Simulation studies of improved die manufacturing techniques

In the production of an extrusion die, the step which consists of drilling thousands of holes into a steel hlank is extremely expensive. Several potential improvements for this drilling process have been proposed. This paper will attempt to evaluate the benefits of each proposed strategy using simulation. Substantial post-analysis of the simulation data is discussed to develop further potential improvements in the production process.     

Applying manufacturing batch techniques to fraud detection with incomplete customer information

Fraud detection is an important issue in service industries. Its technical challenges include the existence of complex patterns, its multivariate nature, and the incompleteness of records. As similar problems are observed in batch manufacturing process analysis, existing batch manufacturing techniques can be adapted and mapped to the fraud detection problem in the service sector. In particular, the batch library method can be modified to incorporate new information into incomplete customer records for analysis, while controlling the overall type I error rate. A real case is used to demonstrate the effectiveness of this approach, and simulation results are presented to show that the proposed approach consistently outperforms existing approaches.     

The effect of void size and distribution on ductile fracture

The ductility of materials with different distributions of voids is examined theoretically. The theory of Thomason [7] is used which assumes that the material deforms homogeneously until localized deformation between the voids intervenes. The fracture is expected to occur so rapidly after the onset of localized deformation that the transition from homogeneous to inhomogeneous deformation is used as a criterion for ductility. Upper bound solutions are used to derive a criterion for the fracture strain.Void size distributions with equal numbers of voids of two sizes are examined. It is also investigated how a distribution of inter void distances influences the ductility. The importance of small secondary voids in a distribution of large primary voids is studied. The effect of the shape of the voids is also considered. In all cases analytical expressions are derived for the fracture strain. The void distributions are centered on a plane orthogonal to the tensile axis and all voids are of rectangular shape.

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Résumé On examine sur le plant théorique la ductilité de matériaux présentant différentes distributions de cavités. On recours à la théorie de Thomason, qui suppose qu'un matériau se déforme de manière homogène jusqu'à ce que suive une déformation locale entre deux cavités. Le processus de rupture doit se produire tellement vite après l'apparition de cette déformation locale, que la transition entre déformation homogène et déformation hétérogène sert de critère de ductilité. L'enveloppe supérieure des solutions obtenues permet de déduire un critère de dilatation de rupture.On examine des distributions des dimensions de cavités où se présentent, en nombre égal, des cavités de deux dimensions. On étudie également comment une distribution donnée de ligaments entre deux cavités influence la valeur de la ductilité et quelle est l'importance de petits trous secondaires dans une distribution de cavités primaires d'une certaine taille. L'effet de la forme des cavités est également analysé. Dans tous les cas envisagés, des expressions analytiques sont données pour la dilatation de rupture. Les distributions des cavités sont toutes concentrées sur un plant orthogonal à l'axe de la mise en charge, et les cavités sont supposées être de forme rectangulaire.

     

Moments-based clustering techniques for manufacturing cell formation

Clustering and data organization algorithms and array sorting methods are most widely used in solving machine-part grouping problems in Group Technology (GT). One of the most recent search algorithms for part-family identification is the close-neighbour search algorithm. However the method does not suggest a solution that tries to eliminate exceptional elements after the block diagonal structure is produced. This paper presents a Method of Moments approach such as Weighted Moment, End Load Ratio and Differential Moment Methods to solve this problem. The effectiveness of these algorithms is tested against sixteen problems from the literature. The results show that the algorithms are very efficient and reliable.     

Application of additive manufacturing techniques in sports footwear

Additive manufacturing (AM) enables faster prototype development for design visualisation, performance studies and personalisation in the sports footwear industry. Among the available AM techniques, stereolithography (SLA), PolyJet (PJ), selective laser sintering (SLS) and three-dimensional printing (3DP) have been used for sports footwear prototyping. A five-point scoring system was used to rate the performance of AM techniques in four important characteristics namely accuracy, surface finish, range of materials supported and building time. Key elements of AM-based footwear personalisation and customisation methodology were also discussed.     

Lexicographic fuzzy multi-objective model for minimisation of exceptional and void elements in manufacturing cell formation

This research proposes a lexicographic fuzzy multi-objective model based on perfect grouping for concurrent solving the part-family and machine-cell formation problems in a cellular manufacturing system. New simplified mathematical expressions of exceptional and void elements are proposed, opposing conventional quadratic and absolute functions. The main objectives of the proposed solution model, that is, the minimisation of both the number of exceptional elements and the number of void elements is defined by fuzzy goals as pre-emptive ordering. A lexicographic fuzzy goal model is developed to enhance cell performance and machine utilisation simultaneously. A satisfactory efficient solution can easily be obtained, and alternative solutions can also be generated by capturing flexibility of the proposed fuzzy multi-objective programming model. The formulated model can be solved by existing integer programming solvers. Finally, the evaluation of cell formation problems is briefly discussed to show the performance of the proposed model.     

Additive manufacturing techniques for scaffold-based cartilage tissue engineering

Articular cartilage damage is of great concern as it creates chronic pain and reduction of joint movement, leading to osteoarthritis. In current treatments, the resulting healing tissues lack structural organisation of cartilage and consequently have inferior mechanical properties when compared to native cartilage, therefore being prone to failure. Tissue engineering has long worked on cartilage regeneration and several requirements have been identified for the engineered structures to meet the desired function, by combining biodegradable and biocompatible materials, cells and growth factors, aiming at the production of biological structures closely resembling the native tissue. Within the scaffold based techniques for cartilage tissue production, conventional methods have shown limitations, especially regarding the control over the micro-structure and repeatability of the produced constructs. Therefore, additive manufacturing techniques grew popular, allowing for a high level of control over the internal scaffold architecture and external shape of the construct, as well as guaranteeing its reproducibility.     

网络化制造系统联邦集成的关键技术

联邦集成架构(FIA)是异构网络化制造系统集成的新方法.本文按照FIA接口规范,实现了FIA中的联邦执行支撑环境(FEI).对系统的关键技术--分布自治结构的联邦管理技术、支持跨系统任务协作的访问控制与授信技术、跨系统的分布式共享资源调度技术、服务搜索与匹配技术等进行了研究,并给出了相应的解决方案.该联邦集成系统已在北京网络化制造系统集成中得到了实际应用.应用结果表明,联邦模式的集成方案是一种适用于构建大规模服务共享的集成模式,能够适应网络化制造服务异构及运营目标多样化的应用环境.     

Overview of non-destructive evaluation techniques for metal-based additive manufacturing

Three-dimensional printing/digital or additive manufacturing is an area that is taking off with considerable rapidity and magnitude. In the same time, non-destructive evaluation (NDE) is playing an important role in the acceptance of additively manufactured parts, in order to provide the required confidence in the quality of the part and its expected safety and performance while in service. This article represents a summary addressing the subject of applicable NDE techniques to detect manufacturing anomalies and service-induced flaws. The topic is relatively new, attracting much research attention and funding, while in the meantime manufacturing processes are continuously improving. The number of publications covering additive manufacturing is increasing exponentially, and everyday new articles, conferences, and workshops are bringing out new information.     

Diffusion behavior at void tip and its contributions to void shrinkage during solid-state bonding

Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via experiments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to examine the interface characteristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.     

Antireflective subwavelength structures on microlens arrays-comparison of various manufacturing techniques

Antireflective subwavelength structures (ARS) resembling nanostructures found on the cornea of night-active insects reduce the reflection of light by providing a gradual change in the refractive index at the interface. These artificial ARS have mainly been fabricated by a combination of conventional lithography and reactive ion etching, which constrains their application to planar substrates. We report on the fabrication of ARS using three different techniques including bottom-up and top-down methods as well as their combination on microlens arrays (MLAs) made of fused silica. The optical performance of the resulting ARS on the MLAs is as good as ARS fabricated on planar substrates with increased transmission of up to 96% at certain wavelengths.     

Mechanics of void growth and void collapse in crystals

The mechanics of void deformation in single crystals is studied in a fully three-dimensional setting, taking into account all twelve slip systems for fcc and bcc crystals. The increments of the local field variables are calculated analytically using Eshelby's approach for the three-dimensional inclusion problem. The collapse or growth of voids in three dimensions is investigated when a rate-dependent elastoplastic material is subjected to compression and tension at a high rate. The deformation of an initially spherical cavity is calculated incrementally, and, it is shown that, even under all-around uniform loading, a void deforms into a complicated shape which is defined by the structure and symmetry of the slip systems. An equivalent ellipsoid is used to approximate the deformed void shape at each incremental step, and the procedure is continued until the equivalent ellipsoid collapses into a crack or a needle, or it expands or shrinks in a self-similar manner. Several numerical examples are presented, and the numerical results are compared with the experimental observations, obtaining good correlation. The significant effects of loading rate on the material response are illustrated. It is shown that the material becomes stronger at higher loading rates. The three-dimensional final void geometry under various loading conditions is studied. The difference between void deformation mechanism under tension and compression is illustrated. The possible overall failure mechanism caused by collapse and/or growth of pre-existing cavities is discussed. From the comparison of the corresponding results with those of the two-dimensional case it is shown that the double-slip system in two dimensions can be used effectively to simulate the three-dimensional problem.     

Numerical simulations of the void distribution characteristics of crushed rock masses in mine gobs

The internal stress levels of the crushed rock masses will change the movement states of the rock masses in the gob, and then affect the void distributions of crushed rock mass, and finally change the flow of gas in the gob. In this study, under the Lagrange framework, based on a discrete element method and a Hertz-Mindlin contact model, self-programming was used to simulate the compaction processes of a rock mass in mining gobs. The compression amounts were set as 0%, 5%, 10%, 15%, 20%, and 25%, respectively. The effects on the void distributions of the crushed rock masses of the internal stress levels of the crushed rock masses under the external load conditions were examined by changing the motion state of the rock blocks within in the gobs. The results showed that during the compression processes, the external loads could not be uniformly transmitted from the top of the crushed rock masses to the lower sections. Therefore the stress levels in the upper sections of the crashed rock masses were significantly higher than those of the lower sections. In addition, due to the rock blocks in the upper section of the crushed rock masses experiencing higher degrees of interference from the external forces, the sliding speeds of the upper rock blocks were also larger. At the same time, the rock blocks in the upper sections of the crushed rock masses tended to slide downward down longer. The migration of the rock blocks caused the upper rock blocks to become densely packed, and the coordination numbers of the rock blocks were large. However, the lower rock blocks were loosely distributed, and the coordination numbers of the rock blocks were small. This resulted in the void ratios in the lower sections of the crushed rock masses being higher than the void ratios in other layers of the crushed rock masses, with the void ratios of the lower sections of the rock masses determined to be 1.1–1.4 times that of the upper sections.     

Flow modeling of the VARTM process including progressive saturation effects

Modeling of vacuum based liquid composite molding methods (e.g., VARTM) relies on good understanding of closely coupled phenomena. The resin flow depends on the preform permeability, which in turn depends on the local fluid pressure; the preform compaction behavior, and the membrane stresses in the vacuum bag. It has also been shown that for many preforms there is a significant unsaturated region behind the flow front, and that the flow in this region affects the overall flow behavior of the process. Studies of preform compaction have shown that the preform stiffness, as well as being non-linear and exhibiting significant hysteresis, is dependant on the fluid saturation. For this reason most researchers model the preform compaction based on the pressure-compaction behavior of saturated preforms during unloading. This assumption leads to an effective discontinuity in preform thickness at the flow front, which is not observed in actual experiments. In this paper an improved compaction model incorporating the saturation dependence of the compaction pressure in the partially saturated region, is used in a one-dimensional model of the VARTM process. The model gives physically more realistic results for the thickness in the flow front region, and an improved model for the consolidation of the preform at the end of infusion.     

Effect of curing cycle on void distribution and interlaminar shear strength in polymer-matrix composites

The effect of temperature cycle on the void volume fraction, shape and spatial distribution was determined by means of X-ray microtomography in [0]₁₀ AS4/8552 composite laminates manufactured by compression molding. Cure temperatures were designed to obtain different processing windows while the overall degree of cure was equivalent, leading to laminates with average porosities in the range 0.4% and 2.9%. Regardless of the final porosity, voids were elongated, oriented parallel to the fibers and concentrated in channels along the width of the laminate as a result of the inhomogeneous process of consolidation and resin flow along the fibers. The interlaminar shear strength was found to be controlled by the void volume fraction in panels with porosity above 1%.     

A comparison of three array-based clustering techniques for manufacturing cell formation

This paper examines three array-based clustering algorithms—rank order clustering (ROC), direct clustering analysis (DCA), and bond energy analysis (BEA)—for manufacturing cell formation. According to our test, bond energy analysis outperforms the other two methods, regardless of which measure or data set is used. If exceptional elements exist in the data set, the BEA algorithm also produces better results than the other two methods without any additional processing. The BEA can compete with other more complicated methods that have appeared in the literature.     

A statistical analysis of void size distribution in a simulated narrowly graded packing of spheres

The void microstructure of a simulated packing of polydisperse spheres has been investigated by means of a radical Delaunay tessellation. We have focused on creating sphere packings by mimicking processes involved in the construction of embankment dams: the polydisperse spheres are collectively released under gravity and denser states are mainly obtained by means of shearing cycles. This study has been performed on a narrowly graded material for four porosities ranging from 0.42 to 0.36. The void structure is quantified in terms of probability density functions of pore and constriction sizes, cumulative distributions and connectivity functions. We emphasize the implications of the sample construction technique on the geometric packing arrangements, among them a well disordered medium where tetrahedra remain the most represented unit void structure. We point out that when porosity decreases, void distributions become narrower but the initial structure is never destroyed. Nevertheless, the densification modifies significantly the computed mean void quantities. In this study, usual geometric arrangements obtained for very dense materials are not encountered.     

Experimental Study of Thickness Gradient Formation in the VARTM Process

Although the vacuum assisted resin transfer molding (VARTM) process has been the focus of much attention in the past several years, it is only recently that research tools have been developed to investigate fundamental process mechanisms associated with it. One area of concern for composites manufacturers is the ability to maintain dimensional tolerances throughout the process cycle. It has been well known that a thickness gradient forms during VARTM, leading to corresponding gradients in fiber volume fraction and the associated mechanical properties. In this work, the formation of these thickness gradients is investigated using an array of linear variable differential transformers (LVDTs) to monitor surface displacements during infusion. SMARTweave sensors are used to correlate resin flow with the surface displacements for infusions, using either a line resin source or point resin source. Software is used to display the surface displacements as a three-dimensional plot so that the entire part surface may be visualized during infusion.     

Correlation between manufacturing conditions and properties of carbon fibre reinforced Mg

Abstract

Continuous carbon fibre preforms (M40), with an average fibre content of 66 vol.-%, were infiltrated with liquid Mg by gas pressure at various temperatures and pressures in order to determine a relationship between manufacturing conditions and the mechanical properties of the material. A saturation curve describes the infiltration behaviour of liquid Mg into the preforms and the relationship between infiltration pressure, pore volume, and mechanical properties. The maximum bending strength of the composites exceeds 1400 MPa and is insensitive to melt temperature between 680 and 720°C. The density of the Mg composite is 1.77 Mg m^-3, 20% lighter than the Al–C composites produced and tested by the authors in an earlier investigation, but yields the same mechanical properties in bending tests at room temperature.