Introduction to Fused Deposition Modeling (FDM)

A diagram of Layer-by-Layer printing.

Fused Deposition Modeling (FDM) is an additive manufacturing process where an object is formed by extruding melted material in a pre-determined path layer by layer. The process is as follows:

1. A computer program “slices” a 3D object into hundreds of thin cross sections.
2. The 3D printer accepts the sliced 3D model and begins heating a metal nozzle.
3. A long strand of thermoplastic is fed into the hot nozzle by a system of gears.
4. The nozzle is displaced horizontally by two belts to deposit the melted filament onto a build platform in a pattern that corresponds to a single layer of the sliced model.
5. The build platform and the deposited plastic layer lowers by a fraction of a millimeter.
6. The nozzle prints the next layer.

This continues until every layer has been deposited and the model is complete. The process can take anywhere from 30 minutes to multiple days depending on the size and resolution of the object. An average print in the Fabrication Farm takes 3 hours of operating time on a machine.

The MIC is capable of printing in three different types of plastic filament.

PLA, or Polylactic acid, is a corn-based thermoplastic polymer, meaning that it softens under heat, and becomes solid again once it cools. Thermoplastics are the lifeblood of FDM printing, and PLA is the most affordable of them all. Additionally, it is the easiest to use because it becomes malleable at a relatively low temperature (185C).

ABS, or Acrylonitrile Butadiene Styrene, is another common thermoplastic. It is valued for its thermal and impact resistance, but it is more difficult to print with (240C). The MIC no longer prints with ABS. Instead, ABS print requests are fielded by the AFL.

TPU, or Thermoplastic Polyurethane, is a flexible filament compatible with select printers. The elasticity of the material lends itself to special projects and uses, but makes the printing process more difficult. The MIC only prints Ninjatek’s Cheetah flexible filament on the MakerBot Replicator 2.

The MakerBot Innovation Center inherits its name from the 3D printer that populates the shelves: The MakerBot Replicator. Four versions of the machine perform the daily functions of the lab:

MakerBot 5th Gen Replicator	MakerBot Replicator +
MakerBot Z18	MakerBot Replicator 2

This machine comprises the majority of the lab’s operation. Rep(licator) 5’s use the detachable Smart Extruder, and are beneficial to a print farm because a malfunctioning extruder can be replaced in a matter of minutes.

The Rep + is a small upgrade from the Rep 5, featuring a slightly enlarged build volume and a flexible Build-Tak print bed that improves adhesion of the first layer and aids removal of the finished part. The Rep + uses the Smart Extruder attachment.

The Z18 is much like the Rep 5, but it has a significantly larger build volume for extra large prints. The heated chamber reduces warping in the product, a necessity for large format printing. The Z18 uses the Smart Extruder attachment.

The Rep 2 is an early, open-source iteration of the MakerBot line. It is capable of printing in ABS and Flexible Filament, but it does not use the Smart Extruder. The extruder is not removable, reducing the machine’s uptime when it malfunctions.

The MakerBot Replicator has five primary components.

Glass Bed

Build-Tak Bed

The build platform is a plastic tray that holds a detachable bed made of either glass or plastic. In order to adhere the plastic from the extruder to the glass bed of the Rep 2 and Rep 5, you must apply either painter’s tape or stick glue. The MIC uses painter’s tape sheets manufactured by MakerBot. Precut painter’s tape sheets are available on the shelf where customer prints are stored. The tape should be replaced when it becomes rippled or if a hole larger than a penny is present.The Build-Tak surface of the Rep + and Z18 provides ample adhesion on its own, and does not require glue or tape. Adhesion is important to a print because it prevents the corners of a print from lifting off the bed in a process called warping.

The platform descends gradually over the course of the print so that the extruder nozzle is always level with the current layer. Two adjustable screws must be corrected monthly to keep the print bed level.

The front panel of a Rep 5

Much of the printing process is handled remotely from the ICMP, but some tasks require the use of the front panel on the upper frame of the Rep 5.

The user interface

Print. The Makerbot supports printing directly from internal or USB memory, but this does not collect usage statistics about the printer, so we do not use the Print option from the panel.

Filament. This button is part of the filament replacement process, detailed in a dozuki guide later on.

Hot parts of the Extruder

Preheat. The ability to heat an extruder without initiating a print can be beneficial to extruder repair because it makes it possible to clear jammed plastic in the extruder nozzle. Take caution: the metal parts of the smart extruder, including the exposed fins above the nozzle, will burn you at this temperature. The hot parts of the extruder have been annotated above with red rectangles. Wear heat resistant gloves before handling a hot extruder.

Settings. Printer settings, tools, and diagnostics are accessible here, but the majority of the important settings are determined when you export the sliced file from the MakerBot’s slicing software, MakerBot Print

Extruder. This section allows you to view information about the Smart Extruder or to attach a new one.

Info. Information about the printer’s history and statistics are available here.

Print progress screen

Print Progress. While a print is underway, you can use the circular knob to scroll between four pages. One of these pages is the print progress screen, which displays the print time elapsed and remaining. This information is additionally available on the ICMP at the printer’s page.

Rail System and Z-Stage

Rail System

The extruder moves about along the x and y axis using a rail system mounted to the upper frame of the MakerBot. The rail system is articulated by sprockets and rubber belts. The extruder is magnetically latched to a socket on the rails.

The build platform moves up and down via a corkscrew system. This axis is known as the Z-Stage. The extruder does not move up or down.

MakerBot Smart Extruder

The extruder is the most crucial component of any FDM printer. It is responsible for heating and depositing the thermoplastic that composes the final product. The Smart Extruder is remarkable for its simple detachment and replacement, driven by a magnetic connection to a dock on the MakerBot Rep 5, Rep +, and Z18. When a printer malfunctions, the extruder responsible is removed and catalogued for repair. Meanwhile, a new extruder is attached to the MakerBot printer, and it is ready to continue operation.

Extruder repair is a complicated process that is covered in detail in the coming shifts.

Ejected filament tray

The Guiding Tube

A removable spool of filament is stored in a tray at the back of the MakerBot. The line of filament feeds through a tube that guides it to a port on top the Smart Extruder. The processor of replacing the filament is explained in detail in a Dozuki guide later on.

When a spool of filament is expended, the loss is tracked via the Asset Management System. This process is explained later on as well.