# Conductive PLA Applications / Tansforming Multi-Material Prints With Localized Heater Function

## Introduction

Here's a folded 3D printed cube I made using a conductive filament path:

Conductive PLA sucks at low voltages, since whatever you print will end up in the kOhm range. There are essentially three domains that stick out with that in mind:

- high voltage (electrostatics for adhesion, dust separation, ?)
- very low current (embedded tamper detection, charge dissipation for ESD safety, maybe capacitive sensing)
- large acceptable voltage drop (improvised potentiometers, **embedded heaters**, thermal display segments)

I started the link collection below with a focus on embedded heater structures, since this unlocks controlled modification of 3D parts printed as flat sheets, which means we're looking at 3D printing crossing into

- sheet metal paradigms (and prototyping thereof)
- rigid origami of functional parts set in shape after cooling
- multi-function printing, where part of the print can be controlled to turn into an adhesive

### Limited conventional equivalent

At its most essential, line bending of bulk thermoplastics uses their low thermal conductivity and heat applied to a narrow zone right above a heating element (hot wire) to create and lock into place a bend upon cool-down.

(source: https://centros.edu.xunta.gal/iesfontexeria/aulavirtual/mod/page/view.php?id=13815)

A more controlled variant is laser-assisted bending. The videos below are 9 and 12 years old at the time writing and they've certainly stayed in memory, perhaps also contributed inspiration, so it's always worth mentioning them:

- [\[Stefanie Mueller\] LaserOrigami: laser-cutting 3d objects](https://www.youtube.com/watch?v=arjRtCjI9AQ )
- [\[Azzys Design Works\] : Bending plastic with a laser?](https://www.youtube.com/watch?v=oRt6ne_y0oE)

LaserOrigami processing: A pair of C-shaped cuts plus a connecting heating line creates an inverted U-shaped part thanks to gravity:


Please don't expect a polished write-up below. This is more of a collection of ideas and resources I've been sitting on for 2 years, and it's perhaps time to just publish it and watch what happens. If you end up using this to fold-up a smooth-side-out airplane wing or anything for that matter, please drop a comment and link to your stuff.

### Heating Techniques

#### ProtoPasta Electrically Conductive Composite PLA

This is the material used in the dual extrusion print above.

as per https://3d.nice-cdn.com/upload/file/TDS_Conductive_PLA_1.0.1.pdf :

How Conductive Is It?
- Volume resistivity of molded resin (not 3D Printed): 15 ohm-cm
- Volume resistivity of 3D printed parts along layers (x/y): 30 ohm-cm
- Volume resistivity of 3D printed parts against layers (z): 115 ohm-cm
- Resistance of a 10cm length of 1.75mm filament: 2-3kohm
- Resistance of a 10cm length of 2.85mm filament: 800-1200ohm

Hints:
- this needs a HV source to work.
- Vertical interconnects need to have x5 cross-section of the lengthwise ones.
- Ensure long continuous lines are printed. No hatch patters, just perimeters.
- make contact tabs that can be trimmed off. Electrodes can be made to bite into them, and will probably also melt a bit. For small parts, contacting with needles is appropriate (e.g. pressed into the sheet by inserting the needle through one side of a laundry clip)

#### Microwave Heating

Heating without linear conduction paths and terminals can be achieved through differences in RF absorption, similar to e.g. just printing in black and white / clear materials and putting the print under a high powered halogen lamp.

Experimentational - looking for suitable materials and recipes (dimensions, heating time etc.)

##### Iron Composite Filaments

Teck Yang Koh, Alok Sutradhar, "Untethered selectively actuated microwave 4D printing through ferromagnetic PLA" (2022)
https://doi.org/10.1016/j.addma.2022.102866

**High Density Iron-filled HTPLA (60 wt%)**
https://proto-pasta.com/products/high-density-iron-filled-metal-composite-htpla
SKU: HTPC1710-HFE
https://filamentworld.de/fact-sheets/ProtoPasta_HTPLA-Metall_Datenblatt_EN.pdf

"High Density Iron HTPLA Filament has 60wt% iron for 3D prints with 2x the magnetic force and 3x the temperature resistance (when heat treated) compared to Protopasta's original Iron PLA with 45wt% iron."


**ProtoPasta Composite Iron PLA (<30 wt% ?)**
https://proto-pasta.com/products/magnetic-iron-pla
SKU: FEP11705
https://3d.nice-cdn.com/upload/file/TDS_Iron_PLA_1.0.1.pdf

SEM cross-sectional images of iron-filled PLA

https://www.researchgate.net/publication/316057785_Thermal_properties_of_3-D_printed_polylactic_acid-metal_composites
Laureto, John & Tomasi, Julie & King, Julia & Pearce, Joshua. (2017). "Thermal properties of 3-D printed polylactic acid-metal composites." Progress in Additive Manufacturing. 2. 10.1007/s40964-017-0019-x.
Figure 5: SEM-BSE Image of Magnetic Iron PLA Cross-Section

"Ferromagnetic PLA is chosen for this study for a balance of good microwave absorptivity and low possibility of outgassing or generation of gas plasma [19]."

"The structures had been shown to be capable of specific local
deformation upon exposure to microwaves, only heating and actuating the programmed regions. Investigation of these structures show that we can control the timing, magnitude and location of the programmed deformation."

Own microwave absorption experiment (Protopasta Iron PLA):


After microwave heating, the dark gray filament is visibly hotter, but not sufficiently so.


##### Carbon Fiber Composite Filaments

"Drying" of filament gone wrong is an interesting pointer towards heatability.

Happy little accidents:

https://www.youtube.com/watch?v=jDmE-F72Suo&t=1m20s

Breiss, Hanadi & Assal, Aicha & Benzerga, Ratiba & Méjean, Chloé. (2020). "Long Carbon Fibers for Microwave Absorption: Effect of Fiber Length on Absorption Frequency Band." (2020) Micromachines. 11. 1081. 10.3390/mi11121081.

"This work presents lightweight epoxy foams loaded with very low weight percentages (≤0.5 wt.%) of carbon fibers (CFs) with different lengths (3 mm, 6 mm, and 12 mm) as broadband microwave absorbing materials for anechoic chamber application."

https://www.researchgate.net/publication/347400920_Long_Carbon_Fibers_for_Microwave_Absorption_Effect_of_Fiber_Length_on_Absorption_Frequency_Band

**Fiberon PA6-CF 20%**

"Inslogic Predried Fiberon PA6-CF Carbon Fibre Nylon Filament 1.75 mm, Black PA6-CF 0.25 kg Refill with 20% Carbon Fibre"


The 250g refill pack (from [amazon](https://www.amazon.de/dp/B0F7LDX8L9)) was the cheapest way to get 20% CF filament, although PA6 is the worst-case scenario for heating with its melting temperature around 223°C. The surface turned glossy, and there is some bubbling in localized regions. Very good at absorbing microwaves nonetheless.


## Bulk Parts With Conductive PLA

https://all3dp.com/2/conductive-filament-brands-compared/

https://www.filamentworld.de/shop/special-filament/conductive/3dxtech-abs-1-75-mm-esd-conductive-filament/

contacting for plating: https://www.youtube.com/watch?v=xOXaC-Jh70g



## Functional Structures

### Electrostatic adhesion plate

https://github.com/Jana-Marie/electrostatic-adhesion-plate

### Thermochromic paint covered display

3D print meandered line filling in 7 segment digits

### embedding electronic components

https://www.youtube.com/watch?v=pBztvEJJGwA

## Actuators

### amplified or flexural actuators combined with bistable compliant mechanisms

plastic expands like crazy when heated, so one can build motion-amplifying actuators, or flexural actuators and embed them into one big compliant mechanism

-> make it bistable and you can implement e.g. an electrically actuated, bistable valve

### inchworm drive actuators for antenna tuning

### bi-stable mechanisms with thermo-mechanical actuators

### annealing of compliant mechanism segments to extend life?

https://hackaday.io/project/25307-6-axis-micro-manipulator/log/61933-fatigue-design-in-pa-12-nylon

## Folding

Below is my first proof-of-principle model and 3D print from 2023:



add hooks, tie a rubber band through them to make the cube fold itself


https://www.creativemechanisms.com/blog/compliant-mechanisms.-part-3

array of strips to define bending rate -> airplane wings

### Locking mechanisms that would be bi-stable if not for the stiffness of the material

push-in locking mechanisms that need to be softened first, then solidify in place and are guaranteed to not pop back out.

### rigid origami


https://www.researchgate.net/figure/a-3D-object-post-deformed-by-heat-and-b-functional-objects-created-by-combining-3D_fig6_332747983

Image blow is by [Chris] as covered on
https://hackaday.com/2022/05/01/bend-your-prints-to-eliminate-supports/

thinking about combining rigid origami and compliant mechanisms to achieve stronger 3D printed compliant mechanisms...

https://www.semanticscholar.org/paper/Monolithic-2-DOF-fully-compliant-space-pointing-Merriam-Jones/e554d26d667622708ca45c658dc5f7eb2deb8754

Rigid segments with line connections that soften, get folded and finally freeze in place for optimally aligned layers without 5 axis printing

fold-into-shape compliant mechanisms in 3D, but printed as sheets

https://www.youtube.com/shorts/_l9J9H1169U

Real rigid origami with compliant hinges and solving material fatigue by offsetting:

https://www.patreon.com/posts/3d-printed-pack-146182558 (3D models for sale)

Matthew Lim's video presentation: https://www.youtube.com/watch?v=FNVBK7-h9Fs

Papers referenced:

- Yan Chen, Rui Peng, and Zhong You, "Origami of thick panels" (2015) https://www.science.org/doi/10.1126/science.aab2870
- Shadi Khazaaleh, Ravindra Masana, Mohammed F. Daqaq, "Functional, Durable, and Scalable Origami-Inspired Springs" (2021) https://arxiv.org/abs/2105.06769

### Fusion after folding

expose conductive filament at the surface and wire it up such that current flows through the contact points, creating localized heating right when it's being folded together

"might even allow parts to be plugged into each other, then fused to adhere

unless the conductive filament stops conducting becond Tg, or melting point"

#### PLA conductive filament: hot melting repair patch

### Torsion Actuator For Self-Assembly

How can flat sheets be made to fold into place?

## Blow forming

hollow objects with spiral or otherwise defined heating zones can be inflated to modify the shapes.

## line-heated vacuum forming or bulging

Contours on printed sheets can be heated and depressed into shape, much like vacuum forming.

## "Kneading"

Tool holders and fixtures need to conform to free-form surfaces which may be complex or require 3D scanning to individualize a fixture solution. Thus, no general print-and-forget solution could be offered. As an extension of rigid origami, heated folds and areas could be designed to crush / compress to conform to a surface.

Application example: holder for a cordless drill to align and retain it in a fixture, where flexible elements and zip ties won't cut it.

#### vs. Thermoforming

Single-material thermoforming demonstrated by \[Uncle Jessy\] : "I Printed This Flat Then Bent It Into 3D!"
"A very fine fance between heat and force"

https://www.youtube.com/watch?v=TsG89NgZJO8

-> mostly hard to control, entire object heated, probably better to handle with hot water.

## Printed Heating Elements

I tried something similar with a combination of a conductive PLA heating element and low-temperature melting hot glue. It didn't work as well as hoped, since the PLA overheated before the larger volume of glue got melty.

Source of the screen caps below: BigClive

Setup and result:



## HV sources

I used a 200V lab PSU for my experiments, and ended up adding contact tabs to the prints, mounting positions for screws and heat set inserts. It's best not to touch anything while it's energized. Maybe put the part on a silicone baking mat for processing, and cobble together needle probers that stab it where you need it to heat up.

There's a lot of spicy HV stuff available through the popular e-commerce sites... exercise common sense (and maybe use HV resistors for current limiting).


For reference, this is what a moment of 30V, 20 mA did:


ps.: I'll be damned if conductive PLA can also be selectively heated in a microwave without heating the rest. Anyone feel like trying?

## Relying on material thickness and hot water alone

(think "control experiment")


The results were ... nothing of that sort.

And here's the cube:

left: heated in hot water
right: selectively heated with high voltage applied to conductive path


Practical applications of selective heating in additively manufactured multimaterial structures could transfer into functional origami, establishing creases such that sheets can be pushed to drive the initiated folding to completion:

Yves Klett: "Technical Tessellations: Origami, Aerospace and Architecture" - MathArt Colloquium
https://www.youtube.com/watch?v=xh6UNYjjjUA

Further Exploration:
- Selective solvent softening of multimaterial prints that harden again after transformation without having to introduce heat via microwaves when the objects are large.