Laser Welding Processes PDF

Advanced Joining Processes Laser, plasma and electron beam welding Eduardo A. S. Marques Eduardo Marques Advanced Joining Processes – Welding Processes 1  Contents Laser welding (LW) Pl...

Advanced Joining Processes Laser, plasma and electron beam welding Eduardo A. S. Marques Eduardo Marques Advanced Joining Processes – Welding Processes 1  Contents Laser welding (LW) Plasma welding (PW) Electron beam welding (FW) Eduardo Marques Advanced Joining Processes – Welding Processes 2 2  Laser welding Eduardo Marques Advanced Joining Processes – Welding Processes 3 3  Laser welding Introduction Laser types and applications Material-laser interaction Process parameters Defects Operation modes Welding of polymers Eduardo Marques Advanced Joining Processes – Welding Processes 4 4  Laser welding Introduction Laser welding is a process used to join metals or thermoplastics using a laser beam to form a weld. Due to the high heat concentration, laser welding can be carried out at high welding speeds in thin materials, and produce narrow, deep welds between square-edged thick parts. Eduardo Marques Advanced Joining Processes – Welding Processes 5 5  Laser welding Introduction Key process characteristics High quality at very high-power densities, high precision and high process speed; Small heat affected zone; Process flexibility; Non-contact tool, free of wear; Highly moveable tool, suitable for automation. Eduardo Marques Advanced Joining Processes – Welding Processes 6 6  Laser welding Introduction Basic operation of a laser LASER - Light Amplification by Stimulated Emission of Radiation” Eduardo Marques Advanced Joining Processes – Welding Processes 7 7  Laser welding Introduction Source: Fraunhofer ILT Eduardo Marques Advanced Joining Processes – Welding Processes 8 8  Laser welding Introduction Laser soldering Use of third element (solder) to connect base materials No fusion of the base materials Limited in scope and applications Laser bonding Solid state joining process (no fusion) Bonding achieved via chemical bonds Suitable for micro-systems, with limited structural loads Laser welding Narrow seams Low thermal distortion No filler metal used Eduardo Marques Advanced Joining Processes – Welding Processes 9 9  Laser welding Introduction Lithography Processing Photolytic and thermal Annealing with laser processes (below melting temperature) Chemical vapour deposition radiation Etching Laser bonding Soldering Melting based processes (below vaporization temperature) Welding Additive manufacturing / Sintering Cutting Ablation Plasma based processes (above vaporization temperature) Drilling Physical vapour deposition Cutting Eduardo Marques Advanced Joining Processes – Welding Processes 10 10  Laser welding Laser types and applications Source: Fraunhofer ILT Eduardo Marques Advanced Joining Processes – Welding Processes 11 11  Laser welding Laser types and applications Diode laser 400-2000 nm Soldering and polymer welding Solid state laser 600-2940 nm Micro welding and polymer welding Nano-second laser 355-1080 nm Ablation and glass processing Excimer laser 157-351 nm Micro ablation CO2 laser 10600 nm Cutting and metal and polymer welding Eduardo Marques Advanced Joining Processes – Welding Processes 12 12  Laser welding Laser types and applications Laser usage is highly dependent on the achievable beam intensity and the necessary exposure time. Source: Fraunhofer ILT Eduardo Marques Advanced Joining Processes – Welding Processes 13 13  Laser welding Laser types and applications High power CO2 lasers are predominantly used for the welding of automotive components, such as gears and transmission components, which require circular and annular welds and in tailored blank applications. Most CO2 lasers have a power of 6kW or less. Eduardo Marques Advanced Joining Processes – Welding Processes 14 14  Laser welding Laser types and applications High power Nd:YAG are solid state lasers, of up to 4kW, coupled with fibre-optic beam delivery. The welding applications are multiple and include body-in-white assembly. Eduardo Marques Advanced Joining Processes – Welding Processes 15 15  Laser welding Laser types and applications Within the laser industry, one of the main advances in the past years has been in diode lasers, where 2 kW systems are now commercially available. However, the power densities required for welding of sheet materials used in the automotive industry (about 1x106 W/cm2) are still not possible. Eduardo Marques Advanced Joining Processes – Welding Processes 16 16  Laser welding Laser types and applications CO2 lasers Multi material gears Battery casings Eduardo Marques Advanced Joining Processes – Welding Processes 17 17  Laser welding Laser types and applications Nd-YAG lasers Electrical connections Nitinol medical guidewires Eduardo Marques Advanced Joining Processes – Welding Processes 18 18  Laser welding Laser types and applications Diode lasers Galvanized steel sheets Copper batery connectors Eduardo Marques Advanced Joining Processes – Welding Processes 19 19  Laser welding Material-laser interaction Different materials will react differently to the laser radiation, with different levels of reflection, absorption and transmission. Eduardo Marques Advanced Joining Processes – Welding Processes 20 20  Laser welding Material-laser interaction Glass Metal 300 nm 300 nm 1000 nm 1000 nm 10000 nm 10000 nm Eduardo Marques Advanced Joining Processes – Welding Processes 21 21  Laser welding Material-laser interaction Eduardo Marques Advanced Joining Processes – Welding Processes 22 22  Laser welding Material-laser interaction The interaction of the laser with the base material varies with the time scale and influences the welding process. Source: Fraunhofer ILT Eduardo Marques Advanced Joining Processes – Welding Processes 23 23  Laser welding Material-laser interaction A typical laser welding process will occur in a few milliseconds, with the formation of the melt pool and (in some cases) a keyhole. Laser beam t=4.92 t=4.46 t=4.97 ms t=2.94 aluminum melt melt poolpool pool melt keyhole boundary surface keyhole copper collapse 0.5 mm Source: Siebold et al Eduardo Marques Advanced Joining Processes – Welding Processes 24 24  Laser welding Process parameters Peak power Pulse repetition Advance rate rate Wave length Shielding gas Laser beam Process parameters parameters Pulse shape Shielding gas flow Pulse width Filler material (?) Spot diameter Eduardo Marques Advanced Joining Processes – Welding Processes 25 25  Laser welding Process parameters Maximum peak power of a pulse laser depends on: Pulse duration and pulse frequency; Pumped energy used to build up the inversion. To increase pulse peak power: Shorten pulse duration Shorten the repetition frequency or repetition rate of the laser Eduardo Marques Advanced Joining Processes – Welding Processes 26 26  Laser welding Process parameters Average power results from the pulse energy and the repetition rate. Average power can be increased by increasing the peak power and increasing the repetition rate. Eduardo Marques Advanced Joining Processes – Welding Processes 27 27  Laser welding Process parameters In a full laser welding process, a variety of process parameters affects the weld joint quality. Laser welding process parameters mainly include laser power, welding speed, shielding gas flow, pulse rate, focal distance and gap. The parameters which affect the weld bead the most are laser power and welding speed. Eduardo Marques Advanced Joining Processes – Welding Processes 28 28  Laser welding Process parameters Source: Kim et al Laser power has major influence on the weld penetration, with an almost linear relationship Eduardo Marques Advanced Joining Processes – Welding Processes 29 29  Laser welding Source: Kristensen et al Defects Solidification cracking Elements such as sulphur and phosphorous can occur in steel. Some aluminium alloys have a wide solidification temperature range which makes them particularly susceptible to cause solidification cracking when welding. Source: Shaik et al. Eduardo Marques Advanced Joining Processes – Welding Processes 30 30  Laser welding Defects Solidification cracking High depth-to-width ratio of laser welds means that high thermal stress acts across the weld where the solidification fronts meet, causing centerline cracking. Full-penetration laser welds are less prone to solidification cracking than partial penetration laser welds since the former do not suffer from the high restraint at the weld root. Source: Farrokhi et al Eduardo Marques Advanced Joining Processes – Welding Processes 31 31  Laser welding Source: Zhou et al Defects Porosity Porosity is a less critical defect in laser welds than solidification cracking. Porosity in laser welds can be caused by plate or surface contamination or inadequate pre-clean. However, in laser welds, porosity can also result from laser keyhole instability and collapse during partial penetration high-power laser welding (picture to the right). Eduardo Marques Advanced Joining Processes – Welding Processes 32 32  Laser welding Defects Porosity If gas shielding is used but not adequate (due to either too high or too low gas flow rate) then porosity can result. Porosity can be a particular problem for laser welds in aluminium, caused by hydrogen evolution in the weld metal, originating from moisture or surface Source: Pastor et al oxides. Eduardo Marques Advanced Joining Processes – Welding Processes 33 33  Laser welding Operation modes The most common laser operation modes are conduction limited welding and keyhole welding. The mode in which the laser beam will interact with the material it is welding will depend on the power density across the beam hitting the workpiece. Eduardo Marques Advanced Joining Processes – Welding Processes 34 34  Laser welding Operation modes Conduction limited welding Conduction limited welding occurs when the power density is typically less than 105 W/cm2. The laser beam is absorbed only at the surface of the material and does not penetrate it. Conduction limited welds often then exhibit a high width-to-depth ratio. Eduardo Marques Advanced Joining Processes – Welding Processes 35 35  Laser welding Operation modes Deep penetration/keyhole welding At higher power densities (> 106-107 W/cm2), a keyhole mechanism occurs, where the material in the path of the beam not only melts but also vaporizes. The focused laser beam then penetrates the workpiece forming a cavity called a 'keyhole', filled with metal vapour (which in some cases can even be ionised, forming a plasma). Eduardo Marques Advanced Joining Processes – Welding Processes 36 36  Laser welding Other operation modes Scanner/smart welding In scanner welding, the beam guidance is done using mobile mirrors. The beam is guided by changing the angles of the mirrors. Eduardo Marques Advanced Joining Processes – Welding Processes 37 37  Laser welding Other operation modes Scanner/smart welding Source: Trumpf Eduardo Marques Advanced Joining Processes – Welding Processes 38 38  Laser welding Other operation modes Hybrid welding Hybrid techniques refer to processes in which laser welding is combined with other welding methods. Compatible processes are MIG (metal inert gas) or MAG (metal active gas) welding as well as TIG (tungsten inert gas) or plasma welding. Eduardo Marques Advanced Joining Processes – Welding Processes 39 39  Laser welding Other operation modes Hybrid welding In shipbuilding, large steel plates that can be up to 30 meters long and 15 millimeters thick are welded together. The gaps between the plates are too large and laser welding is combined with MIG welding. The laser delivers the high-power densities needed for the deep welds and high welding speeds. MIG bridges the gap between the parts using filler wire. Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 40 40  Laser welding Other operation modes Soldering and brazing In soldering, the parts are joined by a filler material, or solder. The melting temperature of the solder is lower than that of the base materials. As a result, only the solder is melted. Source: Japan Unix Eduardo Marques Advanced Joining Processes – Welding Processes 41 41  Laser welding Other operation modes Soldering and brazing The soldered joint is only as strong as the solder material. In brazing, solders made of copper and zinc can produce joints that are as strong as those attained during welding. The surface of the solder seam is smooth and Source: Laserline clean, forming a nicely curved transition to the workpiece. Eduardo Marques Advanced Joining Processes – Welding Processes 42 42  Laser welding Other operation modes Source: Scansonic Soldering Eduardo Marques Advanced Joining Processes – Welding Processes 43 43  Laser welding Welding of polymers In general, thermoplastics can be laser welded to themselves relatively easily. For dissimilar thermoplastics, melting temperatures should ideally have a 50° C overlap range, allowing for compatible melting phases. Large voids and exposure of the fibers If the polymer contains a large proportion of glass fibers, this may result in somewhat brittle joints, as the fibre is isolated and exposed. A glass fiber content of 40% should not be exceeded. Source: Silva et al. Eduardo Marques Advanced Joining Processes – Welding Processes 44 44  Laser welding Welding of polymers Polymers of the same type have the highest level of connection stability after laser welding. Eduardo Marques Advanced Joining Processes – Welding Processes 45 45  Laser welding Welding of polymers A suitable jig is commonly used to position components in a reproducible manner. The joining force is established by pressing the component against a conformal clamping device or a special glass, able to transmit the laser light through. Eduardo Marques Advanced Joining Processes – Welding Processes 46 46  Laser welding Welding of polymers Many weldable thermoplastics only absorb a small proportion of the laser radiation. Additives such carbon black can be added to improve this. Source: Chen et al. Eduardo Marques Advanced Joining Processes – Welding Processes 47 47  Laser welding Welding of polymers Source: Silva et al. Heat effect Thermoplastics do not have a classic heat affected zone. However, exposure to the different temperature gradients can create changes in the mechanical properties. Eduardo Marques Advanced Joining Processes – Welding Processes 48 48  Laser welding Welding of polymers Transmission welding Contour welding Polymer welding processes Simultaneous welding Quasi-simultaneous welding Eduardo Marques Advanced Joining Processes – Welding Processes 49 49  Laser welding Welding of polymers Transmission welding Source: Trumpf In transmission welding method, two types of thermoplastics are joined with one another. The laser passes through the transparent part and the absorbing part is directly heated. Eduardo Marques Advanced Joining Processes – Welding Processes 50 50  Laser welding Welding of polymers Transmission welding Source: LPKF The absorbing plastic melts the adjacent transparent plastic, and the joined parts must be pressed together in order to ensure sufficient heat transfer with minimal gap. In order to ensure a permanent connection, the melted plastic must solidify completely before pressure is removed. Eduardo Marques Advanced Joining Processes – Welding Processes 51 51  Laser welding Welding of polymers Contour welding Source: Trumpf During contour welding, round parts are rotated at up to 25 m/min under a laser beam. The contour to be welded is rotated underneath the laser beam and heated. Eduardo Marques Advanced Joining Processes – Welding Processes 52 52  Laser welding Welding of polymers Contour welding Source: Leisterlaser Large three-dimensional components are also suitable for contour welding. However, residual stresses may occur in very bulky components since all parts of contour are not heated up simultaneously. Eduardo Marques Advanced Joining Processes – Welding Processes 53 53  Laser welding Welding of polymers Simultaneous welding Source: Trumpf The laser beam is formed so that it adapts optimally to the component (beam shaping). In this manner, the contour to be welded is heated simultaneously. Eduardo Marques Advanced Joining Processes – Welding Processes 54 54  Laser welding Welding of polymers Source: Leisterlaser Simultaneous welding Components that have a low level of complexity and are produced in high quantities are particularly suitable for this process, although a very specialized lens setup is fundamental. Eduardo Marques Advanced Joining Processes – Welding Processes 55 55  Laser welding Welding of polymers Quasi-simultaneous welding Source: Trumpf In this case, a single scanning laser beam heats up the welding contour. The laser beam circulates at up to 15 m/s and all the contour is heated almost simultaneously before it has the chance to cool down. Eduardo Marques Advanced Joining Processes – Welding Processes 56 56  Laser welding Welding of polymers Quasi-simultaneous welding Source: Extol Inc. Eduardo Marques Advanced Joining Processes – Welding Processes 57 57  Plasma welding Eduardo Marques Advanced Joining Processes – Welding Processes 58 58  Plasma welding Introduction Plasma arc welding (PAW) is very similar to TIG welding as the arc is formed between a pointed tungsten electrode and the workpiece. However, by positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. Plasma is then forced through a fine-bore copper nozzle which constricts the arc. Eduardo Marques Advanced Joining Processes – Welding Processes 59 59  Plasma welding Introduction Source: Lincoln Electric Eduardo Marques Advanced Joining Processes – Welding Processes 60 60  Plasma welding Advantages High welding speed; High energy welding, suitable to weld hard and thick work pieces; The distance between tool and work piece does not affect the arc formation; Low power consumption for same size weld; More stable arc produced by PAW method; High intense arc or high penetration rate; It can work at low amperage. Eduardo Marques Advanced Joining Processes – Welding Processes 61 61  Plasma welding Disadvantages Higher equipment cost than alternative methods; Noisy operation; Larger radiation emission than classical welding methods; High skilled labor required; Very high maintenance cost. Eduardo Marques Advanced Joining Processes – Welding Processes 62 62  Plasma welding Applications Surgical instruments Stainless steel piping for petrochemical industry Electronical relays Eduardo Marques Advanced Joining Processes – Welding Processes 63 63  Electron beam welding Eduardo Marques Advanced Joining Processes – Welding Processes 64 64  Electron beam welding Introduction Electron beam (EB) welding is a fusion welding process whereby electrons are generated by an electron gun and accelerated to high speeds using magnetic fields. This high-speed stream of electrons is focused using magnetic coils and aimed at the materials to be joined, creating kinetic heat as it impacts. Eduardo Marques Advanced Joining Processes – Welding Processes 65 65  Electron beam welding Introduction Source: TWI Eduardo Marques Advanced Joining Processes – Welding Processes 66 66  Electron beam welding Advantages Very precise technique and is also highly repeatable due to the automation required; Strong and consistent joints that can be used across a number of high-end applications; Offers precise weld penetration control; Provides a small heat affected zone due to the high depth-to-width ratio, which minimises distortion and material shrinkage. Eduardo Marques Advanced Joining Processes – Welding Processes 67 67  Electron beam welding Advantages As the technique is performed in a vacuum environment there are no impurities left by the process; Highly automated and easily controllable process; Also being excellent for joining materials, such as refractory or dissimilar metals, that are not weldable with conventional processes. Eduardo Marques Advanced Joining Processes – Welding Processes 68 68  Electron beam welding Disadvantages Requires a perfect vacuum to be maintained, which means that components changes are very slow; Electron beam welding technology is expensive and requires frequent maintenance to ensure the equipment is functioning correctly; The support required to maintain this technology is demanding. Eduardo Marques Advanced Joining Processes – Welding Processes 69 69  Electron beam welding Applications Gearbox parts Metal strip resistors Piping and turbine blades Eduardo Marques Advanced Joining Processes – Welding Processes 70 70  Thank you [email protected] Eduardo Marques Advanced Joining Processes – Welding Processes 71 71