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The operating pressure of gas-assisted laser cutting and the resulting exit jet pattern is one of the most important process parameters in high-pressure laser cutting. Many studies have been done to illustrate the effect of this parameter on both laser cutting quality and laser cutting capability. However, most of these studies have been done using conical nozzles. In this paper, the exit jet from supersonic nozzle has been studied, analyzed, and simulated under three different operating conditions, namely desired design, under-expansion, and over-expansion to illustrate the effect of these operating conditions on the dynamic characteristics of the exit jet. Quasi 1-D gas dynamics theory has been used to calculate the desired design operating condition, and then an axisymmetric 2-D model has been created using the OpenFOAMⓇ Computational Fluid Dynamics (CFD) toolbox to simulate the gas-assisted laser cutting flow through the modeled supersonic nozzle. Finally, the proposed simulations have been validated by comparing the results with experimental observations reported in previous literature. The effect of the turbulent viscosity has been considered through the proposed model to better simulate real conditions. Moreover, the model has been optimized to be effectively used for engineering purposes. The simulation results are qualitatively consistent with the reported experimental measurements and they demonstrate that in the case of supersonic nozzles, the exit jet pattern is characterized by high uniformity, absence of Mach disks, and bounded shape for a long distance especially under the desired design operating conditions.

In the present work, a novel set of software tools for the rapid development of shoes and footwear is presented aimed at strongly reducing the design time and then the time-to-market of the products. These tools are mainly based on an implementation of Constrained Free Form Deformation techniques and on the use of modern surface scanning methods. The proposed approach allows, in many cases, to avoid the mathematical surface reconstruction and to quickly generate the complex geometries that CAM systems will process in order to generate the tool paths for mold manufacturing.

Highly regular laser-induced periodic surface structures (HR-LIPSS) have been fabricated on surfaces of Mo, steel alloy and Ti at a record processing speed on large areas and with a record regularity in the obtained sub-wavelength structures. The physical mechanisms governing LIPSS regularity are identified and linked with the decay length (i.e. the mean free path) of the excited surface electromagnetic waves (SEWs). The dispersion of the LIPSS orientation angle well correlates with the SEWs decay length: the shorter this length, the more regular are the LIPSS. A material dependent criterion for obtaining HR-LIPSS is proposed for a large variety of metallic materials. It has been found that decreasing the spot size close to the SEW decay length is a key for covering several cm2 of material surface by HR-LIPSS in a few seconds. Theoretical predictions suggest that reducing the laser wavelength can provide the possibility of HR-LIPSS production on principally any metal. This new achievement in the unprecedented level of control over the laser-induced periodic structure formation makes this laser-writing technology to be flexible, robust and, hence, highly competitive for advanced industrial applications based on surface nanostructuring.

In this brief review the advances on Direct Laser Patterning (DLP) for the synthesis of photo-luminescent semiconductor quantum dots (QDs) belonging to II-VI groups, especially in solid state using laser-assisted conversion are reported and commented. The chemistry of the precursor synthesis is illustrated because it is a crucial step for the development of the direct laser patterning of QDs. In particular, the analysis of cadmium (bis)thiolate and cadmium xanthates precursors after thermal and laser treatment is examined, with a special focus on the optical properties of the formed QDs. The second part of the review examines how the laser parameters such as the wavelength and pulse duration may regulate the properties of the patterned QDs. The DLP technique does not require complex laser systems or the use of dangerous chemical post treatments, so it can be introduced as a potential method for the patterning of pixels in quantum dot light emitting diodes (QD-LEDs) for display manufacturing.

The synthesis of colloidal photo-luminescent semiconductor quantum dots (QDs), belonging to II-VI groups, even from single source precursors is presented. Since three decades their synthesis has been pursued implementing new and easier synthetic conditions that standardize their production. In this work is reported the production of luminescent of CdS QDs in a polymeric film induced by laser processing (www.miledi-h2020.eu/). A film of PMMA doped with two types of precursors (cadmium xanthates) is irradiated with an UV laser source with different energy doses. The structured film will then be observed with confocal fluorescent microscope. The interesting results shows that the two different xanthates display a different behavior under the laser source even if their absorption spectrum is similar. The second interesting result is that the effect of the laser is the production luminescent pattern only for certain fluences and that the same film treated with the temperature did not show any luminescence.The synthesis of colloidal photo-luminescent semiconductor quantum dots (QDs), belonging to II-VI groups, even from single source precursors is presented. Since three decades their synthesis has been pursued implementing new and easier synthetic conditions that standardize their production. In this work is reported the production of luminescent of CdS QDs in a polymeric film induced by laser processing (www.miledi-h2020.eu/). A film of PMMA doped with two types of precursors (cadmium xanthates) is irradiated with an UV laser source with different energy doses. The structured film will then be observed with confocal fluorescent microscope. The interesting results shows that the two different xanthates display a different behavior under the laser source even if their absorption spectrum is similar. The second interesting result is that the effect of the laser is the production luminescent pattern only for certain fluences and that the same film treated with the temperature did not show any luminescence.

Picosecond laser-induced periodic surface structures (PLIPSS) have been fabricated on surface of Si in uniform and burst-mode regimes at a high speed. The effects of burst-mode respect to uniform one are examined in term of chemical, mechanical and morphological properties.

Laser Texturing and Laser Engraving of free form surfaces are interesting alternative to EDM and micro milling in the fabrication of moulds and dies. The material removal rate of this process is typically very low and the maximum working area is limited by the maximum travel range of the galvanometric scanning head and also by the maximum deflection of the scanner or the surface curvature. As a consequence, in order to manufacture large or free form surfaces, a set of placements of the scanning head respect to the work piece must be calculated and controlled by the CNC. The number of these placements can be quite high due the small amount of material removed in each of them and the non-operative time spent to move the scanning head can be relevant compared to the overall time. In this work a method based on the solution of the Traveling Salesman Problem is proposed with the aim to optimise the number of displacements of the scanning head and generally in order to reduce the number of movement of the numerically controlled axes. The method that takes into account both the architecture and the dynamic characteristics of a 5 axis CNC system was implemented in the CALM (Computer Aided Laser Manufacturing) software used to program the laser path for part texturing and applied in industrial cases.

Plasmonic properties of gold nanoparticles self-assembled on silicon surfaces are significantly enhanced by a periodic surface ripples induced by ultrashort laser pulses. The nanostructured surfaces open new perspectives for production of photonic and plasmonic-sensor elements.

Sub-MHz repetition rate femtosecond laser pulses produce extremely regular periodic surface structures on silicon surface due to competition between ultrafast heating and electron-emission. They allow manufacturing of novel devices for solar, optoelectronic, and biomedical applications.

New method based on HR-LIPSS for diffraction grating formation on preliminary fabricated p-n junction on Si substrate are suggested. This allows to produce surface plasmon-polariton photodetectors based on periodically corrugated thin metal plasmon-carrying films.

Femtosecond laser pulses of sub-MHz repetition rate induce highly regular periodic surface structures on silicon by combining electron emission and ultrafast heating. They are favorable for photovoltaic, optoelectronic, and biomedical applications.

Silicon is one of the most abundant materials which is used in many areas of modern research and technology. A variety of those applications require surface nanopatterning with minimum structure defects. However, the high-quality nanostructuring of large areas of silicon surface at industrially acceptable speed is still a challenge. Here, we report a rapid formation of highly regular laser-induced periodic surface structures (HR-LIPSS) in the regime of strong ablation by infrared femtosecond laser pulses at sub-MHz repetition rate. Parameters of the laser-surface interactions and obtained experimental results suggest an important role of electrostatically assisted bond softening in initiating the HR-LIPSS formation.

In this study an application of free form deformation for the editing of clouds of points or tessellated surfaces representing industrial parts is presented. The application is based on an efficient implementation of NURBS based free form deformation and the implementation of functions for imposing constraints to position, directions and curvatures of embedded objects. The developed functions permit the direct manipulation of triangulated surfaces eliminating the surface reconstruction stage, reducing the time requested in the reverse engineering process and, at the end, reducing the time to market.

In this study a series of procedures were implemented to compare acquired surfaces with the nominal data or to directly compare different scanned surfaces. In particular a morphological evaluation algorithm based on the extended Gaussian curvature (EGC) and a method to compare features based on aggregate normal orientation are presented. To perform the comparing feature method a simple procedure for segmentation was developed. The main characteristic of the two methods is robust behavior referring to the scan orientation. The procedures were implemented as software modules in a graphic environment.

Lithium ion battery electrodes have been exposed to 1064nm nanosecond pulsed laser irradiation with pulse energy in the range 8μJ – 1mJ and fluence in the range 3.2 – 395J/cm2. Experiments have been executed at translational velocities of 100mm/s and 1m/s, allowing individual characterization of the graphite and lithium metal oxide coatings of the copper anode and aluminum cathode, respectively, as well as that of the complete multi-layer structures. A 3D optical profiler has been utilized to measure the incision depth of all samples and allow observation of the process quality. At high velocity, partial or complete removal of the upper coating layers was achieved with little or no impact on the underlying metallic layers. At low velocity, complete cuts were possible under certain conditions, with process efficiency found to be almost entirely governed by the response of the metallic layers. While the coating layers of each electrode exhibited different responses than the metallic layer, the influence of the latter was found to be dominant for cutting operations. Shorter pulses with fluence in the range 30 – 60J/cm2 were found to lead to optimum process outcomes with the employed laser source.Copyright © 2014 by ASME

none 3 In this paper a 5 axes CAM procedure for the laser milling of free form surfaces has been developed and experimentally verified. The laser beam is deflected by a galvanometric scanning head and is directly moved on the working surface by the CNC controlled axes of a machine center. The procedure has been implemented in a software called CALM (computer aided laser manufacturing) able to generate the laser paths and the movements of the controlled axes reducing the defects on the workpiece. The approach is based on the sequential overlapping of the scanning passes on the working area. The different working areas in every laser displacement are obtained directly from the triangulation of the whole surface to machine. G. Cuccolini; L. Orazi; A. Fortunato G. Cuccolini; L. Orazi; A. Fortunato

This paper reports the results concerning the simulation of a laser surface hardening process of a cylindrical surface. In particular it focuses on the problems related to the definition of the physical parameter values necessary in order to achieve an accurate and reliable simulation. The strict dependency of laser process simulation results on the physical parameters describing the target material is, in fact, a well known matter, especially considering that the values of these parameters change during the process dependently on temperature and time. Moreover in laser surface hardening this problem is even more important because melting of the target material should be avoided, surface roughness plays an important role and, sometimes, the surface is coated with absorbent layers. These factors increase the complexity of the simulations and make the evaluation of the physical parameters more difficult and critical. The results presented in this paper are obtained on AISI420B steel, coated with graphite and treated with a direct diode laser. Considering the above mentioned conditions, a plausible temperature dependent reflectivity coefficient was evaluated and its robustness was investigated. This reflectivity coefficient can be used with a good approximation for the simulation of laser hardening treatments of many carbon steels.

In this paper, a laser surface micromachining process planning system is presented. In this system, based on a regression model approach, the empirical coefficients, which provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. Numerical models generally present some limits due to the elevated calculation time requested to simulate the laser micromachining of industrial features, especially when transient solutions are considered, and, for this reason, to carry out a useful industrial tool for the evaluation of the material removal rate, the regression model represents the best solution. The presented statistical method, avoiding physical considerations, correlates the material removal rate with the process parameters in a very short calculation time. The automatic procedure for the generation of the coefficients of the regression polynomial permits to easily extend the regression model to any working material and system configuration allowing us to determine the best process parameters in a very short period of time. The results of this work have been patented.

In this work an original system for the geometrical characterization of root canals for dental implants was developed and tested. The aim of this work is to determine the shape and the size of the posts that best fit a statistical population of root canals with a defined maximum amount of removed tissue. The task is performed by an accurate acquisition of the shape of a statistically significant batches of root impressions: the geometry are then processed to obtain the post geometry. The acquisition is carried out using a conoscopic laser scanning device mounted on a 4 axis controlled CNC measurement system. The shape of the root canals were measured for each type of tooth, obtaining an average 3-D computer design of the canal profiles. Several comparisons between the acquired geometry and the representative forms of commercial posts are finally presented.Copyright © 2008 by ASME

In this paper a numerical simulation of laser hardening process is presented. The Finite Dierence Method(FDM) was used to solve the heat transfer and the carbon diu sion equations for a de“ned workpiece geometry.The model is able to predict the thermal cycle into the target material, the phase transformations and theresultingmicro-structuresaccordingtothe laserparameters,the workpiecedimensions andthe physicalpropertiesof the workpiece. The eects of the overlapping tracks of the laser beam on the resulting micro-structures is alsoconsidered.The initial workpiece micro-structure is taken into acco unt in the simulation by a digitized photomicrographof the ferrite perlite distribution before the thermal cycle.Experimental tests were realized on a C43 plate and the good agreement between the theoretical and exper-imental results is shown.Keywords: Laser hardening, numerical simulation, process planning. 1. INTRODUCTION LaserHardeningofsteel componentsis a stable processwhere veryhard, wearresistancesurfacescan be uniformlyobtained into the workpiece when the correct process pa rameters are set. It allows to treat complex shapes,usually very diculty to realize with conventional surface hardening, with less distortions than that caused by”ame or induction hardening.This process is becoming widely used in industrial environment due to the development of new generationlaser sources. Diode laser with high power density, high eciency and very uniform distribution are commonlyavailable together with the last generation of high power “ber lasers. These new types of sources usually havevery compact resonators like the diode ones, or the laser beam can be easily delivered to the workpieces bymeans of optic “bers, like the “ber or the Nd:Yag lasers. For these reasons, surface heat treatment, usually anoutsourcing operation for the small-medium mechanical company, always more often is realized from the samecompany which realize the cutting operations. Many eorts are nowadays conducted to integrate in a machinecenter for metal cutting the operations of surface hardening considering the laser beam as a conventional tool.The economic aspect is crucial for the development of the laser technology in Industry. For the completeexploitation of the laser resources, in fact, it is fundamental to consider the technological advantages of thelaser together with the high capital costs of the systems: widespread use of lasers in industry for heat treatingmainly depends on the cost of the treated component. In general, laser hardening can be more economicallyapplied respect to the conventional processes when batches of small dimensions or when complex shapes mustbe hardened. In this direction, the challenge is to increase the ”exibility of the laser technology.Laser hardening is a quite complex process which involves many parameters:€ the laser parameters like the power density and distribution, the spot dimension and the laser beam velocitywhich determine the heat cycle in the workpiece

In this paper a laser milling simulator package is shown and discussed. The software system has been developed to simulate the micromanufacturing process using solid state lasers with pulse width in the range of 10–100 ns, but it can simulate every spatial and temporal distribution of the laser beam, so it is well suited to simulate both continuous and pulsed emission and every kind of laser spot distribution and trajectory. The system can simulate the effect of the laser beam on the workpiece, keeping into account the surface conditions, the evolution of the work-piece temperature field, the phase changes in the material and, at the end, the ablation rate. Particular attention has been focused in considering the influence of the plasma plume. Modeling and simulating the plasma plume creation and expansion is a very hard task, in the proposed package a simplified model is developed avoiding the fluid dynamic effects. In this work two empirical tuning parameters are considered: the first one is a global dispersion factor that keep in account the fraction of energy lost in the environment by the plume; the second one is a spreading factor that permits to model the irradiated energy of the laser beam hitting the workpiece and due to the plasma plume. The direct and coupled effects of these two parameters are evaluated and discussed.Copyright © 2007 by ASME

Excitation of surface plasmon resonances has been observed on laser-induced highly-regular 1D periodic Si surface covered with Au nanoparticles. The nanostructured surfaces open new perspectives for production of photonic and plasmonic sensor elements.

Date of Conference: 10-15 May 2015 Conference name: 2015 Conference on Lasers and Electro-Optics (CLEO) This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL). © 2015 OSA.