Inside the printer’s head
When you first see an FFF printer you can be quite astonished how it kept pulling the filament in, heating it up, and laying down the molten plastic to become solid again. It kinda looked like magic, which is all happening inside a small part of the printer; the hot end.
A quality hot end is crucial for good prints, and it’s more complex than it might look at first glance. Its basic role is to lead the solid filament to the heated melt-zone and let the molten plastic ooze out from the nozzle. What makes this seemingly easy task difficult is that the filament mustn’t melt before the melt-zone, or else, it will expand and jam the printhead.
There are basically two types of hot ends; PEEK-based and all-metal.
PEEK is a superb, durable plastic used for its excellent thermal insulating properties. The filament comes in through a low-friction PTFE tube and is driven towards the melting zone, typically made of metal (aluminium or steel). To keep the heat from spreading back, a PEEK part keeps these two zones separated. PEEK can withstand temperatures up to about 250-260°C which fits most popular materials, like PLA and ABS.
An all-metal hot end can handle much more higher temperatures, which makes it suitable for printing with special types of filaments. But metal is a relatively good thermal conductor, therefore the upper part needs either an active, or a really good passive cooling to maintain the comfortable, low temperature of the incoming filament, and a stainless steel heat break has to be included that insulates the incoming tunnel from the heated melt-zone.