Welding Basics

Welding Definition

• A process used to permanently joining two pieces of metal, usually by means of heat.

Welding Uses

Used in manufacturing to produce or repair…• Barges• Ships• Storage tanks• Pipelines• Trains• Automobiles• Airplanes• Home Appliances

Welding Uses (continued)

Used in construction to build…BridgesBuildingsRoller coasters

Welding Classification

There are many welding processes, which can be classified into one of three groups1. Fusion welding2. Solid-state bonding3. Brazing and soldering

Fusion Welding

• Uses heat to partially melt the metal surfaces that are to be joined.

Common fusion welding processes• Arc Welding• Oxy-fuel welding• Electric resistance welding• Laser beam welding• Electron beam welding• Thermite welding

Solid-state bonding

• Uses pressure as well as heat to bond metal and other materials.

Common solid-state bonding processes• Diffusion welding• Roll welding• Friction welding• Forge welding• Ultrasonic welding• Explosion welding

Brazing and Soldering

• Uses a melted filler metal to join usually close fitting parts. The parts being joined do not melt.

Brazing- uses fillers such as bronze, brass or a silver alloy.

Soldering- uses fillers with lower melting points such as lead-tin alloys.

Filler metal

• Most fusion welding uses a filler metal, which is also melted and mixed with the material being welded.

• The filler metal can either be a rod (stick) or a consumable electrode.

Shielding

• Most fusion welding requires that the heated metals be shielded from hydrogen, nitrogen and oxygen in the atmosphere.

• If metals absorb these gases, the weld could be weak or brittle.

ShieldsShielding is done by flux, a vacuum or an inert gas

• Flux- a chemical substance used to clean metal of oxides and other impurities.

• Vacuum- a space without matter

• Inert gas- A gas that normally does not combine chemically with the base metal or filler metal.

Arc Welding

• Uses a welding power supply to create an electric arc between the electrode and the base material to melt the metals at the welding point.

Electric Arc- The flow of electric current present between two electrodes, formed when electricity jumps from one electrode to another.

Electrode- A conductor that passes an electrical current from one medium to another.

Common types of Arc Welding

• Shielded metal arc welding (SMAW) also called manual metal arc welding (MMAW) or stick welding

• Gas metal arc welding (GMAW) also called Metal inert gas (MIG) welding

• Flux-cored arc welding (FCAW)• Submerged arc welding (SAW)• Gas tungsten arc welding (GTAW) also called

tungsten inert gas (TIG) welding

Flux-cored arc welding (FCAW)

• FCAW wire is actually a fine metal tube filled with powdered flux materials. An externally supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the necessary protection from the atmosphere.

Submerged arc welding (SAW)

• A high-productivity welding process in which the arc is struck beneath a covering layer of granular flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux.

Gas tungsten arc welding (GTAW) also called tungsten inert gas (TIG) welding

• A manual welding process that uses a non-consumable electrode made of tungsten, an inert or semi-inert gas mixture, and a separate filler material.

http://www.youtube.com/watch?v=FD7fcdFESos&feature=c4-overview-vl&list=PLDFAD0F77CEEE7654

Shielded metal arc welding (SMAW) or stick welding

• An electric current is used to strike an arc between the base material and a consumable electrode rod or stick.

• http://www.youtube.com/watch?v=JEF0_yTTL7w

Gas metal arc welding (GMAW) Metal inert gas (MIG) welding

• Uses a continuously fed consumable wire acting as both electrode and filler metal, along with an inert or semi-inert shielding gas flowed around the wire to protect the weld site from contamination.

http://www.youtube.com/watch?v=UeiPOQQirk4&list=PLDFAD0F77CEEE7654&feature=c4-overview-vl

MIG Diagram

MIG Diagram

Common Welding Joints