TPU - clumpy areas

[Rpmaguire 0]

Im printing in TPU and there are parts that are clumping, that are exactly where the white "starts" (line type) are.

 

Are the "starts" where the nozzle physically starts for each layer?

 

and is there any way to minimize that clumping and stringyness. 

 

if you see in the photos some edges of the model without white parts printed perfectly so its not a mesh issue.

 

printed in ultimaker TPU95 @ 20mm/s speed, .100mm layer height

 

Thank you

Edited March 7 by Rpmaguire

[Slashee_the_Cow 438]

If you could share your Cura project file (.3mf, get it ready to print then go to File > Save Project) that would help as then we can see your print settings to see if anything stands out.

 

2 hours ago, Rpmaguire said:

Are the "starts" where the nozzle physically starts for each layer?

Not just each layer, after any travel move with retraction. If you turn on Travels in line type view you'll be able to see.

 

2 hours ago, Rpmaguire said:

printed in ultimaker TPU95 @ 20mm/s speed, .100mm layer height

What size nozzle are you using? A 0.1mm layer height can be hard to pull with the 0.4mm nozzle most printers come with, especially with TPU.

 

2 hours ago, Rpmaguire said:

if you see in the photos some edges of the model without white parts printed perfectly so its not a mesh issue.

I'd guess those are cases where it started and went a long distance, whereas the others, it might just be jumping from one to the next.

 

Some general tips for TPU (I've been printing a fair amount of it lately, because it's fun fun fun):

• Make sure it's dry: TPU is hygroscopic, meaning it absorbs moisture from the atmosphere (fun in an Australian summer when it's >90% humidity more days than not). The two common options are storing it in a bag with desiccant while you're not using it, or you could buy a filament dryer (more expensive than desiccant but still not very expensive, and my preferred method because it's a lot less hassle). If it has moisture in it then it's more likely to clump instead of string.
• Retract it to heck: Not knowing what printer you have I can't give you an exact recommendation. But on my Ender-3 V3 SE, which has a direct drive extruder, I retract PLA 0.8mm, PETG 2mm and TPU 3mm (all at 40mm/s), to give you an idea of relative distance. I've heard people with Bowden extruders having to retract 8mm for TPU.
• TPU is stringy, even in a best case scenario: You can tell this just by stretching out a bit of raw filament, it has elasticity. An extruder (direct drive or otherwise) can't grab onto it well enough to avoid strings because it will just pull on whatever's in the system.
• Take it slow: but you already have this one covered. If you haven't already, you should probably turn down your acceleration rate so that it flows along, rather than just starting with a small bit and zooming off with that, which will definitely pull on whatever you already have down.
• Cleanup is hard: If you have any support interface or anything left over on a model, it can be very hard to get rid of, since TPU is too soft to file or cut with a knife (you need a serrated blade and a careful hand, or else you'll just cut into your print). Strings will usually come off fairly easily but clumps not so much; I'd generally advise against trying to pull them off because there's a chance you'll pull the material that's supposed to be there with it.

Any advice for your specific situation? It's always hard to tell based on screenshots (and photos), but my main suggestions would be "make sure it's dry" and "turn on expert settings and play with the Z seam settings in the Walls category". Ideally you want to have as few starts as possible, and you want them to be in the least visible locations, but it doesn't look like there's anywhere for them to go for a lot of the height of your model. You can also try lowering Travel > Retraction Minimum Travel so that it will retract even for very short moves (and it looks like that outside "folds" of your model are fairly close together).

[Rpmaguire 0]

thanks slashee,

 

I have a ultimaker s5 with material station, should be dry from the material station.

 

the majority of it is printing perfect, just the starts. but maybe thats as good as it gets with TPU?

 

I am using a .4 nozzle, which would be better?

i do have a .6 CC

 

If you see the picture i attached.. you can see the far left edge is perfect

and the cura file has no starts on that edge.  

 

and the clumping does appear to only be where starts are located.

cura file.3mf

[Slashee_the_Cow 438]

Okay so looking through your settings there are several things which are making it overextrude (and a couple of other things), and that extra material has to go somewhere, right? ...into clumps, by the looks of it.

• Walls > Outer Wall Wipe Distance: Set to 0. This setting is designed to help hide seams in smooth walls (or corners less acute than these) by running slightly past the end without extruding, the idea being whatever's left in the nozzle will cover up the tiny gap you often get when starting. We want the nozzle to go straight from seam to seam, so turn this off.
• Material > Flow > Wall Flow: Try reducing to 100%. When it's higher than 100% it's extruding more material than it should have to for a wall. Normally this just makes your walls expand a bit, but we're trying to get rid of all excess material.
• Speed > Print Acceleration > Wall Acceleration: TPU needs to go slow, and not just when it comes to overall speed. Try moving off too fast and you'll just drag a bit still clinging on to the nozzle. Try lowering it 500mm/s².
• Speed > Print Acceleration > Travel Acceleration (after enabling Enable Travel Acceleration) Also try lowering this one to 500mm/s².
• Travel > Retraction Speed > Retraction Prime Speed: Usually you set this the same as the retract speed. You don't want an empty nozzle when you hit the end of a travel.
• Travel > Retraction Extra Prime Amount: This extrudes slightly more than you retracted, which is the last thing we want. Set it to 0.
• Travel > Z Hop When Retracted: Okay, this is more of a personal preference thing but in this case since it's moving almost exclusively outside the model it's just putting your Z motor through a bit of unnecessary work. But you can leave it on if you want.
• Cooling > Fan Speed > Regular Fan Speed: This should be at 100%. TPU isn't the quickest setting material in the world (and it's not very sensitive to temperature variation) so you want to help it set before you start moving around.

Hopefully those should help. The problem with printing TPU is due to how slow you have to print it, the anticipation to see if something I did is working kills me.

[Rpmaguire 0]

Wow! Thank you.

I honestly didn't even know of all those in depth settings.

Now I feel the need to do a deep dive through the documentation to get a feeling for it all.

 

I adjusted the recommended settings and i will post the results when completed.

[Slashee_the_Cow 438]

There's an awesome plugin called "Settings Guide" (just click Marketplace at the top right and search for it if necessary, but it's often at the top of the list). It brings up detailed explanations of what settings actually change and the effect they can have when you hover over a setting.