jian chen, zhili feng (pi), c. david warren · reflection reduction/minimization as-welded surface...

Managed by UT-Battellefor the Department of Energy

Nondestructive Inspection of RSW of

AHHS by Infrared Technology

Jian Chen, Zhili Feng (PI), C. David Warren

Oak Ridge National Laboratory

April, 2014

2 Managed by UT-Battellefor the Department of Energy

Industry has been relying on pry-check and teardown for resistance spot weld (RSW) quality inspection and control– Labor intensive and expensive (rework and scraps)

– Less effective for advanced high-strength steels, aluminum and other lightweight materials, impeding the widespread use for light-weighting

AMD 605: In-Line Resistance Spot Welding (RSW) Control and Evaluation System Assessment for Light Weight Materials

Background

In 2007-2008, USCAR conducted an assessment of the industry needs and state-of-the-art of NDE technologies (AMD605)– Industry needs: real-time inspection and postmortem (post-welding)

inspection

– Lack of viable NDE may discourage the use of lightweight materials: high strength steel and aluminum

– “No economically reliable method exists today to inspect resistance spot welds at production rates, and the only technical needs identified in the project for further development consideration were in infrared thermography technology”


Objective

• Develop a fully automated online non-destructive evaluation (NDE) technology for RSW quality monitoring based on infrared (IR) thermography that can be adopted reliably and cost-effectively in high-volume auto production environment for weld quality assessment An expert system including hardware and software

Capable for both post-weld and real-time on-line weld quality inspection

Weld quality database covering wide range of weld configurations (materials, thickness, coatings) common in auto-body structures


Past Attempts on IR NDE Postmortem NDE with mostly

limited to laboratory trials– Flash lamp heating source: pulsed

heating in milli-seconds

– Positive correlation with weld quality

– However, minimal surface temperature change (low signal-to-noise ratio) Highly sensitive to surface condition

and environment interference Requiring painting of weld surface –

impractical in auto production line

No successful attempts as real-time NDE


Major Problem of Conventional IR NDE

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Peak IR intensity at weld centerPeak IR intensity at weld center

Due to the unknown surface condition (i.e. emissivity), peak IR intensity vs. targeted weld size is very noisy.

),( totWfT

Measured IR intensity

Surface emissivity (unknown)

Temperature


Our New Approach

Special IR image/signal analysis algorithms have been developed – Comparing IR intensity over the entire image pixels of

a single frame and throughout multiple image frames.

– Relying on dynamic change of the IR intensity, instead of the absolute IR intensity

– Insensitive to surface emissivity.


Conventional IR thermography Non-contact, non-intrusive, whole field image

– Sensitive to low and non-uniform material surface emissivity

– Requiring painting of the weld surface (impractical in auto production line)

– Low signal/noise ratio

– Mostly limited to lab trials for post-weld inspection

– No successful attempts in real-time application

Our new IR-based technology Capable for both real-time and post-weld

inspection

Insensitive to surface condition

No surface treatment is needed

Easy for implementation and automation

Fast and repeatable

Advantages against Conventional IR NDE


Principles of new IR NDE Technique

Utilize the heat generated during welding

Post-weldReal-time

Aux. localized heating (~50 °C)

Utilize auxiliary heating source


Major Tasks/Efforts

Weld coupons and auto body weld structures with controlled weld quality/defects attributes– Destructive and ultrasonic NDE examinations

for weld characterizations

Post-weld IR inspection– Increasing the IR signal-to-noise ratio

Better heating techniques Digital image processing Reflection reduction/minimization As-welded surface condition

– Heating and heat transfer modeling to guide inspection and data analysis

Real-time IR Monitoring– Using the heat flow during welding

Development prototype system Beta testing in production environment Tech transfer and commercialization


Weld Quality Metrics

Ranked by industry advisory committee in the order of importance (high to low)– Weld with no or minimal fusion

– Cold or stuck weld

– Weld nugget size

– Weld expulsion and indentation

– Weld cracks

– Weld porosity

Most critical

Excessive indentation

Stuck weld (insufficient fusion)

Less critical

Cracks

Porosity


Material Matrix Tested Steel Grades, Coating,

Thickness

• DP590 galvanized 1.2mm• DP590 galvanized 1.2mm

• DP590 galvanized 1.8mm• DP590 galvanized 1.8mm

• DP600 HDG 1.0mm• DP600 HDG 1.0mm

• DP600 bare 1.0mm• DP600 bare 1.0mm

• DP600 HDG 1.0mm• DP600 HDG 2.0mm

• DP600 bare 2.0mm• DP600 HDG 2.0mm

• DP980 cold rolled 1.2mm• DP980 cold rolled 1.2mm



Steel Grades, Coating,Thickness

• Boron bare 1.0mm• Boron bare 2.0mm• Boron bare 1.0mm

• Boron aluminized 1.0mm• Boron aluminized 2.0mm• Boron aluminized 1.0mm

• Boron bare 1.0mm• Boron aluminized 2.0mm• Boron bare 1.0mm

• Boron aluminized 1.0mm• Boron bare 2.0mm• Boron aluminized 1.0mm

Steel Grades, Coating,Thickness

• Boron bare 1.0mm• Boron bare 1.0mm

• Boron aluminized 1.0mm• Boron aluminized 1.0mm

• Boron bare 1.0mm• Boron aluminized 1.0mm



• Boron aluminized 1.0mm• Boron bare 2.0mm



• Boron bare 2.0mm• Boron aluminized 2.0mm

Welds made with different combinations of materials, thickness, stack-up configurations and coatings.

Each combination includes spot welds with varying attributes (i.e., nugget size, indentation, etc.)


Controlled Welding Investigated

New caps

Worn caps

Electrodes misalignment=~1mm

Welding conditions– Varying welding current

– Varying welding hold time

– New vs. worn electrodes

– Perfectly aligned vs. misaligned electrodes

– Perfectly stacked steel plates vs. separated plates

1mm-thick washers were inserted to introduce gaps

Good weld Gap between plates


Weld Characterization Methods

Sectioning welds– Nugget size and shape

– Porosity and expulsion

– Surface indentation

Dye penetrants– Surface cracking

Surface micro-profiling– Surface indentation– Surface cracking

Ultrasonic C-Scan (underwater)– Nugget and weld shape– Porosity


Hardware Requirement

WELDING MACHINE

Post-weldReal-timeI/O

Triggering signal

I/O

Induction heater

IR camera I/O device Computer

IR camera Induction heater I/O device Computer


Weld Quality Analysis Software

Post-weld

Real-time

Measurable weld attributes– Nugget size and shape– Cold/stick weld defect– Weld thickness/indentation

Measurable weld attributes– Nugget size– Cold/stick weld defect– Expulsion


Real-time NDE System Operation Demonstration (Movie clip)


Post-weld NDE System Operation Demonstration (Movie clip)


Example 1 (3T flat coupons)

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Post-weld predicted diameter (mm)

3.13.23.33.43.53.63.73.83.9

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Post-weld predicted thickness (mm)



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Real-time predicted diameter (mm)

Post-weld predicted shape


Example 2 (2T flat coupons)

2.42.52.62.72.82.9

33.13.23.33.4

2.4 2.9 3.4

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• DP980 cold rolled 1.2mm• DP980 cold rolled 2.0mm• DP980 cold rolled 1.2mm• DP980 cold rolled 2.0mm


* Note: In this case, some of the welds are not symmetric due to the misalignment of electrodes during welding.


no weld

Destructive measurement

Post-weld signature

Example 3 (auto body components)


Example 4 (Detection of stick welds)

• DP600 HDG 1.2 mm• DP600 HDG 1.2 mm• DP600 HDG 1.2 mm• DP600 HDG 1.2 mm

Normal-size welds (generated by normal welding conditions)

Stick weld (generated by decreasing welding current)

Real-time signature

Post-weld signature

Threshold value related to nugget size


Real-time signature

Post-weld signature

Example 5 (Detection of abnormal welds due to separation of steel plates)

Normal welding condition

Abnormal welding condition (simulated by inserting washers)

• DP600 bare 2.0mm• DP600 HDG 2.0mm• DP600 bare 2.0mm• DP600 HDG 2.0mm

0.770.64 0.72 0.67

0.31


More Examples

Results from a combination of

– Materials

– Plate thickness

– Stack up configurations (2T/3T)

– Surface coatings

IR

IR


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Influence of Coil/Weld Alignment (Post-weld)

Weld center

offset

Aux. heater center

• Experiments were conducted on the same weld.

• Inspection at each offset location was repeated twice.

Predictions were fairly repeatable.1mm coil/weld alignment offset resulted in about 0.2mm

error for predictions of both nugget size and weld thickness

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Summary

Successfully developed an IR-based spot weld NDE inspection prototype system capable for both real-time and post-weld on-line applications.

Reliable detection of weld size, cold weld, and surface indents with sufficient accuracy for various combination of materials, thickness, stack-up configuration, surface coating conditions and welding conditions.

Application Measurable weld attributes Inspection time

Real-time• Nugget size and weld shape• Cold/stick weld defects• Expulsion

1.5~3s

Post-weld• Nugget size• Cold/stick weld defects• Weld thickness/indentation

~3s

jian chen, zhili feng (pi), c. david warren · reflection reduction/minimization as-welded surface...

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