1,720,980 research outputs found
The influenceof plasma plume in Laser milling for mould manufacturing
No full textThe paper refers to the modeling of the plasma plume influence on the shape of the crater ob-tained 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 pro-posed in the model in order to evaluate the plasma plume self-emission energy lost towards the en-vironment 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 ex-perimentally 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 (La-ser 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
An efficient model for laser surface hardening of hypo-eutectoid steels
No full textThis 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–off 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
A numerical model for laser ablation with plasma characterization
No full textIn this paper a 3-D transient model for laser ablation modelling with plasma plume characterization is presented. The plasma plume was 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. Then, the physical state of the plasma plume was evaluated by means of the energy balance into the plume which makes it possible to determine the plasma temperature, the plasma ionization and, subsequently, the optical thickness of the plasma. This model predicts the time dependent laser energy delivered to workpiece according to the process parameters and it represents a part of a laser milling simulator previously developed by the authors. A simplified model of the plume geometry is also performed. Numerical simulations have been conducted to quantify this influence on the plasma plume physical state. Several simulation runs are presented in order to show the LAS accuracy and facilities
An automated procedure for material removal rate prediction in laser surface micromanufacturing
No full textIn 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 ABLATION MODELLING FOR CNC MACHINE TOOL APPLICATION IN MOULD MANUFACTURING
No full textIn this paper an original mathematical model of laser ablation is presented. Laser ablation optimization is quite a complex activity due to the high number of parameters involved and nowadays the most common way to set up the process, in industrial environments, is based on a “trial and error” activity. In order to reduce the set-up time, which can be very long when different materials and shapes have to be processed, a mathematical model is presented where the process parameters are related to the most important machining results such as ablated volume, temperature in work piece, resulting surface conditions. The plasma plume effects on the machining operations are considered. The comparisons between the theoretical and experimental results are finally presented
AUTOMATED CHARACTERIZATION OF THE MATERIAL REMOVAL RATE IN LASER MANUFACTURING OF TIAL6V4 AND INCONEL 718
No full textIn 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
PROCESS PLANNING IN LASER MILLING
No full textIn this paper two different laser milling processes simulators,
developed by the authors, are presented. The first one is a mathematical model where the most important physical phenomena
such as the work piece heating and vaporization and the plasma
plume formation are considered. As result, the process parameters
are directly related to the most important machining outputs
like the ablated volume and shape of the crater, the temperature
in work piece, the resulting surface conditions
3-D MODELLING OF LASER ABLATION OF METALS IN MOULD MANUFACTURING
No full textAn original model for laser milling characterization is presented in this paper. A 3D 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
A New Computationally Efficient Method into Laser Hardening Modelling,
No full textLaser 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 with the aim to predict the optimal laser process parameters such as laser power density, laser 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 in laser hardening, hysteresis phenomena should be taken into account for pearlite to austenite and martensite to austenite transformations during heating and martensite tempering during multiple passes.
In this paper the crucial problems that have to be faced in laser surface hardening modelling are discussed according to the 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 to take into account the hysteresis phenomena in martensite and pearlite transformations into austenite and martensite tempering.Finally, experimental examples are proposed to validate the assumptions
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