Basics in Additive Manufacturing These are the most important 3D printing materials
With the increasing popularity and advancement of 3D printing, the need for specialised materials is growing accordingly. This article gives an overview of the most important plastics, metals and other materials used in 3D printing.
Today, a wide range of different 3D printing materials are used in the industry. In addition to plastics, metals are becoming increasingly popular. These metal materials are used in the field of additive manufacturing for the production of manufacturing tools (rapid tooling) or for final components (rapid manufacturing), among other things. However, most industrial and private users still use plastics for 3D printing. For a long time, 3D plastic printing was mainly used for the production of prototypes and models. Now, however, final components and entire products are increasingly being created by means of additively processed polymers.
In the shadow of polymer and metal materials, however, other 3D printing materials are also finding more and more new areas of application. These include sand, ceramics, glass and concrete. Sand materials are gaining more and more importance in the field of industrial mould making: many foundries now produce their moulds with the help of 3D sand printers. 3D concrete printing has also experienced rapid technical development in recent years. In 2020, for example, the first 3D-printed residential building in Germany was built out of concrete.
The most important plastics in 3D printing
The following materials are used:
- PLA (polylactide)
- ABS (acrylonitrile butadiene styrene)
- PEEK (Polyetheretherketone)
- HIPS (High Impact Polystyrene)
- PA (nylon/polyamide)
- PET (polyethylene terephthalate)
- PETG (PET with glycol)
PLA is one of the most popular 3D printing materials. It is a synthetic polymer, which belongs to the category of polyesters. Since PLA is obtained from regenerative sources, for example corn starch, it is biocompatible and recyclable.
Compared to other polymers such as ABS, PLA can be processed at a low melting temperature of only 70 °C. This makes the material interesting for amateur users as well. In addition, PLA usually remains dimensionally stable during the cooling process and there is little deformation. Both professional and private users also benefit from the fact that printable PLA is now available in a large number of colours. However, PLA cannot be used for highly stressed components because it cannot endure heavy loads and heat.
Besides PLA, other biodegradable polymers are being developed or are already available.
ABS (Acrylonitrile Butadiene Styrene)
Apart from PLA, ABS is one of the most widely used plastic materials in 3D printing. This synthetic polymer is made from acrylonitrile, 1.3 butadiene and styrene. Some of the biggest advantages of ABS are its rigidity, toughness and strength that can be achieved with it. Therefore, it is suitable for manufacturing both final products and prototyping.
However, its weather resistance is not particularly good, but still better than that of PLA. In addition, ABS is relatively cheap and available in many colours. Especially for amateur users, however, the material has a decisive disadvantage: ABS is printed at temperatures between 220 and 250 °C. Therefore, it is recommended to use a heated print room or print bed. This is the only way to ensure that the components can cool down in a controlled manner, which prevents deformation.
PEEK is a synthetic polymer from the group of polyether ethers. With it, it is possible to produce highly resilient components that are also temperature-resistant. It is also biocompatible and resistant to chemicals. PEEK is about 70 % lighter than metals with similar properties, yet it offers comparable thermal and mechanical stability. These properties make it a popular material in the automotive, chemical and aerospace industries. Since PEEK has a processing temperature of 360 to 380 °C, it is generally unsuitable for amateur users. This high temperature also requires a heated build chamber in which the parts can cool down in a controlled manner.
HIPS (High Impact Polystyrene)
This thermoplastic polymer is produced by polymerising polybutadiene into polysterol. HIPS possesses a very high hardness and impact strength, which distinguishes it from materials such as ABS. Probably the most important property of HIPS is its solubility in some chemicals, with limonene often being used in the industry. Because of this solubility, it is particularly suitable as a support material for other polymers. Since it is not removed mechanically but chemically, it is easier to meet strict tolerances for final components.
Nylon was originally developed as a substitute for silk. It has a high tensile strength, is non-toxic and melts at around 250 °C. The use of nylon in 3D printing is still relatively new. However, it is becoming increasingly popular because the printed objects it produces are tough and damage resistant. Because it is widely used in other industries, it is inexpensive and will not be damaged by most common chemicals.
Nylon requires higher temperatures of around 250 °C, which is more than many amateur printers can handle. It is also more difficult to get nylon to adhere to the print bed than ABS or PLA. It usually requires both a heated print bed and white glue to adhere during printing.
PET (polyethylene terephthalate)
Many people are familiar with PET in the form of beverage bottles. A major advantage of the material is that it is safe for contact with food and can be used for packaging. In addition, no vapours are produced during the melting process that would require a closed building chamber. Since no heated building chamber is necessary, PET is particularly popular with private 3D printing users. In addition, PET is relatively robust and remains flexible at the same time. It is therefore ideally suited for amateur users who print gadgets or everyday items.
PETG (PET with glycol)
PETG is PET modified with glycol. This modification allows a high transparency of the material to be achieved. In addition, the printing properties are improved by the addition of glycol. Thus, a lower melting temperature as well as less crystallisation can be achieved. In addition, PETG can be extruded more quickly due to its lower viscosity (toughness) compared to PET. Since PETG is weather-resistant, it is often used for vases or garden furniture and equipment.
The most important metals used in 3D printing
The following metals are used:
- Stainless steel
Aluminium alloys combine good strength and thermal properties with low weight and flexible finishing options. For these reasons, this material is widely used in the automotive and aerospace industries. Applications include housings, air ducts, engine parts, production tools and moulds, both for prototypes and final components. Porsche and Mahle are demonstrating the material's performance: additively manufactured high-performance aluminium pistons are being used for the first time in this Porsche 911 GT2 RS. With 730 hp, it is one of the most powerful vehicles Porsche has ever built.
Titanium is one of the best known alloys in metal 3D printing. It combines excellent mechanical properties with a very low specific weight. This material is corrosion resistant and is used in a variety of demanding technical environments such as aerospace. Applications include functional prototypes, solid end-use parts, medical devices and spare parts.
Stainless steel alloys are low in carbon and extremely corrosion resistant. In addition, stainless steel components offer excellent strength. 3D printed stainless steel also has high ductility and good thermal properties. Stainless steel can be used for food-safe applications, machine components and production tools. Other applications include piping, durable prototypes, spare parts, medical instruments and wearables.
Further 3D printing materials
The following materials are used:
In principle, ceramics are suitable as a 3D printing material because they can be processed in a liquid state into virtually any geometry and shape. By now, 3D printing technology using ceramics can produce 3D printed objects without large pores or cracks. Ceramic components feature high strength, durability as well as fire resistance. Today, ceramic 3D printing materials are used in the dental and aerospace industries. The main application is for dental implants.
Additive manufacturing of sand cores and moulds has attracted the attention of many foundries in recent years because the process has the unique ability to form cores that would not be possible using conventional core-making techniques. This is done by a process known as 'binder jetting': A reactive resin, usually a furfuryl alcohol (FA) based binder formulated for the application, is applied to a substrate. Typically, the substrate is a quartz sand that has been pre-treated with an acid catalyst, but it can also be a range of other aggregates used in metal casting, such as zircon and synthetic ceramics. In this way, a mould is created layer by layer.
Core and mould making with sand has some distinct advantages: The part complexity of a casting can be much greater than in typical sand casting, as the need for distortion and parting lines is greatly reduced; more complex moulds can be created; multiple cores can be combined into one; and several different core geometries can be combined in the modular volume.
3D printing with concrete works similarly to filament 3D printing. However, instead of a spool of filament, concrete is extruded. In theory, standard concrete or mortar can be used. For larger building projects, however, it is better to use materials specially developed for 3D concrete printing. For the construction of the first 3D-printed houses, for example, I.Tech3D from Heidelberg Cement was used. This is a ready-to-use dry mortar that has been optimised for 3D printing. The material contains mineral components and additives that should enable it to be easily pumped to the print head while remaining dimensionally stable after extrusion.
Making glass objects using a 3D printing process is not easy. Only a few research groups worldwide have attempted to produce glass using additive processes. Some of them created objects by printing molten glass. This has the disadvantage of requiring very high temperatures and heat-resistant equipment. Others used powdered ceramic particles that could be printed at room temperature and are later sintered into glass. However, the complexity of the objects made from them has been rather low until now.
Researchers at ETH Zurich succeeded in 2019 in developing a special resin that can be processed on commercially available SLA printers. SLA printing makes it possible to produce highly complex and fine structures. After a part has cured, it is baked at two different temperatures. This eventually condenses the objects into glass.
Composites for the high performance industry
Composites with exceptional versatility, light weight and tailored properties are often used in high performance industries. Examples of composites are carbon fibre reinforced polymer composites and glass fibre reinforced polymer composites. Carbon fibre reinforced polymer composite structures are used in the aerospace industry due to their high specific rigidity, strength, good corrosion resistance and favourable fatigue behaviour. At the same time, glass fibre-reinforced polymer composites are widely used for various applications in 3D printing and have great application potential due to their cost efficiency and performance. These materials feature high thermal conductivity and a relatively low coefficient of thermal expansion. In addition, glass fibres cannot burn and are not affected by curing temperatures in manufacturing processes, making them very suitable for use in 3D printing applications.
This article was first published on Mission Additive