3d printing multiple objects at once vs single object 3D printing (one-by-one) - same strength?

I was curious, if there is any difference in strength (layer adhesion) between parts printed one at the time and those printed with other parts at the same time. Advantage of multi part 3D printing is that we have start printing only once, and printer will do the rest. There are 3 disadvantages to this method: risk, same color, stringing.
My checklist and risky factors mentioned in the video (edited according to suggestions in comment):
- small contact area
- too big overhang
- too big bridging
- tall, thin objects
- are supports added where needed
- check printing parameters

If you like my work, you could support me:

Test object used in the video can be downloaded from:

Contents:
0:00 Introduction
0:27 The theory
2:42 About layer adhesion
3:22 Preparing test specimens
4:32 Layer adhesion test
5:48 Results
5:59 Conclusions

#3dprinting

[MyTechFun]

OK, closer to solving the mistery (thx to comments), I have to figure out how to check this. Possible reasons:
- with multiple 3D printing extrusion stops (even retract 0.8 mm back to nozzle) and filament melts more in nozzle during the travel. And it stick to next layer better
- in prusa slicer "Slow down if layer printing time is below: 15 seconds", nut sure how can this make layer weaker, but this also may resulted the weaker adhesion with single printing.

[olafmarzocchi]

You are really testing all aspects of 3D printing no one else touched. Really well done!

[FluffieWolf]

Another thing that stands out is one of your multi had the same breaking point as the singles. Only one of your multi was printed in the center of the bed, like all the singles. Could the placement on the bed be causing this? EDIT: the multi that broke at 80 does look like the center one, you put a slightly longer 1st stroke on the M.

Hypothetically bed could be higher at the corners giving a better squish to each layer. Could be due to heat differences from center to corner or retraction etc etc. Could rule this out by marking the multi parts with a seperate number (0-4) and single parts with s in future test. Or by printing singles in the same points as multi (m0-m4) (s0-s4). Perhaps print s3 and s4 after the multi part print.

[diegovd]

I did not expect that. We need a specialist on FDM materials who would know about layer adhesion, cristalisation point (T°), cooling, time spent on the bed... and other factors I am not aware of.
Thank you for your time and effort !

[stephenwinslow]

The outcome you are seeing has to do with two different effects. One is surface tension and the other is plasticize flow. When the lower layer is still plasticize its surface tension will cause it to move out of the way of the new layer being placed on top rather than mixing with the top layer. In other words the lower layer will just squish down because of its semi-solid state rather than mixing with the upper layer because of the surface tension. Once the lower layer has cooled to a more solid state it will re-melt but because of its solid state it can't as readily move out of the way of the new layer material and will be forced to mix with the new layer being added on top.

[RubixBy]

My guess is if you look at the gcode preview your fan speed will be higher on the single printed object because the layer times are shorter. This would cause the reduced layer adhesion you're experiencing.

I would like to see your print settings and sliced gcode to confirm.

[ryanlandry]

Convection? I noticed there was 1 multi print that was similar to the singles and I'm guessing it was in the center of the bed. Also the 84 kg multi may have been next to the control panel and all the others were on the outside where bed convection brought in cool air. It's the same reason why you use walls to keep a steady temperature for materials that don't like having temperature differences. I would print the multi prints again and mark the bed location on each part. You could also print the singles on an outside corner of the bed to see if they are different. For extra credit you could look at the convection flow with a schlieren setup. 😉👍

[avejst]

Wow, not what I would have expected either
Thanks for sharing your experiences with all of us :-)

[NicksStuff]

With Octoprint, you can delete an element from the plate when it fails and keep printing the others. You may need a plugin, I can't remember

[dannyyang]

Very cool that you are doing these experiments! Not the result I was expecting either. Thank you for your efforts and sharing.

[billereses]

I'm happy both times that I didn't bet on the last two tests what the results would be! :-)

[federiconoble]

Thanks for sharing your knowledge and all these essays. They are very useful for people who are entering the world of 3d printing and obtain good results.

Gracias por compartir tu conocimiento y todos estos ensayos. son muy utiles para las personas que estamos entrando al mundo de la impresion 3d y obtener buenos resultados.

Saludos desde Argentina!

[moshumzy]

Once you know the answer to why the Multi was stronger, can you please make a follow-up video to explain these results?

[seangreenhalgh]

Just an idea what may be causing this is that if the plastic is molten and gives better adhesion with layers (single part) then it may create a single homologous solid which means that when the part cracks the crack will propagate throughout the part. This means a singe crack would break the whole part more easily. With the multiple parts the layers still adhere to each other but more like multiple strands of plastic. This would add to strength similar to how rope and carbon fibre work. It would add strength but also prevent a single crack from propagating throughout the whole part. Just an idea though 😜

[janetmorris]

This appears to be the resting time between layers allowing the previous layer to cure more prior to putting on the next layer, What was the cycle time between layers as it had to print the other 4 objects before the next layer is added on the 5th one. Would you have the same effect if you printed one at a very slow speed or a faster cooling fan speed. We are looking for the scientific answer. Any boffins out there.

[pablofr]

The difference is that in the single the layers are printed on hot layers, in the multi the layers are printed on cold layers.

[awilliams]

I generally print mono color copies as single prints because I get them faster. I never thought about strength. It's interesting though. For multi-color prints I print copies together. Color swaps are expensive both in using a massive amount of purge for the color change, but also you have to wait for the actual swap per layer. I can go from a print where nearly half the time is purge and half the material as well down to a lot less with relative amounts. The color change is essentially free for each additional object.

[brezovprut]

It would be great to see some desktop FDM manufacturers to implement budget laser technology (eg. LIDAR) for live 3D monitoring and detecting irregular layer paths that leads to issues (bird nest, warping, bad extrusion etc.) and automaticaly excluding part from printing, pausing whole print, or even more advanced - calculating live corrections.

[mikekb]

The multi part print has better layer adhesion because the layers have time to cool.
You have to think about that 3rd layer below your two working layers. On a single small part print it's still soft when the new layer goes down so it's getting moved and heated a little and compromised. It's like wiggling two objects you are trying to glue together.

[randomname]

Please try it with different material, this result is really interesting.