Papers by John Giannatsis
Applied Sciences, 2021
Data Envelopment Analysis (DEA) is an established powerful mathematical programming technique, wh... more Data Envelopment Analysis (DEA) is an established powerful mathematical programming technique, which has been employed quite extensively for assessing the efficiency/performance of various physical or virtual and simple or complex production systems, as well as of consumer and industrial products and technologies. The purpose of the present study is to investigate whether DEA may be employed for evaluating the technical efficiency/performance of 3D printers, an advanced manufacturing technology of increasing importance for the manufacturing sector. For this purpose, a representative sample of 3D printers based on Fused Deposition Modeling technology is examined. The technical factors/parameters of 3D printers, which are incorporated in the DEA, are investigated and discussed in detail. DEA evaluation results compare favorably with relevant benchmarks from experts, indicating that the suggested DEA technique in conjunction with technical and expert evaluation could be employed for ev...
3D Printing (3DP) technologies are increasingly being employed for the production of consumer pro... more 3D Printing (3DP) technologies are increasingly being employed for the production of consumer products and mechanical components in the manufacturing sector, because of the advantages they exhibit as far as fabrication speed and flexibility are considered. This shift of focus in the application of 3DP technologies puts a new emphasis on the study of some of the process planning problems and issues that are related with the cost efficient use of 3DP systems and the quality of their products. As a result, the packing or platform layout optimization problem for the simultaneous fabrication of different parts has been identified as one of the most crucial tasks encountered in the process planning phase of 3DP. In the present paper a study of this problem that focuses on 3DP technologies that due to technical or quality reasons exclude the fabrication of a part on top of another, e.g. Stereolithography (SL) is presented. The methodologies discussed in the paper, employ a heuristic optimi...
A Heterogeneous Infill Technique for Fused Deposition Modeling
Fused Deposition Modeling (FDM) is one of the most commonly employed Additive Manufacturing techn... more Fused Deposition Modeling (FDM) is one of the most commonly employed Additive Manufacturing technologies worldwide. FDM parts are composed by layers of thermoplastic materials deposited through the controlled movement of one or more extrusion heads. Material deposition is usually performed in two distinct steps, the first involving the construction of the layer’s boundary and the second concerning the inner structure or infill. In the present paper an infill technique for the fabrication of parts with heterogeneous internal structure is proposed. To achieve this, the layer area is subdivided into sections which are covered by deposition paths of appropriate length according to material mapping information. Two path construction approaches are employed: one for establishing deposition paths for inner sections and another for drawing paths of peripheral sections. In order to test the effectiveness of the approach several test cases, involving relatively complex layer shapes and materi...
International Journal of Energy Optimization and Engineering, 2020
In the guise of artificial neural networks (ANNs), genetic/evolutionary computation algorithms (G... more In the guise of artificial neural networks (ANNs), genetic/evolutionary computation algorithms (GAs/ECAs), fuzzy logic (FL) inference systems (FLIS) and their variants as well as combinations, the computational intelligence (CI) paradigm has been applied to nuclear energy (NE) since the late 1980s as a set of efficient and accurate, non-parametric, robust-to-noise as well as to-missing-information, non-invasive on-line tools for monitoring, predicting and overall controlling nuclear (power) plant (N(P)P) operation. Since then, the resulting CI-based implementations have afforded increasingly reliable as well as robust performance, demonstrating their potential as either stand-alone tools, or - whenever more advantageous - combined with each other as well as with traditional signal processing techniques. The present review is focused upon the application of CI methodologies to the - generally acknowledged as - key-issues of N(P)P operation, namely: control, diagnostics and fault dete...
3D Printing of Parts with Intra-Layer Variable Density
Key Engineering Materials, 2019
3D Printing can be considered as one of the most innovative manufacturing processes of our time. ... more 3D Printing can be considered as one of the most innovative manufacturing processes of our time. Part of the innovative potential of 3D Printing is associated with the production of geometrically complex parts in a relatively short time. In the present paper, a methodology for the production of parts with complex internal structure and intra-layer density variability (ILDV) is presented. The proposed methodology may be used to produce structures composed by two materials, such as functionally graded parts and composites. The variability of the internal structure and composition is captured through voxel modeling, where at each voxel a unique relative density value for each material is assigned. These relative density values are then translated to predefined extrusion paths, which the 3D printer follows for the construction of layers composed by one or two materials. Representative cases and examples of parts with ILDV are presented and discussed.
Fabrication of graded structures by extrusion 3D Printing
2015 IEEE International Conference on Industrial Engineering and Engineering Management (IEEM), 2015
3D Printing allows the cost-effective and fast fabrication of parts with intricate/complex extern... more 3D Printing allows the cost-effective and fast fabrication of parts with intricate/complex external and internal structure through the controlled addition of thin layers of material. This way, heterogeneous structures, i.e. structures with non-uniform density, can be constructed. In the present paper a method for the production of gradient structures with extrusion-type 3D Printing is discussed. The method involves three main steps: defining the geometry and material distribution of each layer in the form of a grayscale image, generating a set of points distributed according to the gray tone of the image and constructing a continuous path through the points for guiding material deposition by the 3D printer. In order to better present and test the method, two test cases of gradient structures are examined.
Efficient parts nesting schemes for improving stereolithography utilization
Computer-Aided Design, 2013
ABSTRACT In the present paper, the platform layout optimization problem for the simultaneous fabr... more ABSTRACT In the present paper, the platform layout optimization problem for the simultaneous fabrication of different parts, which is addressed in the batch planning of Stereolithography Additive Manufacturing technology, is studied. The methodology proposed in the paper employs a Genetic Algorithm technique for the 2D nesting of parts on the platform of the stereolithography machine. The build orientation of the parts is assumed fixed and is decided prior to layout optimization, according to part-specific quality and cost requirements. Three placement schemes, appropriately adapted to the problem, are considered for the parts nesting and fabrication layout definition. The algorithms and placement schemes developed are evaluated in several test cases/benchmarks involving parts with both simple and complex geometries. The computational results included in the paper indicate that the proposed methodology can lead to satisfactory layout/packing–nesting arrangements in a time efficient manner, leading, therefore, to substantial improvement of stereolithography machine utilization.
Fabrication of parts with heterogeneous structure using material extrusion additive manufacturing
Virtual and Physical Prototyping, 2021
ABSTRACT Additive manufacturing technologies (AM) have a unique capacity for handling geometrical... more ABSTRACT Additive manufacturing technologies (AM) have a unique capacity for handling geometrical complexity and are, therefore, ideal for producing parts with geometrically complex form and structure. In this paper, a methodology for fabricating parts of heterogeneous internal structure by thermoplastic Material Extrusion (MEX) is proposed. Construction of the corresponding layer deposition paths is performed according to locally-defined material density, encoded in the form of a voxel part model. Specific algorithms for constructing a single layer deposition path by joining elementary deposition paths of semi-random or standard shape are developed and tested. Computational tests of the developed algorithmic procedures indicate that the associated computer processing time, is comparable to that implied by conventional slicing and path planning techniques. Results of fabrication tests employing an open-hardware MEX system further prove the feasibility of the approach.
Developing competitive products using Stereolithography Rapid Prototyping tools
The competition that manufacturing industries are facing in today's economic environment is treme... more The competition that manufacturing industries are facing in today's economic environment is tremendous. Nowadays international markets ask for better and cheaper products with a higher `innovative content'. In order to achieve these goals the manufacturing industry has to resort to computer aided-driven, practices and tools that shorten the overall product development cycle and increase the product innovation dynamic. Some of the most important such tools are those collectively known as rapid prototyping tools, which can build physical prototypes, production tools or even small batches of the actual product itself, within a few hours. The purpose of this paper is to present the most prominent and mature of the rapid prototyping technologies, namely stereolithography, and investigate its role in the design and development process. The presentation is carried out by discussing specific successful test cases that concern the development of new plastic products and the improvement of `older' versions of them.
Effective nesting of Layer Manufacturing fabricated parts using a Genetic Algorithm and a bottom-left ray casting procedure
Two aspects have been identified to be the key elements to the effective utilization of Layer Man... more Two aspects have been identified to be the key elements to the effective utilization of Layer Manufacturing (LM) technologies, that is maximization of the build volume and part orientation. The present work examines the utilization of a Genetic Algorithm in conjunction with effective placement rules as a mean of optimizing the build volume of LM technologies. The optimization is achieved via the dense nesting of parts, to be fabricated, on the LM machine platform. The software tool developed tackles the 2D nesting problem associated with the parts projections on the machine platform. The effectiveness and reliability of the proposed methodology is demonstrated via a case study concerning representative “real-world” parts/objects with quite general free form geometry.
Determination of the Pareto-optimal build orientations in Stereolithography
The selection of build orientation for a given part is one of the most important tasks encountere... more The selection of build orientation for a given part is one of the most important tasks encountered in the process planning phase of Layer Manufacturing in general and Stereolithography in particular. The orientation selection is by definition a multi-criteria optimization problem in which the operator seeks to achieve the optimum trade-off between cost and quality depending on the given fabrication constraints and requirements. In the present work a solution approach that focuses on the determination of the set of Pareto-optimal orientations is examined. Pareto-optimal orientations could be considered as a set of good choices for the selection of the optimum orientation for both single part and multiple (batch) fabrication. For the construction of this set in a time-efficient manner a Genetic Algorithm is employed. In order to investigate the efficiency of the proposed approach a case study is examined and the corresponding results are presented.
Stereolithography assisted redesign and optimisation of a dishwasher spraying arm
Rapid Prototyping Journal, Jan 1, 2004
The aim of this paper is to show how models fabricated via stereolithography (SL) served as “func... more The aim of this paper is to show how models fabricated via stereolithography (SL) served as “functional prototypes” for the redesign and optimisation of the spraying arm of a small dishwashing machine. The redesign process depended entirely on systematic experimental testing. SL modelling was employed in order to realise the various geometries proposed for the “new” spraying arm. The SL
International Journal of Advanced Manufacturing Technology, Jan 1, 2009
Build orientation is an important fabrication parameter in layer manufacturing (LM) since it affe... more Build orientation is an important fabrication parameter in layer manufacturing (LM) since it affects the part fabrication accuracy, cost, and time. Despite its importance, orientation selection relies quite heavily on the experience and skill of the operator of the LM system, which does not guarantee optimality of the decision. In the present work, a decision support system that automates the orientation selection task is proposed. The proposed system utilizes genetic algorithms and multi-criteria optimization techniques for the definition of (near) optimum build orientation for parts fabricated with stereolithography. Build time, surface roughness, and post-processing time are considered as the main optimization criteria.
Decision support tool for selecting fabrication parameters in stereolithography
International Journal of Advanced Manufacturing Technology, Jan 1, 2007
The selection of fabrication (build) parameters is the most important task performed by the opera... more The selection of fabrication (build) parameters is the most important task performed by the operator of a layer manufacturing (LM) system. In order to select the best parameter configuration for a part, the operator should be able to compare different alternatives and evaluate them under specific constraints, in terms of fabrication cost and quality. In the present paper, a software
Architectural scale modelling using stereolithography
Rapid Prototyping Journal, Jan 1, 2002
The purpose of this paper is to investigate the applicability and effectiveness of Stereolithogra... more The purpose of this paper is to investigate the applicability and effectiveness of Stereolithography rapid prototyping to the field of scale modelling for architectural design evaluation and demonstration purposes. Two scale models concerning a modern renovated track and field sports facility and a reconstructed ancient stadium are examined. Both models were constructed by assembling together resin parts fabricated with Stereolithography
Additive fabrication technologies applied to medicine and health care: a review
International Journal of Advanced Manufacturing Technology, Jan 1, 2009
Additive fabrication (AF) and rapid prototyping (RP) technologies are mostly associated with appl... more Additive fabrication (AF) and rapid prototyping (RP) technologies are mostly associated with applications in the product development and the design process as well as with small batch manufacturing. Due to their relatively high speed and flexibility, however, they have also been employed in various non-manufacturing applications. A field that attracts increasingly more attention by the scientific community is related to the application of AF technologies in medicine and health care. The associated research is focused both on the development of specifically modified or new methods and systems based on AF principles, as well as on the applications of existing systems assisting health care services. In this paper, representative case studies and research efforts from the field of AF medical applications are presented and discussed in detail. The case studies included cover applications like the fabrication of custom implants and scaffolds for rehabilitation, models for pre-operating surgical planning, anatomical models for the mechanical testing and investigation of human bones or of new medical techniques, drug delivery devices fabrication, as well as the development of new AF techniques specifically designed for medical applications.
Robotics and Computer-integrated Manufacturing, Jan 1, 2001
In this paper the problem of build-time estimation for Stereolithography systems is examined. Exp... more In this paper the problem of build-time estimation for Stereolithography systems is examined. Experimental results from various case studies indicate that the accuracy of estimation greatly depends on the type of part geometry representation processed and the uncontrolled laser power fluctuations. It is shown that estimation based on sliced (CLI) representation can be extremely accurate, assuming that the average laser power during fabrication can be predicted. On the other hand, estimations based on tessellated (STL) representation, although not so accurate, satisfy the accuracy requirements imposed at early stages of the Stereolithography process, where no slice data are available. As part of this study, build-time itself is also analyzed and factors affecting it are identified and investigated experimentally. Results indicate that hatching time depends not only on the hatching distance and speed, as originally assumed, but also on the number of hatching vectors employed.
Applied Ergonomics, Jan 1, 2010
Proper bicycle fit is very important for cycling performance, efficiency, comfort and injury prev... more Proper bicycle fit is very important for cycling performance, efficiency, comfort and injury prevention. This is especially true in the case of children cyclists that do not have the necessary cycling experience, balance and the fully developed musculoskeletal system of the adults. Bicycle fit depends on both the design and dimensions of the bicycle as well as on the anthropometric dimensions of the cyclist. In the present paper a case study concerning the ergonomic evaluation and redesign of a series of bicycles for children and teenagers 7-14 years old is presented. The study has been commissioned by a major Greek bicycle manufacturer who wanted to gain competitive advantage by introducing new anthropometrically-designed bicycles. Employing virtual modelling techniques and the method of Principal Component Analysis, bicycle affordance for selected representative cases and various bicycle sizes has been examined. Based on the results of the study redesign recommendations that improved bicycle fit for specific groups were proposed and a formal bicycle size selection method has been defined. The redesigned bicycles are now in full production and distribution is underway in many commercial outlets in Greece.
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Papers by John Giannatsis