UNIT—II JOINING PROCESS WELDING: Process of joining similar metals with the application of heat and with or without the application of pressure. While welding the edges of metal pieces are either melted or brought into plastic condition. Used in the manufacturing of Auto mobiles bodies, structural work, tanks, and general machine repair work. In the industries , welding is used in refineries and pipe line fabrication.

TYPES OF WELDING PROCESS Plastic Welding (or) Pressure Welding: Metal pieces are heated to plastic state and pressed together. Ex: Electric resistance welding Fusion Welding (or) Non-pressure welding: Metal is heated to molten state and they are allowed to solidify Ex: Gas welding, Arc welding

Classification of welding processes: 1: Gas Welding (a) Air Acetylene (b) Oxy  Acetylene (c) Oxy Hydrogen Welding 2: Arc Welding (a) Carbon Arc welding (b) Plasma Arc welding (c) Shield Metal Arc Welding (d) T.I.G. ( Tungsten Inert Gas Welding) (e) M.I.G. ( Metal Inert Gas Welding)

(c) Projection welding (d) Resistance Butt welding 3: Resistance Welding: (a) Spot welding (b) Seam welding (c) Projection welding (d) Resistance Butt welding (e) Flash Butt welding 4: Solid State Welding: (a) Cold welding (b) Diffusion welding (c) Forge welding (d) Fabrication welding (e) Hot pressure welding (f) Roll welding

5: Thermo Chemical Welding (a): Thermit welding (b): Atomic welding 6:  Radiant Energy Welding (a): Electric Beam Welding (b): Laser Beam Welding

GAS WELDING Joining of metals with the help of high temperature flame and filler rod. Flame is generated by mixture of Oxygen and Acetylene. Mixture of combustible gases are also be used.

Oxy-Acetylene welding

The temperature generated during the process is 33000c When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld. Fluxes are added to the welded metal to remove oxides Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid.solid coating or gas.

FLAT HORIZONTAL OVERHEAD VERTICAL Welding Positions INCREASING DIFFICULTY FLAT HORIZONTAL OVERHEAD VERTICAL

TYPES OF FLAMES

NEUTRAL FLAME CARBURISING FLAME Oxygen and Acetylene ratio is equal. Temperature about 3250° C. Used to weld carbon steels, Cast iron, Copper, Al etc. CARBURISING FLAME Oxygen and Acetylene ratio is 0.95 to 1 Three Zones Luminus Zone. Intermediate cone of white colour. Outer envelope. Temperature about 3150° C Used to weld monel metal, high carbon steel, alloy steel.

Equipments OXIDISING FLAME Gas Cylinders Pressure Regulators Oxygen and Acetylene ratio is 1.2 to 1.5 Temperature about 3480° C Used to weld Copper, Bronze, Zinc-Bearing alloys.. Equipments Gas Cylinders Pressure Regulators Pressure Gauges Welding Torch Hose and Hose fittings Safety Devices

FLUX

ARC WELDING Metal pieces are joined melting their edges by an electric arc. Electric Arc produced between Two Conductors Elctrode is one conductor and Workpiece os another conductor. Small Air-gap 3mm.

ARC WELDING EQUIPMENTS

Arc Welding Equipments

Arc welding electrodes Non-consumable electrodes Made of Carbon, Graphite, Tungsten Carbon and Graphite – D.C Welding Tungsten – Both Filler material added separately. Consumable electrodes Bare Electrodes Flux or lightly coated electrodes Coated or extruded electrodes

Coated electrodes Electrode size 1-2 mm layer 15-30% of the weight of the electrode rod. Electrode size 3.2, 4, 5, 6, 8, 9, 12 mm diameter and length 350 or 450 mm.

TIG Welding Also called as Gas Tungsten Arc Welding (GTAW). Inert Gas – Gas which does not combine chemically with the metal being welded. Argon & Helium Strong welds Alloys of Al, SS, Ni, Cu, CS. Dissimilar metals can be welded.

Mig welding Tungsten electrode is replaced with consumable electrode. Electrode is driven through same type collet that holds a tungsten electrode by a set of drive wheels.

Difference between TIG and MIG welding

Submerged Arc welding Flux powder is fed into the hopper. Arc submerged in the flux material. No Spatter or gases. No reaction with atmosphere. High strength and ductility.