There are four chief manufacturing methods: CASTING (Zero process) FORMING(Zero process) MACHINING ( Negative process) WELDING (Positive process) These methods are based on different principles of shaping metals. CASTING AND FORMING involve shifting of metal in controlled way to get the required size and shape of product. Hence, these are termed as zero processes.

MACHINING Machining is considered as negative process because unwanted materials are removed in form of chip for shaping metal.

WELDING  In manufacturing, it is frequently required to join the simple shape component to get desired product. Hence, joining processes are called positive process.  Three joining techniques are commonly used viz. Mechanical joint (nuts & bolts, clamps, rivets), Adhesives ( epoxy resin, fevicol ),Welding & allied process (welding, brazing & soldering).

WELDING PROCESS: Introduction Ship Structures Under Water Welding Robotic MIG

Selection of type of joint Selection of type of joint depends on the following factors:  Types of joint : Temporary, permanent  Metal to be joined : steel, cast iron, aluminium and dissimilar metals or any other combination.  Requirements of the service : Temperature, corrosion, nature of load and reliability.  Economy

WELDING PROCESS: Introduction  J Joining two or more elements to make a single part is termed as a fabrication process  W Welding is used as a fabrication and repairing process for two similar or dissimilar metals; gives permanent joint  I It uses raw material obtained from primary manufacturing processes thus termed as secondary manufacturing process  I It joins different metals/alloys by fusion, with or without the application of pressure and with or without the use of filler metal.  T The fusion of metal takes place by means of heat generated in a different way SSome of the typical applications of welding include the fabrication of ships, pressure vessels, automobile bodies, off- shore platform, bridges, welded pipes, sealing of nuclear fuel and explosives, etc.

 The weldability may be defined as property of a metal which indicates the ease with which it can be welded with other similar or dissimilar metals.  Weldability of a material depends upon various factors like the metallurgical changes that occur due to welding, changes in hardness in and around the weld, gas evolution and absorption, extent of oxidation, and the effect on cracking tendency of the joint.  Plain low carbon steel (C-0.12%) has the best weldability amongst metals. WELDING PROCESS: Weldability

WELDING Fusion Welding Pressure Welding HomogeneousHeterogeneous BrazingSoldering Gas Welding Electroslag High Energy Beam Electric Arc MIG TIG Shielded Metal Arc Friction Welding WELDING PROCESS: Types

Some Important Terms  Backing  Base Metal  Weld bead  Crater  Deposition Rate  Fillet weld  Penetration  Puddle  Root  Weld face  Weld metal  Torch