FFF or Fused Filament Fabrication printing, also known by FDM or Fused Deposition Modeling (a term trademarked by Stratysys, Inc.), is a printing method that heats a solid thermoplastic filament to a semi-liquid state and extrudes it in thin layers, one upon the other. Once the material cools, the part becomes solid. This is a very common type of 3D printing. Parts printed using this process are brittle and not sustainable for mechanical parts. Being that parts are printed in layers, they are weaker in one direction than the other. See FFF in action.

SLA or Stereolithography printing uses vat polymerization. A photo-polymer resin in a vat is selectively cured by a light source. Unlike FFF printing, this method produces a smooth finish with fine detail. Like FFF printing, this process also creates brittle parts that are not suitable for mechanical parts. See SLA in action.

SLS or Selective Laser Sintering uses powder bed fusion. A bed full of powdered plastic provides the material to buld parts. A laser is used to heat the desired areas, fusing the plastic powder together to create the desired part. The bed drops after each layer, the powder is distributed evenly, and the process is repeated until the final dimensions have been reached. A similar process can be used to fuse metal powder into usable parts. This process is known as DMLS or Direct Metal Laser Sintering.  See SLS in action. See DMLS in action. 

Exotic filaments (sometimes seen as hybrid filaments) are becoming more popular and the range is widening. Some of these include wood, metal, and clay, which all contain a powder or fiber mixed with the polymer to produce a unique look. Since these filaments contain other materials, they behave differently, as well. Other exotic filaments look normal but have altered properties. They can be magnetic, conductive, glow-in-the-dark, color changing, or flexible. Some even dissolve in water!

Flexible filaments generally consist of TPC (thermoplastic copolyester), TPE (thermoplastic elastomer) and TPU (thermoplastic polyurethane). These materials are much like a printable rubber. The difference between the two lies in their hardness values. Nylon filament is also gaining in popularity.

Rigid filaments are the typical, everyday filaments. The most prevalent are ABS (Acrylonitrile Butadiene Styrene) and PLA (polylactic acid), but there are a variety of others. Some other significant rigid filaments include PETG (glycol-modified polyethylene terephthalate),  PC (polycarbonate), ASA (acrylonitrile styrene acrelate), POM (acetal), and PMMA (polymethyl methacrylate).

PLA is the most popular filament. It is easy to print with, has a lower printing temperature than ABS, doesn't warp easily, does not produce intense fumes when printing, is biodegradable, and can be food-safe (check the manufacturers specifications). It is more environmentally friendly than many other filaments as it is made from renewable resources like corn starch and sugar cane. The main issue with PLA is that it is brittle. Avoid using it when making items that might be bent, twisted, or dropped repeatedly.

ABS is the second most common filament. It is slightly more difficult to print with than PLA, as it has a tendency to warp during cooling. ABS is tough and able to withstand high stress and temperature and it is moderately flexible. It does, however, emit very strong fumes when printing. ABS is used for many household and consumer goods, like LEGO's and bicycle helmets. An important thing to keep in mind, though, is that 3D printed parts are significantly weaker (70% or more) than their injection molded counterparts.

Click here to learn more about the other materials listed or to find more specific information about ABS or PLA.

Soluble filaments include HIPS (high impact polystyrene) and PVA (polyvinyl acid). These materials can be used as support materials and later dissolved away to create parts that would otherwise be or impossible to print. HIPS can be dissolved in limolene, where PVA can be dissolved in water.

When preparing to print, there are a number of considerations to be made. Initially, you import your file and place it on the build surface. How the part sits on the print bed can affect the quality of the print. Next, the quality of the print must be considered. Is the part to be printed meant to be a quick test run or a final part? 3D printers can be fully automatic or fully customizable, depending on the brand. For those that have at least some settings that can be adjusted, it is important to know which settings to select.

Part alignment: How the part will sit on the print bed will affect the amount of material used, print time, and print quality. You want to print objects so they will require the least amount of fill material possible. This adds print time and adds to material usage. Also, the layering of plastic upon itself creates a grain pattern. Like a piece of wood, it is easier to break the part with the grain than it is across the grain.

Printing for speed: Thicker layers and increased speeds can reduce print time, but can also affect print quality. There is a point where thicker layers also begin to use more filament (~0.3 mm). Also, the infill amount and pattern can affect the speed and quality of the part being printed. Increasing the speed will not have a significant impact on smaller prints. This can run the nozzle through corners too quickly, having drastic [negative] effects on overall quality. 

Printing for quality: As one may imagine, using settings opposite that used for speed will result in higher quality. Thinner layers and reduced speeds result in higher quality. But there is a definite trade-off between speed and quality. Also, the amount and pattern of infill will affect the quality. This is the amount of material that is printed inside "solid" objects. Something that is designed to be solid is often not printed that way.

Layer Height: Higher layer height results in stronger prints but makes the outer surface of the printed object rougher. Larger nozzles are capable of printing greater layer heights than smaller nozzles. A standard nozzle is 0.4mm and generally prints layer heights ranging from 0.05mm to 0.25mm. Printing at 0.05mm will produce smooth edges but decreases strength and greatly increases print time. Items printed at 0.25mm are often drafts used to quickly print an item and check to see if it will work as desired. Often, people print many useful objects at 0.2mm or use 0.1mm - 0.15mm for prints requiring smoother edges (like models). 

Perimeters: Perimeters are the number of shells that form the outer walls of an object. More perimeters can add strength to a 3D printed object. It can also help with elasticity - an objects ability to spring back to its original shape after a load is applied, deforming the shape. For this concept, think of a rubber band and how it springs back to its original shape after being stretched. Additional perimeters can also help create hollow angled shapes without failing - this is because it reduces gaps that may occur if there are not enough perimeters. 

The infill refers to the inner structure of a 3D printed part. The inside is not solid. Some infill patterns are standard across various slicers while others are unique to one program or brand. In class, your designs will be printed on Prusa printers, so the options below are those available on PrusaSlicer. A slicer is a type of software that takes a 3D model and slices it into layers that can be printed. 

There are also infill options for the top and bottom layers. As seen in the image below, they can alter the aesthetic of the top and bottom layers. Rectilinear and monotonic appear identical below, but rectilinear can produce odd textures on the surface of a part where monotonic will not. Aligned rectilinear is great for parts that have top layers in multiple heights ( think of stairs). Concentric, like above, will follow the outer shape. Archimedean chords create a spiral that can save time printing certain shapes. And the Octogram spiral is creates aesthetic interest but increases print time. 

The picture below shows ironing. In 3D printing, ironing smooths flat top surfaces. As the hot nozzle travels over the just printed top layer, it flattens any plastic that might have curled up. The nozzle also extrudes a small amount of filament to fill in any holes in the top surface. The spacing between individual ironing passes is usually a fraction of the nozzle diameter. That means the nozzle will go over the same spot several times. Ironing is angled at a fixed 45 degrees compared to the first phase of normal top infill as this approach produces better results.

The main downside is increased print time as the second phase of the top infill is performed with very small spacing between ironing lines. You can see how much print time will be spent on ironing in the preview.

If ironing a big surface area, some machines might experience heat creep and eventually, a clogged hotend because the extrusion is very small and slow during ironing. This might be a problem mainly when printing with PLA, because of its low-temperature resistance. The risk is increased during summer heatwaves.

Another downside is that the edges will be a tiny bit fuzzy or less sharp. The ironing toolpath is planned for a small extrusion, but the nozzle is physically still the same size, so some plastic will bleed over the edge.

Ironing is useful for prints with flat top surfaces, like nameplates, logos, badges, boxes, lids, etc. Ironing can also be useful when two pieces  will be glued together and need the surfaces to be as flat as possible so that the gap between them is minimized.

Ironing is not useful for round objects, figures, and organic shapes in general. It is also not useful for objects that do have flat areas, but these flat areas are not aligned parallel to the print bed. With that said, ironing will not have a significant negative impact when printing such models, but will unnecessarily increase print time.