Papers by Keyword: Laser

Abstract: The paper presents a comparative analysis of the dynamic loading of a polymethyl methacrylate (PMMA) target by a polyethylene (PE) projectile exposed to laser radiation with similar initial energy characteristics of the projectile and the laser pulse. The similarities and differences in the mechanisms of the target's response and its destruction to high-speed mechanical and laser action are shown. A higher efficiency of laser irradiation in the destruction of PMMA was found, and the conditions for the transition of the fracture mechanism from brittle to elastic-plastic were shown.

Abstract: This paper presents the laser surface polishing of titanium alloy (Ti6Al4V) by using a nanosecond pulse laser. Air, nitrogen and argon were employed as a shielding gas in this study, where the areal roughness (Sa) of laser-polished surface was measured and compared. The results showed that argon was the suitable assist gas for improving the metal surface without causing the oxidation. The effect of laser pulse repetition rate and scan speed on the surface roughness was also investigated in this study. The use of high repetition rate together with slow scan speed was able to reduce the surface roughness of titanium alloy. The roughness was found to be reduced by 47% when the pulse repetition rate of 500 kHz and scan speed of 50 mm/s were applied.

Abstract: In this paper, the effect of laser surface heat treatment on wear resistance and hardness of an aluminum alloy Al-6061 as a base material with different ratios of SiC particles as an additive was studied. The composite material was prepared from Al-6061 aluminum alloy and particles with a granular size of (10-70) μm with different weight ratios (15%, 12%, 9%, 6%, 3%), where the stirred plumbing technique was used to ensure An increase in the wettability of SiC particles in the base alloy fuse and the possibility of distributing it uniformly. The laser surface heat treatment of the composite material prepared using the Neodymium - YAG laser was performed with a power of 1J, a wavelength of 1.06 μm, a pulse time of 5 m sec, and a distance of 30 cm between the exit area of the laser from the system and the piece to be thermally treated. The results showed an improvement in the mechanical properties of the prepared composite material (hardness, wear resistance) after performing the surface heat treatment by laser. The increase in the hardness amount was 12.9% when adding 15% of particles to the base alloy. The results showed that the wear rate value decreases with increasing the added percentages of SiC particles. The results also showed that the surface heat treatment of the laser led to an improvement in the wear resistance of the prepared composite material and for all the added ratios of SiC particles at different loading pressures used and in close proportions. Also, the prepared samples were photographed using a regular optical microscope before and after the laser surface heat treatment.

Abstract: In this work, the experimental research was carried out on the processing of the cutting surface of a grinding wheel with a ceramic bond via continuous laser radiation with a wavelength of 10.6 μm. The influence of laser radiation power, processing speed on the depth and width of the obtained cut was investigated. A full factorial experiment was carried out with varying factors at two levels. In the form of a regression equation, a mathematical model of the effect of radiation power and processing speed on the output parameters of the process is obtained. Using Fisher's criterion, it is shown that the resulting equation adequately describes the process under the study. The analysis of the regression equation makes it possible to assess the relative influence of each factor and the effects of the interaction of factors on the depth and width of the cut on the surfaces of the grinding wheel.

Abstract: The paper presents the results of studying the microstructure of samples obtained with laser processing of AK4-1 aluminum alloy powder. It has been found that increasing the initial temperature of the substrate to 100...150 °C allows to use this powder material in directed energy deposition (DED) additive process to create stiffening elements on the surface of thin-walled aluminum parts. When the specified temperature condition is satisfied, the crystallization rate decreases, allowing to obtain samples with almost no internal cracks. The results of comparing the microstructure and the microhardness of commercial AK4-1 wrought alloy and the samples obtained with DED process are presented. The structure of the samples prepared with laser cladding is more disperse in comparison with wrought alloy. The microhardness of the sample prepared at pre-heated substrate is comparable with wrought alloy. The conceptual architecture of the decision support software for laser powder cladding processes is presented. Its information and software components are briefly described.

Abstract: Cyclic voltammetry is a widely used technique in electrochemistry due to its simplicity and large amount of data and information that can be obtained. This study utilises this technique to study chlorophyll a and total chlorophyll (Tchl) alongside a laser light to induce photosynthesis. No oxidative peak was observed, regardless of the solution pH in either a dark or light environment when using a solution with an electrolyte of tetrabutylammonium perchlorate (TBAP) in both dichloromethane (DCM) and acetonitrile (MeCN), whereas in a solution of aqueous HCl a small anodic peak was observed. The concentration of the droplet of Tchl pigment on the surface of macro glassy carbon electrode (GCE) was increased, which resulted in a similar trend and the oxidation peak was observed to be slightly larger when in the presence of light. It was observed that the filtered solution of Tchl pigment produced a weaker signal than the unfiltered solution and there were slightly reduced oxidative peak currents when the concentration of VK₁ was increased. were no observed changes in the peak charges or currents over a wide potential range (0.0, 0.2, 0.4, 0.6 and 0.8 V) in the presence or absence of light by using coulometry and amperometry methods, therefore, more information on the 3-D formation is required for the photoreduction processes.

Abstract: Many natural materials have the ability to rotate the polarization level of linearly polarized laser beam and pass through it. This phenomenon is called optical activity. In the event that a light beam (linearly polarized) passes through an optically active material, such as a quartz crystal, and projected vertically on the optical axis, the output beam will be polarized equatorially, and the vibration level will rotate at a certain angle [1], [2], [3]. A number of crystals, liquids, solutions, and vapors rotate the electric field of linearly polarized light that passes through them [4], [5], [6], [7]. Many different physical effects are applied to optical isotropic and transparent materials that cause them to behave as optical active materials, where they are able to rotate the polarization level of the polarized light linearly and pass through it [8], [9], [10]. These effects include mechanical strength, electric field, and magnetic field. By placing one of these effects on an optically transparent medium, it changes the behavior of the light travelling through it [11].

Abstract: Laser polishing technology plays an increasingly important role in the material processing technology.In order to study the influence of scanning interval on the polishing effect of S136D die steel, the single factor experiment method is used in this paper. The continuous fiber laser is used to carry out many laser polishing experiments and the influence of laser scanning interval on the surface morphology of S136D die steel is analyzed.The results show that the surface roughness of polished samples decreases first and then increases with the of scanning interval. When the scanning interval is in the range of 0.03-0.1mm, the surface roughness of samples is relatively flat, and the lowest surface roughness can be reduced to 0.781μm, and the reduction rate of surface roughness can reach 90.2%.

Abstract: The work investigates refractory metals (bulk W, W produced via plasma spraying, W-1% La₂O₃ and Mo) of interest as plasma facing materials in future nuclear fusion reactors. They have been irradiated by a single Nd:YAG laser pulse to simulate the effects of transient thermal loads of high energy occurring in a tokamak under operative conditions and then examined by SEM observations. In all the materials the laser pulse induces a crater in the central area of laser spot surrounded by a ridge due to movement of molten metal while in a more external area a network of cracks is observed. Diameter and depth of the crater, ablated volume and morphological features of the surrounding area exhibit differences depending on the specific metal, its physical and microstructural characteristics which affect vaporization, melting and heat propagation from the irradiated spot.

Abstract: The surface treatment of tools plays an important role for the operational behaviour of forming processes. Up to now, industrial standard is the manual finishing of tool surfaces, which can lead to a varying quality of the surface finish and therefore influence the tool service life and the forming results. One method to perform the polishing operation automatically is to remelt the top layer of materials by laser polishing. This is accompanied by a considerable change in the material properties in this zone. Therefore, the effect of laser polishing with respect to the local modification of the tool surface is investigated in this study. The results of the investigations reveal that a precise adjustment of the laser parameters is required in order to reduce the roughness of the surface. The heat input also leads to a significant influence on the microstructure of the material. In this study laser polishing remelts the material up to a depth of approximately 20 µm. Furthermore, it can be observed that the heat input during the process results in a heat affected zone of up to a depth of 30 µm. As a contrast to laser polishing, abrasive blasting is investigated as a roughness increasing surface modification.