Showing papers in "Materials and Manufacturing Processes in 2003"

Research and Progress in Laser Welding of Wrought Aluminum Alloys. II. Metallurgical Microstructures, Defects, and Mechanical Properties

Abstract: With the wide application of aluminum alloys in automotive, aerospace, and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought aluminum alloys are critically discussed from different perspectives. The primary objective of the review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of aluminum alloy joints. Two main types of industrial lasers, carbon dioxide (CO2), and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In the preceding article of this review (part I), the laser welding processing parameters, including the laser-, process-, and material-related variables and their effects on welding quality, have been examined. In this part of the review, the...

Potential Magnesium Alloys for High Temperature Die Cast Automotive Applications: A Review

Abstract: Magnesium, as a lightweight construction material, has rapidly grown its applications in the automotive industry since the early 1990s. To maximize the weight reduction of vehicles by lightweight magnesium alloys in the coming years, the use of newly developed high-temperature magnesium alloys is expected to increase significantly, particularly in the powertrain applications where the creep resistance is always required. This article reviews recent developments of the creep-resistant magnesium alloys. Fundamental aspects of the creep deformation theory and mechanisms are described. The metallurgical principles for designing the creep-resistant alloys are highlighted. The creep behavior of magnesium and its conventional alloys is discussed based on some microstructure analyses. The mechanical properties, microstructure, and manufacturability of the newly developed creep-resistant magnesium alloys are also overviewed. The further research and development work is outlined in terms of developing magn...

Research and Progress in Laser Welding of Wrought Aluminum Alloys. I. Laser Welding Processes

Abstract: With the wide application of Al alloys in automotive, aerospace and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought Al alloys have been critically discussed from different perspectives. The primary objective of this review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of Al alloy joints. Two main types of industrial lasers, carbon dioxide (CO2) and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In this part of the review, the main laser welding processing parameters including the laser-, process-, and material-related variables and their effects on weld quality are examined. In part II of this article in this journal, the metallurgical microstruc...

Integrated Genetic Programming and Genetic Algorithm Approach to Predict Surface Roughness

Abstract: In this article we propose a new integrated genetic programming and genetic algorithm approach to predict surface roughness in end-milling. Four independent variables, spindle speed, feed rate, depth of cut, and vibrations, were measured. Those variables influence the dependent variable (i.e., surface roughness). On the basis of training data set, different models for surface roughness were developed by genetic programming. The floating-point constants of the best model were additionally optimized by a genetic algorithm. Accuracy of the model was proved on the testing data set. By using the proposed approach, more accurate prediction of surface roughness was reached than if only modeling by genetic programming had been carried out. It was also established that the surface roughness is most influenced by the feed rate, whereas the vibrations increase the prediction accuracy.

Vibration-Assisted Precision Machining of Steel with PCD Tools

Abstract: This article presents experimental results of precision machining of steel alloys with polycrystalline diamond tools. Ultrasonic vibration-assisted cutting was tried out for expanding the application of diamond tools for high-precision and high-quality machining of ferrous materials. The experimental results show that compared with conventional turning, the cutting performance, in terms of cutting force, surface finish, and tool life, was improved by applying ultrasonic vibration to the cutting tool. The cutting forces and tool wear measured in vibration cutting are much lower than those in conventional cutting. The tool wear mechanism was discussed on the basis of the observation of wear zone.

Optimal Scheduling of Casting Sequence Using Genetic Algorithms

Abstract: Scheduling a casting sequence involving a number of orders with different casting weights and satisfying due dates of is an important optimization problem often encountered in foundries. In this article, we attempt to solve this complex, multi-variable, and multi-constraint optimization problem by using different implementations of genetic algorithms (GAs). In comparison with a mixed-integer linear programming solver, GAs with problem-specific operators are found to provide faster (with a subquadratic computational time complexity) and more reliable solutions to very large (more than 1 million integer variables) casting sequence optimization problems. In addition to solving the particular problem, the study demonstrates how problem-specific information can be introduced in a GA for solving complex real-world problems.

The Optimal Scheduling of a Reversing Strip Mill: Studies Using Multipopulation Genetic Algorithms and Differential Evolution

Abstract: This article addresses a problem of minimizing the hot rolling time of an ingot, from a given initial thickness to a prescribed final one, subject to a number of system constraints. The idea is to determine the minimum possible odd number of passes, so that the ingot leaves in the same direction as it entered, which would ensure the necessary degree of reduction without violating the prescribed upper limits of the available torque and roll force. A maximum rolling velocity was also prescribed and additional restrictions were imposed on the rates of acceleration and deceleration inside the mill. The problem was solved by using a number of variants of genetic algorithms, including a multipopulation island model and differential evolution, besides the simple genetic algorithms. The results are compared with some earlier work based on a discrete dynamic programming technique, and a model based on an improved formulation is also presented.

Applications of Genetic Algorithm in Polymer Science and Engineering

Abstract: In the last several years, genetic algorithm (GA) has gained wide acceptance as a robust optimization algorithm in almost all areas of science and engineering. Polymer science and engineering is no exception. Researchers in this field have devoted considerable attention to the optimization of polymer productionusing objective functions and constraints that lead to products having desired material properties. Multiple-objective functions have been optimized simultaneously. An example is the minimization of the reaction time in a reactor (lower costs) while simultaneously minimizing the concentration of side products (that affect the properties of the product adversely). Several end-point constraints (equality or inequality) may also be present, as, e.g., obtaining polymer of a desired molecular weight. Again, this requirement stems from producing polymer having desired strength. Solving such problems usually result in Pareto sets. A variety of adaptations of GA have been developed to obtain optima...

Grinding of Single-Crystal Silicon Along Crystallographic Directions

Abstract: This article studies the effect of grinding along crystallographic directions on the surface finish of single-crystal silicon. It also discusses new and/or improved processes for precision machining brittle materials, including silicon. Silicon samples were cut from (100) silicon wafers. These samples were then subjected to grinding along different crystallographic directions under the same experimental conditions. The surface roughness and the surface texture of these samples were then analyzed. The R a and R q values and the microphotographs of the ground silicon surfaces showed the dependency of surface finish on the grinding direction. Better surface finish was achieved when (100) silicon was ground along ⟨110⟩ directions. Samples ground along these directions also showed more ductile streaks on the silicon surfaces, compared with surfaces ground along the other directions.

Comparison of Laser and Gas Tungsten Arc Weldments of Stabilized 17 wt% Cr Ferritic Stainless Steel

Abstract: One of the major factors influencing weldability of stabilized 17 wt% Cr ferritic stainless steels is extensive grain coarsening in the fusion zone (FZ) and in the heat affected zone (HAZ). This study aimed at exploiting low heat input characteristics of laser welding to effectively control grain coarsening in the FZ and HAZ of 1.2-mm thick stabilized 17 wt% Cr ferritic stainless steel weldment. The study demonstrated that as compared with gas tungsten arc welding (GTAW), laser welding brought about significant grain refinement in the FZ and HAZ. Laser weldments exhibited superior ductility over their GTA counterparts. An important observation of the study was that, in contrast to GTA weldment, laser weldment was associated with weaker interfaces along columnar grain boundaries in the FZ that served to arrest crack propagation normal to them.

Conversion of an Investment Casting Sprue Wax to a Pattern Wax by Chemical Agents

Abstract: In this research, the properties of a commercial investment casting sprue wax (B97) were modified to improve its properties so it can be used as a pattern wax in investment casting. For this purpose, some colloids (gum arabic, pectin, agar, polyvinylpyrrolidone-40, polyvinylpolypyrrolidone, alginic acid, cellulose, carboxymethyl cellulose, silicon, tannic acid, saponin), some surface active agents (sodium dodecyl sulfate, sorbitane oleostearate, glycerine), and activated charcoal and palmitic acid were used as additives or fillers. The effect of these chemicals on the surface roughness, solidification shrinkage, apparent viscosity, hardness, tensile strength, and wettability of B97 wax were investigated. These additives modified the properties of B97 sprue wax to such an extent that it had properties superior to those of a commercial investment casting pattern wax (B140).

Development of Microreplication Process—Micromolding

Abstract: A microreplication process, micromolding, was developed to replicate three-dimensional microcomponents. It included modifying a conventional molding machine, developing a thermal control unit to control the mold temperature, and developing a vacuum unit to evacuate the microcavity before filling it with plastic melt. Focused ion beam sputtering, a maskless patterning of material, was used to fabricate a microcavity that was then used as a mold insert. Feasibility of the micromolding process was investigated by simulation, and results were verified with the replication of polymer microcomponents (e.g., microgear, gear-train). Commercial simulation software was used to reveal possible issues in micromolding by integrating the microcomponent with a larger base. The simulations predict the filling time, pressure distribution, volumetric shrinkage, stress distribution, etc., of the microcomponent.

Combinatorial Search to Optimize Vent Locations in the Presence of Disturbances in Liquid Composite Molding Processes

Abstract: In liquid composite molding processes, the resin is injected into a mold cavity containing preplaced reinforcement fabrics through openings known as gates, and the air leaves the mold through openings called as vents. Under nominal conditions, the last points to fill are chosen as vent locations. However, due to imperfect preform placement, gaps and channels may form along the edges and at curvatures in a mold, offering a path with less resistance for resin flow. The faster advance of resin through these gaps and channels, a common disturbance known as racetracking, will cause the last filled regions to vary, which complicates the vent selection process. We introduce a methodology that uses set and probability theories to forecast racetracking conditions in a mold and have developed a combinatorial search algorithm to locate corresponding optimal vent locations. The accuracy, efficiency and usefulness of the approach is illustrated with three case studies.

Experimental Evaluation of Properties of Cross-Linked Polyethylene

Abstract: This article describes several aspects of the production of cross-linked polyethylene. Advantages and disadvantages of chemical, or electron beam irradiation, cross-linking processes are discussed. The material under test is thermoshrinking low density polyethylene, produced at the Megarad s.r.l. (Cassino, Italy) firm. It is mostly used as blanket insulation for low and medium electrical voltage cables and as anticorrosion protection for gas pipes. The performance of end products is verified through destructive tests. In particular, we evaluated the gel fraction, the modulus of elasticity at 150°C and the elongation percent on commercial pipes and on specimens manufactured by varying certain parameters, such as the irradiation dose.

Evolutionary Neural Network Modeling of Blast Furnace Burden Distribution

Abstract: A neural network-based model of the burden layer thickness in the blast furnace is presented. The model is based on layer thicknesses estimates from a single radar measurement of the burden (stock) level in the furnace and describes the dependence between the layer thickness and key charging variables. An evolutionary algorithm is applied to train the network weights and connectivity by optimizing the model structure and parameters simultaneously, tackling part of the parameter estimation by linear least squares. This enhances convergence and results in parsimonious and transparent network models with actions that can be explained. Finally, the networks are used in a hybrid model for analyzing novel charging programs and for studying the limits of the charging process.

Effect of Erodent Particle Hardness on Velocity Exponent in Erosion of Steels and Cast Irons

Abstract: This article reports the effect of hardness of erodent particles on velocity exponent of some weld deposited alloys. Three steels and two alloy cast irons were selected for the present investigation. The bulk hardness of the alloys was in the range of 300 to 800 HV, whereas erodnet particles were having hardness in the range of 400 to 1875 HV. Erosion tests were conducted with 125–150 µm cement clinker, 125–150 µm blast furnace sinter, 100–150 µm silica sand, and 125–150 µm alumina particles and at impingement angles of 30° and 90° and with impingement velocities in the range of 25 to 120 m sec−1. The erosion rate showed power-law dependence on impingement velocity, E = k V n , where kis a constant and nis the velocity exponent. The velocity exponents obtained in the present work were in the range of 1.91 to 2.52. The velocity exponent showed an increasing trend with increasing hardness of the alloys irrespective of the hardness of the erodent particles and the impingement angle. The velocity exp...

Material processing with a high frequency millimeter-wave source

Abstract: A millimeter-wave beam based on a 15-kW, continuous-wave, 83-GHz gyrotron with superconducting magnets system is being investigated for use in material processing. The millimeter-wave beam can be focused to a few millimeters and manipulated quasi-optically and has been used in the following experiments: joining of ceramics (both similar and dissimilar materials), brazing of poled piezoelectric ceramics without significant heating and depoling, and coating of metals and polymers. Joining has been done directly and with reactive brazes. In coating, the beam's short wavelength and absorption depth permit effective ceramic-coating deposition on lower temperature materials, e.g., polymers and metals, without significant substrate heating, and localized deposition of coatings as well. Finally, the millimeter-wave source has been used in the efficient production of nanophase metal and ceramic powders, via a greatly accelerated modified polyol process producing smaller powders of greater uniformity. The results a...

Optimization of Hot Rolled Coil Widths Using a Genetic Algorithm

Abstract: This paper focuses on the assortment problem in the steel industry; with the help of the genetic algorithm, it attempts to determine the optimum width of the parent stock given a set of forecasted customer widths so that the trim loss is minimized. For each given set of forecasted customer widths, an attempt is made to find a single width of the mother coil to be manufactured and kept in stock. In the genetic algorithm, six different selection schemes are considered. A number of test problems are taken up for different selection schemes. Evaluated against the maximum fitness value, the optimal mother coil width, and the generation number at which they are achieved, the elitism selection scheme shows consistently good results in all the test problems compared with the other selection mechanisms.

Effects of Gravitational Orientation on Surface Deformation and Weld Pool Geometry During Gas Tungsten Arc Welding

Abstract: Effects of gravitational orientation on gas tungsten arc (GTA) welding of nickel were studied to determine the impact of free-surface deformation on weld-pool shape. This was accomplished through GTA welding and a numerical study of the welding process. Welding was conducted by varying scan velocity and gravitational orientation, e.g., welding upward opposing gravity (parallel-up weld), welding downward with gravity (parallel-down weld), and welding perpendicular to gravity (perpendicular weld). Slower scan velocity produced more significant free surface deformation. Gravitational orientation caused 21% deeper penetration in the parallel-up weld compared with the parallel-down weld (resulting from 50% or more maximum surface deformation). Weld penetration of the perpendicular weld was between that of parallel-up and parallel-down cases. A model of the welding process, in which an experimentally generated free surface was implemented as a boundary condition, supported the results by showing similar trends.

Influence of Ni Interlayers on the Mechanical Properties of Ti6Al4V/(WC-Co) Friction Welds

Abstract: Ni interlayers were introduced prior to dissimilar friction welding of Ti6Al4V base material to three cemented carbide substrates. The fracture strength of Ti6Al4V/(WC-6 wt% Co) welds were poor and were markedly improved when 20-µm thick Ni interlayers were introduced prior to dissimilar friction welding. These results were only produced when the (WC-6 wt% Co) cermet was electroplated prior to friction welding. When the Ti6Al4V alloy was electroplated prior to friction welding, fractured WC particles and cracking were observed in the (WC-Co) carbide substrate. The fracture strengths of Ti6Al4V/(WC-11 wt% Co) and Ti6Al4V/(WC-24 wt% Co) welds were not improved when 20-µm thick Ni interlayers were introduced prior to friction welding. During mechanical testing, the Ni layer retained at the dissimilar joint interface created a region of weakness.

Multiobjective Robust Design by Genetic Algorithms

Abstract: One key feature of Japanese products is that their design quality is robust—it remains unaffected by the deleterious impact of environmental or other factors often beyond the user's control. As a result, designing and producing such high-quality products have become the challenge for all manufacturers aspiring to be world-class in today's marketplace. This article shows how expressly crafted genetic algorithms can uncover and then exploit the dependency among the key design factors (the choice of materials, parts, configurations, manufacturing methods, etc.) and the final product's performance, to obtain “robust” performance. The methodology presented extends single objective design prototyping procedures called Taguchi methods to multiobjective robust design problems—problems for which no convenient methods presently exist.

Fractal Roughness Structure of Diamond-Turned Copper Mirrors

Abstract: Single-point diamond turning of suitable materials (copper, aluminum, and electroless-plated nickel, etc.) can generate high precision mirrors and aspherical optics rapidly and repeatedly. We have examined the diamond-turned copper mirrors that exhibit a high-frequency periodic feature with an atomic force microscope on various scales. Like other super-smooth surfaces, such as super-ground surfaces, single-point-diamond-turned surfaces may also be identified as a self-affine fractal in the stochastic sense with its correlation length. The exponent for root-mean-square roughness was obtained to be 0.28 for a feed rate of 1.4 μm/rev. With this value, we can predict the roughness value of the single-point-diamond-turned copper mirrors at any scale length, if the scale is within the correlation length, and provided that one such value of a scale is known. The roughness exponent is a very useful parameter, knowledge of which helps to improve the quality of the mirror surface and evaluate its performance in opt...

Surface Topography Analysis When High-Speed Rough Milling Hardened Steel

Abstract: This study is part of a bigger picture on investigating three main cutter path strategies—raster, single-direction raster, and offset—in order to evaluate the feasibility of employing high axial depths of cut (10 mm ≤ A d ≤ 20 mm) when high-speed rough milling hardened AISI H13 hot work tool steel with the aim of achieving high volume of metal removed with short machining time. Here, comparative studies were made of the surface topography maps induced at various axial depths of cut in order to gain an in-depth understanding of their effects on the surface texture obtained via the parametric study of alternative cutter path strategies. Previous work has shown that the use of an offset cutter path strategy when high-speed rough milling hardened steel using an axial depth of 15 mm resulted in the lowest tool life, as compared with the use of raster and single-direction raster strategies.[1]This article also describes a novel approach on improving the offset cutter path strategy by selecting the pro...

Application of Genetic Algorithms to Geometry Optimization of Microclusters: A Comparative Study of Empirical Potential Energy Functions for Silicon

Abstract: Evolutionary computation techniques (in particular, genetic algorithms) have been applied to optimize the structure of microclusters. Various empirical potential energy functions have been used to describe the interactions among the atoms in the clusters. A comparative study of silicon microclusters has been performed.

Synthesis of Hydroxylapatite from Sand Dollar and β-Tricalcium Phosphate by Solid-State Method

Abstract: Synthesis of porous hydroxylapatite from the sand dollar (Mellita eduardobarrosoi sp. nov.) and β-tricalcium phosphate (β-TCP) by solid-state reaction was performed. Reaction conditions were explored at different molar ratios of the precursors and at different temperatures. X-ray diffraction was used to determine the crystalline structure of the sample at molar ratio of 1.25 TCP : 1 sand dollar at 1473 K. The morphology of the product obtained under these conditions is a porous structure, which is a requirement for better clinical application of the hydroxylapatite as a biomaterial. Chemical analysis carried out by energy-dispersive spectroscopy on the product presented a molar ratio of Ca/P closer to the stoichiometric molar ratio of the pure hydroxylapatite. This crystalline structure was analyzed by transmission electron microscopy, and large single hydroxylapatite crystals were observed. Electron diffraction patterns in different directions are discussed.

Optimizing the Hot Isostatic Pressing Process

Abstract: A genetic algorithm (GA) is used to optimize the hot isostatic pressing (HIPing) process for beryllium powder. The GA evaluates a HIPing model with different processing schedules in an effort to minimize temperature, pressure, processing time, ramp rates, grain growth, and distance to target relative density. It is shown that this is a constrained, multiobjective, noisy, optimization problem to which the GA is able to evolve a large number of viable solutions. However, for the GA to work in such a large multidimensional search space, it is suggested that the constraints be treated as objectives and then penalize the Pareto ranking for each constraint violated. This approach is necessary because a large-dimensional objective space naturally results in most members being Pareto rank 1.

Experimental Studies on the Grind-Hardening Effect in Cylindrical Grinding

Abstract: In recent years high-strength and high-temperature alloys are used for structural and other applications. These newer high-performance materials are inherently “more difficult to machine” and also necessitate the need for higher dimensional and geometrical accuracy. Grinding is one of the most familiar and common abrasive machining processes used for the finishing operation. Compared to other machining processes such as turning, milling, etc., the specific energy developed during grinding is very high. At a critical level of specific grinding energy, the temperature rise[1]experienced by the workpiece may be such that thermal damage is induced. Heat damage induced by the grinding process is well documented and may be categorized by temper colors that are at least unsightly and probably indicative of more serious damage, including thermal cracks, tempered zone, etc.,[2]which can lead to catastrophic failure of critical machine parts that shortens the life of products subject to cyclic loading. In this work...

Morphological and Compositional Changes on Sand Dollar Biomaterials Induced by Heat Treatments

Abstract: The microstructural characterization of Mellita Eduardobarrosoisp. Nov, a marine skeleton, subjected to thermal treatments of 400°, 600°, 800°, and 900°C is presented. The results show that this species has pores with diameters ranging between 10 and 20 μm and is constituted mainly of O, Ca, C, and Mg as (Ca, Mg)CO3. This particular compound transforms into CaO when heated higher than 800°C. This change is observed in FTIR spectra as the disappearance of two absorption bands at 875 cm−1and 878 cm−1, which correspond to loss of CO2.

Synthesis and Magnetic Properties of Ni-Zirconia Composites

Abstract: A novel method has been developed for the fabrication of composite magnetic films on various conductive substrates. Cathodic electrolytic deposition was used as the technique to obtain thin films from solutions of nickel and zirconium salts. The hydroxide deposits were converted to Ni-ZrO2composites after sintering in reducing conditions. Deposit yield was studied in the constant current deposition mode. Deposits were evaluated using X-ray analysis and magnetic measurements. Results of dc and ac measurements performed in different magnetic fields, temperatures, and frequencies demonstrated the magnetic properties of the composites.

Dielectric Relaxation in Glassy Se75Te20Ag5

Abstract: Frequency and temperature dependences of dielectric constant (ϵ′) are studied in glassy Se75Te20Ag5in the frequency range (400 Hz–10 kHz) and in the temperature range 291°K to 327°K. The results indicate that the dielectric dispersion exists in the above frequency and temperature range. The dielectric loss (ϵ″) and loss angle (tan δ) have been calculated from the measured values of the real part of dielectric constant (ϵ′) using Gevers' formula. Cole–Cole diagrams have been used to determine the distribution parameter (α) and the relaxation time (τ). The temperature dependence of α and τ indicate that the dielectric losses are dipolar in nature in the present material.