WELDING PROCESSES

THE MIG-WELDING PROCESS:-

MIG (METAL INERT GAS) OR AS IT EVEN IS CALLED GMAW (GAS METAL ARC WELDING) USES ALUMINIUM ALLOY WIRE AS A COMBINED ELECTRODE AND FILLER MATERIAL. THE FILLER METAL IS ADDED CONTINUOUSLY AND WELDING WITHOUT FILLER-MATERIAL IS THEREFORE NOT POSSIBLE. SINCE ALL WELDING PARAMETERS ARE CONTROLLED BY THE WELDING MACHINE, THE PROCESS IS ALSO CALLED SEMI-AUTOMATIC WELDING.

THE MIG-PROCESS USES A DIRECT CURRENT POWER SOURCE, WITH THE ELECTRODE POSITIVE (DC, EP). BY USING A POSITIVE ELECTRODE, THE OXIDE LAYER IS EFFICIENTLY REMOVED FROM THE ALUMINIUM SURFACE, WHICH IS ESSENTIAL FOR AVOIDING LACK OF FUSION AND OXIDE INCLUSIONS. THE METAL IS TRANSFERRED FROM THE FILLER WIRE TO THE WELD BEAD BY MAGNETIC FORCES AS SMALL DROPLETS, SPRAY TRANSFER. THIS GIVES A DEEP PENETRATION CAPABILITY OF THE PROCESS AND MAKES IT POSSIBLE TO WELD IN ALL POSITIONS. IT IS IMPORTANT FOR THE QUALITY OF THE WELD THAT THE SPRAY TRANSFER IS OBTAINED.

THERE ARE TWO DIFFERENT MIG-WELDING PROCESSES, CONVENTIONAL MIG AND PULSED MIG:

CONVENTIONAL MIG USES A CONSTANT VOLTAGE DC POWER SOURCE. SINCE THE SPRAY TRANSFER IS LIMITED TO A CERTAIN RANGE OF ARC CURRENT, THE CONVENTIONAL MIG PROCESS HAS A LOWER LIMIT OF ARC CURRENT (OR HEAT INPUT). THIS ALSO LIMITS THE APPLICATION OF CONVENTIONAL MIG TO WELD MATERIAL THICKNESSES ABOVE 4 MM. BELOW 6 MM IT IS RECOMMENDED THAT BACKING IS USED TO CONTROL THE WELD BEAD.

PULSED MIG USES A DC POWER SOURCE WITH SUPERIMPOSED PERIODIC PULSES OF HIGH CURRENT. DURING THE LOW CURRENT LEVEL THE ARC IS MAINTAINED WITHOUT METAL TRANSFER. DURING THE HIGH CURRENT PULSES THE METAL IS TRANSFERRED IN THE SPRAY MODE. IN THIS WAY PULSED MIG IS POSSIBLE TO OPERATE WITH LOWER AVERAGE CURRENT AND HEAT INPUT COMPARED TO CONVENTIONAL MIG. THIS MAKES IT POSSIBLE TO WELD THINNER SECTIONS AND WELD MUCH EASILY IN DIFFICULT WELDING POSITIONS. FOR THICKNESSES: < 12,5 MM OF MATERIAL, ARGON IS THE BEST GAS TO USE FOR THE PROCESS.

MIG-WELDING IS A GENERAL PURPOSE WELDING PROCESS FOR WELDING OF ALUMINIUM AND APPLICABLE IN MOST CASES IN ALL WELDING POSITIONS FROM ABOUT 1 MM SHEET THICKNESS TO THICK WALLED SECTIONS.

MIG-WELDING ALSO OFFERS HIGH QUALITY WELDS WITH A HIGH PRODUCTIVITY. THERE ARE TWO MAIN VARIANTS CONVENTIONAL MIG-WELDING AND PULSED MIG-WELDING.

THE TIG-WELDING PROCESS:-

TIG-WELDING (TUNGSTEN INERT GAS) OR GTAW-WELDING (GAS TUNGSTEN ARC WELDING) USES A PERMANENT NON-MELTING ELECTRODE MADE OF TUNGSTEN. FILLER METAL IS ADDED SEPARATELY, WHICH MAKES THE PROCESS VERY FLEXIBLE. IT IS ALSO POSSIBLE TO WELD WITHOUT FILLER MATERIAL.

THE MOST USED POWER SOURCE FOR TIG-WELDING GENERATES ALTERNATING CURRENT (AC). DIRECT CURRENT CAN BE USED, BUT DUE TO HIGH HEAT GENERATION ON THE TUNGSTEN ELECTRODE WHEN DC-EP (ELECTRODE POSITIVE) WELDING, THAT PARTICULAR POLARITY IS NOT FEASIBLE. IN SOME CASES DC-EN (ELECTRODE NEGATIVE) IS USED, HOWEVER, THIS REQUIRES SPECIAL ATTENTION BEFORE WELDING, DUE TO THE ARC'S POOR OXIDE CLEANING ACTION.

AC TIG-WELDING USUALLY USES ARGON AS A SHIELDING GAS. THE PROCESS IS A MULTI PURPOSE PROCESS, WHICH OFFERS THE USER GREAT FLEXIBILITY. BY CHANGING THE DIAMETER OF THE TUNGSTEN ELECTRODE, WELDING MAY BE PERFORMED WITH A WIDE RANGE OF HEAT INPUT AT DIFFERENT THICKNESSES. AC TIG-WELDING IS POSSIBLE WITH THICKNESSES DOWN TO ABOUT 0,5 MM. FOR LARGER THICKNESSES, > 5 MM, AC TIG-WELDING IS LESS ECONOMICAL COMPARED TO MIG-WELDING DUE TO LOWER WELDING SPEED.

DC TIG-WELDING WITH ELECTRODE NEGATIVE IS USED FOR WELDING THICKNESSES ABOVE 4 MM. THE NEGATIVE ELECTRODE GIVES A POOR OXIDE CLEANING COMPARED TO AC-TIG AND MIG, AND SPECIAL CLEANING OF JOINT SURFACES IS NECESSARY. THE PROCESS USUALLY USES HELIUM SHIELDING GAS. THIS GIVES A BETTER PENETRATION IN THICKER SECTIONS. DC TIG-WELDING IS APPLICABLE FOR WELDING THICKNESSES IN THE RANGE 0,3Ñ12 MM. MORE AND MORE POPULAR IS ALSO PULSED DC TIG-WELDING, WHICH MAKES IT POSSIBLE TO WELD UNIFORM WELDS WITH DEEPER PENETRATION AT THE SAME HEAT INPUT. PULSE FREQUENCY IS USUALLY IN THE RANGE 1 -10 HZ.

AC TIG-WELDING: 0,5 Ñ4 MM

DC TIG (ELECTRODE NEGATIVE) 0,3Ñ12 MM (EVEN MORE FOR 2-SIDED WELDING)

APPLICATIONS OF TIG-WELDING

TIG-WELDING IS A GENERAL PURPOSE WELDING PROCESS FOR WELDING OF ALUMINIUM. ESPECIALLY AT THINNER SHEET THICKNESSES (0,5Ñ3 MM) THE PROCESS IS QUALIFIED.

THE PROCESS IS WIDELY USED FOR WELDING OF PRESSURE VESSELS, HEAT EXCHANGERS AND PIPES WHERE TIGHTNESS IS IMPORTANT SINCE THE PROCESS PRODUCES WELDS WITH VERY LOW PORE FRACTIONS.

TIG-WELDING IS ALSO BENEFICIAL FOR WELDS WITH FREQUENTLY STARTS AND STOPS AND FOR SHORT WELDS DUE TO EXCELLENT QUALITY WITH LOW POROSITY.

DC TIG (NEGATIVE ELECTRODE) COULD IN ADDITION ALSO BE BENEFICIAL FOR WELDING THIN WALLED STRUCTURES AND PROFILES.

SPOT WELDING:-

SPOT WELDING: IS A TYPE OF RESISTANCE WELDING USED TO WELD VARIOUS SHEET METALS. TYPICALLY THE SHEETS ARE IN THE 0.5-3.0 MM THICKNESS RANGE. THE PROCESS USES TWO SHAPED COPPER ALLOY ELECTRODES TO CONCENTRATE WELDING CURRENT AND FORCE BETWEEN THE MATERIALS TO BE WELDED. THE RESULT IS A SMALL "SPOT" THAT IS QUICKLY HEATED TO THE MELTING POINT, THIS FORMS A NUGGET OF WELDED METAL AFTER THE CURRENT IS REMOVED. THE AMOUNT OF HEAT RELEASED IN THE SPOT IS DETERMINED BY THE AMPLITUDE AND DURATION OF THE CURRENT. THE CURRENT AND DURATION ARE CHOSEN TO MATCH THE MATERIAL, THE SHEET THICKNESS AND TYPE OF ELECTRODES. APPLYING THE CURRENT FOR TOO LONG CAN RESULT IN MOLTEN METAL BEING EXPELLED AS WELD SPLASH, OR CAN EVEN BURN A HOLE RIGHT THROUGH THE MATERIALS BEING WELDED

APPLICATIONS:-

SPOT WELDING IS TYPICALLY USED WHEN WELDING PARTICULAR TYPES OF METAL STEEL SHEET METAL. THICKER STOCK IS DIFFICULT TO HEAT UP FROM A SINGLE SPOT, AS THE HEAT CAN FLOW INTO THE SURROUNDING METAL TOO EASILY. SPOT WELDING CAN BE EASILY IDENTIFIED ON MANY SHEET METAL GOODS, SUCH AS METAL BUCKETS. ALUMINUM ALLOYS CAN ALSO BE SPOT WELDED. HOWEVER, THEIR MUCH HIGHER THERMAL CONDUCTIVITY AND ELECTRICAL CONDUCTIVITY MEAN THAT UP TO THREE TIMES HIGHER WELDING CURRENTS ARE NEEDED. THIS REQUIRES LARGER, MORE POWERFUL, AND MORE EXPENSIVE WELDING TRANSFORMERS.

WHERE IT IS USED ALMOST UNIVERSALLY TO WELD THE SHEET METAL TO FORM A CAR. SPOT WELDERS CAN ALSO BE COMPLETELY AUTOMATED, AND MANY OF THE INDUSTRIAL ROBOTS FOUND ON ASSEMBLY LINES ARE SPOT WELDERS (THE OTHER MAJOR USE FOR ROBOTS BEING PAINTING).

A FURTHER PLACE WHERE SPOT WELDING IS USED IS IN THE ORTHODONTIST'S CLINIC, WHERE SMALL SCALE SPOT WELDING EQUIPMENT IS USED WHEN RESIZING METAL "MOLAR BANDS" USED IN ORTHODONTICS.

ELECTRICAL NOTES: THE VOLTAGE NEEDED FOR THE WELDING DEPENDS ON THE RESISTANCE OF THE MATERIAL TO BE WELDED, THE SHEET THICKNESS AND DESIRED SIZE OF THE NUGGET. WHEN WELDING A COMMON COMBINATION LIKE 1.0 + 1.0 MM SHEET STEEL, THE VOLTAGE BETWEEN THE ELECTRODES IS ONLY ABOUT 1.5 V AT THE START OF THE WELD BUT CAN FALL AS LOW AS 1 V AT THE END OF THE WELD. THIS DROP IN VOLTAGE STEMS FROM THE RESISTANCE REDUCTION CAUSED BY THE STEEL MELTING. THE OPEN CIRCUIT VOLTAGE FROM THE TRANSFORMER IS MUCH HIGHER THAN THIS, TYPICALLY IN THE 5-10 V RANGE, BUT THERE IS A VERY LARGE VOLTAGE DROP IN THE ELECTRODES AND SECONDARY SIDE OF THE TRANSFORMER WHEN THE CIRCUIT IS CLOSED.

DUE TO CHANGES IN THE RESISTANCE OF THE METAL AS IT STARTS TO LIQUEFY, THE WELDING PROCESS CAN BE MONITORED IN REAL-TIME TO ENSURE A PERFECT WELD EVERY TIME, USING THE MOST RECENT ADVANCES IN MONITORING/FEEDBACK CONTROL EQUIPMENT. THE RESISTANCE IS MEASURED INDIRECTLY, BY MEASURING THE VOLTAGE AT AND CURRENT THROUGH THE ELECTRODES.

CURRENT STATUS

SPOT WELDING IS ONE OF THE OLDEST WELDING PROCESSES. IT CAN BE USED ON VERY THIN FOILS OR THICK SECTIONS BUT IS RARELY USED ABOVE ABOUT 6MM THICKNESS. IT IS USED IN A WIDE RANGE OF INDUSTRIES BUT NOTABLY FOR THE ASSEMBLY OF SHEET STEEL VEHICLE BODIES WHERE MORE THAN 100 MILLION WELDS ARE MADE PER DAY IN EUROPE ALONE. HIGH QUALITY WELDS CAN ALSO BE MADE IN STAINLESS STEELS, NICKEL ALLOYS, ALUMINUM ALLOYS AND TITANIUM FOR AEROSPACE APPLICATION.

IMPORTANT ISSUES

THE MAIN AREAS OF RESEARCH ARE IN MATERIALS, QUALITY CONTROL AND EQUIPMENT.

• HIGH STRENGTH AND ULTRA-HIGH STRENGTH STEELS, COATED STEELS AND ALUMINUM ALLOYS ARE OF GREAT INTEREST TO THE AUTOMOTIVE INDUSTRY BUT CAN HAVE WELD ABILITY PROBLEMS. ALTHOUGH THE PROBLEMS ARE UNDERSTOOD, FURTHER IMPROVEMENTS IN WELD ABILITY AND ELECTRODE LIVES ARE STILL BEING SOUGHT. THERE ARE ALSO LIMITATIONS IN THE ABILITY OF SPOT WELDING TO JOIN SHEET TO TUBE, WHICH NEED TO BE ADDRESSED.
• WELD QUALITY IS CONTROLLED MAINLY BY GOOD PROCESS CONTROL TOGETHER WITH PERIODIC TESTING OF SAMPLES. WHILE A NUMBER OF MONITORS HAVE BEEN DEVELOPED, THERE IS STILL A DESIRE TO PRODUCE A LOW COST, RELIABLE AND ROBUST IN-PROCESS WELD QUALITY MONITOR, IN ORDER TO REDUCE OR ELIMINATE PERIODIC DESTRUCTIVE TESTS. SOME CONTROLLERS NOW INCORPORATE FEEDBACK CONTROL SYSTEMS THAT MONITOR CURRENT AND VOLTAGE (RESISTANCE) ON THE WELDING MACHINE AND, WITH LIMITED SETTING UP, ALLOW AUTOMATIC, IN-PROCESS ADAPTION OF THE WELDING PROCEDURE (TIME AND CURRENT) TO MAINTAIN WELD QUALITY FOR DIFFERENT THICKNESS AND MATERIAL STACK-UP COMBINATIONS, FOR EXAMPLE. WHILE NOT NECESSARILY GUARANTEEING WELD QUALITY COMPLETELY, THESE CONTROLLERS CAN ALSO PROVIDE SOME CORRECTION FOR VARIATION IN OTHER PROCESS FACTORS, SUCH AS CONTAMINATION, CURRENT SHUNTING AND PART FIT-UP.
• ULTRASONIC NON-DESTRUCTIVE TESTING HAS BEEN PROVED AND WIDELY APPLIED AT VEHICLE MANUFACTURERS. DESPITE IMPROVEMENTS IN AUTOMATIC SIGNAL ANALYSIS FOR EASE OF OPERATION AND WELD QUALITY INDICATION, THE TECHNIQUE STILL REQUIRES SKILL AND TRAINING TO ACHIEVE HIGH ACCURACY.
• OTHER RECENT EQUIPMENT DEVELOPMENTS HAVE INCLUDED IMPROVED MEDIUM FREQUENCY POWER SUPPLIES, SERVO OPERATED GUNS AND AUTOMATIC ELECTRODE DRESSING AND CHANGING TOOLS

BENEFITS:-

SPOT WELDING OFFERS A NUMBER OF ADVANTAGES OVER OTHER TECHNIQUES, INCLUDING HIGH SPEED, EASE OF AUTOMATION AND ENERGY EFFICIENCY.

RISKS:-

THERE ARE SOME LIMITATIONS ON MATERIAL WELD ABILITY BUT ATTENTION TO CORRECT SETTING UP AND GOOD PROCESS CONTROL CAN SOLVE MOST PRODUCTION PROBLEMS. THE MAIN SAFETY HAZARDS ARE (I) THE RISK OF CRUSHING FINGERS OR HANDS AND (II) BURNS OR EYE DAMAGE FROM SPLASH METAL. LITTLE FUME IS PRODUCED BUT MAY NEED ATTENTION WHEN WELDING COATED STEELS OR WHEN OILS OR ORGANIC MATERIALS ARE PRESENT.

RESISTANCE SPOT WELDING:-

INTRODUCTION:-

RESISTANCE SPOT WELDING IS ONE OF THE OLDEST OF THE ELECTRIC WELDING PROCESSES IN USE BY INDUSTRY TODAY. THE WELD IS MADE BY A COMBINATION OF HEAT, PRESSURE, AND TIME. AS THE NAME IMPLIES, IT IS THE RESISTANCE OF THE MATERIAL TO BE WELDED TO CURRENT FLOW THAT CAUSES A LOCALIZED HEATING IN THE PART. THE PRESSURE IS EXERTED BY THE TONGS AND TIPS. THE TIME IS HOW LONG CURRENT FLOWS IN THE JOINT, WHICH IS DETERMINED BY THE MATERIAL THICKNESS AND TYPE, AMOUNT OF THE CURRENT AND CROSS-SECTIONAL AREA OF THE WELDING TIPS AND CONTACT SURFACES.

PROCESS HAZARDS OVERVIEW:-

RESISTANCE SPOT WELDING, UNLIKE MANY OTHER WELDING OR CUTTING PROCESSES, PRODUCES LITTLE FUMES AND ONLY NEGLIGIBLE ARC RAYS. EVEN THE FIRE HAZARD FROM FLYING SPARKS IS MODEST TO LOW COMPARED TO OTHER PROCESSES. HOWEVER, BECAUSE OF THE TONGS AND LINKAGES, THERE IS HIGHER RISK OF MECHANICAL HAZARDS, SUCH AS PINCHING AND CRUSHING THE FINGERS AND HANDS, THAN OTHER PROCESSES. EYE OR FACE INJURY FROM FLYING METAL AND SPARKS IS ALSO PRESENT; SINCE THESE PARTICLES ARE OFTEN THROWN OFF FROM THE WELD.

HOW THE PROCESS WORKS:-

FUNDAMENTALLY, RESISTANCE SPOT WELDING OCCURS WHEN CURRENT FLOWS THROUGH THE TIPS AND THE SEPARATE PIECES OF METAL TO BE JOINED. THE RESISTANCE OF THE BASE METAL TO THE ELECTRICAL CURRENT FLOW CAUSES LOCALIZED HEATING IN THE JOINT, AND THE WELD IS MADE. THE WELD IS UNIQUE BECAUSE THE ACTUAL WELD NUGGET IS FORMED INTERNALLY WITH RELATION TO THE SURFACE OF THE BASE METAL. A MIG OR TIG SPOT WELD, ON THE OTHER HAND, STARTS AT THE SURFACE OF ONE PIECE AND GOES THROUGH IT AND INTO THE SECOND PIECE TO FORM THE WELD NUGGET. THE MIG OR TIG WELD IS MADE FROM ONE SIDE ONLY, WHILE THE RESISTANCE SPOT WELD IS NORMALLY MADE WITH ELECTRODES ON BOTH SIDES OF THE WORKPIECES.

SAFETY HAZARDS:-

• RESISTANCE SPOT WELDING IS NOT AN OPEN-ARC PROCESS. SINCE THE WELD IS MADE INSIDE THE WORKPIECES, THERE ARE DIFFERENT AND UNIQUE HAZARDS TO CONSIDER. HERE ARE THE MAJOR ONES TO BE AWARE OF AND PREPARE FOR BEFORE ACTUALLY MAKING A WELD.
• FLYING SPARKS CAN CAUSE FIRE AND EXPLOSION.
• FLYING SPARKS AND HOT METAL ARE OFTEN THROWN OFF FROM THE WELD JOINT AND CAN BURN OR INJURE EYES AND SKIN.
• ELECTRIC SHOCK FROM WIRING IS A POSSIBLE HAZARD.
• HOT METAL AND PARTS CAN CAUSE BURNS.
• MOVING PARTS, SUCH AS TONGS, TIPS, AND LINKAGES, CAN INJURE FINGERS AND HANDS.
• FUMES FROM SPOT WELDING ON PARTS COATED WITH CLEANERS, PAINTS, AND PLATINGS CAN BE HAZARDOUS.

HOW TO AVOID THE HAZARDS:-

• WEAR SAFETY GOGGLES OR A FACE SHIELD.
• WEAR LONG SLEEVED SHIRTS.
• DO NOT WELD NEAR FLAMMABLES––MOVE THEM AWAY.
• KEEP A FIRE EXTINGUISHER NEARBY, AND KNOW HOW TO USE IT.
• WEAR DRY INSULATING GLOVES.
• INSTALL AND GROUND UNIT ACCORDING TO ALL CODES.
• DISCONNECT ILNPUT POWER BEFORE SERVICING.
• DO NOT PUT HANDS BETWEEN TIPS.
• KEEP AWAY FROM LINKAGES AND PINCH POINTS.
• KEEP ALL GUARDS AND PANELS IN PLACE.
• DO NOT BREATHE THE FUMES.
• USE PROPER VENTILATION.
• READ MATERIAL SAFETY DATA SHEETS (MSDSS) FOR METALS, COATINGS, AND CLEANERS.
• DO NOT TOUCH HOT WORKPIECE, TIPS, OR TONGS WITH BARE HANDS.
• ALLOW TONGS AND TIPS TO COOL BEFORE TOUCHING.
• WEAR PROPER INSULATING GLOVES IF HANDLING HOT WORK OR PARTS IS NECESSARY.

WHAT IS WELDING:-

TO JOINT THE TWO DIFFERENT/SAME MATERIAL AT PERTICULAR TEMP. WITH ORW/O PRESSURE IS CALLED WELDING.

HOW TO DO WELDING:-

ELECTRIC ENERGY CONVERTED IN TO HEAT FUSION BY BASE METAL AND FILLER A HOMOGENIOUS FILLER MAINTAIN AND CONVERTED INTO BEAD.

HOW TO DO WELDING:-

ELECTRIC ENERGY CONVERTED IN TO HEAT FUSION BY BASE METAL AND FILLER A HOMOGENIOUS FILLER MAINTAIN AND CONVERTED INTO BEAD.

FUSION WELDING:-

DIFFERENT TYPES OF FUSION WELDING ARE IN USE:

1. SHIELDING METAL ARC WELDING. (SMAW) (INCLUDE, MANUAL ARC, STICK, COATED ELECTOD WELDING)
2. SUBMERGED ARC WELDING (SAW)
3. FLUX CORED ARC WELDING (FCAW)
4. GAS TUNGESTEN ARC WELDING. (GTAW)

5. PLASMA ARC WELDING. (PAW)
6. GAS METAL ARC WELDING. (GMAW) DOING AT OMAX
7. ELECTROSLAG WELDING. (ESW)
8. ELECTRON BEAM WELDING. (EBW)
9. RESISTANT WELDING. (RW)
10. ATOMIC HYDROGEN WELDING. (AHW)

SHIELDING GAS FUNCTION:-

1. PROTECT THE WELD FROM ATMOSPHERIC CONTAMINATION
2. STABLIZE THE WELDING ARC
3. DEFINE METAL TRANSFER MODE
4. CONTROL WELD GEOMETRY
5. CONTOL WELD. COMPOSITION OR

PROPERTY

WHAT IS GAS METAL ARC WELDING:-

ONLY INERT GASES (HELIUM OR ARGON) AND CO₂ FOR SHIELDING THE ARC.

BENIFTS:

1. HIGH DEPOSITION RATE
2. EASY TO WELDING IN ALL POSITIONS.
3. LESS SKILL OPTR MAY USE
4. ADOPTABILITY TO WELD. ALMOST ALL TYPES OF METAL
5. HIGH QUALITY WELDING W/O THE PROBLEM OF FLUX, MOISTURE AND SLAG
6. FOR GOOD IMPECT STRENGTH (MIXTURE OF CO₂ + AR)

MODES OF METAL TRANSFER:-

1 - DIP TRANSFER

2 - GLOBULAR TRANSFER

3 - SPRAY TRANSFER

DIP TRANSFER:-

LESS VOLTAGE & LESS FEED SPEED CALLED DIP TRANSFER

I- ARC LENGTH TO BE MAINTAIN: 8 – 10 MM.

II- CURRENT BELOW : 200 AMP.

III –VOLTAGE : 18 ~ 22 V

IV - POSITION VERTICAL & OVER HEAD (THIN SHEET)

V – DEPOSITION RATE IS : 0.9 ~ 2.7 KG. / HOUR

VI - SHEET THICKNESS BELOW : 2.0 MM.

VII -ADVANTAGE: LESS SPATTER, PENITRATION GOOD, SMOOTH WELDING

PROCESS VARIATION:-

1 - WELDING CURRENT

2 - ARC VOLTAGE

3 - TRAVEL SPEED

4 - MIG WIRE EXTENTION

5 - MIG WIRE INCLINATION

6 - MIG WIRE SIDE

7 - WELD JOINT POSITION

GLOBULAR TRANSFER:-

1- SOME LESS VOLTAGE & FEED SPEED CALLED GLOBULAR TRANSFER

2 - DROP SIZE OF DIAMETER GREATER THAN THAT OF WIRE DIA.

CURRENT : 200 ~ 300 AMP.

VOLTAGE : 24 ~ 28 V

SHEET THICKNESS : 2 ~ 3.0 MM.

POSITION : MIDIUM GAGE FLAT

DEPOSITION RATE : 1 .8 ~ 3.2 KG. / HOUR

ARC LENGTH : 10 ~ 15 MM.

DISADVANTAGE : MORE SPATTER, WASTAGE OF MIG WIRE

SPRAY - TRANSFER:-

1- HIGH VOLTAGE & HIGH FEED SPEED CALLED SPRAY

TRANSFER

2– DROPLET SIZE OF MIG WIRE IS EQUEL TO OR LESS

THAT OF WIRE DIAMETER

CURRENT : 220 ~ 500 AMP.

VOLTAGE : 28 ~ 40 V

SHEET THICKNESS : 3.0MM MIN.

POSITION : THICK PLATE FLAT

DEPOSITION RATE : 2.7 ~ 5.4 KG. / HOUR

ARC LENGTH : 10 ~ 15 MM.

ADVANTAGE : SPATTER FREE, SMOOT WELDING, SAVINGS IN MIG WIRE

WELDING DEFECTS:-

Ø POROCITY

Ø BLOW HOLES

Ø PENINTRATION LESS

Ø WELDING BEAD NOT SIMILAR

Ø MELTING IMPROPER

Ø CRACKING

Ø UNDER CUT

Ø SPATTER

POROCITY:

1- GAS FLOW TOO MUCH OR LESS.

2- NOZZEL BLOCK (JAMMED WITH SPATTER) &

SHIELDING IMPROPER.

3- LEAKAGE OF GAS LINE.

4- WELDING METHOD WRONG DURING WELDING

5- MORE DISTANCE BETWEEN JOB & NOZZEL.

6- DUST, PAINT, RUST, GREESE, WATER DEPOSITED ON SURFACE.

7- MIG WIRE USE RUSTY OR WET CONDITION.

8- COPPER COATING IMPROPER IN MIG WIRE

LESS PENITRATION:

1- LESS CURRENT.

2- LESS GAP OR NOT GAP IN WELD JOB.

3- MORE GAPS BETWEEN METAL TO METAL.

4- CONTACTOR BURNT DURING WELDING

(CURRENT, VOLTAGE, FLUCTUATE)

5- WRONG POSITION OF TORCH.

6-WELD JOINT GETTING NOT SIMILAR.

7- NON AVALIBILITY OF MIG WIRE FROM FEEDER TO JOB

8- LEFT HAND (PULL) WELDING DONE ON JOB.

WELD BEAD NOT SIMILAR:

1- TENTION IN MIG WIRE.

2- ROLLER PRESSURE IMPROPER.

3- LESS TRAVEL SPEED.

4- WIRE DOES NOT STRAIGHT OUT FROM TIP.

5- HIGH VOLTAGE & LESS CURRENT.

MELTING IMPROPER:

1- LESS VOLTAGE.

2- SOME TIMES CURRENT AND VOLTAGE MORE

3- JOB SURFACE NOT SIMILAR

4- TORCH DRIVE IN WRONG DIRECTION.

CRACKING:

1- JOB TO BE PRE HEATED.

2- RIGHT QUANTITY OF SULPHER & MAGENESE

NOT MAINTAIN IN MIG WIRE.

3- TOO MUCH LESS THICKNESS OF ROOT BEAD

UNDER - CUT:

1-MORE WELD SPEED

2-MORE CURRENT

3-WIRE FEED LESS & VOLTAGE MORE

4-OVER HEAT OF JOB

5-TORCH ANGLE NOT PROPER

6-GAS FLOW IMPROPER

SPATTERS :

1-MAXIMUM VOLTAGE

2-PURITY OF SHIELDING GASES

3-IMPROPER SHIELDING

4-VARIATION IN ARC STICK

5-MIG WIRE BEND, RUSTY, DUSTY MELTING

TEMPRATURE MORE, MAGNISE IMPROPER

6-TORCH ANGLE NOT PROPER

7-GAS FLOW IMPROPER