Gabriele Cuccolini

Laser Ablation of Metals: A 3D Process Simulation for Industrial Applications

A model for laser milling simulation is presented in this paper. A numerical model able to predict the physical phenomena involved in laser ablation of metals was developed where the heat distribution in the work piece, the prediction of the velocity of the vapor/liquid front, and the physical state of the plasma plume were taken into account. The model is fully 3D and the simulations makes it possible to predict the ablated workpiece volume and the shape of the resulting craters for a single laser pulse or multiple pulses, or for any path of the laser spot. The numerical model was implemented in C+ + and an overview of the code capacities is presented.

A Comprehensive Model for Laser Hardening of Carbon Steels

This article illustrates the development of a complete and exhaustive mathematical model for the simulation of laser transformation hardening of hypo-eutectoid carbon steels. The authors propose an integrated approach aimed at taking into consideration all the the phenomena involved in this manufacturing process, with particular attention to implementing easy mathematical models in order to optimize the trade-off between the accuracy of the predicted results and the computational times. The proposed models involve the calculation of the 3D thermal field occurring into the workpiece and predict the microstructural evolution of the target material exploiting an original approach based on the definition of thermodynamic thresholds which can be considered as a physical constant of the material itself. Several parameters and phenomena are taken into consideration in order to accurately simulate the process: laser beam characteristics, fast austenization of the steel and tempering effect due to mutually interacting beam trajectories.Copyright

Laser hardening process simulation for mechanical parts

In this paper a numerical simulation of laser hardening process is presented. The Finite Difference Method (FDM) was used to solve the heat transfer and the carbon diffusion equations for a defined workpiece geometry. The model is able to predict the thermal cycle into the target material, the phase transformations and the resulting micro-structures according to the laser parameters, the workpiece dimensions and the physical properties of the workpiece. The effects of the overlapping tracks of the laser beam on the resulting micro-structures is also considered. The initial workpiece micro-structure is taken into account in the simulation by a digitized photomicrograph of the ferrite perlite distribution before the thermal cycle. Experimental tests were realized on a C43 plate and the good agreement between the theoretical and experimental results is shown.

3-D Modelling of Laser Ablation of Metals in Mould Manufacturing

An original model for laser milling characterization is presented in this paper. A 3-D numerical model able to simulate the physical phenomena involved in laser ablation of metals was developed where the heat distribution in the work piece, the prediction of velocity of the vapour/liquid front and the physical state of the plasma plume were taken into account. The numerical model was implemented in C++ and an overview of the code capacities is presented.Copyright

Optimization Strategies of Laser Hardening of Hypo-eutectoid Steel

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.

An exhaustive model for the laser hardening of hypo eutectoid steel

This article presents an exhaustive mathematical model for the simulation of hypo-eutectoid carbon steel trans- formations during laser hardening. The proposed model takes into consideration all the the phenomena involved in the process with particular attention to implementing easy mathematical formulas in order to optimize the trade-o between the accuracy of the predicted results and the computational times. The proposed model calculates the 3D thermal eld occurring into the workpiece and predicts the microstructural evolution of the target material exploiting an original approach based on the de nition of thermodynamic thresholds. Several parameters and phenomena are taken into consideration in order to accurately simulate the process: laser beam characteristics, scanning strategy of the target and tempering e ect due to mutually interacting beam trajecto- ries.

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. “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.Copyright

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 impressions: 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 posts are finally presented.Copyright

A New Computationally Efficient Method in Laser Hardening Modeling

Laser hardening is a laser assisted process devoted to the surface hardening of the mechanical components. This process is highly suitable for medium carbon steels with carbon content comprised between 0.2 – 0.6% or for low alloy steels which are usually surface hardened during their manufacturing process. Laser hardening technology is gaining a great industrial interest in the last years in fact, the possibility of integrating the heating source directly on the production line, together with the absence of the quenching medium, meets the production needs of modern industries. Laser hardening optimization could be complex especially when tempering due to multiple passes effects must be considered. Many research studies have been proposed in the last years aimed at predicting the optimal laser process parameters such as beam power density, beam velocity and scanning strategies. Many Authors agree with the assumption that the whole austenite resulting from the heating is transformed into martensite during the quenching. This is a valid approximation for single pass but could be a rough hypothesis in multiple-passes when the cooling rate could be not so high. Moreover hysteresis phenomena, due to the severe heat cycle occurring in laser hardening, should be taken into account for pearlite to austenite and martensite to austenite transformations during heating and for martensite tempering during multiple passes. In this paper the crucial problems to be faced regarding laser surface hardening modeling are discussed with respect to current literature. In particular, partial austenitization of the pearlite is suggested as a solution of the hardness prediction of the profile depth. Then three transformation parameters are proposed in order to take into account the hysteresis phenomena in martensite and pearlite transformations into austenite and in martensite tempering. Finally several experimental examples are proposed in order to validate the mentioned assumptions.© 2008 ASME

Laser Milling Simulation System for Moulds Manufacturing

This paper refers to the development of a numerical simulator for Laser Milling process useful for industrial applications able to predict the machining results when different materials are processed, different surface conditions are encountered and spatial and temporal distributions of the pulsed beam are set. The original software presented, developed by the authors, are well suited for simulating laser milling or laser micromachining operations with power density up to 1014 W/m2 and pulse duration in the order of nanoseconds. The temperature of the solid phase is evaluated by solving the Fourier equation by using the finite difference method (FDM). The recession velocity of the ablating surface is evaluated according to the Hertz-Knudsen equation assuming that the explosive effects are negligible. The plasma plume is considered in local thermodynamical equilibrium (LTE) and the energy balance permits to evaluate the plume temperature, ion distribution and pressure under the assumption that the gas expansion, from the surface target, produces a sonic front. The plume energy balance is influenced by the energy lost for irradiation from the plume and by the quantity of laser beam energy reflected from the target surface. Numerical simulations have been conducted to quantify this influence on the plasma plume physical state and, consequently, on the ablation process considering a Nd:YAG diode pumped source and three different target materials: Fe-C alloy, copper and aluminum.