The joining of two pieces of metal at a temperature close to their fusion point. The goal of welding is to form as homogeneous a joint as possible. Welding requires that the surfaces being joined should either melt or reach a plastic state, unlike soldering in which the solder melts and wets the surfaces to be joined, holding them together by adhesion. With iron and steel, pressure welds between separate pieces can be achieved by heating and hammering them together. See also Electric arc welding- Fire or Forge welding- Fusion welding- Pattern welding, Manual Metal Arc welding (MMA)- Metal Inert Gas (MIG welding)- Plug weld- Spot welding- Tungsten Inert Gas welding (TIG welding).