Too much part cooling? PLA



  • Hello,
    I wanted to know if there are situations where printing PLA (except 1st layer) requires to not be 100% fan speed. I heard of people saying it could blow the filament away, or produce strings. These are all visual signs, so I can turn down my fan settings if I see them. But what about structural strength, print quality, etc? Are there any other effects from too much part cooling?

    I print at 120mm/s. Only PLA.

    People always talk about how cooling is very important for PLA.
    I have some ideas that I wanted to try.

    200mm fan at slow settings to suck away the hot air that the bed produces. Unheated ambient air would always be entering the box. This would reduce the heat creep from the bed on the first few millimeters of my print and create a consistent environment.

    I use 2 high static pressure fans instead of 1 to really create a good cooling.


    What temperature should PLA be when the nozzle wants to print over it? Example: under 55C so the PLA is fully hardened and when the nozzle extrudes over it, it will not compress or wobble from being soft.



  • @likevvii You just have to experiment and find what works well for you. It's not just about the volume of air but also how it is directed onto the filament. Layer time has an effect too. So for small parts you'll likely need more cooling because there is less time between layers than for larger parts. The volume of molten filament also plays a role. So a large nozzle with course layer height and width will a need a lot more cooling than a small nozzle with low layer height and narrower width. And if the part cooling fan blows air directly onto the nozzle tip, this can lead to a sudden drop in temperature which the firmware interprets as a heater fault. This can happen more at the start of a print when the nozzle in susceptible to cooling air being deflected off the build surface. So staged increases in the fan speed over a few layers can help.



  • I think it is best to have minium of cooling. The less you cool the parts, the stronger they are, as the layers fused better. A lot of areas can be printed without cooling, as long as they have no sharp corners or small perimeters (it could be nice to have a parameter to modulate the fan speed depending on the direction change of the nozzle; so, in straight lines, the fan stays at very minimum).

    I use a berd air pump, which pushes air through 3 little tubes (2mm inside diamter), oriented just below the nozzle, so they cool the filament as soon as it goes out, without cooling the nozzle. On the other hand, I don't print that fast (the melt zone of my hotend is too cshort).

    BTW, blowing air at higher temperature than ambiant should be better. For example, Stratasys machines maintain the chamber at 100°C, and the (big) fans take this hot air and push it onto the nozzle. As they use 300W or so cartrigdes, they donc have heater fault problems 😉 For PLA, I would try to heat the cooling air to 50°C.



  • @fma
    What kind of pump are you using?
    pressure? airflow?
    How does it work out for you?
    What materials do tou print?

    Thanks
    Denes.



  • I use this one: https://fr.aliexpress.com/item/32821282878.html

    I print mostly PLA, and it works great.



  • I second @fma i use the same one with a cooling jet pointing just below the nozzle



  • There absolutely could be to much cooling with pla. With the RailCore printers stock fan, pla speeds should be between 15-30% at 60mm/sec. Anything above that causes issues that present similar to pressure advance tuning issues or z axis issues.

    We went with a fan with high output because the RailCore are great at printing high detail at 120mm/sec at 0.02mm layer height. We had to account for most people printing at that speed or higher which is why we went overkill. Before that we were used to 100% for pla.



  • @projectR3D said in Too much part cooling? PLA:

    There absolutely could be to much cooling with pla. With the RailCore printers stock fan, pla speeds should be between 15-30% at 60mm/sec. Anything above that causes issues that present similar to pressure advance tuning issues or z axis issues.

    We went with a fan with high output because the RailCore are great at printing high detail at 120mm/sec at 0.02mm layer height. We had to account for most people printing at that speed or higher which is why we went overkill. Before that we were used to 100% for pla.

    Thanks for the explanation. The reason why I created this topic was because I watched the railcore video and heard that 30% fan speed was mentioned. May I have some more information on exactly what happened during your testing of pressure advance tuning, etc for you to decide on a 30% or 60% fan speed? Other than reduced layer bond strength, I still can't understand how it could affect pressure advance and other settings.



  • @likevvii said in Too much part cooling? PLA:

    I still can't understand how it could affect pressure advance and other settings.

    Duration of viscosity.



  • @projectR3D said in Too much part cooling? PLA:

    Anything above that causes issues that present similar to pressure advance tuning issues or z axis issues.

    Can you be more specific?

    I will test minimising fan speed. But can't get on that for a few days.


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