# Large scale, fast 3D printing issues

Hi all, Im doing a project where I am attempting to 3D print large objects with a relatively simple geometry at high speeds. The idea is that the printed geometry will act as a mold for a final product and the objects I want to create will be about 0.2x0.2x1m (and preferably up to 1,5-2m in a later stage).

Because Im working at a scale like that and with simple geometry (extruded triangles, squares and circles without any infill, just the outline) surface quality/finish is not very important to me, however strength and proper layer adhesion is.

The material I am using is PLA, 1.75mm and instead of having a traditional 3D printer I have mounted a Flexion extruder on a robot arm. The advantages of this is that I am relatively unconstrained in size, however the drawback is I am more limited in the use of 3D print software etc. as I am custom controlling it using Rhino 3D and an Arduino independently. Also I am not using a heated bed.

I have been doing many tests to see what the maximum speed I can achieve is but this is where I am having issues. With my 0.5mm nozzle and a layer height of 0.38mm the maximum speed I can reach while still having a reasonable surface finish (only some minor layer delamination) is 75 mm/s. Beyond this speed or above this layer height the layer adhesion starts to become such a problem that the objects are not stable anymore. I also drilled out another nozzle with a 1mm drill to see if using a larger nozzle I could improve my printing speed. I hoped to be able to multiply my speed by about 1.5x because of the thicker layers I can use, however this is not really the case. With the 1mm nozzle (probably it is a bit bigger even, 1.1 or 1.2mm I can go up to a layer thickness of 0.7mm, however in order for the layers to properly stick together I also have to decrease the speed to about 30 mm/s. This means actually it is even slower than printing with a smaller nozzle because of the extremely reduced speed.

Ideally I would like to achieve a combination of a layer height of 0.5mm and a speed of 100 mm/s or a layer height of 1mm with a speed of 50 mm/s using a larger nozzle. Even faster would be even better but for now this is a reasonable aim. Do you have any ideas on how to achieve those rates? I was thinking of perhaps switching to 3mm filament so I could use a 2mm nozzle and greatly increase my layer thickness. However this would require me to remodel the entire tool mounted to my robot arm because the extruder I am using does not support the bigger filament. That`s why before making this decision I would like to be sure that it would improve my speeds.

What are your thoughts? Any advice on large scale, high speed, low resolution printing? Should I try other materials? Other types of tools? Any advice is greatly appreciated!

I have worked on a similar project, we were printing large items (y) 200 y mm x (z) 6 mm x (x) 2150 mm - layer adhesion and density was the most important criteria, (it had to be 100 % solid), followed by speed, surface finish was a very distant third. While the project has a number of difference with yours you may be interested with our results.

We found the nozzle diameter to be very critical and needs to matched to the speed. We ended up settling on a 0.8 mm nozzle, this way we could obtain the desired flow rate , any larger nozzle diameter it was harder to keep the extruded volume up to required temp between the time it left the nozzle and before it become part of the object (very small but critical time frame), We could not bump up temp due to exceeding the potential material breakdown point.

Layer height was 0.4 mm, the extruder head needs close enough to the base layer so the extruded material does not have time to slightly cool off. A larger distance then the more time it has to cool, and you need it hot - damn hot - for it to stick. However our project is much smaller than yours in the z direction

Another factor you have not mentioned was extrusion thickness , we used 0.5 mm, as for strength you not only not z layers adherence, but you need it to melt and adhere to the material in both the x and y directions.

As for speed, we actually designed a new type of extrusion system and we found that either 1.75 or 3 mm was capable to achieve desired speed rate with the above parameters so was not considered as critical…

That sounds interesting indeed! Do you have some images or other results of your project perhaps? I have done tests with a 0.8mm nozzle as well but found it to be less effective than my standard 0.5 nozzle but maybe I should finetune it more. Furthermore do you remember what speed you were operating at in the end?

Thanks for the information anyway!

Unfortunately I a not in a position do discuss the actual specifics of the project, however the printing process is outside the scope so I can discuss a little more on that.

The material we were printing with was completely different as it was various TPE’s with a shore hardness of 93A - (not very flexible -how ever much less friction than PLA or equivalent). We were printing at 100 mm / sec.

Like you we found to increase resolution slowed down printing and worse still we could not guarantee adherence quality, which was crucial.

So the compromise was set as posted.

You may have slightly different criteria and obviously different material so our variables may not be suitable, however it is a starting point to consider - look at your extrusion system as if you are relying on a hob gear type extruder you may wish to explore other options as we found that to be the weakest link in the printing work flow system.

As an aside your project sounds similar to the bigrep3D printer which I found recently (no affiliation) just thought I would mention it.