Research ArticleAPPLIED SCIENCES AND ENGINEERING

Welding of 3D-printed carbon nanotube–polymer composites by locally induced microwave heating

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Science Advances  14 Jun 2017:
Vol. 3, no. 6, e1700262
DOI: 10.1126/sciadv.1700262
  • Fig. 1

    (A) 3D-printed parts tend to display weak tensile properties in the y and z directions due to poor interlayer welding. To address this, we coated thermoplastic filament with a CNT-rich layer; the resulting 3D-printed part contains RF-sensitive nanofillers localized at the interface. (B) When a microwave field is applied, the interface is locally heated to allow for polymer diffusion and increased fracture strength.

  • Fig. 2

    (A) Thermoplastic filaments are coated with a CNT/polymer ink and dried to create (B) coaxial filaments, where only the exterior is RF-sensitive. (C) These filaments may be 3D-printed to form structures with CNTs localized at each interface. (D) Optical micrographs of sanded cross sections show that CNTs do not migrate into the filament interior during printing.

  • Fig. 3 The dielectric properties and microwave heating response of CNT-loaded PLA films are probed as a function of nanotube loading.

    (A) Classic percolation behavior is observed for these nanotube networks. (B) Percolation is associated with a marked increase in the dissipated power, but at high loadings, the conductive network becomes reflective. (C) In situ infrared imaging is used to capture the (D) heating response of the nano-filled films, and the same two transitions are observed. This trend is corroborated by (E) COMSOL finite-element simulations of RF heating and heat transfer.

  • Fig. 4

    (A) Tear tests are used to determine that (B) the fracture strength of 3D-printed PLA coupons is increased by 275% when CNT coatings and LIRF welding are applied. (C) Optical micrographs of the fracture surfaces reveal significant necking and crazing in the LIRF-welded sample, whereas the smooth surface of the 3D-printed control sample indicates a brittle fracture. (D) A nanotube-coated, LIRF-welded PLA chain link printed in the z direction is able to support the weight of C.B.S. This LIRF welding enables new, high-strength applications of additive manufacturing.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1700262/DC1

    CNT/PLA hot-pressed films and electrical characterization

    Microwave heating thermometry for hot-pressed films

    COMSOL

    Heating response as a function of thickness

    Microwave bonding of thermoplastic interfaces

    Filament coating method

    Heating response of coated filaments

    3D printing ASTM D1938 tear test coupons

    Microwave exposure of tensile coupons

    Mode III fracture strength (trouser tear) testing method

    Mode III fracture strength (trouser tear) testing results

    table S1. DC conductivity measurement details.

    table S2. Material properties used in COMSOL calculations.

    table S3. Material properties of PLA filament.

    fig. S1. Dielectric measurements using a sample holder placed between two coaxial transmission lines.

    fig. S2. AC dielectric properties including the real part of the relative permittivity, the loss tangent, and AC conductivity.

    fig. S3. FLIR thermal image screenshots of hot-pressed PLA films after 30 s of heating at 15 W.

    fig. S4. Max temperature versus time for various wt % of CNTs in waveguide, 15-W microwave power.

    fig. S5. Geometry used in COMSOL simulations.

    fig. S6. Differential scanning calorimetry data for PLA.

    fig. S7. COMSOL simulation predictions for temperature (average) versus time for all samples.

    fig. S8. Setup for spray coating PLA films outlined in the “COMSOL” section.

    fig. S9. The microwave response of 10 wt % MWCNT spray-coated PLA films (as quantified by the mean temperature of the film at 30 s) versus film thickness.

    fig. S10. Stress versus strain for lap-shear samples.

    fig. S11. Coating bath internal view.

    fig. S12. Microscope image of the 1.75-mm printer filament with CNT coating.

    fig. S13. Microscope image of the coated filament after being extruded from a 0.5-mm nozzle.

    fig. S14. Schematic for calculation of coating thickness.

    fig. S15. Coated PLA filament array glued to polymer film.

    fig. S16. FLIR image of coated filament bundle heating in waveguide and corresponding COMSOL simulation of filament bundle heating in a waveguide.

    fig. S17. Stacker 500 desktop 3D printer.

    fig. S18. Stacker printer nozzle showing heat sink.

    fig. S19. Slicing pattern and G-code preview of the rectangular tear specimens.

    fig. S20. FLIR camera positioned over the waveguide to directly measure sample temperature during exposure to microwaves.

    fig. S21. Microwave choke tube designed to attenuate and contain microwave energy yet still allow for direct viewing of sample.

    fig. S22. Maximum temperature versus time for all five LIRF samples.

    fig. S23. Instron 5944 load frame used for tensile and tear tests.

    fig. S24. Close-up view of sample gripped in the tensile load frame.

    fig. S25. Optical microscope image of a tear test sample viewed edge-on to determine the mean weld line thickness.

    fig. S26. Tear test fracture strength versus extension results for bulk PLA film.

    fig. S27. Tear test fracture strength versus extension results for neat printed PLA.

    fig. S28. Tear test fracture strength versus extension results for CNT-coated printed PLA.

    fig. S29. Tear test fracture strength versus extension results for CNT-coated, LIRF-welded printed PLA samples.

    fig. S30. Tear test fracture strength results for each sample type.

    fig. S31. Tear test fracture strength versus extension results for nozzle temperature sweep.

    fig. S32. Optical microscope image of tear test fracture surface for bulk hot-pressed PLA sample (necking and crazing are clearly visible).

    fig. S33. Optical microscope image of tear test fracture surface for neat 3D-printed PLA control sample (necking and crazing are absent; instead, a clean fracture surface is observed).

    fig. S34. Optical microscope image of tear test fracture surface for LIRF-welded sample (necking and crazing are clearly visible).

    fig. S35. Optical microscope image of tear test fracture surface for LIRF-welded sample (necking and crazing are clearly visible).

    fig. S36. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.

    fig. S37. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.

    fig. S38. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.

    fig. S39. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.

    fig. S40. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear test samples (necking and crazing are clearly visible).

    fig. S41. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear tests.

    fig. S42. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear test samples (necking and crazing are clearly visible).

  • Supplementary Materials

    This PDF file includes:

    • CNT/PLA hot-pressed films and electrical characterization
    • Microwave heating thermometry for hot-pressed films
    • COMSOL
    • Heating response as a function of thickness
    • Microwave bonding of thermoplastic interfaces
    • Filament coating method
    • Heating response of coated filaments
    • 3D printing ASTM D1938 tear test coupons
    • Microwave exposure of tensile coupons
    • Mode III fracture strength (trouser tear) testing method
    • Mode III fracture strength (trouser tear) testing results
    • table S1. DC conductivity measurement details.
    • table S2. Material properties used in COMSOL calculations.
    • table S3. Material properties of PLA filament.
    • fig. S1. Dielectric measurements using a sample holder placed between two coaxial transmission lines.
    • fig. S2. AC dielectric properties including the real part of the relative permittivity, the loss tangent, and AC conductivity.
    • fig. S3. FLIR thermal image screenshots of hot-pressed PLA films after 30 s of heating at 15 W.
    • fig. S4. Max temperature versus time for various wt % of CNTs in waveguide, 15-W microwave power.
    • fig. S5. Geometry used in COMSOL simulations.
    • fig. S6. Differential scanning calorimetry data for PLA.
    • fig. S7. COMSOL simulation predictions for temperature (average) versus time for all samples.
    • fig. S8. Setup for spray coating PLA films outlined in the “COMSOL” section.
    • fig. S9. The microwave response of 10 wt % MWCNT spray-coated PLA films (as quantified by the mean temperature of the film at 30 s) versus film thickness.
    • fig. S10. Stress versus strain for lap-shear samples.
    • fig. S11. Coating bath internal view.
    • fig. S12. Microscope image of the 1.75-mm printer filament with CNT coating.
    • fig. S13. Microscope image of the coated filament after being extruded from a 0.5-mm nozzle.
    • fig. S14. Schematic for calculation of coating thickness.
    • fig. S15. Coated PLA filament array glued to polymer film.
    • fig. S16. FLIR image of coated filament bundle heating in waveguide and corresponding COMSOL simulation of filament bundle heating in a waveguide.
    • fig. S17. Stacker 500 desktop 3D printer.
    • fig. S18. Stacker printer nozzle showing heat sink.
    • fig. S19. Slicing pattern and G-code preview of the rectangular tear specimens.
    • fig. S20. FLIR camera positioned over the waveguide to directly measure sample temperature during exposure to microwaves.
    • fig. S21. Microwave choke tube designed to attenuate and contain microwave energy yet still allow for direct viewing of sample.
    • fig. S22. Maximum temperature versus time for all five LIRF samples.
    • fig. S23. Instron 5944 load frame used for tensile and tear tests.
    • fig. S24. Close-up view of sample gripped in the tensile load frame.
    • fig. S25. Optical microscope image of a tear test sample viewed edge-on to determine the mean weld line thickness.
    • fig. S26. Tear test fracture strength versus extension results for bulk PLA film.
    • fig. S27. Tear test fracture strength versus extension results for neat printed PLA.
    • fig. S28. Tear test fracture strength versus extension results for CNT-coated printed PLA.
    • fig. S29. Tear test fracture strength versus extension results for CNT-coated, LIRF-welded printed PLA samples.
    • fig. S30. Tear test fracture strength results for each sample type.
    • fig. S31. Tear test fracture strength versus extension results for nozzle temperature sweep.
    • fig. S32. Optical microscope image of tear test fracture surface for bulk hot-pressed PLA sample (necking and crazing are clearly visible).
    • fig. S33. Optical microscope image of tear test fracture surface for neat 3D-printed PLA control sample (necking and crazing are absent; instead, a clean fracture surface is observed).
    • fig. S34. Optical microscope image of tear test fracture surface for LIRF-welded sample (necking and crazing are clearly visible).
    • fig. S35. Optical microscope image of tear test fracture surface for LIRF-welded sample (necking and crazing are clearly visible).
    • fig. S36. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
    • fig. S37. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
    • fig. S38. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
    • fig. S39. SEM image of tear test fracture surface for neat PLA 3D-printed tear samples.
    • fig. S40. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear test samples (necking and crazing are clearly visible).
    • fig. S41. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear tests.
    • fig. S42. SEM image of tear test fracture surface for LIRF-welded, 3D-printed PLA tear test samples (necking and crazing are clearly visible).

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