Search

A closed-loop supply chain network involves the manufactured and remanufactured homogeneous products. It comprises operation links to represent business activities including manufacturing/ remanufacturing activities, treatment activities for EOL products, transportation activities, and storage activities, which are performed by the firms. Among all closed-loop supply chain problems, the horizontal merger of oligopolistic firms is so important and attracting to both businessman and researchers. In this paper, the interaction of the competitive firms prior to horizontal merger is analyzed. Three networks including prior to horizontal merger, postpartial merger, and complete merger are studied. Simultaneously, three economical models for these networks on different conditions of mergers are established and discussed. The variational inequality formulations are used for these three models, whose solutions give out the production quantity of new products, and remanufactured products, the product flows for new products, remanufactured products and end-of-life products at every path, the demand quantity, the recovery quantity of end-of-life products and the equilibrium prices. Finally, numerical examples are tested and illustrated for the proposed models. [ABSTRACT FROM AUTHOR]

Single point incremental forming (SPIF) is plagued by an unavoidable and unintended bending in the region of the sheet between the current tool position and the fixture. The effect is a deformation of the region of the sheet in between the formed area and the fixture as well as deformation of the already formed portion of the wall, leading to significant geometric inaccuracy in SPIF. Double sided incremental forming (DSIF) uses two tools, one on each side of the sheet to form the sheet into the desired shape. This work explores the capabilities of DSIF in terms of improving the geometric accuracy as compared to SPIF by using a novel toolpath strategy in which the sheet is locally squeezed between the two tools. Experiments and simulations are performed to show that this strategy can improve the geometric accuracy of the component significantly by causing the deformation to be stabilized into a local region around the contact point of the forming tool. At the same time an examination of the forming forces indicates that after a certain amount of deformation by using this strategy a loss of contact occurs between the bottom tool and the sheet. The effects of this loss of contact of the bottom tool on the geometric accuracy and potential strategies, in order to avoid this loss of contact, are also discussed. [ABSTRACT FROM AUTHOR]

It is widely accepted that variations in manufacturing processes are inevitable and should be taken into account during analysis and design processes. However, estimating uncertainty propagation in an end-product caused by these variations is a very challenging task, especially when a computationally expensive effort is already needed in deterministic models, such as simulations of sheet metal forming. The focus of this article is on the variance estimation of a system response using sensitivity-based methods. A weighted three-point-based strategy for efficiently and effectively estimating the variance of a system response is proposed. Three first-order derivatives of each variable are used to describe the non-linear behaviour and estimate the variance of a system. A methodology for determining the optimal locations and weights of the three points along each axis is proposed and illustrated for the cases where each variable follows either a normal distribution or a uniform distribution. An extension of the weighted three-point-based strategy is introduced to take into account the interaction between parameters. In addition, an extension is given for mean estimation of the system response without requiring more data. The considerable improvement in accuracy compared with the traditional first-order approximation is demonstrated in a number of test problems. The proposed method requires significantly less computational effort than the Monte Carlo method. [ABSTRACT FROM AUTHOR]

Microforming using a small machine (or so-called desktop machine) is an alternative new approach to those using full-size heavy equipment for manufacturing microparts. Microparts are commonly defined as parts or structures with at least two dimensions in the submillimeter range, which are used extensively in electronics and micromechanical products. However; when scaling down a conventional forming process to microscale, the influence of the so-called size effect needs to be considered. The individual micro structure (size, shape, and orientation of grains) and the interfacial conditions show a significant effect on the process characteristics. In this paper; the process of extrusion is investigated to establish it as a viable process for microforming. A forming assembly is fabricated and used in conjunction with a loading substage to extrude micropins with a final diameter of 1 mm. The effect of grain size is investigated by using workpieces heat treated to produce grain sizes varying from 32 µm up to 211 µm. Two extrusion dies with different roughness are used to study the effect of surface finish. While experiments lead to interesting questions and new discoveries, theoretical or numerical solutions are necessary tools for process optimization. Here, knowing the limits of the current widely used numerical simulation tools [i.e., the Finite Element Method (FEM)], a new method, the Reproducing Kernel Element Method (RKEM), has recently been developed to address the limitations of the FEM (for example, remeshing issue), while maintaining FEM's advantages, e.g., the polynomial reproducing property and function interpolation property. The new RKEM method is used to simulate the microextrusion problem. Its results are compared with that obtained from the FEM and the experiment result Satisfactory results were obtained. Future directions on the experimental and simulation work are addressed. [ABSTRACT FROM AUTHOR]

Sheet metal forming is one of the most important and frequently used manufacturing processes in industry today. One of the key parameters affecting the forming process is the blank holder force (BHF). In the past, researchers have demonstrated the advantages of varying the blank holder force during the forming process, that is, the two primary modes of failure in sheet metal forming (wrinkling and tearing) are avoided. This gives rise to improved formability, higher accuracy and better part consistency. In recent years, researchers have also shown increasing interest in forming processes where the blank holder force is varied spatially with the help of segmented binders or flexible binders. In this paper, we have combined the above two aspects and used a robust method to determine the blank holder force trajectories for a non-circular part using segmented binders. The proposed strategy is verified by implementing it into a finite element simulation. Binder force is treated as a system input. The displacement of the binder is used as a measure of the tendency to wrinkle, and is therefore treated as a system output. The parameters of the system are continuously identified and updated using a deterministic Auto-Regressive Moving-Average model (ARMA). The model is then used to control the binder displacement to a prescribed value by adjusting the system input, i.e., the binder force. In this manner, individual binder force profiles for each of the segmented binders are obtained. Due to the generic nature of the ARMA model, the strategy proposed in this paper can be applied to a variety of forming problems, making it a robust approach. [ABSTRACT FROM AUTHOR]

Tailor Welded Blanks (TWBs) offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. In order to take advantage of these benefits, however, designers need to overcome the reduced formability of TWBs and be able to accurately predict unique characteristics related to TWB forming early in the design process. In this paper, an analytical model to predict the weld line movement and forming height for a uniform binder force, TWB forming application is presented. Comparison to numerical simulation results demonstrates the accuracy of this methodology. The analytical model provides designers a valuable tool to determine the location of steps on the die surface to accommodate the weld line movement and the potential forming height for a TWB forming with a uniform binder force. The methodology presented here has the potential to be extended to analyze a non-uniform binder force forming of TWBs. [ABSTRACT FROM AUTHOR]

Cyber-physical systems (CPS) enable unprecedented communication between product designers and manufacturers. Effective use of these technologies both enables and requires a new paradigm of methods and models to identify the most profitable and environmentally friendly production plans for a manufacturing network. The operating system for cyber-physical manufacturing (OSCM) and the paired network operations administration and monitoring (NOAM) software are introduced. These technologies guide our development of a mixed integer bilevel programming (BP) model that models the hierarchy between designers and manufacturers as a Stackelberg game while considering multiple objectives for each of them. Designers select and pay manufacturers, while manufacturers decide how to execute the order with the payment provided by the designer. To solve the model, a tailored solution method combining a decomposition-based approach with approximation of the lower level Pareto-optimal solution set is proposed. The model is applied to a case study based on a network of manufacturers in Wisconsin and Illinois. With the proposed model, designers and manufacturers alike can take full advantage of CPS to increase profits and decrease environmental impacts. [ABSTRACT FROM AUTHOR]

In accumulated double-sided incremental forming (ADSIF), two hemispherical tools impart the local deformation to the sheet via their programed in-plane spiral motion and the depth of the part is achieved via rigid body motion of the already formed part. Unlike single point incremental forming (SPIF) and double-sided incremental forming (DSIF), ADSIF does not impose forces on the already-formed part and, therefore, has the potential of achieving higher geometric accuracy. A systematic method is proposed in this work to study the influences of the relative tool positions on the local formed shape and the final geometry, which is essentially the accumulation of all previously formed local deformations. Meanwhile, the concepts of the stable angle and the peak angle are introduced to better describe the cross-sectional geometry of a formed part with a constant wall angle at that particular cross section. It is recommended that, while multiple combinations of the relative positions of two forming tools may achieve the same stable angle that the positioning parameters should be chosen such that the resultant forming force or the wall angle variation between the stable and peak angles is minimized. [ABSTRACT FROM AUTHOR]

Double-sided incremental forming (DSIF) is a relatively new dieless forming process which uses two hemispherical ended tools, one on each side of the sheet, moving along a predefined trajectory to locally deform a peripherally clamped sheet of metal. DSIF provides greater process flexibility, higher formability, and eliminates the tooling cost when compared to conventional sheet forming processes. While DSIF provides much improved geometric accuracy compared to other incremental forming processes, current toolpath planning strategies suffer from long forming times. A novel mixed double-sided incremental forming (MDSIF) toolpath strategy is proposed in the present study. It simultaneously reduces the total forming time by half while preserving the best currently achievable geometric accuracy. The effect of the forming parameters, i.e., of the incremental depth and of tool positioning on the geometric accuracy of the parts formed with MDSIF was investigated and compared to those formed by traditional DSIF strategies. [ABSTRACT FROM AUTHOR]

Microextrusion has recently emerged as a feasible manufacturing process to fabricate metallic micropins having characteristic dimensions on the order of less <1 mm. At this length scale, the deformation of the workpiece is damn mated by the so-called size effects, e.g., material property and frictional behavior variations at small length scales. In extrusion experiments performed to produce submillimeter-sized pins having a base diameter of 0.76 mm and an extruded diameter of 0.57 mm, the extruded pins exhibited a curving tendency when a workpiece with a relatively coarse grain size of 211 μm was used. This phenomenon was not observed when workpieces with a finer grain size of 32 μm were used. in this paper results from microhardness tests and microstructure analyses for both grain sizes are presented to investigate this phenomenon and to characterize the deformation during microextrusion. The results obtained from this analysis show that as the grain size approaches the specimen feature size, the deformation characteristics of the extruded pins are dominated by the size and location of specific grains, leading to a nonuniform distribution of plastic strain and measured hardness and, thus, the curving tendency. Microhardness tests of the initial billet material and tensile test specimens are also presented as supplementary analyses. [ABSTRACT FROM AUTHOR]

Model validation has become a primary means to evaluate accuracy and reliability of computational simulations in engineering design. Because of uncertainties involved in modeling, manufacturing processes, and measurement systems, the assessment of the validity of a modeling approach must be conducted based on stochastic measurements to provide designers with confidence in using a model. A generic model validation methodology via uncertainty propagation and data transformations is presented. The approach reduces the number of physical tests at each design setting to one by shifting the evaluation effort to uncertainty propagation of the computational model. Response surface methodology is used to create metamodels as less costly approximations of simulation models for the uncertainty propagation. Methods for validating models with both normal and nonnormal response distributions are proposed. The methodology is illustrated with the examination of the validity of two finite element analysis models for predicting springback angles in a sample flanging process. [ABSTRACT FROM AUTHOR]