Extrusion welding is one of the processes used to weld thermoplastics and composites. It can be a manual or automated process.

The process uses a welding head that has a nozzle for hot air and an extruder that pushes filler material out.

The process entails heating of the joining (faying) surfaces by means of heat and addition of molten or plasticized filler material (extrudate) being extruded through a die (shoe).

The extrudate is applied with pressure to ensure good bonding, and then the part is allowed to cool. Main use for extrusion welding is in environmental applications where it is used in the joining of lining material for the construction of landfill waste sites, lagoons, roof coverings and HDPE tanks.