Defect Avoidance Research Articles

Improvement of axial forging process for spline shaft by die design

As an effective method of forming spline shaft, the axial cold forging process is appropriate for long shaft and exhibits high efficiency. The two defects of folds and accumulation were found to result in large forming force and low quality of products in the experiments. To analyse the cause the defects, a finite element model was built with a strain rate-dependent material model, in which the parameters were determined by material test. Metal flow was divided into three different parts, and relevant parameters were proposed to quantify them. An assembling method of three dies and a new die with a variable tooth shape were designed by the fast simulated annealing optimization method using the quantification parameters to improve metal flow and decrease forming force. The differences in metal flow, tooth profile and axial force were compared amongst conventional axial forging, the assembling dies and the new die. The assembling method of three dies decreased the force by 31.2% compared with the conventional axial forging. However, fold defects were significant which might lead to stress concentration. On the basis of the optimisation of the assembling method, the die with a variable tooth shape decreased the load by 55% compared with the conventional axial forging. The shape quality of the product formed by the new die with a variable tooth width was also improved owing to the avoidance of defects.

Density Variations during Solidification of Grey Cast Iron

As part of moving towards a sustainable production of diesel engines for heavy vehicle applications, the ability to predict casting defects has become ever so important. In order to model the solidification process for cast components correctly, it is of essence to know how the material will actually behave. To produce sound castings, often of complex geometry, the industry relies on various simulation software for the prediction and avoidance of defects. Thermophysical properties, such as density, play an important part in these simulations.Previous measurements of how the volume of liquid grey iron changes with temperature has been made with a conventional dilatometer. Measurements have also been made in the austenitic range, then on iron-carbon-silicon alloys with a carbon content lower than 1.5 wt%. Based on these measurements the density variations during solidification were calculated. The scope for this paper is to model the volume changes during solidification with the control volume finite difference method, using data from the density measurements.

Toward defect-free fabrication of extreme ultraviolet photomasks

Defect-free fabrication of extreme ultraviolet (EUV) masks relies on the appropriate detection of native defects and subsequent strategies for their elimination. Commercial unavailability of actinic mask-blank inspection systems motivates the identification of an optical inspection methodology most suitable for finding relevant EUV blank defects. Studies showed that 193-nm wavelength inspection found the greatest number of printable defects as compared with rival higher-wavelength systems, establishing deep ultraviolet inspections as the blank defectivity baseline for subsequent mitigation strategies. Next, defect avoidance via pattern shifting was explored using representative 7-nm node metal/contact layer designs and 193-nm mask-blank inspection results. It was found that a significant percentage of native defects could be avoided only when the design was limited to active patterns (i.e., layouts without dummy fill). Total pattern-defect overlap remained ≤5 when metal layer blanks were chosen from the top 35% least defective substrates, while the majority of blanks remained suitable for contacts layers due to a lower active pattern density. Finally, nanomachining was used to address remaining native/multilayer defects. Native catastrophic defects were shown to recover 40% to 70% of target critical dimension after nanomachining, demonstrating the enormous potential for compensating multilayer defects.

Assimilation of New Steel Alloying Composition for Manufacturing Line Pipes of Strength Classes K52–K55

The contemporary level of pipe rolling technology makes it possible to manufacture line pipes of strength class K42–K65 in corrosion- and cold-resistant versions. Pipes of this type are intended for building oil and gas pipelines that are used for developing fields, including those in the Far North. Avoidance of the main defects of both steel smelting and pipe rolling origin, revealed during pipe piercing and rolling, is an important problem for metallurgists in both domestic and overseas pipe plants. A reduction in scrap of metallurgical origin is facilitated by the use of advanced steel smelting technology in electric-arc furnaces followed by extra-furnace treatment and continuous billet casting. Steel 06GBA has been developed with the aim of improving pipe outer surface quality as a result of reducing carbon content and adding niobium. Replacement of steel grade 10GFBYu by steel 06GBA makes it possible to improve the output of finished pipes considerably.

Editorial

Editorial

Comprehensive defect avoidance framework for mitigating extreme ultraviolet mask defects

Defect avoidance methods are likely to play a key role in overcoming the challenge of mask blank defectivity in extreme ultraviolet (EUV) lithography. In this work, we propose an innovative EUV mask defect avoidance method. It is the first approach that allows exploring all the degrees of freedom available for defect avoidance (pattern shift, rotation and mask floorplanning). We model the defect avoidance problem as a global, nonconvex optimization problem and then solve it using a combination of random walk and gradient descent. For a 8-nm polysilicon layer of an ARM Cortex M0 layout, our method achieves a 60% point better mask yield compared to prior art in defect avoidance for a 40-defect mask. We show that pattern shift is the most significant degree of freedom for improving mask yield. Rotation and mask floorplanning can also help improve mask yield to a certain extent.

Analysis and avoidance of flow-induced defects in meso-forming process: simulation and experiment

In the current metal-forming industries, productivity, product quality, and production cost are three overriding issues. Product quality, however, is the most critical issue and the designed forming process must be able to produce the quality parts with desirable geometries and without defects. In micro- and meso-forming processes, the formation mechanism of flow-induced defects has not yet been fully investigated. In this paper, the flow-induced defects in meso-forming of a designed part are investigated and the defect formation mechanisms are explored and revealed via the finite element simulation of the entire process. To develop a defect-free forming process, a feature-based method for defect-free process design is proposed to identify the best forming sequence/process for defect-free deformation. By employing the proposed method, two meso-forming processes, viz., four steps extrusion and backward extrusion, are proposed to fabricate the designed part without folding defects. The applicability of the meso-forming processes for defect avoidance is verified by numerical simulation and physical experiment. The experiments also corroborate the findings of finite element simulations. On the other hand, the proposed feature-based method is further verified by the effectiveness of the generated two meso-forming processes for their efficiency in forming of the meso-scaled part without the flow-induced defects.

Defect Prevention Based on 5 Dimensions of Defect Origin

“Discovering the unexpected is more important than confirming the known [7]. In software development, the “unexpected” one relates to defects. These defects when unattended would cause failure to the product and risk to the users. The increasing dependency of society on software and the crucial consequences that a failure can cause requires the need to find out the defects at the origin itself. Based on the lessons learnt from the earlier set of projects, a defect framework highlighting the 5 Dimensions (Ds) of defect origin is proposed in this work. The defect framework is based on analyzing the defects that had emerged from various stages of software development like Requirements, Design, Coding, Testing and T imeline (defects due to lack of time during development). This study is not limited to just identifying the origin of defects at various phases of software development but also finds out the reasons for such defects, and defect preventive (DP) measures areproposed for each type of defect. This work can help practitioners choose effective defect avoidance measures. In addition to arriving at defect framework, this work also proposes a defect injection metric based on severity of the defect rather than justdefect count, which gives the number of adjusted defects produced by a project at various phases. The defect injection metric value, once calculated, serves as a yardstick to make a comparison in the improvements made in the software process development b etween similar set of projects.

Controlling the Abruptness of Axial Heterojunctions in III–V Nanowires: Beyond the Reservoir Effect

Heterostructure nanowires have many potential applications due to the avoidance of interface defects by lateral strain relaxation. However, most heterostructure semiconductor nanowires suffer from persistent interface compositional grading, normally attributed to the dissolution of growth species in the common alloy seed particles. Although progress has been made for some material systems, most binary material combinations remain problematic due to the interaction of growth species in the alloy. In this work we investigate the formation of interfaces in InAs-GaAs heterostructures experimentally and theoretically and demonstrate a technique to attain substantially sharper interfaces. We show that by pulsing the Ga source during heterojunction formation, In is pushed out before GaAs growth initiates, greatly reducing In carry-over. This procedure will be directly applicable to any nanowire system with finite nonideal solubility of growth species in the alloy seed particle and greatly improve the applicability of these structures in future devices.

Modelling of the Effect of Process Parameters on Tensile Strength of Friction Stir Welded Aluminium Alloy Joints

Friction stir welding (FSW) process is a promising solid-state joining process with the potential to join low-melting point material, particularly, aluminium alloy. The most attractive reason for joining aluminium alloy with this process is the avoidance of the solidification defects formed by conventional fusion welding processes. In this article, an attempt has been made to develop an empirical relationship between FSW variables and tensile strength. Central composite rotatable design was used by considering four factor and five levels, which enables to quantify the direct and interactive effect of four numeric factors, that is, tool rotational speed, welding speed, axial force, and tapered pin diameter on the tensile strength. The developed relationship is useful for prediction of tensile strength in friction stir welded AA6082 aluminium alloy joints at 95% confidence level. It will also be helpful for selection of process variable to obtain desired strength of the joint. Furthermore, the optimized capabilities in design-expert software were used to numerically optimize the input parameters. At the optimal parameters, three experiments were conducted to compare the predicted value of tensile strength with the experimental value.

Epitaxial Wafer Equivalent Solar Cells with Overgrown SiO2 Reflector

Crystalline silicon thin film solar cells, based on the epitaxial wafer equivalent, require a reflecting interlayer between substrate and active layers to increase the generated current and reach similar efficiencies as wafer based solar cells. With the epitaxial lateral overgrowth technique, a reflecting dielectric layer can be implemented. In this paper results of solar cells with overgrown, patterned SiO2 films are shown. A beneficial optical effect due to the interlayer and also a reduced effective diffusion length within the epitaxially grown silicon layer are observed. Cells with reflecting interlayer and non-optimized absorber layer thicknesses therefore exhibit lower efficiencies than cells without SiO2. Slightly higher currents are observed with textured front sides. Significantly increased effective diffusion lengths and cell performances can be reached with non-merged active silicon layers. Reasons might be the avoidance of defects generated at merging points and of unpassivated surface areas in voids remaining where two growth fronts merge.

Defect Prevention Based on 5 Dimensions of Defect Origin

“Discovering the unexpected is more important than confirming the known. In software development, the “unexpected” one relates to defects. These defects when unattended would cause failure to the product and risk to the users. The increasing dependency of society on software and the crucial consequences that a failure can cause requires the need to find out the defects at the origin itself. Based on the lessons learnt from the earlier set of projects, a defect framework highlighting the 5 Dimensions (Ds) of defect origin is proposed in this work. The defect framework is based on analyzing the defects that had emerged from various stages of software development like Requirements, Design, Coding, Testing and Timeline (defects due to lack of time during development). This study is not limited to just identifying the origin of defects at various phases of software development but also finds out the reasons for such defects, and defect preventive (DP) measures are proposed for each type of defect. This work can help practitioners choose effective defect avoidance measures.

Effect of Process Parameters on Microstructure and Mechanical Properties in Friction Stir Welding of Aluminum Alloy

Friction stir welding process is a promising solid state joining process with the potential to join low melting point materials, particularly aluminum alloys. The most attractive reason for this is the avoidance of solidification defects formed during conventional fusion welding processes. Tool rotational speed and the welding speed play a major role in deciding the weld quality. In the present work an effort has been made to study the effect of the tool rotational speed and welding speed on mechanical and metallurgical properties of friction stir welded joints of aluminum alloy AA6082-T651. The micro hardness profiles obtained on welded zone indicate uniform distribution of grains in the stir zone. The maximum tensile strength obtained is 263 MPa which is about 85% of that of base metal. Scanning electron microscope was used to show the fractured surfaces of tensile tested specimens.

Record Large-Area p-Type CZ Production Cell Efficiency of 19.3% Based on LDSE Technology

A record independently confirmed production cell efficiency of 19.3% is presented for a large-area p-type Czochralski (CZ) silicon solar cell, based on the University of New South Wales (UNSW) laser-doped selective emitter technology. In this paper, the innovative and patented laser-doping technology is simply added to a standard Centrotherm turnkey line, operating with a modified process and the addition of the laser-doping and light-induced plating steps. Impressively, this record efficiency is achieved by using standard commercial grade p-type CZ-grown silicon wafers on standard production equipment and exceeds the previous independently confirmed record for any technology of 19.2% using a standard aluminum back-surface field with full rear coverage. The avoidance of laser-induced defects is discussed in this paper to overcome previous limitations of the laser-doping technology using conventional Q-switched lasers or the laser chemical processing method. It is demonstrated that the use of appropriate lasers can avoid defect formation through thermal cycling while still allowing for the sufficient mixing of dopants and allow laser doping to be performed through a standard SiN layer with contacts formed through a self-aligning metallization scheme.

FE Simulation-Based Folding Defect Prediction and Avoidance in Forging of Axially Symmetrical Flanged Components

In the traditional metal forming product development paradigm, product design is generally based on heuristic know-how and experience, which are basically acquired through many years of practice. This kind of product design paradigm is of more trial-and-error than in-depth scientific calculation and analysis. Product defect prediction and quality assurance is, thus, a nontrivial issue in this product development paradigm. With the aid of finite element (FE) simulation, deformation-related defects can be predicted and analyzed. In this paper, flow-induced folding defect in forging of axially symmetrical flanged components is systematically investigated. A FE model to study the root-cause of the defect based on the material flow behavior is developed and a defect formation mechanism is revealed. The variation of material flow behavior with the changes of part geometry parameters is investigated extensively. Based on the simulation results, the parameter variation characteristics and the sensitivity of each parameter to folding defect avoidance are identified. Using industrial components as case studies, the efficiency of the proposed defect avoidance approach is verified. The approach is further proven to be able to provide practical guidelines for the design of defect-free axially symmetrical flanged components.

Characterization of electron beam welded AA2024

For aerospace manufacturing, the perseverance for improving performance (high strength to density ratio) and reducing weight and costs has motivated consideration of welding techniques applicable to aluminum alloys. During fusion welding of aluminum alloy (AA) 2024, the avoidance of defects (e.g., porosity, oxides, solidification cracking, undercutting) and the optimization of the microstructure-property characteristics are of critical concern. In this work, AA2024 was electron beam (EB) welded as part of a study to determine the influence of parametric conditions on the characteristics of the weldment to optimize the joining process. Specifically, the evolution in the weld geometry, microstructure and mechanical properties was examined as a function of the process conditions, including beam current, beam focus, beam oscillation, and welding speed. For optimized parametric conditions, microstructural examination of the joints revealed narrow fusion and heat-affected zones comprising of dendritic structures without the occurrence of defects that enabled a maximized joint efficiency.

Editorial: software defect detection

The most difficult aspect of producing software is getting it right. Defects plague all software projects and enormous expense and time go into ridding code of the worst of them. Consequently, the ASE Community has devoted much attention to the problem of software defect avoidance. This effort can be broken down into defect prevention and defect detection (and removal). − The defect prevention school of research includes both advanced requirements engineering (RE) methods and software synthesis. In RE, the focus is to avoid defects derived from misunderstanding what the program is supposed to do in the first place. In synthesis sophisticated tools derive code from high level specification models, with the assumptions being both that the specs are so high level and transparent as to be easy for domain experts to get right, and that the tools’ derivations are validated once and for all, leading to code that is correct by construction. − The detection & removal school of research starts by assuming that code is produced using existing state-of-the-practice techniques and then sophisticated tools are brought to bear on these artifacts to detect defects that may have arisen during design and coding. Once detected, the defects can be removed either manually or with the help of additional bug localization and diagnosis tools.

Simulation-enabled study of folding defect formation and avoidance in axisymmetrical flanged components

In metal forming industries, product quality, product cost and time-to-market are three overriding issues. Among these issues, product quality is the most critical one. Defect is one of the key quality issues in forming processes. Defect formation can be caused by irrational material flow and unreasonable stress and temperature distribution in billet and tooling. In forging of axisymmetrical flanged parts, folding is a common flow-induced defect. In this study, the mechanisms of folding defect formation and avoidance in forging of axisymmetrical flanged parts are systematically studied via FEM simulation. Based on the simulated material flow behavior, the defect formation mechanism is revealed and an avoidance mechanism through the dynamic change of tooling geometry is proposed. The mechanism is realized by implementation of a sliding insert in die structure to control material flow and further to avoid the formation of folding defect. In addition, the effects of the initial insert position, frictional factor and the spring stiffness of the moving die module on the material flow behavior and deformation load are investigated. Based on the simulation results of the developed FEM models, a systematic design framework to predict and avoid folding defect via CAE simulation is proposed. Through an industrial case study, the findings and the proposed defect avoidance mechanism are finally verified.

Influence of tempering and fat crystallization behaviours on microstructural and melting properties in dark chocolate systems

Abstract Particle size distribution (PSD) and temper influences on dark chocolate fat crystallization were studied using differential scanning calorimetry (DSC) and microscopy to establish relationships with their melting properties and microstructure. Variations in PSD had no influence on crystallinity of products at all temper regimes. Particle size (PS) increases had limited effects on Tonset, Tpeak, and ΔHmelt independent of temper regime but significant decreases in Tend and Tindex were noted. Contrary, varying temper regime influenced the crystallinity and melting properties (Tend, Tindex and ΔHmelt) of products. Under-tempered chocolate showed widened crystal size distribution (CSD) with significant changes in Tend, Tindex and ΔHmelt of products. Over-tempering caused moderate increases in CSD and melting properties, with significant effect on Tend, Tindex and ΔHmelt but no changes were noted in Tonset, Tpeak of products. Fat–sugar melting profiles showed similar levels in all products independent of temper regime, suggesting fat and sugar components are present in similar amounts in under-, over- and optimally-tempered products. Micrographs revealed clear crystalline network structure and well defined inter-crystal networks among tempered and over-tempered samples. Under-tempered products showed re-arrangement and re-crystallization of unstable fat crystals to smaller numbers of larger agglomerates with formation of solid bridges between the crystalline network structures. Attainment of optimal temper regime during pre-crystallization of dark chocolate is necessary for the achievement of premium quality products and avoidance of defects in structure and melting character.

SCT

Novel strategies are necessary to efficiently test and configure emerging reconfigurable nanoscale devices, in addition to providing defect tolerance. This is mainly due to the high defect densities that are expected for these devices. Among different approaches, reconfiguration-based defect avoidance has proven to be a practical solution. However, configuration time, test time, and defect-map size remain among the major challenges for these new devices. In this article, we propose a new approach (called SCT) that simultaneously performs test and configuration. The proposed method uses a built-in self-test (BIST) scheme for test and defect tolerance. The method is based on testing reconfigurable nanoblocks at the time of implementing a function of a desired application on that block. The SCT method considerably reduces the total test and configuration time. It also eliminates the need for storing the location of defects in a defect map on- or off-chip. The presented probabilistic analysis results show the effectiveness of this method in terms of test and configuration time for architectures with rich interconnect resources. Also, a Verilog simulation model is developed for crossbar-based nano-architectures. This model is used to implement several MCNC benchmarks based on the proposed SCT method. The simulation results demonstrate efficiency of the method in terms of test time and yield under different defect rates.