ELECTRIC WELDING

                        ELECTRIC WELDING

 WELDING

WELDING IS A MATERIALS JOINING PROCESS WHICH PRODUCES COALESCENCE OF MATERIALS BY HEATING THEM TO SUITABLE TEMPERATURES WITH OR WITHOUT THE APPLICATION OF PRESSURE OR BY THE APPLICATION OF PRESSURE ALONE, AND WITH OR WITHOUT THE USE OF FILLER MATERIAL.

#WELDING IS USED FOR MAKING PERMANENT JOINTS.

# IT IS USED IN THE MANUFACTURE OF AUTOMOBILE BODIES, AIRCRAFT FRAMES, RAILWAY WAGONS, MACHINE FRAMES, STRUCTURAL WORKS, TANKS, FURNITURE, BOILERS, GENERAL REPAIR WORK AND SHIPBUILDING AND MANY MORE.

TYPES OF WELDING

1. PLASTIC WELDING OR PRESSURE WINDING

THE PIECE OF METAL TO BE JOINED ARE HEATED TO A PLASTIC STATW AND FORCED TOGETHER BY EXTERNAL PRESSURE. EXAMPLE- RESISTANCE WELDING

2. FUSION WELDING OR NON-PRESSURE WELDING

THE MATERIAL AT THE JOINT IS HEATED TO A MOLTEN STATE AND ALLOWED TO SOLIDIFY. EXAMPLE- GAS WELDING, ARC WELDING

RESISTANCE WELDING

RESISTANCE WELDING IS A PRESSURE WELDING TECHNIQUE USING HIGH CURRENT AND LOW VOLTAGE.

THE CURRENT PASSING THROUGH THE TWO OVERLAPPING WORKPIECE CAUSE LOCAL HEATING AND THE TEMPERATURE OF THE METALLIC PIECES RAISES TO THE FUSION POINT DUE TO RESISTANCE OFFERED BY THE WORKPIECES TO FLOW OF CURRENT.

SUBSEQUENT APPLICATION OF PRESSURE RESULTS IN PERMANENT JOINING OF THE WORKPIECES BY THE FORMATION OF WELD WITHOUT THE USE OF FILLER MATERIAL.

WORKPIECE ARE PLACED BETWEEN TWO RODS OR WHEELS (ROLLS), WHICH SERVE AS CONDUCTOR FOR PRODUCING WELDS

AC ELECTRIC CURRENT IS SUPPLIED THROUGH COPPER ELECTRODES OR ROLLS CONNECTED TO THE SECONDARY COIL OF A WELDING TRANSFORMER. IT IS USED FOR WELDING THIN SHEETS OF SIMILAR METALLIC MATERIALS.

THE FOLLOWING METALS MAY BE WELDED BY RESISTANCE WELDING:-

1. LOW CARBON STEELS - THE WIDEST APPLICATION OF RESISTANCE WELDING

2. ALUMINUM ALLOYS

3. MEDIUM CARBON STEELS, HIGH CARBON STEELS, AND ALLOY STEELS

ADVANTAGES OF RESISTANCE WELDING

1. HIGH WELDING RATE

2. LOW FUMES

3. COST EFFECTIVENESS

4. EASY AUTOMATION

DISADVANTAGES OF RESISTANCE WELDING

1. HIGH EQUIPMENT COST

2. LOW STRENGTH IN CASE

RESISTANCE BUTT WELDING

IT IS OF TWO TYPES:-

1. UPSET WELDING

UPSET WELDING IS USED TO JOIN THE PIECES END TO END THE PROCESS IS BEST SUITED TO RODS, PIPES, AND MANY OTHER PARTS OF UNIFORM CROSS SECTION.

IN UPSET BUTT WELDING, THE PARTS ARE CLAMPED AND BOUGHT IN SOLID CONTACT AND CURRENT IS APPLIED SO THAT THE HEAT IS GENERATED THROUGH THE CONTACT AREAS OF THR PARTS.

WHEN THE TEMPERATURE OF THE INTERFACE REACHES TO PLASTIC STATE, THE CURRENT IS SWITCHED OFF AND THE TWO PARTS ARE PRESSED TOGETHER FIRMLY. THIS RESULTS IN LATERAL FLOW OF THE SURFACES OXIDE LAYERS. THIS ACTION OF PRESSING TOGETHER IS CALLED UPSETTING

2. FLASH WELDING

FLASH WELDING IS SIMILAR TO UPSET WELDING EXCEPT THAT THE HEAT IS OBTAINED BY MEANS OF AN ARC THAN THE SIMPLE RESISTANCE HEATING.

THE TWO PARTS ARE BOUGHT TOGETHER AND THE POWER SUPPLY IS SWITCHED ON. AS THE PARTS ARE MOVED CLOSER, FLASHING OR ARCING RAISES THE TEMPERATURE OF THE PARTS TO A WELDING TEMPERATURE.

NOW POWER IS SWITCHED OFF AND TWO PARTS ARE RAPIDLY PRESSED (FORCED) TOGETHER CAUSING A SMALL UPSER. THIS SQUUZES OUT LIQUID METAL AND OXIDES, FORMED ON THE JOINT SURFACES AND THE TWO PARTS ARE WELDED TOGETHER.

THICK PIPES, ENDS OF BAND SAWS, FRAMES, AIRCRAFT LANDING GEARS ARE PRODUCED BY FLASH WELDING.

SEAM WELDING (RSW)

SEAM WELDING IS A RESISTANCE WELDING PROCESS OF CONTINUOUS JOINING OF OVERLAPPING SHEETS BYPASSING THEM BETWEEN TWO ROTATING ELECTRODE WHEELS. HEAT GENERATED BY THE ELECTRIC CURRENT FLOWING THROUGH THE CONTACT AREA AND PRESSURE PROVIDED BY THE WHEELS ARE SUFFICIENT TO PRODUCE A LEAK-TIGHT WELD.

SEAM WELDING IS HIGH SPEED AND CLEAN PROCESS, WHICH IS USED WHEN CONTINUOUS TIGHT WELD IS REQUIRED ( FUEL TANKS, DRUMS, DOMESTIC RADIATORS, GASOLINE TANKS, AUTOMOBILE MUFFLER)