Papers by Keyword: Laser

Abstract: The paper summarizes the findings of a study of properties and behavior of laser hardened surfaces. The influence of hardening on the service life and tribological resistance of molds and other machine parts will be presented. Furthermore, the influence of process parameters on residual stresses, their direction and magnitude, and related deformation, fatigue behavior under cyclic loading, etc. are described.

Abstract: Underwater laser machining process is a material removal technique that can minimize thermal damage and offer a higher machining rate than the laser ablation in ambient air. This study applied the underwater method associated with a nanosecond pulse laser for turning a commercially pure titanium rod. The effects of laser power, surface speed and number of laser passes on machined depth and surface roughness were investigated in this work. The results revealed that a deeper cut depth and smoother machined surface than those obtained from the laser ablation in ambient air were achievable when the underwater laser turning process was applied. The machined depth and surface roughness were found to significantly increase with the laser power and number of laser passes. The findings of this study can disclose the insight as well as potential of the underwater laser turning process for titanium and other similar metals.

Abstract: In this work, an inverse heat transfer analysis was used to determine thermal conductivity and specific heat of tissue using special iteration. A laser with a long wavelength was utilized to impose heat to the tissue. The heat that induced in the sample causes an increase in the temperature of a tissue which is measured by a thermocouple. The readings were used together with that analytically obtained from the solution of the heat equation in an iterative procedure to obtain the thermal properties of tissue. By using this method, accurate thermal conductivity and specific heat of tissue could be obtained. It was found that the maximum error in output result and the error in input data were in the same order and that there was a linear relationship between output and input errors.

Abstract: To effectively interpret the fluid flow dynamics in the molten metal pool, a numerical model was established. The moving repetitive Gaussian laser pulse is irradiated in the work piece. The consideration of laser scanning speed makes the transport phenomena complex. The continuity and momentum equations are solved to get the flow velocity of the molten metal in the melt pool. The energy equation is solved to know the temperature field in the work piece. The algebraic equations obtained after discretization of the governing equations by Finite Volume Method (FVM) are then solved by the Tri Diagonal Matrix Method. Enthalpy-porosity technique is used to capture the position of the melt front which determines the shape of the melt pool. Marangoni convection is considered to know its effect on the shape of the melt pool. The surface tension coefficient is taken as both positive and negative value while calculating the Marangoni force. The two possible cases will cause the Marangoni force to distort the flow dynamics in the melt pool . It's dominance over the buoyancy force in controlling the melt pool shape is focused in the present study. Further, the present model will present an insight to the consequences of laser scanning velocity over the melt pool dimensions and shape.

Abstract: This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and on the boundary layer of stainless steel processing. A new analytical resolution based on the boundary layer theory is used to deduce the interaction effects of the cutting parameters on the above zones. The results revealed that, the laminar nitrogen assist gas has a negligible effect on the HAZ depth but it has a remarkable effect on the molten boundary layer. It is also noticed that the pressure gradient remains very small compared to the interface shearing and the conductive heat losses from the cutting zone towards the substrate is dominant compared to the convective heat losses towards the gas.

Abstract: The article discusses the manufacturing technology of the impeller of a high-pressure centrifugal fan using high-speed direct laser spraying. The outer diameter of the part is 1200 mm, the total weight is 100 kg. The material used is metal powder stainless steel 316L. Features of the manufactured products were researched, including possible thermal deformations and methods for dealing with them.

Abstract: The temperature- and time-dependent penetration of surface structures is examined in thermal joining between polypropylene and aluminum. Experimental and numerical investigations were carried out for spot joints in order to describe the main effects on structure penetration. Further investigations were performed in a half-section setup to gain information directly from the joining zone. The thermal expansion of the thermoplastic material as well as the temperature distribution in the melting layer were identified as key parameters for structure filling on the metal surface.

Abstract: This paper presents the viability of ultrasound in assisting the performance of laser hardening process. A nanosecond pulse laser was employed as a heat source in this study to heat and introduce hardened phase in AISI H13 tool steel. The influences of laser power and traverse speed on surface roughness and case depth of laser-irradiated region were experimentally investigated. The laser processing with the assist of ultrasound can improve the surface roughness of laser-hardened area by 7.5% and also increase the case depth by 7.65% compared to the non-ultrasound condition. Under a suitable processing condition, the laser can harden and polish the metal surface at the same when the ultrasound was incorporated in the process. The implication of this study will broaden the viability of ultrasound in the laser surface hardening/polishing of metals.

Abstract: The paper studies the surface structure and microhardness of the coating modified by the pulsed laser irradiation. The coating is obtained by plasma-jet hard-facing of the AISI (American Iron and Steel Institute) М2 high speed steel powder. The modes of the laser irradiation differ in peaking capacity, pulse duration and diameters of the focused laser beam. It is demonstrated that the weld penetration shape factor depends on the laser beam fluence and the pulse duration. In its turn, the weld penetration shape factor effects the quality of obtained irradiation zones.

Abstract: The tailoring of mechanical and technological properties of the initial material in sheet metal forming has been widely investigated and successfully applied. The benefits of such an approach can be found in the improvement of both the post-forming performances of the manufactured component and the forming process capabilities. Different strategies can be found and most of them involve a microstructural alteration by a selective heat source (e.g. laser, induction, UV light). The use of aluminium alloys combined with these strategies has been extensively investigated, while magnesium alloys are almost not yet considered from this viewpoint. In this work, we investigated the effect of a selective laser heat treatment on an AZ31 magnesium alloy sheet. After laser heat treating a single track in the centre of a blank with different heat input values, bulge tests at elevated temperatures were conducted. The dome height evolution was continuously acquired during the tests and differences between the untreated specimen and the laser treated ones have been characterized. The effect of the laser treatment was evaluated also in terms of thickness distribution of the formed specimens. A thickness discontinuity was found along the treated specimens in the transition zone between the treated and the untreated material. Results highlighted that an effective change in the forming behaviour can be induced in the treated zone depending on the laser heat input. It has thus been shown that this approach can be employed for tailoring the magnesium alloy blank properties prior to the gas forming at elevated temperatures.