Effect of CO2 laser cutting process parameters on edge quality and operating cost of AISI316L

Laser cutting is a popular manufacturing process utilized to cut various types of materials economically. The width of laser cut or kerf, quality of the cut edges and the operating cost are affected by laser power, cutting speed, assist gas pressure, nozzle diameter and focus point position as well as the work-piece material. In this paper CO2 laser cutting of stainless steel of medical grade AISI316L has been investigated. Design of experiment (DOE) was implemented by applying Box-Behnken design to develop the experiment lay-out. The aim of this work is to relate the cutting edge quality parameters namely: upper kerf, lower kerf, the ratio between them, cut section roughness and operating cost to the process parameters mentioned above. Then, an overall optimization routine was applied to find out the optimal cutting setting that would enhance the quality or minimize the operating cost. Mathematical models were developed to determine the relationship between the process parameters and the edge quality features. Also, process parameters effects on the quality features have been defined. Finally, the optimal laser cutting conditions have been found at which the highest quality or minimum cost can be achieved

Investigation Into Laser Shock Processing

Laser shock processing is a good candidate for surface industry due to its rapid processing, localized ablation, and precision of operation. In the current study, laser shock processing of steel was considered. The numerical solutions for temperature rise and recoil pressure development across the interface of the ablating front and solid are presented. The propagation of elastic-plastic waves in the solid due to recoil pressure loading at the surface is analyzed and numerical solution for the wave propagation was obtained. An experiment was conducted to ablate the steel surfaces for shock processing. Scanning electron microscopy was carried out to examine the ablated surfaces shock processing while transmission electron microscopy was conducted to obtain dislocation densities after the shock processing. It was found that surface hardness of the workpiece increased in the order of 1.8 times of the base material hardness, and the dislocation was the main source of the shock hardening in the region affected by laser shock processing

Entropy Analysis in Pipe Flow Subjected to External Heating

Abstract: In the present study, heat transfer and entropy analysis for flow through a pipe system is considered. The Reynolds number and the pipe wall temperature effects on entropy distribution and total entropy generation in the pipe are investigated. Numerical scheme employing a control volume approach is introduced when solving the governing equations. Steel is selected as pipe material, while water is used as fluid. It is found that increasing pipe wall temperature and Reynolds number increases the entropy production rate, in which case, entropy generation due to heat transfer dominates over that corresponding to fluid friction

Laser nitriding method of making phosphor bronze with surface-embedded titanium carbide particles

The laser nitriding method of making phosphor bronze with surface-embedded titanium carbide particles involves coating a cleaned phosphor bronze workpiece with a thin film formed of a carbonaceous layer mixed with nanosize particles of titanium carbide. The titanium carbide forms about 5 wt % of the thin film, and the phosphor bronze workpiece is composed of about 6.0 wt % tin, about 0.1 wt % phosphorous, and about 93.9 wt % copper. A laser beam is then scanned over the thin film formed on the phosphor bronze workpiece. Coaxially and simultaneously with the laser beam, a stream of nitrogen gas is sprayed on the thin film formed on the phosphor bronze workpiece in order to provide the workpiece with a nitride coating having nanoparticles of titanium carbide embedded therein

Optical method and neural network for surface roughness measurement and surface pattern classification

In this present study, two optical methods employing diffusive and specular reflections from the steel surfaces are considered to measure the surface roughness value (Ra). The first method is introduced for Ra > 2 fim while the second method is employed for 0.1 (im < Ra < 2 (im. The peak intensity of the reflected beam, and a Gaussian curve parameter of a Gaussian function, approximating the peak intensity of the reflected beam, are measured for the first and second methods, respectively. Since a unique Ra value exists for a surface, the data collected for each profile were combined to produce a profile representing the Ra value for that particular surface, which is Gaussian in nature. The relationship between Ra and the standard deviation of Gaussian function (SDGF) was developed. An experimental set up associated with both methods has been designed and built. In this case, a He-Ne laser beam was used to scan the workpiece surface while fiber optic probes were employed to collect the reflected beam. To calibrate the fiber optic probes, Ra is measured initially using a Bendix surface proficoder. A back-propagation neural network classifying the surface patterns resulting from the first method was developed. A network simplification based on the self-pruning of the weights was employed. Control chart patterns resembling the possible surface profiles were developed when training the network. It is found that, the resolution of the surface texture measurement improved considerably in the case of presently employed optical method. The neural network developed for this purpose could classify the resulting surface patterns successfully. Newly introduced selfpruning method results in an improvement in the network performance and minimisation of the network structure and computing time. The first scheme used in the second method gives an improved standard estimate of error. The linear relationship was found between the Ra values and SDGF of the reflected beam intensity. Higher the SDGF values result in higher surface roughness. However, the measurement is limited to a certain range of Ra values; in this case, the accuracy of the measurement drops considerably as the Ra value reduces below 0.1 um

Modelling the influence of laser drilled recast layer thickness on the fatigue performance of CMSX-4

This paper introduces a novel approach to fatigue life prediction modelling considering the laser drilling effect on film cooling holes of turbine vanes. The methodology proposed is based on a stress-life model such as the Basquin law and the introduction of manufacturing damage effect. The proposed empirical model gives a unique versatility compared to other stress-life models by considering surface damage such as the recast layer produced by the laser drilling process. The proposed empirical model has been thoroughly tested and validated using existing fatigue data. The statistical analysis shows that the proposed model is adequate for estimating the fatigue life of laser drilled specimens considering the recast layer thicknesses effect. The proposed model also can estimate the life of untested specimens even when only a small sample of fatigue data is available, thereby reducing the required testing data

Focusing of phase change microparticles for local heat transfer enhancement in laminar flows

Phase change material (PCM) suspensions have received wide spread attention for increased thermal storage in various thermal systems such as heat sinks for electronics and solar thermal applications. To achieve further heat transfer enhancement, this paper investigates the effect of focusing micron-sized phase-change particles (PCMs) to a layer near the heated wall of a parallel plate channel. A numerical model for fully-developed laminar flow with a constant heat flux applied to one wall is developed. Melting of the focused PCMs is incorporated using a temperature-dependent effective heat capacity. The effect of channel height, height of the focused PCM stream, heat flux, and fluid properties on the peak local Nusselt number (Nu∗) and the averaged Nusselt number over the melting length (Nu[subscript melt]) are investigated. Compared to the thermally-developed Nusselt number for this geometry (Nuo = 5.385), Nu[subscript melt]and Nu∗ enhancements of 8% and 19% were determined, respectively. The local heat transfer performance is optimized when the PCMs are confined to within 30% of the channel height. The present work provides an extended understanding of local heat transfer characteristics during melting of flowing PCM suspensions, and offers a new method for enhancing heat transfer performance in various thermal-fluidic systems

Laser Short-Pulse Heating of a Three Layer Assembly and the Seebeck Effect

Laser short pulse heating of a multi-layer assembly, which consists of different layer properties, results in a non-similar electron and lattice site temperature distributions in the layers. This is because the differences in the amount of energy transfer in each layer despite the fact that each layer is very thin. Consequently, an investigation into the temperature distribution in the electron and lattice subsystems in each layer is essential. In the present study, laser short-pulse heating of a three layer assembly, consisting of Au-Cr-Cu, is examined. The electron and lattice site temperature rise in each layer is predicted using an electron lattice theory approach. Three-dimensional heating situation is accommodated in the model study. The Seebeck coefficient in each layer is computed and compared with the results of the previously derived equation. It is found that the electron temperature distribution varies in each layer and that this variation affects the lattice site temperature distribution. The lattice temperature distribution in the radial direction is not influenced by the diffusion of energy in the radial direction. Abrupt changes in the Seebeck coefficient across chromium and copper layers are observed

Investigation Into The Seebeck Coefficient in Two-Layer Assembly During Laser Short-Pulse Heating

The Seebeck coefficient in a substrate varies with electron temperature such that it increases with increasing temperature. The Seebeck coefficient for different materials differs even though the materials have similar thermal properties. In this study, the Seebeck coefficient in a two-layer assembly exposed to laser short-pulse heating is considered. The assembly consists of gold and copper, and the gold layer is situated on top of the copper. In order to investigate the change in the Seebeck coefficient with layer thickness, three different thicknesses of gold layer are accommodated in the simulations. An abrupt change in the Seebeck coefficient occurs across the layers, despite the smooth decay of electron temperatures in this region due to the similar thermal properties of the layer materials. Consequently, the Seebeck coefficient variation across the layers can form the basis for measurement of layer thickness