ANALISI STRUTTURALE LINEARE E NON-LINEARE DI ELEMENTI TUBOLARI STRATIFICATI IN COMPOSITO

L’argomento di questa tesi è l’analisi strutturale di elementi tubolari, traviformi, con geometria cilindrica o conica, incastrati ad un’estremità e caricati all’altra, stratificati e realizzati in composito. Tramite programmi sviluppati in ambiente MATHCAD è stato analizzato il comportamento macromeccanico e micromeccanico per definire le proprietà di rigidezza e di resistenza del materiale. Si sono poi creati, sempre in ambiente MATHCAD, dei moduli per l’analisi di rigidezza e di resistenza degli elementi tubolari. La fase successiva è stata incentrata sulla ricerca in letteratura di modelli, per “shells” cilindriche e/o coniche, che consentissero il calcolo “manuale” delle frequenze proprie e dei carichi critici assiali e trasversi per le condizioni al contorno descritte. Non trovando alcun modello di pratico utilizzo, si è ricorso ad un’analisi agli elementi finiti, tramite il codice ANSYS. Si è studiato come implementare i materiali compositi e si sono creati modelli parametrici in forma “batch” per poter effettuare analisi modali, statiche e a “buckling”, lineari e non lineari, con carichi assiali, traversi o con puro momento flettente. Infine si è impostato una analisi parametrica della sequenza di stratificazione per ottenere un comportamento strutturale con migliori prestazioni

The influence of plasma plume in laser milling for mold manufacturing

The paper refers to the modeling of the plasma plume influence on the shape of the crater obtained by means of nanosecond pulsed laser milling. A transient model of the physical state of the plasma plume is developed according to the laser parameters. Two empirical coefficients are proposed in the model in order to evaluate the plasma plume self-emission energy lost towards the environment and the energy spread from the plasma towards the target surface. These two coefficients, directly correlated to the depth and to the width of the crater, can be experimentally determined, due to the difficulty of their analytical quantification, and they can be used for tuning a complete plasma plume software package for laser milling simulation named LAS (Laser Ablation Simulator) already developed by the authors. In this paper their influence on the crater shape will be proved by means of several simulation runs

AUTOMATED CHARACTERIZATION OF THE MATERIAL REMOVAL RATE IN LASER MANUFACTURING OF TIAL6V4 AND INCONEL 718

In this paper a system for the automatic determination of the material removal rate during laser milling process is presented. \u201dLaser milling\u201d can be defined as an engraving process with a strictly controlled penetration depth. In industrial applications, when a new material have to be machined or a change in the system set-up occur the user has to perform a time-consuming experimental campaign in order to determine the correlation between the material removal rate and the process parameters. In these cases the numerical models present some limits due to the elevated calculation time requested to simulate the laser milling of industrial features. In the proposed system, based on a regression model approach, the empirical coefficients, that provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. A description of the automated method and the results obtained in engraving TiAl6V4 and Inconel 718 superalloy with a fiber laser are presented. The system can be adapted to every combination of material/laser source

An automated procedure for the geometrical characterization of root canals

In this work an original system for the geometrical characterization of root canals for dental implants was developed and tested. The aim of this work is to determine the shape and the size of the posts that best fit a statistical population of root canals with a defined maximum amount of removed tissue. The task is performed by an accurate acquisition of the shape of a statistically significant batches of root replicas: the geometry are then processed to obtain the post geometry. The acquisition is carried out using a conoscopic laser scanning device mounted on a 4 axis controlled CNC measurement system. The shape of the root canals were measured for each type of tooth, obtaining an average 3-D computer design of the canal profiles. Several comparisons between the acquired geometry and the representative forms of commercial pivots are finally presented

Automated characterization of the material removal rate in laser manufacturing of TiAI6V4 and inconel 718

In this paper a system for the automatic determination of the material removal rate during laser milling process is presented. ”Laser milling” can be defined as an engraving process with a strictly controlled penetration depth. In industrial applications, when a new material have to be machined or a change in the system set-up occur the user has to perform a time-consuming experimental campaign in order to determine the correlation between the material removal rate and the process parameters. In these cases the numerical models present some limits due to the elevated calculation time requested to simulate the laser milling of industrial features. In the proposed system, based on a regression model approach, the empirical coefficients, that provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. A description of the automated method and the results obtained in engraving TiAl6V4 and Inconel 718 superalloy with a fiber laser are presented. The system can be adapted to every combination of material/laser source

An Automated Procedure for the Geometrical Characterization of Root Canals

The interest towards LASER hardening of steels has been increasing since the last few years due to its undoubted advantages. The main drawback affecting this manufacturing technology is the tempering effect induced when multiple passes on the same surface must be carried out. In order to minimize the softening effect due to tempering and to speed up the process a numerical model for the simulation of the treatment is proposed. This model is able to detect the optimal LASER path trajectory according to the source parameters and the scanning velocity, and it is able to predict the resulting microstructures and the relating hardness. Some examples on an hypo-eutectoid steel are presented together with validation tests

5 Axes computer aided laser milling

In this paper a 5 axes CAM procedure for the laser milling of free form surfaces has been developed and experimentally verified. The laser beam is deflected by a galvanometric scanning head and is directly moved on the working surface by the CNC controlled axes of a machine center. The procedure has been implemented in a software called CALM (computer aided laser manufacturing) able to generate the laser paths and the movements of the controlled axes reducing the defects on the workpiece. The approach is based on the sequential overlapping of the scanning passes on the working area. The different working areas in every laser displacement are obtained directly from the triangulation of the whole surface to machine

An efficient model for laser surface hardening of hypo-eutectoid steels

This paper presents a model able to predict the austenization of hypo-eutectoid steels during very fast heat cycle such as laser hardening. Laser surface hardening is a process highly suitable for hypo-eutectoid carbon steels with carbon content below 0.6% or for low alloy steels where the critical cooling rate is reached by means of the thermal inertia of the bulk. As proposed by many authors, the severe heat cycle occurring in laser hardening leads to the pearlite to austenite microstructures transformation happening to a temperature much higher than the eutectoid temperature Ac1 and, afterwards, all the austenite predicted during the heating phase become martensite during quenching. Anyway, all these models usually generate a predicted hardness profile into the material depth with an on\u2013off behavior or very complicated and time consumed software simulators. In this paper, a new austenization model for fast heating processes based on the austenite transformation time parameter Ip→a is proposed. By means of the Ip→a parameter it is possible to predict the typical hardness transition from the treated surface to the base material. At the same time, this new austenization model also reduces the calculation time. Ip→a was determined by experimental tests and it was postulated to be constant for low-medium carbon steels. Several experimental examples are proposed to validate the assumptions and to show the accuracy of the model