Welding Basics - PDF

Advanced Joining Processes Welding processes Eduardo A. S. Marques Eduardo Marques Advanced Joining Processes – Welding Processes 1  Contents Basics of welding Arc welding processes Shielded metal arc welding...

Advanced Joining Processes Welding processes Eduardo A. S. Marques Eduardo Marques Advanced Joining Processes – Welding Processes 1  Contents Basics of welding Arc welding processes Shielded metal arc welding (SMAW) Submerged arc welding (SAW) Metal inert gas / Metal active gas (MIG/MAG) Tungesten inert gas (TIG) Weld design basics Eduardo Marques Advanced Joining Processes – Welding Processes 2 2  Basics of welding Eduardo Marques Advanced Joining Processes – Welding Processes 3 3  Basics of welding Introduction Types of welding Anatomy of a weld Heat affected zone Typical microstructures of welds Typical deffects in welds Main steps of a welding process Certification of welders and welding processes Eduardo Marques Advanced Joining Processes – Welding Processes 4 4  Basics of welding Introduction First documented use of fusion welding method was in 1881, done by Auguste de Meritens. Using carbon electrodes, he welded together lead battery plates. Eduardo Marques Advanced Joining Processes – Welding Processes 5 5  Basics of welding Introduction Eduardo Marques Advanced Joining Processes – Welding Processes 6 6  Basics of welding Introduction Eduardo Marques Advanced Joining Processes – Welding Processes 7 7  Basics of welding Introduction Eduardo Marques Advanced Joining Processes – Welding Processes 8 8  Basics of welding Introduction Eduardo Marques Advanced Joining Processes – Welding Processes 9 9  Basics of welding Introduction Welding is a fabrication process whereby two or more parts are joined together by means of heat, pressure or both forming a joint as the parts cool. Fusion welding is a process that uses heat to join or fuse two or more materials by heating them to their melting point. The process may or may not require the use a filler material. Eduardo Marques Advanced Joining Processes – Welding Processes 10 10  Basics of welding Introduction Welding is a fabrication process whereby two or more parts are joined together by means of heat, pressure or both forming a joint as the parts cool. Fusion welding is a process that uses heat to join or fuse two or more materials by heating them to their melting point. The process may or may not require the use a filler material. Eduardo Marques Advanced Joining Processes – Welding Processes 11 11  Basics of welding Anatomy of a weld Butt joint Fillet weld Eduardo Marques Advanced Joining Processes – Welding Processes 12 12  Basics of welding Anatomy of a weld Welded joints can have a wide range of geometries and can be carried out in different positions – with varied degrees of difficulty Eduardo Marques Advanced Joining Processes – Welding Processes 13 13  Basics of welding Anatomy of a weld Welding positions Eduardo Marques Advanced Joining Processes – Welding Processes 14 14  Basics of welding Types of fusion welding Arc welding Friction Electron beam Laser Resistance Eduardo Marques Advanced Joining Processes – Welding Processes 15 15  Basics of welding Types of welding – Arc welding Uses electric power to fuse the base material and often uses a filler material. Very flexible technique, used for joining stainless steel, aluminium, nickel and copper alloys, cobalt and titanium. Eduardo Marques Advanced Joining Processes – Welding Processes 16 16  Basics of welding Types of welding – Friction Friction welding techniques join materials using mechanical friction. The mechanical friction generates heat which softens the materials which mix to create a bond as they cool. Friction welding does not require the use of filler metals, flux or shielding gas. Eduardo Marques Advanced Joining Processes – Welding Processes 17 17  Basics of welding Types of welding – Electron beam This fusion joining process uses a beam of high velocity electrons to melt the materials together. Electron beam welding (EBW) is performed in a vacuum (with the use of a vacuum chamber) to prevent the beam from dissipating. Eduardo Marques Advanced Joining Processes – Welding Processes 18 18  Basics of welding Types of welding – Laser Uses a laser to provide concentrated heat ideal for deep welds and high joining rates. Perfect for high volume applications, such as within the automotive industry. Laser beam welding can be performed in air rather than in a vacuum such as with electron beam joining. Eduardo Marques Advanced Joining Processes – Welding Processes 19 19  Basics of welding Types of welding – Resistance Can be split into resistance spot welding and resistance seam welding. Spot welding uses heat delivered between two electrodes, applied to a small area as the workpieces are clamped together. Seam welding is similar to spot welding but it replaces the electrodes with rotating wheels. Eduardo Marques Advanced Joining Processes – Welding Processes 20 20  Basics of welding Heat affected zone In general, fusion welding processes employ high temperatures and instant heat generation. But how does this heat affect the material? Eduardo Marques Advanced Joining Processes – Welding Processes 21 21  Basics of welding Heat affected zone The heat affected zone (HAZ) is a non-melted area of metal that has undergone changes in material properties as a result of being exposed to high temperatures. The HAZ is the area between the weld and the unaffected base metal. Eduardo Marques Advanced Joining Processes – Welding Processes 22 22  Basics of welding Heat affected zone Eduardo Marques Advanced Joining Processes – Welding Processes 23 23  Basics of welding Heat affected zone In conventional steels, the HAZ can be broken down into the grain coarsened zone (closest to the heated area), the grain refined zone, the partially transformed (intercritically heated) zone and the tempered zone Eduardo Marques Advanced Joining Processes – Welding Processes 24 24  Basics of welding Heat affected zone Reduced corrosion resistance is a common side-effect in stainless steels. Chromium carbides precipitate around the grain boundaries in the HAZ, causing the local chromium content to drop below 10.5%. The steel loses the ability to form a passive film and is no longer stainless, leading to intergranular corrosion. Eduardo Marques Advanced Joining Processes – Welding Processes 25 25  Basics of welding Heat affected zone In conventional steels, hydrogen embrittlement is result of the high temperatures. Atomic hydrogen dissolved in the weld metal is trapped in the cooling weld and is rejected into the transforming HAZ. The hydrogen diffuses to the region of greatest strain (usually the weld toes or HAZ), creating additional pressure within the lattice and potentially causing cracking. Eduardo Marques Advanced Joining Processes – Welding Processes 26 26  Basics of welding Typical microstructures of welds Opposite Typical shrinkage Beam side during solidification Entry Material reflux Source: F. G. Silva et al (2021) Eduardo Marques Advanced Joining Processes – Welding Processes 27 27  Basics of welding Typical microstructures of welds Microstructure analysis (8 mm) (Beam entry) Eduardo Marques Advanced Joining Processes – Welding Processes 28 28  Basics of welding Typical microstructures of welds Microstructure analysis (8 mm) (Mid zone) Eduardo Marques Advanced Joining Processes – Welding Processes 29 29  Basics of welding Typical microstructures of welds Microstructure analysis (8 mm) (Opposite side) Eduardo Marques Advanced Joining Processes – Welding Processes 30 30  Basics of welding Typical microstructures of welds Eduardo Marques Advanced Joining Processes – Welding Processes 31 31  Basics of welding Typical microstructures of welds 500 450 Source: F. G. Silva et al (2021) 400 350 HARDNESS (HV5) 300 250 433 200 150 257 243 100 181 196 139 135 50 0 1 2 3 4 5 6 7 BM HAZ FZ HAZ BM Eduardo Marques Advanced Joining Processes – Welding Processes 32 32  Basics of welding Typical defects in welds Eduardo Marques Advanced Joining Processes – Welding Processes 33 33  Basics of welding Typical defects in welds Incomplete penetration occurs when the depth of the welded joint is insufficient. Penetration is defined as the distance from the base plate top surface to the maximum extent of the weld nugget. Eduardo Marques Advanced Joining Processes – Welding Processes 34 34  Basics of welding Typical deffects in welds Causes of incomplete penetration: Improper joint geometry Wrong hold position of the electrode. Too large electrode diameter and longer arc length. Less arc current and faster arc travel speed. Incorrect polarity while welding with DC. Eduardo Marques Advanced Joining Processes – Welding Processes 35 35  Basics of welding Typical deffects in welds Remedies of incomplete penetration: Increasing the heat input. Reducing travel speed during welding. Ensuring that the surface to be joint fit properly. Changing the joint design. Eduardo Marques Advanced Joining Processes – Welding Processes 36 36  Basics of welding Typical deffects in welds Inclusion maybe in the form of slag or any other foreign material, which does not get a chance to float on the surface of the solidifying weld metal and thus gets entrapped inside the same. Inclusion lowers the strength of the joint and makes it weaker. Eduardo Marques Advanced Joining Processes – Welding Processes 37 37  Basics of welding Typical deffects in welds Causes of inclusion: Too high or too low arc current. Long arc and too large electrode diameter. The too-small included angle of the joint. Insufficient chipping and cleaning of previous passes in multipass welding. Wrongly placed tack welds. Eduardo Marques Advanced Joining Processes – Welding Processes 38 38  Basics of welding Typical deffects in welds Remedies of inclusion: Cleaning the weld bed surface before the next layer is deposited, by means of a wire brush. Providing sufficient shielding gases. Redesigning the joint to permit sufficient space for proper manipulation of the puddle of molten weld metals. Eduardo Marques Advanced Joining Processes – Welding Processes 39 39  Basics of welding Typical deffects in welds Cracks The most serious type of welding defect is a weld crack and it’s not accepted almost by all standards in the industry. It can appear on the surface, in the weld metal or the area affected by the intense heat. There are different types of cracks, depending on the temperature at which they occur. Eduardo Marques Advanced Joining Processes – Welding Processes 40 40  Basics of welding Typical deffects in welds Cold cracks These cracks appear after the weld has been completed and the temperature of the metal has gone down. They can form hours or even days after welding. It mostly happens when welding steel. The cause of this defect is usually deformities in the structure of steel. Eduardo Marques Advanced Joining Processes – Welding Processes 41 41  Basics of welding Typical deffects in welds Crater cracks These occur at the end of the welding process before the operator finishes a pass on the weld joint When the weld pool cools and solidifies, it needs to have enough volume to overcome shrinkage of the weld metal. Otherwise, it will form a crater crack. Eduardo Marques Advanced Joining Processes – Welding Processes 42 42  Basics of welding Typical deffects in welds Porosity usually takes the form of a group of small voids and blowholes are comparatively bigger isolated holes or cavities. They are often the result of entrapped gases. Eduardo Marques Advanced Joining Processes – Welding Processes 43 43  Basics of welding Typical deffects in welds Causes of porosity and blowholes: Use of improper electrode and longer arc Faster arc travel speed. Too low and too high arc currents. Due to gas entrapment during solidification of the weld. Unclean job surface i.e. presence of scales, rust, oil, and grease, etc on the surface of the job. Eduardo Marques Advanced Joining Processes – Welding Processes 44 44  Basics of welding Typical deffects in welds Remedies for porosity and blowholes: Proper selection of electrode and filler materials. Improved welding techniques such as preheating the weld area or an increase in the rate of heat input. Reducing welding speed to allow time for gas to escape. Ensuring proper cleaning of contaminants. Eduardo Marques Advanced Joining Processes – Welding Processes 45 45  Basics of welding Typical deffects in welds Spatter consists in the small metal particles that are thrown out of the arc during welding and get deposited on the base metal around the weld bead along its length. Eduardo Marques Advanced Joining Processes – Welding Processes 46 46  Basics of welding Typical deffects in welds Causes of spatter: Excessive arc current. Use of longer arc, damp electrodes. Electrode being coated with improper flux ingredients. Due to the expansion of gas bubbles entrapped in the molten globules of metal. Eduardo Marques Advanced Joining Processes – Welding Processes 47 47  Basics of welding Typical deffects in welds Remedies for spatter Adjust weld current, arc length and use fresh electrodes. Use of AC power to reduce arc blow. Eduardo Marques Advanced Joining Processes – Welding Processes 48 48  Basics of welding Typical deffects in welds Distortion is the change in the shape and difference between the position of two plates, before and after welding, due to the temperature gradient present at various points along the joints. Is due to unequal expansion and contraction of the weld metal and increases with the volume of metal deposited. Eduardo Marques Advanced Joining Processes – Welding Processes 49 49  Basics of welding Typical deffects in welds Causes of Distortion: A great number of passes with small diameter electrodes. Slow arc travel speed. High residual stresses in the plate to be welded. Using improper welding sequences. Eduardo Marques Advanced Joining Processes – Welding Processes 50 50  Basics of welding Typical deffects in welds Remedies of Distortion: Use the proper amount of weld metal as per the requirement of the joint. It will reduce the contraction forces. Use an appropriate number of weld passes. Place the weld near the neutral axis. Use proper welding sequences. Eduardo Marques Advanced Joining Processes – Welding Processes 51 51  Basics of welding Typical deffects in welds Remedies of Distortion: Reduce the welding time so that too great a volume surrounding metal cannot be expanded. While the large weldments into sub- assemblies. Peening should be done to remove the shrinkage force during or after welding. Eduardo Marques Advanced Joining Processes – Welding Processes 52 52  Basics of welding Main steps of a welding process Preparation of the materials to be welded Making joints (edges) according to existing recommendations Edge cleaning Choice of welding process to be use, depending on Welding geometry and position Materials to be welded Definition of welding parameters Choice of welder (qualification of welders) Welding execution Eduardo Marques Advanced Joining Processes – Welding Processes 53 53  Basics of welding Main parameters Joints Current Base metal Voltage Filler Wire feed rate Position Shielding gas flow Pre-heat Arc distance (CTWD) Heat treatment Work angle Shielding gas Travel angle Electrical characteristics Weld speed Technique Eduardo Marques Advanced Joining Processes – Welding Processes 54 54  Basics of welding Certification of welders and processes Certification of the weld Certification of the welder procedures ISO 9606 ISO 15614 Procedure approval is carried out to demonstrate that a weld will have the requisite mechanical properties such as tensile strength, ductility and toughness. The welder approval test demonstrates that the welder has a sufficient level of skill such that he can deposit a weld of the correct quality, free of welding defects. Eduardo Marques Advanced Joining Processes – Welding Processes 55 55  Basics of welding Certification of welders and processes To carry out a given welding process, it is necessary to have both an approved procedure and a welder certified in that process. Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 56 56  Basics of welding Certification of welders and processes Welder Processes: SMAW; TIG; MIG/MAG; etc Materials: mild steel, stainless steel and aluminum. Welder must pass qualification tests. Eduardo Marques Advanced Joining Processes – Welding Processes 57 57  Basics of welding Certification of welders and processes Welding inspector Personnel who does not have knowledge in welding inspection these qualifications are the efficient way to achieve them. These qualifications have a comprehensive training, covering welding technology, welding inspection and practical training. Eduardo Marques Advanced Joining Processes – Welding Processes 58 58  Basics of welding Certification of welders and processes Welding coordinator Qualifications to ensure that trainees will achieve, at the proper level, the relevant knowledge to perform welding coordination activities, recognised by international organisations. Eduardo Marques Advanced Joining Processes – Welding Processes 59 59  Basics of welding Certification of welders and processes The Welding Procedure Specification A Welding Procedure Specification (WPS) is the formal written document describing welding procedures, which provides direction to the welder or welding operators for making sound and quality production welds as per the code requirements. Eduardo Marques Advanced Joining Processes – Welding Processes 60 60  Arc welding processes Eduardo Marques Advanced Joining Processes – Welding Processes 61 61  Arc welding processes Techniques Shielded metal arc welding (SMAW) Submerged arc welding (SAW) Metal inert gas / Metal active gas (MIG/MAG) Tungesten inert gas (TIG) Eduardo Marques Advanced Joining Processes – Welding Processes 62 62  Arc welding processes Shielded metal arc welding (SMAW) Shielded Metal Arc Welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or stick welding. Suitable for welding ferrous and non-ferrous materials in all positions. Eduardo Marques Advanced Joining Processes – Welding Processes 63 63  Arc welding processes Shielded metal arc welding (SMAW) Eduardo Marques Advanced Joining Processes – Welding Processes 64 64  Arc welding processes Shielded metal arc welding (SMAW) Advantages Lower equipment cost than other techniques. (No bottle, gas hose, flowmeter, and wire feeder needed. Quick change from one material to another. The process lends itself to welding in confined spaces and various positions with few problems. Easy to move from one location to another. Eduardo Marques Advanced Joining Processes – Welding Processes 65 65  Arc welding processes Shielded metal arc welding (SMAW) Advantages Requires no outside shielding gas and can be used outdoors in light to medium wind. The ability to bend the electrode and the small space the electrode takes allows the process to be used in comparatively tight spaces. However, keep in mind that for some jobs one of the other processes may also work or even work better. Eduardo Marques Advanced Joining Processes – Welding Processes 66 66  Arc welding processes Shielded metal arc welding (SMAW) Disadvantages Low deposition rate compared to other techniques. Filler metal cost per weld can be greater due to a low deposition efficiency that can vary greatly with stub length. Production factor is typically lower (Unless welding on various materials) due to rod changes and chipping slag. Needs more hand eye coordination than MIG/MAG. Slag must be removed as compared to MIG/MAG and TIG Eduardo Marques Advanced Joining Processes – Welding Processes 67 67  Arc welding processes Submerged arc welding (SAW) Submerged arc welding uses a continuously-fed consumable electrode and a blanket of fusible flux which becomes conductive when molten and provides a current path between the workpiece and the electrode. The flux prevents spatter and sparks while suppressing radiation and fume emissions. Eduardo Marques Advanced Joining Processes – Welding Processes 68 68  Arc welding processes Submerged arc welding (SAW) Eduardo Marques Advanced Joining Processes – Welding Processes 69 69  Arc welding processes Submerged arc welding (SAW) Advantages High deposition rate. The single-pass can be made in thick plates using normal equipment. Ability to make the deep welds. Flux can be recovered, recycled, and reused. It produces sound and uniform welds, which are corrosion-resistant. Eduardo Marques Advanced Joining Processes – Welding Processes 70 70  Arc welding processes Submerged arc welding (SAW) Advantages The arc is covered under a blanket of flux, which gave no chances for spatter to occur. The process can be performed both indoor and outdoor. High-speed welding can be carried out. Edge preparation is not necessary. Eduardo Marques Advanced Joining Processes – Welding Processes 71 71  Arc welding processes Submerged arc welding (SAW) Disadvantages It is limited to some ferrous metals like steel and stainless steel It is also limited to long straight seams or rotated pipes and vessel Backing strips are required for proper penetration It is better suited to high thickness materials. Eduardo Marques Advanced Joining Processes – Welding Processes 72 72  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) MIG and MAG welding are the most common arc welding processes, in which an electric arc forms between a consumable wire electrode and the workpiece leading them to melt. Both use a shielding gas to protect the weld from airborne contaminants, or oxidation in the case of MIG welding. Eduardo Marques Advanced Joining Processes – Welding Processes 73 73  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) Eduardo Marques Advanced Joining Processes – Welding Processes 74 74  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) Eduardo Marques Advanced Joining Processes – Welding Processes 75 75  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) Eduardo Marques Advanced Joining Processes – Welding Processes 76 76  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) MIG → Metal Inert Gas Only inert gases or gas mixtures are used for the shielding gas when MIG welding. Typical inert gases used for MIG welding are argon and helium. These gases are usually used for MIG welding of aluminium and other non-ferrous metals. MAG → Metal Active Gas Active gas mixtures have been developed primarily for welding steels. Typical shielding gases are mixtures of argon, carbon dioxide and oxygen e.g. CO2 , Ar + 2 to 5% O2 , Ar + 5 to 25% CO2 and Ar + 10% CO2 + 5% O2 Eduardo Marques Advanced Joining Processes – Welding Processes 77 77  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) Advantages Higher welding speeds Greater deposition rates Less post welding cleaning (e.g. no slag to chip off weld) Better weld pool visibility No stub end losses or wasted man hours caused by changing electrodes Eduardo Marques Advanced Joining Processes – Welding Processes 78 78  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) Advantages Low skill factor required to operate the welding torch Positional welding offers no problems when compared to other processes. (Use dip or pulsed mode of transfer) The process is easily automated No fluxes required in most cases Ultra low hydrogen process Eduardo Marques Advanced Joining Processes – Welding Processes 79 79  Arc welding processes Metal inert gas / Metal active gas (MIG/MAG) Disadvantages Higher initial setup cost. Atmosphere surrounding the welding process must be stable (hence the shielding gasses), therefore this process is limited to draught free conditions. Higher maintenance costs due to extra electronic components. Less efficient where high duty cycle requirements are necessary. Radiation effects are more severe. Eduardo Marques Advanced Joining Processes – Welding Processes 80 80  Arc welding processes Tungsten inert gas (TIG) Tungsten inert gas welding uses a non- consumable tungsten electrode to create the arc between the electrode and the base plate. An inert shielding gas is used to protect from oxidation or other atmospheric contamination. This process can be used autogenously on thin parts, but will require the addition of a wire, rod, or consumable to be added for thicker parts. Eduardo Marques Advanced Joining Processes – Welding Processes 81 81  Arc welding processes Tungsten inert gas (TIG) Eduardo Marques Advanced Joining Processes – Welding Processes 82 82  Arc welding processes Tungsten inert gas (TIG) Advantages It produces high-quality welds. It is protected by the inert gas during the process. TIG welding does not produce slag. It can be performed in any welding position. Eduardo Marques Advanced Joining Processes – Welding Processes 83 83  Arc welding processes Tungsten inert gas (TIG) Disadvantages Offers a slow welding process. High skilled labor is needed. Operation cost is much expensive. Welders are exposed to high radiation intensities. Eduardo Marques Advanced Joining Processes – Welding Processes 84 84  Thank you [email protected] Eduardo Marques Advanced Joining Processes – Welding Processes 85 85