Roberto Spina

Assembly and Disassembly Planning by using Fuzzy Logic & Genetic Algorithms:

The authors propose the implementation of hybrid Fuzzy Logic-Genetic Algorithm (FL-GA) methodology to plan the automatic assembly and disassembly sequence of products. The GA-Fuzzy Logic approach is implemented onto two levels. The first level of hybridization consists of the development of a Fuzzy controller for the parameters of an assembly or disassembly planner based on GAs. This controller acts on mutation probability and crossover rate in order to adapt their values dynamically while the algorithm runs. The second level consists of the identification of the optimal assembly or disassembly sequence by a Fuzzy function, in order to obtain a closer control of the technological knowledge of the assembly/disassembly process. Two case studies were analyzed in order to test the efficiency of the Fuzzy-GA methodologies.

Evaluation of filling conditions of injection moulding by integrating numerical simulations and experimental tests

Abstract The authors propose an integrated approach to evaluate gating system configurations to optimize the filling conditions of thermoplastic injection moulded parts. Through data integration between the finite element (FE) analysis and the Design of Experiment approach, the filling of parts with complex geometries was studied to optimize injection process parameters and improve the product quality. The numerical simulation of an injection moulding process allows the evaluation of the component manufacturability at the early stage of the development cycle, without fabricating prototypes and minimizing experimental tests. Normally, the FE analysis interests concerns filling, post-filling and cooling phases of the injection process. Using the FE system, a deeper investigation of stress and strain distributions can be performed to predict defect presence in the final product. However, this methodology is sensitive to existing differences between property of the real part and of its model (material, geometry, etc.).

An artificial intelligence approach to registration of free-form shapes

Abstract Registration, defined as the process of matching geometric entities, is performed when multiple scanned data sets must be aligned or when an existing model must match digitized point clouds. This process is crucial in several applications such as Reverse Engineering, CAD-based inspection and computer vision. The goal of this process is the computation of the optimal rigid transformation for the alignment of several sets of geometric entities (points and/or surfaces). Registration is generally performed by using a two-step procedure necessary to realize coarse and fine alignments. Human intervention is normally required for coarse registration while fine registration is usually a semi-automatic procedure. Consequently alignment is not usually a single step automatic operation and is also affect by errors. In this paper the authors propose a hybrid approach for automatic registration applied to free-form shapes. This hybrid approach employs a asynchronous data communication between an Artificial Neural Network and Genetic Algorithms. The Neural Network performs the coarse alignment giving an initial solution for the registration operation which is then performed by Genetic Algorithms to minimize error deviations between geometrical entities. Several case studies have been investigated in order to validate the proposed approach.

A hybrid approach to the single line scheduling problem with multiple products and sequence-dependent time

The present paper presents a hybrid approach for solving manufacturing scheduling problems, based on the integration between Constraint Logic Programming (CLP) and Genetic Algorithm (GA) approaches. The proposed methodology is applied to a single line with multiple products and sequence-dependent time. This system model derives from a real case of a company producing sheets for catalytic converters. A sensitivity analysis of the hybrid methodology is carried out to compare the performance of the CLP, GA and integrated CLP-GA approaches.

A Quality Evaluation Method for Laser Welding of Al Alloys Through Neural Networks

The authors propose an integrated methodology to evaluate the quality of Aluminium alloy butt joints welded by laser. The method, starting from the observation of the results of an experimental investigation, focuses on the definition of a omni-comprehensive quality index for welded joints. This index is obtained using the limits of imperfections for the quality level defined by the ISO 13919 standard. A neural network system has been developed to classify and evaluate the different welds. The experiments were performed on Al 6110 T61 alloy, welded using a 6 kW CO2 laser beam on plane sheets with a continuous butt joint. Computerised image processing has been used to recognise and to quantify the imperfections in the weld cross section. The defects have been divided into groups, as required by the EN 26520 standard. Due to the huge number of measurements required to imperfections, the artificial neural network very greatly simplifies the relationship between the quality index and the main process parameters. The neural network was trained with a set of data containing very different welding parameter choices. Application of the system aids process parameter selection that has proved to be in good agreement with quality levels measured on experimental welds made under the same conditions.

Evaluation of rapid prototypes obtained from reverse engineering

Reverse engineering (RE) represents a key factor in improving company competitiveness through the fast adaptation of modifications to the original design. In a concurrent engineering environment, the potential of RE can be drastically extended by coupling it with layered manufacturing (LM). The principal bridge between RE and LM is based on the indirect use of STL files. These tessellated representations of products have several drawbacks linked to the shape and topology of the triangular mesh. For this reason, a very time and resource consuming phase is necessary to elaborate STL models for layered manufacturing purposes. In this paper, the application of design of experiments (DOE) techniques to the reduction of STL defects is investigated in order to create error-free tessellated models for LM tasks.

Mesoscale simulation of the solidification process in injection moulded parts

Abstract Due to their wide range of applications and their complex material properties, it is desirable to be able to predict the behaviour of injection moulded parts with the help of simulation tools. For semi-crystalline materials, this can only take place with considerable accuracy if the inhomogeneous material properties are taken into account. Because of this, it is necessary to calculate the microstructure of the solidified melt and to incorporate these findings in the simulation. We present an integrative, multiscale simulation approach in which the manufacturing process is calculated on a macroscale and the solidification process on a mesoscale. A multiphase filling and cooling simulation is done to calculate temperature and velocity fields, which are used as boundary conditions for the calculation of the spherulite distribution in the part. We present the used nucleation and growth model and shortly describe the parallelisation approach of the mesoscale simulation.

Thermal Simulation of Polymer Crystallization during Post-Filling

Crystallization from polymer melt is one of the most fundamental phenomena of material phase transformations. The possibility of controlling crystallization kinetics is essential to achieve the proper polymer microstructure and consequently obtain desired material properties, reducing undesired effects such excessive anisotropy of shrinkage, warping and insufficient dimensional stability. Due to the high transformation rate, the simulation of crystallization is fundamental to mimic this important physical phenomenon under several testing and processing conditions by using commercial software. User subroutines were developed and implemented into finite element-based model to simulate crystal growth in semicrystalline polymers with various crystal morphologies. These subroutines allowed the commercial program Abaqus to be customized for solving the Kolmogoroff-Avrami-Evans equation with Hoffmann-Lauritzen model in order to simulate the variation of the polymer crystallization degree. The micro-structural evolution in non-isothermal conditions and with different cooling rates was considered. The study was performed on isotactic PP (SABIC PP 505) for its simplicity to the measure polymer crystals. A tensile test specimen, produced by injection molding, was chosen as case study to evaluate the crystallization evolution. The paper reports the numerical and experimental results.

Laser Welding of Aluminium-Steel Clad Materials for Naval Applications

Several electronic, naval, aeronautic and automotive components are made by different materials joined together in order to improve mechanical and functional properties. Functionalities provided by clad metals can be grouped into structural, thermal expansion management, thermo-mechanical control, electrical, magnetic, corrosion resistant, joining and cosmetic applications to cite as few (Chen et al., 2005). The demand for dissimilar material joints continuously grows because one material can provide only a small spectrum of chemical, physical and mechanical characteristics required for the investigated application respect to the bior multi-layer material joints. Moreover considerable weight savings can be achieved by using lightweight materials clad to strength ones directly. For these reasons, researchers and manufacturers continuously evaluate the application of traditional and/or advanced joining processes to clad dissimilar materials and obtain transition joints optimally. Focusing the attention on steel/aluminium joints and shipbuilding industry, the development of lightweight and fast-speed vessels requires a great number of aluminium/steel structural transition joints (STJs) in order to connect aluminium superstructures to the steel hull (Chao et al., 1997). Using this solution, the total weight of a ship is reduced due to the lighter aluminium superstructure. However, problems in service may occurred by relations at the atomic level between iron and aluminium and differences existing in physical and chemical properties of the base metals. One of the most undesired effect derives from the large electrochemical difference of 1.22 volts between iron and aluminium that causes a high susceptibility to both inter-crystalline and galvanic corrosion along the STJ interface. Fusion welding processes, initially used to produce the aluminium/steel STJs with desired physical and mechanical features, are narrowly applied because the subsidiary precipitates and brittle Al/Fe inter-metallic phases, created during fusion and solidification and located along the interface, are severely exposed to corrosion, troubling joint cohesion (Durgutlu et al., 2005). The high heat input affects the different thermal properties of the two materials— thermal expansion, heat capacity and thermal conductivity—and may lead to very complex stress fields. Moreover, the heat input causes the lattice transformation and the formation of inter-metallic phases. In iron (cubic body-centred up to 911 °C) and aluminium (cubic facecentred) joints, the inter-metallic phases present a high hardness and low ductility. The 4

Telemanufacturing of reverse engineered parts: A case study

Abstract A product idea is normally transferred between designers and/or manufacturing engineers using digital models. Engineering analyses are directly connected with the presence of these models and only limited to virtual evaluations. For this reason, the use of real prototypes is very important in the first design stage in order to perform a deeper product evaluation. A very attractive way to update product designs while realizing prototypes is offered by the direct data communication between reverse engineering (RE) and rapid prototyping (RP). In this way the reproduction of aesthetic prototypes in different geographical positions becomes a key factor for successful competition. In this article, the authors investigate the efficiency of the data transfer between RE and RP systems in order to speed up product development without sharing design intent. A specialized software tool is described in order to perform product shape acquisition, elimination of redundant point cloud data, retriangulation of the point cloud and generation of a machine file for RP fabrication.