Laser Joining Research Articles

Femtosecond laser irradiation induced heterojunctions between carbon nanofibers and silver nanowires for a flexible strain sensor

We report the direct joining of carbon nanofibers (CNFs) to silver nanowire (Ag NWs) by controlled irradiation with femtosecond (fs) laser pulses. Two separate types of nano-junction dependent on joint geometry, laser fluence and irradiation time are identified in irradiated mixtures. In one type of junction, the tip of an Ag NW is melted and flows to form a bond with an adjacent CNF. The second type of junction occurs without significant heating of the Ag NW and involves the softening and flow of carbon in the CNF in response to the transfer of plasmonic energy from the Ag NW into the CNF. Bonding in a T-type joint configuration can be of either kind depending on the relative orientation of the incident optical field and the long axis of the Ag NW. FDTD simulations were used to explore this effect for different joint geometries and laser polarization. The electrical properties of a heterojunction involving a single Ag NW-CNF structure have been measured, and it is found that the junction resistance can be reduced by six orders of magnitude after laser joining. Finally, we have investigated the properties of a strain sensor based on an Ag NW-CNF hybrid nanowire network and find that this device can exhibit high sensitivity. This sensitivity occurs as nano-junctions induced by fs laser irradiation greatly reduces the initial resistance. This laser-based technique for direct nanojoining of CNF and Ag NWs may enable the design of robust nanowire structures for application in a variety of new devices.

Laser welding of H-phase strengthened Ni-rich NiTi-20Zr high temperature shape memory alloy

Laser welding of a Ni-rich NiTi-20Zr (at.%) high temperature shape memory alloy was performed. The starting base material was aged for 3 h at 550 °C followed by air cooling prior to welding to induce H-phase precipitation. Advanced microstructure characterization encompassing scanning and transmission electron microscopy, coupled with synchrotron X-ray diffraction, were used. Defect-free welds were obtained with a conduction welding mode. The weld thermal cycle altered the microstructure across the heat affected and fusion zones of the joints. The heat affected zone exhibited partial H-phase dissolution, causing a decrease in hardness. In the fusion zone, the H-phase fully dissolved, and the non-equilibrium rapid solidification conditions prevented the H-phase from re-precipitating during cooling, leading to a microstructure resembling that of an as-cast alloy with the same material composition. Mechanical testing revealed that the laser welded samples sustained stresses in the order of 500 MPa and exhibited stress-strain responses comparable to those of the unwelded base material. Thus, this initial study shows new possibilities for using advanced laser joining methods in these alloys.

Assessment of Laser Joining Quality by Visual Inspection, Computer Simulation, and Deep Learning

Polymer joining results are evaluated and compared in different ways, such as visual inspection, computer simulation, and deep learning analysis, to assess the joining quality. For the experiments, energies in the range of 3 to 5 J/mm were used from preliminary experimental data. A total of 15 welding experiment schedules were performed. Weld defects due to a lack of fusion were detected in some regions of specimens treated with a low-power laser region (3 J/mm), where a lack of fusion, in turn, occurred due to underheating. Bubble-shaped weld defects were observed in some specimens treated with a high-power laser region (5 J/mm); melting occurred due to the overheating of the specimen. Computer simulations were used to trace the boundaries of the fusion zone, and yielded results similar to the visual inspection ones. In the lower-energy region, the energy may not be sufficient to fuse the specimen, whereas the high-energy region may have sufficient energy to break down the polymer chains. A novel deep learning algorithm was used to statistically evaluate the weld quality. Approximately 1700–1900 samples were collected for each condition, and the pre-trained quality evaluation indicated a highly reliable (>98%) welding classification (fail or good). According to the results of this study, welding quality assessments based on visual inspection, computer simulation, and DL-based inspection yield similar results.

Experimental investigation of temperature field, defects, and mechanical strength in dissimilar laser bonding of Ti6Al4V and polyethylene terephthalate

Laser welding is one of the most common technologies with various applications in different industries. In this paper, laser joining of the Ti6Al4V alloy and polyethylene terephthalate (PET) as a means of two common materials is discussed. According to the experimental results, the focal length is a very important parameter in this dissimilar laser welding, and because of the low melting point of PET, it is not possible to create welding at low focal lengths. Furthermore, changing the welding parameters such as welding speed and pulse duration changes the temperature field of the molten pool and its surrounding points, as well as the number, distribution, and the shape deformation of the bubbles formed in PET, which plays an important role in welding quality and mechanical strength. The number of bubbles clearly has a significant influence on the surface contact area and the resultant shear load test values. Generally, reducing the surface contact area between PET and the Ti6Al4V alloy evidently reduces the tensile shear load of the joints. The shear load of the joints has had about 40% variation upon changing the focal length. Additionally, the shear load changed only about 10% by changing the pulse duration from 6 to 10 ms. Seemingly, changing the energy density through a variation of focal length has had a higher influence of about 30% than the incident time of laser beam through increasing the pulse duration. Apart from selecting different laser parameters, the measured temperature in ranges between 100 and 120 °C can produce acceptable joints with lower defects.

Correlation of optical signal during laser fusion welding of copper to aluminum

Laser joining of dissimilar metals, copper and aluminum, allows for the precise delivery of laser energy and high process speed. The keyhole-based process is very efficient for welding Al–Cu, considering the high reflectivity and thermal conductivity of the materials joined. For the Al–Cu system, the formation of detrimental intermetallic compounds is the main issue. Fusion welding with laser as a heat source involves the melting of metals. However, the high speed of the laser welding process is advantageous for terminating the excessive melting of Al and Cu and eventually controlling the detrimental intermetallic phases. Therefore, information pertaining to melted material is an important criterion for achieving joint strength. In this paper, the photodiode signal measured during the laser welding of Cu to Al is investigated as a process monitoring technique. In welding from Cu to Al, the melting of Al (bottom sheet) is very critical for joint strength. The amount of Al material that can be intermixed in Cu depends on the solubility limit of the Al–Cu system. The plasma plume emission during laser welding is used to extract the rapid melting of Al. This study shows the correlation of the Al characteristic peak at a wavelength of 396 nm with the shear strength of the joint.

An overview on laser welding of metal foams: techniques, advantages and challenges

Due to the manifold properties of porous materials in general, and metal foams in particular, they are increasingly used in industrial, structural and functional applications. The properties of metal foams depend on: chemical composition, metallurgical aspects, processing morphology (the type of porosity: open or closed), amount of porosity, cells size and shape. There are challenges and difficulties encountered in welding and bonding metal foams from wider use in the production of complex-shaped components. Some of the problems that associate with welding processes in metal foams are reduction in mechanical properties, intermetallic compound formation, microstructural inhomogeneity and low fatigue strength. More complicated challenges are envisaged during welding metal foams with other dissimilar materials. Laser welding technologies seem to be the most promising joining techniques. This paper presents an overview on laser welding and joining techniques involving metal foams based on laser technology in similar and dissimilar combinations, with and without filler metal. The discussion on laser welding of metal foams is presented keeping the focus on CuZn open-cell foams, lotus type porous iron, foam-filled steel sandwich beams, aluminum foam cores inside a hollow profile and sandwich panels.

Nonlinear model identification of dissimilar laser joining of S.S 304 and ABS using the Hammerstein–Wiener method

The nonlinear system identification Hammerstein–Wiener method is used according to the experimental outputs of laser joining of Acrylonitrile Butadiene Styrene (ABS) and stainless steel 304 concerning the temperature distribution in different parameters of a pulsed laser, including welding speed, focal length, pulse duration, frequency, power and current. Limited linear and nonlinear models exist for such processes; however, due to restrictions and complex numerical calculations, their use in the real-time process control is not practical. An accurate model for the dissimilar laser joining of metals and plastic materials is essential for controller design and process automation. Compared to other popular nonlinear compensation techniques, this model has a simpler structure and needs fewer calculations. This paper considers the identification problems of Hammerstein–Wiener nonlinear systems by employing the gradient search technique. Seven available data sets for training and test phases in dissimilar input parameters were used, and root-mean-square error (RMSE), mean absolute percentage error (MAPE) and fitness value were calculated. The results indicated that the identified Hammerstein-Wiener model had acceptable performance in training and test phases and was in good agreement with experimental results.

Laser-induced Joining of Nanoscale Materials: Processing, Properties, and Applications

• Current progress of laser joining of multidimensional nanomaterials are reviewed. • Laser joining of homogeneous and heterogenous nanomaterials are summarized. • Mechanism of laser nanojoining and practical applications are discussed. • Challenges and directions for future research in laser nanojoining are proposed. The rapid development of flexible and wearable nanodevices for a variety of commercial applications has identified a pressing need for targeted research on nanomaterials for use as building blocks in the fabrication of functional devices via bottom-up assembly. In the search for new fabrication technology, nanojoining or nanowelding has been selected as a promising method in this bottom-up approach. While there are a number of methods that can be used for nanojoining, laser processing is of interest because laser nanojoining combines high-precision property with a flexible manufacturing platform. In this review we discuss how this technology can be implemented in practical applications and outline the advantages and limitations of laser-induced nanojoining. We emphasize how laser nanojoining introduces reliability and reproducibility to the joining process, and show that this is due to precise control over heat-input in nanoscale dimensions. We also review the ways in which laser nanojoining can be integrated with other commercial fabrication operations in practical applications. To illustrate the flexibility of laser nanojoining, we give a detailed summary of joining involving a wide variety of multidimensional heterogeneous nanomaterials in the form of zero-dimension, one-dimension and two-dimension as well as the hybrid combination of these building blocks. We also discuss how laser processing can be used to generate hybrid materials with new functionalities as electrodes for various devices, optical systems and in functional circuits. The mechanisms and strategies in laser-induced joining of nanomaterials are systematically discussed in this paper along with a review of the properties and applications of the joined nanostructures. We also review some challenges in the implementation of this technology and discuss some possible directions for future research into laser-induced nanojoining.

Laser joining of CFRTP to titanium alloy via laser surface texturing

Grid pattern was textured on Ti-6Al-4V alloy (TC4) substrate surface by nanosecond laser system. Laser joining of carbon fiber reinforced thermoplastic composite (CFRTP) to TC4 joints were performed, and the effect of texture grid depth was investigated. The contact angle of molten CFRTP on textured TC4 surface was measured and the tensile-shear force was tested. The fracture surface and interface morphology were observed. The results indicated that the wettability of molten CFRTP on TC4 surface improved remarkably after laser textured TC4. Shear force of CFRTP/TC4 joints was increased by 156% after laser textured TC4 surface. When the depth of grid was deeper than 100 μm, contact angle increased and incomplete filling of molten CFRTP in grid occurred, the shear force thus decreased gradually. Resin-carbon fibers mixture was adhered on the fracture surface of TC4, and the variation tendency of adhesion ratio was consistent with that of shear force. TC4 matrix was exfoliated from substrate and adhered at the fracture surface of CFRTP, indicating stronger mechanical interlocking occurred at the joining interface after laser textured TC4 surface. Beside mechanical interlocking, compound layer consisted of CTi0.42V1.58 carburization phase was also confirmed at interface, suggesting that chemical bonding also occurred at the joining interface.

Combined effects of temperature field and ultrasonic vibration on bubble motion in laser joining of plastic to metal

A previous study has found that applying ultrasonic vibration in laser joining of Polyethylene terephthalate (PET) plastic to Ti metal can greatly reduce bubbles formed in the joint. In this study, the theoretical basis on the combined effects of pressure and temperature fields on the trajectory of bubbles was analyzed using finite element simulation. A non-uniform temperature field influences the evaporation momentum pressure acting on a bubble, causing it to travel from a low to a high temperature region. A properly designed ultrasonic transducer tool, however, can create an unbalanced pressure field around a bubble. Under the combined effects of these elements, bubbles in the molten pool can be made to escape from the joint. The predicted results and obtained experimental outcomes matched well, which were also supported by the evidence of captured high-speed camera images.

Retraction notice to “Microstructural variation at interface during fiber laser joining of NiTi/Ti6Al4V and effect of mechanical strength” [PROTEC 282 (2020) 116661

Retraction notice to “Microstructural variation at interface during fiber laser joining of NiTi/Ti6Al4V and effect of mechanical strength” [PROTEC 282 (2020) 116661

Investigation of laser joining process of CFRTP and aluminum alloy

ABSTRACT An experimental investigation on the joining process of 6061 aluminum alloy and carbon fiber reinforced thermoplastics composite (CFRTP) has been carried out with swing laser. The application of the swing laser is beneficial to obtain a larger bonding area. The effects of scanning speed are investigated on the interface formation and fracture load of the hybrid joint. In addition, the formation mechanism of the interface and the fracture mode of the hybrid joint are further elucidated. The results indicate that maximum failure load is obtained with appropriate process parameters (scanning speed: 20 mm/s, laser power: 2000 W), whereas the interface morphology under this process parameter demonstrates that the structurally sound connection between CFRTP and aluminum alloy is realized by the mechanical interlocking effect. At a higher scanning speed, the gaps in the interface caused by insufficient heat input per unit length result in a lower failure load, while at a lower scanning speed, the bubbles and gaps at the interface are observed as a result of resin decomposition and trapped pyrolysis gases in the interface, ultimately reducing the failure load of the joint. Moreover, the fracture mode of the hybrid joint is a mixed failure.

Effect of scanning speed on laser joining of carbon fiber reinforced PEEK to titanium alloy

Laser lap joining of carbon fiber reinforced plastics (CFRP) to titanium (Ti) alloy using various scanning speed was performed and the influence of scanning speed on joining process was investigated. The high speed camera was adopted to visualize the joining process and defects. The tensile-shear force was tested and the fracture surface was observed by optical microscope. Besides, the numerical simulation of temperature field was conducted to reveal the joining mechanism. The results indicated that fewer defects on titanium alloy surface and less bubbles inside CFRP were obtained with the experimental condition of higher scanning speed. Both mechanical interlocking and chemical bonding occurred at the interface. The compound layer was generated and was confirmed as CTi0.42V1.58 phase because of the carburization of titanium alloy. The thickness of compound layer increased with the decrease of scanning speed. Tensile-shear force first increased and then decreased as the travelling speed increased. When the travelling speed was 0.8 m/min, maximum tensile-shear force of 1024 N was obtained. The bonding width of the resin, and bonding ratio of the mixture of carbon fibers and resin also reached the maximum value at this experimental condition. This behavior was verified by results of temperature field simulation that the melting temperature range of CFRP first increased and then declined as the scanning speed increased. The fluctuation of the tensile-shear force of the CFRP/Ti joint was also explained by the developed simulation model.

CFRTP -Al alloy laser assisted joining with a high speed rotational welding technology

To reduce the defects in laser welding of carbon fiber reinforced polymer (CFRTP) and aluminum (Al) alloy and improve the mechanical properties of the joint, a high speed rotational laser welding (HSRLW) technology was introduced. The mathematical model of CFRTP-Al alloy laser joining was established and the temperature was simulated. The weld depth of aluminum alloy and the penetration depth of CFRTP/aluminum alloy joint were calculated and compared with the experimental result. It was found that the pore defects can be significantly reduced, and a high strength joint could be obtained. The simulation results agree well with the experimental results, and the strength of the CFRTP/aluminum alloy joint can be predicted by using the numerical simulation method.

Laser joining of titanium alloy to polyamide: influence of process parameters on the joint strength and quality

Laser-assisted metal–polymer joining (LAMP) is a novel assembly process for the development of miniaturized joints in hybrid lightweight products. This work adopts a design of experiments (DoE) approach to investigate the influence of several laser welding parameters on the strength and quality of titanium alloy (Ti-6Al-4V)–polyamide (PA6.6) assembly. Significant parameters were highlighted using the Plackett Burmann design, and process window was outlined using the Response Surface Method (RSM). A statistically reliable mathematical model was generated to describe the relation between highlighted welding parameters and joint strength. The analysis of variance (ANOVA) method was implemented to identify significant parametric interactions. Results show the prominence of focal position and laser power, as well as significant interaction between laser power and beam speed, on the joint strength. The evolution of weld defects (bubbles, excessive penetration, flashing, titanium coloring, weld pool cavities, and welding-induced deflection) along the process window was investigated using optical microscopy. The resulted deflection in titanium was quantified, and its relationship with welding parameters was mathematically modeled. Robust process window was outlined to maintain insignificant deflection in the welded joints. Results showed that the growth of weld defects correlates with a decline in joint strength. Optimal parameters demonstrated a defect-free joint, maximizing joint strength.

RETRACTED: Microstructural variation at interface during Fiber laser joining of NiTi/Ti6Al4V and effect of mechanical strength

Abstract Welding of nitinol (NiTi) shape memory alloy (SMA) and titanium-based alloy (Ti6Al4V) finds potential application in aerospace and medical industries. However, joining of these materials poses challenging issues because material properties of each material interacts to give rise to hybrid system performance. In the present study, copper was used as an intermediate layer to restrict the formation of brittle intermetallics during welding of NiTi with Ti6Al4V using laser welding. The formation of Cu4Ti3 and CuNi2Ti complex phases attempts to minimize the formation of brittle phases like Ti2Ni. It was observed that the maximum welding strength of 353 MPa could be achieved at 800 W laser power and 17 mm/s scan speed. Physical analysis of weldments indicates the presence of pores at nano-levels (

Model experiment on reactive phase formation and solidification of B4C-BN composites via nanosecond pulse laser processing

In the present work we describe results of a model experiment on reactive phase formation of B4C-BN composites on a steel substrate using high-energy short laser pulses. The model experiment opens a way for high quality laser joining of boron based ceramics with steels through the reactive phase formation at the steel-ceramic interface. The study was focused on changes in microstructure, chemical and phase compositions in surface layers of the resulting B4C-BN-Fe composites. Ultrafine powders of boron carbide and boron nitride were spread on a steel surface and subjected to laser processing with nanosecond pulses. The reactions occur as a result of elevated temperature under action of laser short pulses. Subsequent rapid solidification leads to highly nonequilibrium solidification and metastable phase formation.

Laser Dissimilar Joining of Al7075T6 with Glass-Fiber-Reinforced Polyamide Composite

Dissimilar joining between metal and composite sheets is usually carried out by mechanical or adhesive joining. Laser dissimilar joining between metal and composite sheets could be an alternative to these methods, as it is a cost-effective and versatile joining technique. Previously, textured metallic and composite parts have been held together and heated with a laser beam while pressure is applied to allow the melted polymer to flow into the cavities of the metal part. The main issue of this process relates to reaching the same joint strength repetitively with appropriate process parameters. In this work, both initial texturing and laser joining parameters are studied for Al 7075-T6 and glass-fiber-reinforced PA6 composite. A groove-based geometry was studied in terms of depth-to-width aspect ratio to find an optimal surface using a nanosecond fiber laser for texturing. Laser joining parameters were also studied with different combinations of surface temperature, heating strategy, pressure, and laser feed rate. The results are relatively good for grooves with aspect ratios from 0.94 to 4.15, with the widths of the grooves being the most critical factor. In terms of joining parameters, surface reference temperature was found to be the most influential parameter. Underheating does not allow correct material flow in textured cavities, while overheating also causes high dispersion in the resulting shear strength. When optimal parameters are applied using correct textures, shear strength values over 26 kN are reached, with a contact area of 35 × 45 mm2.

Combined Fuzzy and Genetic Algorithm for the Optimisation of Hybrid Composite-Polymer Joints Obtained by Two-Step Laser Joining Process.

In the present work, genetic algorithms and fuzzy logic were combined to model and optimise the shear strength of hybrid composite-polymer joints obtained by two step laser joining process. The first step of the process consists of a surface treatment (cleaning) of the carbon fibre-reinforced polymer (CFRP) laminate, by way of a 30 W nanosecond laser. This phase allows removing the first matrix layer from the CFRP and was performed under fixed process parameters condition. In the second step, a diode laser was adopted to join the CFRP to polycarbonate (PC) sheet by laser-assisted direct joining (LADJ). The experimentation was performed adopting an experimental plan developed according to the design of experiment (DOE) methodology, changing the laser power and the laser energy. In order to verify the cleaning effect, untreated laminated were also joined and tested adopting the same process conditions. Analysis of variance (ANOVA) was adopted to detect the statistical influence of the process parameters. Results showed that both the laser treatment and the process parameters strongly influence the joint performances. Then, an uncertain model based on the combination of fuzzy logic and genetic algorithms was developed and adopted to find the best process parameters’ set able to give the maximum joint strength against the lowest uncertainty level. This type of approach is especially useful to provide information about how much the precision of the model and the process varies by changing the process parameters.

Hybrid laser joining of RTM acrylic glass fiber composite with stainless steel

Mechanical strength of metal-polymer hybrid joints (Steel AISI304 – Glass fiber reinforced acrylic composite) by laser joining has been analyzed, considering the effect of different input parameters: geometry of the metal textured surface, processing temperature or laser irradiation times. Likewise, temperature in the metal-composite interface was measured and related with mechanical properties. Fracture analysis has shown the predominance of cohesive failure in the fracture for this joining configuration. Lap shear strength was strongly dependent on surface texturing, temperature and irradiation time. Optimization of the process allowed to obtain fully cohesive failure with shear strength over 20MPa, comparable to structural adhesive joints.