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Fused-Filament-Fabrication

FFF printing also referred to by its trademark name, FDM, is the most common 3D printing process and is responsible for the characteristic stair-stepped look of 3D printed parts.

FFF machines can be used for a wide variety of purposes including prototyping, molds and end use parts. The plastic filament that these machines use is the same material used in mass produced parts, making it ideal for testing whether a part will function properly in the real world.

How FFF Printers Work

In 1988, S. Scott Crump was looking for a way to make a toy frog for his daughter. He used a hot glue gun to melt some plastic and extruded it into thin layers. He called the invention Fused Deposition Modeling and more than 30 years later FFF machines are basically hot glue guns attached to robotic gantries.

A 3D model is fed to a slicing program, which slices it into layers. The slicing software converts these layers into machine movement code and then feeds that to the FFF machine, which moves back and forth, tracing these layers while extruding plastic from its Nozzle. When one layer is complete it moves up to the next one.

Image Credit: https://www.mdpi.com/2076-3417/10/8/2899

Support Material

As an FFF machine prints upwards, some layers will eventually end up hanging out in open space. Once printed, they will fall due to gravity. To combat this, support towers are built from the build plate up to the layer so that it will have something to rest on top of once printed. Supports are waste material so designs that are optimized for 3D printing should seek to minimize or remove the need to have them entirely.

Image Credit: AMFG

The Gantry

The gantry is what moves the print head (also known as the “hotend”) back and forth to trace each layer. There are two major kinds; Delta and Cartesian. Cartesian is the most common as it is the simplest to use; three motors drive some combination of the print bed and hotend back and forth in straight lines. Cartesian printers can use a Direct-Drive Extruder or a Bowden Extruder.

Delta printers use three independent arms to move the hotend around. It is more complex to control but theoretically the printer can go much faster because of the smaller amount of mass at the print head. Delta printers typically use a Bowden Extruder setup.

Image Credit: Matterhackers

Cartesian Benefits

  1. Simple to maintain and repair.
  2. Simple to program.
  3. Very common, lots of spare parts to be found.
  4. Often has a Direct-Drive Extruder, which means it is much easier to print flexible filaments.

Delta Benefits

  1. Less mass on the print head means it can be moved much more quickly.
  2. Very large print areas for a much lower price vs. Cartesian machines.
  3. They look heckin’ cool.

The Print Head

The Print Head includes the Extruder Assembly and the Hotend. Starting from the top:

  1. The filament enters through the PTFE tube.
  2. The Drive Roller on the Stepper Motor has teeth, like a gear. These teeth grab the filament and pull it in from above.
  3. The Extruder Arm and Tension Cam work together to squeeze the filament against the Drive Roller to help it grip the filament.
  4. The filament is guided into a PTFE liner that is inside the barrel.
  5. The barrel connects the Mounting Block to the Heater Block. It also serves as a heatbreak, keeping plastic above it from softening or melting too soon.
  6. Inside the Heater Block, a Cartridge Heater pumps in heat, which is regulated by a Temperature Sensor, known as a Thermistor.
  7. The Heater Block also heats up the Nozzle, which is where the filament comes out of. It is pushed out of the Nozzle by the back pressure of the Motor feeding the whole assembly with fresh filament

Extruder Assembly

It is very important that the plastic only gets hot near the nozzle. If it gets hot up by the extruder then it can bend and buckle and cause jams. For this reason; in addition to the heatbreak the Extruder Assembly also has a heatsink on it and a fan to keep the filament near the extruder cool.

For a breakdown of every single part of a 3D Printer, check out this awesome article by Matterhackers.

When should you choose FFF printing?

FFF machines are ideal for any use cases that require:

  1. Low cost. FFF machines are the cheapest to run and maintain. Most materials are less than $50 per kilogram.
  2. Ease of maintenance. They are very simple to maintain and replacement parts are widely available.
  3. Flexible production amount. While they are not particularly fast, they are cheap enough that small to mid-scale production can be spooled up by purchasing additional machines at low prices.
  4. Functional testing. The materials used in FFF machines are the same those in mass production parts, so tests on the 3DP part are closer to reality.
  5. Versatility. FFF machines can accept a wide range of materials; from rubber-like TPU to plastic embedded with steel.
  6. Durability. FFF materials are hard wearing and can be used as end use parts.
Sample parts printed on an SLA machine.

An FFF printer would be unable to produce extremely small parts like the castle on the far right.

When should you consider something else?

While FFF machines can perform a variety of tasks, some machines are better options for different operations.

  1. Large scale production. Eventually the slow speed of printing will cause a bottleneck. SLS machines are a better option (if you can afford them).
  2. Very high performance parts. Some high performance materials like nylon can be difficult to print and since the part is built out of layers it is not as strong as a solid piece. A good rule of thumb is that an FFF part will be 80% as strong as a solid one.
  3. Fine detail. While smaller diameter nozzles can get amazing results from an FFF machine, SLA is a better option for reproducing extremely tiny details.
  4. Watertight parts. FFF parts are not watertight and must be sealed by additional methods.
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