Giancarlo Maccarini

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 Effect of Sheet and Material Properties on Springback in Air Bending

Angle control in air bending is achieved either by exploiting direct angle measurement (adaptive forming) or by controlling punch displacement. In general, the desired angle is supplied as input to CNC press brakes and the choice of punch stroke relies on either analytical or empirical models. Process geometry and material properties affect the outcome, therefore, full knowledge of these values is critical. Since a major source of inaccuracies is due to errors in material description (sheet thickness is critical as well), material data (or, more generally, sheet behavior information) collection in process is advisable. In air bending, process control can be improved by studying the total load as a function of punch displacement. This approach becomes more and more interesting since devices for load measurement are now available on the market. The aim of this work is to analyze some experimental load measures, collected in actual working conditions, to evaluate the accuracy of such technique and its potential for in process applications. Several sheet materials (ferrous and non-ferrous alloys) are studied through both bending and tensile tests; the resulting material properties (tensile and bending) are evaluated and compared. After data treatment of punch force signal, the ability of predicting punch displacement needed to reach a defined bending angle (after springback) is discussed.

The Downsizing Effects in EDM Drilling of Micro Holes

The recent miniaturization trend in manufacturing, has enhanced the production of new and highly sophisticated systems in various industrial fields. In recent years, machining of the so called difficult to cut materials has become an important issue in several sectors. Micro Electrical Discharge Machining (micro-EDM) thanks to its contactless nature, is one of the most important technologies for the machining of this type of materials and it can be considered as one of the most promising manufacturing technologies for the fabrication of micro components. One of the most relevant applications of micro-EDM is micro-drilling. Micro holes in fact, are widely used for example in micro-electromechanical systems (MEMS), serving as channels or nozzles to connect two micro-features, and in micro-mechanical components. The present study is about micro drilling of metal plates by means of micro-EDM technology. In particular, the aim of this work is to investigate the effects of the downsizing of the micro holes diameter on the drilling performances. The influence of the reduction of the diameters in terms of both process performances (e.g., tool wear, taper rate, diametrical overcut) and general quality of the holes was investigated. Steel plates having thickness equal to 0.8 mm were taken into account. The drilling process was carried out using a micro-EDM machine Sarix SX 200 with carbide electrodes having diameter equal to 300, 200, 100 and 50 μm. Since the standard electrodes adopted in this study had a diameter equal to 300 μm, a wire EDM unit was used to obtain the other electrodes. The relationship between the process parameters considered the most significant and the final output, was studied. Furthermore, the geometrical and dimensional properties of the micro-holes were analyzed using both optical and scanning electron microscopes. In particular, it is demonstrated that the diameter size has a significant influence on the final value of the diametrical overcut while peak current and frequency parameters have a negligible effect.

Control System Algorithm for the Prediction of Sprinback in Air Bending

The phenomenon of springback, which is ruled by strain recovery after removal of forming loads, is of remarkable interest in air bending of metal sheets. In this process, the final angle is affected by a number of parameters related to both process geometry (sheet thickness, die and punch radii) and material properties (elastoplastic stress-strain law); because of this, punch stroke has to be calculated in a nontrivial way and a number of input parameters should be taken into account. In this work the study of total load as a function of displacement is used to collect information about material stress-strain law; using this approach, load data may be exploited to fine tune the mathematical description of the material and, finally, to improve springback prediction. A customized press brake able to measure both displacement and force during bending was fabricated for this purpose. The press brake is equipped with a control system algorithm able to collect material information directly during the initial stage of the bending process. These collected data are used to feed a model based on a FEM simulation and the model output is the final punch displacement suitable to obtained a specific bending angle after unloading. The program utilized for the simulation is Deform 2D. Preliminary tests were executed on metal sheets having different thickness.

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.

Surface alteration induced by machining

This paper, dealing with strain hardening in turning, is a comparison of numerical (Finite Element Method (FEM)) and experimental results. Orthogonal cutting was assumed as the reference working condition. A FEM model was set up to simulate experimental conditions and to evaluate the effects of cutting parameters on surfacial strain hardening. Experimental data were recorded by machining thin disks of C20 steel (1CD20 UNI EN 10017: 2005) with radial feed; several values of both cutting speeds and feed were tested. After machining, work hardening was evaluated by micro Vickers test as a function of the distance from the machined surface. Regression techniques were used to fit experimental data and to find out work hardening patterns (depth of the affected zone, maximum hardness of the surface). FEM simulations of the experiments were performed using a commercial code for forming processes. A plane strain model of a rigid-plastic workpiece was set up with suitable material and interface properties. Good agreement between numerical and experimental results was found, therefore FEM was used to model a wider range of process parameters.

A New FMEA Approach Based on Availability and Costs

The paper reports on a new FMEA (Failure Mode and Effects Analysis) technique for the evaluation of operating failures on machine tools. The traditional FMEA methodology focuses the analysis on failure problems and usually does not take into account other parameters, such as availability and costs. This new technique was setup for predicting operating failures during the design process of machine tools, so reducing costs and time to market. This approach is based on a new index depending on machine tool availability and customer costs related to failure time. For the validation and the evaluation of the method, an industrial case was studied; data collected from this analysis proved to be in good agreement with failures detected by the customer. The adopted method showed a higher reliability compared with traditional FMEA results.

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.

Product Cost Modelling for Micro-EDM Drilling

The recent miniaturization of components in manufacturing has increased the production of lightweight and sophisticated systems in many different industrial fields. Micro Electro Discharge Machining (micro-EDM) is one of the most extensively used contactless and chipless machining processes. Although it is one of the most used technology, there are a few research works which investigate the economic implications of this machining. This paper reports a model cost to estimate μEDM-machining costs, including fixed and variable costs. A case study was presented taking into account micro holes on stainless steel obtained using different electrode materials. The capability of the model was demonstrated.