Laser-based Material Processing Research Articles

Laser-Based Selective Material Processing for Next-Generation Additive Manufacturing.

The connection between laser-based material processing and additive manufacturing is quite deeply rooted. In fact, the spark that started the field of additive manufacturing is the idea that two intersecting laser beams can selectively solidify a vat of resin. Ever since, laser has been accompanying the field of additive manufacturing, with its repertoire expanded from processing only photopolymer resin to virtually any material, allowing liberating customizability. As a result, additive manufacturing is expected to take an even more prominent role in the global supply chain in years to come. Herein, an overview of laser-based selective material processing is presented from various aspects: the physics of laser-material interactions, the materials currently used in additive manufacturing processes, the system configurations that enable laser-based additive manufacturing, and various functional applications of next-generation additive manufacturing. Additionally, current challenges and prospects of laser-based additive manufacturing are discussed.

Structuring Surfaces at the Speed of Light

AbstractAn emerging laser-based surface structuring technology (DLIP) uses the interference of light to transfer to materials well-defined periodic features for the large-scale production of novel bio-inspired multifunctional surfaces. In this text, we describe briefly some fundamental aspects of laser-based materials processing, describe the different capabilities of DLIP for producing functional surfaces and give some examples of multifunctional surfaces thus produced. Finally, the main strategies that are being developed to boost the throughput of interference-based patterning technologies are presented.

Ionization dynamics of sub-micrometer-sized clusters in intense ultrafast laser pulses

Sub-micrometer-sized targets are found in intense laser–cluster interaction experiments and laser-based material processing. Here, we investigate the internal field localization due to Mie scattering and its effect on ionization dynamics in sub-micrometer-sized clusters using Mie calculation and particle-in-cell simulations. As a result of intertwined processes of pulse propagation and ionization, sub-micrometer nanofocusing dominates at lower intensity and gives rise to an ionization hotspot at the rear of the targets while plasma shielding wins over at a higher intensity, stopping further rear side ionization. As ionization is often the precursor of other processes, understanding the ionization dynamics of ultrafast laser pulses with wavelength-sized nanostructure can be relevant for intense laser-cluster experiments and femtosecond laser micro-/nanomachining.

High-power, electronically controlled source of user-defined vortex and vector light beams based on a few-mode fiber amplifier

Optical angular momentum (OAM)-based structured light beams provide an additional degree of freedom for practical applications ranging from optical communication to laser-based material processing. Many techniques exist for generating such beams within laser sources and these primarily rely upon the use of specially designed optical components that limit laser power scaling and ready tunability of the topological charge and polarization of the output OAM beams. Here we show that some of these limitations can be overcome by employing a computer controlled reflective phase-only spatial light modulator to adaptively tailor the input (and subsequent output) beam wavefront and polarization in a few-mode fiber amplifier. In this way modal-coupling-induced beam distortion within the fiber amplifier can be mitigated and we are able to generate at will any desired supported spatial mode guided in the fiber, including conventional linearly polarized (LP) modes, scalar OAM modes, and cylindrical vector modes, at average powers > 10 W and with a peak power of > 11 kW . Our results pave the way to the realization of practical high-power structured laser sources with tunable chirality and polarization.

Predictive modeling approaches in laser-based material processing

Predictive modeling represents an emerging field that combines existing and novel methodologies aimed to rapidly understand physical mechanisms and concurrently develop new materials, processes, and structures. In the current study, previously unexplored predictive modeling in a key-enabled technology, the laser-based manufacturing, aims to automate and forecast the effect of laser processing on material structures. The focus is centered on the performance of representative statistical and machine learning algorithms in predicting the outcome of laser processing on a range of materials. Results on experimental data showed that predictive models were able to satisfactorily learn the mapping between the laser’s input variables and the observed material structure. These results are further integrated with simulation data aiming to elucidate the multiscale physical processes upon laser–material interaction. As a consequence, we augmented the adjusted simulated data to the experiment and substantially improved the predictive performance due to the availability of an increased number of sampling points. In parallel, an information-theoretic metric, which identifies and quantifies the regions with high predictive uncertainty, is presented, revealing that high uncertainty occurs around the transition boundaries. Our results can set the basis for a systematic methodology toward reducing material design, testing, and production cost via the replacement of expensive trial-and-error based manufacturing procedures with a precise pre-fabrication predictive tool.

Overview of Laser Applications in Manufacturing and Materials Processing in Recent Years

Abstract This article is to capture some of the important developments in the rapidly growing areas of laser-based manufacturing and materials processing and also to describe important technological issues pertaining to various laser-based manufacturing processes. The topics to be covered in this paper include more popularly used processes in industry such as laser additive manufacturing, laser-assisted machining, laser micromachining, laser forming, laser surface texturing, laser welding, and laser shock peening, although there are several additional areas of laser applications. In each section, a brief overview of the process is provided, followed by critical issues in implementing the process, such as properties, predictive modeling, and process monitoring, and finally some remarks on future issues that can guide researchers and practitioners.

Influence of global and local process gas shielding on surface topography in laser micro polishing (LμP) of stainless steel 410

Laser micro polishing (LμP) is a new laser-based material processing method that has a high potential to overcome common disadvantages of traditional polishing techniques. A special challenge in LμP is the processing of large areas since processing in a process gas atmosphere is deemed necessary to avoid undesired oxidation and minimize surface roughness. Therefore, a new process strategy for LμP on stainless steel AISI 410 was investigated in which a gas nozzle was used to create a local process gas shielding and therefore to significantly increase the field of maximal processing. Using a Nd:YAG high power Q-switch laser, we demonstrated that local process gas shielding is feasible for LμP in terms of avoidance of surface defects and achieved micro-roughness. In addition, a wide process window in terms of nozzle distances and gas flow exists for LμP. The resulting surfaces are highly reproducible in terms of surface roughness. Besides Argon, Nitrogen is another process gas that is highly suitable for LμP of AISI 410. The use of Nitrogen might therefore significantly lower future production costs in LμP. Finally, spatially resolved LμP was explicitly demonstrated on a textured press plate.

Reconfigurable structured light generation in a multicore fibre amplifier

Structured light, with spatially varying phase or polarization distributions, has given rise to many novel applications in fields ranging from optical communication to laser-based material processing. However the efficient and flexible generation of such beams from a compact laser source at practical output powers still remains a great challenge. Here we describe an approach capable of addressing this need based on the coherent combination of multiple tailored Gaussian beams emitted from a multicore fibre (MCF) amplifier. We report a proof-of-concept structured light generation experiment, using a cladding-pumped 7-core MCF amplifier as an integrated parallel amplifier array and a spatial light modulator (SLM) to actively control the amplitude, polarization and phase of the signal light input to each fibre core. We report the successful generation of various structured light beams including high-order linearly polarized spatial fibre modes, cylindrical vector (CV) beams and helical phase front optical vortex (OV) beams.

Temperature Measurement of Laser-Irradiated Metals Using Hyperspectral Imaging

Accurate noncontact surface-temperature measurements during laser-based materials processing remain challenging due to the difficulty of establishing reliable emissivity values as a function of temperature and wavelength. Direct measurement of emissivity is difficult, as the emissivity may be changing constantly in the laser-material interaction region, where the temperature gradients are extreme and surface displacement can complicate the measurement. Here, we present a hyperspectral imaging method using a multiwavelength camera to capture the spectral radiance in eight different bands and fit the wavelength-dependent radiance to Planck's law. Time-resolved temperature measurements during microsecond pulsed-laser irradiation of a metal plate made of the titanium alloy $\mathrm{Ti}$-6$\mathrm{Al}$-4$\mathrm{V}$ provide temperature information about the irradiated surface with an estimated accuracy of $\ifmmode\pm\else\textpm\fi{}10\mathrm{%}$. The extracted wavelength-dependent emissivity slope compares well with reported results for macroscale titanium melts obtained using IR spectroscopy, which measure temperature without any built-in assumptions about the emissivity. The results are directly applicable to temperature monitoring during welding, additive manufacturing, and semiconductor growth.

Progress in Photonic-Crystal Surface-Emitting Lasers

Photonic-crystal surface-emitting lasers (PCSELs) have attracted considerable attention as a novel semiconductor laser that surpasses traditional semiconductor lasers. In this review article, we review the current progress of PCSELs, including the demonstration of large-area coherent oscillation, the control of beam patterns, the demonstration of beam steering, and the realization of watt-class and high-beam-quality operation. Furthermore, we show very recent progress in the exploration of high brightness of more than 300 MW cm−2 sr−1, obtained with a high output power of about 10 W while maintaining a high beam quality M2 ~ 2. The PCSELs with such high performances are expected to be applied to a variety of fields, such as laser-based material processing, optical sensing (light-detection and ranging (LiDAR)), and lighting, as they retain the benefits of compact and high-efficiency semiconductor lasers.

Radiation-Pressure-Enabled Traceable Laser Sources at CW Powers up to 50 kW

Radiation pressure has recently been shown to have practical application for multikilowatt continuous wave (CW) laser power measurement. One key advantage lies in its ability to measure without absorbing the laser beam. This enables a new measurement paradigm where laser power can be measured traceable to the SI without perturbing the beam. Combining this measurement scheme with a laser constitutes a “traceable source” where laser output power is traceable to the SI in real time. This greatly simplifies the calibration process for multikilowatt laser power meters and yields a path to high-accuracy laser-based material processing. Here, we discuss the state of the art of this approach by describing recent results from calibrations of laser power meters performed using a radiation-pressure-enabled traceable source at CW powers from 1 to 50 kW. We describe measurement results and uncertainty contributions with expanded uncertainties at or below 1.7% for powers above 10 kW. We also briefly discuss the status of development of a radiation-pressure-based technology designed to provide source traceability in the laser manufacturing environment.

Determining thermal conductivity, specific heat capacity and absorptivity during laser based materials processing

In this work, an inverse method is proposed to estimate the thermal conductivity, absorptivity and specific heat capacity for a laser irradiated sheet by measuring the data for transient-temperature distribution at two locations. The corresponding data is also obtained using a finite element method based direct model that takes the average thermal properties of the material as input. The inverse estimation of thermal conductivity, absorptivity and specific heat capacity is carried out by minimizing the difference between actual and direct model predicted data. For this purpose, a novel heuristic algorithm is developed. The efficacy and accuracy of the method is ascertained by carrying out simulation-experiments considering temperature-dependent properties in a finite element package. Later on, shop floor experiments were also conducted, which revealed that inversely obtained parameters are sufficiently accurate in predicting the temperature distribution at changed operating conditions. The effect of measurement errors on the inverse estimated results is also discussed.

Ion assisted deposition of Silica-Titania multilayer optical filter for beam steering of Nd:YAG laser

In the present study, a multilayer reflective optical filter consisting of 24 alternate layers of SiO2 and TiO2 was designed and fabricated on BK7 glass substrate using Ion Assisted electron beam Deposition (IAD) technique. The spectroscopic characterization of the filter was carried out in Vis-NIR range with Universal Measurement Accessory (UMA) to measure its optical performance at normal and oblique angles of incidences. The measurements confirmed the optical peak reflectance of more than 99.98% at design wavelength of Nd:YAG laser centred at 1064 nm. The tuning of refractive indices of the constituent layers during deposition resulted in a Full-Width at Half-Maximum (FWHM) bandwidth of 330 nm of the fabricated filter which enables its use at any angle of incidences between 0 and 60° for manipulating the laser beam. Qualitative assessment of the mechanical stability of the coated filter with respect to its adhesion and abrasion resistance was carried out in accordance with MIL-F-48616 and MIL-E−12397 respectively. The achieved optical performance of the coated filter is suited for beam steering and folding of high power laser beams for metal cutting, diamond processing and in other laser based material processing instruments.

Deriving spectral information upon the laser welding process employing a hyperspectral imaging technique

In this paper we present results from process observations of deep penetration laser welding using a hyperspectral imaging (HSI) technique. For monitoring different types of laser-based material processing, we developed an appropriate high-speed camera-based HSI system. This system enables us to derive spectra of the deep penetration welding process with high time resolution. These spectra can be used for temperature determination or to extract spectral characteristics, both of which can help to further investigate process dynamics and properties of the vapor. The presented results contain particularly HSI-derived spectral information of the evolving vapor plume that is related to corresponding high-speed images and spectra acquired with a conventional VIS-spectrometer.

Development of a hyperspectral imaging technique for monitoring laser-based material processing

In this paper, a new observation technique for monitoring laser-based material processing on the basis of hyperspectral imaging (HSI) is presented. HSI techniques integrate both spatial and spectral information upon the object/process to be investigated. Essentially, the spectral information can be used to derive the absolute temperature of the object/process. The presented observation tool employing HSI-techniques comprises a high-speed camera and a self-developed HSI-lens system. It offers a time resolution in the microsecond-range and a spectral resolution of ∼4 nm. A proof-of-concept of temperature determination based upon HSI-derived spectra is given, and the initial observation results of the laser welding process are presented. These observations include the temperature evolution of the melting process of two different metal alloys over time. Moreover, we can show that the maximal temperature in the process zone does not exceed the evaporation temperature when processing construction steel and aluminum.

Theoretical and experimental analysis of scan angle-depending pulse front tilt in optical systems for laser scanners

Abstract For realising fast and highly dynamical laser-based material processing, scanner systems are already utilised for many different industrial applications. Furthermore, ultra-short pulsed (<1 ps) laser sources provide possibilities of processing most different materials with highest accuracy. Owing to the large spectral bandwidth of ultra-short laser pulses, dispersion in optical components becomes relevant. The dispersion in optical systems for laser scanners may lead to scan angle-depending pulse properties as, for example, pulse front tilt. The investigation of these effects is not state of the art today but absolutely necessary to exploit the full potential of laser scanners for ultra-short pulse applications. By means of an exemplary focusing lens, the simulation and experimental analysis of scan angle-depending pulse front tilt is presented for the first time.

Innovative manufacturing technology enabling light weighting with steel in commercial vehicles

Improved manufacturing technology is often needed when working with high strength steel. In this respect manufacturing technology has to adapt to the altered (and typically reduced) formability and weldability of modern high strength steel. However, this is a rather passive approach from a manufacturing point of view. An indeed much more powerful approach is to generate synergies between innovative manufacturing technology, design and material enabling additional weight savings and efficiency gains. Laser-based material processing, in particular laser welding, offers a wide range of opportunities in this sense. Furthermore, hot stamping and roll forming open up new possibilities for advanced manufacturing of commercial vehicle components. Applications and examples of these technologies will be given in terms of producing innovative semi-products as well as final components.

Grey Relational Analysis Based Optimization of Underwater Nd: YAG Laser Micro-channeling on PMMA

Laser based micro-channeling is emerging as the most widely used process for fabrication of polymer based micro-fluidic devices. Nd:YAG lasers are one of the most favoured laser system by industries involved in laser based material processing. However, they have not been fully explored for micro-level processing. In this research work, Nd:YAG laser has been utilized in fabrication of micro-channels on PMMA in underwater condition. The input parameters have been chosen as lamp current, scanning speed, pulse frequency and pulse width. Depth, burr height and burr width of the micro-channel have been taken as output quality characteristics. Taguchi methodology in combination with grey relational analysis has been employed to determine the optimal parametric condition for satisfying multiple objectives at same time. Underwater laser processing has resulted in minimization of undesirable effects of laser processing like heat affected zone and redeposition around the micro-channels resulting in cleaner and finer structure than open air processing.

Laser applications in nuclear power plants

This paper reports the state of the art of using a solid-state Nd:YAG laser for material processing applications such as cutting, welding and drilling of several components of operational nuclear reactors in radioactive environment. We have demonstrated several advantages of laser-based material processing over conventional methods, and these are discussed briefly. At NPCIL, we have used laser techniques to cut stainless steel sheets up to 14 mm thickness and stainless steel weld up to a depth of 3 mm. This remotely operable laser system has been engineered for its robustness with proper fixtures and tooling for various material processing operations on industrial scale.

Optical trap assisted laser nanostructuring in the near-field of microparticles

Particle based near-field nanostructuring is an excellent possibility to overcome the optical diffraction limit in laser based material processing. In the near-field of microspheres which are irradiated with pulsed laser radiation, it is possible to generate nanoholes with diameters below 100 nm using a laser wavelength of 800 nm. To improve this approach, it is possible to position the microparticles with an optical trap to generate arbitrary structure geometries. In this paper, the authors describe the basic principle of optical trap assisted nanostructuring and present simulational and experimental results demonstrating the potential of this innovative nanoscale optical material processing technology.