Inspection and Testing

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Inspection and Testing

• Radiography
• Drawbacks
• The time element in developing the negative and
  obtaining the necessary information
• Impracticability of taking the welded parts to
  the X-ray machine with the attendant time element
  involved
• Not all faults are revealed
• Interpretation of radiographs requires a highly
  skilled technician

• Peel Test
• Shown in the figure
• Visual Inspection

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Peel Test and Chisel Test
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Button Size as a Measure of Weld Quality
Button Diameter
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Modes of Failure in Spot Welds
Full Button Irregular Button
Interfacial Failure
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Long Life Test
-- on 1.3-mm Thick 6009-T4 Arc Cleaned/Conversion-
Coated Sheet with Truncated Cone Electrodes and
Current Stepping
Percent Heat ()
Button Diameter (mm)
Reference SAE 840291, Patrick, Auhl, and Sun
Undersized Buttons/Strip
Number of Welds
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Shear-Strength Data for Long Life Test
-- on 6009-T4 Arc Cleaned/Conversion-Coated Sheet
Shear Strength (kN/Spot)
Reference SAE 840291, Patrick, Auhl, and Sun
Number of Welds
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Minimum Tensile-Shear Strength of Spot Welds in
Aluminum Alloys
Reference Resistance Welding Manual, p.11-26,
RWMA
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Resistance Spot Weld Radiographs 1 mm Sheet
6009/6009 5182/5182 2036/2036
Large Cracking
Small Cracking
Large Center Porosity
Reference Joining of Aluminum Alloys 6009/6010,
Hoch
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Types of Defects Revealed by Radiography

• Undersize nugget
• Inadequate diameter
• Inadequate penetration
• Oversize nugget
• Excessive diameter
• Excessive penetration
• Odd and misshapen nuggets
• Extent of Alclad inclusion into the nugget
• Extrusion of the nugget

• Cracking of the nugget
• Porosity
• Expulsion from faying surfaces
• Segregation of eutectic in parent material
• Electrode pickup
• Size or extent or granular zone
• Nugget penetration

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Setup Procedures and Suggested Schedules

• Step 1 Insert electrode of proper size and tip
  contour for the gauge combination. Align
  electrodes.
• Step 2 Set pressure gage for suggested welding
  force, and check with an electrode force gauge.
• Step 3 Adjust the control to provide the
  approximate suggested weld and postheat time.

• Step 4 The welding currents shown are
  approximate and intended to be a guide. The
  magnitude of the welding current is usually
  controlled by a heat dial or phase-shift control.
• Step 5 Check the machine for consistency of
  operation by making and testing twenty single
  spot tension-shear specimens and five macroscopic
  examination specimens.

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Typical Oscillograph Record during Welding
Voltage
1 V
Force
Forge Force
1 kN
Welding Force
0.25 mm
Displacement
Current
5.0 kA rms
0.1 sec
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Typical Oscillograph Record
5.2 kA RMS
Current
0.7 kN
Force
0.2 mm
Zero line for force
Displacement
1.0 V (p-t-p)
Voltage
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Resistance Spot Weld Data
Reference Guidelines to Resistance Spot
Welding Aluminum Automotive Sheet, p.9, The
Aluminum Association
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Shunting Effect on 2024-T Alclad

• Factors Influencing Shunting
• Effect Include
• Thickness and resistance of the alloy being
  welded
• Shunting effect increases as the stock thickness
  and resistance decrease
• Surface resistance of the faying surface
• Shunting effect increases as the faying surface
  resistance increases
• Spot spacing
• Shown in left figure

Shunt Path Resistance, Microohms
Joint Strength, lb/weld
Joint Strength Shunt Resistance
Weld Spacing, in.
Reference Resistance Welding Manual, p.11-19,
RWMA
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Suggested Minimum Weld Spacing Edge and Flange
Distance
Reference Resistance Welding Manual, p.11-20,
RWMA