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FDM vs Resin 3D Printing

Fused Deposition Modeling (FDM) vs Resin Printing. Join 3D Junkie as we compare the two most popular types of 3D printers, to help you decide which technique is ideal for your business.
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Uncategorized January 17, 2023

In recent years we have seen rapid change in the 3D printing market, following technological advancements. No longer confined to the world of hobbyists, these highly capable desktop machines have developed into tools  which are essential for business. Quickly becoming the go-to tool for prototyping and product development, 3D printers have expanded across industries such as manufacturing, jewellery, dentistry, to name a few.

Fused deposition modelling (FDM) and Resin printing are the two most recognised types of 3D printers on the market. Both of these printing techniques have been adapted and refined for the desktop. These developments have made them more affordable, easier to use, and highly capable to deliver results in even the most intensive of projects.

In this comprehensive 3D Junkie buyer’s guide, we FDM and Resin 3D printing under the microscope. Read on to see how they compare in terms of print quality, materials, speed, workflow, applications, and more to help you decide which technique is ideal for your business.

What is Fused Deposition Modelling (FDM) 3D Printing?

Fused deposition modelling is the most widely used form of 3D printing at a consumer level. FDM works by extruding thermoplastics, commonly ABS or PLA, through a heated nozzle, then melting the material with layer by layer plastic application to a build platform. Each layers build one at a time until the part is complete. A very simple comparison would be that of a hot glue gun, with a solid strand being pushed into a hot nozzle that melts it and allows it to flow and be laid down in flat layers.
FDM 3D printers are suited for basic proof-of-concept models, as well as quick and low-cost prototyping of simple parts, which may typically be machined.

What is Resin 3D Printing?

‘Resin printing’ is more of an umbrella term for 3D printing technologies that fall within the additive manufacturing category of vat polymerisation.
Most resin printers have a container with a clear, flexible bottom sheet, also called a vat, which is filled with a photosensitive resin that cures, or solidifies, when coming into contact with UV light. A build platform is then submerged into the vat and a light source beneath the clear bottom cures the resin according to a specific pattern, binding the hardened first layer to the platform.
The build plate then moves up to create space for the next layer and allow new resin to flow in between the previous layer and the bottom of the vat. This new layer is then cured via the light source, and the process repeats until the finished 3D object is created.
Resin 3D printers have become vastly popular for their ability to produce high-accuracy parts in a range of advanced materials, with fine features and smooth surface finish. Resin formulations offer a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics.

Popular variations of Resin Printers

LCD Printing

LCD is the most accessible form of resin printing. An LCD printer uses a powerful UV light source that can illuminate an entire layer at once. This light is selectively blocked and let through by a liquid-crystal display (LCD) screen sitting above the UV light. The LCD displays a negative image of the layer to only let light pass where the resin needs to be cured.

The resolution of the LCD screen (4K or 8K for example) will determine the resolution of the print. In return, LCD is also the fastest type of resin printing and by far the cheapest. They are therefore very attractive for beginners and hobbyists.

SLA Printing

SLA (Stereolithography) was the world’s first 3D printing technology, invented in the 1980s, and is still one of the most popular technologies for professionals.
This technology is very similar to LCD, however, the light source used is a laser. This laser is aimed around the resin vat by a motor-controlled mirror that can change its reflection angle. The laser traces over the resin in the shape of the current layer, much like a regular FDM 3D printer nozzle traces a new layer point by point.
This technology is often more expensive than LCD because of the increased complexity and number of moving parts.

DLP Printing

DLP printing technology makes use of a digital light processing (DLP) projector. The technology is quite similar to LCD printing in that a whole layer is exposed at the same time. The difference between the two is how the light hits the resin in a specific shape. The projector flashes an image onto an array of mirrors, which in turn direct the reflected image onto the bottom of the vat, without the need for an additional screen to block off unnecessary light.

This printing method is the least common of the three mentioned here. From a ‘historical’ perspective, DLP printing could be said to have paved the way from SLA to LCD printing.

Comparison of Materials

By nature of how they work, there are big differences between the materials used for FDM and resin printing. However, within each of the two groups, there is a lot of variety.

FDM Printing

The main requirement for an FDM printing material is that it has a thermoplastic base. These materials come in the form of a long plastic strand, with a 1.75 or 2.85mm diameter, wound up on a spool.
FDM 3D printers work with a range of standard thermoplastics, such as ABS, PLA, and their various blends. The popularity of FDM in the hobbyist space has led to an abundance of colour options hitting the market. Various experimental filaments blends also exist to create parts with a wood, or metal-like surface.
Engineering materials, such as Nylon, PETG, PA, or TPU and high-performance thermoplastics like PEEK or PEI are also available. As such, the versatility offered by filaments and the printing technology behind them shouldn’t be underappreciated. Wood, carbon fibre, silk, metal, transparent, glow-in-the-dark and colour-changing, are just a few of the PLA options. FDM prints can take many different forms and uses.

Resin Printing

With resin printers, the material selection is similarly diverse, often characterised by attribute or end-use. You can find high-precision, flexible, water-washable resins, as well as castable, high-temperature and functional resins with superior engineering qualities. Various resin formulations offer a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics.
This range does mean that different resins will have different print settings (such as exposure time), so it is important to check each ‘resin profile’ against your printer. Vice versa the technology used can also affect the resin selected. Resins cure differently depending on the light’s wavelength, and as such, correct compatibility has to be checked depending on the printing setup.

All resins are stored in either a UV-resistant bottle or bag, which prevent UV rays from entering and hitting the liquid, which would harden the resin before use.

Print Resolution & Quality

FDM and resin printing tend to differ in the quality and resolution of their finished prints. These factors range from general appearance to the quality of small details but also include mechanical factors like strength.

FDM Printing

One of the most obvious differences between FDM and resin is print resolution. Because FDM printers use molten plastic layers to create models, results tend to be less precise and accurate, as the material is typically deposited in lines that are 0.4mm in width. The actual layers are also large in comparison to resin printing, ranging from 0.1 to 0.35mm per layer. This layer height creates visible lines on all surfaces and often prevents FDM-printed parts from being used as final models.
To resolve the issue of visible layer lines, a finished print can be sanded or even smoothed using solvent vapours. These methods can make FDM prints appear completely smooth, but take time and skill to do well and will also fade out small surface details.
Another quality of finished prints is their strength. On this stage, FDM generally performs better than resin printing and, depending on the material being used, is affected by certain print settings. For example, using a high infill percentage, an appropriate infill pattern, and an increased wall thickness will make a part stronger, but in turn, print time will be increased.

Resin Printing

In comparison, resin printers generally create a much higher detailed model. For this reason, resin printing is great for miniatures or high-detail models that are worth the extra effort.

Because of the technologies, layer heights are incredibly small, around a quarter that of FDM printing. XY resolution is also in this range. This tiny layer height enables the printing of incredible details and high-quality objects, with finished prints often having no signs of the layers themselves, but rather looking like one smooth solid piece of plastic. The finished prints can also be sanded to achieve even greater smoothness. However this step is unnecessary in most cases, as the layers are already so small.

When it comes to strength, tough resins produce printed parts that are generally stronger than FDM ones. However, it’s a tricky comparison because it depends on which FDM materials they’re being compared to.

Print Speed

Another big difference between FDM and resin printing is print speed. This is dependent on many factors, including the specific technology used and the print settings.

FDM Printing

The time it takes for an FDM printer to finish a print depends mostly on the size of the object being printed, as well as the selected layer height, infill, and speed. Simply put, the larger the item and the smaller the layer height, the longer the print will take.

Another setting that affects print time is the density of the infill. The higher the density of the infill, the more filament needs to be laid down by the printer and the longer the print takes.

Resin Printing

When it comes to resin printing, the print time is a bit more straightforward. With LCD and DLP printing, layers are cured quickly due to a whole layer being solidified in 2 to 10 seconds, no matter how much resin is being hardened per layer. With SLA machines, the print time is significantly longer, as the laser needs to travel to every point.
Other variables that affect print time are the Z-axis height, the layer height, and the time it takes for the printer to move the print bed up and back down for the next layer. Nevertheless, assuming the use of an LCD printer, resin printing can be said to be significantly faster than FDM printing in most cases.

Workflow and Ease of Use

The ease of use of a 3D printer is a concern for beginners and advanced users alike. Across the various FDM and resin technologies are numerous advantages and challenges. But fundamentally the workflow for both FDM and resin 3D printing consists of three steps: designing, 3D printing, and post-processing.

FDM Printing

FDM printers are generally easy to use and therefore considered beginner friendly. After loading filament, starting the print is pretty much all that needs to be done. After the print is done, it should be easy to remove and can in most cases immediately be used as intended. Some prints, like watertight containers, may require either very precise settings or some form of coating to get them fully ready to use. Post-processing may then be necessary to achieve a particular aesthetic.
Naturally, there are still some problems with FDM printers, including stringing, warping, and elephant’s foot. FDM machines typically require more maintenance and calibration to prevent these problems from occurring.
  • Stringing – As an FDM printer nozzle travels across an open space to get to the next point, it may sometimes ooze melted plastic, which then solidifies and sticks to the printed parts. This is 3D printer stringing, and it leaves your 3D printed parts with thin strands of plastic that resemble cobwebs or strands of hair.
  • Warping – This problem occurs when the extruded filament cools too quickly on the build plate and shrinks. This, in turn, creates tension within the model. When it becomes too much, lower layers start to drag or lift up at the corners, creating a warp.
  • Elephant’s Foot – Sometimes when printing without a raft, you may notice that the first layer is slightly larger than the rest. This is known as elephant’s foot. This defect often arises in larger prints, as it’s caused by the weight of the object pushing down on the first layer. If it’s not yet fully cooled, this weight results in bulging of the first layer. Elephant’s foot drastically decreases tolerances, making it much harder to fit pieces together for practical applications.

The FDM process does have the benefit that it doesn’t require cleaning. Unsupported finished parts are ready for use or further post-processing once the printing process is complete.

Resin Printing

In contrast to FDM printing, resin printing requires a bit more attention. Firstly, resin is toxic, meaning it’s not safe to touch, and the vapours aren’t safe to inhale. Due to this danger, gloves and masks are required when handling resin and prints before they’re fully cured.
A key feature of all resin printers is that they have a hood that covers the build area and resin vat. Their main jobs are to block UV rays from hitting the uncured resin in the vat and to protect onlookers’ eyes from the UV light in the printer. Additionally, the hood is meant to keep the toxic and often smelly fumes from spreading.
After the resin is loaded into the machine’s vat, the printing process is relatively simple. But a print newly removed from a printer is still covered in uncured resin. This resin needs to be washed off using a solvent, in most cases isopropyl alcohol (IPA). The print then needs to be fully cured under a UV light source like a dedicated lamp to bring it to its final state. After all these steps have been completed, the print can now be handled normally and is no longer toxic.
These extra steps mean that resin 3D printing has a higher learning curve, so it’s not necessarily as beginner friendly as FDM printing. And as a final and just as important note, proper disposal of resin is a must.

Side by Side Comparison

Each 3D printing technology has its own strengths, weaknesses, and requirements. They will also be more or less suitable for different applications and businesses. Let us summarise some key characteristics for your consideration.
In general, if you’re looking to have a machine that you can customise to print a little bit of everything across the board, FDM is a solid choice. These machines are perfect for printing a wide variety of objects at a reasonable quality. From large structural brackets that are strong enough to withstand heavy loads, to smaller low-detail models and accessories.
When it comes to small models and impressive details, resin printing would be the recommended way to go. Resin prints benefit from the versatility of the material and characteristics for functional use, such as transparency, strength, or flexibility. While the learning curve may be a bit steeper and the initial investment may be a bit higher, resin printing can still be a hobbyist-friendly option.

After comparison of the two technologies, both FDM and Resin technologies have similar, often complimentary features. As such, the two types of 3D printers are not always competing; many businesses use both FDM and Resin machines alongside one another. This can mean the best of both worlds: low-cost rapid prototyping coupled with high quality, functional parts for a wider range of applications.

Making the call in one direction or another (if it’s needed) will basically boil down to this: What do you want to print and what for?

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