What is FDM 3D Printing? A Simple Guide

Fused deposition modeling (FDM) is an additive manufacturing process that selectively deposits melted material layer by layer in a predetermined path to create a three-dimensional object.

FDM 3D printing technology is popular for its affordability, ease of use, and customization options, making it an attractive choice for hobbyists and professionals.

This post looks deeper into FDM 3D printing technology, explaining how it works and what goes into making a 3D part.

What is FDM 3D Printing?

FDM 3D printing is a 3D printing process that works by heating and extruding thermoplastic filament layer by layer to build an object.

FDM uses a thermoplastic filament wound on a coil fed into an extrusion nozzle head. The hot end melts the material and deposits it onto the build platform.

Hobbyists and professionals widely use filament printing, also known as Fused Filament Fabrication (FFF), because of its simplicity and low cost. 

Today, you can get a decent entry-level 3D printer like the Ender 3 for under $300. The low price point of 3D printers makes it incredibly easy for hobbyists to get started in the world of 3D printing.

How Does FDM 3D Printing Work?

With FDM technology, you can create simple and complex objects.

First, you need a computer-aided design (CAD) file, which is then converted to a format that FDM 3D printers can interpret.

The file is “sliced” in specialized software that creates a special code telling the printer how to build the model. The “Gcode” is essentially a set of instructions telling the printer how to replicate the object.

Material extrusion plays a key role in the FDM 3D printing process.

The thermoplastic filament, used as the printer’s raw material, is heated and pushed through a nozzle. The toolpath creates the object layer by layer, ensuring that each layer fuses with the previous layer to build a part.

An excellent way to think about this is by imagining yourself using a hot glue gun. If you were to draw a circle with hot glue and then keep building processes on top of the first, you would slowly and iteratively build a cylindrical part.

This is precisely how FDM printing works; the only difference is the layer heights are much smaller, and the machine takes care of the path for you.

When I first started 3D printing, I was lucky enough to use an FDM printer and was amazed at how it could “magically” build apart from a string of plastic.

Let’s dive into the details of each component of FDM 3D printing.

CAD Files

You’ll need a 3D model created using Computer-Aided Design (CAD) software to start.

Once you’ve designed your model, you’ll want to export it in the Standard Triangle Language (STL) format for further processing.

There are many file formats for 3D part files. However, slicing software most commonly uses and accepts the STL file type.

An STL file describes the surface of a 3D object as a mesh of interconnecting triangular faces. The triangles help define critical points on the model’s surface but don’t include information about color or texture.

The resolution and accuracy of the STL file depend on how finely the triangular mesh approximates the original surfaces. A higher-density mesh creates larger STL files but more closely represents curved or complex surfaces.

If you notice that curved surfaces of your parts have squared-off edges, you can likely blame the refinement of your STL mesh. You can increase the mesh density for better resolution of curved surfaces, which smooths out the hard lines at the cost of a larger file size.

Slicer and Gcode

Once you’ve exported your model, you can open the STL file in your slicing software.

Slicing software takes a 3D model file, such as an STL, and slices it into thin horizontal layers based on specified print settings. It creates a set of instructions for the printer to follow and make your model.

You can adjust the slicing settings, like layer height, infill density, support structures, print speed, and print temperature, among others, to fine-tune your print results.

The slicer analyzes the model geometry and generates a precise toolpath for how the print head should move to deposit material and build each object layer. It calculates where support material is needed to brace overhangs and bridges in the design.

Popular slicing software includes:

• Ultimaker’s Cura (most popular)
• PrusaSlicer (best for Prusa 3D printers)
• Simplify3D
• ChiTuBox (for resin printing)

Slicing converts the STL file to a G-code file containing instructions for the 3D printer to follow layer-by-layer.

Gcode is the numerical control programming language used to instruct 3D printers.

The Gcode file contains specific commands directing the 3D printer on moving, building, and printing the 3D model.

Common Gcode commands include G0 for moves without extrusion, G1 for moves that include extrusion, and G28 for homing the print head axes.

Your 3D printer’s firmware reads and follows these Gcode instructions precisely to control the motor movements, temperatures, and material flow.

The instructions are sent to the printer by SD card, USB, or WiFi connection.

The Printing Process

Now that the G-code is generated, it’s time for the actual 3D printing process. Your FDM printer has two key parts: the cold and hot ends.

• Cold end: This part feeds the thermoplastic filament (typically 1.75 mm or 2.85 mm in diameter) into the extruder.
• Hot end: This part consists of the extrusion head and nozzle (usually 0.4 mm in diameter), which heats, melts, and extrudes the plastic.

The extruder moves along the X- and Y-axis, while the print bed or hot end assembly moves along the Z-axis. The extruder deposits melted filament onto the build platform layer by layer, according to the G-code instructions.

As each layer cools and solidifies, it fuses with the previous layer, forming your 3D object.

Print Quality

FDM 3D printing offers a range of print qualities depending on your printer’s settings and the material you use. Layer height, nozzle diameter, and print speed can all affect the final result.

Generally, FDM prints show visible layer lines and may require some post-processing for a smooth finish.

Cleaning up the surface finish by sanding or painting the part is possible to achieve a smooth finish, but it requires some extra steps.

How Does This Compare To Other Forms Of 3D Printing?

Ease of Use

FDM 3D printers are generally easy to use and maintain compared to other processes like SLA or SLS. SLA and SLS 3D printers create objects from UV-cured resin. The liquid 3D printing resin is toxic, so several safety precautions and additional steps are required when working with resin printers.

Print Quality

Resin printing technologies like SLA and SLS printers produce better print quality than FDM. While FDM printers can create intricate and detailed pieces, resin printers can print at much finer layer heights.

FDM produces good quality prints but with more visible layer lines than SLA or SLS. You can achieve very smooth prints from resin printers, especially with the recent 8K and 12K printers on the market.

Cost

FDM 3D printers are more cost-effective than other printing technologies. You can get a good FDM printer for under $300.

There are several great sub-$300 resin printers as well. However, the build size of resin printers is less than half of what you’d find on a similarly priced FDM printer.

When comparing the price of the printer to the build volume, it’s clear that FDM printers are more cost-effective.

But we also need to compare filament and resin pricing.

Here, too, FDM printers take the win.

Standard 1kg PLA filament spools for FDM printing typically cost $15-30. In contrast, one-liter containers of photopolymer resins for SLA printing are sold for $50-75 per liter.

Overall, SLA resins are significantly more expensive than FDM filaments.

Additionally, SLA printing requires ongoing purchases of replacement FEP screens, isopropyl alcohol, and protective equipment, further increasing material costs.

Filament Materials

FDM 3D printers use a spool thermoplastic filament. Thermoplastics are a type of plastic that softens and melts when heated.

They are generally compared to another type of plastic called thermosets, which burn (not melt) when heated.

In general, thermoplastics offer better, more well-rounded mechanical properties. The filaments used in 3D printing are recyclable, making them a more eco-friendly solution.

Another attractive point is there are many types of filament materials available. And they’re available in a range of colors.

Here are some of the best 3D printing filaments:

• PLA (Polylactic Acid): PLA filament is the most common type of 3D printing material. PLA is a low-cost, easy-to-use, and environmentally friendly material derived from renewable resources like cornstarch. It’s easy to print with, available in various colors like red and tan, and doesn’t emit harmful fumes. However
• ABS (Acrylonitrile Butadiene Styrene): ABS is another popular thermoplastic material known for its durability, strength, and heat resistance. It can be a little trickier to print with than PLA due to its tendency to warp and shrink, but its excellent properties make it a perfect choice for many applications. ABS gives off harmful fumes during printing, so you’ll want to ensure proper ventilation while working with the filament.
• PETG (Polyethylene Terephthalate Glycol): PET and its modified form, PETG, offer high strength and flexibility. PETG is easier to print than ABS but stronger and more durable than PLA. The filament provides excellent layer adhesion, making it a popular choice for functional parts.
• Nylon: Nylon is a strong, flexible, and durable thermoplastic with high impact resistance. It’s used for end-use parts and can be a bit challenging to print due to its sensitivity to moisture.
• TPU (Thermoplastic Polyurethane): TPU is a flexible, rubber-like material with excellent durability, making it perfect for creating flexible parts or protective cases. The flexible filament is difficult to work with and requires a high-temperature nozzle, which isn’t common on budget-level 3D printing machines.

Post-Processing Prints

Support Material Removal

After completing your FDM 3D print, you’ll need to remove any support materials. Support structures are essential for preventing warping and ensuring the success of your print, especially for parts with overhangs and complex geometries.

To remove these supports, carefully use pliers or a similar tool to break them away from the main print. Ensure you don’t damage the actual print in the process.

It’s a good idea to wear puncture-resistant gloves and eyewear, as support pieces are sharp and can fly off the model during removal.

Surface Finishing

The post-processing stage also involves improving the surface finish of your FDM 3D printed part. FDM printing leaves visible layer lines, which can affect the appearance and functionality of the piece.

There are several ways you can go about smoothing the surface:

• Sanding: Use progressively finer grits of sandpaper to manually sand the surface, starting with a rough grit and moving to a finer grit for a smooth finish. This method requires patience but can produce impressive results.
• Chemical smoothing: Some materials, like ABS, can be smoothed using chemicals such as acetone. Take caution when handling chemicals, and ensure you work in a well-ventilated area.
• Painting: Painting your 3D part with paint or primer can fill some of the gaps and low spots between layers. I recommend choosing a good filler primer (Amazon) designed to fill small crevasses.