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Large scale, high speed, low resolution printing advice

Posted by Joburger 
Large scale, high speed, low resolution printing advice
November 06, 2017 05:12PM
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!
Re: Large scale, high speed, low resolution printing advice
November 06, 2017 07:13PM
Typically, systems become optimised at a "sweet spot" where several bottlenecks coincide. When you want to move away from that sweet spot (increased size and speed) you'll need to bypass those bottlenecks. An ad hoc process of resolving one bottleneck at a time will just expose another, and another, and another, and you may end up repeatedly changing the same item.

I'd suggest doing a bit of engineering; find out how much power you need to melt 0.5*0.5*100mm = 25mm^3 of PLA every second. Think about cooling systems (or better yet, heat recycling) to remove that amount of heat. Figure out how you're going to extrude 25mm^3 of material per second (about 2.5mm of 1.75mm filament, 1mm of 3mm filament); maybe a NEMA17 won't be powerful enough?

It sounds like your XYZ positioning isn't a limit (yet)... I assume it can move at 100mm/s? How fast can your extruder drive filament? How fast can your heater melt filament? Is your power supply up to this? How quickly does the filament cool enough to print the next layer?

Printing large volume layers (e.g. a 2mm nozzle) means you will have a generate a lot of heat to melt the filament, and then remove all that heat to solidify it again. Maybe have a look at how 1.75mm filament is produced; presumably they have the same issues to deal with.

Your large volume objects will presumably contain over a kg of material each, so you're going to have to deal with changing filament spools too. You may be better off skipping the filament part of the process and extruding directly from PLA (or whatever) beads to your finished product.Should be a lot cheaper than using filament too.

There may be mechanical issues to do with expansion and contraction of the material due to heating and cooling
Re: Large scale, high speed, low resolution printing advice
November 07, 2017 07:30AM
It would be nice to know what you identified as the problem when you try and print faster.
As Frank suggested its possible the limit is due to the hot end/extruder and not the nozzle.
If you can feed the filament fast enough it still needs to be in the hot end long enough to melt.
So you can open the diameter of the internals of the hot end to allow more material to sit there for longer - makes disassembly difficult and a lot of other modifications..
Or keep the same size and heat over a longer path - bit like stacking 2 heater blocks on top of each other. You would have to move or avoid using the PTFE tube. But you still need a good heat brake. In both cases oozing is likely to increase and as its PLA you probably can't have a lot of retraction.
Due to the faster heat lose to the filament you may need another heater. Bit of thought on this suggests it may be better to have the heaters stacked with a pre heater running lower power than the one at the nozzle so the PID control is on the one at the nozzle as that is the temperature you want controlled. If you just add another heater at the nozzle you wont get any more heat just 2 heaters at low power.
Normally the nozzle diameter needs to be lower than the filament diam to prevent it going straight through without melting.
Re: Large scale, high speed, low resolution printing advice
November 07, 2017 12:41PM
@frankvdh: You are right about the bottlenecks, indeed I am not sure what is exactly the main bottleneck in my system.

XYZ positioning is not the problem as I am able to move much faster, furthermore I am using this extruder and heating block. I also feel as if the extruder is not the problem at the moment because I can run it faster and it still works - however if I run it faster I do not think I am actually extruding material faster as well, maybe because I am pushing the heating block to the limit. Someone suggested me to look at the e3d volcano because apparently it can really push material and it also comes with a 1.2mm nozzle. When I am going to be printing a lot bigger warping will most definitely a problem, however because the objects will be more like tall towers I think it is less of an issue than when printing objects that are large in length and width.

@MCcarman: Here are a few different images of my prints. The first one is printed at 0.30mm layer thickness and 75 mm/s, the second one at 0.38mm layer thickness and 83 mm/s and the last one at 0.42mm layer thickness and 78 mm/s. This is all done using the smaller (0,5mm) nozzle however the problems of delamination you can see also occur at 0.6mm layers and 35 mm/s speed. When going too fast / layers too high I think they just don`t adhere properly to the previous layer, which creates gaps and then these gaps are even reinforced on the layer after that.

0.30mm / 75 mm/s

0.38mm / 83 mm/s

0.42mm / 78 mm/s

What you said about the hot end also makes me think of maybe switching to the Volcano and see how that works. Furthermore actually I am not even using a PID Controller, the heating system is very simple in that it just turns on when the temperature reaches 210 degrees and turns off with 230. The result is that there is of course quite a high temperature fluctuation however I do not feel as this is affecting my prints that much.
Re: Large scale, high speed, low resolution printing advice
November 08, 2017 07:42AM
Assuming 1.75mm diam filament it has to feed at 4.67mm/s, 6.55, 6.81 and for the 0.6mm height it was 3.74.
So tends to get worse with feed rate - may be the temperature issue. You may want to increase temperature with the feed rate.
0.6 layer height will be an issue as it just falls out the nozzle without any compression.
Re: Large scale, high speed, low resolution printing advice
December 12, 2017 05:56AM
i've made good (well, i'd say so) and strong prints with a 1mm nozzle. It's makes very fast printing with high layer heights possible. I do not remember exactly, but i think i used up to 1mm height with .8mm width which gave me the highest possible speed - using standard parts like the common 40w-cartridge etc..

Nothing for small parts, and it uses a whole lot of filament this way, but when i need something large (like the leg-extensions for the ikea-lack enclosure), i put in an inexpansive filament from china and it works very good and fast.
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