What does FDM printing mean?

FDM is an abbreviation for "Fused Deposition Modeling", also known as FFF, or "Fused Filament Fabrication". This technology falls under the category of material extrusion in 3D printing additive manufacturing processes. In FDM printing, objects are constructed by selectively depositing molten material layer by layer in a predetermined path. The material used is a thermoplastic polymer that is filamentous.

FDM 3D printing technology principle (printing process)

Step: The thermoplastic material filament is first loaded into the printer. Once the nozzle reaches the desired temperature, the wire is fed into the extrusion head and nozzle to melt.

Step 2: The extrusion head is connected to a 3-axis system that allows it to move in the X, Y, and Z directions. The molten material is extruded into filaments and deposited layer by layer at a predetermined location, cooled and solidified. If necessary, the cooling and curing of the material is accelerated by using a cooling fan attached to the extrusion head.

Step 3: Fill an area that requires multiple reciprocating motions to print. When the single layer is complete, the build platform moves down (or, in other devices, the extrusion head up) to begin depositing a new layer. Repeat this process until the part is complete.

Advantages and disadvantages of FDM 3D printing

Pros:

1. FDM is a cost-effective way to produce custom thermoplastic parts and prototypes.

2. Due to the high availability of technology, FDM has a short lead time.

3. A wide range of thermoplastic materials are available, both for prototyping and for some non-commercial functional applications.

Cons:

1. Compared with other 3D printing technologies, FDM has dimensional accuracy and resolution, so it is not suitable for parts with intricate details.

2. FDM parts may have visible layer lines, so post-processing is required to obtain a smooth surface.

3. The interlayer adhesion mechanism makes FDM parts inherently anisotropic.

FDM printing parameters

Most FDM systems allow for adjustment of multiple process parameters, including nozzle and build platform temperature, build speed, layer height, and cooling fan speed. But from a designer's point of view, what matters is the build size and layer height.

The build sizes for general equipment are as follows:

Desktop 3D printer: 200 x 200 x 200 mm Accuracy: ±0.5% (***±0.5mm)

Industrial 3D Printer: 1000 x 1000 x 1000 mm Accuracy: ±0.15(***±0.2mm)

Single layer printing height between 50 - 400 um. Smaller layer heights result in smoother parts that capture curved geometries more accurately, while larger heights produce parts faster and at a lower cost. Under normal circumstances, the commonly used layer height is 200 microns.

The supporting structure is connected to the bridge

1. Bridge connection

The heated material is semi-molten, in which the material can be stretched over short distances between two points. The bridge allows the material to print without support and with small sagging allowed. However, if the bridge distance exceeds 5mm, support is usually required to provide accurate printing processing. In addition, when printing some epitaxial cantilevers, if the cantilever angle is within a certain range, it can also be printed without support.

2. Support

The FDM printing method employs two types of supports:

Flat accordion or lattice shape, which is the most common and suitable for most FDM prints.

The second type is the "tree" support, which is widely used in most FDM devices today. The "tree" support ensures that the support has less contact with the printed surface and can achieve better surface post-treatment results.

Support is essential in FDM printing, but it also has some problems, such as the need for post-processing, imperfect layers, increased printing costs, etc.

Filling density vs. shell thickness

FDM parts are typically not printed solid to reduce print time and save material. Instead, a shell is printed based on the outer perimeter of the object, and then a low-density structure (called a "filler") is filled inside.

The density of the filling and the thickness of the shell greatly affect the strength of a section. For desktop FDM 3D printers, the default setting is 25% fill density and 1 mm case thickness, which is a good solution between fast print strength and speed.