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foehnsturm

Multi-material adventures #1 - rigid & flexible

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[media=11818]I expect multi-material printing to become a hot topic the next years (at least I hope so). If it's just about colors, other technologies show way more potential. In contrast, exploring the possibilities and limitations of multi-material printing is certainly worth it.

The actual printing hardware is only one part of the story. BCN3D made a promising step forward, there are other approaches as well and I'm using my tool changer ;)

But part design and slicing becomes really interesting and sometimes demanding.

I started to play with the soft & rigid combination, like PLA and Flexifil (or some other flexible filament). There's a multitude of possible use cases: varying surface quality (like with 2k injection molding -> tooth brushes), partly flexible parts, integrated sealings ...

But there are challenges as well. The most fundamental one: Thermoplastic Co-Polyesters like Flexifil don't really stick to PLA. So you have to take this into account when designing a part. Which I did not here:

stopper.thumb.jpg.d38fcb84f8620094ba8c1bd44700ae7e.jpg

stopper.thumb.jpg.d38fcb84f8620094ba8c1bd44700ae7e.jpg

Edited by Guest

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stopper.thumb.jpg.d38fcb84f8620094ba8c1bd44700ae7e.jpg

for some strange reason, the picture only shows up in the reply but not in the first post ...

OK, will be a serial then ;)

While the stopper works and looks quite nice I ended up with glueing the flex parts to the PLA ... multi-material printing was more or less useless as parts started to separate mid-print.

stopper.thumb.jpg.d38fcb84f8620094ba8c1bd44700ae7e.jpg

Edited by Guest

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stopper.thumb.jpg.d38fcb84f8620094ba8c1bd44700ae7e.jpg

for some strange reason, the picture only shows up in the reply but not in the first post ...

OK, will be a serial then ;)

While the stopper works and looks quite nice I ended up with glueing the flex parts to the PLA ... multi-material printing was more or less useless as parts started to separate mid-print.

 

Did you try to add like an overlap? So the flex is like merged into the PLA? Instead of layed against it.

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The toothbrushes use PP over moulded with TPE which are very chemically similar so they bond together well (PP is technically a rubber, just with a high shore hardness), so one way is to find materials that are chemically similar. I've always wondered why they don't make PP reels for the FDM's....anyone know?

The other way as above is to create a mechanical bond as shown above in the paint image, this kind of approach is used a lot in industry, over moulding rubber onto moulded plastic.

This subject is really interesting and gets more so i think when you start looking at conductive filaments so we can embed electronics into the print, whilst having them naturally insulated by the exterior plastic.

foehnstrum - i couldn't make out which machine you are using... are you using an UM or BCN3D?

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sandervg, thanks i also updated my profile a bit :), I'm using an UM2.

Yes, i meant in terms of filament.....seems strange why there is no PP available as the glass trans temp is lower than ABS. If we can get PP in filament then i think TPE should be possible then they should bond together well. Either way there is actually a lot of info out there about bonding of different plastics to rubbers, just google "overmolding rubber to abs/pp/etc...." most companies give you a nice chart. Could be something worth looking at for developing new materials for UM.

foehnstrum - maybe try and make the mechanical bond work in 2 planes to get a really solid interlock. The parts in your photo have the mech bond in 1 plane, if you can model it so it works in 2 planes then it will be fully interlocked. Its nice because the rubber can start acting as the support material for the PLA within the interlocks you form.

Edited by Guest

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This is a another idea of using 2 printheads: https://markforged.com/mark-two/

for making strong parts. Different approach, but interesting..

the first head is used as a normal fdm print, printing a base structure (in nylon) and leaving some open space for the next printhead: carbon fiber, fiber glass or kevlar. But this second printhead doesn't change the size of the filament, it uses the real diameter and just melts this one into the open spaces. This way the characteristics of carbon fiber keep their long/strong shape, the fibers are not 'chopped'.

Their (browser based) software calculates what the best place for the fiber filament is.

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A colleague of mine printed a box with some bolts embedded into the print using the pause feature, which I thought was cool.

But he then used Primalloy as a sealant for the box, similar to what you guys did.

Anyone tried that? Don't think he had a problem sticking it to PLA.

I'll try and get a picture uploaded tomorrow if I remember.

We also used some PLA Flex white to make an e-nable hand. It had a wrist fastening type thing, we used the PLA as a section of it, and then printed the top layer in PLA Flex which allowed the wrist band to bend. Again no issues with it sticking. So just reiterating what Sander said, maybe it's the particular filament you used.

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