Open vs Enclosed 3D Printers: Passive & Active Chamber Cooling Explained

All plastics, when extruded at high temperature, undergo a shrinkage during cooling which can be between 0.3 % and 4 %. This shrinkage can cause deformations, if the cooling is not smooth and homogeneous, giving rise to problems such as warping, delamination of layers or dimensional deformations of the part.

Material	% of contraction during cooling
PLA	0.3 - 0.5
PETG	0.2 - 1.0
Nylon 12	0.7 - 2.0
Nylon 6-6	0.7 - 3.0
ABS	0.7 - 1.6
ASA	0.4 - 0.7
PP	1.0 - 3.0
HIPS	0.2 - 0.8
PC/ABS	0.5 - 0.7
Fibre-reinforced nylon	0.5 - 1.0
PEEK	1.2 - 1.5
Fibre-reinforced PEEK	0.5 - 0.8
PVDF	2.0 - 4.0

Table 1. Percentage shrinkage of various plastics used in FFF 3D printing. Source: SpecialChem.com

To avoid this problem, the temperature around the part should ideally be slightly lower than the material's glass transition temperature (Tg) throughout the printing process, and should be slowly reduced to room temperature after printing.

Material	Tg (ºC)	Printing temperature (ºC)
PLA	40 - 60	190 - 215
PETG	75 - 85	220 - 260
Nylon 12	55 - 65	260 - 290
Nylon 6-6	75 - 85	255 - 280
ABS	90 -100	220 - 240
ASA	90 - 100	240 - 260
HIPS	80 - 90	210 - 240
PC/ABS	100 - 150	270 - 285
PEEK	140 -160	380 - 400
PEI	190 - 210	350 - 400

Table 2: Tg and printing temperature of various filaments. Source: Filament2print

Those materials that suffer low shrinkage rates (less than 0.5%) do not require heating the part environment, as the shrinkage effects are practically negligible, so they can be printed perfectly well on open 3D printers, even large parts. These materials are mainly PLA and most PETg filaments (but not other copolyesters such as PET or CPE), as well as their derivatives.

It is possible to print materials with higher shrinkage percentages on open printers, however this possibility is limited to small parts, so with this type of materials it is advisable to use closed printers or printers with an active heated chamber.

Image 1: An open 3D printer. Source: Prusa3D

Open printers are mainly recommended for printing PLA, PETg and flexible filaments.

Closed printers or printers with a passive heated chamber

Closed printers are those whose printing area is completely enclosed. Some manufacturers use the term passive heated chamber, as they tend to accumulate the heat generated by the printing platform.

The internal temperature that these printers can reach varies greatly from one printer to another depending on the material they are made of, their volume, the temperature of the printing platform, the quality of the insulation and the temperature of the room where they are located. In general, the best quality printers are capable of providing temperatures between 45°C and 65°C at best.

Although these temperatures are not very high, they are close to the Tg of materials such as Nylon, ABS or ASA, making them easier to print and allowing the production of larger parts. Although these types of printers substantially improve the printing of these types of materials, they can fail with large volume parts. These printers are recommended for printing small to medium sized parts in PETg, ABS, ASA, Nylon or HIPS.

Image 2: A 3D printer with a passive heated chamber. Source: Raise3D

In general, it is not advisable to use PLA in this type of printers when they are completely closed, as the heat generated can exceed the Tg of the filament, causing it to soften inside the hotend and cause a jam.

Closed printers with an active heated chamber

These are 3D printers capable of controlling the temperature inside the chamber. They are usually more complex and cost more than the previous ones. They also incorporate high temperature hotends (400 ºC - 500 ºC) and liquid cooling systems.

There are two types: high temperature and low temperature.

Low-temperature heated chamber

Low-temperature active heated chamber printers typically allow controlled maximum temperatures of between 80 ºC and 120 ºC. These printers are designed for the production of high quality, large ASA, ABS, Nylon or PC parts.

Image 3: A 3D printer with a low-temperature heated chamber. Source: 3ntr

Although these types of 3D printers are sometimes advertised as compatible with PEEK, they are not usually compatible with all types of PEEK, only with some low-temperature PEKK, and always limited to small parts.

These types of 3D printers are ideal for producing ABS, ASA, Nylon and PC parts that require good dimensional stability and low deformations, making them the best option when producing technical parts or functional components with these materials.

High temperature heated chamber

In general, they allow temperatures in the range of 160 ºC - 180 ºC to be controlled. These printers are specifically designed for the production of parts in PEEK, PEKK and PEI, so it is not common to use other types of materials. This equipment is expensive and requires specialized and trained personnel for its use.

Image 4: A 3D printer with a high temperature heated chamber. Source Dynamical3D

When selecting a type of printer, it is very important to determine beforehand what type of parts and materials will be used.

This guide discusses the concepts in a general way and does not focus on a specific make or model, although they may be mentioned at some point. There may be important differences in calibration or adjustment procedures between different makes and models, so it is recommended that the manufacturer's manual be consulted before reading this guide.