SAW, FCAW, Electrogas, Electro Slag, AHW, PAW, By A Nirala Email:-niralaiitk@gmail.com

Submerged Arc Welding The submerged arc welding process is similar to the gas metal arc welding process except the arc is struck under a blanket of granular flux, hence the name submerged arc welding. The filler metal is a continuously-fed wire electrode like GMAW and FCAW. However, higher deposition rates can be achieved in SAW by using larger diameter electrodes (up to 1/4”) and higher currents (650-1500 Amperes). Since the process is almost fully mechanized, several variants of the process can be utilized such as multiple torches and narrow gap welding.

Advantages High deposition rates No arc flash or glare Minimal smoke and fumes Flux and wire added separately - extra dimension of control Easily automated Joints can be prepared with narrow grooves Can be used to weld carbon steels, low alloy steels, stainless steels, chromium-molybdenum steels, nickel base alloys SAW has the highest deposition rate of all the deep penetrating arc welding processes making it ideal for thick section and multi-pass welding. Variations of the process can utilize dual arc welding, twin arc welding, multiple torch, and narrow groove welding to increase productivity. Since the arc is completely submerged in the flux, there is no arc radiation. Screens or light filtering lenses are not needed. Additionally, the smoke and fumes are trapped within the flux and thus minimizing smoke and fumes . Since the process is simple to mechanize and easily automated, it is extremely consistent once a procedure is qualified. And it can be used on a wide variety of materials.

Limitations Flux obstructs view of joint during welding Submerged Arc Welding Flux obstructs view of joint during welding Flux is subject to contamination Þ porosity Normally not suitable for thin material Restricted to the flat position for grooves - flat and horizontal for fillets Slag removal required Flux handling equipment

Flux Cored Arc Welding (FCAW)

There are two basic process variants: self shielded FCAW (without shielding gas) and gas shielded FCAW (with shielding gas) The difference in the two is due to different fluxing agents in the consumables, which provide different benefits to the user. Usually, self-shielded FCAW is used in outdoor conditions where wind would blow away a shielding gas. The fluxing agents in self shielded FCAW are designed to not only deoxidize the weld pool but also to allow for shielding of the weld pool and metal droplets from the atmosphere. The flux in gas-shielded FCAW provides for deoxidation of the weld pool and, to a smaller degree than in self-shielded FCAW, provides secondary shielding from the atmosphere. The flux is designed to support the weld pool for out-of position welds. This variation of the process is used for increasing productivity of out-of-position welds and for deeper penetration.

There are two basic process variants; self shielded FCAW (without shielding gas) and gas shielded FCAW (with shielding gas). The difference in the two is due to different fluxing agents in the consumables, which provide different benefits to the user. Usually, self-shielded FCAW is used in outdoor conditions where wind would blow away a shielding gas. The fluxing agents in self shielded FCAW are designed to not only deoxidize the weld pool but also to allow for shielding of the weld pool and metal droplets from the atmosphere. The flux in gas-shielded FCAW provides for deoxidation of the weld pool and, to a smaller degree than in self-shielded FCAW, provides secondary shielding from the atmosphere. The flux is designed to support the weld pool for out-of position welds. This variation of the process is used for increasing productivity of out-of-position welds and for deeper penetration. Linnert, Welding Metallurgy, AWS, 1994

Advantages High deposition rates Deeper penetration than SMAW High-quality Less pre-cleaning than GMAW Slag covering helps with larger out-of-position welds Self-shielded FCAW is draft tolerant. The FCAW process combines the best characteristics of SMAW and GMAW. It uses a flux to shield the weld pool, although a supplemental shielding gas can be used. A continuous wire electrode provides high deposition rates. The flux for FCAW consumables can be designed to support larger weld pools out of position and provide higher penetration compared to using a solid wire (GMAW). Larger welds can be made in a single pass with larger diameter electrodes where GMAW and SMAW would need multiple passes for equivalent weld sizes. This improves productivity and reduces distortion of a weldment.

Limitations Slag must be removed More smoke and fumes than GMAW and SAW Spatter FCAW wire is more expensive Equipment is more expensive and complex than for SMAW As with SMAW, the slag must be removed between passes on multipass welds. This can slow down the productivity of the application and result in possible slag inclusion discontinuities. For gas shielded FCAW, porosity can occur as a result of insufficient gas coverage. Large amounts of fume are produced by the FCAW process due to the high currents, voltages, and the flux inherent with the process. Increased costs could be incurred through the need for ventilation equipment for proper health and safety. FCAW is more complex and more expensive than SMAW because it requires a wire feeder and welding gun. The complexity of the equipment also makes the process less portable than SMAW.

Electrogas Welding Electrogas welding (EGW) is an vertical positioned arc welding process, is used for welding the edges of sections vertically and in one pass with the pieces placed edge to edge (butt joint). It is classified as a machine-welding process, because for its operation requires special equipment. The weld metal is deposited into a weld cavity between the two pieces to be joined. The space is covered by two water-cooled copper dams(shoes) to prevent the molten slag from running off; mechanical drives move the shoes upward.

Electro Slag Welding Electroslag welding (ESW) and its applications are similar to electrogas welding. The main difference is that the arc is started between the electrode tip and the bottom of the part to be welded. Flux is added, which then melts by the heat of the arc. After the molten slag reaches the tip of the electrode, the arc is extinguished. Heat is produced continuously by the electrical resistance of the molten slag. Because the arc is extinguished, Electroslag welding is not strictly an arc-welding process. Single or multiple solid as well as flux-cored electrodes may be used.

Atomic hydrogen welding Atomic hydrogen welding (AHW) is an arc welding process that uses an arc between two metal tungsten electrodes in a shielding atmosphere of hydrogen. The process was invented by Irving Langmuir in the course of his studies of atomic hydrogen. The electric arc efficiently breaks up the hydrogen molecules, which later recombine with tremendous release of heat, reaching temperatures from 3400 to 4000 °C. Without the arc, an oxyhydrogen torch can only reach 2800 °C.  An acetylene torch merely reaches 3300 °C. This device may be called an atomic hydrogen torch, nascent hydrogen torch or Langmuir torch. The process was also known as arc-atom welding.

Plasma arc welding(PAW) Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode (which is usually but not always made of sintered tungsten) and the workpiece. The key difference from GTAW is that in PAW, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities (approaching the speed of sound) and a temperature approaching 28,000 °C (50,000 °F) or higher. Arc plasma is the temporary state of a gas. The gas gets ionized after passage of electric current through it and it becomes a conductor of electricity. In ionized state atoms break into electrons (−) and cations (+) and the system contains a mixture of ions, electrons and highly excited atoms. The degree of ionization may be between 1% and greater than 100% i.e.; double and triple degrees of ionization. Such states exist as more electrons are pulled from their orbits.

Electron Beam Welding (EBM or EBW) Electron Beam Welding is a fusion welding process in which a beam of high-velocity electrons is applied to the material to be joined. The work-piece melt as the kinetic energy of the electrons is transformed into heat upon impact. The EBW process is well-positioned to provide industries with highest quality welds and machine designs that have proven to be adaptable to specific welding tasks and production environments.

Electron Beam? In an electron beam welder electrons are “boiled off” as current passes through filament which is in a vacuum enclosure. An electrostatic field, generated by a negatively charged filament and bias cup and a positively charged anode, accelerates the electrons to about 50% to 80% of the speed of light and shapes them into a Beam. Fig 2:Electron beam source for EB disposal

How does the Process Work? The electron beam gun has a tungsten filament which is heated, freeing electrons. The electrons are accelerated from the source with high voltage potential between a cathode and anode. The stream of electrons then pass through a hole in the anode. The beam is directed by magnetic forces of focusing and deflecting coils. This beam is directed out of the gun column and strikes the work piece. The potential energy of the electrons is transferred to heat upon impact of the work piece and cuts a perfect hole at the weld joint. Molten metal fills in behind the beam, creating a deep finished weld.

LASER BEAM WELDING (LBM & LBW)

WHAT IS LASER BEAM? The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation. A laser beam is a powerful, narrow, monochromatic and directional beam of electromagnetic radiation. Often, these beams are within the visible spectrum of light. A laser device excites the atoms in a losing medium. The electrons of these atoms move to a higher orbit, then release photons, creating a laser beam.

Properties of Laser Beam A LASER beam is highly intense in nature. LASER beam is having strictly monochromatic. LASER light is highly powerful and capable of propagating over long distance & are not easily absorbed by water. LASER beam is also said to be highly directional. This beam is coherent with the wave train in phase with each other.

Types of laser Beam Types of lasers include gas, liquid and solid. 1. Gas lasers excite the electrons in gases, such as helium, neon, cadmium, carbon dioxide and nitrogen. 2. Liquid lasers include the dye laser, which uses organic dye molecules in liquid form to produce a wavelength of radiation that can be tuned. 3. Solid lasers include the ruby laser, which uses a precious stone to produce a beam of red light.

Laser beam welding process In general cases heat is required to fuse the metals for any types of welding, in laser beam welding process the heat is obtained from the application of a concentrated coherent light beam which striking upon the weld metal and melt the metal, such this weld joint is obtained, this welding process is called laser welding.

Principle of LBW A laser beam is produced inside of the Ruby Crystal. The Ruby Crystal is made of aluminium oxide with chromium dispersed throughout  it. Which is forming about 1/2000 of crystal, this less than natural ruby. Silver coated mirrors are fitted internally in the both side of  crystal. The one side of mirror has a tiny hole, a beam is come out through this hole. A flash tube is placed around the Ruby Crystal, which is filled with xenon inert gas. The flash is specially designed such as which is made flash rate about thousands flashes per seconds.

Schematic diagram of LBW

The electrical energy is converted into light energy, this is worked by flash tube. The capacitor is provided for storage the electrical energy and supply the high voltage to flash tube for performed appropriately. The electrical energy discharged from capacitor and xenon transform the high energy into white flash light rate of 1/1000 per second.

The chromium atoms of Ruby Crystal are excited and pumped into high energy. Due to heat generating the some of this energy is lost. But some light energy reflected mirror to mirror and again chromium atoms are excited until loss their extra energy simultaneously to form a narrow beam of coherent light. Which is come out through the one end tiny hole of crystal’s mirror. This narrow beam is focused by a optical focusing lens to produce a small intense of laser on the job.

Parameters of LBW Medium Normal atmosphere Tool High power laser beam Critical parameters Beam intensity ,beam dia, melting temperature. Materials application All material

LBW Process Advantages: Works with high alloy metals without difficulty Can be used in open air Can be transmitted over long distances with a minimal loss of power Narrow heat affected zone Low total thermal input Welds dissimilar metals No filler metals necessary

Advantages contd.. No secondary finishing necessary Extremely accurate Produces deep and narrow welds Low distortion in welds High quality welds Can weld small, thin components No contact with materials

LIMITATIONS Rapid cooling rate may cause cracking in some metals High capital cost for equipment Optical surfaces of the laser are easily damaged High maintenance costs The maximum joint thickness that can be welded by laser beam is somewhat limited. Thus weld penetrations of larger than 19 mm are difficult to weld.