I think you have some wet filament. PETG-HF requires drying before printing. It definitely doesn’t need to be printed that slow to come out well.
If you’re going to be doing a lot of printing you will want to investigate a filament drier, you can go down a whole rabbit hole on those, I suggest SunLu S2 or S4.
With the Bambu brand filament the defaults work pretty well, so use that as a starting point. I usually use the ‘0.20mm standard’ profile, I see you have the ‘strength’ profile selected, that probably adds a few walls and infill percent, not a huge difference.
Depending on the size and fineness of details for the model in question you may benefit from a lower layer height profile or variable layer height.
If you require tuning from there you will want to calibrate your dry filament, PETG-HF can definitely benefit from this. Use the calibration tab in Bambu Studio to run flow dynamics and flow rate calibration.
From there it’s just about gaining experience, there are many issues that can occur most of which can be solved with a few settings tweaks that you will learn along the way or by studying the forums here.
Besides drying the filament, you may want to take care of the solid infill pattern as well as running through the calibrations.
While my main experience is with the old PETG Basic rather than the newer PETG HF variant, I expect it to still be more prone to curling/warping as well as increased nozzle adhesion when compared to PLA.
So try to avoid crossing surfaces and infills (go for a Monotonic line solid infill pattern).
While you have slowed down drastically for the top surface, I am not sure if that is actually needed or wise. Looking closely at the top surface, you do appear to have some overextrusion there, which is punished severely by PETG’s love for sticking to the nozzle. So it may be beneficial to dial in the flow more precisely and maybe lower it for the top surface to the calibrated value rather than the default “1”.
PETG HF is quite different from the former BBL PETG Basic. It is said to print much easier, but has a much lower heat deflection temp. The 40 - 60 mm/s does sound a bit low though, probably from pre-Bambu times or for overhang speeds. Nevertheless, for PETG Basic, I usually stay below 120 mm/s. For small features (<2mm) I also lower accelerations to 25% as the X1/P1 needs 2mm to get up to speed at maximum acceleration. Can’t speak for PETG HF yet though, sorry.
Following your advice :
1° I dried my filament
2° I calibrated the flux (I obtained 0.9879)
3° I calibrated the pressure in advance (I obtained 0.044).
With this settings my impressions are good (black PETG)
But I still have lines on the top surface though.
And on the other print (white PETG) there are small problems at the ends
Filaments are default Bambu PETG-HF settings except flow and k pressure adavance.
Is it possible to get a better result ?
What should I change?
To tweak for even better performance, you will probably nee to experiment a bit more.
Personally, I would advise not to use ironing with PETG.
However, you could try concentric or spiral top surface patterns. They may give a better, more uniform funish
Regarding those tiny areas in the white print, I would suggest trying to reduce accelerations to 25%. You may also see minor improvements by dropping those 120mm/s speeds to 100.
Finally, adaptive layer height works wonders on ramps.
At maximum acceleration, the printhead will need 2mm to get to the maximum default speed. So any feature below 2mm has a bit of a risk to not actually see any dynamic changes from slowing speeds. That is why for small features, reducing accelerations can give big improvements.
