Why is a 3D printer hot and not cold?

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Why does the 3D printer heat up? Wouldn’t the print melt? Shouldn’t it instead cool down so the print would freeze?

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It needs to get hot enough to melt the filament through a nozzle which lays it in place. The ambient air temperature is cool enough for it to solidify. The bed heats up so the freshly extruded filament can stick to it, but not nearly hot enough for it to melt.

There are many different kinds of 3d printers, and they all use different methods. I’m not familiar with them all but the kind I have SLA:

Works with a liquid resin that is kept at room temperature and exposed to UV light from a small screen that sits under the print surface.

It will heat some, but even after 8-10 hour prints I doubt it’s much more than a few degrees of temp.

I can’t speak of other kinds.

It needs to be both hot and cold at different points.

The bed needs to be warm, otherwise the print doesn’t stick to it and moves around.
The nozzle needs to be hot to melt the plastic so it can be squeezed out and formed.

The plastic that exited the nozzle and is now part of the printed part needs to cool, otherwise it deforms. That’s why 3D printers have a fan pointed directly at the exit of the nozzle.

The plastic that is going into the nozzle also needs to stay cool and solid so it can be pushed consistently. Printers have a second fan and a heat sink just on top of the nozzle to prevent the heat from the nozzle to creep up.

Different plastics also need different temperatures and cooling rates, otherwise they might not melt enough, or be too soft, or warp from cooling to fast.

The filament used to print is a solid plastic. The printer has to heat that up to melt it, and then place it down, and it uses the ambient air temperature to cool it back down so it can freeze again. If we wanted a 3D printer to use liquid water to 3D print out of ice, then it would be cold.