Transcript Document
JOINING • Soldering • Produces coalescence of materials by heating to soldering temperature (below solidus of base metal) in presence of filler metal with liquidus < 450°C • Brazing • Same as soldering but coalescence occurs at > 450°C • Welding • Process of achieving complete coalescence of two or more materials through melting & re-solidification of the base metals and filler metal SOLDERING & BRAZING • Advantages • Low temperature heat source required • Choice of permanent or temporary joint • Dissimilar materials can be joined • Less chance of damaging parts • Slow rate of heating & cooling • Parts of varying thickness can be joined • Easy realignment • Strength and performance of structural joints need careful evaluation WELDING • Advantages • Most efficient way to join metals • Lowest-cost joining method • Affords lighter weight through better utilization of materials • Joins all commercial metals • Provides design flexibility WELDABILITY • Weldability is the ease of a material or a combination of materials to be welded under fabrication conditions into a specific, suitably designed structure, and to perform satisfactorily in the intended service • Common Arc Welding Processes • Shielded Metal Arc Welding (SMAW) • Gas Tungsten Arc Welding (GTAW) or, TIG • Gas Metal Arc Welding (GMAW) or MIG/MAG • Flux Cored Arc Welding (FCAW) • Submerged Arc Welding (SAW) ARC WELDING • Arc welding is a process used to join two pieces of metal together. • How does it work? • A welder creates an electric arc that melts the metal and filler rod to create a pool of molten metal that hardens to fuse the two pieces of metal together. • Why is welding important? • Many of the things you use need to be welded. • Your car • Power line towers • Your school desk • Your bicycle • Why Learn to Weld? • Welding can help build a successful career to earn money. • Skilled Welders are in high demand. • Welding is challenging and high tech. BASIC ELECTRICITY AND THE SCIENCE OF WELDING Voltage – The electrical potential or pressure that causes current to flow Measured in Volts Current – The movement of charged particles in a specific direction Measured in Amps Polarity DC- (Direct Current Electrode Negative) DC+ DC+ (Direct Current DC Electrode Positive) AC (Alternating Current) AC BASIC ELECTRICITY AND THE SCIENCE OF WELDING • The electricity flows from the power source, through the electrode and across the arc, through the base material to the work lead and back to the power source BASIC ELECTRICITY AND THE SCIENCE OF WELDING • The electron flow you just learned about is what creates the arc in arc welding. • This is a form of electrical energy • How do we use that electrical energy to fuse metals together? BASIC ELECTRICITY AND THE SCIENCE OF WELDING • Here are some places to look to learn more about energy and energy transfers. • Forms of Energy • Energy Transformations BASIC ELECTRICITY AND THE SCIENCE OF WELDING • Changes of State and Chemical Reactions • During the welding process the metal changes states or forms. • What are the states of matter? • Solid • Liquid • Gas • Plasma Click here to learn more about the changes of state BASIC ELECTRICITY AND THE SCIENCE OF WELDING • Changes of State and Chemical Reactions • So what changes of state occur during welding? • Initially the metal is a solid • When the arc starts the solid is converted into a liquid • Some of the liquid is converted into a gas vapor • When the arc stops the liquid cools to form a solid again – this is the newly formed weld joint Liquid Solid Solid weld joint (gas vapor) BASIC ELECTRICITY AND THE SCIENCE OF WELDING • Changes of State and Chemical Reactions • Chemical Reactions • During the welding process certain chemical reactions take place. • Hydrogen, Oxygen, and Nitrogen can react in the weld puddle and cause changes in the structure of the weld weakening the weld.