This document discusses various welding processes. It separates welding into two categories: fusion welding processes that melt the base metals like arc welding, and solid state welding processes that join metals without melting, like friction welding. The document focuses on describing several common arc welding processes including: shielded metal arc welding, gas metal arc welding, flux-cored arc welding, gas tungsten arc welding, plasma arc welding, and submerged arc welding. It also covers resistance spot welding, a type of resistance welding used to join sheet metals.