Papers by Nikolaos I Galanis
Hip joint surgeries, including total hip replacement or resurfacing, have increased tremendously ... more Hip joint surgeries, including total hip replacement or resurfacing, have increased tremendously in the last decades. Number of patients of all ages, replace their hip, due to severe injuries or trauma problems, so as to have a better life. According to these factors, new material and processes in implants manufacturing are imported to medicine, through research programs, every year. In the scope of one of these programs, that has to do with ceramic coatings on metallic resurfacing implants, a new 3axis Hip simulator was designed and manufactured in the Laboratory of Manufacturing Technology of the National Technical University of Athens. The scope of this paper is to present the main parts, materials and process used to manufacture the simulator as well as the way the simulator is working and how its movement in 3axis is accomplished. Furthermore, the evaluation of the machine and its use to examine resurfacing implants is presented.
Proceedings of the 7 th International Conference on Tribology (BALKANTRIB’11), 2011
The surface integrity state of a machined component contributes a significant factorfor reliabili... more The surface integrity state of a machined component contributes a significant factorfor reliability and functionality. Surface roughness comprises one of the most crucialparameters of surface integrity and affects the time-life and the operational behaviorof the machined component. Based on this concept, in the present paper highturning was performed on high-alloyed tool steel specimens and the influence of themain machining parameters (cutting speed, feed rate and depth of cut) on surfaceroughness was studied. For the selection of machining parameters, full factorialdesign of experiments was applied and multi-parametric statistical analysis wasperformed. From the analysis via response surface method (RSM), it was shownthat the surface roughness is affected by each one of the three cutting parameterswith different degrees of importance with the feed rate to dominate against cuttingspeed and cutting depth.
Machines, 2002
Impellers are the most crucial components of pumps, as they directly determine the velocity profi... more Impellers are the most crucial components of pumps, as they directly determine the velocity profile of the fluid flowing through the pump and its efficiency. Given that the impellers have a complex geometry, they pose an important challenge to the manufacturer in order to construct them with the best possible dimensional accuracy and surface quality, and also achieve short machining times. In the present paper, the machining operations for the manufacture of a radial impeller were designed and implemented for the case of a single-entry semi-closed radial flow impeller. At first, the best milling strategies, optimum cutting conditions, and appropriate cutting tools were selected for each of the three machining phases, namely, roughing, semi-finishing, and finishing. Then, an experimental investigation was conducted, especially for the optimum process conditions during finishing of impeller blades, using Taguchi L16 orthogonal array. After the analysis of surface roughness was conducted for the 16 experiments, it was found that the most important parameters were spindle speed and feed. Furthermore, the optimum settings were determined as the maximum spindle speed and the lowest feed per tooth value and a regression model correlating process parameters with surface roughness was established with a high degree of accuracy.
The design and manufacturing of medical implants constitutes an active and highly important field... more The design and manufacturing of medical implants constitutes an active and highly important field of research, both from a medical and an engineering point of view. From an engineering aspect, the machining of implants is undoubtedly challenging due to the complex shape of the implants and the associated restrictive geometrical and dimensional requirements. Furthermore, it is crucial to ensure that the surface integrity of the implant is not severely affected, in order for the implant to be durable and wear resistant. In the present work, the methodology of designing and machining the femoral component of total knee replacement using a 3-axis Computer Numerical Control (CNC) machine is presented, and then, the results of the machining process, as well as the evaluation of implant surface quality are discussed in detail. At first, a preliminary design of the components of the knee implant is performed and the planning for the production of the femoral component is implemented in Computed Aided Manufacturing (CAM) software. Then, three femoral components are machined under different process conditions and the surface quality is evaluated in terms of surface roughness. Analysis of the results indicated the appropriate process conditions for each part of the implant surface and led to the determination of optimum machining strategy for the finishing stage.
The finite element method has been extensively used for the simulation of manufacturing processes... more The finite element method has been extensively used for the simulation of manufacturing processes and especially machining. In this paper, finite element models of high speed machining are presented. More specifically, orthogonal and oblique cutting models are presented, where the geometrical and material properties of the cutting tool are investigated. Orthogonal models pertain to the simulation of cutting with three different CBN tool types. Chip formation, cutting forces and temperatures are compared for each model, at the same cutting conditions. Additionally, 3D models are presented, where the back rake angle of the cutting tool is varied. From the results it may be concluded that 3D models provide more realistic results but they are computationally more demanding than 2D models. Finite element modelling of high speed machining can provide data for the process that would be either difficult or in some cases even impossible to obtain through extensive experimental work.
This study focuses on Ti–6Al–4V ELI titanium alloy machining by means of plain peripheral down mi... more This study focuses on Ti–6Al–4V ELI titanium alloy machining by means of plain peripheral down milling process and subsequent modeling of this process, in order to predict surface quality of the workpiece and identify optimal cutting parameters, that lead to minimum surface roughness. For the purpose of accomplishing this task a set of experiments were performed on a CNC milling centre and design of experiments based on Box Behnken Design (BBD) for a three factor and three level central composite design concept was conducted. Depth of cut, cutting speed and feed rate were selected as input parameters and surface roughness was measured after each experiment performed. At first, Response Surface Methodology (RSM) was employed for establishing a quadratic relationship between input and output parameters. Analysis of variance (ANOVA) was then conducted for the evaluation of the proposed formula. RSM was also used for the optimization analysis that followed for the determination of milling cutting parameters for minimum surface roughness. The analysis indicates that the use of BBD can reduce the number of experiments needed for modeling and optimizing the milling operation of Titanium alloys. Furthermore, this method is able to provide models that can reliably be used for any cutting conditions within the limits of the input data. Finally, Artificial Neural Networks (ANN) models were developed to allow for a more robust simulation model to be built and comparison between ANN and RSM models to be performed. From the presented results, for RSM, the mean square error and the correlation coefficient were determined to be 8.633 Â 10 À3 and 0.9713, respectively; for ANN models, the corresponding values were 2 Â 10 À3 and 0.9824, for the test group of the optimum model. Simulations indicated that, although input data were too few, a considerably reliable ANN model was able to be built and despite of its complexity compared to RSM model, it was proven to be superior in terms of prediction accuracy.
Cutting fluids (CFs) besides their considerable impact on machining cost result in problems in th... more Cutting fluids (CFs) besides their considerable impact on machining cost result in problems in the working environment and in the waste disposal. The recent imposition of stringent pollution control regulations has forced the metal working industry to search for reliable processes to solve these problems. By replacing conventional cooling lubricants with the technological routes of dry machining or minimum quantity lubrication (MQL) related problems can be reduced significantly. The present paper addresses the issues concerning the machining routes applied for the reduction of CFs usage and especially the cutting technologies without the use of CFs (dry machining, hard machining, high speed machining), towards environmental-friendly or clean machining. The advantages and the disadvantages of dry machining and the solutions proposed (new tools materials, cryogenic cooling systems) for its successful implementation are also presented.
Proceedings of the World Congress on …, Jan 1, 2009
In the last years new methods have been investigated for the manufacturing of artificial implants... more In the last years new methods have been investigated for the manufacturing of artificial implants for hip joints. For some parts of these implants, like femoral heads, the method of high speed machining is used to get manufactured. In this paper it was investigated the connection between cutting parameters and forces, in high speed turning of metallic femoral heads. This method is widely used in the industry combined with hard part machining, and leads to having better surface roughness and to decreasing of cutting time. It is also investigated the connection of the surface roughness and this manufacturing method with the measuring of the spheres using Atomic Force Microscopy according to the strict Standards of ISO 7206.
This paper presents a study on the development of a surface roughness model of
milled parts made... more This paper presents a study on the development of a surface roughness model of
milled parts made of Ti-6A6-4V ELI alloy with HSS tool. The model is developed
considering depth of cut, cutting speed and feed rate as input variables. Machining tests,
based on design of experiments, were carried out with HSS 8% Cobalt cutting tool under
various conditions for both plain and end milling. Second-order models predicting
equations for surface roughness have been established by using experimental data. The
validity of the models is tested with analysis of variance and they are found to be
adequate for this problem. The proposed equations show that feed rate was the main
influencing factor for surface roughness. The predicted surface roughness of the samples
has been found to lie close to that of the experimentally observed ones, for plain and end
milling.
International Journal of Manufacturing, Materials and Mechanical Engineering, Vol. 1 (4), pp. 1-18, 2011
Impeller blade geometry plays a dominant role on the velocity profile of the fluid flowing throug... more Impeller blade geometry plays a dominant role on the velocity profile of the fluid flowing through the pump. Although blades’ design is based on fluid dynamics considerations, it is sometimes limited by the available manufacturing methods, due to the required complexity in the geometry. In the present paper, the evolution of the velocity field in the blade passages of two anew designed radial pump impellers with different curvature and outlet blade angle is examined in order to verify their optimum design and characteristics. The numerical solution of the discrete three-dimensional, incompressible Navier-Stokes equations over a structured grid is accomplished with a commercial CFD finite-volume code. For each impeller, pressure and relative velocity distributions are presented and analyzed. The flow patterns in the blade passages are monitored and the mechanisms that dominate the flow field in the different regions of the impeller geometry are discussed. Furthermore, the new impellers that were tested numerically are manufactured in a CNC Milling Centre under the operation of sculptured surfaces; thus the feasibility of manufacturing the improved geometries is exhibited.
In the last years new methods have been investigated for the manufacturing of artificial implants... more In the last years new methods have been investigated for the manufacturing of artificial implants for hip joints. For some parts of these implants, like femoral heads, the method of high speed machining is used to get manufactured. In this paper it was investigated the connection between cutting parameters and forces, in high speed turning of metallic femoral heads. The machining of such parts, with spherical geometry, has the
problem that the cutting depth is continuously changing as the cutting tool follows its cyclical route to make the sphere. Finally according to these parameters a function was introduced to describe the forces, and the numerical results were compared with the experimental ones.
Journal of Machining and Forming Technologies, Vol. 3(3/4), pp. 149-162, 2011
In this paper high speed turning and milling are considered through 3D FEM models and chip format... more In this paper high speed turning and milling are considered through 3D FEM models and chip formation and cutting forces are investigated. For the simulation the Finite Element Modeling software AdvantEdge from Third Wave Systems is employed and the cutting forces results as well as the morphology of the chip are compared with the results of experiments conducted with CNC machine tools. For the experimental work the principles for design of experiment were used in order to minimize the required amount of experiments and obtain useful results at the same time. All parameters and cutting conditions were chosen to be close to the common industrial ones, with the material of the workpiece being C45 steel and the tools being coated carbides. The validation of the numerical data with the experimental ones show a good agreement and the proposed models can be used for the prediction of various machining parameters.
Manufacturing Technology, Vol. 13(4), pp. 437-444, 2013
Titanium alloys are used for the manufacturing of femoral heads for orthopaedic implants. Poor ma... more Titanium alloys are used for the manufacturing of femoral heads for orthopaedic implants. Poor machinability of these materials, especially at high speeds, creates the need for more detailed investigations on this subject. The at hand study analyzes the construction of 3D Finite Element Method (FEM) models pertaining to the manufacturing of femoral heads made from Ti-6Al-4V. For this purpose a commercial FEM programme is employed, specialising in machining modelling, namely AdvantEdge. The validation of the model is provided through experiments on actual femoral heads cut in a CNC lathe at high cutting speeds. Comparison between experimental and numerical results on cutting forces and chip morphology exhibits a good agreement, indicating the success of the proposed models. These 3D models can be used for realistically estimating the influence of cutting conditions on the final product, without performing time and money consuming experiments.
… of Materials, 2011
This work investigates the feasibility of applying die sinking Electrical Discharge Machining (ED... more This work investigates the feasibility of applying die sinking Electrical Discharge Machining (EDM) for blind hole drilling of carbon fibre reinforced composite (CFRC) materials. Machining was performed with copper electrodes, at various currents, pulse durations and polarities. The machined surfaces are evaluated in terms of dimensional accuracy, material removal rate and surface roughness and are also examined by microscope. Research indicates that EDM is a feasible method for blindhole drilling of CFRC materials however; proper selection of operational parameters is needed. Optimal results are, in general, obtained by low pulse currents and pulse durations and by using tool with positive polarity.
International Journal of Machining and Machinability of Materials, 2009
In the present paper is reported the manufacturing of femoral heads, using the technique of the h... more In the present paper is reported the manufacturing of femoral heads, using the technique of the high speed turning. This method is widely used in the industry combined with hard part machining, and leads to having better surface roughness and to decreasing of cutting time. The femoral heads where manufactured in a CNC lathe in a range of cutting speeds between 150 and 480m/min, made of Steel AISI 316L. After the manufacturing the surface roughness was measured using Atomic Force Microscopy according to the strict Standards of ISO 7206. The results are presented in this paper, shows the surface becomes better as the speed increases, and accomplice the international standard.
International Journal of Advanced Manufacturing Technology, 2010
This paper is dealing with the development of a surface roughness model for turning of femoral he... more This paper is dealing with the development of a surface roughness model for turning of femoral heads from AISI 316L stainless steel. The model is developed in terms of cutting speed, feed rate and depth of cut, using response surface methodology. Machining tests were carried out with TiN-Al2O3-TiC coated carbide cutting tools under various conditions. First-order and second-order models predicting equations for surface roughness have been established by using the experimental results. The established equation shows that the depth of cut was the main influencing factor on the surface roughness. It increased with increasing the depth of cut and feed rate, respectively, but it decreased with increasing the cutting speed. In addition, analysis of variance for the second-order model shows that the interaction terms and the square terms are statistically insignificant. The predicted surface roughness of the samples was found close to the experimentally obtained within a 95% confident interval.
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Papers by Nikolaos I Galanis
milled parts made of Ti-6A6-4V ELI alloy with HSS tool. The model is developed
considering depth of cut, cutting speed and feed rate as input variables. Machining tests,
based on design of experiments, were carried out with HSS 8% Cobalt cutting tool under
various conditions for both plain and end milling. Second-order models predicting
equations for surface roughness have been established by using experimental data. The
validity of the models is tested with analysis of variance and they are found to be
adequate for this problem. The proposed equations show that feed rate was the main
influencing factor for surface roughness. The predicted surface roughness of the samples
has been found to lie close to that of the experimentally observed ones, for plain and end
milling.
problem that the cutting depth is continuously changing as the cutting tool follows its cyclical route to make the sphere. Finally according to these parameters a function was introduced to describe the forces, and the numerical results were compared with the experimental ones.
Books by Nikolaos I Galanis
milled parts made of Ti-6A6-4V ELI alloy with HSS tool. The model is developed
considering depth of cut, cutting speed and feed rate as input variables. Machining tests,
based on design of experiments, were carried out with HSS 8% Cobalt cutting tool under
various conditions for both plain and end milling. Second-order models predicting
equations for surface roughness have been established by using experimental data. The
validity of the models is tested with analysis of variance and they are found to be
adequate for this problem. The proposed equations show that feed rate was the main
influencing factor for surface roughness. The predicted surface roughness of the samples
has been found to lie close to that of the experimentally observed ones, for plain and end
milling.
problem that the cutting depth is continuously changing as the cutting tool follows its cyclical route to make the sphere. Finally according to these parameters a function was introduced to describe the forces, and the numerical results were compared with the experimental ones.
carbide, although material removal rate is generally low. Moreover, average roughness is very low, especially when negative electrode polarity is used. After processing optical microscopy / metallography, SEM and surface roughness measurements were performed for assessing the surface integrity of the sparkeroded surfaces
These materials are intensively used in the aerospace and the
automotive industries. The advantages of high-speed
machining lie not only in the speed of machining (lower costs
and higher productivity) but also in attaining higher surface
quality (prescribed surface roughness without surface defects).
Based on this concept, in the present paper the high speed-dry
turning of AISI O, (manganese-chromium-tungsten / W.-Nr.
1.2510) tool-steel specimens is reported. The influence of the
main machining parameters i.e., cutting speed, feed rate and
depth of cut on the resulted center-line average surface
roughness (Ra) is examined. Types of wear phenomena
occurred during the course of the present experimental study as well as tool wear patterns were also monitored.
The design and the final inspection of these implants have a very important place in the whole procedure of their manufacturing, and of course in their tendency to failure. [2] For this rea-son strict international standards were instituted to protect and make reliable the design and the machining of them. In both these procedures the dimensional and geometrical accuracy are very important and the limits of the acceptance of any inaccuracy are very narrow.
In this paper it will be presented the whole procedure of producing such parts, using specific CAD/ CAE / CAM software for that, and the inspection of the implants, femoral heads which were made, with the use of AFM for its surface roughness accuracy.
elements in predicting the cutting forces of machined parts of
stainless steel AISI 316L through turning. The process were
held in high speed machining which continuously improves and
it has be found application in more and more manufacturing
processes like aerospace industry, in die and mold companies
and in the last years also in bioengineering in manufacturing
hip joint implants. The cutting forces, which were measured
through experimental process, were compared with predicted
ones from the finite element modulation, and it was exported
that they can be predicted with good precision when machining
with the FEM model.