Does string trouble you a lot on 3D printing?
Today we are going to explain string.
Maybe it is incomplete but a big tip to avoid annoying trouble,offer the confidence for your printing business.
A common issue in FDM 3D printing is the so-called stringing effect, which leads to stringy or hairy parts, not smooth surface ,even full printing stuff ruins.
Usually, this is because when the nozzle is moved from A position to B position,the material is not completely cured,then the filament would hang out of the nozzle.
This artifact happens because of the sticky nature of the hot plastic. When the plastic is hot enough ,it becomes fluid and that enables it to be extruded through the nozzle.
However, the plastic is prone to stick to the model, and when extrud moving, it can leave a trace in the form of a plastic string. Just the same as the glue, pizzar with cheese, or any other viscous and sticky fluid.
PLA is a highly popular 3D printing filaments, when the printer nozzle is still moving with few filaments,there will be a small amount of melting PLA outflow because of its high fluidity.
Honestly,It's important to note that the degree of stringing is not the same for all different filaments material.
PETG and TPE/TPU filaments are more affected by this issue than PLA or ABS. This is due to the chemical and physical nature of those materials themselves.
PETG is more viscous and sticky than PLA. The extra stickiness make the stuff stronger aginst impact resistance but the disadvantage producing a worse stringing effect.
When our 3D printers are printing a model, sometimes the nozzle is extruding material while moving, but other times the nozzle is traveling from one region of the model to another without extruding. This is the time when the stringing happens.
The extruder stops pushing, but the melted plastic in the tip of the nozzle is in contact with some edge of the part, and when the print-head moves, a trail of plastic is left even despite the extruder is not pushing filament at all,you should be aware of it's hot nozzle.
Well,now we have two parts improve the issues:
1- Slicer-level actions.
2- Printer-level actions(Next Article).
I will start talking about the things we can do within the slicer because sometimes a little, fast tunning drive the problems go away.
However, if it still exist then I recommend following the printer-level actions. We no need to waste of our time and our money.
- Lower the temperature
If we were to give one single tip that would be to decrease printing temperature. In fact, high temp is the most common cause behind printing quality problems. This is also true when it comes to stringing.The temperature is higher, the melted plastic more likely leak down.
- Adjust retraction
Retraction plays an important role in FDM 3D printing.
There are some situations when the nozzle needs to move but we don't want filament to come out of the it. For example, if we print several parts at the same time, the nozzle needs to travel from part A to part B but we don't want to extrude plastic during this movement.
Unfortunatelly, it is not enough just stopping the extruder to prevent some melted plastic be out of the nozzle, because of gravity and momentum .
For that reason, FDM 3D printers use the retraction mechanic when we want to suddenly stop depositing material.
When retracting, the extruder pulls up the filament releasing some pressure inside the hot-end and finally preventing the unintended deposition of material.
The retraction movement is defined by 2 parameters, the retraction speed, and the retraction distance/size.
The optimal retraction distance and speed depends on several factors such as the material used, the printing temperature, the hot-end, and the extruder. So it's difficult to give general settings what work well for every user. The best way to run is to perform a retraction iterative test to find the properly settings in each case.
In any case, we can set the following retraction parameters.
ABS/PLA in Bowden printer: 4 mm & 40 mm/s
ABS/PLA in Direct extruder printer: 1.5 mm & 30 mm/s
PETG in Bowden printer: 3.5 mm & 30 mm/s
PETG in Direct extruder printer: 1.5 mm & 30 mm/s
Just try to increase the retraction distance by 1 mm each time to observe the improvement,note the difference between Bowden and Direct Extruder,becasue of the distance the driver and the hot nozzle is bigger on Bowden.
- Increase travel speed
We explained how the string happens during nozzle traveling without extrusion. Therefore, one way to reduce stringing is to increase speed of movement so the time filement of leak is shorter.
Normally, travel speed is limited by the firmware, so we can only choose a speed lower than that. Too high travel speed could lead to step loss and compromise quality due to vibrations.
The maximum traveling speed can be found using a retraction test.
In our SUNLU S8, we use a speed of 150 mm/s