Leonardo Orazi | Università degli studi di Modena e Reggio Emilia (original) (raw)

Papers by Leonardo Orazi

… and Technologies for …, Jan 1, 2008

The interest towards LASER hardening of steels has been increasing since the last few years due t... more 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.

Optics & Laser Technology, 2012

This paper deals with an experimental campaign carried out on AA6082 8 mm thick plates in order t... more This paper deals with an experimental campaign carried out on AA6082 8 mm thick plates in order to investigate the role of process parameters on porosity formation in hybrid LASER-GMA welding. Bead on plate weldments were obtained on the above mentioned aluminum alloy considering the variation of the following process parameters: GMAW current (120 and 180 A for short-arc mode, 90 and 130 A for pulsed-arc mode), arc transfer mode (short-arc and pulsed-arc) and mutual distance between arc and LASER sources (0, 3 and 6 mm). Porosities occurring in the fused zone were observed by means of X-ray inspection and measured exploiting an image analysis software. In order to understand the possible correlation between process parameters and porosity formation an analysis of variance statistical approach was exploited. The obtained results pointed out that GMAW current is significant on porosity formation, while the distance between the sources do not affect this aspect.

Surface and Coatings …, Jan 1, 2012

This paper reports the results concerning the simulation of a laser surface hardening process of ... more This paper reports the results concerning the simulation of a laser surface hardening process of a cylindrical surface. In particular it focuses on the problems related to the definition of the physical parameter values necessary in order to achieve an accurate and reliable simulation. The strict dependency of laser process simulation results on the physical parameters describing the target material is, in fact, a well known matter, especially considering that the values of these parameters change during the process dependently on temperature and time. Moreover in laser surface hardening this problem is even more important because melting of the target material should be avoided, surface roughness plays an important role and, sometimes, the surface is coated with absorbent layers. These factors increase the complexity of the simulations and make the evaluation of the physical parameters more difficult and critical. The results presented in this paper are obtained on AISI420B steel, coated with graphite and treated with a direct diode laser. Considering the above mentioned conditions, a plausible temperature dependent reflectivity coefficient was evaluated and its robustness was investigated. This reflectivity coefficient can be used with a good approximation for the simulation of laser hardening treatments of many carbon steels.

Cirp Annals-manufacturing Technology, 2011

Laser Texturing and Laser Engraving of free form surfaces are interesting alternative to EDM and ... more Laser Texturing and Laser Engraving of free form surfaces are interesting alternative to EDM and micro milling in the fabrication of moulds and dies. The material removal rate of this process is typically very low and the maximum working area is limited by the maximum travel range of the galvanometric scanning head and also by the maximum deflection of the scanner or the surface curvature. As a consequence, in order to manufacture large or free form surfaces, a set of placements of the scanning head respect to the work piece must be calculated and controlled by the CNC.
The number of these placements can be quite high due the small amount of material removed in each of them and the non-operative time spent to move the scanning head can be relevant compared to the overall time. In this work a method based on the solution of the Traveling Salesman Problem is proposed with the aim to optimise the number of displacements of the scanning head and generally in order to reduce the number of movement of the numerically controlled axes.
The method that takes into account both the architecture and the dynamic characteristics of a 5 axis CNC system was implemented in the CALM (Computer Aided Laser Manufacturing) software used to program the laser path for part texturing and applied in industrial cases.

In this study an application of free form deformation for the editing of clouds of points or tess... more In this study an application of free form deformation for the editing of clouds of points or tessellated surfaces representing industrial parts is presented. The application is based on an efficient implementation of NURBS based free form deformation and the implementation of functions for imposing constraints to position, directions and curvatures of embedded objects. The developed functions permit the direct manipulation of triangulated surfaces eliminating the surface reconstruction stage, reducing the time requested in the reverse engineering process and, at the end, reducing the time to market. #

This paper considers the micro-closed seam laser welding of two nearly eutectoid carbon steel gra... more This paper considers the micro-closed seam laser welding of two nearly eutectoid carbon steel grades. These materials are difficult to weld due to their poor ductility. In particular, in closed seam welding, the laser beam starts and finishes in the same point thus increasing the risk of cracks. A numerical simulation of micro-welding of nearly eutectoid steels by nanosecond pulsed laser is carried out to evaluate the weld pool dimension and the heat-affected zone extension. Optimized welding parameters and strategy are determined by means of simulation and they are successfully applied in the welding of a 1.0%C shaft and a 0.7%C gear.

The bottleneck in laser hardening principally occurs when large surfaces have to be treated becau... more 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 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.

In this paper, a laser surface micromachining process planning system is presented. In this syste... more In this paper, a laser surface micromachining process planning system is presented. In this system, based on a regression model approach, the empirical coefficients, which provide the material removal rate, are automatically generated by a specific software according to the different materials that have to be processed. Numerical models generally present some limits due to the elevated calculation time requested to simulate the laser micromachining of industrial features, especially when transient solutions are considered, and, for this reason, to carry out a useful industrial tool for the evaluation of the material removal rate, the regression model represents the best solution. The presented statistical method, avoiding physical considerations, correlates the material removal rate with the process parameters in a very short calculation time. The automatic procedure for the generation of the coefficients of the regression polynomial permits to easily extend the regression model to any working material and system configuration allowing us to determine the best process parameters in a very short period of time. The results of this work have been patented.

Laser hardening is a laser assisted process devoted to the surface hardening of the mechanical co... more 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 ...

JLMN—Journal of Laser Micro/Nanoengineering (online), 2008

In this paper a mathematical model solved by means of the finite differences method (FDM) for las... more 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.

Optics & Laser Technology, Dec 27, 2011

CIRP Annals-Manufacturing Technology, Dec 31, 2011

Manufacturing Systems and Technologies for the New Frontier, 2008

Proc. of SPIE: High Energy/Average Power Lasers and Intense Beam Applications, Feb 8, 2007

In this paper a numerical simulation of laser hardening process is presented. The Finite Differen... more 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 microstructure, phase composition and microhardness of multilayered Ti/Al, Ti/Cu, Ti/Fe and T... more The microstructure, phase composition and microhardness of multilayered Ti/Al, Ti/Cu, Ti/Fe and Ti/Zr
condensates produced on stainless steel substrates via vacuum-arc evaporation of pure metals were studied.
The sublayer periods () were regulated in the range 80–850 nm by varying the vacuum discharge
current and the duration ofthe successive depositions of metallic plasma onto the substrates while maintaining
the total deposition time constant. The regularity ofthe obtained nanostructures was investigated
by scanning and transmission electron microscopy while phase compositions were identified with X-ray
diffraction (XRD) analysis in order to evidence the presence of interdiffusion and the amount of intermetallics.
Condensates cross sections were mechanically characterized by means of microhardness tests.
Measurements were correlated to the periods and to the presence of intermetallics.