Welcome to 3DPrinterChat.com, this article is part of the DIY 3D Printer from scratch, and you will learn a bit more about how the Heated bed works.
What is a heated bed and how it works?
The heated bed is a device that should provide a warm surface to the plastic stick, heated-beds have a huge advantage against warping and other adhesion issues when compared to cold beds. The heated bed have the heating element and the surface material, that can be glass, aluminium or the heating element itself.
The heating element works by converting electrical energy into heat, this happens when electric current flows through an resistance or non-ideal electronic, the amount of energy converted into heat is measured in watts. for example, an ordinary heated bed produces about 80W of heat.
There are two main kinds of heated beds, the printed circuit board and the resistor bank, since the resistor bank is not used due its disadvantages, we wont cover it, but here is a image of how it looks.
How a PCB Heated bed works
The heated bed is made using the printed circuit board concept, which is basically a board (which is usually made of glass or fenolite) with a thin layer of copper on one side (or even multiple layers), then this board is printed or treated in a way that will protect some lines of copper, and leave the rest exposed, then this copper will receive a treatment with acid to remove the parts not protected, this process will leave us with only the useful circuits and connections,
Those tiny lines of copper will behave like an resistor (remember that everything in the universe poses some resistance to electrical flow, and this resistance is dissipated as heat), When we connect those “wires” to a power supply will we will generate heat, exactly what we were expecting.
The PCB has the great advantage of using a small amount of space when compared to other kinds of heating elements, it also can contain multiple layers, which will increase the power/cm² dissipated dramatically.
If properly designed, the printed circuit board is capable of distributing the heat more efficiently than any other kind of heated bed, since the power distribution can be drawn and simulated.
Heat distribution and why it matters
See these two examples below:
As you can probably guess, a deficient heat distribution is bad, but why is it bad? For materials with high “warping rate”, or technically speaking: with high contraction propensity. These temperature differences will create opposite forces (contraction and expansion), that will force the material to bend, see the image below:
On the first example, we have a cold bed, you can see the red area which the nozzle has just passed by, and the heat it leaves behind, this is likely to cause warping. On the second example, with the heated bed, we can see that the printed part is also hot, this will reduce the contraction and expansion forces because the temperature difference is lower (ΔT), this part is not likely to have issues with warping.
Now that you understood why a proper bed heat distribution matters, i’ll take as example the famous MK2 Heated bed
RepRap MK2 | $14 – 18
The MK2 Heated bed is by far the most used heated bed on the DIY community, it is an printed circuit board heated bed, which has the advantage of being capable of handling 12 or 24v just by changing the wires position.
Bed dimensions: 200×200 mm (heated area)
The Mk2 is a good and cheap bed, for lower temperatures the heat distribution is fair, but is good to mention, if you will print something with the maximum allowed size (200×200) on a material that can be printed with 60ºC (like PLA) the warping propensity is smaller than a material that needs 110º (like ABS).
Improving my current bed
If you don’t want to replace your current heated-bed, there are some workarounds, like adding a glass on the top of the heating element, 3-5mm gives the best result. (keep in mind that this will slow down the heating process, but it also will makes the temperature distribution better)
Example image of a MK2 with 4mm glass. source
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