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I hear that heated beds can help with removing finished prints, but not all printers have them!

  • Is this a nice to have or must have feature?
  • Are there any downsides to heated beds?
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I'll try to give it a shot as the other answer (perfectly sound answer b.t.w.) does explain "how" we use heated beds, but not "why" they are actually needed for good prints.

Plastics or polymers are mostly amorphous (no macro crystalline structure) and usually relatively hard and brittle at low temperatures (this is referred to as "glassy"). By increasing the temperature of the plastics the state of the material changes as it becomes soft and more ductile (called the viscous or rubbery state). The temperature at which this transition takes place is called the "glass transition temperature". It is this temperature where you would heat your bed too (or close to this temperature). Below the glass temperature, the expansion is reduced/low because the polymer chains cannot move easily due to the closer packing and stronger inter-molecular forces; increasing the temperature increases the expansion lowering inter-molecular forces. The difference in stress between the bed and your print is therefore reduced (as of the expansion of the heated polymer).

This explains why we use heated bed to get the prints to stick to the bed. To answer your question why it helps in removing prints is that when the temperature is lowered, the polymer gets back into its "glassy" state, shrinks a bit and automatically loosens the print from the bed.

Indeed for printing PLA you can print without a heated bed, but for materials with a higher glass transition temperature and higher printing temperature it's almost a must to have. Downsides of heated beds are that they require a lot of power and when improperly installed lead to burned wires and connectors. It's usually wise to strain relief the wires from the bed and use proper gauge silicone leads and connectors.

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  • $\begingroup$ Overall a good answer, but this bit is inaccurate: "..as the internal stresses are lower because of the more viscous state of the material". There is no intrinsic "lower internal stresses" associated to the viscous state. The reason why the print sticks better is that there is not as much shrinkage from the moment the plastic is extruded as it would be with a cold bed. Internal stresses within the print are not due to the "state" of the plastic either, but to the differential of expansion between layers, if that is what you were referring to. :) $\endgroup$ – mac Apr 7 '18 at 1:38
  • $\begingroup$ @mac Indeed, not related to the state, I edited the answer. $\endgroup$ – 0scar Apr 7 '18 at 6:25
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It can help with bed adhesion. However, most 3D printing plastics will warp without a heated bed (since they shrink as they cool). ABS is notorious for this, although PLA is not so bad, and you can get away without a heated bed for small parts. ABS is so sensitive that you may need a heated (or at least draught-proof) enclosure, as well as a heated bed. If you are considering buying a 3D printer, it is best to get one with a heated bed, unless you are on a very restricted budget. If you buy a printer without a heated bed, you will soon realise that you need one.

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There is no simple answer. I will only cover the three main filaments: PLA, ABS, and PETG.

  • ABS:

    • ABS likes to warp, and dislikes breezes and temperature changes. so a heat bed is required, as is some way to keep breezes off and heat in (I use a plastic tarp over my printer).
    • Although there are print surfaces that will claim to stop the warp. but a print surface can not change the nature of the filament.
    • A heated bed is pretty much required for ABS
  • PLA:

    • PLA is currently the most popular filament, it has low warping tendencies and it likes breezes, and prints really easy.
    • PLA does not need a heated bed, but if the part is big it may peel off the print surface.
    • A heated bed is optional but will help with any warping you may encounter.
  • PETG:

    • PETG is described as combining the printability of PLA and the strength of ABS.
    • PETG is quite stringy and has a higher slightly chance of warping then PLA.
    • A heated bed is recommended, and will help keep it from warping.

Now, for print removal, a heated bed can help as well:

  • Most PLA prints, especially smaller ones will remove just fine without a heated bed,
  • Medium prints having a removal tool will get those off
  • A heated bed is really helpful for removing large prints or prints that won't release using other methods.
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