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I have a dual-extruder printer with a separate heating element for each head, thus able to combine materials in a single print job even if they don't share a single temperature range.

Now the question: When (outside of using expensive dedicated support material or doing multicolor prints for aesthetic reasons) is this actually useful?

Of common printable filaments (PLA, PETG, TPU, ABS, nylon):

  • Do some of these materials work well (which is to say, substantially better than just doing a single-material print with same-material supports) as breakaway supports for others?
  • Can some of these materials be dissolved in household solvents that don't harm others?
  • Do some of these materials adhere to each other strongly enough (and have sufficiently similar profiles in how they shrink on cooling) to reliably generate finished pieces comprising of both? (Especially relevant for anything+TPU, where one might want to generate a design with some soft or rubbery components).
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  • $\begingroup$ Of course you can only have one bed temperature. Switch materials during the print will probably be like starting a new first layer. $\endgroup$ – Perry Webb Aug 14 '19 at 9:30
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    $\begingroup$ @Perry I would hope the OP isn't going to switch materials in the middle of the first layer! So long as he doesn't, the bed temp can remain constant. $\endgroup$ – Carl Witthoft Aug 14 '19 at 13:08
  • $\begingroup$ To be fair, in the breakaway-support case, I could very well end up wanting to switch materials in the middle of the first layer, so bed temperature compatibility is an important consideration! Moreover, as I read the second half of @Perry's comment, it's advising that some of the concerns involved in getting a good first layer could be equally involved on getting a solid immediate-post-switch layer, making similar workarounds/adjustments (such as short-term overextrusion, temperature increase, or fan reduction) necessary; that's solid advice, and something I hadn't thought about before. $\endgroup$ – Charles Duffy Aug 15 '19 at 2:11
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The answers are

  1. yes

  2. yes

  3. probably

Which is to say, if you only want to use MaterialNumberTwo for disposable supports, then you should be fine. Presumably the slicer software is material-aware and adjusts the feed so the layer heights are the same for both materials. BUTbe careful that the support material isn't higher-temp than the object material, or supports which start from the object rather than the bed may cause local melting or distortion when the first layer is deposited on the cooler-melt material.

But if you want to try to intertwine two materials for the final product, then certainly bonding will be a major risk, as will shrinkage during cooling (not to mention the risk of melting the lower-temp material while depositing the higher-temp material on top of it!). If at all possible I'd recommend printing such parts separately and fitting them together post-print.

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  • $\begingroup$ For bonding it's probably best for the materials to have close to the same thermal coefficient of expansion. For supports it would be better for them to be as different as possible so that maybe the supports will release after cooling down the bed. $\endgroup$ – Perry Webb Aug 14 '19 at 20:23
  • $\begingroup$ I suppose this is what I deserve for asking if any members of a class exist, rather than for specific examples of same :) -- I appreciate the advice given; that said, I might end up doing some experiments looking for specific combinations that work in practice, and adding my own answer should that yield useful results. $\endgroup$ – Charles Duffy Aug 15 '19 at 2:04
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    $\begingroup$ @CharlesDuffy I'd imagine PETG + TPU should work well. Similar nozzle temperatures, similar bed temperatures. Only the thermal expansion coefficients seem to differ, and, for TPU, highly depend on hardness. $\endgroup$ – towe Aug 15 '19 at 14:34
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I have printed ABS on top of PLA and it has bonded well. It was simple, then "campaign"-style buttons with Prusament Galaxy Black on the bottom and HatchBox white ABS on top. There was no tendency to warp, as I would expect if the ABS were shrinking more than the PLA.

I expected this to not work, but I needed white on black and these were the filaments I had.

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