So you have a spool of PLA filament that states 180°C to 220°C.
That means you can print using 180°C, right?
Wrong!
You may be able to print with a 180°C nozzle temperature, but this may even result in under extrusion due to extruder skipping and even clogging.
The temperature range specified on the spool describes the range where the filament is melted and able to be extruded without causing clogging.
So why can´t you print always successfully at 180°C?
In a perfect world this would work. The hotend is always 180°C, the filament gets molten and extruded properly and the print result is perfect.
Unfortunately this isn´t the universe where everything turns out perfect.
First: Your heater is constantly loosing temperature to the surrounding air. Yes, you can add a silicone sock or tape the heater block with thermal resistant tape (which works IMHO better than a sock), but this only makes your hotend a little more efficient. It still looses energy along the heat pipe (hence the extruder fan to prevent heat creep).
Second: Heat is transferred to the filament within the heater block, which is not a loss in general, but a loss to the overall temperature of the heater block.
“But I have a 24V heater, which is better than a 12V version.”, you may say. Well, yes. A 24V system is more efficient and also can produce the same amount of heat faster than a 12V version, but it still is not instant.
Third: The sensor is not where the filament is. It should be as close to the filament chamber as possible and as far as possible away from the heater cartridge, which is not always the case and even possible. So the sensor values are lower or higher than the actual temperature inside the chamber where the filament is. Usually the sensor detects a higher temperature. So the filament may be a little colder than shown on your printer display.
So while printing the temperature within the heater block is constantly going up and down while printing. This depends on the print itself. If you print a bottom or top layer, it is lower, because more filament is constantly going through the heater block. When printing other sections like pillars, there is a lot of travel involved, where the filament inside the chamber gets and keeps the heat, causing the heater to switch off. And there is the first issue with using the lowest temperature. You may end up, printing below the specified lower example temperature of 180°C.
Usually you get away with this, but there is another value that hits the equation: Print speed!
When printing faster, more filament goes through the print head and therefor the heater. More heat is drained per second and the heater needs to compensate. Again a 24V system has a small advantage here, as it can push more energy in to compensate, but this can have a side effect, as after a section of continuously fast print lines there may be a travel and the print temperature may overshoot. So going by default to the maximum print temperature (in this exampled 220°C) is not a good idea, while e.g. 215°C, may be fine. Usually the drop is bigger than the overshoot (while printing, not during initial heating) Also the sensor issue mentioned above of detecting the temperature higher than it actually is, is helping here.
Sure, you can print temperature towers and find the perfect spot here, but in my opinion this does not reflect real world printing situations ether as there are no longer extrusion phases and also no longer travels. As well as the use calibration cubes I don´t see much benefit in these. Sure they give you a rough and easy value to use, but in the end they only reflect one print speed. Just like a calibration cube must not be used for calibration, as you calibrate against slicer settings and filament and not against the actual hardware.
If you check the results of those test tower prints you may notice that they are all more or less in the middle of what is printed on the spool. Usually a little at the upper end. If you e.g. insulate your heater block, the results are different as they represent the current hardware and filament situation and not a specific filament property alone.
Printing in that range prevents from getting to low temperature wise, when when increasing the print speed and fluctuations in temperature are always inside the filament specifications.
I personally just take the middle and add a few degrees to that and do not waste filament on towers. Done.
If you want to save energy and therefor keep the temperature down, I must say: That is not gonna work.
If you want to print faster, you need to increase the temperature as the heater will cool much faster as the filament is passing through. You even can go higher than the max temperature on the spool, but keep in mind that long travel moves, may push your filament into non specified temperature areas. Consider this a risk. Swapping to 24V or some volcano style hotend may a valid choice here. As long as you print around 60-90mm/s you should be fine, with going close to the max temperature of your filament.
Every failed print is a multi level energy lost and the only way to compensate clogging or bad looking prints at low temperature is to reduce the print speed, but then you print longer, which needs to keep the heating on longer. Especially the heated bed is eating up the earning here, where all the empty space is heating the room/chamber.
Setting up the PID values for your printer properly is probably the best way to keep the temperature as close to the desired temperature and to same the maximum amount of energy.
As always: This is just my personal opinion based on my printing experience.
PS: when talking about the “normal” print speed, I mean 55-60mm/s, which is usually the default. For TPU this is 25-30mm/s.
