Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)

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Open Access
A cyber-physical system for quality assessment in welding electric vehicle batteries
Σαμπατακάκης, Κυριάκος; Sabatakakis, Kyriakos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
The battery of an electric vehicle consists of cells assembled into modules which in turn are assembled to create a battery pack. Most of these connections are permanent and are made using a welding process. However, due to the involvement of non-ferrous, inhomogeneous and multilayer materials, the creation of welds with low electrical resistance, high strength and quality characteristics that can be reproduced with minimal deviation is a challenge. This fact combined with the assembly process, in which the interconnection of tens or even hundreds of cells take place, makes the existence even of a single joint that is out-of-spec, crucial for the safe and efficient operation of the battery, but also for its longevity. This fact makes quality inspection of every joint necessary, which cannot be achieved by using sample-based destructive or non-destructive methods. And while the scientific community has developed and described solutions and approaches for non-destructive real-time inspection and assessment in welding a very small amount of them concerns battery assembling applications and in general the welding of non-ferrous dissimilar metals. On the other hand, none of these studies yet has addressed the issue of inspecting or assessing the electrical quality of the joints. In this study based on the design practices of Cyber-Physical systems a novel quality assessment approach for the assembly of batteries in terms of electrical and mechanical quality is developed in the context of the Laser welding of aluminum and copper battery tabs. The assessment approach is based on infrared vision data using machine learning. The classification accuracy for the electrical and mechanical quality of the welds on the training and test data was set at 100% under specific conditions.
Open Access
A smart shop-floor monitoring system through Internet of Things and wireless sensor networks
Μήλας, Νικόλαος; Μούρτζης, Δημήτριος; Μούρτζης, Δημήτριος; Χρυσολούρης, Γεώργιος; Παπαδόπουλος, Χρήστος; Milas, Nikolaos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
With the advent of the fourth industrial revolution manufacturing systems are transformed into digital ecosystems. In this transformation, the Internet of Things (IoT) and other emerging technologies pose a major role. Small and medium enterprises (SMEs) in manufacturing, often employ outdated equipment which does not have connectivity capabilities. Therefore, smart sensor systems are required to connect these resources into the digital world. To address this issue, this master thesis presents a monitoring framework and the development of a data acquisition device for machine-tools. The system is designed for installation into the electrical cabinet of the machine-tools and transmits the data related to their operation to a Cloud server via a wireless sensor topology. The data transmission is performed in two levels i.e. locally in the shop-floor using a star wireless sensor network topology coordinated by a microcomputer gateway, and from the microcomputer to Cloud using Internet protocols. The collected data provide information about the status of the resources, along with a set of performance indicators to support decision making. The developed system follows the IoT paradigm in terms of connecting the physical with the cyber world and offering integration capabilities with existing industrial systems. The gateway level supports connectivity with industrial networks through the OPC-UA standard, while the higher level supports integration with industrial software tools via Web-Services. The operation of the system was evaluated in a 3-axis machine-tool under actual machining operations. Moreover, the capabilities for knowledge reuse were validated through the case-based reasoning methodology in the subject of the energy consumption estimation.
Open Access
Additive manufacturing digital twin integrating theoretical process models
Μιχαήλ, Χρήστος; Michail, Christos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Η προσθετική παραγωγή καθιστά δυνατή τη δημιουργία περίπλοκων γεωμετριών. Ωστόσο, αυτού του είδους οι λειτουργίες στερούνται βελτιστοποίησης και ασυνέπειας της διαδικασίας. Το Digital-Twin θα μπορούσε να είναι μια τεράστια ευκαιρία για την αντιμετώπισή τους, αλλά το DT βασίζεται στην επικοινωνία και την προσομοίωση σε πραγματικό χρόνο. Η παρούσα διπλωματική εργασία πραγματοποιεί προσομοίωση στις θερμικές πτυχές της διαδικασίες “Laser Powder- Bed Fusion” κι δημιουργώντας ένα υποκατάστατο μοντέλο με τη χρήση αλγορίθμους βαθιάς μηχανικής μάθησης, προσφέροντας έτσι γρήγορη μοντελοποίηση. To υποκατάστατο μοντέλο λειτουργεί ως το εικονικό δίδυμο της διεργασίας LPBF επικοινωνώντας σε πραγματικό χρόνο. Το φυσικό δίδυμο εκτελείται μέσω “Dummy Data Generator, για την ελαχιστοποίηση της εισβολής με το πραγματικό σύστημα. Τέλος, μια πλατφόρμα του ψηφιακού διδύμου πραγματοποιείται για την επίδειξη της υλοποιησιμόητας σε πραγματικό χρόνο.
Open Access
Algorithms for hydrodynamic and magnetohydrodynamic incompressible internal flows
Βαφάκος, Γεώργιος; Παπαδόπουλος, Πολύκαρπος; Παπαδόπουλος, Πολύκαρπος; Μάργαρης, Διονύσιος; Σιακαβέλλας, Νικόλαος; Vafakos, Georgios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Τhe aim of the present thesis is to study and compare algorithms for both hydrodynamic and magnetohydrodynamic incompressible internal flows. The study of magnetohydrodynamics is one of the most complicated fields of fluid dynamics because it is governed not only by the laws of classical fluid mechanics, but also of electromagnetism. That alone makes the flow equations more complicated and greater in number. It is obvious, then, that in order for a scientist to model and study a problem like this, there is a need of efficient computational power and deep understanding of the natural laws that govern the flow. The first half of the thesis deals with the calculation of the incompressible hydrodynamic flows and the comparison of the well established PISO pressure-velocity coupling algorithm with the IPOT algorithm. The IPOT method has been used successfully in the past for calculating both external and internal flow problems, but with the disadvantage that oscillations are generated in the flowfield due to the method. In the present thesis the Rhie-Chow interpolation has been successfully implemented in the algorithm in order to address the previous problem. It will be shown that not only the IPOT method with the Rhie-Chow interpolation produces accurate ρesults, but it converges faster that the PISO algorithm. The second half of the present thesis studies the engineering application of the magnetohydrodynamic flow of a conductive fluid through both a two and three dimensional channel. Once the specific boundary and initial conditions of the problem are set, the results for the axial velocity, the pressure drop and the induced magnetic field are presented for the cases of electrically insulating and conducting pipe walls, for a wide range of the parameters of the flow. The flow is considered laminar and the results correspond to developing flow. The results show that when the Hartmann number is increased, the axial velocity changes throughout the cross section, whereas the pressure drop increases along the pipe. The conductivity of the wall increases dramatically the pressure drop and the induced magnetic field, which can have a great effect on certain technological applications.
Open Access
Analysis, design, and development of advanced product-service systems in the era of digitalized manufacturing : a collaborative approach
Μπόλη, Νικολέτα; Μούρτζης, Δημήτριος; Boli, Nikoleta
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
A new generation of collaborative manufacturing systems where all the components are connected exploiting the Internet of Things is envisioned in the era of Digitalized Manufacturing. Industries nowadays try their best to adapt to digitalized manufacturing paradigm in order to remain competitive and to ensure their sustainability in a globalized world that undergoes a digital transformation driven by advanced technology and connected devices. Products up to now have been designed in every minimum detail to provide the best product experience. However, they are not, still, the most efficient and sustainable solutions. Solutions to fulfill our needs and not another products are mandatory. The phenomenon of manufacturers shifting their business models to add a services dimension to their product offering is widespread. Servitization has allowed manufacturers to maintain their competitive advantage in the face of competitive pressures arising from globalization, and at the same time create greater value for customers. The shift of profit margins from products to services, has transformed traditional production equipment supplier industries to providers of Product-Service Systems (PSS). PSS is a solution resulted from the synergetic integration of tangible and intangible elements coupled with supportive systems (resources and infrastructures) and heterogeneous knowledge describing stakeholders’ viewpoints. The design and planning of such a system involves a complex network of stakeholders coming from private or public Sector. More than that providing an integrated Product-Service System (PSS), as a smart solution, is increasingly offered by industrial machinery and also Energy sector strives to provide services on top of energy selling. In order to contribute to the realization of such a vision, the present thesis investigates the analysis, design, and development of advanced Product-Service Systems in the era of digitalized manufacturing following a collaborative approach. This thesis contributes in three directions. The first one is the Analysis, Design, and Development of advanced PSSs. The analyzed, designed and provided services on top of the provided products can be grouped into three categories namely: Process and health monitoring of manufacturing equipment, Remote maintenance assistance for the preventive and unscheduled maintenance of manufacturing equipment and Energy Management Services which are reflecting to three industrial cases. In particular, following the trends of the digitalized manufacturing and considering that Manufacturing, SMEs and Energy Utilities are at the first positions of the EU agenda, a Machinery Equipment Provider (Original equipment manufacturer - OEM), a Mold Making Small and medium-sized enterprise (SME) and an Energy Supplier are the three industrial cases of this thesis. The PSS “value co-creation” to improve the firm’s capabilities is established by network’s actors collaboration through the whole lifecycle. Due to this complexity, a central point is to support the development process of PSS as such the second contribution of this thesis is the analysis and design of a resource planning tool for Product-service systems production and installation supported by a procurement module as a part of collaborative PSS production. This part explores the consequent changes in production planning in order to tightly integrate products and services and as a result, delivers a Planner capable to support every PSS type. Following that, considering the PSS Complexity, the third direction is the creation of a decision making support methodology for the quantification of PSS customization complexity, considering Industry 4.0 aspects based on the fact that the design and evaluation of Product-Service Systems (PSS) constitute a challenging problem due to its multidimensionality. This challenge becomes bigger when the PSS customization is required, within the new manufacturing paradigm of Industry 4.0. Nevertheless, the literature work regarding the customization of PSS and the PSS investigation within the Industry 4.0 is rare. The proposed PSSs and tools are validated using real data from the aforementioned cases. The opportunity to follow these studies driven by real case studies under the Horizon 2020 “An Integrated Collaborative Platform for Managing the Product-Service Engineering Lifecycle” - ICP4Life project makes this work more interesting and challenging. To this end, the present thesis is divided into 9 chapters. After an introduction (Chapter 1) which examines the vision and motivations behind this work, Chapter 2 reviews the literature related to the main aspects of this study. Accordingly, Chapter 3 presents the methodology followed and also the collaborative approach of the present work. Chapter 4-7 are the core of the thesis and present the four main outcomes including the related industrial applications. In particular, a) the developed Energy Based Offered PSSs, b) the developed Manufacturing Equipment PSSs for process and health monitoring and also for Remote maintenance assistance, c) the PSS production and installation planning methodology and finally d) the Product-Service System complexity calculation methodology are presented. Accordingly, an overview of the results and a discussion of them is given in Chapter 8. Finally, Chapter 9 draws the conclusions, summarizing the main outcomes and pointing out some possible future works.
Open Access
Augmented reality applications in the shopfloor towards operator 4.0
Ζωγόπουλος, Βασίλειος; Μούρτζης, Δημήτριος; Χρυσολούρης, Γεώργιος; Χονδρός, Θωμάς; Zogopoulos, Vasileios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
As manufacturing moves towards the 4th Industrial Revolution, new technologies gradually become integrated in new applications. Industry 4.0, as it is called, affects different levels of the existing business models and approaches, ranging from high level management to the core of production: the shopfloor. The last decades, production was leaning towards higher automatization, replacing humans with automation in tasks that were repetitive and required high precision and/ or high loads. This made the new technologies be perceived as a threat for operators. However, new technologies also aim to enhance the capabilities of the human. New wireless networks allow information to be available everywhere in high speed, connecting multiple sources. Exploiting information in a meaningful and easy-to-perceive way renders the operator capable of receiving information from various sources so as to improve decision making and support him in operations. Augmented reality proposes a new way of visualizing information (text, geometries, data) in the users field of view, enhancing his environment.
Open Access
Automated path planning based on point-cloud data for hybrid manufacturing
Αθανασοπούλου, Λυδία; Athanasopoulou, Lydia
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Due to the significant capabilities and new opportunities on the optimization of manufacturing processes, Hybrid Manufacturing has drawn significant interest from both industry and academia within the past years. Hybrid Manufacturing is expected to be incorporated to the main production line, providing major benefits in terms of quality, flexibility and performance within an interconnected environment. This study focuses on the implementation of a tool path planning framework for Hybrid Manufacturing using point cloud data within the context of automation. The entire framework is being distinguished into four phases, namely the data preparation, extraction of the disparity map, the detection of the contours of the subtracted region of the scanned model and, finally, the generation of the tool path using a conditional offsetting method. The entire strategy is considered to be applicable to Additive and Subtractive Hybrid Manufacturing processes. The proposed approach has been investigated and validated through a case study.
Open Access
Centralized and decentralized manufacturing networks in the concept of circular economy
(2023-02-23) Ζούπινα, Φωτεινή; Zoupina, Foteini
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
A number of environmental issues have arisen in recent decades, as available natural resources are limited and emission levels are high and must be kept below certain limits. Due to the high variety of products, complexity occurs during production which in turn results in an increase in energy consumption. Since centralized mass production cannot cope with the production demands imposed by globalization there is a transition to "mass customization". The result of this adjustment is the reduction of the cost of transportation of the production products, the low cost of human labor in specific locations as well as the better quality of the products. Also, several countries have begun to orchestrate initiatives concerning the design and development of the human-centered aspect of technologies, systems and services, which has been coined as Industry 5.0. The developments focus on the social and human-centric aspect of the tools and technologies introduced in the context of Industry 4.0. The impact of Industry 5.0 will extend to social transformation, which ultimately leads to the creation of a new society, Society 5.0. Therefore, sustainability and human well-being will be at the heart of what follows, Industry 5.0, as a subset of Society 5.0. Industry 5.0 builds on the foundations laid during Industry 4.0 by emphasizing human-centered, resilient and sustainable design. The aim of this master's thesis is to study the concept of Industry 5.0 and Society 5.0 as well as to present the applications of Industry 5.0, the applications of circular models in Industry 5.0 and the sustainability with which they are largely connected. The circular economy is a concept which is linked to both Industry 5.0 and Society 5.0. as well as sustainability. In order to carry out the study of the concepts of Industry 5.0 and Society 5.0 a critical literature review was carried out through the use of VOSviewer software.
Open Access
Data modelling and algorithms for symbiotic assembly operations
Αργυρού, Άγγελος; Χρυσολούρης, Γεώργιος; Μούρτζης, Δημήτριος; Ανυφαντής, Νικολαος; Argyrou, Angelos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
In modern assembly lines, humans and robots coexist and collaborate for the execution of complex tasks. The sequence and the assignment of tasks to suitable resources, constitute a technological challenge. For the collaboration of humans and robots, in a single assembly station, a common modelling language is required. This work examines the way that resource capabilities of both humans and robots could be described, by the same modeling language, including common attributes for the various types of resources. In the current work a two stage optimization system is presented which allocates resources into tasks based on the preferences of the operator. The tool was implemented as a java application and it has been tested in a pilot case stemming from the automotive industry.
Open Access
Design analysis and optimization of an aircraft composite seat under dynamic loading conditions according to far 25.562
Τζανάκης, Γεώργιος; Tzanakis, Georgios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
The increase of the air transfer requires an extensive variety of legal regulations that focus on the safety of the flight. The main objective of these regulations is the safe flight of the aircraft and the survival of the occupants in the event of an emergency landing. One of the most important mechanical structures responsible for the safety of the occupants is the aircraft seat, which consist an interface between the passenger and the aircraft. Aircraft seats must ensure the protection of occupants from fatal injuries in the occasion of crash landing, increasing their probability of safely evacuating the cabin. Except for the occupant’s safety, the manufacturing of lightweight structures is considered one of the most important factors that affect greatly the aircraft seat’s study, making the use of low density materials, such as aluminum alloys or composites, a valuable choice. Rapid growth of fiber polymer composite materials in aerospace has made them an important section of the aircraft structure study. Their significant mechanical properties and low density characteristic, in accordance with their efficient applicability, has accelerated their growth in aerospace structures and made them one of the most commonly used material. Aircraft structures certification requires a great number of time consuming and high cost tests, including full scale tests, which must be conducted in order to reach an acceptable design of the seat configuration that meets the structural and injury criteria requirements. Thus, computer simulations and Finite Element Methods have become an essential engineering tool, for the purpose of the efficient and accurate seat design. The objective of this thesis is the development of an aircraft seat configuration of three passengers, which is designed to satisfy the dynamic criteria of the FAR 25.562 regulation for the scenario of the aircraft’s emergency landing. There are developed two versions of the seat configuration, where the second is an optimized version, as a matter of the mass reduction of the structure, with the use of fibrous composite materials, while maintaining the structural and occupant safety requirements.
Open Access
Design and analysis of low cost aerodynamic aids for heavy duty trucks using composite materials for fuel saving purposes and CO2 reduction
Μπιράτσης, Αντώνιος; Κωστόπουλος, Βασίλειος; Κωστόπουλος, Βασίλειος; Πολύζος, Δημοσθένης; Λούτας, Θεόδωρος; Biratsis, Antonios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Freight transports by means of heavy duty trucks constitute nearly 75% of the total transportation in the EU. Billions of euros are spend every year in fuel importations (Eurostat, 2016) in order to cover these needs and in addition with the reduction of global fuel reserves the cost of transportation is constantly rising. Studies have shown that aerodynamic drag, on tractor trailer combination, is the main contributor of fuel consumption on highway speeds (50% at 80km/h and up to 70% at 113km/h). This study will investigates the effect of add-on devices have on the fuel consumption of heavy duty trucks travelling on highway speeds. Target areas are the forefront of the trailer, the underbody area and the base trailer region where nearly 75% of the total drag is observed. Analysis of the airflow where performed on Solidworks Flow Simulation and analysis of the composite panels where performed Patran-Nastran.
Open Access
Design and simulation of a network based on IoT for Illumination : a smart city case study
Μπαρούνη, Αικατερίνη; Barouni, Aikaterini
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
The tendency of people, especially in recent years, to head to large urban centers, has led to a number of economic, social, environmental and organizational problems. The street lighting of a city is one of the most basic parts of its design as it offers the feeling of security, comfort and quality of life to the citizens at night. However, municipal lighting is a huge expense for both the environment and society. With the development of new methods of managing resources, capital and time, the reduction of energy consumption and carbon dioxide emissions is ensured while at the same time the quality of life of the citizens is improved. This master thesis focuses on the design of smart street lighting in a small part of a city using CupCarbon software for autonomy and more efficient operation. By simulating different scenarios and changing the conditions of programmable sensors, such as motion, weather conditions, brightness, etc., the corresponding energy consumption, efficiency, light pollution, etc. are studied, concluding that smart lighting can improve some of the disadvantages of conventional lighting.
Open Access
Design end of arm tool from lightweight materials and structural analysis with finite element analysis
Λαμπρόπουλος, Μάριος; Μούρτζης, Δημήτριος; Χρυσολούρης, Γεώργιος; Μούρτζης, Δημήτριος; Νικολακόπουλος, Παντελής; Lampropoulos, Marios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
In the present work is being studied the end of arm tool of a robot arm for in-mold labeling applications. The first part of the current thesis is an introduction to injection molding and in-mold labeling process. Next is being analyzed all the different types for in-mold labeling. In the second part there is all the experimental measurements that have been done in order to calculate the forces the end of arm tool receives. In the end there is the design and the structural analysis with finite element analysis of the four different proposed end of arm tool.
Open Access
Design of a framework for assessing the quality of human-robot collaborative operations
(2022-09-23) Κοκοτίνης, Γεώργιος; Kokotinis, Georgios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Human-robot collaboration and Interaction (HRC/I) for industrial applications is considered as a challenging topic which involves not only technological aspects but also extends to social sciences and humanities (SSH) research. One of the main difficulties in human-robot collaborative assembly lines is to achieve an efficient process scheduling. However, a proper and efficient human-machine cooperation can increase productivity rates and quality of the overall process. This study proposes an approach focusing on the task planning of Human-Robot Collaborative (HRC) layouts for the assembly of large-scale parts. The implementation of a Human-Robot Operation Planning (HROP) module is presented, analyzing its architecture and the respective functionalities, which aim at the allocation of multiple operations between multiple and different types of resources. This development main pilar is a dynamic decision-making logic that combines both constraints, that exclude resources from the detailed evaluation, as well as multiple mathematical criteria, that provide the most valuable solution. The particularity of HROP is that it is developed under the Behavior Trees (BT) architecture. In addition, a novel and simple Human-Robot Collaboration - Quality Index (HRC – QI) is proposed, aiming to assess the flexibility, performance, cost, and quality aspects of applications involving the co-existence and collaboration of such production entities. The definition of this index considers several metrics for capturing the contributions and drawbacks introduced by the involvement of either humans or robots depending on their attributes and roles within the production operation. Four distinct case studies involving different HRC schemes in different production sectors are used to verify the effectiveness and ease of application of the suggested index, while one under a real industrial environment of the automotive industry, which is based on the assembly of large-scale parts, such as buses, in a hybrid cell of both human operators and multi-type robots is used for the validation of the decision-making logic proposed.
Open Access
Extension of the virtual sources method for prediction of the sound field around complex geometries
Ρουβάς, Διονύσιος-Μάριος; Μενούνου, Πηνελόπη; Μενούνου, Πηνελόπη; Μάργαρης, Διονύσιος; Σιακαβέλλας, Νικόλαος; Rouvas, Dionysios-Marios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
The prediction of the acoustic field produced by a known sound source around a complex geometry is investigated. On the triangulated surface of a solid object sound is reflected from the planar surfaces of the triangles and is diffracted by edges of two adjacent triangles that are not co-planar. The present thesis involves the use of existing frequency-domain solutions to describe the contribution of each part of the geometry and an algorithm, suited for complex geometries with large number of triangles, which replaces each part of the geometry with its corresponding virtual source. Specifically, planar surfaces are replaced with virtual sources according to the image source method (to account for reflections), while the edges of adjacent non-planar surfaces by virtual sources according to the Directive Line Source Model (to account for edge diffraction). This method has been proven by Menounou, Klagkos to be quite accurate even though multiple-diffraction propagation paths could not be calculated and were ignored by the algorithm. In this thesis, the method is extended to include multiple and higher-order diffraction by wedges using the enhanced Directive Line Source Model . The algorithm we propose here proves to be able to identify every propagation path regardless the geometry of the problem. Complex propagation paths that include multiple reflections between diffractions can now be handled, making sure that no physical path is ignored. The virtual source method, being an image source method, does not suffer from numerical or undersampling errors which occur in ray and beam tracing methods and computational aeroacoustics methods. Moreover, the computational cost remains the same irrespective of the sound source frequency or the propagation distance. Thus, it is applicable to any geometry and for any frequency, unlike the finite element and boundary element methods which encounter problems when the frequency is high or when the geometry is complex. The geometries considered span from noise barriers on the ground and desks configurations inside an office, to airfoil geometries. In the cases examined the surrounding fluid was considered quiescent and homogenous, the sound source an omni-directional spherical source, while the surfaces of the objects rigid or partially absorbing. The results obtained with our model show good agreement with experimental data and/or results from other numerical methods, especially in the cases where parallel edges are present like double or triple knife-edge barriers, single wide barriers and the doubly inclined barrier. The discrepancies that appear in the case of the desk geometry can be eliminated by increasing the order of diffraction and the order of reflection in order to achieve convergence and by employing more realistic absorption coefficients. In the case of the airfoil, despite not having experimental data for comparison, the predicted acoustic pressure field seems to be realistic as we increase the order of diffraction. The predicted diffraction paths illuminate areas that were previously in the shadow regions. The results produced by the algorithm validate the analytical approach that we use. Even in the case where there is not an absolute agreement with the experimental data, the algorithm proves to be able to produce the correct pattern and the discrepancies that appear are due to false values of the absorption coefficients that we use.
Open Access
Friction-wear modelling in drilling process
Παναγόπουλος, Γεώργιος; Νικολακόπουλος, Παντελής; Ανυφαντής, Νικόλαος; Σταυρόπουλος, Παναγιώτης; Νικολακόπουλος, Παντελής; Panagopoulos, George
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Η κατεργασία μετάλλων αποτελεί μία από τις πιο συνηθισμένες διεργασίες κοπής στην μεταποιητική βιομηχανία. Διακρίνεται σε τρείς υποκατηγορίες οι οποίες είναι η τόρνευση, το φρεζάρισμα και η διάτρηση. Εκτεταμένες μελέτες έχουν πραγματοποιηθεί με στόχο την βελτίωση των διεργασιών αυτών και η ψηφιακή προσομοίωση πλέον αποτελεί αναπόσπαστο κομμάτι της ανάπτυξης προϊόντων. Παρόλα αυτά, η προσομοίωση της κατεργασίας μετάλλων είναι περίπλοκη από φυσικής αλλά και αριθμητικής πλευράς. Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της διαδικασίας διάτρησης και το τεχνικό και επιστημονικό υπόβαθρο σχετικά με αυτόν το τομέα κατεργασίας μετάλλων. Αρχικά, πραγματοποιείται μια σύντομη αναφορά στην κατεργασία της διάτρησης. Πιο συγκεκριμένα, γίνεται βιβλιογραφική ανασκόπηση ως προς την ανάγκη της δημιουργίας οπών στην κατασκευαστική βιομηχανία. Γίνεται σύντομη αναφορά στα υλικά κατασκευής των τρυπανιών και στα πιο συνήθη προβλήματα που εμφανίζονται κατά την συγκεκριμένη κατεργασία. Επίσης, παρουσιάζονται τα πιο χρήσιμα και συνήθη γεωμετρικά χαρακτηριστικά των τρυπανιών, των οποίων οι τιμές καθορίζουν τον τομέα εφαρμογής τους καθώς και συνθήκες κοπής που θα χρησιμοποιηθούν κατά την χρήση τους. Έχοντας ως γνώμονα την γεωμετρία, παρουσιάζονται οι σύγχρονες τροποποιήσεις που έχουν πραγματοποιηθεί στα τρυπάνια συστροφής με στόχο την βελτιστοποίηση της συνολικής τους απόδοσης, όπως η χρήση επικαλύψεων. Στο παρόν κεφάλαιο πέρα από τα παραπάνω γίνεται αναφορά στα μαθηματικά μοντέλα που χρησιμοποιούνται για τον υπολογισμό των αναπτυσσόμενων δυνάμεων κατά την διαδικασία της διάτρησης. Ακολουθεί περιγραφή ενός συγκεκριμένου προβλήματος επί της κατεργασίας διάτρησης παράλληλα με μια ανάλυση των κυριότερων παραγόντων που οδηγούν στην εμφάνιση του πρώτου. Αναλυτικότερα, προβάλλονται τα πιο συνήθη μοντέλα που εφαρμόζονται στην ξηρή τριβή μεταξύ δύο επιφανειών, και έπειτα αναφέρονται οι τύποι φθοράς που εμφανίζονται στις διεργασίες κοπής. Στο παρόν κεφάλαιο γίνεται συσχέτιση μεταξύ των διαφόρων μοντέλων που χρησιμοποιούνται για τον υπολογισμό του ρυθμού φθοράς, και επιλέγεται ο ακριβέστερος για την εύρεση της συγκολλητικής φθοράς. Επιπροσθέτως, παρουσιάζονται οι κυριότεροι μηχανισμοί φθοράς που εμφανίζονται κατά την διάτρηση. Το επόμενο κεφάλαιο αποτελείται από μια εκτεταμένη βιβλιογραφική ανασκόπηση στον τομέα της διάτρησης. Παρουσιάζονται μελέτες που έχουν γίνει αναφορικά με την χρήση τρυπανιών. Πιο συγκεκριμένα, γίνεται αναφορά σε μελέτες που αφορούν την τροποποίηση των κοπτικών ακμών σε τρυπάνια συστροφής με στόχο την βελτίωση της αποδοτικότητας τους αλλά και την διάρκεια ζωής τους. Πέραν τούτου, παρουσιάζονται πειραματικές μελέτες που έχουν πραγματοποιηθεί με διάφορες γεωμετρίες εργαλείων διάτρησης σε διάφορους τύπους μετάλλων όπως ο ανοξείδωτος χάλυβας, τα κράματα τιτανίου αλλά και διάφορα άλλα ανθεκτικά μέταλλα που βρίσκουν εφαρμογή σε εξαιρετικά απαιτητικές συνθήκες λειτουργίας, όπως πολύ υψηλές θερμοκρασίες ή καταπονήσεις από μεγάλα φορτία. Κλείνοντας, στο παρόν κεφάλαιο παρουσιάζονται και μελέτες που σχετίζονται με την μοντελοποίηση της διαδικασίας διάτρησης με την χρήση λογισμικού. Στην συνέχεια, γίνεται σύντομη αναφορά στις υπολογιστικές μεθόδους επίλυσης διεργασιών κοπής που εφαρμόζονται σε λογισμικά προσομοίωσης. Πραγματοποιείται λεπτομερής παρουσίαση του μοντέλου που θα αναπτυχθεί και θα αναλυθεί μέσω λογισμικού, καθώς και τρισδιάστατος σχεδιασμός των κοπτικών εργαλείων αλλά και του προπλάσματος που θα χρησιμοποιηθεί ως κατεργαζόμενο υλικό. Ακολούθως, αναπτύσσονται ψηφιακά μοντέλα και εκπονούνται οι απαραίτητες προσομοιώσεις με την μέθοδο των πεπερασμένων στοιχείων για διάφορες περιπτώσεις, ώστε να εξεταστεί η σχέση μεταξύ της διαφορετικής γεωμετρίας εργαλείων. Επιπροσθέτως, πραγματοποιούνται πειράματα με στόχο την συγκέντρωση πληροφοριών σχετικά με την διεργασία διάτρησης τα οποία συγκρίνονται με τα ψηφιακά πρότυπα. Εν κατακλείδι, η παρούσα εργασία συνοψίζεται, και τα ανωτέρω αποτελέσματα αξιολογούνται όσον αφορά τις διεργασίες διάτρησης. Οι τελευταίες παράγραφοι της παρούσας μελέτης περιγράφουν πως θα μπορούσαν να εφαρμοστούν στην πράξη τα συγκεκριμένα ευρήματα και ποια κατεύθυνση θα μπορούσαν να έχουν μελλοντικές έρευνες.
Open Access
Human robot collaboration (HRC) for assembly operations using industrial robots
Δημουλάς, Κωνσταντίνος; Μούρτζης, Δημήτριος; Μούρτζης, Δημήτριος; Χρυσολούρης, Γεώργιος; Χόνδρος, Θωμάς; Dimoulas, Konstantinos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Today’s European industry faces the challenge of achieving flexibility and efficiency in order to improve its competitive position in the world market. There are numerous industrial applications, where the assembly process is mainly performed by human operators. The introduction of robots to support assembly operators reduces the need for physical strength and repetitive tasks. By allowing a safe human robot collaboration (HRC) in a fenceless and safe environment, the synergy effect of the robot’s precision, repeatability and strength with the human’s intelligence and flexibility will be much greater, especially in the case of small scale production, where re-configurability and adaptability are of great importance.
Open Access
Integration of a dual robot configuration in the grasping and manipulation process of commercial goods
Ξυθάλης, Σωτήριος - Μάριος; Μούρτζης, Δημήτριος; Μούρτζης, Δημήτριος; Χόνδρος, Θωμάς; Παπαδόπουλος, Χρήστος; Xythalis, Sotirios - Marios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
The main objective of this thesis is to integrate a single or dual robotic arm(s) in the production line of consumer goods industry, specifically for the grasping and manipulation of parts fed in random positions and orientations and the assembly of parts to create final products. Implementation of such a solution could dramatically increase flexibility compared to a current production method that is based on vibratory feeder bowls or similar devices, which are product specific. A key element of the procedure for satisfying those requirements is the development of a versatile end effector suitable for high speed and delicate manipulation of consumer goods, accompanied by a flexible control strategy Additionally, exploitation of the developed solution in other areas of the assembly process is examined. Implementation of such a solution could dramatically increase flexibility compared to existing production methods, mainly based on vibratory feeder bowls or similar devices, which are product specific. In the current study, the development of a novel electromechanical manipulator and the control strategy complementing the device are presented. Successful implementation of the proposed method (as evidenced by the pilot case of the study) revealed the potential of such a solution towards successful implementation in a versatile robotic cell in the assembly process of consumer goods.
Open Access
Knowledge-based manufacturability assessment of AM
Τζιμάνης, Κωνσταντίνος; Tzimanis, Konstantinos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Metal-based AM processes, although mature enough for small-batch production, are seldom first-time-right. This means that the user needs to print at least a few parts to test and validate that the process is performing as intended, while modifying both the geometry and the process plan (process parameters, path planning strategy etc.). This thesis aims at using pre-existing data (from metrology, real time process monitoring, inspection of the final part) and knowledge generated through additively manufacturing different components and apply them in an intelligent way to assess the manufacturability of a new part. A twofold methodology is proposed that evaluates the manufacturability of a part in terms of shape accuracy and structural integrity. Although, the inputs for both individual models are coming from different sources, however, they are combined in a common data structure, also being registered in time and place, in order to facilitate the data processing and to understand how the process parameters and the part design can lead to defects (cracks-non manufacturable features). Prior to the modelling, detailed analysis has been conducted to prove which of the available datasets could be used for predictors of the machine learning model, ensuring the high accuracy of the results. The first model aims to give as output the probability for the initiation or the propagation of the crack and the exact location by utilizing metrics and indicators that rely on existing knowledge. In addition, the second model utilizes the .stp format of the 3D CAD so as to detect critical geometries and to compare them with experimentally obtained thresholds that indicate if a part is manufacturable as is or design modifications are needed. Both models are related to the machine specifications and the processed material. However, re-calibration of model is possible by following the described methodology. The intuitive user interface of the developed software tool will give an insight about the manufacturability of the part, indicating where the defect is found, either manufacturing or shape.
Open Access
Modelling of key performance indicators (KPIs) for manufacturing processes
Κομηνέας, Γεώργιος; Μούρτζης, Δημήτριος; Χρυσολούρης, Γεώργιος; Νικολακόπουλος, Παντελής; Komineas, Georgios
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
Material Extrusion (ME) is one of the most common additive manufacturing processes. ME makes objects from 3D data joining materials layer upon layer using thermal extrusion process. In the scope of this study several build time estimation modelling approaches for the Material Extrusion (ME) process has been developed. Moreover, a methodology for the experimental characterization of the kinematic properties of ME AM machines is suggested.