What occurs during the second step of FDM?

In the context of Fused Deposition Modelling (FDM), the second step typically involves the extrusion of the filament through the deposition head, where the material is heated to a semi-molten state. During this step, the volumetric pump plays a crucial role by pushing the filament into the heated nozzle, where it is melted just enough to become extrudable.

This process is significant because the molten polymer allows for precise control of material flow, enabling the printer to create layers that will adhere to one another. The extrusion of semi-molten polymer is essential for the subsequent layers to be deposited effectively. Each layer is formed as the material is extruded, cooled, and then solidified in its new shape, leading to the finished 3D object.

If one considers the other options, unwinding the filament from the spool occurs before the actual printing process begins, and the printing of the first layer and the solidification of the plastic occur later in the FDM process. Thus, the extrusion of semi-molten polymer is a pivotal step that directly sets the stage for successful layer deposition.