Welding of high thicknesses using a fibre optic laser up to 30 kW

The industrial applications of high-power fibre optic lasers include welding, 2D and 3D cutting, remote cutting and welding, brazing and surface treatments. The availability of fibre optic lasers with power outputs in excess of 10 kW might allow the development of novel fields of application in the welding of high thickness pieces: shipbuilding and offshore industries, pipe and cable manufacture and other heavy industry sectors. Carrying the beam by fibre optics allows high flexibility, even for the production of very large pieces, such as in the shipbuilding sector. This study describes the laser welding of high thickness pieces using a 30 kW laser and a 200 μm diameter fibre. On the one hand, such lasers allow a weld penetration depth of over 30 mm in a single pass, and very high process speeds for thinner materials on the other. Combining lasers with conventional arc welding techniques (hybrid welding) allows further optimization of weld quality and makes it possible to weld butt joints with a ‘gap’ of up to 1 mm. This paper presents the most recent results from very high-power fibre optic laser welding along with new applications in the manufacturing sector.     

Dissimilar Ti/Mg alloy butt welding by fibre laser with Mg filler wire – preliminary study

Abstract

A fibre laser was used to join Ti–6Al–4V alloy to AZ31B Mg alloy with the same thickness of 2 mm, and a filler wire was used to avoid weld underfill resulting from Mg vaporisation. The acceptable joints were only obtained when the laser beam was offset from the edge of the weld seam at 0·2 mm to the AZ31B side of the joint. Cross-weld tensile testing found joint strengths of up to 200·3 MPa, which is 85·1% of the AZ31B tensile strength. All the joints were fractured at the Ti/fusion zone interfacial layer. When the laser offset increased from 0·2 to 0·3 mm or laser power reduced to 1·2 kW, the joining mode of the interfacial layer changed from a semimetallurgical joining with high strength to a mechanical joining with poor strength. Moreover, the fracture surface of acceptable joints was characterised by scraggly remaining weld metal, while that of poor joints was almost only characterised by smooth Ti surface.     

Research on laser weld penetration monitoring with laser induced plasma signals

In this paper, laser induced plasma signals were analyzed during keyhole welding through three methods. According to the results, the relativity between optical and acoustic signals of plasma is shown when welds are in fullpenetration, or partial-penetration and non-penetration.     

Comparative impact assessment for flax fibre versus conventional glass fibre reinforced composites: Are bio-based reinforcement materials the way to go?

In many applications the use of composite materials can offer significant weight reduction opportunities, which can have a positive influence on the life cycle impact of a component or system primarily through energy saving effects in the use phase. The impact associated with the production and end-of-life (EOL) phases, however, forms a possible counter indication for systematic replacement of conventional structures by composite solutions.     

The effect of fibre fractures in the bridging zone of fatigue cracked Ti–6Al–4V/SiC fibre composites

The aim of the paper is to study the partitioning of stress between bridging and broken fibres and the nearby matrix in the region around a fatigue crack in the matrix of a Ti–6Al–4V/SCS–6 SiC fibre composite. This was achieved by using synchrotron X-ray radiation to perform a combination of high spatial resolution tomographic imaging and strain mapping. The average elastic fibre strain for each ply was mapped with distance from the crack, ply by ply. Two samples were examined; one in which there were no broken fibres and one in which some fibres in ply 1 had broken. The contributions of broken and bridging fibres were separated using a double peak fitting routine. The interfacial stress variation and the extent of interfacial debonding were deduced from the fibre strain profiles. Contrary to most micromechanical models the interfacial frictional sliding stress was not found to be constant along the fibre length, but to decrease approximately linearly towards the crack plane. Upon unloading the fibres were found to undergo reverse sliding at the interface.     

Optimisation of the processes of laser,microplasma and hybrid laser–microplasma welding of aluminium alloys

The results of investigation into laser, microplasma and hybrid laser–microplasma methods of welding aluminium alloys are presented. The optimum energy values for welding with the radiation of CO₂ lasers are determined. Shortcomings of microplasma welding are outlined and the main advantages of hybrid laser–microplasma welding are discussed. Detailed study of the macro- and microstructures of the welded joints and the heat affected zone shows that in all cases the structure is sufficiently equiaxed, dense, without visible defects and is dendritic.     

YAG laser welding with surface activating flux

YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coeffwient, thus, the change of fluid flow pattern in weld pool due to the flux.     

Effect of laser characteristics on the weld shape and properties of penetration laser weld of BT20 titanium alloy

The laser beam welding of BT20 titanium alloy was conducted to investigate the weld shape, microstructures and properties. The full penetration weld characteristics produced by CO2 laser and by YAG laser were compared. The results show that the full penetration weld of YAG laser welding closes to “X” shape, and weld of CO2 laser welding is “nail-head” shape.Those result from special heating mode of laser deep penetration welding. The tension strength of CO2 laser and YAG laser joints equal to that of the base metal, but the former has better ductility. All welds consist mainly of the acicular a phase and a few β phase in microstructure. The dendritic crystal of CO2 laser weld is a littlefiner than YAG laser weld. According theresearch CO2 laser is better than YAG laser for welding of BT20 titanium alloy.     

Selective laser sintering mechanism of polymer-coated molybdenum powder

A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine （HLRP-350I）. The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting/solidification when the temperature is above 160 ℃.     

Ignition time of self-propagating high-temperature synthesis by laser

1　ＩＮＴＲＯＤＵＣＴＩＯＮＳＨＳ ,ｔｈｅｓｅｌｆ ｐｒｏｐａｇａｔｉｎｇｈｉｇｈ ｔｅｍｐｅｒａｔｕｒｅｓｙｎ ｔｈｅｓｉｓ,ｗａｓｆｉｒｓｔｄｉｓｃｏｖｅｒｅｄｂｙＭｅｒｚｈａｎｏｖａｎｄＢｏｒｏｖｉｎｓｋａｙａｗｈｅｎｔｈｅｙｓｔｕｄｉｅｄｓｏｌｉｄｆｕ     

Resistance welding of carbon fibre reinforced polyetheretherketone composites using metal mesh and PEI film

Weldability of polyetheretherketone( PEEK) with polyetherimide( PEI) is tested. And carbon fiber reinforced PEEK laminates are resistance welded using stainless steel mesh heating element. The effects of the welding time and welding pressure on the lap shear strength of joints are investigated. Results show that PEEK can heal with PEI well in welding condition and the lap shear strength of PEEK/CF(carbon fibre) joint increases linearly with welding time, but reaches a maximum value when welding pressure ranging from 0.3 MPa to 0.5 MPa with constant welding time. The fracture characteristics of surface are analyzed by SEM techniques, and four types of fracture modes of lap shear joints are suggested.     

Localized CO2 laser bonding process for MEMS packaging

The packaging poses a critical challenge for commercialization of MEMS products. Major problems with the packaging process include degraded reliability caused by the excess stress due to thermal mismatch and altered performance of the MEMS device after packaging caused by thermal exposure. The localized laser bonding technique for ceramic MEMS packaging to address above-mentioned challenges was investigated. A continuous wave CO2 laser was used to locally heat sealing material for ceramic MEMS package lid to substrate bonding. To determine the laser power density and scanning speed, finite element analysis thermal models were constructed to simulate the localized laser bonding process. Further, the effect of external pressure at sealing ring on the bonding formation was studied. Pull testing results show that the scanning speed and external pressure have significant influence on the pull strength at the bonding interface. Cross-sectional microscopy of the bonding interface indicates that the packages bonded with relatively low scanning speed and external pressure conditions have higher bonding quality. This research demonstrates the potential of localized laser bonding process for ceramic MEMS packaging.     

Study on laser welding of the tin-plate can body

Laser beam welding is a new technique for the food can making.Thisresearch studied the welding technology and parameters for the tin-plate can andtheir influences on welding speed and quality,investigated the microstructureand properties of the weld,analysed distribution of tin in the weld metal andcarried out the flanging test of the can body.The results show that laser weld-ing of the can body is characterized by high welding speed,fine appearance,good quality and stable and reliable process.This technology can fulfill the re-quirements of can making.     

Fluxless laser brazing of aluminium alloy to galvanized steel using a tandem beam – dissimilar laser brazing of aluminium alloy and steels

Tandem beam brazing with aluminium filler metal (BA4047) was conducted in order to develop the fluxless laser brazing technique of aluminium alloy (AA6022) to galvanized steels (GA and GI steels). Laser powers of tandem beam and offset distance of preheating beam from the root to the steel base metal were varied. Sound braze beads could be obtained by optimizing the preheating and main beam powers under the offset distances of 0–1 mm. A small amount of zinc remained at the braze interface between galvanized steels and the braze metal. The reaction layer consisting of Fe–Al intermetallic compounds was also formed at the steel interface, and the thickness of reaction layer could be predicted during the laser brazing (thermal cycle) process based on the growth kinetics with the additivity rule. The metal flow analysis of the melted filler metal on joints revealed that wettability and spreadability of the filler metal on the GI steel joint were superior to those on the GA steel joint. The fracture strength of the lap joint attained approx. 55–75% of the base metal strength of aluminium alloy. It was concluded that fluxless laser brazing could be successfully performed by using a tandem beam because the zinc coat layer acted as the brazing flux.     

Preparation of textile preform with sewing machines and bending properties of stitched woven glass fibre fabrics

With the increasing demand of light structure composite in industry, carbon and glass fibres are more and more used, because of their light mass, high strength, high temperature endurance and erosion resistance. This paper focuses on the process of forming a preform. Up to the finished preform, the multilayer reinforced fabrics are subjected to the following procedures., pattern design, cutting and sewing. Considering the fabric properties, the 3dimensional CAD software and sewing machines, which are generally used in the clothing industry, are also suitable for the processing of the reinforced fabrics. This study aims also to the changes of property arising from the sewing process. Bending stiffness and changes of thickness after sewing are studied. These properties will provide input data for CAD pattern design.     

Accuracy analysis of the part made by selected laser sintering

The effects of different factors, including the precision of selected laser sintering (SLS) equipment, sintering temperature, sintered thickness of individual layer and laser scanning route, on the SLS part accuracy have been analyzed and studied. Some measures are suggested in order to improve the part accuracy made by SLS.     

Molten pool and temperature field in CO2 laser welding

Two measuring methods, high-speed camera and optical monitoring system, were used to study processes of laser welding. Molten pool, cooling time and temperature field were analyzed based on real measured images and optical signal data. The results show that the width of molten pool is almost equal to the width of weld, and length is about 7. 8 mm. The solidification time is about 0. 5 s and the temperature gradient is great, so HAZ is very small. The method and results will be of benefit to build the relationship between welding parameters and microstructure.     

Single-crystal laser deposition of superalloys: processing–microstructure maps

In order to extend the life cycle of modern single-crystal (SX) high-pressure high-temperature gas turbine blades, repair of cracked or worn parts is of great interest. The success of the repair technique depends critically on a close process control in order to ensure SX repair. Based on solidification theory a process called epitaxial laser metal forming (E-LMF) has been developed. This paper presents the important concepts necessary for any process control for SX repair based on processing maps which relate the expected solidification microstructures and growth morphologies to the processing conditions. These maps are obtained in two steps. Firstly, the relationships between local solidification conditions and the resulting solidification microstructures, i.e. columnar or equiaxed, are formulated. Secondly, the local solidification conditions as a function of the laser processing parameters are calculated with an analytical heat flux model. By a combination of both approaches, processing–microstructure maps are obtained which define processing windows for SX generation and repair by laser deposition.     

Numerical simulation of temperature field in multilayer heterogeneity lamination laser soldering

A temperature field numerical simulation is carried out using the finite dement method for laser soldering on PECT (piezoelectric ceramics transformer). A three-dimensional model of laser soldering temperature field of multilayer materials is established. Then, the model was simplified in order to perform an efficient finite dement analysis. Moreover, the temperature distribution characteristic in the laser soldering is investigated and verified by experiments. In all cases, the numerical results are in good agreement with the experimental measurements.