Alessandro Fortunato

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.

Dynamic Hybrid Modeling of the Vertical Z Axis in a High-Speed Machining Center: Towards Virtual Machining

This paper describes the modeling and simulation of the Z axis of a five axis machining center for high-speed milling. The axis consists of a mechanical structure: machine head and electro-mandrel, a CNC system interfaced with the feed drive, and a pneumatic system to compensate for the weight of the vertical machine head. These subsystems were studied and modeled by means of: (I) finite element method modeling of the mechanical structure; (2) a concentrated parameter model of the kinematics of the axis; (3) a set of algebraic and logical relations to represent the loop CNC-Z feed drive; (4) an equation set to represent the functioning of the pneumatic system; and (5) a specific analytical model of the friction phenomena occurring between sliding and rotating mechanical components. These modeled subsystems were integrated to represent the dynamic behavior of the entire Z axis. The model was translated in a computer simulation package and the validation of the model was made possible by comparing the outputs of simulation runs with the records of experimental tests on the machining center. The firm which promoted and financed the research now has a virtual tool to design improved machine-tool versions with respect to present models, designed by traditional tools.

A New Computationally Efficient Model for Tempering in Multitrack Laser Hardening in Medium Carbon Steels

The bottleneck in laser hardening principally occurs when large surfaces have to be treated because this process situation leads to multitrack laser scanning in order to treat all the component surfaces. Unfortunately, multitrack laser trajectories generate an unwanted tempering effect that depends on the overlapping of two close trajectories. To reduce the softening effects, a simulator capable to optimize the process parameters, such as laser power and speed and number and types of trajectories, could sensibly increase the applicability of the process. In this paper, an original model for the tempering is presented. By introducing a tempering time factor for the martensitic transformation, the hardiness reduction can be predicted according to any laser process parameters, material, and geometry. Experimental comparisons will be presented to prove the accuracy of the model.

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.

A New Computationally Efficient Model for Tempering in Multi-Tracks Laser Hardening

The bottleneck in laser hardening principally occurs when large surfaces have to be treated because this process situation leads to multi-tracks laser scanning in order to treat all the component surface. Unfortunately, multi-tracks laser trajectories generate an unwanted tempering effect that depends on the overlapping of two close trajectories. To reduce the softening effects, a simulator capable to optimize the process parameters such as laser power and speed, number and types of trajectories, could sensibly increase the applicability of the process. In this paper an original model for the tempering is presented. By introducing a tempering time factor for the martensitic transformation, the hardness reduction can be predicted according to any laser process parameters, material and geometry. Experimental comparisons will be presented to prove the accuracy of the model.Copyright

3D Modelling of Laser Hardening and Tempering of Hypo-eutectoid Steels

In this paper a mathematical model solved by means of the finite differences method (FDM) for laser surface hardening of complex geometries is presented. The 3-D transient model characterizes a software package named Laser Hardening Simulator (LHS), which makes it possible to predict the extension of the treated area into the mechanical components and thus the hardened depth into the bulk material. The obtained microstructures and the resulting hardness with respect to the laser parameters and to the laser beam path strategy can be determined by considering the quenching and the tempering effects due to the overlapping trajectories. The initial workpiece microstructure is taken into account in the simulation by a digitized photomicrograph of the ferrite-pearlite distribution before the thermal cycle. In order to show the accuracy of the model, experimental trials were conducted on the keyway for spline machined on a hub made of SAE 1043. The domain discretization for the solution of the heat flux problem into the workpiece and for the diffusion of the carbon is carried out by means of a mesh generator strategy implemented into the code.

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.

From Traditional to Virtual Design of Machine-Tools: A Long Way to Go ... Part 2 — The Talk Between Two Worlds

To allow easy and fast interaction between the simulation modules developed by the authors in a Virtual Design environment and the data bases set up in the past by an Italian manufacturer for the traditional design of Machining Centers for High Speed Milling, a graphic interface was created. The work was done utilising advanced features of Matlab suitable, through Microsoft Windows assisted procedures, to extract from Microsoft Excel sheets all sensitive data regarding the machine-tool components, feeding the input module of the simulation package. In this way it is now possible to perform intensive simulation campaigns quickly and easily avoiding the very burdensome procedures demanded for the input to the simulation language. This graphic module also makes it possible to quickly present and compare the results of experimental tests with the outputs of simulation runs.Copyright

From Traditional to Virtual Design of Machine-Tools: A Long Way to Go ... Part 1 — Problem Identification and Model Validation

This paper reports the final results of research devoted to providing a package of tools for the Virtual Design of Machining Centers for an Italian manufacturer involved until today with traditional design procedures. The general thematics of Virtual Design have been realistically defined and focalised on the topics of particular interest for the firm; these constraints are analysed and the chosen solutions discussed. The paper also reports on the experimental validation of some complex parameters of the models of the Machining Centers already set up.Copyright