András Kovács

Aggregation - the key to integrating production planning and scheduling

In this paper we suggest an integrated planning and scheduling framework with a special emphasis on the link between these control levels. Our planning model is generated automatically by performing aggregation on de facto standard product and technology related data in the dimensions of time, resource capacities and operations. The method addresses make-to-order production environments. An industrial case study is also presented, demonstrating how our algorithms work on large-scale problem instances.

Project Scheduling Approach to Production Planning

Abstract We suggest a novel approach to modelling and solving production planning (PP) problems in make-to-order production environments. This approach unifies the capacity and the material flow oriented aspects of PP. Orders are modeled as projects that compete for limited resources. The projects consist of networks of variable-intensity activities which may require several resources at the same time. The goal is to generate production plans that satisfy all the temporal and resource constraints and minimize additional or external resource usage over the planning horizon. The model is applicable at different aggregation levels of PP, as we show with two real-life case studies. Although the capacity and material flow aspects of PP are coupled, a special solver developed for the project model efficiently solves problems of real-life sizes.

Constraint-based process planning in sheet metal bending

Abstract The majority of research dealing with computer-aided process planning of sheet metal bending approaches this problem as heuristic search. Since relevant engineering knowledge mostly consists of declarations that prohibit collisions and just a handful of generative rules, there are no useful means to drive these heuristics. In order to find a new way, we have made experiments with a constraint-based approach: using predefined constraint types and geometric constraint satisfaction, complex bending problems have been solved. By returning not just a single solution but a Pareto-optimal set of solutions (i.e., operation sequences, with appropriate part orientations and tools assigned) we have left the engineers freedom to apply further, not yet modeled parts of their domain knowledge.

Real-Life Scheduling Using Constraint Programming and Simulation

Abstract The paper presents an integrated production planner and job shop scheduler system with flexible modelling capabilities and powerful, scalable solution methods. The system generates close-to-optimal production and capacity plans on the medium term, and detailed production schedules on the short-term. However, the constraint-based, deterministic scheduling model can hardly account for all the uncertainties on the shop floor. Hence, we included such factors into a discrete-event simulation model that is applied to evaluate the robustness of schedules in face of various uncertainties

Hierarchical Knowledge-Based Process Planning in Manufacturing

Artificial intelligence planning methods haven’t been used until recently to address the problem of computer-aided process planning (CAPP) in manufacturing in its entirety. They were simply not developed enough to tackle real-world problems of that complexity. In the paper we show that with so-called Hierarchical Task Networks, a recently matured general-purpose domain-independent planning method, we could model the planning process itself, represent and utilize different kinds of technological knowledge and keep in check the complexity of the plan generation process. To this aim the planner was extended with search methods for finding the best plans and supporting mixed-initiative, interactive planning. The proposed CAPP system deals with geometry analysis, setup planning, selection and ordering of machining operations and the assignment of resources. The first experiments with prismatic and rotational parts show considerable merit of the approach.

Mutagenicity and Phthalate Level of Bottled Water Under Different Storage Conditions

Mutagenicity and phthalate level of bottled water are still under-investigated. Five brands of still or carbonated mineral water bottled in PET, glass, or polycarbonate bottles were kept in sunlight or darkness at ambient temperatures or 37xa0°C for 0, 1, or 4xa0months. The ultraviolet (UV)-filtering capacity of bottles was also assessed. Concentrated organic fractions were analysed using the Ames test. Diisobutylphthalate (DIBP), diethylhexylphtalate (DEHP), and dibutylphthalate (DBP) were quantified by gas chromatography. Mean values of UVA and UVB reduction by bottle walls were 17 and 70% in PET, 16 and 70% in glass, and 66 and 86% in polycarbonate, respectively. Salmonella TA100 strain proved to be more sensitive than TA98 in the Ames test, and according to the test, we isolated direct-acting mutagens. The most mutagenic samples were identified after 1xa0month, stored at 37xa0°C and in sunlight. Water stored in bisphenol A-free polycarbonate was non-mutagenic. Phthalate concentrations were low initially and then ranged between <0.026–0.16xa0μg/L (DIBP), <0.29–11.72xa0μg/L (DEHP), and <0.005–0.2xa0μg/L (DBP); levels were the highest also after 1xa0month of storage. The highest mutagenicity and phthalate levels were detected similarly after 1xa0month of storage in mineral water, but mainly in different samples, and we found no significant correlation between them. Levels of phthalates were independent of bottle material. To sum up, natural organics in water can be important sources of mutagenic compound and phthalate formation. However, further analytical measurements should be performed to identify and follow-up the presence of genotoxic compounds in bottled mineral waters.

Analysing current density in the solder joints of chip-size Surface Mounted resistors

The paper discusses a numerical modelling research, where different sized Surface Mounted Device (SMD) chip-size resistors and their solder joints are analysed from the aspect of current density. The solder joint structure and the connecting traces to the Printed Circuit Board (PCB) solder pads define the route of the current in the structure, where corners may form areas with higher current density, increasing the possibility of electromigration. In our research, we used 0201, 0402 and 0603 jumper resistors for the highest applicable current load. The paper presents the process of 3D modelling, where the shape of the solder joint is calculated with Surface Evolver. The current routes and the possible regions with high current stresses are calculated with Finite Element Method (FEM). The results highlight the critical configuration of solder joint shape, connecting trace direction and current load on the given components.

Effects of high current density on lead-free solder joints of chip-size passive SMD components

Purpose n n n n nThe purpose of this paper is to present a novel approach on investigating critical current densities in the solder joints of chip-size surface mounted device (SMD) components. The investigation involves a numerical approach and a physical validation with selected track-to-pad connections and high current loads (CXs). n n n n nDesign/methodology/approach n n n n nDuring the investigations, shape of solder fillets was calculated in Surface Evolver, and then the current densities were calculated accordingly in the given geometry. For the verification, CX tests were performed on joints at elevated temperatures. The joints were qualified with X-ray microscopy, cross-section analysis and shear tests. n n n n nFindings n n n n nThis study ascertained that the inhomogeneity in current density depends on the track-to-pad structure of the joint. Also this study found that the heavy CX decreases the mechanical strength, but the degradation does not reach the level of electromigration (EM)-induced voiding. n n n n nPractical implications n n n n nThe heavy CX significantly affects joint reliability and the results point out to EM-induced failure-limitations on printed circuit board (PCB)-based assemblies due to the thermomechanical weakness of the FR4 material. n n n n nOriginality/value n n n n nThe experiments investigate current density from a novel aspect on more frequently used small-scale components with different track-to-pad configurations – pointing out possible failure sources.

Investigating current density in the lead free solder joints of surface mounted resistors with experimental approach

The paper presents a research, where modeling and experimental investigation of current density was performed in the lead-free solder joints of different surface mounted chip-size resistors. The currently presented work is based on previous research in the field, where the footprints, the interconnecting copper track on the printed circuit board and the three dimensional joint structure defined the local current routes in the solder meniscus. Investigated corner effects at selected track-to-pad joining angles result in higher local current densities at given points of the solder volume, increasing the possibility of electro-migration. For the experiments 0402 and 0603 zero ohm jumper resistors were used. Soldering was performed with conventional SAC305 lead-free solder alloy, on 1.5 mm thick FR4 boards. The paper presents the results of modelling, and the respective physical experiments to validate the results obtained with the simulation. The test board, and the measurement setup is optimized to help the validation procedure. Failure analysis methods (X-ray, cross-section analysis with optical and scanning electron microscopy) are used to reveal any possible alterations due to the increased current density. The results present the critical configuration of the interconnecting tracks and findings of the failure analysis.

Collaborative Media Content Management

The paper presents the design and implementation of an original integrated media content management system. In this very fast developing area where numerous changes occur even in a year’s time it is really hard to foresee future trends and successful directions. The primary goal was to develop an example of a Collaborative Media Content Management System where different media types and other online contents can simply be stored integrated in one system and can easily be managed and shared by users and communities as well. Right at the beginning, we were aware of the fact that the project would last one year. Therefore, it was not enough to include the then newest features in the plan: it was also necessary to predict future trends and requirements, so that by the time the project is finished, it would still be innovative. The functional design of the application was based on the observation of new internet user generations who are heavily involved in real-time messaging and community portals. Based on our innovative ideas the system has been finished and besides our successful project many similar solutions have been appeared all over the world. The paper presents the most important features of our approach and the outcome: a Collaborative Media Content Management system, called simply Media-store, and emphasizes the innovative services of the system (visual tagging, mediashow, mediablog, common media arrangement).