The Importance/Need for a Heated Bed in an FDM/FFF based 3D Printer
Heated Beds In 3D Printers
Heated beds are used to avoid print failures due to a change in the ambient temperature of 3D printed material.
Generally, PLA material is less likely to warp during the printing time and don’t require a heated bed but materials like ABS and other petroleum-based materials need a specified ambient temperature to stick to the bed, avoid warping and not crack in between layers.
Heat-beds have two main purposes
Increasing the surface energy of the print bed for improving the bonding strength of the first layer (particularly important when we are using surfaces like PEI or Kapton)
Keep the bottom a few millimetres of the print hot enough to provide a warp-free foundation for the rest of the print.
The bit about surface energy is straightforward.
Most of the materials are easy to stick when they are hotter compared to when they are cold. In comparison, pure mechanical-bonding bed surfaces like fibrous painter's tape and perfboard don't particularly benefit from bed heat.
Warp is a common defect caused by plastic on the edges of the part cooling down at an uneven rate when compared to the plastic inside of the part.
The basic cause of warping is when the previous layer is allowed to cool and thermally contract before the next layer is deposited. When you stick hot, expanded material on top of cold, contracted material, large shear stresses are generated as a result of fresh material cooling and contracting.
Those inter-layer shear stresses then accumulate over many layers into large-scale bending stresses that try to lift the edges of the print off the bed, the result is that corners warp up and deform your model.
The extruder heats up the filament as it extrudes and pumps a bit more heat into the print as it deposits another layer of molten plastic and even radiates a little bit of heat. So in order to avoid the defects as discussed above we need to set the heat-bed temperature a little below the glass point to ensure the print is able to cool solid.
We face an issue here because everyone has a different print bed temperature sensor. What matters is bed surface temp. So in order to avoid this issue most of them have to set their bed temperature quite a bit higher than the actual surface temperature. It is just something that you have to calibrate with print results. The blend is also depended on the exact filament glass point (Tg).
These rules don't work for Nylon as it is a semi-crystalline, which means it "freezes" far above its glass point(Tg) and thus starts accumulating warping stress at fairly high temperatures.
Along with heated beds as some materials do require a closed chamber to avoid sudden cooling and warping during the print, ABS and Polycarbonate need a controlled environment for print to be successful.