Welding differs from lower-temperature metal-joining methods such as brazing or soldering which don't melt base metal. A filler material is usually added to the joint in addition to melting the base material. This pool of molten materials (the pool) cools to form the joint that is based on the weld configuration. The base metal (parent metal) can be stronger than the filler material. Pressure can be used alone or in combination with heat to create a weld. To protect filler metals and melted metals from being contaminated, welding requires a shield. There are many energy sources that can be used to weld, including a gas flame (chemical), electric arc (electrical), and a laser. To further your readings buy a copy.......