This paper is dedicated to laser engraving and drilling process of the alumina ceramics. Both processes are characterized by exquisite features in comparison with conventional ones. The main benefits are high speed, high precision and good quality along with flexibility. Moreover ceramics are hardly processed by conventional methods due to their high hardness and brittleness. Analysis of Nd:YLF laser engraving alumina ceramics concerning the influence of parameters like output power, processing speed and number of runs on various mark characteristics was carried out. Mark width, mark depth and contrast were evaluated and it was found out that output power determines both mark depth and width. Higher power caused generation of deeper and wider marks characterized by high contrast. Processing speed controls the overlapping of spots and the laser-material interaction time, thus having impact on the mark depth and contrast. Laser drilling was examined in dependence of output power that had crucial effect on the hole depth not on diameter. The research clarified that high output powers are necessary for producing deep holes so as high output powers together with low processing speeds are the optimal parameters to get maximal mark width and depth with satisfactory quality during engraving. Samples were analyzed using confocal microscope and contact profilometer.
Deep penetration welding is a typical industrial application of high power lasers, where plasma can be generated above
the keyhole. Thanks to the plasma plume presence welding process can be controlled on-line by means of the plasma
intensity measurements. Various on-line monitoring methods have been developed in research centers all over the world.
Goal of them is to enable promptly operator action to avoid enormous economical looses if un-expected defect is
detected. Our laboratory was participated in project CLET - “Closed loop control of the laser welding process through
the measurement of plasma” as a responsible partner for developed system testing both in the laboratory with pulsed
Nd:YAG laser and in the real welding facility with high power continual CO2 laser. Control system is based on the
electron temperature computation from the relative intensities of couple of emission lines belong to certain metal ion
present in plasma plume. Our experiment was realized using Ocean Optics HR2000+ spectrometer within the stainless
steel tube longitudinal welding. Several couples of emission lines were tested to acquire a good signal at actual welding conditions. Then power calibration was made to obtain the electron temperature dependence on increasing power. Samples were prepared for microanalysis and measured by laser confocal scanning microscope to find optimal power range for full penetrations achieving without thermal distortion of the tube or weld humping. Numerical model of the remelted area cross section was made to display temperature distribution dependence on increasing power.
Research of the optical radiation interaction with human tooth tissues has started early after the first laser construction.
Absorptivity of the particular tissue is dependent on the wavelength, thus CO2, Er:YAG and Nd:YAG lasers were used in many experimental works all over the world. Near infrared radiation of the pulsed Nd:YAG laser was found to be
suitable for dentine hypersensitivity treatment by sealing of the open tubules with melted and re-solidified dentin. Series
of experiments were performed to find suitable process parameters in the laser laboratory equipped with the industrial
pulsed Nd:YAG laser system. Tooth samples were prepared and classified into five groups according to their different
degree of the surface grinding and polishing. Two types of antireflective agents, erythrosine and black ink, were applied
on the samples surfaces. Coated samples and reference ones without any agents were treated with a set of increasing
pulse energy values. Pulse frequency, pulse length, laser beam diameter on the sample surface and relative speed
remained constant. Lines of the melted spots were displayed by confocal microscope; surface profiles were scanned by
contact profilometer. Dimensions of the dentine melted spots were extracted from the measured data and their
dependence on the laser pulse energy, degree of the surface grinding and type of antireflective agent were evaluated.
Laser beam of the infrared pulsed Nd:YAG laser was used to re-melting PVD coatings on the steel substrates. Chemical composition of these layers contains carbide Cr3C2 with alloy NiCr or nitrides TiN, TiAlN, TiAlSiN and CrAlSiN. First coatings were prepared by method of high velocity oxygen fuel (HVOF) that protects the machine component surfaces from abrasion, corrosion or ensures thermal isolation, nitrides by PVD (Physical Vapor Deposition). Processing parameters such as pulse energy, pulse length and frequency were optimized in many experiments to achieve the sufficient surface energy density to melting without vaporization of the material. Multimode beam diameters about some millimetres were computed and adjusted in the suitable distance from focus plane. High laser power re-melting decreases their porosity, increases adhesion to basic material. In case of high laser energy gas vapours escape from basic material and cause fissures, re-melted surfaces have to be carefully controlled. New approach to evaluation of the quality surface structure was realized by laser confocal microscopy. Direct measuring or 3D surface model is possible with resolution less than hundred nanometres, depressions along laser beam path or rises on the laser spot edges were determined. Particles and grains with dimensions about one micron in re-melting structures can be observed better then by optical microscopy. Parallel measurements of the surface roughness were realized by the contact inductive profilometer Talysurf, collected data were displayed by software tool Talymap in a plane or spatial pictures.
Pulsed Nd:YAG laser with maximal power 150 W is used in our laboratory to cut, drill and weld metal and non-metal
thin materials to thickness 2 mm. Welding is realized by fixed processing head or movable fiber one with beam diameter
0,6 mm in focus plane. Welding of stainless and low-carbon steel was tested before and results are publicized and used in
practice. Now the goal of our experiment was optimization of process parameters for aluminum that has other physical
properties than steels, lower density, higher heat conductivity and surface reflexivity. Pure alumina specimen 0,8 mm and
Al-Mg-Si alloy 0,5 mm prepared for butt welds. Problem with surface layer of Al2O3 was overcome by sanding and
chemical cleaning with grinding paste. Critical parameters for good weld shape are specimen position from beam focus
plane, pulse length and energy, pulse frequency and the motion velocity that determines percentage of pulse overlap.
Argon as protective gas was used with speed 6 liters per second. Thermal distribution in material can be modeled by
numerical simulation. Software tool SYSWELD makes possible to fit laser as surface heat source, define weld geometry,
and make meshing of specimen to finite elements and compute heat conduction during process. Color isotherms, vectors,
mechanical deformations and others results can be study in post-processing.
Material surface modification was carried out by laser alloying technology with an additional material. The final effects
are based on micro-structural changes in the surface layer, furthermore by changing the material composition in the
surface. Sic powder was applied on CSN 41 20 10 steel into melting pool generated by interaction with the moving C02
laser beam. Numerical modelling of the temperature field on the substrate appears like a good way to optimalization of
process parameters. The final surface structures are presented and analysed by scanning electron microscopy. The
microhardness of treated layers in comparison with substrate is described too.
Symptom of cervical dentine hypersensitivity attacks from 10% to 15% of population and causes an uncomfortable pain
during contact with any matter. Sealing of open dentinal tubules is one of the methods to reach insensibility. Laser as a
source of coherent radiation is used to melt dentine surface layers. Melted dentine turns to hard mass with a smooth, non-porous surface. Simulation of this therapy was made in vitro by means of LASAG Nd:YAG pulsed laser system KLS
246-102. Eighty human extracted teeth were cut horizontally to obtain samples from 2 mm to 3 mm thick. First
experiments were done on cross section surfaces to find an optimal range of laser parameters. A wide range of energies
from 30 mJ to 210 mJ embedded in 0,3 ms long pulse was tested. Motion in X and Y axes was ensured by a CNC driven
table and the pulse frequency 15 Hz was chosen to have a suitable overlap of laser spots. Some color agents were
examined with the aim to improve surface absorption. Scanning Electron Microscopy was used to evaluate all samples
and provided optimal values of energies around 50 J.cm-2. Next experiments were done with the beam oriented
perpendicularly to a root surface, close to the real situation. Optical fibers with the diameter of 0,6 mm and 0,2 mm were
used to guide a laser beam to teeth surfaces. Laser processing heads with lens F = 100 mm and F = 50 mm were used.
The best samples were investigated by means of the Atomic Force Microscopy.
Pulsed laser system LASAG with maximal average power 150 W is used in our laboratory for experiments with various kinds of materials, process parameters optimisation for cutting, welding, drilling and surface treatment. Alignment of optical elements and good laser beam quality is critical parameter for successful result of laser treatment. Active medium - crystal in solid state laser is warmed up during laser action, because only some percent of input electrical power is turn to optical energy. Warm crystal has properties like a thick lens, which optical power is dependent on process parameters and kind of resonator. Also some defects in optical system - dirty or damaged mirrors or lens must be detect. Properties of non-visible near infrared beam can be tested by means of laser beam analyzer SPIRICON. In our system there are movable and changeable end mirrors and diaphragms to obtain five different types of resonators - basic one for welding and fibre applications and four ones for fine cutting and drilling. Measurements of beam profile for all these resonators were made with safety values of pulse length, energy and frequency. Control of losses in optical system was made to inspect quality of optical elements. Also measurement of laser beam outputting from three different fibre processing heads was realised. Control measurements on continual industrial Nd:YAG laser system were made. All data and capture pictures are stored and practical lessons for students in next school years were prepared.
CVD diamond has many outstanding physical properties. Because of its extreme hardness, this material is difficult to cut and polish and laser cutting and shaping is a technology of choice. Thick polycrystalline diamond layers were deposited by microwave plasma enhanced chemical vapor deposition on silicon substrates. After synthesis, the silicon substrate was dissolved in an acid mixture and diamond wafer has to be cut into desired shapes according to their future use. With LASAG Nd:YAG pulsed laser system KLS 246-102 we found cutting parameters for different thickness of diamond wafers from 0,1 mm to 0,7 mm. A special support with connection to vacuum was developed to keep small and light parts fixed during processing. To avoid undesirable cracks, laser scribing was used at first. Laser pulse with energy 30 mJ-200 mJ according wafer thickness and velocity 3mm.s-1-15 mm.s-1 goes two or four times along cutting lines. High temperature is the origin of black graphite layers, where absorption of laser radiation continues. Peak power contained in 0,2 ms pulse was up to 1000 W. Developed method helps to prepare CVD diamond samples of any desired shape.
KEYWORDS: Cladding, Chemical elements, Laser applications, Laser processing, Carbon dioxide lasers, Scanning electron microscopy, Chemical analysis, Transmission electron microscopy, Gas lasers, Nickel
Structures analysed in that paper were produced by the laser cladding technology on CSN 41 1373 steel with a Ni-based alloyed powder "K50" using CO2 laser. The point of view of an investigation is the structure mapping and an experimental verification of the process parameters. A dendritic structure in individual regions of the selected clad layer and material composition are point of balance of micro-analyses which were carried out by the scanning electron microscopy and analysis of elements hence distribution of material.
Both types of industrial lasers, CO2 and Nd:YAG, are used for welding with wide range of maximal power values. Successful results of laser welding depend on many different factors: energy, diameter, mode structure, polarization and focus position of laser beam; thickness, accurate positioning and gap of welded parts, kind of shielding gas. With LASAG Nd:YAG pulsed laser system KLS 246-102 we made optimization of welding parameters for different metals 0.5 mm thick and some types of the weld geometry. Our experimental results were used for welding of the side joint of the steel motor covers. These precious parts are used in automobile racing models. Finite elements model is used to predict a heat affected zone.
Laser cladding is one of the technologies of material surface treatment. A series of laser-clad specimens have been produced using continual 2,5 kW CO2 laser. There is introduced a description of the powder injection laser cladding method in the present paper. For some numerical calculations of laser beam induced temperature field in treated material were used the finite difference method and the finite element method. Results of this modeling led to an optimalization of cladding process parameters. Some layers of Ni-based alloy K50, Stellit6 alloy and SiC powders were applied on low-carbon CSN 11 373 and CSN 12 010 steels. Shape characteristics and some properties such as microhardness of clad layers in comparison with substrate values were analyzed.
This paper describes a numerical finite element method modeling of laser applications, especially laser cutting and drilling a steel, concrete or brick. In the first part of this contribution there is a very brief description of laser processing in metal (a kind of carbon steel) and non-metal material (concrete and brick), possibility of mathematical modeling and needful parameters for this modeling. One of the systems, that uses this method, is ANSYS. The ANSYS computer
code is a large-scale multipurpose finite element program, which may be used for solving several classes of engineering analyses, for example thermal analyses, that calculates the temperature distribution and related thermal quantities in a system or its components. The main part of this paper deals with examples of temperature field computed by ANSYS in carbon steel, concrete and brick after incident of the high-power laser beam upon their surfaces. In conclusion we compare various theoretical results mutually and also with practically obtained facts.
This paper describes a possibility of mathematical modeling of laser applications, especially laser cutting and drilling and its use in practice. In the first part of this contribution there is a very briefly description of contemporary use of high-power lasers in industry and also basic principles of interaction between laser beam and treated material. Next part of the paper deals with a mathematical modeling of temperature field. Two numerical methods are used for the calculation of the temperature field: the finite difference method and the finite element method. Two examples of results of these both methods are demonstrated and some problems occurring when creating the matheniatical models are described. In the conclusion we made a brief comparison between theoretical and experimental results.
In this paper, there is described the influence of various modifications of the laser resonator on the energy of laser radiation studied for the application of material drilling. We used pulsed 150W Nd:YAG laser from LASAG AG company, Switzerland. This laser was developed for industrial material processing - cutting, welding and drilling. The diameter and divergence of the output laser beam can vary by replacement of optical elements in the laser resonator and by change of the distance between them. Heating of Nd:YAG crystal during laser action resulting in its function as an internal lens has an important effect on a beam quality. This quality is characterized by a beam parameter product depending on a charging power and type of resonator. The goal of our experiment is to find minimal parameters for cutting and drilling of some metallic sheets with thickness from 0.1 mm to 10 mm and to verify an increasing beam quality by reducing a laser output power and by modification of a resonator arrangement. Nitrogen was used as an assist gas. Measured experimental results were summarized in graphs and tables and were prepared for quick reference of laser parameters used for processing various work-pieces.
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