methods of polymer weld quality evaluation
TRANSCRIPT
Methods of Polymer Weld Quality Evaluation
Miranda Marcus Applications Engineer, [email protected]
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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