Here is an article written by our engineering team that will guide you on how to make the most out of your design experience. We hope to give you a succinct yet complete depiction of the different kinds of 3D Printing technologies available. This would help you optimize your design to ensure that they can perform the intended role best!
To someone who hasn’t seen a 3D printer, seeing one for the first time is absolutely magical! The ability to create a physical part you’ve designed out of a roll of filament or a bottle of resin, seems like science fiction. In layman terms, 3D printing refers to constructing a 3D part of a digital design. There are many ways to 3D ‘print’ something, but some of the more popular processes definitely have things in common.
For starters, they’re all (mostly) additive processes. This is in sharp distinction to conventional manufacturing processes such as milling or turning which are subtractive processes. In the former you build parts from ground-up, and in the latter, you break of chunks from a larger block to get to the desired part. Both have advantages in terms of the quality, cost, strength and parts that can be manufactured. The user may need to decide on a process based on his/her requirements. Needless to say, 3D printing has significant use cases in prototyping due to the short lead time and cost for high-mix, low-volume parts. It is also extensively used in the medical, aviation, automotive, construction and healthcare sectors.
All 3D printing processes use filaments, which act as the building block, to construct parts from the ground up. In our segregation of the processes, we’ve classified them based on the type of filament/raw material used, followed up by a bonus section of metal 3D printing.
In SLS, layers of powder-based filaments are deposited, partially melted and cured. This leads to a process that helps create complex geometries and forms. The process itself, involves the deposition of a layer of powder-based filament that is subsequently cured by a CO2 laser beam. A significant advantage being that no support structures are needed since the powder filament itself acts as a pseudo-support structure. Surface finish is rough and may require additional polishing and strength is weak, unless the part is infused with other substrates. But where SLS lacks some features, it makes up for in the ability to create complex geometries, minimum material wastage and the availability of a variety of raw powder filaments; even including metal alloys.
Like SLS, SLM also uses a powder based filament, to make parts from the ground up. The core difference between SLS and SLM is that in the former, the powder is sintered, and in the latter its melted. Sintering refers to heating a sample close to its melting point that allows particles to stick to each other. Melting on the other hand refers to heating the substrate above its melting point before curing. SLM has better material strength compared to SLS due to lesser air gaps, but tolerances and dimensions are more difficult to control due to non-uniform heating and cooling.
SLA uses a photopolymer resin that is deposited and cured layer by layer. Parts printed using SLA have excellent surface finish and quality due to the relatively thin layers of material deposited at a time. The process itself consists of a base plane, dipped into a vat of resin, that helps build up the parts. The biggest advantage of an SLA printer is that prints are extremely quick, and quality is excellent. The users can choose from a range of colors and materials, even transparent/translucent ones.
A disadvantage of SLA printing is that the parts may need to be cured/cleaned after fabrication due to support structures and/or support material and the resin is extremely toxic. These makes SLA a fast, process with excellent surface finish. but with added cost and thus criteria must be weighed before choosing it.
Poly-jet/Multi-jet and SLA printers both belong to the family of resin-based filaments. The main difference between the two is that while the latter uses a tank filled with resin, which is cured layer by layer, the former uses a technique much like conventional inkjet printers. Layers are deposited with multiple nozzles and are subsequently cured with UV light. The physical properties are somewhat similar, but poly-jet printing has been shown to have better part strength, uniformity and the printing process is significantly faster. It is also not uncommon for poly-jet/multi-jet printers to have a different support material that is deposited in parallel. These support materials are water-soluble/IPA soluble and thus can help create a part with better surface finish. Moreover, some poly-jet printers, may even enable multiple filaments and can help create parts with different colors/materials within them.
FDM is probably the most popular as well as affordable 3D printing technology used. Using FDM, users can print not only functional prototypes of various sizes and configurations but even ready-to use products. The process consists of a filament which is extruded line-by-line and layer by layer to form the final part. All filaments for FDM printing must be thermoplastics, as they need to be melted before deposition into layers. FDM can be used to print ABS, PLA, Nylon and even some flexible filaments. The biggest advantage being that filament is cheap and readily available.
Support material is generated with the same material and can be removed by hand; however some sanding/post processing is needed to ensure that the surface is smooth. Some up-market 3D printers have multiple extrusion heads and can print support structures with water-soluble materials. The rule of thumb with FDM is that if you just want to prototype a form-fit part and don’t need excellent surface strength or quality, then FDM is your best bet.
In general products manufactured using Powder Bed Fusion are void of internal imperfections and residual stresses. This makes them highly applicable for usage in the automotive and aerospace industries. Under this category of 3D printing are the technologies of Direct Laser Metal Sintering (DLMS) and Electron Beam Melting (EBM).
The distinction between melting and sintering is that sintering uses a consolidation of heat and pressure to cause the metal particles to stick together whereas melting is when high temperatures are used to allow the metal to completely melt and fuse. Consequently, sintered components have high porosity, have lesser strength than if they were forged and so require heat treatment for strengthening. Melted products on the contrary are near solid and do not require any strengthening. Additionally, sintering can work with alloys whereas melting can only work with one metal at a time.
Powder Bed Fusion technology allows for products with any geometry to be manufactured using a plethora of materials with material properties sometimes exceeding than that of forging. All the while retaining the ability for them to be machined, coated and treated like traditional products. This comes at the cost of wastage of materials for support structures, bounded printing sizes and high danger of handling powdered metals while having high materials, machinery and operational costs.
Both these technologies allow the user to print a range of metals, from aluminum alloys to even types of steel.
Quite similar to welding, it includes Laser Engineering Net Shaping (LENS) and Direct Metal Deposition (DMD) machines which achieve melting using a plasma arc, laser or electric beam. Being the most affordable form of metal 3D printing, able to perform 5 or 6 axis motion allowing printing of overhangs without supporting material and is fast printing in high volume. This technology is mostly used for repair work of broken metal parts or to add new components to existing parts. Common materials that can be 3D printed are Steel (316L and 17–4 PH), Titanium and Inconel.
For both families of metal 3D printing, surface finishes are rough and post-processing may be needed to obtain an aesthetic finish
If you’d like to know more about surface finishing and post processing for 3D Printed parts, please refer to our whitepaper highlighting different kinds of surface finishing and post processing methods available, here: Surface Finishing for Metal and 3D Printed Parts
When we get customer enquiries, they usually ask which process is the best fit for them. While there’s no one answer to this question, choosing a process is a careful balance between cost, strength and finish quality! If you’re reading this as an experienced designer, this information should be a good revision. If you’re reading this as someone looking to learn more, here’s some tips.
Thanks for reading!
