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3D Printers
3D Printers
3D Printers

FDM Printing

Fused deposition modeling (FDM) is a 3D printing technology that prints objects using thermoplastic filament. Filament is basically a cord of material capable of being melted, selectively deposited, and cooled to form a 3D printed object. Layers are added on top of each other, building up the whole 3D printed object.
Through FDM, rapid prototyping has seen new horizons. Now, complex and intricate objects can be printed on a FDM printer in a matter of a few hours.

Contents

Types of FDM Printers
Build Platform
Hotend and Nozzle
Filament and its holder
Mechanical Parts
Graphical User Interface
Fans and Air-circulation

Types of FDM Printers

Based on the type of motions of the bed and printing nozzle, FDM printers can be categorized in the following types:

  • Cartesian Printer
  • Delta Printer
  • Polar Printer
  • Robatic Arm Printer

Cartesian printers are the ‘stereotypical’ printers in the lot. They are further divided into subcategories such as Prusa i3 type, H-bot and CoreXY. In Prusa i3 type printers, the nozzle moves up and down along the z-axis and in the H-bot type printers, the build plate moves up and down along the z-axis. H-bot type printers are best for larger parts due to stability of build plate but they are relatively expensive as compared to Prusa type printers. Examples of i3 type printers are Creality Ender 3 V2, HatchBot X, etc while the examples of H-bot printers are Ultimaker S3, Makerbot, etc

Z-Bed Printers and Y-Bed Printers.

Build Platform

Build Platform or Print Bed is a flat surface where all the objects are printed. It is one of the most critical areas for your printing experience. If it has errors in its setup, either its misaligned or has surface defects; the complete 3D printed object can be ruined. No matter how much expensive material you use or how perfect settings you use to make the file for printing. So, along with the correct settings in the printing file preparation software, it is also necessary to maintain physical optimum conditions for the print.

Leveling of Build Surface

Before printing any file on an FDM 3D printer, it is recommended to check and set leveling of the build surface/ platform. There are few kinds of bed leveling options depending on the printer brand and type such as:

  • Manual Bed leveling
  • Assisted Manual Bed leveling
  • Automatic Bed leveling
 

The bottomline of build surface leveling is the checking of distance between nozzle and printing surface on different points along the entire build surface followed by the measures for its correction. The manual leveling is done by maneuvering the print head near each corner by hands and adjusting leveling screws on the bottom of the build platform using a paper as measuring guide between nozzle and build surface. In assisted leveling, the print head automatically moves to different positions and lets users adjust leveling screws. Whereas in automatic leveling, the sensor reads depth variations along the build surface and accommodates those variations during printing. Most of the latest printers come with the feature of automatic bed leveling.

Build Surfaces and Adhesion

There are various kinds of build surfaces depending on the type of printer or the type of material being printed. These surfaces can be interchanged for a given 3D printer. The first layer of any 3D printed part needs to stick on the build surface and the rest of the layers are printed over one another so the build surface and its adhesion is responsible to hold the part until the whole object is completely printed. Some materials like PLA do not require a very specialized printing surface and can be printed on most of the surfaces while other materials like ABS, PET-G and TPU require special surfaces and preparations for printing.

Some common printing surfaces are:

PEI (Polyetherimide)

This material is coated on the build surface. As it gets heated, the object being printed firmly sticks on it and when it gets cooled it releases the 3D printed object.

Glass

Glass build plate is suitable for all commonly used materials and provides excellent bottom surface finish on 3D printed objects. However, glue stick is used on glass for PLA, TPU and PET-G while Hair spray or ABS slurry is used for adhesion in ABS parts. ABS slurry is basically ABS residual parts dissolved in acetone.

Acrylic sheet with Kapton Tape

This combination is used for PLA material only. Kapton tape or paper tape is flat pasted on an acrylic sheet without overlapping the tape layers.

Metal spring sheet

Magnetic sheet comes in two parts. One part is fixed on the build platform while the other is magnetically attached on top of it. Upon printing objects on this setup, the user can easily remove the magnetic part and flex it to remove the 3D printed object from the surface.

Heated Build Platform

Generally, build platforms are attached with a heating system to achieve a heated build surface for specialized applications. Although PLA can be printed without a heated build surface, it is recommended to have a surface temperature of 50℃. Similarly, for ABS it is required that the build surface is heated to 100℃ for adhesion.

Hotend and Nozzle

Hotend or Printhead are the terms used for the section of a 3D printer that has a filament heater and a nozzle that extrudes the printing material.

Nozzle

Nozzle is basically a metal piece having a small hole through which the melted 3D printing filament comes out. Nozzles are subjected to continuous high temperatures and material pressure so they need to be made from hard and wear-resistant materials. Nozzles are commonly machined from Brass and are classified in terms of their thread type and outlet diameter (0.4mm diameter is commonly used).

Feeder

Feeder is the section of 3D printer where 3D printing filament is inserted and is pushed towards the hotend to 3D print objects in a controlled manner. There is a tensioner wheel which presses the filament against the brass gear. The brass gear is attached with a motor which turns, bites and pushes the filament at a specified rate.

Filament and its holder

The printing material of FDM printers is called ‘Filament’. It is basically a flexible plastic cord wound on a spool. The filaments usually come in two sizes which are 1.75mm and 3.0mm in thickness. Furthermore, a variety of materials are available like PLA, ABS, PET-G. The filament is to be always used with a separate filament holding stand or with an integrated spool holder that comes with most of the latest printers.

During printing, the filament spool needs to be able to turn and unwind freely without getting stuck. Because if it gets stuck then the extruder won’t be able to push it further towards the nozzle; pulling the whole spool towards itself. This might cause the spool to fall out from the holder which may damage the printer or other parts being printed.

Mechanical Parts

The 3D printer is a beautiful blend of mechanical and electrical engineering. There are numerous electrical and mechanical components that make 3D printing possible. Critical mechanical parts and peripherals are discussed as follows.

Motors

All motions of the 3D printer are actuated by stepper motors. In general, 3 motors are used for x, y and z axis movements of the nozzle while a 4th motor is used at the extruder to feed the filament to the hotend. However in large printers, dual motors are also used at any of the 3 axes for added strength during the motion.

Belts and Pulleys

Belts and pulleys are used as a medium to carry the motor’s motion to the whole assembly. Belts are made of rubber while the pulleys are bearings, on which the belt rides. Belts need to be in tension (fully stretched/ tightened) for accurate motion transmission. If the belts are loose, they might miss a turning step from the motor and for a machine where the precision that we speak of is 0.2mm then a mis-step can be devastating for the print. Similarly, the pulleys should always be free from friction for precise motion transmission. The printer operator/ user should always keep a check on the belts’ path so that no dust or other particles are present which may result in damaging the belt or jamming the pulleys in the long run. Moreover, proper cleaning and lubrication of belts and pulleys should be done once a month to keep the printer running smoothly and without motion errors.

Limit Switches

Limit switches are basically boundaries of the overall motion of the FDM 3D printer. They stop the motion of the motors when the respective movement tends to go beyond the printable area. Whenever home/ auto-home command is given, the printer head moves to the extreme ends of all three axes triggering all the limit switches. So, it is necessary that nothing comes in the way of limit switches else it will result in inaccurate home point calibration.

Graphical User Interface

Graphical User Interface or GUI is the control system of the 3D printer. It can be a touch screen or it may be a display with a control knob. Internal functionalities and options almost remain the same. Common terms that are usually used from the GUI are:

  • Auto Home or Home
  • Bed Heating
  • Nozzle heating
  • Move Axis
  • Print from SD card
  • Stop/Pause print

Whenever a temperature for the nozzle or bed is set, the display screen shows the set temperature as well as the current temperature. The other thing that can be seen on the display are fan conditions (On/Off, Speed), real time coordinates of the nozzle, name of the file being printed, printing progress (time to complete), feed rate (speed of printing), flow (flow of material), etc

 

Firmware

Firmware is the internal controlling program that manages all the background operations of the 3D printer from controlling the steps of the stepper motor till reading the lines of the g-code file. Firmware should not be modified by non-professionals of this field. However, for the official firmware updates that are launched by printer manufacturers, installation guidelines are also provided by manufacturers which must be strictly followed to avoid malfunctioning of the printer.

G-code file is basically a file that contains a set of commands for printing a specific part. It contains the sequential information about coordinates through which the nozzle of the printer has to move and deposit material in order to achieve the printed part. It also has all the information about speed of printing and flow of material. G-code file is generated from slicing software such as Ultimaker Cura which takes 3D models as input.

Fans and Air-circulation

FDM 3D printers require more than a couple of air-circulation units. The fans can be categorized into three categories namely, electronics heat dissipation fan, hotend temperature control fan and print cooling fan.

Electronics Heat Dissipation Fan

A fan is required to keep the electronics cool as there are 3 or more stepper motor drivers which need to dissipate heat due to long duration operations. This fan or set of fans need to run throughout the printing so that no electronics component fails due to excessive heat or burns out.

Hotend Temperature Control Fan

The heater at the hotend whose job is to heat and melt the printing material needs to maintain the same temperature to achieve smooth printing finish and uniform mechanical properties. The heater is assembled with a temperature sensor and cooling fan, which perform together to achieve desired temperatures quickly. This fan runs during the whole printing. If this fan fails to operate, the heater will overheat and would take excessive time to reach the desired temperature due to natural convection instead of forced convection (caused by fan).

 

Print Cooling Fan

During printing, the molten plastic layers need to cool at a specific rate to achieve uniform mechanical properties and surface finish. So, a fan or a couple of fans are assembled and their flow is positioned on the part being printed. During the initial layer of the print, this fan does not run, enabling the proper bed-adhesion of the layer. Once the initial layer is done, this fan starts and runs till the completion of the print. If this fan fails to operate, the printing object will be left to cool at ambient temperature resulting in warping and cracking between the layers because of non-uniform cooling between the layers

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