Large scale, high speed, low resolution 3D printing with custom printer

[Joburger]

Hi all, I`m 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 I`m 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!

[curious aardvark]

bear in mind that 3d printing is always a balance between material flow, temperature and cooling rate.

It also makes an awful lot of difference what pla you use.
The only ones I can use at 150mm/s and 0.4mm layer height, have so far been flashforge and cheapo clear filament I got on amazon - who's name currently escapes me.

So that being said, the biggest issue with printing with large beads is how fast you can cool it to set the bead before it starts to slump.
If you can cool the filament fast enough, then you can up your printing temp and print larger beads faster.

What is your current print area cooling setup ?

[Joburger]

I have noticed a huge difference between filaments indeed, before I was using PLA from Dutch Filaments and this gave me very bad results. Now I switched to higher quality PLA from Creamelt and it is already much better. Will check out the Flashforge as well!

I`m not sure why cooling would be the biggest issue though? Currently I am not cooling my print area at all, basically just printing directly onto a wooden plate. I do think a limiting factor in my current setup is the hot end of the extruder, probably this is too small to allow for faster extrusion. Actually I have also heard that in order to get better layer adhesion I would need to employ a heated chamber for the print. One suggestion was a semi enclosed heated volume to print into using the robotic arm so that when the print is done the model can cool evenly and during printing better layer adhesion would ensue.

[curious aardvark]

layer adhesion not an issue - but it's essential to have cooling on the area currently being printed.

You are extruding a cylindrical bead of plastic at between 200-220c (for pla) At this temperature the plastic is fairly fluid.
The slicer worked the printing out based on a perfectly cylindrical bead. The larger the bead the longer it will take to cool to a point where it stops being fluid and the more chance that it will slump and deform away from a perfect cylinder.
So the faster you can cool the plastic bead, the less it will slump and the rounder it will set. This will not only give you better prints with better layer adhesion but also allow you to print a larger bead hotter and thus faster. But you absolutely need fans or ducts blowing on the print area to set the extruded bead as fast as possible.

pretty sure you mount these on the end of the robot arm and run ducts to the nozzle.