Dr. Konstantinos Ninikas

University of Thessaly

Dr. Konstantinos Ninikas

University of Thessaly

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Academic Career Length

8Years (2019-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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31 March 2021 in Materials and Manufacturing Processes

Journal Article

An investigation of surface quality characteristics of 3D printed PLA plates cut by CO2 laser using experimental design

John (Ioannis) Kechagias

Konstantinos Ninikas

Markos Petousis

N. Vidakis

N. Vaxevanidis

In this work, two typical surface characteristics, i.e., mean surface roughness and angle of the kerf during laser processing of 3D-printed Polylactic Acid (PLA) plates with 4.00 mm in thickness, are investigated. A carbon dioxide laser was utilized to separate 27 work pieces of rectangular shape. The governing laser parameters, speed of cutting and laser power, were varied according to full factorial experimental methodology. An orthogonal array (OA) having nine combinations was implemented, and nine specimens were cut with the same set-up and the same parameters three times (27 replicates in total). The experimental results were analyzed using descriptive statistical analysis, i.e., histograms, box plots, interaction charts and optimized using analysis of means (ANOM) plots as well as ANOVA analysis. The data analysis indicated that laser speed is the dominant parameter for the kerf angle, whilst both the laser velocity and power are important for mean surface roughness of the cut surface for PLA 3D-printed parts. The spread of the data is smaller in Y direction, which indicates that the weaving phenomenon affects the laser cut performance.

29 September 2021 in Materials and Manufacturing Processes

Journal Article

Surface characteristics investigation of 3D-printed PET-G plates during CO2 laser cutting

John (Ioannis) Kechagias

N.A. Fountas

Konstantinos Ninikas

Markos Petousis

N. Vidakis

N. Vaxevanidis

This study investigates the influence of the stand-off distance (SoD), laser speed (LS) and laser power (LP) on kerf geometry (upper width Wu, down width Wd and kerf angle KA) and mean surface roughness (Ra) during CO₂ laser cutting of 3D-Printed Polyethylene-Terephthalate-Glycol (PET-G) thin plates. A full factorial design is implemented, having two levels for SoD and three levels for LS and four levels for LP, resulting in twenty-four (24) cuts. The specimens were manufactured with the Fused Filament Fabrication (FFF) process and had a thickness of 4 mm. First, the Wu, Wd, and KA parameters were measured. Then, the specimens were cut into 24 smaller parts, and the Ra of the processed surfaces was measured. After analyzing the results using descriptive statistical analysis and contour plots corresponding to the two objectives of KA and Ra, a feed-forward and backpropagation neural network (FFBP-NN) was applied. After a series of subsequent training, it was found that the 3-10-2 NN architecture was quite efficient in explaining the variation in terms of the responses, thus having merit in practical applications related to laser cutting. The LC surfaces showed much better Ra (7.2-12 μm) than those in the literature for FFF parts surfaces without post-processing (10.3-30 μm).

17 May 2021 in Journal of Composites Science

Journal Article

Thermal and Mechanical Properties of Green Insulation Composites Made from Cannabis and Bark Residues

Konstantinos Ninikas

ANDROMACHI MITANI

Dimitrios Koutsianitis

GEORGIOS NTALOS

Hamid Reza Taghiyari

Antonios Papadopoulos

The objective of this paper was to investigate the technical feasibility of manufacturing low density insulation particleboards that were made from two renewable resources, namely hemp fibers (Cannabis sativa) and pine tree bark, which were bonded with a non-toxic methyl cellulose glue, as a binder. Four types of panels were made, which consisted of varying mixtures of tree bark and hemp fibers (tree bark to hemp fibers percentages of 90:10, 80:20, 70:30, and 60:40). An additional set of panels was made, consisting only of bark. The results showed that addition of hemp fibers to furnish improved mechanical properties of boards to reach an acceptable level. The thermal conductivity unfavorably increased as hemp content increased, though all values were still within the acceptable range. Based on cluster analysis, board type 70:30 (with 30% hemp content) produced the highest mechanical properties as well as the optimal thermal conductivity value. It is concluded that low density insulation boards can be successfully produced using these waste raw materials.

7 July 2021 in Journal of Manufacturing and Materials Processing

Journal Article

The Impact of Process Parameters on Surface Roughness and Dimensional Accuracy during CO₂ Laser Cutting of PMMA Thin Sheets

Konstantinos Ninikas

John (Ioannis) Kechagias

Konstantinos Salonitis

This study investigated the impact of the laser speed and power, and the position and orientation of the samples, on the average surface roughness (Ra) and dimensional accuracy (DA) during CO₂ laser cutting of polymethyl methacrylate (PMMA) thin sheets. A mixed five-parameter fractional factorial design was applied, and thirty-six measurements for the Ra and DA were obtained. The experimental results were analysed using ANOM diagrams, ANOVA analysis and interaction plots of all parameters. It was concluded that the laser speed is the critical parameter for both surface roughness and dimensional accuracy, resulting in strong interactions with laser power and positioning parameters. It was also shown that Ra values are affected by the orientation of the specimen and can be minimized when the samples are aligned in the laser travel direction. Finally, it was proved that lower laser speed improves the average roughness but reduces the dimensional accuracy.

18 April 2023 in Journal of Manufacturing and Materials Processing

Journal Article

Kerf Geometry and Surface Roughness Optimization in CO₂ Laser Processing of FFF Plates Utilizing Neural Networks and Genetic Algorithms Approaches

John (Ioannis) Kechagias

Nikolaos A. Fountas

Konstantinos Ninikas

Nikolaos Vaxevanidis

This work deals with the experimental investigation and multi-objective optimization of mean kerf angle (A) and mean surface roughness (Ra) in laser cutting (LC) fused filament fabrication (FFF) 3D-printed (3DP), 4 mm-thick polylactic acid (PLA) plates by considering laser feed (F) and power (P) as the independent control parameters. A CO₂ laser apparatus was employed to conduct machining experiments on 27 rectangular workpieces. An experimental design approach was adopted to establish the runs according to full-combinatorial design with three repetitions, resulting in 27 independent experiments. A customized response surface experiment was formulated to proceed with regression equations to predict the responses and examine the solution domain continuously. After examining the impact of F and P on mean A and mean Ra, two reliable prediction models were generated to model the process. Furthermore, since LC is a highly intricate, non-conventional machining process and its control variables affect the responses in a nonlinear manner, A and Ra were also predicted using an artificial neural network (NN), while its resulting performance was compared to the predictive regression models. Finally, the regression models served as objective functions for optimizing the responses with an intelligent algorithm adopted from the literature.

30 October 2019 in Resources

Journal Article

Recovery and Valorisation of Energy from Wastewater Using a Water Source Heat Pump at the Glasgow Subway: Potential for Similar Underground Environments

An installation of a Water Source Heat Hump (WSHP) at Glasgow’s Underground Station, has been using the subsurface wastewater ingress to heat the office at St. George’s Cross station. The performance of the Glasgow Subway’s new heating system was observed for a few months. The energy output readings are being presented. An average coefficient of performance (CoP) of 2.5 and a 60% energy input reduction for the heating system based on the old heating system’s energy demand indicates the actual system’s performance. The purpose of this research is to detect the likelihood of implementing the same setup in similar underground environments where the excess wastewater may support a viable and eco-friendly heating system. Fifteen cities across Europe have been identified and presented, with the adequate water quantities, where similar heating systems may be applied. The output of this study indicates not only the financial benefit but also the energy and carbon reduction of this trial. It highlights main subjects which were encountered in such a challenging subway system. Future steps to commercialize the excess heat energy output are explored together with opportunities to promote the same setup in similar cases.

About Me

I am an Associate Researcher and member of the teaching staff at the Department of Forestry, Wood Sciences & Design, School of Technology, University of Thessaly, Greece. I hold a Bachelor of Engineering in Mechanical Engineering, an MSc in Energy Potentials from Waste, and a PhD in Renewable Heat Energy from Waste from Glasgow Caledonian University, UK. I have over ten years of professional experience as a self-employed engineer specialising in materials and energy. My academic career spans 2009 to 2019 at the University of Applied Sciences (TEI) of Thessaly and 2019 to the present at the University of Thessaly. I have also collaborated with Glasgow Caledonian University as an Associate Researcher on a two-year project investigating the feasibility of generating heat energy from waste within the SPT Glasgow subway tunnels. I have received further training at the Massachusetts Institute of Technology (MIT) in Energy, Sustainability and Product Life Cycle, and at Harvard University in Strategy and Innovation. Currently, I teach undergraduate and postgraduate courses in timber-related subjects at the UTH and serve as an occasional lecturer at Glasgow Caledonian University, delivering MSc-level courses. My research and teaching activities involve interdisciplinary collaboration on projects related to materials and energy from wood waste, sustainable design, and upcycling. I also contribute to international education through joint China–UK undergraduate programmes.

Dr. Konstantinos Ninikas

Dr. Konstantinos Ninikas

Research Focus & Metrics

Academic Career Length

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Representative Publications

About Me