Papers by Author: Eneko Ukar

Abstract: Present work deals with laser polishing process on GGG70L spheroidal cast iron, which is widely used in die making for the automotive industry. Free graphite in the structure of GGG70L makes difficult the polishing and surface roughness reduction because the high melting temperature. In this work a complete study is presented, where main process parameters are identified and free graphite is eliminated from surface. The quantification of surface improvement is presented in terms of resulting surface roughness, hardness, and heat affected layer thickness. Thus, using optimal parameters, laser polishing with 2D scan head gives satisfactory results on GGG70L cast iron with roughness reduction rates up to 80% and minimum mean roughness R_a of 0.5 μm.

Abstract: The main disadvantage for industrial application of new processes based on laser surface treatments, such as laser hardening, quenching or precipitation hardening, is the prior experimentation needed to determinate the optimum conditions for processes. The presented work is focused on the development of a tool based on a semi-empirical model to predict accurately the thermal field and thickness of the head affected zone in laser surface treatments in order to avoid the previous experimental setups of this processes. The conventional thermal models are focused on solving the differential equation of temperature field, considering the laser as heat source and thermal properties of each material. However, during the rapid heating treatment processes of metal surfaces are some unknown heat sinks such us metallurgical transformations or a changeable material absortivity that must be taken into account. The model has been adjusted and validated with experimental data for AISI 1045.

Abstract: In laser surface treatment the laser beam is used as energy source for surface modification improving aspects such as mechanical properties, tribology or surface texture. Modeling tools have special interest in processes with many variables, like laser surface processing, in order to minimize the tryout testing to find the optimal process parameters. The work presented here focuses on the prediction of the final topography in laser polishing process. By FFT analysis of the surface profile it is possible to get the different frequency components of the initial topography. On the other hand, thermal field simulation was carried out to evaluate the melt duration. Matching this with the spatial frequency damping during process, the reconstruction of the processed topography was obtained.

Abstract: In recent years laser polishing is becoming an alternative for automated surface finishing of dies and molds. This process involves melting and subsequent solidification of the material. Depending on the initial topography, the energy density necessary to reduce surface asperities can cause excessive heat damage, and thus, limit the applicability of the process. The work presented here focuses on the use of a high quality laser beam, with a spot diameter below 50 microns driven by a 2D scanner for processing of materials typically used in dies and mold manufacturing. So, the highly focused beam ensures minimal thermal damage, and the scan head allows high productivity rates. A new processing strategy based on two stages surface processing was developed to process topographies with strong directionality.

Abstract: The laser cladding process is based on the generation of a melt-pool in a substrate where a filler material is injected, generating a high quality clad with a minimum heat affected zone. This process is industrially used to generate coatings over wear or damaged surfaces, being an alternative to traditional deposition techniques. One of the most important aspects for its industrial application is to know the clad geometry in order to calculate the deposited layer thickness. This work presents a model in which, starting from the concentration of injected material and the melt-pool geometry, clad height is finally estimated. Both input variables are obtained by two previous validated models. On one hand, the melt pool is estimated by a thermal model based on the finite difference method, and on the other hand, concentration of injected material is provided by a particle concentration CFD model. This data is used in a mass balance over melt-pool area in order to estimate the deposited clad height.

Abstract: The presented article proposes a laser based polishing operation which consists in the application of a laser beam in a very controlled way. The work presents several polishing tests carried out with CO2 and High Power Diode Lasers, for a DIN 1.2379 tool steel tempered up to 62HRC. This material is commonly used for injection moulds and inserts for stamping dies. The Laser Polishing tests results have been used as the input data for a design of experiments (DoE), therefore the optimum operation parameters for the process as well as its degree of influence in the melted surface have been defined. Experimental tests have been performed from different initial roughness values obtained by High Speed Milling operations. Reductions of final roughness higher than 80% have been obtained with respect to the initial roughness, with values below 0.8μm Ra.