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This study aimed to assess and to understand the effect of modulation frequency on weld bead porosity. A fiber laser source with a maximum power of 10 kW was used on SAE 1020 plates. A square wave modulation with pulse power at 4 kW and base power at 0 kW was applied, which resulted in a power average of 2 kW. Welding speed was set at 1 m/min, and frequency varied from 20 to 100 Hz. To analyze the pores, longitudinal cross-sections were prepared. The results indicate that the welds produced at low frequencies (20 Hz and 25 Hz) contained a significant amount of large spherical pores. On the other hand, a reduced number of smaller pores were found for high frequencies (50 Hz and 100 Hz). This can be correlated to the penetration depth oscillation, linked to the weld pool fluid flow and the keyhole collapse, which was greater at lower frequencies. In addition, other effects could be noted, such as the widening of the weld bead for low-frequency values, which can be beneficial when the process requires low geometrical tolerances and higher penetration depths for increased degrees of overlap at higher frequencies.

The premature wear and/or failure of components and equipment used for ore comminution can result in unscheduled downtime and, therefore, significant losses for the mining industry, in which it is estimated that about half of the total maintenance cost in mining is due to the manufacture of damaged parts and the other half due to downtime and labor. In this sense, approaches to improve the wear resistance of this kind of equipment are of great interest. Therefore, the present work aims to evaluate the potential of coating a high manganese Hadfield steel used to manufacture grinding hammers with Metco 1030A alloy (Fe–C–Mo–V–B) via laser cladding (DED-L). The coatings were deposited on Hadfield steel substrates (cast) using different levels of laser power and scanning speed. The coatings were characterized in relation to the presence of surface and internal defects, morphology, microstructure, chemical composition, and microhardness. The wear resistance of the coatings was evaluated by pin-on-drum tests. For all deposition conditions, continuous tracks were formed. Despite the superficial cracks, the layers did not detach, confirming the metallurgical bond with the substrate. The microstructure of the coatings is typically composed of vanadium carbides (VCs) and molybdenum borides (Mo2B) in a martensitic matrix. For the same scanning speed, carbides and borides tend to become larger and more widely spaced with increasing laser power. Compared with the Hadfield steel substrate, the coatings have significantly higher hardness and wear resistance. Despite the cracks, normally acceptable in the intended application, it can be said that the application of the Metco 1030 alloy via laser cladding has the potential to increase the service life of Hadfield grinding hammers.

Welding processes are present in most industry sectors. Conventional arc welding processes, such as the gas metal arc welding (GMAW) process, have limitations when applied to join thick materials. In this scenario, the laser beam welding (LBW) process has proved to be an alternative to achieve high penetration depths, eliminating the need for joint beveling, although not without limitations. Proneness to surface and internal discontinuities are some of them. Recently, hybrid laser-arc welding (HLAW) process has come up as a promising joining process, combining the advantages of the GMAW and LBW processes on a single melting pool, counteracting defects, and enhancing process efficiency. Despite the high complexity of the hybrid process, its advantages derive not only from geometrical and mechanical issues but also from metallurgical features or characteristics. Twelve LBW and HLAW welding tests were performed using 5, 6, 7, 8, 9, and 10 kW of laser power. The HLAW results show higher robustness against weld defects, as well as greater penetration depths and bead widths then pure LBW. The microstructures in all regions of the welds were analyzed, showing their correlation between the welding parameters and processes performed. Due to a distinct thermal cycle resulting from the two simultaneous heat sources, the weld bead produced by the HLAW process presented reduction of 100 HV in the microhardness on the upper region and consequently reduction of its brittleness. The results obtained clearly indicate the metallurgical and operational advantages of the HLAW process compared with the individual LBW process.

Laser cladding is a complex manufacturing process. As the laser beam melts the feedstock powder, small changes in laser power or traverse speed reflect on deviations of the deposition’s geometry. Thus, fine-tuning these process parameters is crucial to achieve desirable results. In order to monitor and further understand the laser cladding process, an automated method for clad bead final geometry estimation is proposed. To do so, six different convolutional neural network architectures were developed to analyze the process’ molten pool image acquired by a 50-fps coaxial camera. Those networks receive both the camera image and the process parameters as inputs, yielding width and height of the clad beads as outputs. The results of the network’s performances show testing error mean values as little as 8 μm for clad beads around a millimeter in height. For the width dimension, in 95% of the cases, the error remained under 15% of the bead’s width. Plots of the target versus the estimated values show coefficients of determination over 0.95 on the testing set. The architectures are then compared, and their performances are discussed. Deeper convolutional layers far exceeded the performance of shallower ones; nonetheless, deeper densely connected layers decreased the performances of the networks when compared with shallower ones. Those results represent yet another alternative on intelligent process monitoring with potential for real-time usage, taking the researches one step further into developing a closed-loop control for this process.

Temperature measurement in welding constitutes relevant information for process understanding and simulation, as it can be used to validate and predict microstructure. Monitoring can be performed at specific points through transducers. The typical one is the thermocouple. In laser welding processes, due to the high energy concentration of the beam, the acquisition with thermocouples should be performed closer to the bead when compared to electric arc welding processes. This measurement is critical because of overheating by spatters, which can result in damage. The present work covers developing a Capacitive Discharge Welding device for thermocouple fixing and assessing possible temperature acquisition positions in keyhole laser welding. The study performed all tests with a fiber laser of 9 kW power and 3 m/min scanning speed. When placed at 2 mm from the weld centerline, the results showed a high probability of spattering due to the 71° range of incidence angle. Therefore, the thermocouple should be placed far from the weld centerline to minimize the spattering. However, it must be close enough to acquire temperatures above 727 °C. This temperature corresponds to the envisaged austenitization microstructure correlation. The study found the maximum distance at 3.5 mm based on an interpolation map, where the incidence spatters angle reduced to 59°. At a 2 mm distance from the weld centerline, the weld cross section temperatures reached more than 727 °C. However, the microstructural changes did not occur due to insufficient austenitization time. The Heat Affected Zone boundary was at 1.64 mm from the weld centerline. Therefore, to correlate microstructure with thermal cycles, it is necessary to place thermocouples at a distance below this value. However, spatter can be a problem since the range of incidence angle is about 75°. Therefore, this work recommends using more than one thermocouple for each position (redundancy) to increase valuable data.

Penetration depth is a relevant output for laser welding, since its increment enables the joining of thick plates in one pass, thus contributing to productivity. A usual way of achieving higher penetration is utilizing heat input, increasing power, decreasing welding speed, or decreasing laser diameter. However, this approach may result in defects. Power modulation can be an alternative to reach this objective without discontinuities, but it is usually applied in a square format. It is still unclear how different power wave shapes can influence penetration. The present paper aims to assess the effect of different power modulation formats (square, triangle, and trapezium) on penetration while maintaining the same energy input (power to welding speed ratio). A YLS 10,000 fiber laser source from IPG Photonics with a nominal maximum power of 10 kW was used on SAE 1020 plates. Results show that it is possible to achieve a 77% improvement in penetration after power modulation for a 120 kJ/m energy and square wave, which is greater than found in the literature. For 240 kJ/m energy and different power wave formats, penetration level can be enhanced through time balancing on higher powers. Beads presented depth values between 18 and 67% deeper when compared to continuous emission conditions. Square and trapezium waves are recommended when penetration is envisaged.

Despite the industrial relevance of LASER welding, determination of sustainable parameterization is still a challenge. Trial and error, or even not totally justified methodologies, are frequently applied on LASER welding parametrization. This approach potentially leads to a decrease of the process tolerance and, consequently, increasing the likelihood of imperfections, which means extra operational time and raising of the final cost. The present paper addresses a comparative discussion about five factors experimentally determined and frequently used to predict depth of penetration in LASER welding. The experiments were performed with a 10-kW fiber LASER. In a first batch, power was varied while welding speed was fixed at 1 m/min. In a second batch, welding speed was varied and power was kept at 10 kW. The first demonstrated concern on using these popular factors is the definition and quantification of LASER energy. For evidencing this aspect, two samples were processed with the same welding energy of 120 kJ/m, yet resulting in completely different penetrations. Eventually, an empirical model based on power as a factor allowed a more reliable prediction of the depth of penetration.

The laser remelting technique is considered a promising and effective method for improving the surface of thermally sprayed coatings, eliminating microstructural defects such as pores and cracks, increasing the life of parts and equipment by increasing microhardness and increasing anchoring force between coating and substrate. In the present work, tungsten carbide alloy (WC–12Co–4Cr) coatings were deposited on properly prepared SAE 1016 substrates using the high velocity oxy-fuel technique. An ytterbium fiber laser was used to remelt the surface of the coating by accurately varying the scanning speed and laser beam power to achieve a pore and crack-free coating and better metallurgical anchorage to the substrate through the optimization of the studied parameters. The samples were characterized by scanning electron microscopy and microhardness. The results show that it is possible to obtain higher hardness coatings after the laser remelting process, free of pores or pronounced imperfections and metallurgically bonded to the substrate. We also found a processing range for the ytterbium laser remelting of the WC–12Co–4Cr coating aiming at high productivity and microstructural optimization of the coating for different thicknesses.

A microscopic model is employed to calculate the spectrum of dipole-exchange spin waves in multilayers in which thin ferromagnetic films are separated by non-magnetic spacers. Two configurations are considered: in one the films have magnetizations parallel to each other, in the other the magnetizations are antiparallel. The calculations extend a previous microscopic formalism that allows the calculation of the dipole-exchange spin wave spectrum in thin films. The results show the splitting of the frequency bands and the mode mixing caused by the dipolar interaction between the films as a function of spacer thickness.

A method is presented for calculating the frequencies of non-retarded surface plasmons propagating on a semi-infinite medium with a surface profile described by a one-dimension quasiperiodic function. The profiles are generated, in analogy with previous work on quasiperiodic superlattices, by repeating unitary cells constructed according to an inflation rule. Dispersion relations are obtained for a semi-infinite free-electron metal as the active medium, with surface profiles obeying the Fibonacci and Thue-Morse sequences.