3D printing with composite materials. What to have in mind

It is becoming increasingly common to find filaments made of composite materials. These materials are formed by a plastic matrix and a filler of particles or fibers. The purpose of this filler can vary greatly, from enhancing the final mechanical properties of the material to improving its aesthetic appearance or adding a new property such as conductivity. Thus, we can find three types of composite materials:

Fiber-reinforced materials

These are materials whose goal is to enhance the overall mechanical properties of the matrix. The plastic matrix can be any 3D printing material while the most commonly used reinforcements are fiberglass, carbon fiber, and aramid fiber.

• Fiberglass: Provides greater resistance to tensile stresses. It has good flexibility and improves bending strength. It provides a higher working temperature to the final material.
• Carbon Fiber: Like fiberglass, it increases tensile and bending resistance, but it also provides greater stiffness.
• Aramid Fiber: Mainly known for its high impact and fatigue resistance.

Fiber-reinforced filaments are considered technical materials and are mainly intended for the production of high-performance functional components. In general, materials with loads between 10% and 20% can be found.

Image 1: Part printed with carbon fiber reinforced Nylon. Source: Fillamentum

The most common fiber-reinforced materials are those based on nylon, although it is increasingly common to find other types of matrices such as ABS, PLA, PC, or especially PETG.

Materials with aesthetically functional loads

These are materials loaded with various types of particles and fibers, whose main function is to alter the aesthetic finish of the base material. We can mainly find 4 types of loads:

• Wood fibers or particles: These are materials with a high load of vegetable particles or fibers whose function is to provide a finish similar to wood.

• Mineral or ceramic particles: Generally gypsum particles with different colorants. They are used to achieve finishes similar to ceramics, stone, or clay.

• Vegetable fibers: Mainly used with PLA. Their function is to provide a matte finish.

• Phosphorescent particles: The most commonly used material is strontium aluminate powder, which provides a characteristic green glow. It is used in "Glow" or glow-in-the-dark filaments.

Image 2: Toy car produced with PLA loaded with wood fibers. Source: Fillamentum

In general, this type of load is combined with a PLA matrix to maximize compatibility with all types of printers, as good mechanical behavior is not sought, but rather a specific aesthetic finish.

Materials with loads that provide new properties

Sometimes, the function of the loads is not to improve the properties of the matrix itself, but to provide a new physical property. The most common ones are conductivity through the use of graphene and magnetism through ferrite particles, although it is possible to find other more exotic ones such as electromagnetic shielding provided by boron carbide.

Video 1: Piece made with ferromagnetic filament. Source: Protopasta

These are less common materials developed for specific applications.

Materials with metallic and ceramic loads for sintering.

These are filaments with a high load of metallic or ceramic powder, intended for printing parts that will subsequently be processed by debinding and sintering treatments. In general, the matrix is composed of low-temperature materials based on PLA or waxes to facilitate debinding tasks, which can be thermal, chemical, or a combination of both.

How to print loaded filaments

Nozzle Diameter Selection

Some loaded filaments require the use of nozzles with diameters greater than 0.4. In general, manufacturers of loaded filaments include in the technical data sheet the recommended minimum nozzle size; however, if not specified, the following indications should be taken into account:

• Glass fiber: It is advisable to always use nozzles of at least 0.6 mm, because it usually includes large fibers.

• Carbon fiber: If it is specified that the filament uses short fiber, it is likely that a 0.4 mm nozzle can be used without the risk of clogging. In case it is not specified that it contains short fiber, it is recommended to start with a 0.6 mm nozzle and try using a 0.4 mm one when printing satisfactorily with the larger nozzle.

• Aramid fiber: It is recommended to start with a 0.6 mm nozzle and try using a 0.4 mm one when printing satisfactorily with the larger nozzle.

• Wood fibers or particles: It is advisable to always use nozzles of at least 0.6 mm, and in some cases even 0.8 mm.

• Mineral or ceramic particles: Except in cases where the load is very high, it is generally possible to print this type of filament with 0.4 mm nozzles.

• Vegetable fibers: It is recommended to start with a 0.6 mm nozzle and try using a 0.4 mm one when printing satisfactorily with the larger nozzle.

• Phosphorescent particles: In general, they can be printed with 0.4 mm nozzles.

• Particles with metallic or ceramic loads: There is usually quite a variability from one material to another and even among the same material from different suppliers. If the manufacturer does not specify a minimum size, it is advisable to always start with a 0.6 mm nozzle and try using a 0.4 mm one when printing satisfactorily with the larger nozzle. In some specific materials, it may be necessary to use 0.8 mm nozzles.

Image 3: Nozzles of different diameters. Source: E3D

Use of hardened nozzles and component wear.

It should be noted that all loaded filaments cause greater wear on the components of the hotend and the extruder, especially on the nozzle, heat break, extruder wheels, and PTFE tubes or inserts.

Some filaments are particularly abrasive, such as carbon fiber, aramid, and glass fiber filaments or metallic, ceramic, and phosphorescent particles. When using these filaments, it is advisable to use hardened nozzles.

Image 4: Comparison of nozzle wear for different materials. Source: 3DVerkstan

If these abrasive filaments are used regularly, it is advisable to use, in addition to hardened nozzles, heat breaks made of more resistant materials such as titanium and extruders with hardened steel wheels. In addition, these components should be periodically checked, along with PTFE tubes and inserts, and replaced when signs of wear are present.

Printing Speed and Temperature

Loaded filaments have higher viscosity than their unloaded counterparts, so it is advisable to use lower maximum printing speeds. It may also be necessary to use slightly higher printing temperatures to reduce viscosity when high printing speeds are used.

Base Adhesion and Warping

Loaded filaments generally undergo less shrinkage during cooling, making them less prone to warping. The higher the proportion of fibers or particles, the less the shrinkage.

On the other hand, loads also usually affect the adhesion of the material to the print bed, slightly reducing it. It is advisable to use adhesion solutions such as adhesives or lacquers when using this type of filament, especially those with a high percentage of load.

Filament Fragility

A general characteristic of filaments loaded with particles is their greater fragility, especially those with high load percentages or based on PLA. This is why it is very important to properly position the spool so that the path to the extruder is as straight and short as possible. Additionally, the use of direct extruders is advisable, although some of these filaments can also be printed on bowden printers. In the latter case, it is advisable to position the PTFE tubes so that they have the largest possible curvature radius, as well as to position the parts at the front of the print bed.

Image 5: Spool holder placed directly on the extruder to feed the filament straight. Source: Raise3D

Loaded filaments are a special category that includes very diverse materials, and generally require special printing configurations. This is why it is recommended to always consult all the information provided by the manufacturer and follow their printing recommendations.

This guide discusses concepts in a general way and does not focus on a particular 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.