Laser Grooving Research Articles

Functionally gradient ceramic/metallic coatings for gas turbine components by high-energy beams for high-temperature applications

Failure of turbine blades generally results from high-temperature oxidation, corrosion, erosion, or combinations of these procedures at the tip, and the leading and trailing edges of a turbine blade. To overcome these limitations, functionally gradient ceramic/metallic coatings have been produced by high-energy beams for high-temperature applications in the aerospace and turbine industries to increase the life of turbine components. Thermal spray processes have long been used to apply high-temperature thermal barrier coatings to improve the life of turbine components. However, these processes have not met the increased demand by the aerospace and turbine industries to obtain higher engine temperatures and increased life enhancement as a result of the inhomogeneous microstructure, unmelted particles, voids, and poor bonding with the substrate. High-energy beams, i.e. electron beam-physical vapour deposition (EB-PVD), laser glazing, laser surface alloying, and laser surface cladding, have been explored to enhance the life of turbine components and overcome the limitations of the thermal spray processes. EB-PVD has overcome some of the disadvantages of the thermal spray processes and has increased the life of turbine components by a factor of two as a result of the columnar microstructure in the thermal barrier coating (TBC). Laser glazing has been used to produce metastable phases, amorphous material, and a fine-grained microstructure, resulting in improved surface properties such as fatigue, wear, and corrosion resistance at elevated temperatures without changing the composition of the surface material. Laser surface alloying and laser surface cladding have shown promising results in improving the chemical, physical, and mechanical properties of the substrate's surface. Metal-matrix composite coatings have also been produced by a laser technique which resulted in increased wear and oxidation-resistant properties. The advantages and disadvantages of thermal spray processes, EB-PVD, laser glazing, laser surface alloying, and laser surface cladding will be discussed. Microstructural evolution of thermal barrier coatings, recent advancements in functionally gradient coatings, laser grooving, and multilayered textured coatings will also be discussed.

Study on Analyses of Frequency Characteristics of Laser Processing Sound.

The final goal of this research is to construct a laser processing system to manufacture stepped shapes or freeform surfaces using detected sound. In order to achieve this goal, basic investigations concerning the analysisof characteristics of the laser processing sound are necessary. The purposes of this study are to determine therelationship between transfer functions and sound frequencies when a work material, its dimensions, andprocessing conditions are changed, and to calculate the frequency characteristics of sound if a high frequencylaser beam is utilized for laser grooving. The main findings are as follows. 1) It was shown experimentallythat the distribution of transfer functions versus sound frequencies has almost the same pattern even if the laserenergy per pulse, the work material, and its dimensions are changed. 2) The numerical analyses revealed thatthe pattern of the distribution of sound pressure level qualitatively coincides with that of the experimentalresults.

The anisotropic heat-affected zone in the laser grooving of fiber-reinforced composite material

A heat-affected zone is frequently associated with the laser processing of materials. In the shaping of composite material after curing, thermal damage is found, such as matrix recession, matrix decomposition, and delamination, which lead to poor assembly tolerance and long-term performance deterioration. The current study analyzes the peculiar growth of the heat-affected zone due to laser energy and the anisotropy of heat conductivity from the anisotropic arrangement of the fiber reinforcement in the composite material. It further applies the concept that the cut quality can be improved by reducing the resulting temperature of the workpiece, which leads to laser machining at low temperature. The paper investigates the cutting of unidirectional laminated carbon/epoxy composite perpendicular to and parallel to the fiber axis, using a cool nitrogen jet to reduce thermal damage. A theoretical analysis based on moving-point heat-source theory is adopted to determine the extent of thermal damage in correlation with process parameters and material properties. The analytical solution is modified by the ‘mirror image method’ for a specimen of finite thickness. The range of the heat-affected zone is estimated by the isotherm of the matrix char temperature. Heat conduction is maximum along the carbon fibers, the heat-affected zone shape thus being affected by the beam scanning direction relative to the fiber orientation.

Analysis of the laser grooving and cutting processes

Laser grooving is a very complicated process to analyse, due to the molten material's behaviour. Based on the assumption of complete removal of molten material, a theoretical analysis is performed to derive groove depth as a function of process parameters. The heat balance at the cutting front is used as the governing equation to determine groove depth. Conduction heat direction and area change are approximated to obtain a closed form of the groove depth. The theoretical results show good agreement with experimental data. This approach provides a simple way of predicting groove depths and is applied to the prediction of depths of cuts in laser cutting.

Theoretical Model of Laser Grooving for Composite Materials

The influence of directionally-dependent thermal properties on laser machining effectiveness is analyzed theoretically and experimentally. A laser grooving model was developed which incorporated the effects of directionally-dependent thermal conductivity. Laser grooving experiments on graphite/vinylester composites showed differences in groove depth and profile depending on the laser beam direction relative to fiber orientation. The groove depth predictions from the composite grooving model showed an improved correlation with experimental data compared to predictions from the model with homogeneous material properties. The predictions of groove profiles and centerlines from the composites model are also presented for laser beam impingement parallel and perpendicular to fiber orientation.

685 mV open-circuit voltage laser grooved silicon solar cell

Abstract The recombination limiting the voltage of the present buried contact solar cell (BCSC) can be reduced by replacing the present high recombination sintered aluminium back with a floating rear junction for passivation, heavy boron diffusion below the rear contact, and by limiting the rear surface contact area. Analysis of these implementations in the double sided laser grooved (DSLG) structure shows that the floating junction passivation is effective in reducing the recombination component at the rear surface and that the boron diffusion in the rear groove comprises up to half of the total saturation current. Limiting the area of the heavily diffused boron grooves allows open-circuit voltages of 685 mV while maintaining the simplicity of the BCSC processing sequence. An open-circuit voltage of 685 mV represents nearly a 50 mV increase over the conventional BCSC.

Investigation of acoustic sensing for laser machining processes Part 2: Laser grooving and cutting

This paper presents an analysis of acoustic sensing for laser grooving and cutting processes. Theoretical models of the interaction between the coaxial gas jet and the erosion front were developed using the wave equation to relate acoustic emission to the geometry of the groove or kerf. Theoretical estimates are compared with experimental results for acrylic, aluminum oxide and stainless steel. Process control schemes for groove depth regulation for laser grooving and beam break-through regulation for laser cutting are introduced.

Laser Grooving of Composite Materials With the Aid of a Water Jet

This paper presents a method for reducing the thermal damage of composite materials during laser grooving. The method utilizes a water jet in tandem with the laser beam in an attempt to control the heat conducted into the workpiece. The paper presents a theoretical analysis for determining the relationships between groove depth and heat affected zone, and the laser and water jet operating parameters. The theoretical analysis accounts for the effect of the heat transfer due to the water jet. The predictions of the analysis are compared with experimental results whereby the heat-affected zone is reduced up to 70 percent by using a water jet. The paper includes experimental findings regarding the optimum operating point of the water jet for minimizing the heat-affected zone (HAZ) and maximizing the achievable groove depth.

Process Control of Laser Grooving Using Acoustic Sensing

This paper discusses a closed-loop control concept for laser machining. A key development in the proposed control scheme is an acoustic sensor for inferring hole, kerf, and groove geometry in real time during laser machining. By sensing the acoustic signal emitted from the impingement of a gas jet on the erosion front, correlations between resonant frequency and hole, kerf or groove geometry were found. A process model was developed from applying the wave equation to the case of an elliptically-expanding or a constant-area jet. Experiments showed an inverse relationship between depth of cut and resonant frequency for grooving, cutting, and drilling cases. The paper also includes preliminary simulation results of a closed-lop control scheme for laser grooving using acoustic sensing and a PID controller.

ＩＣプラスチックパッケージのＹＡＧレーザ照射によるマーキング

Generally, in the laser marking, surface roughness or grooves produced by laser irradiation are utilized for distinction; however, it is hard to distinguish the marked characters or symbols clearly. In this report, the laser marking of IC plastic package making use of the change in color has been described. By this marking method, the characters and symbols marked can be distinguished clearly. Effects of laser irradiation conditions for the change in color are studied, and the laser marking experiment of IC package, which consists of SiO2 powder, carbon black and epoxy resin matrix is conducted. Occurrence of the change in color is controlled by varying irradiation power, irradiation time and irradiation atmosphere. It is found that the change in color occurs under the suitable energy power density, and the O2 gas has the effect on shortening the irradiation time until the change in color occurs. The mechanism of the change in color can be explained as follows : after epoxy resin matrix and carbon black are removed, SiO2 powder is melted by laser irradiation; SiO2 powder which includes many pores are sintered; this sintered SiO2 changes the color from black to white by diffused reflection. These phenomena can be applied to laser marking of IC package for subtle distinction.

16.7% efficient, laser textured, buried contact polycrystalline silicon solar cell

In the evolution of single-crystal silicon solar cells, crystallographic texturing of the cell surface using anisotropic etches was an important step in improving cell performance. Unfortunately, this technique is ineffective for polycrystalline silicon solar cells due to generally unfavorable grain orientation. This limitation has been overcome by employing a new laser texturing technique on the top surface of a laser grooved, buried top contact polycrystalline silicon solar cell. This approach has demonstrated an independently confirmed 16.7% (air mass 1.5, 25 °C) efficiency for a 10.5 cm2 polycrystalline silicon solar cell, the highest efficiency ever reported for a polycrystalline cell of this size.

High-efficiency, laser grooved, buried contact silicon solar cells

Improvements in the performance of silicon solar cells based on a novel, laser grooved, buried contact approach are described. Independently confirmed energy conversion efficiencies as high as 19.8% are reported for cells of 12 cm2 area, as are the resistivity dependence of efficiency, spectral response data, and the results of laser beam induced current scans. The potential for further improvement is also discussed.

Investigation of Laser Grooving for Composite Materials

An analysis of the laser grooving process was conducted for several composite materials. An analytical model was developed to determine groove depth from process parameters and thermal properties of the material. Experimental measurements of groove depth, groove width and damage width were taken for variations in scanning velocity, beam power, and beam passes. A close agreement was found between model predictions and experimental results for groove depths in carbon/teflon. Model predictions consistently overestimated depth values for glass-fiber composites, and correction for heat losses was added to the model to improve agreement with data. Glass/polyester also showed differences in groove depth, width and damage width for variations in beam scanning direction relative to fiber orientation. The groove width and damage width results for all three materials were compared with surface quality standards for laser cutting of composites.