Types and materials in 3D Printing
Different types and materials in 3D Printing
3D printing empowers you to prototype and manufacture parts for a wide range of applications quickly and cost-effectively.
In various products we can see many different materials. Different materials enable you to create parts with the desired mechanical properties, functional characteristics or looks. But also they need different approaches for manufacturing. Different approaches, in turn, have specific limitations.
So, engineers, technicians and designers have to know the capabilities offered by different technologies.
3D Printing of plastics
Plastic materials are most widely used in the world. The majority of 3D Printers today are printing plastics and there are hundreds of plastic materials available for 3D printing, each with its unique proporties, that make them best to specific use cases.
To simplify the process of finding the material best suited for a given part or product, let’s first look at the main types of plastics and the different 3D printing processes.
There are the two main types of plastics:
Thermoplastics is the most commonly used type of plastic. The main feature that sets it apart from thermosets is their ability to go through numerous melt and solidification cycles. Thermoplastics can be heated and formed into the desired shape. The process cab be reversible which makes recycling or melting and reusing thermoplastics feasible. A common analogy for thermoplastics is butter, which can be melted, re-solidify, and melted again. With each melting cycle, the properties change slightly.
Thermosetting plastics (also referred to as thermosets) remain in a permanent solid state after curing. Polymers in thermosetting materials cross-link during the curing process that is induced by heat or light. Recycling thermosets or returning the material back into its original form is not possible. A thermosetting material is like cake dough- once baked into a cake it cannot be melted back into batter again.
Plastic 3D Printing Processes
The three most established plastic 3D printing processes today are the following:
- Fused deposition modelling (FDM)
Also known as fused filament fabrication (FFF), is the most widely used type of 3D printing at the consumer level. FDM 3D printers work by extruding thermoplastic filaments, such as PLA; ABS; Nylon; TPU or PLA through a heated nozzle, melting the material and applying the plastic layer by layer to a build platform. Each layer is laid down one at a time until the part is complete.
FDM is the most cheapest and is very well-suited for basic proof-of-concept models, as well as quick and low-cost prototyping of simple parts, such as parts that might typically be machined.
Consumer level FDM has the lowest resolution and accuracy when compared to other plastic 3D printing processes and is not the best option for printing complex designs or parts with intricate features. Higher-quality finishes may be obtained through chemical and mechanical polishing processes. Industrial FDM 3D printers use soluble supports to mitigate some of these issues and offer a wider range of engineering thermoplastics or even composites, but they also come at a steep price.
As the melted filament forms each layer, sometimes voids can remain between layers when they don’t adhere fully. This results makes them not watertight and so strong, which is important to consider when you are designing parts meant to bear load or resist pulling.
FDM printer starting price- is about 200 EUR! Filament 25 EUR!
Advantages of FDM:
Non-toxic, but some filaments like ABS produce toxic fumes. Usually it is environmentally safe process.
Wide range of colorful printing materials, not so expensive, and with high utilisation.
Low or moderate costs of equipment.
Low or moderate post-processing costs (support removal and surface finishing).
Best for medium-sized elements.
The porosity of the components is virtually zero.
High structural stability, chemical, water and temperature resistance properties of materials.
Rather big build volume comparing to other desktop technologies: 600 x 600 x 500 mm.
Disadvantages of FDM
Limited design options. Can’t produce thin walls, acute angles, sharp edges in vertical plane.
Printed models are weak in vertical build direction because of the layers in material.
Supports are needed.
Not very accurate, with the tolerance between 0.10 to 0.25 mm.
Tensile strength is approximately two-thirds of the same material that has been injection-moulded.
Difficult to control build chamber temperature, which is crucial for best results.
Problem of “stair-stepping” in vertical build plane.
- Stereolithography (SLA) 3D printers
Have become vastly popular for its ability to produce high-accuracy, isotropic, and watertight prototypes and end-user parts in a range of advanced materials with fine features and smooth surface finish.
Stereolithography was the world’s first 3D printing technology, which was invented in the early 1980s, and is still one of the most popular technologies for professionals.
SLA parts have the highest resolution and accuracy, the clearest details, and the smoothest surface finish of all plastic 3D printing technologies. Resin 3D printing is a great option for highly detailed prototypes requiring tight tolerances and smooth surfaces, such as molds, patterns, and functional parts. SLA parts can also be highly polished and/or painted after printing, resulting in client-ready parts with high-detailed finishes.
Parts printed using SLA 3D printing are generally isotropic—their strength is more or less consistent regardless of orientation because chemical bonds happen between each layer. This results in parts with predictable mechanical performance critical for applications like jigs and fixtures, end-use parts, and functional prototyping.
SLA printer starting price is about 1200 EUR, Resin - 30 EUR
Advantages of SLA
Excellent surface finish with layer thickness between 0.05 – 0.15 mm.
Finished parts can be painted.
Moderately fast.
Economical for low production (1-20) parts.
Disadvantages of SLA
Expensive materials.
Post-processing is not only required but also multithreaded, messy process. After the print is done, the resin needs to be washed in an ultrasonic bath or by dunking a part in IPA (isopropyl alcohol), then the supports must be removed and after that, the printouts needed to be cured with UV light.
The resin alone is toxic, but mixed with IPA is even more dangerous. The liquid should be secured and sent for disposal to a specialized company.
Waste material is not recyclable and is hard to manage
Supports are needed
Printouts are the weakest in vertical build direction due to anisotropy in material properties because of the additive layer method.
Laser needs to be calibrated periodically
The layer-thickness may vary in different resins
Photopolymers are toxic, as well as the fumes that are escaping during the process.
- Selective laser sintering (SLS) 3D printers
Selective Laser Sintering (SLS) is an additive manufacturing process that belongs to the Powder Bed Fusion family. In SLS 3D printing, a laser selectively sinters the particles of a polymer powder, fusing them together and building a part, layer by layer. The materials used in SLS are thermoplastic polymers that come in a granular form.
SLS 3D printing is trusted by engineers and manufacturers across different industries for its ability to produce strong, functional parts. Low cost per part high productivity and established materials make the technology ideal for a range of applications from rapid prototyping to small-batch, bridge, or custom manufacturing.
As the unfused powder supports the part during printing, there’s no need for dedicated support structures. This makes SLS ideal for complex geometries, including interior features, undercuts, thin walls, and negative features.
Just like SLA, SLS parts are also generally more isotropic than FDM parts. SLS parts have a slightly rough surface finish due to the powder particles, but almost no visible layer lines.
SLA printer starting price - about 5000 EUR, Powder - 50 EUR
Advantages of SLS
No support structures needed.
Movable parts with complicated inner geometry.
Smooth surfaces – it is hard to notice the layer.
Durable printouts.
Powder is reusable after printing.
Low to moderate material costs, while using the full working area.
Desktop SLS 3D printers are inexpensive compared to industrial machines.
Skilled labour is not required (only desktop SLS 3D printers).
Disadvantages of SLS
Industrial machines are expensive.
Long lead time.
Cleaning of the machine must be done precisely when changing material to avoid contamination.
Long printing time (for larger objects).
For a powder management during post-processing a vacuum cleaner and compressed air is recommended as it can get dusty.
3D Printing of metals
Printing of metal parts can revolutionize manufacturing in many industries.
However, there are many limitations in 3D printing of metals today. Different technologies can build parts with different properties. Users have to know the process specifics to select the most suitable technology and design the parts that could be printed.
Popular Metal 3D Printing Materials
Titanium - lightweight and has excellent mechanical characteristics. It is strong, hard and highly resistant to heat, oxidation, and acid.
Stainless steel - has high strength, high ductility, and is resistant to corrosion.
Aluminum - is a lightweight, durable, strong, and has good thermal properties.
Tool steel - is a hard, scratch-resistant material that you can use to print end-use tools and other high-strength parts..
Nickel alloys - have high tensile, creep and rupture strength and are heat and corrosion resistant.
The two most established metal 3D printing processes today are the following:
Metal FDM
Metal FDM printers work similarly to traditional FDM printers, but use extrude metal rods to held together by polymer binders. The finished parts are then post- processed. Usually parts are made out of more than 80% 316L stainless steel particles with a polymer base. After a part is printed, the polymer is removed from the part in the debinding process and the metal is further densified or compacted in the sintering step. In the sintering furnace, the part will shrink considerably but consistently.
Image source: https://bit.ly/3BxHCqM
Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS)
SLM and DMLS printers work similarly to plastic powder SLS printers, but instead of fusing polymer powders they fuse metal powder particles together layer by layer using a laser.
SLM and DMLS 3D printers can create strong, accurate, and complex metal products, making this process ideal for aerospace, automotive, and medical applications.
Image source: https://bit.ly/3Hz0PMx