Which method is NOT considered a fixing method?

The correct choice is welding as the method that is not primarily considered a fixing method. Welding is a fabrication process that involves joining materials, typically metals or thermoplastics, by melting the base material and adding a filler material to form a strong joint once the material solidifies. While welding does create a connection similar to fixing, it does so through a thermal and chemical process rather than merely affixing separate components together.

In contrast, nailing is a straightforward fixing method that involves driving nails into materials to hold them together. Extrusion is a manufacturing process where material is pushed through a die to create objects with a fixed cross-sectional profile, but it is not used primarily for joining items together. Tube bending shapes materials without necessarily joining them, which can also be viewed as a forming process rather than a fixing one.