George-Christopher Vosniakos

George-Christopher Vosniakos
National Technical University of Athens | NTUA · School of Mechanical Engineering - Section of Manufacturing Technology

MSc, PhD

About

206
Publications
113,791
Reads
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3,385
Citations
Introduction
(a) Human-Robot collaboration in Manufacturing (b) Additive Manufacturing: control, path planning, part shape optimisation (c) Intelligent Monitoring of manufacturing processes (d) Virtual Reality in Manufacturing (e) Automation of fabric reinforced composites manufacturing
Additional affiliations
January 1998 - present
National Technical University of Athens
Position
  • Professor
January 1989 - December 1990
University of Manchester Institute of Science and Technology
Position
  • CAD-CAPP intelligent integration

Publications

Publications (206)
Article
Full-text available
This work reports on the design and manufacture of an efficient system for powder deposition into layers in an open Selective Laser Sintering machine. The system comprises mainly two subsystems, i.e., one that deposits a dose of powder onto the worktable and another that levels the powder upon its deposition. The design was conducted in two phases,...
Article
Full-text available
One of the most important aspects of Powder Bed Fusion (PBF) processes is the powder layer spreading. The powder layer needs to be applied in such a way that its evenness and homogeneity is ensured. This, in turn, will ensure that no inconsistencies or defects of the non-sintered powder layers, internal or superficial, will be inherited to the fini...
Article
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This paper examines the issues pertaining to the design and development of robotic welding stations for large intricate products, by example of a fabric dying machine, combining large sheet metal parts into a shell and smaller parts in the form of pipes, ducts and flanges. The main relevant issues concern: (a) layout of the workstation considering...
Article
Traditionally, metal surface polishing has been an important high precision process that has mostly been carried out manually, due to its high complexity and the difficulty in controlling many process parameters simultaneously. In this work a prototype polishing jig that offers elementary force control capability is utilised in order to perform fla...
Article
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Single point incremental forming (SPIF) that will produce non-symmetric sheet metal parts has been rarely dealt with so far. SPIF of a Francis hydro-turbine vane made of aluminum alloy is studied as a typical example in this work. At first, a concave geometry, encompassing the desired vane shape is designed, from which the formed part will be ultim...
Article
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This study presents a temperature regulation methodology for Laser Based Additive Manufacturing. A Surrogate Model based on Artificial Neural Networks is trained by Finite Element simulations to predict peak temperature on the powder bed under a moving laser beam. The beam may follow a discretized trajectory of arbitrary shape, while laser power is...
Article
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Guillotine shearing machines for metal sheet may be inadvertently operated at increased blade clearance. Typical cases were studied using commercially available finite element software with an explicit solver. Loads causing elastic deformation to the machine structure arise from plastic deformation of the sheet metal being processed, its behavior b...
Article
In Selective Laser Sintering and Melting it is necessary to protect metal powder deposited on the powder bed from contact with atmospheric air, which may lead to oxidation and downgrading of the properties of the powder in the presence of high temperature that is necessary for achieving full or partial melting. Thus, the building chamber of commerc...
Article
In studying manufacturing processes it is often necessary to compare nominal or reference product shapes that are expected to be ideally achieved after applying a nominal set of process parameters and the actual product shape achieved. The latter is usually obtained by metrological equipment such as profilometers, tomographs and 3D scanners, whilst...
Article
High-end commercially available CAD/PLM systems support virtual simulation of assembly procedures using digital avatars. An advanced solution involves real people in virtual manufacturing environment. This work presents development of a Virtual Reality environment based on an open game engine. This is developed in order to test assembly plans execu...
Conference Paper
Full-text available
This work focuses on human-robot collaboration as exemplified in modern assembly cells. Assembly with robotic assistance was studied, in order to investigate in quantitative terms the robot contribution in collaboration with the human towards better efficiency and avoidance of musculoskeletal strain. The above were studied, presented and discussed...
Conference Paper
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This work focuses on automated recognition of clogging in the nozzle of a typical material extrusion 3D printer, a fault that has potentially severe consequences for both the printer and the printed part, should it not be rectified in a timely manner. Several methods were considered initially, such as monitoring temperature or vibrations at low-cos...
Conference Paper
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Cellular structured parts are designed by repeating a unit cell in 3 dimensional space. Dimensional accuracy of such parts that were 3D printed through Material Extrusion process is assessed in this paper. Focus is put on the influence of process parameters on cell accuracy. A pertinent Taguchi experiment was designed and the samples were 3D printe...
Conference Paper
Full-text available
Commercial Selective Laser Sintering (SLS) machines possess their own embedded powder deposition systems (PDS), most of which are based on the principle of powder containing piston in combination with a roller for powder spreading. These systems are factory-calibrated and do not offer the possibility to actively modify any pertinent powder depositi...
Conference Paper
Full-text available
In Selective Laser Sintering, powders of various materials are deposited layer by layer in order to form 3D objects of complex geometries via sintering or melting by a concentrated laser source. The evaluation of the quality of the non-sintered powder layer is of paramount importance, because it is among the parameters that influence the mechanical...
Article
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Porous collagen-based scaffolds are biostructures with demonstrated ability to induce regeneration in animal models as well as in human patients. In addition to their porous structure and physicochemical properties that have been shown to affect the regeneration process, channel-like features inside the scaffolds could provide additional beneficial...
Article
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Material Extrusion (ME) is one of the established processes in Additive Manufacturing (AM) realm. The process involves deposition of adjacent material strands that are bonded together in order to create successive layers that are stacked one upon the previous until the three-dimensional part is fabricated. One of the key factors for increased perfo...
Article
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This work focuses on the efficient design of a controller for a Flexible Manufacturing System (FMS) using Agents. The necessary agents were selected and defined according to the Design of Agent-based Production Control Systems (DACS) methodology. The Contract Net Protocol (CNP) was applied for agent communication and interaction. A particular Algeb...
Preprint
Full-text available
This paper presents a system for monitoring and regulating the injection of resin into technical fabric pieces laid up against a die, a process that is commonly used in the production of composite materials by vacuum (VARI). To implement this system, a conventional webcam was used to capture the flow of resin and standard machine vision routines we...
Article
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Injection moulding of plastic parts is a long established manufacturing process requiring rich experience both on mould design and on machine settings. It is customary to use process simulation software, which is considered mature enough, in order to validate tooling design and machine settings before these are tested in production. In this work, t...
Preprint
Full-text available
Sheet metal bending on press brakes is one of the most widespread manufacturing processes. A common issue in press brake bending is the deviation of the actual bending angle from the theoretical one due to elastic spring-back of the sheet metal. This is typically rectified by a systematic trial-and-error process, which has to be based on a suitable...
Article
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Composite materials are increasingly exploited in industry especially replacing metallic structures due to their strength/weight ratio. Amongst the notable applications, for which composite materials have not challenged metals yet are hydro-turbines, which are overwhelmingly made of steel or copper alloys. Replacing blade material by laminate compo...
Article
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Drones have become an advanced supply chain implementation instrument, especially in connecting warehouses to outlet points or even individual customers. However, their potential application in an intra-logistics framework has not been studied, let alone explored so far. Modeling and simulations in virtual environments can help explore and evaluate...
Article
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Design optimization for Additive Manufacturing is demonstrated by the example of an industrial robot link. The part is first redesigned so that its shape details are compatible with the requirements of the Selective Laser Sintering technique. Subsequently, the SIMP method of topology optimization is utilized on commercially available software in or...
Article
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This study predicts in real time the evolution of temperature and density for arbitrary long tracks in laser-based additive manufacturing using artificial neural networks (ANNs). First, a random laser path is transformed appropriately to serve as an ANN input via a custom trajectory decomposition method providing a local description of each traject...
Article
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The subject of this work is layout planning of machinery, especially for Flexible Manufacturing Systems (FMS), using Augmented Reality tools. The goal is for the user to evaluate suggested layouts by taking into account non-measurable factors, such as operator experience, empirical or non-tacit knowledge and on-site impression. By reference to exis...
Preprint
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A low-cost portable stereolithography (SLA) device is designed to cure polymer resin at suitable laser light wavelength. Required motions are imparted by any three-axis CNC machining center exploiting serial communication interface, macro programming and machine data manipulation facilities. The device consists of three subsystems: laser beam, resi...
Preprint
Full-text available
This study predicts in real time the evolution of temperature and density for arbitrary long tracks in Laser Based Additive Manufacturing using Artificial Neural Networks (ANNs). First, a random laser path is transformed appropriately to serve as ANN input via a custom trajectory decomposition method providing a local description of each trajectory...
Article
Full-text available
Industrial robots need to be programmed quickly in order to be practically deployable in the production of small batches. In programming by teaching or demonstration, when most of the program’s content involves handling tasks, gesture recognition or other multimodal interfaces may be exploited. However, when the main task concerns manufacturing pro...
Article
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Dimensional accuracy in additive manufacturing and especially for parts produced via material extrusion has been actively investigated in an effort to proceed from a prototyping process to a mature technology capable of manufacturing functional parts. Typically, accuracy in material extrusion is not the same along the different printing directions...
Article
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The concept of smart factory includes collection and distribution of information in real time to help human operators in their work. Machine setup instructions are notable examples of such information. This paper advocates the use of augmented reality (AR) to present such information addressing in an intuitive manner the demonstration of setup task...
Article
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Despite significant advances and established advantages of material extrusion additive manufacturing, limitations still exist regarding ability to increase productivity and still maintain high shape fidelity and defect-free parts within the range of process parameter values that a 3D printer may support. In the present study, a predictive process-p...
Article
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Programming of an industrial robotic arm is demonstrated in this work, so as to adapt the robot’s prescribed movements in order to guarantee safety of the human with whom the robot shares its workspace. The robot must either stop or change trajectory or slow down when it detects a human in its course. The approach is applicable not at robot operati...
Article
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“beWare of the Robot” is a custom-designed Virtual Reality application and implemented as a platform for simulating in real-time Human-Robot collaboration in manufacturing tasks. This work reports on its use for investigating two alternative safe collaboration strategies, namely ‘Reduce Speed’ and ‘Move Back’, in the task of handling fabric when bu...
Article
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This paper investigates selective laser sintering/melting (SLS/SLM) processes by a thermal model solved with a finite difference scheme. The density equation is semi-empirical based on the Arrhenius equation and experimental results taken from literature. Energy distribution function in the laser beam is appropriately considered. The main input par...
Conference Paper
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The article presents in some detail two CNC machine tool metrology applications using laser systems. The first application concerns the measurement of position error of a linear axis of a turning center conducted with a laser Doppler interferometry system, according to the ISO-232-2 standard. This was followed by a compensation procedure on the con...
Article
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Automation of polishing planar surfaces on 3-axis machining centers is treated from the point of view of defining suitable tool paths that provide full and even coverage of the surface both along and across straight line guide curves, which are routinely produced by any CAM system. A fast but approximate and a slower but precise trochoidal path cal...
Article
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This paper reports on the construction of a virtual environment on top of a commercially available authoring platform that simulates an industrial robotic arm in pick-and-place movement scenarios. The user interface constructed follows in functionality the well-known teach pendants but exploits just a normal PC keyboard. However, both forward and i...
Article
Material removal volume calculations in machining processes are important in a variety of milling simulation applications, including material removal rate estimation and machining force calculation. In this paper two different approaches are presented to this end, i.e., Z-maps and Boolean operations with solid models. The Z-map method is simple but...
Article
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This paper reports on the design, manufacture, control and implementation of a robotic head for filament winding, typically carbon, glass etc. employed in shell-like part manufacturing with composite materials. The head is attached to a 6 axis industrial robot collaborating with a rotary axis on which a die is secured. Concept development and preli...
Article
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A prototype Fused Deposition Modelling (FDM) head is reported on, attached to an industrial robot, in this case 6-axis arm with high repeatability, to form a robotic 3D printer. The detailed design is presented including theoretical calculations regarding pressure drop in the nozzle. Selection of the off-the-shelf electronic components and their in...
Article
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Application of immersive Virtual Reality is advocated for assessing human-based assembly of large mechanical parts, including assembly jigs and fixtures as well as tools used and procedures followed. The primary aim is to enable subjective/customised assessment of the assembly system by the participating human. The secondary aim is to allow recordi...
Article
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The need to manufacture a copy of a mechanical part typically arises when a single replacement part is necessary and is out of stock or out of production altogether. For parts with intricate details and associated accuracy requirements, investment casting may be preferred to machining, for size and detail reasons, or 3D printing, for material reaso...
Conference Paper
Full-text available
Tools of CNC press brakes are attached to the ram of the press by conventional clamping systems ensuring firm support but not easy exchange, because they rely on tightening and loosening of a large number of screws. Some non-conventional proprietary systems are available in the market exploiting pneumatic, hydraulic or mechanical clamping principle...
Article
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This paper presents the methodology and development tools employed to specify the path of an industrial robot in a virtual environment (VE) that is typically used for game development. Initially, the cell and the robot are designed and then imported into the VE, followed by the development of the kinematic chain of the robot. Forward and inverse ki...
Article
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A highly immersive and interactive virtual environment was constructed as an experimentation platform for human–robot collaboration in constricting panels from preimpregnated carbon fibre fabrics. The application involves highly collaborative tasks such as handover, removal of adhesive backing strip and fabric layup in a mould. Furthermore, the use...
Article
Human-Robot Interaction (HRI) has emerged in recent years as a need for common collaborative execution of manufacturing tasks. This work examines two types of techniques of safe collaboration that do not interrupt the flow of collaboration as far as possible, namely proactive and adaptive. The former are materialised using audio and visual cognitiv...
Article
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This work proposes an interactive method of view planning for capturing the whole surface of an object with minimum prior knowledge of its shape and with the assistance of standard computer vision algorithms. Two notions have been defined, i.e. Main Face Groups (MFGs) and Difficult Regions (DRs) and are central to the method. The method aims to hel...
Article
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The Internet of Things (IoT) can be regarded as an attempt to bring together the physical and the digital world by using devices for seamlessly exchanging and processing information that can be used anywhere, anytime. For industrial automation and manufacturing, the Industrial Internet of Things (IIoT) is regarded as the next step of industrial rev...
Article
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A polishing jig was designed and manufactured to enable polishing of metal surfaces on CNC machining centres, on which these surfaces are normally finish-machined first. The jig accommodates ring-type tools rotated by a high speed spindle, rendering the machining centre’s own spindle redundant. Passive control of the polishing force is materialized...
Article
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In laser processing of surfaces, typically to impart some texture or to drill shallow holes, it is necessary to correlate pulse properties (wavelength, power, beam radius and quality, duration) and material properties (reflectivity, melting temperature, conductivity, diffusivity) mainly with the depth of the formed crater. Crater shape is assumed t...
Article
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Programming of computer numerical control (CNC) machining centres using computer aided manufacturing (CAM) software is efficient provided that machining operations and their sequence has been correctly determined by the user. Such decisions, however, are a largely matter of experience. If the user is inexperienced, then Computer Aided Process Plann...