Rapid Prototyping by 3D Printing

Stereolithography
Stereolithography, or SLA, is an additive manufacturing process that involves a liquid photopolymer resin that is cured and solidified, layer by layer, using an ultraviolet laser. After the entire model has been "scanned" by the laser, it is fixed in an ultraviolet oven to maintain its final form.

SLA has many advantages, including being accurate, relatively affordable, and freely available. The models also have smooth and detailed textures, making it easy to paint or add different finishes. You can add a lot of fine detail to SLA-printed models, which you can't do as well with many other processes. The result is also heat resistant to an extent.

On the downside, SLA doesn't create the strongest of models. It's not the ideal solution if the rapid prototype needs to handle a lot of strain, and UV light and moisture can also degrade its quality.

Stereolithography printers can be hefty since they have tanks to hold the photopolymer resin. The size has an added advantage since the larger your printer, the bigger the models you can print.

Fused Deposition Modelling
FDM is the most common and popular 3D printing technology because of its simplicity and affordability. It's the rapid prototyping technology most commonly taught at schools and most often used at home for business or pleasure.

The process involves thermoplastic filament, usually bought on a spool, that gets fed into a nozzle where it's melted and extruded onto a printing bed in layers. These layers build the model from the bottom up.

FDM has several benefits, not least of which is its cost. The machines and filaments are exceptionally affordable compared to other 3D printing technologies. They are also relatively fast, and the building quality is decent.

Unfortunately, FDM is not a good solution for prototypes that require high durability. The textures can also be a bit rough, but you can tweak many settings to improve this. Another potential drawback is that you must prepare support structures, where needed, for FDM to work correctly since molten plastic will sag if there's nothing to support it.

CNC Machining
CNC machining, or Computer Numerically Controlled machining, is another typical rapid prototyping technique that's often used, but it works oppositely from most others. Instead of building a model using various materials, it starts with a base material and uses a subtractive method to remove parts of it.

CNC starts with a rod stock (a fancy way of saying "solid block") of either plastic or metal. The block is clamped into a CNC lathe or mill, which then moves around three axes to remove layer after layer of the stock material to manufacture the model.

Manufacturers often use CNC to add finishing touches to models manufactured using other additive methods, but it's also possible to create a model entirely using only CNC processes.

CNC models are remarkably strong because they aren't formed using layers. You start with a solid block of whichever material you're using, so the material will retain its structural integrity for the most part. The results can also look highly polished, or you can add fine details by hand after the process.

Selective Laser Sintering
SLS, or Selective Laser Sintering, is similar to SLA because it uses a laser to 3D print your rapidly prototyped models. Unlike SLA, though, it uses a CO2 laser to do this instead of a UV laser. SLS also uses resin in a powdered form rather than liquid.

The CO2 laser "draws" your model in the powder layer by layer, fusing the powder into a solid unit (a process called "sintering"). The model doesn't require baking in a UV oven after it's finished.

SLS creates very sturdy models. Some engineers use SLS to manufacture replacement parts for larger machines rather than just models. The plastic parts can be fully functional and have isotropic mechanical characteristics. There's a lot of fine detail in the prototypes.

However, the finish isn't smooth, and your prototype will have a rough surface with no transparent options. Material is also more challenging to find than other 3D printer materials. But the process of SLS is so effective that it gave rise to other rapid prototyping processes that use different materials but the same method as SLS.

Direct Metal Laser Sintering
DMLS stands for Direct Metal Laser Sintering. It works on the same principle as SLS, but instead of using resin powder, it uses powdered metal. You can use DMLS to make prototypes using aluminum, stainless steel, titanium, Inconel, maraging steel, or cobalt chrome. A high-powered laser beam fuses the powder to "draw" your model one layer at a time.

Because it uses actual metal, DMLS is perfect for heavy-duty and final-prototype projects. This is ideal if you want a model that can withstand lots of strain and would be suitable as a production unit. People have used DMLS to 3D print many models, including a titanium electric guitar.