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

Peel Test and Chisel Test

Button Size as a Measure of Weld Quality

ButtonDiameter

Modes of Failure in Spot Welds

Full Button Irregular Button

Interfacial Failure

Long Life Test-- on 1.3-mm Thick 6009-T4 Arc Cleaned/Conversion-Coated Sheet

with Truncated Cone Electrodes and Current Stepping

Per

cent

Hea

t (%

)B

utto

nD

iam

eter

(m

m)

Und

ersi

zed

But

tons

/Str

ip

Number of Welds

[Reference: SAE 840291, Patrick,Auhl, and Sun]

Shear-Strength Data for Long Life Test

-- on 6009-T4 Arc Cleaned/Conversion-Coated Sheet

Number of Welds

Sh

ear

Str

eng

th (

kN/S

po

t)

[Reference: SAE 840291,Patrick, Auhl, and Sun]

Minimum Tensile-Shear Strength of Spot Welds in Aluminum Alloys

[Reference: Resistance Welding Manual, p.11-26, RWMA]

Resistance Spot Weld Radiographs 1 mm Sheet

[Reference: Joining of Aluminum Alloys 6009/6010, Hoch]

6009/6009 5182/5182 2036/2036

Small Cracking

Large CenterPorosity

LargeCracking

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

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.

Typical Oscillograph Record during Welding

Voltage

Force

Forge ForceWelding Force

Displacement

Current

1 V

1 kN

0.25 mm

5.0 kA rms0.1 sec

Typical Oscillograph Record

Current

Force

Displacement

Voltage

5.2 kA RMS

0.7 kN

0.2 mm

1.0 V (p-t-p)

Zero linefor force

Resistance Spot Weld Data

[Reference: Guidelines to Resistance Spot Welding Aluminum Automotive Sheet,p.9, The AluminumAssociation]

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

[Reference: Resistance Welding Manual, p.11-19, RWMA]

Sh

unt P

ath

Re

sist

ance

, Mic

roo

hm

s

Join

t Str

eng

th, l

b/w

eld

Weld Spacing, in.

JointStrengthShuntResistance

Suggested Minimum Weld Spacing Edge and Flange Distance

[Reference: Resistance Welding Manual, p.11-20, RWMA]