Fused Deposition Modeling

FDM is the most common 3D printing method used in desktop 3D printing. Thermoplastic filament is heated and extruded through an extrusion head that deposits the molten plastic in X and Y coordinates, while the build table lowers the object layer by layer in the Z direction.

Effectively, the object is built from the bottom up. If an object has overhanging parts, however, it will need support structures that can be removed after the printing is finished.

This type of 3D printers is a cost-effective means for product development and rapid prototyping in small business and education sectors since it’s capable of fabricating robust parts reliably and quickly.

Source : all3dp.com

Dual Extrusion

Dual extrusion is the process of 3D printing with multiple filaments. 

​

You can mix colors or different materials with a print head that has two extruders and nozzles. 

​

With two spools loaded, the printer alternates between them by printing one at a time.

It's not actually faster at printing because its still using only one extruder at a time.