Is all 3D printing the same? Is it as simple as defining the material for a part as plastic or metal? Here we will define and compare three different plastic printing technologies. Let’s start with a recap of some of the technologies.
What is Fused Deposition Modeling (FDM)?
Fused deposition modeling, also known as Fused Filament Fabrication (FFF) uses a thermoplastic filament which is extruded through a heated nozzle. The nozzle is mounted on a gantry system, allowing the extruder head to trace the profile of a part on both the x and y axis. Think of a glue gun, and you’ll have a decent idea of how the extruder works. This process is repeated layer by layer to complete the part. FDM has a variety of thermoplastics available, and is often used for prototyping, shop fixtures and end effectors.
FDM is very popular amongst hobbyists and small shops for its ease of use, cost of materials and part durability.
What types of filament are used in FDM?
The filament used is generally going to be a thermoplastic, as FDM relies on heat to fuse each layer together. Types of thermoplastic filament commonly used in FDM are PLA (polylactic acid), ABS (ammunobutylsterine), and PETG (Polyethylene Terephthalate Glycol-modified).
What is Stereolithography (SLA)?
Stereolithography, or SLA, is also known as vat photopolymerization under ASTM terminology. It was the first form of 3D printing fully commercialized. A reservoir of liquid plastic resin (photopolymer) is cured by UV light exposure. A tray dips down into the surface of this vat of resin. The UV laser cures the top surface of the resin. The process continues curing the profile of the part layer by layer, descending into the vat with each layer, until the part is complete.
What types of resins are used in SLA?
The resins used in SLA are generally thermoset resins, as SLA requires UV cured photopolymers to be used in the process. The thermoset resins are custom designed to simulate common engineered plastics like polypropylene, ABS, polyethylene and others, there are even extremely high temperature (300C) and composite materials available.
What is Selective Laser Sintering (SLS)?
Selective Laser Sintering, or SLS, is also known as powder bed fusion of plastics. With SLS a fine plastic powder is thinly spread across a build platform and fused together with a low-wattage laser which scans the profile of a part. With SLS the powder bed supports the parts, which upon completion are excavated from the loose powder.
How do FDM, SLA, and SLS 3D Printing Technologies Compare?
With a basic understanding of the processes described above, it’s time to start diving into how the processes compare. All of these technologies are widely used in prototyping and tooling for plastic components, some of them are even appropriate for end use parts. They all have different strengths and weaknesses and even different barriers to entry.
FDM is the most affordable technology to get into, it is the easiest to use, and also the most widely available. Consumers can buy an entry level machine for around $200.
Besides which technology is used, there are other factors to include, like the size of the part, or the complexity of the part. They all require a certain amount of post-processing. SLA and FDM require the use of a support structure to anchor the part. This has to be factored into the design, and the material used to print the support structure ends up thrown out and counts as waste. SLS doesn’t require support structures, as the unused powder props up the design within the power bed. The unused powder in SLS is easily recyclable, resulting in much less wasted material. When you consider the fact that multiple parts can be compactly nested together in SLS, it is easily the most cost efficient.
SLA has the best surface finish out of the three technologies. Since it starts with a liquid resin, and it’s cured at or right below the surface level of the photopolymer, the surface finish is smoother and finer compared to the other technologies. FDM has a propensity to show the layer lines and step-overs from layer to layer. With SLS you get a high resolution part but it has more of a grainy texture to the finish since the raw material is a powder.
With FDM, the method of extruding material requires the printer to trace the same pattern each time per number of parts needed. It doesn’t scale very well – the time needed to make 5 parts is very close to 5 times the amount of time needed for a single part.
With SLA & SLS, you are able to achieve an economy of scale with the more parts required in the build. Since raw material is spread, then fused or cured with a laser, the time it takes to fuse a profile of a part is much faster. SLS can be 8 to 9 times faster on average than FDM, and even faster for large scale projects.
These three plastic technologies all have pretty generous volumes available. FDM type machines can be configured as large as a semi-truck – these are typically industrial machines customized for the aerospace or construction industries. SLA can go up to 60” by 36” by 24”. The typical machine used in industry is 20” by 20” by 20”. SLS is smaller yet, the largest machines of this type are about 36” by 24” by 24” with typical machines sized around 12” x 12” x 18”.
Common applications for each technology:
FDM and SLS are more conducive to shop floor or production parts. Even though SLA is one of the more mature technologies, it’s primarily used for prototyping parts that will eventually be injection molded.
How do different 3D Printing materials compare?
Costs: How do material costs compare? SLS is probably the least expensive of the materials. Generally the nylon based powders are highly recyclable which helps keep the cost really low. FDM material costs are pretty low as well but you do throw away waste material for the support structures.
SLA is typically the most expensive of the materials. There is a lot of chemistry involved in creating the photopolymers used in SLA. You also end up throwing away waste material used for support structures. They are not recyclable and are one-use materials. They are not true thermoplastic resins – they are basically a simulated thermoplastic. They are not a commodity, like nylon is for SLS, or the commodity type plastics used in FDM. The materials available for SLA are created for SLA and there are not really other applications for these materials.
How do these materials compare in strength and durability?
There are a variety of uses for these parts and materials so this can vary. ABS used in FDM is true ABS so it has good mechanical properties and mechanical resistance. Nylons used in FDMs are incredibly hardy and can be flame-retardant or used for composite materials such as glass-filled or carbon fiber-filled nylons. SLA has very durable materials available, but because it is a UV-cured material, it has a tendency to degrade over time, with the mechanical properties lessening as time and wear goes on.
As one can see, there are a variety of factors at play in choosing the right technology for your needs. With the multitude of technologies and materials available knowing which combination will provide the best results. If you’d like to learn more, contact one of our experts today.