A heated bed helps greatly to avoid the warp problems and permits the print without using raft!
There had been some good results using ABS and PLA on it. Here are some links of tests made with results:
- The heated bed of NopHead;
- NopHead tests on ABS using heated bed - (Casainho follow the same steps and got the same results);
- NopHead tests on PLA, PCL and HDPE, using heated bed;
Some people already uses heated bed but there is no documentation and they looks like experimental. We started a discussion on forum with the goal to develop it, so after we can use the best ideas to implement and document it.
We should use kapton tape on top of the heated bed, since hot extruded plastic sticks very well to it and also it's easy to peel off the piece from it in the end of print, without damage the piece and the kapton tape.
The tested temperature values for the heated bed are 220ºC for ABS plastic and 55ºC for PLA plastic. Bed should be heated to that temperature values before starting printing and keep that values during printing. The first layer should be printed at a slower speed, like 3mm/s.
Heated bed can be build using a flat aluminium sheet of 6mm. It needs to be flat and be aluminium because it is a very good conductor, so the heat will be even across the whole bed with only a few heating elements.
Heated be should be insulated on bottom side, maybe using foam board. Also it should use insulating stand-offs.