The plastic extrusion process is shown in this video where it is explained that the process starts by heating a thermoplastic to a molten state. The polymer in liquid state is then pushed through a die in the desired profile of the extrusion and cooled. This process can be used to make sections such as bar, rod, tube, sheet, films, filament, wiring insulation and profiles of complex cross-section. The video also takes us through some more detail on both profile and blown film extrusion processes.
It is interesting to see the feed and drag flow is very much the same as the initial process used in injection molding to melt and feed the plastic.