Daniel Teixidor

Multiobjective Optimization of Laser Milling Parameters of Microcavities for the Manufacturing of DES

A multiobjective optimization of the laser milling process of microcavities for the manufacturing of drug eluting stents (DES) is presented. The diameter, depth, and volume error are considered to be optimized in function of the process parameters (scanning speed, laser intensity, and pulse frequency). Several experiments are carried out following a design of experiments in a nanosecond pulsed Nd:YAG laser machine on 316 L Stainless Steel as a work material. Two different geometries are studied, and they are considered as another variable for the model. The multiobjective optimization problem is solved by NSGA-II algorithm, and the nondominated Pareto-optimal fronts are obtained. The capability of the process to manufacture within a level of error is also investigated. Relative error capability maps for different scale of features are presented.

Experimental Introduction to Surface Roughness Parameters Measurement

Surface roughness influences the performance of a finished part. In machining operations, the surface roughness generated is influenced by an enormous set of factors. In ball end milling operations, the geometric characteristics of the cut clearly affect the surface crests generated. This paper presents an experimental methodology that permits engineering students to identify and analyze the surface roughness. The methodology is applicable to training courses and surface texture generation as well.

Experimental Analysis of Laser Micro-Machining Process Parameters

This paper reports the characterization of laser machining (milling) process to manufacture micro-channels in order to understand the incidence of process parameters on the final features. Selection of process operational parameters is highly critical for successful laser micromachining. A set of designed experiments is carried out in a pulsed Nd:YAG laser system using AISI H13 hardened tool steel as work material. Several micro-channels have been manufactured as micro-mold cavities varying different process parameter. Results are obtained by evaluating the dimensions and the surface finish of the micro-channel. The dimensions and shape of the micro-channels produced with laser-micro-milling process exhibit variations. In general the use of low scanning speeds increases the quality of the feature in both surface finishing and dimensional.

Modelling Laser Milling of Microcavities for the Manufacturing of DES with Ensembles

A set of designed experiments, involving the use of a pulsed Nd:YAG laser system milling 316L Stainless Steel, serve to study the laser-milling process of microcavities in the manufacture of drug-eluting stents (DES). Diameter, depth, and volume error are considered to be optimized as functions of the process parameters, which include laser intensity, pulse frequency, and scanning speed. Two different DES shapes are studied that combine semispheres and cylinders. Process inputs and outputs are defined by considering the process parameters that can be changed under industrial conditions and the industrial requirements of this manufacturing process. In total, 162 different conditions are tested in a process that is modeled with the following state-of-the-art data-mining regression techniques: Support Vector Regression, Ensembles, Artificial Neural Networks, Linear Regression, and Nearest Neighbor Regression. Ensemble regression emerged as the most suitable technique for studying this industrial problem. Specifically, Iterated Bagging ensembles with unpruned model trees outperformed the other methods in the tests. This method can predict the geometrical dimensions of the machined microcavities with relative errors related to the main average value in the range of 3 to 23%, which are considered very accurate predictions, in view of the characteristics of this innovative industrial task.

Experimental Introduction to Forced and Self-Excited Vibrations in Milling Processes and Identification of Stability Lobes Diagrams

In milling operations, cutting edge impacts due to the interaction between the cutter and the workpiece excite vibrations. It is possible to distinguish between free, forced and self-excited vibrations. Chatter is a self-excited vibration that can occur in machining processes, and is considered to be a common limitation of productivity and quality. Stability lobes diagrams (SLDs) show the frontier between chatter-free milling operations, i.e. stable dominated by forced vibrations, and operations with chatter, i.e. unstable. These diagrams are usually obtained from impact hammer testing. However, this method requires trained personnel with advanced knowledge and it is not easily applied in engineering studies or operator training. This paper presents an experimental method that allows engineering students and operators-in-training to observe the chatter phenomenon and to distinguish between forced and chatter vibrations and identify process stability diagrams.