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Not all FDM (Fused Deposition Modelling) 3D printers are the same. Depending on the extrusion system they have, it can be a direct extrusion or bowden type printer. In general, there is a lot of ignorance on this subject. This does not mean that it is necessary to have a degree in engineering when printing in 3D, but it is convenient to have some basic notions about certain features of the printer, which are essential, as they will affect the choice of the machine itself and the material with which we want to print. Next we will distinguish the two extrusion modes that a 3D printer can have.
What is an extruder?
And first of all, let's see what an extruder is. An extruder is one of the most important parts of any 3D printer with FDM technology. It is the mechanism that is responsible for pushing the filament from the spool to the hotend to be melted. There are two extrusion systems, the direct system and the indirect or bowden type.
Let's see below what each of these drive systems and their types of extruders consist of.
There are two types of extruders:
- direct extruders
- bowden type extruders
This type of extruder is the most common in 3D printers, although in recent years this trend is being reversed. Its main feature is that the extruder, with all its components, is mounted all in one piece.
Direct extrusion consists of placing the motor that pushes the filament directly on the hotend. That is, in this drive system, both the extruder and the hotend would be joined in the moving head of the 3D printer without being separated by a tube. It is the ideal system for extruding flexible filament, since its advantage is that it pushes the filament close to the hotend and it is easier to calibrate it. In this way, a good control of the material retractions is achieved to obtain a better finish in the parts. In addition, and most importantly, it allows us to print flexible filament such as Filaflex.
On the other hand, the indirect extrusion or bowden type consists of removing the filament pusher motor from the moving parts and placing it in the structure of the printer. So that the filament does not pass directly from the motor to the hotend, as in direct extrusion, but with this technique the filament is guided to the hotend through a tube. This tube is usually made of PTFE (polytetrafluoroethylene, better known as Teflon) and usually has an internal diameter larger than that of the filament to compensate for manufacturing tolerances that the filament may have and to prevent jamming.
Bowden extrusion has the advantage of reducing the weight of the moving parts, which means being able to print at higher speeds. But it has the disadvantage of being a system susceptible to jamming and more difficult to control shrinkage. In addition, given the complexity of pushing a flexible filament through a tube, from the bowden to the hotend, it is very difficult to print with flexible filaments. The greater the flexibility of the material, the greater the probability of jamming in the tube.
That is why we know many myths about the impossibility of printing flexible filament in 3D printers with extruder and bowden tube. But there are multiple solutions that will allow us to print flexible and even very flexible materials on these machines, which we will see below.
Differences between direct extrusion and bowden extrusion
The following is a detailed description of the advantages and disadvantages of each type of extrusion.
- Allows printing with flexible filaments such as Filaflex.
- Possibility of printing with all types of materials.
- Compact and completely removable extruder.
- Easy access and manipulation to check malfunctions or clogging.
- Allows better control of shrinkage.
- Reduction of calibration problems.
- Difficulty of mobility in the X and Y axes due to the weight it adds (inertia).
BOWDEN TYPE EXTRUDER
- Less weight on the X and Y axes. The inertia is reduced and the printing speed can be higher improving the printing quality.
- Increased filament pulling power from the spool to the hotend.
- Limits possibilities to print with any material.
- Problems to print with flexible filaments of 1.75 mm due to the tube.
- Increased probability of malfunctions.
We hope we have been able to help you better understand the differences between the different types of extrusion on 3D printing machines so that you can better assess or understand how they work and what you need.