G. D’Urso

Micro-electro discharge machining drilling of stainless steel with copper electrode: the influence of process parameters and electrode size

This article is about the implementation of an acquisition system for the measurement of micro-electro discharge machining process parameters and the statistical analysis of their influence on the process performance. The micro-electro discharge machining drilling of 316L stainless steel with copper tubular electrodes was studied and the exchanged power was taken into account as a comprehensive variable able to represent the effect of the peak current and voltage on the final result. The direct proportionality between the exchanged power and the nominal process parameters was verified. A linear and non-linear regression approach was used in order to obtain predictive equations for the most important aspects of micro-electro discharge machining process, such as the machining time and the electrode wear.

Electrical Discharge Machining of Micro Holes on Titanium Sheets

Micro-Electrical Discharge Machining (μEDM) has become a widely accepted non-traditional material removal process for micro-manufacture of conductive materials considered difficult to be cut using traditional machining technologies. Moreover, EDM is an ideal process for obtaining burr-free micron-size apertures with high aspect ratios. Aim of this work was to investigate the feasibility of drilling micro holes on titanium using μ-EDM technology. Titanium plates having a thickness equal to 0.5 mm were taken into account and the holes were performed using a carbide electrode having a diameter equal to 0.3 mm. The Design Of Experiment (DOE) method was used for planning the experimental campaign and ANOVA techniques were applied to study the relationship between process parameters and final output. In particular, the most important process parameters such as peak current, pulse duration, frequency and electrode rotation speed were investigated as a function of material removal rate, wear rate and machining accuracy. Geometrical and dimensional analyses were carried out on micro-holes using both optical and scanning electron microscopes to evaluate both the over cut and the rate of taper.Copyright

The effects of electrode size and discharged power on micro-electro- discharge machining drilling of stainless steel

This article is about the measurement of actual micro-electro-discharge machining parameters and the statistical analysis of their influence on the process performances. In particular, the discharged power was taken into account as a comprehensive variable able to represent the effect of peak current and voltage on the final result. Thanks to the dedicated signal acquisition system, a correlation among the discharged power and the indexes representing the process parameters was shown. Finally, linear and non-linear regression approaches were implemented in order to obtain predictive equations for the most important aspects of micro-electro-discharge machining, such as the machining time and the electrode wear.

Mechanical and metallurgical analyses of longitudinally friction stir welded tubes: the effect of process parameters

Friction stir welding (FSW) is a welding technology used to join materials considered difficult to be welded. Mechanical properties of FSW joints are generally evaluated by means of tensile tests that might provide insufficient information because maximum strain obtained before necking is small and that cannot be used when the joint path is not linear or when the welds are executed on curved surfaces. The present work investigates the mechanical properties of FSW tubes by means of tube bulge tests. An experimental campaign was performed on tubular specimens (thickness equal to 3 mm, external diameter equal to 40 mm). In particular, bent plates in AA6060 alloy were longitudinally friction stir welded by means of a CNC machine tools varying the welding parameters. The burst pressure, the stress state and the wall thickness were measured for each tested tube. Finally, macro and micro analyses were carried out on the joints.

The Formability of Aluminum Foam Sandwiches: Experimental and FEM Analysis

This work deals with the formability of metal foams and it is focused on three point bending of aluminum foam sandwich panels. In this study bending can be considered as both a process for shaping of foamed panels and a mean for metal foam testing. Several tests were carried out by varying bending conditions and collecting load-displacement data. Specimens showed an interesting behaviour during bending since the sample deformation was related to the occurrence of foam cells failure or collapse. Moreover, once the process is terminated specimens retained a significant bending strength. During the experimental campaign several samples showed irregular fracture behaviour. In these cases cells fracture often starts in a generic part of the specimen (in correspondence of some non-eligible material defects) and propagates through the foam. The reasons of this problem and the possibility of failure prediction were investigated using different approaches. In particular, thickness measurements (using a ultrasound feeler) and X-ray analysis were carried out for this purpose. In addition, a study based on foam density showed a remarkable data scatter that can be considered as a characteristic of the state of the art in foamed panels manufacturing (in terms of process control and product variability). Finally, load-stroke curves were taken into account for this purpose. Computer simulations of the experiments were performed using the commercial FEM code (Deform 2D). Foam compressibility was simulated using a porous material model and the onset of foam instability was simulated by means of a specific damage criterion. Good agreement between simulative and experimental results was found.

Thermo-Mechanical Characterization of Friction Stir Spot Welded AA7050 Sheets by Means of Experimental and FEM Analyses

The present study was carried out to evaluate how the friction stir spot welding (FSSW) process parameters affect the temperature distribution in the welding region, the welding forces and the mechanical properties of the joints. The experimental study was performed by means of a CNC machine tool obtaining FSSW lap joints on AA7050 aluminum alloy plates. Three thermocouples were inserted into the samples to measure the temperatures at different distance from the joint axis during the whole FSSW process. Experiments was repeated varying the process parameters, namely rotational speed, axial feed rate and plunging depth. Axial welding forces were measured during the tests using a piezoelectric load cell, while the mechanical properties of the joints were evaluated by executing shear tests on the specimens. The correlation found between process parameters and joints properties, allowed to identify the best technological window. The data collected during the experiments were used to validate a simulation model of the FSSW process, too. The model was set up using a 2D approach for the simulation of a 3D problem, in order to guarantee a very simple and practical solution for achieving results in a very short time. A specific external routine for the calculation of the thermal energy due to friction acting between pin and sheet was developed. An index for the prediction of the joint mechanical properties using the FEM simulations was finally presented and validated.

Characterization of Friction Stir Welded Tubes by Means of Tube Bulge Test

Mechanical properties of friction stir welded joints are generally evaluated by means of conventional tensile test. This testing method might provide insufficient information because maximum strain obtained in tensile test before necking is small; moreover, the application of tensile test is limited when the joint path is not linear or even when the welds are executed on curved surfaces. Therefore, in some cases, it would be preferable to obtain the joints properties from other testing methods. Tube bulge test can be a valid solution for testing circumferential or longitudinal welds executed on tubular workpieces. The present work investigates the mechanical properties and the formability of friction stir welded tubes by means of tube bulge tests. The experimental campaign was performed on tubular specimens having a thickness of 3 mm and an external diameter of 40 mm, obtained starting from two semi‐tubes longitudinally friction stir welded. The first step, regarding the fabrication of tubes, was performe...

Cost Index Model for the Process Performance Optimization of Micro-EDM Drilling on Tungsten Carbide

The present work deals with the execution of through micro-holes on tungsten carbide plates using a micro-electrical discharge machining (micro-EDM) machine. The experiments were carried out by varying peak current, voltage and frequency in order to achieve suitable technology windows. Tubular electrodes, made of two different materials (tungsten carbide and brass), were used. The investigation focuses on the influence of variable process parameters on the process performances and their optimization. The performance indicators taken into account were Material Removal Rate (MRR) and Tool Wear Ratio (TWR). A general model based on a cost index was defined for the process performances optimization and the optimal conditions were identified through the minimization of the objective function.

Simulative model for the evaluation of thermo-mechanical effects in Friction Stir Spot Welding (FSSW) of Aluminum sheets

A study was performed to evaluate how the Friction Stir Spot Welding process parameters affect both the thermal distribution in the welding region and the welding forces. An experimental campaign was performed by means of a CNC machine tool and FSSW lap joints on AA6060-T6 aluminum alloy plates having a thickness of 2+2 mm were executed. Five thermocouples were inserted into the samples at a specific distance from the specimen center. A set of tests was carried out by varying the process parameters, namely rotational speed, axial feed rate, plunging depth and dwell time. Axial welding forces were also measured during the execution of the experiments by means of a piezoelectric load cell. The experimental data collected were used to set up and to validate a simulative model of the process. In particular, a 2D FEM model was set up using the commercial code Deform 2D. A 2-dimensional FEM code was preferred in order to guarantee a very simple and practical model able to achieve results in a very short time. Since it is not possible to simulate the rotation of the tool in a 2D configuration, a specific external routine for the calculation of the developed thermal energy due to the friction between tool and workpiece was set up and implemented into the code starting from the local pressure distribution along the contact area.

Characterization Of An EBL System: The Influence Of Process Parameters On Thickness Resist And Engraving Shapes

In LIGA process, the low flexibility due to the use of masks might be overcome using the electron beam of a scansion electron microscope (SEM) instead of the synchrotron radiation. In this way, through the vector control of the beam, it is possible to irradiate a specific path on the resist without using any mask. Anyway, it is important to remark that the Electron Beam Lithography (EBL) can not include all the applications of the X‐ray LIGA technique but it could be a valid alternative only for some specific uses. In particular, some limits concerning the impression of high thickness resists are expected. An EBL system based on a SEM was recently implemented by the authors and some tests were carried out to characterize the device performances. Aim of this work is to asses the system performances in terms of maximum impressible thickness resist and shape of the engraved entities. Several tests were carried out by varying the resist thickness and the process parameters.