FEM based investigation on thrust force and torque during Al7075-T6 drilling

As modern industry advances, the demand for more time and cost effective machining is rising. In order to achieve high levels of standard during machining it is necessary to employ sophisticated techniques for precise prediction of various important parameters that relate to the machining processes. Such technique is the implementation of finite element modelling (FEM) which can become a valuable tool for researchers and industry engineers alike. In this work, the 3D modelling of Al7075-T6 drilling process with solid carbide tooling is being presented. DEFORM3D™ finite element analysis (FEA) software was utilized for simulating the drilling process based on frequently used cutting conditions; cutting speed of 100m/min and feed of 0.15mm/rev, 0.20mm/rev and 0.25mm/rev respectively. In order to approximate the complex phenomena that occur during drilling, the most critical factors were considered in the presented model such as the developed friction, heat transfer and damage interaction between the tool and the workpiece. Additionally, a validation of the generated results for thrust force and torque was performed by comparing the simulated results with experimental data. Three drilling experiments were carried out with the aid of a CNC machining center and a four component dynamometer in order to acquire the experimental values of thrust force and torque. Most of the simulations yielded results in accordance to the experimental ones with the agreement percentage reaching 95% in most cases for both the thrust force and torque, confirming the validity of the models and the accuracy of the simulated results

Determination of the Efficiency of Hot Nano-Grinding of Mono-Crystalline Fcc Metals Using Molecular Dynamics Method

Abrasive processes are essential to the manufacturing field, due to their capability of rendering high-quality surfaces with minimum effect on workpiece integrity. As it is especially difficult to perform sufficient experimental work, numerical studies can be successfully employed to evaluate techniques for the improvement of the efficiency of nanometric abrasive processes. In the present study, for the first time, cases of nanogrinding on workpieces of three different fcc metals, namely, copper, nickel, and aluminum are investigated under different preheating temperatures, in order to determine the efficiency of the hot nano-grinding technique. For the simulations, a molecular dynamics model for peripheral nanogrinding is developed including multiple abrasive grains and realistic grain trajectory and grinding forces, and chip characteristics and subsurface alterations are evaluated. The results indicate that using elevated preheating temperatures is beneficial for nanogrinding, as forces can be considerably reduced and material removal can be facilitated, especially for temperatures over 40% of the material melting temperature (Tm). However, the detrimental effect on workpiece integrity is also evident at higher preheating temperatures, due to the high temperature on the whole workpiece, posing limitations to the applicability of the hot nano-grinding technique. Based on the findings of this study, preheating temperatures in the range of 0.4–0.55 Tm are recommended

Development of methods and software for the fully coupled aeroelastic optimization using the continuous adjoint method.

σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Υπολογιστική Μηχανική”Σε αυτήν τη μεταπτυχιακή εργασία αναπτύχθηκε η συνεχής συζυγής μέθοδος για περιπτώσεις πλήρως συζευγμένης αεροελαστικής βελτιστοποίησης και υλοποιήθηκε το αντίστοιχο λογισμικό. Αρχικά, αφού παρουσιάστηκε η εξαγωγή της εξίσωσης κατάστασης για το δομικό τμήμα του προβλήματος βελτιστοποίησης, αναπτύχθηκε η συνεχής συζυγής μέθοδος για περιπτώσεις δομικής βελτιστοποίησης και προγραμματίστηκε ο αντίστοιχος κώδικας, ο οποίος και πιστοποιήθηκε. Έπειτα, υλοποιήθηκε και πιστοποιήθηκε ένα λογισμικό στατικής αεροελαστικότητας το οποίο αποτελείται από έναν οικείο ρευστοδυναμικό επιλύτη των 3Δ εξισώσεων Euler της ΜΠΥΡ&Β και έναν επιλύτη δομικής μηχανικής που χρησιμοποιεί το μοντέλο πεπερασμένων στοιχείων δοκού που προγραμματίστηκε για το σκοπό αυτό. Στη συνέχεια, αναπτύχθηκε η συνεχής συζυγής μέθοδος για τον υπολογισμό των παραγώγων ευαισθησίας του προβλήματος πλήρους συζευγμένης αεροελαστικής βελτιστοποίησης, στο οποίο χρησιμοποιείται η μέθοδος της απότομης καθόδου. Στην ανάπτυξη της μεθόδου λαμβάνεται υπόψη η σύζευξη του ρευστοδυναμικού και του δομικού τμήματος τόσο στο πρωτεύον όσο και στο συζυγές πρόβλημα. Τέλος, υλοποιείται το ολοκληρωμένο λογισμικό πλήρως συζευγμένης αεροελαστικής βελτιστοποίησης, εφαρμόζεται σε περίπτωση αεροελαστικής βελτιστοποίησης μορφής προκειμένου να πιστοποιηθεί. Από τα αποτελέσματα που προκύπτουν, εξάγονται χρήσιμα συμπεράσματα για την αξιοπιστία και τη σύγκλιση της συζυγούς μεθόδου.Ιn this MSc. Thesis, the continuous adjoint method for fully coupled aeroelastic optimization cases was developed along with the relevant software. Initially, after the state equation derivation was presented for the structural part and the continuous adjoint method was developed for structural optimization cases, the relevant code was programmed and validated. Afterwards, a static aeroelastic software, which consists of a CFD 3D Euler equation solver by PCopt and a CSM solver using the beam FEM model, was implemented from scratch and validated. Subsequently, the continuous adjoint method for the calculation of sensitivity derivatives of the fully coupled aeroelastic optimization problem, using the steepest descent method was developed. In the development of the continuous adjoint method, the coupling of the fluid and structural part, both for the primal and adjoint problems, was taken into consideration. Finally, the aeroelastic optimization software is programmed and tested in an aeroelastic shape optimization case and useful conclusions for the reliability and rapid convergence of the adjoint method were made.Νικόλαος Ε. Κάρκαλο

Molecular dynamics simulation of multi-pass nano-grinding process

Grinding involves the use of a large number of micrometric abrasive grains in order to remove material from workpiece surface efficiently and finally render a high quality surface. More specifically, grinding in the nano-metric level serves for attaining nano-level surface quality by removing several layers of atoms from the workpiece surface. The abrasive grains act as individual cutting tools, performing primarily material removal but also induce alterations in the subsurface regions. In order to study the nano-grinding process, Molecular Dynamics (MD) method is particularly capable to provide comprehensive observations of the process and its outcome. In this study, MD simulations of multi-pass grinding for copper substrates, using two abrasive grains, are performed. After the simulations are carried out, results concerning grinding forces and temperatures are presented and discussed

Programming of software for the aeroelastic analysis and optimization based on the discrete adjoint method for inviscid flows. Applications and Assessment

165 σ.Στην παρούσα διπλωματική εργασία μελετήθηκε η ανάπτυξη ενός κώδικα στατικής αεροελαστικότητας για εφαρμογή σε πτέρυγα αεροσκάφους, ο οποίος χρησιμοποιεί την προσέγγιση χαλαρής σύζευξης μεταξύ του κώδικα ανάλυσης της ροής και του κώδικα δομικής ανάλυσης. Ο κώδικας αυτός χρησιμοποιεί έναν πιστοποιημένο επιλύτη της Μονάδας Παράλληλης Υπολογιστικής Ρευστοδυναμικής και Βελτιστοποίησης (ΜΠΥΡ&Β) του Εργαστηρίου Θερμικών Στροβιλομηχανών για την επίλυση των 3Δ εξισώσεων Euler (εδώ γύρω από πτέρυγα AGARD 445.6) και κώδικες υπολογιστικής δομικής μηχανικής που αναπτύχθηκαν και πιστοποιήθηκαν στο πλαίσιο της παρούσας εργασίας. Διερευνήθηκε η αποδοτικότητα της χρήσης διαφόρων ομοιόμορφων δομημένων πλεγμάτων για το δομικό κομμάτι και διατυπώθηκαν συμπεράσματα όσον αφορά τη σύγκλιση και την ακρίβεια του αλγορίθμου. Επίσης, αναπτύχθηκε κώδικας για δομική βελτιστοποίηση (structural optimization) για μοντέλο δοκού με τη μέθοδο της απότομης καθόδου στην οποία οι παράγωγοι ευαισθησίας υπολογίστηκαν με τη χρήση της διακριτής συζυγούς μεθόδου. Τέλος, η ίδια μέθοδος εφαρμόστηκε σε ένα πιο σύνθετο πρόβλημα, στην περίπτωση βελτιστοποίησης σχήματος μιας πτέρυγας αεροσκάφους υπό την επίδραση αεροδυναμικών φορτίων στην οποία χρησιμοποιήθηκε κώδικας πεπερασμένων στοιχείων δοκού για το δομικό κομμάτι και πιστοποιημένος επιλύτης της ΜΠΥΡ&Β για επίλυση των 2Δ εξισώσεων Euler για το αεροδυναμικό κομμάτι. Διαπιστώθηκε η ταχεία σύγκλιση της διαδικασίας στην επιθυμητή λύση και προτάθηκαν αλλαγές στον κώδικα για να συμπεριληφθεί και η συνεισφορά αεροδυναμικών μεγεθών στη διαδικασία της βελτιστοποίησης.In this diploma thesis, a static aeroelastic code for aircraft wings was programmed, using the loosely coupled approach between the flow solver and the structural analysis code. The final software comprises of a tested Computational Fluid Dynamics solver by the Parallel CFD and Optimization Unit of the Laboratory of Thermal Turbomachines which solves the 3D Euler equations (herein around an AGARD 445.6 wing) and Computational Structural Mechanics (CSM) solvers which were programmed and validated in this diploma thesis. The efficiency of using several uniform grids was investigated for the structural analysis part of the aeroelastic code and conclusions were made concerning the convergence and accuracy of the algorithm. In addition to the aeroelastic code, a structural optimization code was programmed for a beam element Finite Elements (FE) model using the steepest descent method in which sensitivity derivatives where calculated with the discrete adjoint method. Finally, the same method was applied to a more complicated case, the case of the shape optimization of an aircraft wing under aerodynamic loading for which a CSM beam FE model was used (in FORTRAN 77 language) along with a tested 2D Euler equations CFD solver by the Parallel CFD and Optimization Unit. The fast convergence towards the optimal solution was noted and adjustments were proposed in order to include the contribution of aerodynamic quantities in the optimization process.Νικόλαος Ε. Κάρκαλο

A Comprehensive Study on the Challenges of Using Pure Water Jet as Post-Treatment of Abrasive Water Jet Milled Pockets in Titanium Alloy

Abrasive waterjet (AWJ) machining offers the possibility of creating a wide range of features on mechanical parts with different degrees of complexity with a relatively high efficiency. However, after the roughing passes, the surface quality of features such as blind pockets is rather low, with unfavorable implications for surface waviness and form deviations apart from high surface roughness. Apart from the traditional methods for finishing, such as grinding or lapping, it is worth attempting either to improve the surface quality obtained during roughing by an AWJ or to integrate a post-processing step by using a pure WJ in the existing process in order to ameliorate the surface quality. Thus, in the current study, the effect of pure waterjet (WJ) post-processing of machined pockets by AWJ milling on a Ti-6Al-4V workpiece using recycled glass beads was investigated under different conditions. The findings indicate that although the different post-processing treatments by a pure WJ can affect the surface quality on average, these differences are not considerably important, probably due to an insufficient capability of material removal, which hinders the smoothing effect on machined surfaces. Thus, it was indicated that a higher number of post-processing passes under different conditions than those of the roughing pass can be more favorable for efficient post-treatment by a pure WJ

Determination of the Efficiency of Hot Nano-Grinding of Mono-Crystalline Fcc Metals Using Molecular Dynamics Method

Abrasive processes are essential to the manufacturing field, due to their capability of rendering high-quality surfaces with minimum effect on workpiece integrity. As it is especially difficult to perform sufficient experimental work, numerical studies can be successfully employed to evaluate techniques for the improvement of the efficiency of nanometric abrasive processes. In the present study, for the first time, cases of nanogrinding on workpieces of three different fcc metals, namely, copper, nickel, and aluminum are investigated under different preheating temperatures, in order to determine the efficiency of the hot nano-grinding technique. For the simulations, a molecular dynamics model for peripheral nanogrinding is developed including multiple abrasive grains and realistic grain trajectory and grinding forces, and chip characteristics and subsurface alterations are evaluated. The results indicate that using elevated preheating temperatures is beneficial for nanogrinding, as forces can be considerably reduced and material removal can be facilitated, especially for temperatures over 40% of the material melting temperature (Tm). However, the detrimental effect on workpiece integrity is also evident at higher preheating temperatures, due to the high temperature on the whole workpiece, posing limitations to the applicability of the hot nano-grinding technique. Based on the findings of this study, preheating temperatures in the range of 0.4–0.55 Tm are recommended

Applicability of ANN models and Taguchi method for the determination of tool life in turning

Tool life is an important parameter in machining processes, affecting directly the quality of machined components and the process cost. It is already shown that various parameters can affect tool life such as process parameters, i.e. depth of cut, cutting speed and feed, or material properties of cutting tool and workpiece. The determination of the effect of each parameter on tool life is of crucial importance when designing the manufacturing process of a product in order to select suitable process parameter values and tool types. Several empirical formulas for the determination of tool life exist in the relevant literature; especially in the case of CBN cutting tools for turning, a cubic polynomial formula was proposed to model the relationship between tool life and cutting speed. The determination of the polynomial parameters was performed by conducting cutting experiments for several cutting speeds, without the aid of a design of experiments (DoE) method in order to model properly this non-linear relationship. In this paper, the feasibility of determining this non-linear relationship by conducting experiments designed by Taguchi method and using artificial neural networks (ANN) is investigated for several cases and conclusions on the applicability of this approach are presented

A Comparative Study of Efficient Modeling Approaches for Performing Controlled-Depth Abrasive Waterjet Pocket Milling

Non-conventional processes are considerably important for the machining of hard-to-cut alloys in various demanding applications. Given that the surface quality and integrity, dimensional accuracy, and productivity are important considerations in industrial practice, the prediction of the outcome of the material removal process should be able to be conducted with sufficient accuracy, taking into consideration the computational cost and difficulty of implementation of the relevant models. In the case of AWJ, various types of approaches have been already proposed, both relying on analytical or empirical models and developed by solving partial differential equations. As the creation of a model for AWJ pocket milling is rather demanding, given the number of parameters involved, in the present work, it is intended to compare the use of three different types of efficient modeling approaches for the prediction of the dimensions of pockets milled by AWJ technology. The models are developed and evaluated based on experimental results of AWJ pocket milling of a titanium workpiece by an eco-friendly walnut shell abrasive. The results indicate that a semi-empirical approach performs better than a two-step hybrid analytical/semi-empirical method regarding the selected cases, but both methods show promising results regarding the realistic representation of the pocket shape, which can be further improved by a probabilistic approach

Applicability of ANN models and Taguchi method for the determination of tool life in turning

Tool life is an important parameter in machining processes, affecting directly the quality of machined components and the process cost. It is already shown that various parameters can affect tool life such as process parameters, i.e. depth of cut, cutting speed and feed, or material properties of cutting tool and workpiece. The determination of the effect of each parameter on tool life is of crucial importance when designing the manufacturing process of a product in order to select suitable process parameter values and tool types. Several empirical formulas for the determination of tool life exist in the relevant literature; especially in the case of CBN cutting tools for turning, a cubic polynomial formula was proposed to model the relationship between tool life and cutting speed. The determination of the polynomial parameters was performed by conducting cutting experiments for several cutting speeds, without the aid of a design of experiments (DoE) method in order to model properly this non-linear relationship. In this paper, the feasibility of determining this non-linear relationship by conducting experiments designed by Taguchi method and using artificial neural networks (ANN) is investigated for several cases and conclusions on the applicability of this approach are presented