MANUFACTURING PROCESS - WELDING & ITS CLASSIFICATION

WELDING

INTRODUCTION:

WELDING WHICH IS THE PROCESS OF JOINING TWO METALLIC COMPONENTS FOR THE DESIRED PURPOSE, CAN BE DEFINED AS THE PROCESS OF JOINING TWO SIMILAR OR DISSIMILAR METALLIC COMPONENTS WITH THE APPLICATION OF HEAT, WITH OR WITHOUT THE APPLICATION OF PRESSURE AND WITH OR WITHOUT THE USE OF FILLER METAL. HEAT MAY BE OBTAINED BY CHEMICAL REACTION, ELECTRIC ARC, ELECTRICAL RESISTANCE, FRICTIONAL HEAT, SOUND AND LIGHT ENERGY. IF NO FILTER METAL IS USED DURING WELDING THEN IT IS TERMED AS ‘AUTOGENOUS WELDING PROCESS'.

DURING ‘BRONZE AGE' PARTS WERE JOINED BY FORGE WELDING TO PRODUCE TOOLS, WEAPONS AND ORNAMENTS ETC, HOWEVER, PRESENT DAY WELDING PROCESSES HAVE BEEN DEVELOPED WITHIN A PERIOD OF ABOUT A CENTURY. 

FIRST APPLICATION OF WELDING WITH CARBON ELECTRODE WAS DEVELOPED IN 1885 WHILE METAL ARC WELDING WITH BARE ELECTRODE WAS PATENTED IN 1890. HOWEVER, THESE DEVELOPMENTS WERE MORE OF EXPERIMENTAL VALUE AND APPLICABLE ONLY FOR REPAIR WELDING BUT PROVED TO BE THE IMPORTANT BASE FOR PRESENT DAY MANUAL METAL ARC (MMAW) WELDING AND OTHER ARC WELDING PROCESSES. 

IN THE MEAN TIME RESISTANCE BUTT WELDING WAS INVENTED IN USA IN THE YEAR 1886. OTHER RESISTANCE WELDING PROCESSES SUCH AS SPOT AND FLASH WELDING WITH MANUAL APPLICATION OF LOAD WERE DEVELOPED AROUND 1905.

WITH THE PRODUCTION OF CHEAP OXYGEN IN 1902, OXY – ACETYLENE WELDING BECAME FEASIBLE IN EUROPE IN 1903.

WHEN THE COATED ELECTRODES WERE DEVELOPED IN 1907, THE MANUAL METAL ARC WELDING PROCESS BECOME VIABLE FOR PRODUCTION/FABRICATION OF COMPONENTS AND ASSEMBLIES IN THE INDUSTRIES ON LARGE SCALE.

SUBSEQUENTLY OTHER DEVELOPMENTS ARE AS FOLLOWS: 

•  THERMIT WELDING (1903)

•  CELLULOSIC ELECTRODES (1918)

•  ARC STUD WELDING (1918)

•  SEAM WELDING OF TUBES (1922)

•  MECHANICAL FLASH WELDER FOR JOINING RAILS (1924)

•  EXTRUDED COATING FOR MMAW ELECTRODES (1926)

•  SUBMERGED ARC WELDING (1935)

•  AIR ARC GOUGING (1939)

•  INERT GAS TUNGSTEN ARC (TIG) WELDING (1941)

•  IRON POWDER ELECTRODES WITH HIGH RECOVERY (1944)

•  INERT GAS METAL ARC (MIG) WELDING (1948)

•  ELECTRO SLAG WELDING (1951)

•  FLUX CORED WIRE WITH CO 2 SHIELDING (1954)

•  ELECTRON BEAM WELDING (1954)

•  CONSTRICTED ARC (PLASMA) FOR CUTTING (1955)

•  FRICTION WELDING (1956)

•  PLASMA ARC WELDING (1957)

•  ELECTRO GAS WELDING (1957)

•  SHORT CIRCUIT TRANSFER FOR LOW CURRENT, LOW VOLTAGE WELDING WITH CO 2 SHIELDING (1957)

•  VACUUM DIFFUSION WELDING (1959)

•  EXPLOSIVE WELDING (1960)

•  LASER BEAM WELDING (1961)

•  HIGH POWER CO 2 LASER BEAM WELDING (1964) 

ALL WELDED ‘ LIBERTY ' SHIPS FAILURE IN 1942, GAVE A BIG JOLT TO APPLICATION OF WELDING. HOWEVER, IT HAD DRAWN ATTENTION TO FRACTURE PROBLEM IN WELDED STRUCTURES. 

APPLICATIONS:

ALTHOUGH MOST OF THE WELDING PROCESSES AT THE TIME OF THEIR DEVELOPMENTS COULD NOT GET THEIR PLACE IN THE PRODUCTION EXCEPT FOR REPAIR WELDING, HOWEVER, AT THE LATER STAGE THESE FOUND PROPER PLACE IN MANUFACTURING/PRODUCTION. PRESENTLY WELDING IS WIDELY BEING USED IN FABRICATION OF PRESSURE VESSELS, BRIDGES, BUILDING STRUCTURES, AIRCRAFT AND SPACE CRAFTS, RAILWAY COACHES AND GENERAL APPLICATIONS. IT IS ALSO BEING USED IN SHIPBUILDING, AUTOMOBILE, ELECTRICAL, ELECTRONIC AND DEFENSE INDUSTRIES, LAYING OF PIPE LINES AND RAILWAY TRACKS AND NUCLEAR INSTALLATIONS ETC. 

GENERAL APPLICATIONS:

WELDING IS VASTLY BEING USED FOR CONSTRUCTION OF TRANSPORT TANKERS FOR TRANSPORTING OIL, WATER, MILK AND FABRICATION OF WELDED TUBES AND PIPES, CHAINS, LPG CYLINDERS AND OTHER ITEMS. STEEL FURNITURE, GATES, DOORS AND DOOR FRAMES, BODY AND OTHER PARTS OF WHITE GOODS ITEMS SUCH AS REFRIGERATORS, WASHING MACHINES, MICROWAVE OVENS AND MANY OTHER ITEMS OF GENERAL APPLICATIONS ARE FABRICATED BY WELDING. 

PRESSURE VESSELS:

ONE OF THE FIRST MAJOR USE OF WELDING WAS IN THE FABRICATION OF PRESSURE VESSELS. WELDING MADE CONSIDERABLE INCREASES IN THE OPERATING TEMPERATURES AND PRESSURES POSSIBLE AS COMPARED TO RIVETED PRESSURE VESSELS. 

BRIDGES:

EARLY USE OF WELDING IN BRIDGE CONSTRUCTION TOOK PLACE IN AUSTRALIA . THIS WAS DUE TO PROBLEMS IN TRANSPORTING COMPLETE RIVETED SPANS OR HEAVY RIVETING MACHINES NECESSARY FOR FABRICATION ON SITE TO REMOTE AREAS. THE FIRST ALL WELDED BRIDGE WAS ERECTED IN UK IN 1934. SINCE THEN ALL WELDED BRIDGES ARE ERECTED VERY COMMONLY AND SUCCESSFULLY. 

SHIP BUILDING :

SHIPS WERE PRODUCED EARLIER BY RIVETING. OVER TEN MILLION RIVETS WERE USED IN ‘QUEEN MARY' SHIP WHICH REQUIRED SKILLS AND MASSIVE ORGANIZATION FOR RIVETING BUT WELDING WOULD HAVE ALLOWED THE SEMISKILLED/ UNSKILLED LABOR AND THE PRINCIPLE OF PRE-FABRICATION. WELDING FOUND ITS PLACE IN SHIP BUILDING AROUND 1920 AND PRESENTLY ALL WELDED SHIPS ARE WIDELY USED. SIMILARLY SUBMARINES ARE ALSO PRODUCED BY WELDING. 

BUILDING STRUCTURES:

ARC WELDING IS USED FOR CONSTRUCTION OF STEEL BUILDING LEADING TO CONSIDERABLE SAVINGS IN STEEL AND MONEY. IN ADDITION TO BUILDING, HUGE STRUCTURES SUCH AS STEEL TOWERS ETC ALSO REQUIRE WELDING FOR FABRICATION. 

AIRCRAFT AND SPACECRAFT:

SIMILAR TO SHIPS, AIRCRAFTS WERE PRODUCED BY RIVETING IN EARLY DAYS BUT WITH THE INTRODUCTION OF JET ENGINES WELDING IS WIDELY USED FOR AIRCRAFT STRUCTURE AND FOR JOINING OF SKIN SHEET TO BODY. 

SPACE VEHICLES WHICH HAVE TO ENCOUNTER FRICTIONAL HEAT AS WELL AS LOW TEMPERATURES REQUIRE OUTER SKIN AND OTHER PARTS OF SPECIAL MATERIALS. THESE MATERIALS ARE WELDED WITH FULL SUCCESS ACHIEVING SAFETY AND RELIABILITY. 

RAILWAYS:

RAILWAYS USE WELDING EXTENSIVELY FOR FABRICATION OF COACHES AND WAGONS, WHEEL TYRES LAYING OF NEW RAILWAY TRACKS BY MOBILE FLASH BUTT WELDING MACHINES AND REPAIR OF CRACKED/DAMAGED TRACKS BY THERMIT WELDING. 

AUTOMOBILES:

PRODUCTION OF AUTOMOBILE COMPONENTS LIKE CHASSIS, BODY AND ITS STRUCTURE, FUEL TANKS AND JOINING OF DOOR HINGES REQUIRE WELDING. 

ELECTRICAL INDUSTRY:

STARTING FROM GENERATION TO DISTRIBUTION AND UTILIZATION OF ELECTRICAL ENERGY, WELDING PLAYS IMPORTANT ROLE. COMPONENTS OF BOTH HYDRO AND STEAM POWER GENERATION SYSTEM, SUCH AS PENSTOCKS, WATER CONTROL GATES, CONDENSERS, ELECTRICAL TRANSMISSION TOWERS AND DISTRIBUTION SYSTEM EQUIPMENT ARE FABRICATED BY WELDING. TURBINE BLADES AND COOLING FINS ARE ALSO JOINED BY WELDING. 

ELECTRONIC INDUSTRY:

ELECTRONIC INDUSTRY USES WELDING TO LIMITED EXTENT SUCH AS FOR JOINING LEADS OF SPECIAL TRANSISTORS BUT OTHER JOINING PROCESSES SUCH AS BRAZING AND SOLDERING ARE WIDELY BEING USED. SOLDERING IS USED FOR JOINING ELECTRONIC COMPONENTS TO PRINTED CIRCUIT BOARDS. ROBOTIC SOLDERING IS VERY COMMON FOR JOINING OF PARTS TO PRINTED CIRCUIT BOARDS OF COMPUTERS, TELEVISION, COMMUNICATION EQUIPMENT AND OTHER CONTROL EQUIPMENT ETC. 

NUCLEAR INSTALLATIONS:

SPHERES FOR NUCLEAR REACTOR, PIPE LINE BENDS JOINING TWO PIPES CARRYING HEAVY WATER AND OTHER COMPONENTS REQUIRE WELDING FOR SAFE AND RELIABLE OPERATIONS. 

DEFENCE INDUSTRY:

DEFENCE INDUSTRY REQUIRES WELDING FOR JOINING OF MANY COMPONENTS OF WAR EQUIPMENT. TANK BODIES FABRICATION, JOINING OF TURRET MOUNTING TO MAIN BODY OF TANKS ARE TYPICAL EXAMPLES OF APPLICATIONS OF WELDING. 

MICRO-JOINING:

IT EMPLOYS THE PROCESSES SUCH AS MICRO-PLASMA, ULTRASONIC, LASER AND ELECTRON BEAM WELDING, FOR JOINING OF THIN WIRE TO WIRE, FOIL TO FOIL AND FOIL TO WIRE, SUCH AS PRODUCING JUNCTIONS OF THERMOCOUPLES, STRAIN GAUGES TO WIRE LEADS ETC.

APART FROM ABOVE APPLICATIONS WELDING IS ALSO USED FOR JOINING OF PIPES, DURING LAYING OF CRUDE OIL AND GAS PIPELINES, CONSTRUCTION OF TANKERS FOR THEIR STORAGE AND TRANSPORTATION. OFFSHORE STRUCTURES, DOCKYARDS, LOADING AND UNLOADING CRANES ARE ALSO PRODUCED BY WELDING. 

CLASSIFICATION OF WELDING PROCESSES:

WELDING PROCESSES CAN BE CLASSIFIED BASED ON FOLLOWING CRITERIA;

1. WELDING WITH OR WITHOUT FILLER MATERIAL.
2. SOURCE OF ENERGY OF WELDING.
3. ARC AND NON-ARC WELDING.
4. FUSION AND PRESSURE WELDING.

1. WELDING CAN BE CARRIED OUT WITH OR WITHOUT THE APPLICATION OF FILLER MATERIAL. EARLIER ONLY GAS WELDING WAS THE FUSION PROCESS IN WHICH JOINING COULD BE ACHIEVED WITH OR WITHOUT FILLER MATERIAL. WHEN WELDING WAS DONE WITHOUT FILLER MATERIAL IT WAS CALLED ‘AUTOGENOUS WELDING'. HOWEVER, WITH THE DEVELOPMENT OF TIG, ELECTRON BEAM AND OTHER WELDING PROCESSES SUCH CLASSIFICATION CREATED CONFUSION AS MANY PROCESSES SHALL BE FALLING IN BOTH THE CATEGORIES.
2. VARIOUS SOURCES OF ENERGIES ARE USED SUCH AS CHEMICAL, ELECTRICAL, LIGHT, SOUND, MECHANICAL ENERGIES, BUT EXCEPT FOR CHEMICAL ENERGY ALL OTHER FORMS OF ENERGIES ARE GENERATED FROM ELECTRICAL ENERGY FOR WELDING. SO THIS CRITERION DOES NOT JUSTIFY PROPER CLASSIFICATION.
3. ARC AND NON-ARC WELDING PROCESSES CLASSIFICATION EMBRACES ALL THE ARC WELDING PROCESSES IN ONE CLASS AND ALL OTHER PROCESSES IN OTHER CLASS. IN SUCH CLASSIFICATION IT IS DIFFICULT TO ASSIGN EITHER OF THE CLASS TO PROCESSES SUCH AS ELECTROSLAG WELDING AND FLASH BUTT WELDING, AS IN ELECTROSLAG WELDING THE PROCESS STARTS WITH ARCING AND WITH THE MELTING OF SUFFICIENT FLUX THE ARC EXTINGUISHES WHILE IN FLASH BUTT WELDING TINY ARCS I.E. SPARKS ARE ESTABLISHED DURING THE PROCESS AND THEN COMPONENTS ARE PRESSED AGAINST EACH OTHER. THEREFORE, SUCH CLASSIFICATION IS ALSO NOT PERFECT.
4. FUSION WELDING AND PRESSURE WELDING IS MOST WIDELY USED CLASSIFICATION AS IT COVERS ALL PROCESSES IN BOTH THE CATEGORIES IRRESPECTIVE OF HEAT SOURCE AND WELDING WITH OR WITHOUT FILLER MATERIAL. IN FUSION WELDING ALL THOSE PROCESSES ARE INCLUDED WHERE MOLTEN METAL SOLIDIFIES FREELY WHILE IN PRESSURE WELDING MOLTEN METAL IF ANY IS RETAINED IN CONFINED SPACE UNDER PRESSURE (AS MAY BE IN CASE OF RESISTANCE SPOT WELDING OR ARC STUD WELDING) SOLIDIFIES UNDER PRESSURE OR SEMISOLID METAL COOLS UNDER PRESSURE. THIS TYPE OF CLASSIFICATION POSES NO PROBLEMS SO IT IS CONSIDERED AS THE BEST CRITERION.

BRAZING AND SOLDERING: 

BOTH BRAZING AND SOLDERING ARE THE METAL JOINING PROCESSES IN WHICH PARENT METAL DOES NOT MELT BUT ONLY FILLER METAL MELTS FILLING THE JOINT WITH CAPILLARY ACTION. IF THE FILLER METAL IS HAVING MELTING TEMPERATURE MORE THAN 450°C BUT LOWER THAN THE MELTING TEMPERATURE OF COMPONENTS THEN IT IS TERMED AS PROCESS OF BRAZING OR HARD SOLDERING. HOWEVER, IF THE MELTING TEMPERATURE OF FILLER METAL IS LOWER THAN 450°C AND ALSO LOWER THAN THE MELTING POINT OF THE MATERIAL OF COMPONENTS THEN IT IS KNOW AS SOLDERING OR SOFT SOLDERING. 

DURING BRAZING OR SOLDERING FLUX IS ALSO USED WHICH PERFORMS THE FOLLOWING FUNCTIONS: 

•  DISSOLVE OXIDES FROM THE SURFACES TO BE JOINED.

• REDUCE SURFACE TENSION OF MOLTEN FILLER METAL I.E. INCREASING ITS WETTING ACTION OR SPREADABILITY.

•  PROTECT THE SURFACE FROM OXIDATION DURING JOINING OPERATION.

THE STRENGTH OF BRAZED JOINT IS HIGHER THAN SOLDERED JOINT BUT LOWER THAN WELDED JOINT. HOWEVER, IN BETWEEN WELDING AND BRAZING THERE IS ANOTHER PROCESS TERMED AS ‘BRAZE WELDING'. 

BRAZE WELDING:

UNLIKE BRAZING, IN BRAZE WELDING CAPILLARY ACTION PLAYS NO ROLE BUT THE FILLER METAL WHICH HAS LIQUIDUS ABOVE 450 ° C BUT BELOW THE MELTING POINT OF PARENT METAL, FILLS THE JOINT LIKE WELDING WITHOUT THE MELTING OF EDGES OF PARENT METAL. DURING THE OPERATION, THE EDGES OF THE PARENT METAL ARE HEATED BY OXY-ACETYLENE FLAME OR SOME OTHER SUITABLE HEAT SOURCE TO THAT TEMPERATURE SO THAT PARENT METAL MAY NOT MELT BUT MELTING TEMPERATURE OF FILLER METAL IS REACHED. WHEN FILLER ROD IS BROUGHT IN CONTACT WITH HEATED EDGES OF PARENT METAL, THE FILLER ROD STARTS MELTING, FILLING THE JOINT. IF EDGES TEMPERATURE FALLS DOWN THEN AGAIN HEAT SOURCE IS BROUGHT FOR MELTING FILLER ROD. THE MOLTEN FILLER METAL AND PARENT METAL EDGES PRODUCE ADHESION ON COOLING RESULTING INTO STRONG BRAZE WELD. 

THE BRAZE WELDING FILLER MATERIAL IS NORMALLY BRASS WITH 60% CU AND REMAINING ZN WITH SMALL ADDITIONS OF TIN, MANGANESE AND SILICON. THE SMALL ADDITIONS OF ELEMENTS IMPROVE THE DEOXIDIZING AND FLUIDITY CHARACTERISTICS OF FILLER METAL. 

BRAZING:

THE MOST COMMONLY USED FILLER METAL IS COPPER BASE ZINC ALLOY CONSISTING OF NORMALLY 50-60% CU, APPROXIMATELY 40% ZN, 1% NI, 0.7 % FE AND TRACES OF SI AND MN, WHICH IS BRASS AND TERMED AS 'SPELTER'. IN SOME CASES AROUND 10% NI MAY ALSO BE ADDED TO FILLER ALLOYS. COPPER BASE ALLOYS MAY BE AVAILABLE IN THE FORM OF ROD, STRIP AND WIRE. SILVER BRAZING FILLER METAL MAY CONSISTS OF 30-55% AG, 15-35% CU, 15-28% ZN, 18-24% CD AND SOMETIMES 2-3% NI OR 5% SN. SILVER BRAZING ALLOYS ARE AVAILABLE IN FORM OF WIRE, STRIP, RODS AND POWDERS. 

BORAX AND BORIC ACID ARE COMMONLY USED FLUXES FOR BRAZING WITH COPPER BASE FILLER METALS. MANY OTHER COMMERCIAL FLUXES MAY BE AVAILABLE IN THE FORM OF PASTE OR LIQUID SOLUTION LEADING TO EASE OF APPLICATION AND ADHERENCE TO THE SURFACE IN ANY POSITION. 

VARIOUS COMMONLY USED METHOD OF BRAZING ARE FOLLOWINGS: 

•  TORCH BRAZING

TORCH BRAZING UTILIZES THE HEAT OF OXY-ACETYLENE FLAME WITH NEUTRAL OR REDUCING FLAME. FILLER METAL MAY BE EITHER PREPLACED IN FORM OF WASHERS, RINGS, FORMED STRIPS, POWDERS OR MAY BE FED MANUALLY IN FORM OF ROD.

•  DIP BRAZING

IN DIP BRAZING COMPONENTS WITH FILLER METAL IN PROPER FORM IS PREPLACED AT THE JOINT AND ASSEMBLY IS DIPPED IN BATH OF MOLTEN SALT WHICH ACTS AS HEAT SOURCE AS WELL AS FLUX FOR BRAZING. PREPLACED PREFORM MELTS AND FILLS THE JOINT. ANOTHER VARIANT IS TO DIP ASSEMBLED PARTS IN METALLIC BATH AND METAL OF BATH FILLS THE JOINT.

•  FURNACE BRAZING

SELF FIXTURING ASSEMBLY WITH PREPLACED FILLER METAL IS PLACED INSIDE ELECTRICALLY HEATED FURNACE WITH TEMPERATURE CONTROL FOR HEATING AND COOLING. THESE FURNACES MAY ALSO BE USING PROTECTIVE ATMOSPHERE WITH INERT GASES LIKE ARGON AND HELIUM OR VACUUM FOR BRAZING OF REACTIVE METAL COMPONENTS.

•  INFRA-RED BRAZING

THE HEAT FOR BRAZING IS OBTAINED FROM INFRA-RED LAMPS. HEAT RAYS CAN BE CONCENTRATED AT DESIRED AREA OR SPOT WITH CONCAVE REFLECTORS. SUCH METHOD OF BRAZING REQUIRES AUTOMATION AND PARTS TO BE JOINED SHOULD BE SELF FIXTURING. FILLER METAL IS TO BE PREPLACED IN THE JOINT. THE OPERATION CAN BE PERFORMED IN AIR OR IN INERT ATMOSPHERE OR IN VACUUM.

•  INDUCTION BRAZING

THE HEAT IS GENERATED BY INDUCED CURRENT INTO THE WORKPIECE FROM A WATER COOLED COIL WHICH SURROUNDS THE WORKPIECES TO BE BRAZED. HIGH FREQUENCIES EMPLOYED VARY FROM 5 TO 400 KHZ. HIGHER THE FREQUENCY OF CURRENT, SHALLOW IS THE HEATING EFFECT WHILE LOWER FREQUENCIES OF CURRENT LEAD TO DEEPER HEATING AND SO IT CAN BE EMPLOYED FOR THICKER SECTIONS. FLUXES MAY OR MAY NOT BE USED DURING BRAZING.

•  RESISTANCE BRAZING

IN RESISTANCE BRAZING THE HEAT IS GENERATED AT THE INTERFACES TO BE BRAZED BY RESISTIVE HEATING. THE COMPONENTS ARE CONNECTED TO HIGH CURRENT AND LOW VOLTAGE POWER SUPPLY THROUGH TWO ELECTRODES UNDER PRESSURE. ONLY THOSE FLUXES ARE USED WHICH ARE ELECTRICALLY CONDUCTIVE AND FILLER METAL IS PREPLACED. 

SOLDERING:

THE SOLDERING FILLER METAL IS CALLED SOLDER. THE MOST COMMONLY USED SOLDER IS LEAD AND TIN ALLOY CONTAINING TIN RANGING FROM 5 TO 70% AND LEAD 95 TO 30%. HIGHER THE CONTENTS OF TIN, LOWER THE MELTING POINT OF ALLOY. OTHER FILLER METAL ARE TIN-ANTIMONY SOLDER (95% TIN AND 5% ANTIMONY), TIN-SILVER SOLDER (TIN 96% AND SILVER 4%), LEAD-SILVER SOLDER (97% LEAD, 1.5 TIN AND 1.5 SILVER), TIN-ZINC SOLDER (91 TO 30% TIN AND 9 TO 70% ZINC), CADMIUM-SILVER SOLDER (95% CADMIUM AND 5% SILVER). THESE ARE AVAILABLE IN THE FORM OF BARS, SOLID AND FLUX CORED WIRES, PREFORMS, SHEET, FOIL, RIBBON AND PASTE OR CREAM. 

FLUXES USED IN SOLDERING ARE AMMONIUM CHLORIDE, ZINC CHLORIDE, ROSIN AND ROSIN DISSOLVED IN ALCOHOL. 

VARIOUS SOLDERING METHODS ARE SOLDERING WITH SOLDERING IRONS, DIP SOLDERING, TORCH SOLDERING, OVEN SOLDERING, RESISTANCE SOLDERING, INDUCTION SOLDERING, INFRA-RED AND ULTRASONIC SOLDERING. 

SOLDERING IRON BEING USED FOR MANUAL SOLDERING, CONSISTS OF INSULATED HANDLE AND END IS FITTED WITH COPPER TIP WHICH MAY BE HEATED ELECTRICALLY OR IN COKE OR OIL/GAS FIRED FURNACE. SOLDER IS BROUGHT TO MOLTEN STATE BY TOUCHING IT TO THE TIP OF THE SOLDERING IRON SO THAT MOLTEN SOLDER CAN SPREAD TO THE JOINT SURFACE. 

ULTRASONIC SOLDERING USES ULTRASONICS I.E. HIGH FREQUENCY VIBRATIONS WHICH BREAK THE OXIDES ON THE SURFACE OF WORKPIECES AND HEAT SHALL BE GENERATED DUE TO RUBBING BETWEEN SURFACES. THIS HEAT MELTS THE SOLDER AND FILLS THE JOINT BY CAPILLARY ACTION. 

FLUX RESIDUE TREATMENT:

WHEN BRAZING OR SOLDERING IS COMPLETED THEN THE FLUX RESIDUES ARE TO BE REMOVED BECAUSE WITHOUT REMOVAL THE RESIDUES MAY LEAD TO CORROSION OF ASSEMBLIES. 

BRAZING FLUX RESIDUES CAN BE REMOVED BY RINSING WITH HOT WATER FOLLOWED BY DRYING. IF THE RESIDUE IS STICKY THEN IT CAN BE REMOVED BY THERMAL SHOCK I.E. HEATING AND QUENCHING. SOMETIMES STEAM JET MAY BE APPLIED FOLLOWED BY WIRE BRUSHING. 

SOLDERING FLUX RESIDUES OF ROSIN FLUX CAN BE LEFT ON THE SURFACE OF JOINT, HOWEVER, ACTIVATED ROSIN FLUX AND OTHER FLUX RESIDUES REQUIRE PROPER TREATMENT. IF ROSIN RESIDUES REMOVAL IS REQUIRED THEN ALCOHOL, ACETONE OR CARBON TETRACHLORIDE CAN BE USED. ORGANIC FLUX RESIDUES ARE SOLUBLE IN HOT WATER SO DOUBLE RISING IN WARM WATER SHALL REMOVE IT. RESIDUE REMOVAL OF ZINC CHLORIDE BASE FLUXES CAN BE ACHIEVED BY WASHING FIRST IN 2% HYDROCHLORIC ACID MIXED IN HOT WATER FOLLOWED BY SIMPLE HOT WATER RINSING. 

 References :- www.nptel.iitm.ac.in/