Gianluca Tristo

Assessment of Electrode Wear Measurement in Micro EDM Milling

In micro electrical discharge milling (micro EDM milling), the tool electrode kinematics is the same as in conventional milling, but the material removal is obtained by the heat and electrical forces in the gap between the tool electrode and the workpiece. The electrode wear in micro EDM milling is one of the main problems to be solved in order to improve machining accuracy. Most common, the electrode linear wear is measured on machine by touching the reference point with the electrode after machining a certain number of layers. The reduction of the electrode length due to the wear is used to modify the electrode trajectory. This paper presents an assessment of the electrode wear on micro EDM milling machine. The experiments were performed on state-of-the-art micro EDM equipment. The electrode wear was measured on the machine in a conventional manner as already described. Additionally, a Laser Scan Micrometer (LSM), implemented on machine as well, was used in two ways, namely to detect only the coordinates of the electrode tip before and after machining, and by acquiring the electrode profile. Experiments were performed by machining micro features in steel using several layer thicknesses and various process parameters. The results show that the accuracy of the electrode length measurement by touching the reference point is enough accurate for the estimation of the electrode linear wear. But to accurately measure the electrode volumetric wear, it needs to be calculated from electrode profiles acquired before and after machining.

Preliminary Study on Staggered Herringbone Micromixer Design Suitable for Micro EDM Milling

This paper discusses interplay between the design of a Staggered Herringbone Micromixer (SHM) and micro Electrical Discharge Machining (EDM) milling technology. SHM consists of a main channel and many herringbone lookalike grooves at the bottom, which enhance mixing. Firstly, a brief overview on how the technological model of micro EDM milling was constructed is presented. Anticorrosive stainless steel was used as a workpiece material on the basis of which the database for the technological model was established. In the second part the technological model was used for micromixer design optimization. Different SHM designs that can be machined in the same amount of time, were compered via their mixing efficiency. Mixing efficiency was estimated by performing Computational Fluid Dynamics (CFD) simulations. The results show, that smaller and shallower grooves are not efficient in the terms of mixing. An important design parameter is also the orientation of the grooves. In the end, a favorable SHM design is presented.

Effects of the cavity surface finishing on the polymer filling flow in micro injection moulding

In micro-injection moulding, dimension and shape of the cavity microscale factors, normally negligible in conventional injection moulding, play an important role. More specifically, cavity roughness, which in large scale moulding is relevant only for surface finishing and appearance, at the micro-scale can not only significantly change the cavity volume but also influence the polymer flow and the heat transfer between polymer melt and mould. In the present work the effect of the mould cavity finishing on the micro-injection moulding process was investigated. The phenomenon was analyzed using different channels for melt flow separation and taking advantage of localization of weld lines for differential characterization. To this end different micro-cavities with different surface finishing where generated by means of micro electro discharge machining (μEDM). Cavities surfaces where characterized integrating metrological information from different instruments: scanning probe microscopy (surface roughness), optical profilometry (roughness and volumes) and scanning electron microscopy (weld lines localization).