converter
Reference Resistance Welding Manual, p.11-22,
RWMA
29
Various Types of Equipment

• Single-Phase AC Machines
• Without slope control
• With Slope control

• Stored-Energy Machines
• Electromagnetic Type
• Electrostatic Type
• Electrochemical Type
• Home-Polar Type

• Single-Phase DC Machines
• - Rectified DC
• - Medium Frequency DC

• Polyphase Direct-Energy Machines
• Frequency Converter
• Rectifier Type

30
Typical Current-Force Diagram for Three-Phase
Rectifier Type Machines
Forge-Delay Time
Final Force
Weld Time
Postheat Current
Welding Current
Initial Force
Postheat Time
Hold Time
Total Weld Time
Squeeze Time
Reference Resistance Welding Manual, p.11-20,
RWMA
31
Spot Welding Schedule of Typical Three-Phase
Direct Current Rectifier
Reference Resistance Welding Manual, p.11-22,
RWMA
32
SUMMARY
33
Process Parameters

• Electrode Design/Material
• Due to the required higher current levels,
  electrodes with high current capacity, such as
  Class 1 and Class 2, are commonly used
• Electrode designs have mainly been dome-shaped
• Electrode tips must also be dressed frequently
• Forging
• Forging cycles are commonly used to prevent weld
  cracking in aluminum alloys

• Weld Current
• High current levels are required to break down
  the surface oxide and generate the heat necessary
  for developing an acceptable weld nugget
• Weld Time
• Require short weld time due to high current
  levels
• Upslope/Downslope
• Generally not recommended for welding aluminum
  alloys

34
Weld Defects

• Surface Burning and Tip Pickup
• Cracks
• Excessive Indentation
• Sheet Separation
• Porosity

• Weld Metal Expulsion
• Unsymmetrical Weld Nugget
• Inclusion of Unwelded

35
Surface Burning and Tip Pickup

• Remedy Those Conditions
• Improper surface conditions
• Electrode skidding
• Improper Electrode Material - conductivity too
  low
• Dirty or improper cleaned electrodes
• Excessive weld time
• Excessive welding current
• Inadequate welding force

• Cause
• Surface burning is caused by excessive heat on
  the metal surface under the electrode and is
  indicated by burned, pitted and discolored welds.
• Excessive electrode pickup is caused primarily by
  the same factors.

36
Cracks

• Cause
• Internal and external cracks in welds, generally
  caused by improper thermal and pressure
  conditions, are observed in the weld structure
  and surface, respectively.

• Remedy Those Conditions
• Excessive penetration
• Insufficient force
• Improper rate of current rise
• Improper electrode cooling
• Improper electrode contour
• Delayed application of forging force
• Electrode skidding

37
Excessive Indentation

• Remedy Those Conditions
• Excessive force
• Weld metal expulsion
• Improper electrode contour
• Excessive surface heating
• Improper forging cycle
• Excessive Welding Current

• Cause
• Excessive indentation, generally caused by
  improper force application, is indicated by
  depression on the weld surface.

38
Sheet Separation

• Cause
• Excessive sheet separation, generally caused by
  poor fitup of parts and excessive surface
  deformation, is indicated by a wide separation of
  the base metal adjacent to the weld.

• Remedy Those Conditions
• Excessive force
• Improper fitup of parts
• Weld metal expulsion
• Incorrect electrode contour
• Excessive welding current
• Tip misalignment
• Excessive weld time

39
Porosity

• Cause
• A porous weld structure, generally caused by
  improper application of heat and force, is
  observed by sectioning and etching the weld.

• Remedy Those Conditions
• Insufficient weld time
• Improper rate of current rise
• Improper electrode contour
• Incorrect sequencing of weld and forging force
• Insufficient force

40
Weld Metal Expulsion

• Cause
• Weld expulsion, generally caused by extreme heat
  and improper force, is indicated by expelled
  metal from the weld.

• Remedy Those Conditions
• Insufficient force
• Tip misalignment
• Erratic contact resistance
• Foreign substance at faying surface
• Electrode skidding
• Excessive welding current
• Excessive weld time

41
Unsymmetrical Weld Nugget

• Cause
• Unsymmetrical welds, generally caused by
  unsymmetrical gauge combination, improper
  electrode contour, poor fitting workpiece or
  surface preparation, may be observed by
  sectioning the weld.

• Remedy Those Conditions
• Improper electrode contour
• Inadequate surface preparation
• Improper fitup of workpieces
• Electrode misalignment
• Electrode skidding