methods of polymer weld quality evaluation

Methods of Polymer Weld Quality Evaluation

Miranda Marcus Applications Engineer, Ultrasonics614.688.5213mmarcus@ewi.org

June 3, 2019

Summary

Evaluation of the quality of polymer welds is essential to the development and production maintenance of a welding process

Wide variety of options─ Non-Destructive vs. Destructive─ Quantitative vs. Quantitative

A comparison of some popular weld quality evaluation methods is discussed in this paper, as well as the preparation procedures for each and what can be learned from each method.

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Options for Weld Analysis

Quantitative Methods Pressure decay leak

testing Tensile testing Shear testing Peel testing Push-out testing Bend testing Torsional testing Creep testing Fatigue testing Dimensional analysis

Qualitative Methods Cross-sectional

analysis Computerized

tomography (CT) scanning

Microtome slicing Visual inspection X-ray Ultrasonic testing Fractography

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Testing Standards

AWS G1.2M/G1.2 (1999)─ Specification for Standardized Ultrasonic Welding Test

Specimen for Thermoplastics─ I-beam design and tensile testing method

ASTM E2930-13 (2013)─ Standard Practice for Pressure Decay Leak Test Method

ASTM E2015-04 (2014)─ Standard Guide for Preparation of Plastics and Polymeric

Specimens for Microstructural Examination Compositional and Failure Analysis of Polymers: A

Practical Approach by John Scheirs (2000)─ Cryotome preparation

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Method

14 parts analyzed─ 7 material, process, and parameter combinations─ All 14 pressure decay leak tested─ 7 CT-scanned, then tensile tested─ 7 cross sectioned, 4 also cryomicrotome sliced.

Intentional defects created:─ Over welding─ Under welding─ Insufficient amplitude─ Insufficient power─ Insufficient pressure─ Insufficient collapse─ Notches cut into the joint

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Test Part

Dukane ISTeP™-style standard test parts

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Ultrasonic Welding Approach

20-kHz Branson pneumatic ultrasonic welder ─ Weld-by-distance capability

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Set PlasticWeld Settings

Amplitude (μm)

Collapse (% ED)

Force(N)

A PBT 40 233 654B PBT 18 100 654C PC 29 100 654D PC 12.7 67 654E PBT-PC 29 100 654

Laser Welding Approach

Laserline 980-nm ND:Yag─ Mounted to an XY table with

small pneumatic press

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Set PlasticWeld Settings

Power (W)

Speed (cm/min)

Force(N)

F PA-15GF 103 152 698G PA-15GF 67 152 138

Testing Equipment

Pressure decay leak testing─ Cincinnati Test Systems Sentinel C28 air decay leak tester

Tensile testing─ Instron machine, pulled at a speed of 2.5 mm/minute

CT scans ─ Nikon XTH 225 CT System with 130 kV and 30 W of power─ Rotating target

Cryomicrotomes─ Leitz Kryostat 1720 cryomicrotome

Imaging─ Olympus BX51 microscope

─ Reflective lighting for the sections ─ Transmissive lighting for the cryomicrotome slices

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Cross-Section Preparation

Part fixed in overnight epoxy, then mounted in 20-min cured acrylic, then ground and polished

Hot air used to soften surface of polished sample to reveal polymer flow lines and heat-affected zone:

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Before After

Tensile and Leak Testing Results

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Material Defect Max Tensile (N)

Leak Rate (cm3/min)Sectioned CT Scanned

Ultr

ason

ic

PBT Overweld 2734 Major LeakPBT Notched 118 -1.4 Major LeakPC Overweld 5551 Major LeakPC Notched 2032 0.41 Major Leak

PBT-PC Dissimilar 2740 -0.06 237

Lase

r PA-15GF Degraded 2080 0.93 1.08PA-15GF Low Pressure 1506 169.42 328.16

Imaging Results –Ultrasonic, PBT

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Overwelded Underwelded

Imaging Results –Ultrasonic, PC

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Overwelded Underwelded

Imaging Results –Ultrasonic, PC-PBT

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Dissimilar Materials

Imaging Results –Laser, PA15GF

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Uneven Insufficient Pressure

Summary

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Method Flaw

Leak Test

Tensile Test

Cross Section

Microtome Slice

CT Scan

Lack of Fusion X XMisalignment X X X

Porosity X X X XDegree of Collapse X X X X

Discrete Gap/ Inclusion X X

Change in Crystallinity X

An X indicates the flaw can be detected with the method

Acknowledgements

Thanks to Branson for providing the welding press Thanks to Dukane for the donation of the ISTeP™

parts Thanks to Wayne Papageorge for expertise in

polymer cross-section preparation Thanks to Daniel Kmiotek for CT scanning Thanks to Steve O’Mara for tensile testing

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