1,721,146 research outputs found
Laser metal deposition employing scanning optics
No full textLaser metal deposition (LMD) as an additive manufacturing (AM) processes is characterized by high deposition rate, high material usage and possibility of building on existing components. The combination of directed powder with scanning optics can open up different possibilities combining high deposition rates and improved detail on demand. The main aim of this work is to present a preliminary study on the application of laser metal deposition with scanning optics and 1 kW multi-mode fibre laser. First, the hardware developed for the LMD process with scanning optics, in particular the custom nozzle for powder delivery is presented. Then, a simplified thermal model is discussed for a better comprehension of the effect of the scanning parameters on the thermal cycle. LMD experiments are carried out implementing the outcomes of the analytical model, varying laser power and feeding speed. The results depict the feasibility of concept for high area deposition with further flexibility in track width control
Effect of pulsed and continuous wave emission on the densification behaviour in Selective Laser Melting
No full textThe majority of commercially available Selective Laser
Melting (SLM) systems operates with high brilliance fiber laser
sources. These sources are most commonly operated in continuous
wave (CW). On the other hand, a few employ pulsed wave (PW)
emission by fast power switching, resulting in pulses with s level
durations, kHz level repetition rates and low peak powers. No clear
consensus is present in the academic and industrial communities over
the choice of the emission regime. Clearly, the laser temporal
emission mode can have an impact over key quality aspects, namely
part density, geometrical errors, and roughness. The purpose of this
paper is to investigate the effect of laser emission regime on the
densification of AISI 316L stainless steel in the SLM process. In
particular, single track formation was investigated by varying
temporal overlapping of laser pulses from pulsed wave until
continuous wave. A single mode fiber laser installed on a prototype
SLM system constituted the experimental setup. The open hardware
allowed for varying with high flexibility the laser emission. The CW
and PW emission strategies were compared at fixed fluence levels per
single track melting. The effect of duty cycle was evaluated starting
from CW (i.e. 100% duty) moving towards PW. Furthermore, the
densification behaviour was analysed at single and multiple layers,
depicting the molten track stability in terms of volume. Results show
that at fixed fluence, analogous operating conditions can be
determined in the CW and PW processing of single tracks. The
amount of deposited material is significantly higher when single
tracks are produced with CW emission, although a lower variability
may be identified when exploiting power modulation. Therefore,
industrial systems could be more flexible enabling both CW and PW
regime to exploit their peculiar advantages, where required
In-line monitoring of focus shift by kerf width detection with coaxial thermal imaging during laser cutting
Full text linkNowadays, industrial laser cutting systems employ a fixed set of process parameters throughout the cut of the same workpiece, which results in a good compromise between maximum productivity and surface quality. The process parameters are commonly set by trial-and-error experiments carried out on different materials and thicknesses or less frequently by physical modelling. However, the final cut quality is not constant even though the process parameters are kept fixed due to degradation of the initial status of the laser cutting system. One of the common issues in the laser cutting process is the local heating of the optical components due to contamination and/or high powers commonly employed, which cause shifting of the focus position. This can worsen the cutting-edge quality, and even result with loss of cut. Therefore, the online measurement of the position of focus is a requirement for a consistent process. An empirical method used in the industrial practice for initially setting and successively examining and adjusting the focus position is to measure the kerf width of a straight-line cut performed with constant process parameters. This paper proposes an algorithm to monitor the kerf width and yield the estimated focus position in real-time during the cutting process. The kerf width is observed during the process with a coaxial camera module mounted on the laser head which monitors the thermal interaction between the laser beam and the material. An image processing algorithm was developed for extracting the kerf width from the acquired images, and the algorithm parameters were experimentally calibrated such that the extracted value of the kerf width matches with its physical measure. To understand the influence of the focus position on the cutting kerf, an experimental campaign was conducted and subsequently a regression model was fitted. The real-time monitoring and computation of the kerf width and its correlation to the focus position give the opportunity for a closed-loop control of the focus shift, that would eventually lead to a gain of process stability and repeatability
Coaxial and synchronous monitoring of molten pool height, area, and temperature in laser metal deposition
Full text linkLaser Metal Deposition is an additive manufacturing technology that enables to realize of one-of-a-kind large components with a free-form geometry. However, the advantages of laser metal deposition from the economic and sustainability points of view can be attenuated by the presence of defects in the realized components. The process should be real-time monitored to immediately identify the onset of defects or process drifts that may undermine the outcome of the build, also enabling the possibility to immediately act against them with feedback control. Many of the proposed solutions in monitoring the Laser Metal Deposition process exploit the use of only one sensor or more but decoupled ones, which does not provide a comprehensive overview of the process. In this work, a coaxial multi-sensor monitoring system is proposed and exploited to capture the variation of three different process signatures. A custom laser triangulator, a near-infrared camera and a ratio pyrometer for simultaneous monitoring of the molten pool height, molten pool area, and molten pool temperature, respectively, are coaxially integrated. Thanks to the possibility to extract concurrent (in spatial and time domains) signals directly from the workpiece area and in real-time, a comprehensive status of the deposition can be deduced. The influence of the process parameters on the sensed outputs is investigated, and the relationships between the process signatures can be researched. While the molten pool area and its temperature are mostly affected by the laser power, the scan speed is more impactful on the molten pool height. A good linear correlation between the molten pool temperature and the area is assessed, while no correlation with the molten pool height is found, making it almost independently manipulatable
Modelling of the Transient Thermal Field in Laser Surface Treatment Test
No full textprinted on line (2008), will be published soon (2009
Effect of in-source beam shaping and laser beam oscillation on the electromechanical properties of Ni-plated steel joints for e-vehicle battery manufacturing
Full text linkLaser welding is a key enabling technology that transitions toward electric mobility, producing joints with elevated electrical and mechanical properties. In the production of battery packs, cells to busbar connections are challenging due to strict tolerances and zero-fault policy. Hence, it is of great interest to investigate how beam shaping techniques may be exploited to enhance the electromechanical properties as well as to improve material processability. Industrial laser systems often provide the possibility to oscillate dynamically the beam or redistribute the power in multicore fibers. Although contemporary equipment enables elevated flexibility in terms of power redistribution, further studies are required to indicate the most adequate solution for the production of high performance batteries. Within the present investigation, both in-source beam shaping and beam oscillation techniques have been exploited to perform 0.2-0.2 mm Ni-plated steel welds in lap joint configuration, representative of typical cell to busbar connections. An experimental campaign allowed us to define process feasibility conditions where partial penetration welds could be achieved by means of in-source beam shaping. Hence, beam oscillation was explored to perform the connections. In the subset of feasible conditions, the mechanical strength was determined via tensile tests alongside electrical resistance measurements. Linear welds with a Gaussian beam profile enabled joints with the highest productivity at constant electromechanical properties. Spatter formation due to keyhole instabilities could be avoided by redistributing the emission power via multicore fibers, while dynamic oscillation did not provide significant benefits
Sensor Selection and Defect Classification via Machine Learning During the Laser Welding of Busbar Connections for High-Performance Battery Pack Production
Full text linkThe transition towards electric mobility requires the development of manufacturing systems capable of realising products with elevated electrical and mechanical performance and in-line qualification. Laser welding of thin sheets is an enabling technology for the production of battery packs. Given the numerosity of the joints and the stringent requirements, in-situ monitoring of the process and advanced data analysis with Machine Learning (ML) algorithms are fundamental tools which need to be explored. The current study presents a methodological approach for the process development and integration of a monitoring architecture for the realisation of dissimilar material busbar connections (0.2 mm Ni-plated steel over 0.6 mm Cu in lap joint configuration) for the production of a high-performance battery pack for an electric racing motorbike. A single mode fiber laser welding system was equipped with different sensors to retrieve data during the laser-material interaction. The monitoring system was composed of three photodiodes positioned off-axis respectively observing the visible, thermal near-infrared and laser back-reflection region. A spectroscope also sampled process emission from an off-axis perspective whilst another photodiode was positioned within the laser source to observe the process coaxially. Following a preliminary phase required to characterise the process and data provided by the sensors, experiments were designed to identify defects and variations with respect to the reference condition. On a single sensor basis, supervised classification machine learning algorithms were trained to discern joints performed on an out of focus workpiece or in the presence of gap between the sheets. Results indicate that photodiodes observing the laser back-reflected light are capable of providing process relevant information which can be exploited to identify drifts from the reference processing condition. ML algorithms exhibited high accuracy classification even with a reduced amount of data
External Illumination Enables Coaxial Sensing of Surface and Subsurface Molten Pool Geometry in LPBF
Full text linkLaser powder bed fusion (LPBF) attracts the attention of high-end manufacturing sectors for its capability of depositing free-form components with elevated mechanical properties. However, due to the intrinsic nature of the feedstock material and the interaction with the laser beam, the process is prone to defect formation and manufacturing inaccuracies. Therefore, the development of a monitoring architecture capable of measuring the geometrical features of the process tool (i.e., the melt pool generated by the laser-material interaction) is of paramount importance. This information may then be exploited to evaluate process stability. In this work, a high-speed camera was implemented coaxially in the optical chain of an LPBF system to extrapolate the geometrical features of the molten pool surface and its oscillatory behaviour, with elevated spatial and temporal resolution. A secondary light source was tested in both coaxial and off-axis configuration to dominate process emission and assess optimal illumination conditions for extracting the molten pool’s geometrical features. Preliminary results showed that the off-axis configuration of the illumination light enabled direct measurement of the molten pool surface geometry. A newly developed image processing algorithm based on illuminated images obtained via the coaxial observation frame was employed to provide automated identification of the melt pool geometry. Moreover, bright reflections of the external illumination over the melt surface could be clearly observed and used to characterise the oscillatory motion of the molten material. This information may therefore be taken as an indirect indicator of the molten pool penetration depth, hence providing information regarding the subsurface geometry. A successive experimental investigation showed the capability of the monitoring architecture to resolve the molten pool’s length, width and area with elevated acquisition frequency. Molten pool surface oscillations in the kHz range could be correlated to the penetration depth while the molten pool width measured via the high-speed imaging setup corresponded to the track width of the depositions. Hence, the methodological approach for the concurrent measurement of the molten pool’s geometry in three spatial dimensions was demonstrated and may be used to track the stability of LPBF depositions
Exploring wire laser metal deposition of 316L stainless steel as a viable solution for combined manufacturing routes
No full textThe combined manufacturing approach has the potential to facilitate large-scale manufacturing processes, enable on-site manufacturing, and limit welding and joining processes currently used to create complex and flexible components. Laser Metal Wire Deposition (W-LMD) has emerged as a highly promising technology in the field of additive manufacturing (AM). The use of wire feedstock as a cost-effective and safe alternative to powder ensures optimal productivity and meets the demands of the industry. W-LMD would be employed in combined manufacturing for the repair of existing components or the incorporation of intricate features into existing components, thereby facilitating the integration of additive manufacturing across a range of sectors. Nevertheless, an investigation is necessary to determine whether the inherent AM process-related defect or inhomogeneity affects the performance of the hybrid components in question. This study examines the microstructural and mechanical performance of hybrid W-LMD components in continuous, interrupted, and combined manufacturing scenarios. The results demonstrated that the process development strategy is of vital in the production of fully consolidated components (density > 99.9%) for a stable process, irrespective of the deposition scenarios. The tensile properties varied with the process conditions, emphasizing the importance of considering deposition conditions for heat-sensitive alloys in combined manufacturing. The findings aim to provide valuable insights applicable to the production of real industrial components using W-LMD
Understanding the effects of temporal waveform modulation of the laser emission power in laser powder bed fusion: Part I - Analytical modelling
Full text linkThe architecture of contemporary fiber laser sources enables users a wide choice in terms of spatial and temporal profiles during the laser powder bed fusion (LPBF) process. Given the range of possibilities, the need for analytical modelling approaches to predict the consequences of waveform modulation in terms of both thermal and fluid-dynamic aspects over the powder bed, process dynamics and resulting part quality is of great interest. Within the present investigation a moving point source analytical model was developed to study the effect of temporally modulated laser beams over the temperature distribution and recoil pressure induced over the molten region during single track LPBF depositions. This study configures as the first part of an investigation on the topic presented with the aim of developing the modeling framework to predict the effects of temporal waveform modulation in the LPBF process. The model developed was implemented numerically to simulate the single track LPBF deposition of stainless steel AISI316L with different waveform shapes ranging from the conventional Square Wave emission to Ramp Up, Ramp Down and Triangle waveforms. Modulation at different amplitude levels and different waveform frequencies were also investigated. Results show that temperature variations followed the temporal profile of the power exposed over the material. Consequently, recoil pressure oscillations over the melt region exhibited a periodic profiles correlated to the waveform modulation of the laser power indicating that melt flow may be controlled by means of such techniques. Peak values of recoil pressure, which might be symptomatic of melt pool instabilities, could be reduced employing higher levels of modulation frequency or lower oscillation amplitudes between non-zero values of the emission power
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