Geometrical features and metallurgical characteristics of Nd:YAG laser drilled holes in thick IN718 and Ti–6Al–4V sheets
TL;DR: In this paper, Nd:YAG laser drilling of 4 and 8mm thick sections of IN718 and Ti-6Al-4V materials has been investigated and relevant geometrical features of the drilled holes, like hole diameter and taper angle, have been comprehensively investigated.
Abstract: Laser drilling is increasingly becoming the method of choice for precision drilling of a variety of components, particularly in the aircraft industry. Notwithstanding the current level of acceptance of laser drilling in the aerospace industry, a number of defects such as spatter, recast and taper are associated with laser drilled holes and elimination of these defects is the subject of intense research. The present paper deals with Nd:YAG laser drilling of 4 and 8 mm thick sections of IN718 and Ti–6Al–4V materials. The influence of type of material and its thickness, as well as parametric impact of key process variables like pulse frequency and pulse energy, have been determined. In the course of this study, relevant geometrical features of the drilled holes, like hole diameter and taper angle, have been comprehensively investigated. In addition, all metallurgical characteristics of interest, viz extent and nature of spatter, recast and heat-affected zone, have been evaluated. Effort has also been made to obtain some insights into the evolution of a through-thickness hole during laser percussion drilling of thick sections by careful experimentation involving monitoring the progression of the drilled hole with increasing number of laser pulses. Issues pertaining to variation of taper with depth of hole, change in crater depth with progressive drilling and specific energy consumption are also discussed.
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TL;DR: The experimental and theoretical studies of LBM show that process performance can be improved considerably by proper selection of laser parameters, material parameters and operating parameters, and the trend for future research is outlined.
Abstract: Laser beam machining (LBM) is one of the most widely used thermal energy based non-contact type advance machining process which can be applied for almost whole range of materials. Laser beam is focussed for melting and vaporizing the unwanted material from the parent material. It is suitable for geometrically complex profile cutting and making miniature holes in sheetmetal. Among various type of lasers used for machining in industries, CO2 and Nd:YAG lasers are most established. In recent years, researchers have explored a number of ways to improve the LBM process performance by analysing the different factors that affect the quality characteristics. The experimental and theoretical studies show that process performance can be improved considerably by proper selection of laser parameters, material parameters and operating parameters. This paper reviews the research work carried out so far in the area of LBM of different materials and shapes. It reports about the experimental and theoretical studies of LBM to improve the process performance. Several modelling and optimization techniques for the determination of optimum laser beam cutting condition have been critically examined. The last part of this paper discusses the LBM developments and outlines the trend for future research.
754 citations
Cites background from "Geometrical features and metallurgi..."
...Also, parameters effect show that on increasing the pulse frequency and pulse energy recast layer reduces while increases with material thickness [34]....
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...Low material thickness and pulse energy gives smaller HAZ while pulse frequency has no significant effect on HAZ for laser cutting of thick sheets of nickel base superalloy [34]....
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...[34] have investigated the effect of material type and its thickness on hole taper during Nd:YAG laser drilling of titanium alloy and nickel alloy sheets of different thicknesses....
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TL;DR: In this paper, the effect of various factors/process parameters on the performance of Nd:YAG laser beam machining has been investigated and the importance of different design of experiments (DOE) methodologies used by various investigators for achieving the optimum value of different quality characteristics has also been discussed.
Abstract: Since last four decades laser beams are being used in various manufacturing processes. CO2 and Nd:YAG lasers are most widely used in machining of engineering materials. In recent years the researchers have explored the number of ways to improve the quality of cutting, drilling and micromachining of different materials (metals, alloys, ceramics and composites) using Nd:YAG lasers. This paper reviews the experimental investigations carried out to study the effect of various factors/process parameters on the performance of Nd:YAG laser beam machining. The importance of different design of experiments (DOE) methodologies used by various investigators for achieving the optimum value of different quality characteristics has also been discussed in paper.
179 citations
TL;DR: In this article, a Ti-6Al-4V alloy was machined under varying traverse speeds of 60, 80, 120, 150, 200, and 250 mm/min by abrasive waterjet (AWJ) machining.
Abstract: In the presented study, Ti–6Al–4V alloy, known as one of the difficult-to-machine materials using conventional machining processes, was machined under varying traverse speeds of 60, 80, 120, 150, 200, and 250 mm/min by abrasive waterjet (AWJ) machining. After machining, the profiles of machined surfaces, kerf geometries and microstructural features of the machined surfaces were examined using surface profilometry and scanning electron microscopy (SEM). The experimental results indicate that the traverse speed of the jet is a significant parameter on the surface morphology, and the widths and features of different regions formed in the cutting surface change according to the traverse speed. It was also observed that the kerf taper ratio and surface roughness increase with increasing traverse speed in chosen conditions.
163 citations
TL;DR: In this paper, a typical cutting regime for pulsed Nd:YAG laser cutting of 1mm thick Hastelloy-X sheet has been constructed and explained in terms of extent of spot overlap.
Abstract: Although CO2 lasers have been widely employed for commercial sheet metal cutting operations, increased recognition of the processing benefits afforded by pulsed Nd:YAG lasers has recently fuelled interest in the latter. Pulsed Nd:YAG laser cutting differs from conventional continuous wave laser cutting as it involves overlapping of a series of individual spots generated by each pulse. In this paper, a typical cutting regime for pulsed Nd:YAG laser cutting of 1 mm thick Hastelloy-X sheet has been constructed and explained in terms of extent of spot overlap. The characteristics of single holes drilled employing the same process parameters as those employed for cutting were investigated and correlated with the obtained processing regime. Additionally, the influence of key process parameters like pulse duration on the shift in the constructed processing regime was investigated. Cut quality attributes like kerf width, cut edge kerf profile and surface roughness were also studied and their dependence on process parameters has been discussed.
154 citations
References
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01 Jan 1989
TL;DR: In this article, the first law of thermodynamics and the third law of Nernst heat theorem are used to construct tables of thermochemical data of pure substances, which are then used for thermodynamic calculations.
Abstract: Part 1 Basic principles: thermodynamic functions and relations - the basic concepts, the first law of thermodynamics, Joule-Thomson effect, the second law of thermodynamics, the third law of thermodynamics (Nernst heat theorem), fundamental relations of thermodynamics, closed system with reactions, chemical potential, chemical equilibrium, mixtures, Gibbs phase rule, electrochemical reactions calculations of thermochemical functions - units and conventions, calculations of the thermochemical functions of pure substances, equilibrium calculations, exergy and entropy balances. Part 2 Compilation and presentation of thermochemical data: compilation of thermochemical data - basic thermochemical data, existing compilations, thermochemical tables. Part 3 Tables in the present work: preparation of the tables - general remarks, data sources, accuracy, units, standard states, reference phase for the elements at 298.15K and 1 bar construction of the tables - arrangement of substances, order of the phases in the tables contents and structure of the tables - formula, name and relative molar mass, tabulated functions, sequence of temperatures, phase transitions, the final temperature in the tables, references for the sources of data, abbreviations and symbols. Part 4 Examples of the use of the tables: examples of thermodynamic calculations - enthalpy changes, exergy and entropy balance calculations, equilibrium calculations, equilibrium in simplified systems with several phases and components, electrochemical energy conversion, high temperature fuel cell, the calculation of equilibria in multi-phases, multicomponent systems. Part 5 Information on the tables: fundamental constants and conversion factors - fundamental constants, conversion factors for energy units, conversions for entropies of gases, relative atomic masses of the elements based on A...=12 for 12C. Part 6 Symbols, abbreviations and references: symbols and abbreviations used in the tables reference phases of elements at 1 bar references for the data in the tables. Part 7 The tables: tables of thermochemical data of pure substances.
4,691 citations
TL;DR: In this paper, a one-dimensional steady-state model describing the damage caused by materials removal by vaporization and liquid expulsion due to laser-material interaction is developed and presented.
Abstract: A one‐dimensional steady‐state model describing the damage caused by materials removal by vaporization and liquid expulsion due to laser‐material interaction is developed and presented. When vaporization occurs, there exists a discontinuity across the Knudsen layer of a few molecular mean free paths. This discontinuity is modeled by a Mott–Smith‐type solution. The vaporization process creates a recoil pressure that pushes the vapor away from the target and expels the liquid. The materials are, therefore, removed in both vapor and liquid phases. The materials‐removal rates are incorporated in the moving boundary immobilization transformation. The vapor phase is assumed to be optically thin so that its absorption of the high‐energy beam is negligible. Closed‐form analytical solutions are obtained and presented. The effect of heat‐source power on removal rates, vaporization rate, liquid‐expulsion rate, surface temperature, and Mach number are presented and discussed. Results are obtained for three different materials: aluminum, superalloy, and titanium.
195 citations
TL;DR: In this article, the mechanisms of some laser-drilling processes, the types of laser used, the quality characteristics of a laserdrilled hole, the effects of drilling parameters, and the advantages and limitations of the laser hole-dilling operation are reviewed.
Abstract: Drilling cooling holes in aerospace materials with a neodymium-doped: yttrium aluminum garnet (Nd:YAG) laser is an established technique used in the aerospace industry. However, there are new challenges as the industry begins to use materials that can witstand higher temperatures and pressures. In this paper, the mechanisms of some laser-drilling processes, the types of laser used, the quality characteristics of a laser-drilled hole, the effects of drilling parameters, and the advantages and limitations of the laser hole-drilling operation are reviewed.
160 citations
TL;DR: In this article, the effect of the laser parameters and the material properties on the hole quality when drilling is examined, and a statistical approach, referred to as factorial design, is employed to test the significance level of the factors that affect hole quality.
Abstract: In the laser drilling process, the quality of the drilled holes is the main task. A method of studying the influence on the quality of the main process variables needs to be developed, which seeks to improve the quality and explains the drilling mechanism. In the present study, the effect of the laser parameters and the material properties on the hole quality when drilling is examined. A statistical approach, referred to as factorial design, is employed to test the significance level of the factors that affect the hole quality. Three materials, stainless steel, nickel and titanium, are considered. The experimental study yields tables of significance of each factor on the aspects that determine the quality of the holes. The hole geometry is evaluated by assigning marks for each geometric feature, the marking scheme being conducted relevant to the importance of the hole feature.
125 citations
TL;DR: In this article, the authors investigated the cutting capability of COIL and Nd:YAG laser and found that the cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed.
Abstract: The most widely used high power industrial lasers are the Nd:YAG and CO2 lasers. The chemical oxygen iodine laser (COIL), whose wavelength (1.315 μm) is between that of the Nd:YAG (1.06 μm) and CO2 (10.6 μm) lasers, is another high power laser for industrial applications. The cutting capability of these lasers is investigated in this paper. The cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed. The absorptivity is an unknown parameter for which experimental data at high temperatures are currently unavailable. Theoretical values of the absorptivities of various metals are obtained using the Hagen‐Ruben relationship. It is found that the absorptivity of a metal is linearly proportional to the square root of its resistivity and also inversely proportional to the square root of the wavelength. The absorptivities of the COIL and Nd:YAG lasers are 2.84 and 3.16 times larger than that of the CO2 laser, respectively. Based on these theoretical values of the absorptivity, the cut depths for several metals are analyzed at various laser powers and cutting speeds for these lasers. For identical cutting parameters, the cut depths for stainless steel and titanium are deeper than those of most other metals. Due to the wavelength dependence of the absorptivity, the cut depths for COIL and Nd:YAG lasers are expected to be 2.84 and 3.16 times deeper than that for the CO2 laser.
96 citations