THE INDIAN INSTITUTE OF WELDING - MUMBAI
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Welding and joining processes Process terminology The European standard, EN 24063:1992 Welding, brazing, soldering and braze welding of metals (Nomenclature of processes and reference numbers for symbolic representative on drawings), assigns a unique number to the main welding processes. These are grouped as follows: Arc welding Resistance welding Gas welding Forge welding Other welding processes Brazing, soldering and braze welding Each process is identified within the group by a numerical index or reference number. For example, the MIG welding process has a reference number of 131 which is derived as follows: 1 - Arc welding 3 - Gas-shielded metal arc welding 1 - Metal arc inert gas welding The main arc welding process reference numbers are: 111 MMA with covered electrodes 114 Flux cored wire (self-shielded) 112 Submerged arc 131 MIG (inert gas) 135 MAG (CO2,active gas) 141 TIG 15 Plasma welding The reference numbers are used as a convenient way of identifying the welding process in documentation such as welding procedure (EN 288) and welder qualffication (EN 287) records. Process options Factors which must be taken into account when choosing a suitable welding or joining process are: material type plate or tubular quality and strength requirements degree of mechanisation capital cost Although consideration of these factors will identify the most suitable welding process, the choice within a company may be restricted by the cost of implementing a new process, availability of plant or current workforce skill. Welding and joining processes available to the welding engineer can be separated into the following generic types: Fusion arc gas power beam resistance Thermomechanical friction flash explosive Mechanical fasteners Solid state adhesive soldering brazing The suitability of the processes for welding and joining materials, joint types and components are shown in Table 1. Process Index no. Steel Stainless Al Butt joint Lap joint Plate Tube Portability Manual Mechanised Automated Site Arc 1 Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Gas 3 Yes Possible Possible Yes Yes Yes Yes Yes Yes No Yes Laser 751 Yes Yes Possible Yes Yes Yes Yes No No Yes No Resistance 2 Yes Yes Yes Possible Yes Yes Possible Possible Yes Yes No Friction 43 Yes Yes Yes Yes No Yes No No No Yes No Brazing 9 No Yes Yes No Yes Yes Possible Yes Yes Possible Yes Fasteners none Yes Yes Yes No Yes Yes No Possible Yes Yes Yes Adhesives none Yes Yes Yes No Yes Yes Yes Yes Yes Possible Yes In selecting a suitable process, consideration must also be given to the type of application, for example, the portability of equipment, whether it can be used on site, whether it is manual or mechanised, and the overall cost of the welding plant. Fusion welding processes When welding using a fusion process, the edges of a component are melted together to form weld metal. Process Heat source Shield Parent metal thickness mm Deposition rate Kg/hr Arc MMA Arc Gas/flux 1-100 1-2 MIG Arc Gas 0.5-100 1-8 TIG Arc Gas 0.1-100 1-4 SAW Arc Flux 5-100 5-20 ES/EG Resistance/arc Gas/flux 5-100 - Stud Arc - 4-20 - Gas Oxyfuel Flame Gas 0.6-10 1-2 Power beam Laser Radiation Gas 0.2-100 - EB Electrogas Vacuum 0.2-100 - Resistance Spot/Seam Arc - 0.2-10 - Thermit Thermit Chemical Gas 10-100 - Table 2 shows heat source, mode of shielding, thickness range and metal deposition rates for a range of fusion processes. Although fusion welding is one of the simplest joining techniques, problems likely to occur include porosity in the weld metal, and cracking in either the weld or heat affected zone (HAZ). Porosity is avoided by ensuring adequate shielding of the weld pool and, for materials such as aluminium, the addition of filler wire. Consideration of the joint design and the chemistry of the weld metal will prevent weld metal cracking. HAZ cracking which might be caused by hydrogen, is avoided by using low hydrogen consumables (MMA) and controlling the heat input and the rate of cooling of the parent metal.