B. Izquierdo

Computer simulation of performance of electrical discharge machining operations

The electrical discharge machining (EDM) process is optimum for accurate machining of complex geometries in hard materials, as those required in the tooling industry. It has become by far the most popular among the non-conventional machining processes. However, although a large number of EDM machines are sold every year, available knowledge of the process is still very empirical. Experimental trials are required in many cases to set up the optimum conditions for an EDM operation, resulting in increases in lead-time and cost for the final part. The reason for this is the complex nature of the process, highly stochastic, that involves simultaneous interaction of thermal, mechanical, chemical and electrical phenomena. Therefore, research efforts must be directed towards process modelling in order to reduce the experimental cost associated to the technology. In this work, an original computer simulation model of the EDM process is presented. The model is based on the numerical calculation of temperature fields within the workpiece, from which the amount of part material removed per discharge can be estimated. The objective is to theoretically predict material removal rate (MRR) and the final surface finish of the machined part using as input variables the EDM process parameters and the properties of the work material. The model has been validated by carrying out tests on an industrial EDM machine, showing that it can adequately predict MRR and surface roughness with errors below 9%.

Analysis of Micro-Pin Manufacturing Using Inverse Slab Electrical Discharge Milling (ISEDM) Process

Abstract. This paper analyses the technological capabilities of a novel rotary (EDM) electrical discharge machining process for the manufacturing of high aspect ratio cylindrical micro-components. The process is called Inverse Electrical Discharge Grinding (ISEDM). An experimental analysis has been carried out on high speed steel (tool steel Vanadis 23), using a conventional EDM machine and graphite electrode. The effect of pulse off-time, work piece final diameter and machining length on material removal rate, electrode wear ratio, radial accuracy and surface roughness has been quantified. From the study, optimum strategies that involve the use of different EDM regimes for achieving the optimum requirements can be defined. Micro-pins of 0.3 mm diameter with aspect ratio as high as 100:1 have been successfully manufactured.

Modeling recast layer and surface finish in the manufacturing of high–aspect ratio micro-tools using the inverse slab electrical discharge milling process

Electrical discharge milling–based processes are a good alternative for the manufacturing of micro-tools. However, some limitations must be considered both on the fields of process cost and control of surface characteristics. The inverse slab electrical discharge milling (ISEDM) process is an economic alternative to other high-precision high-cost machining processes because a conventional slab electrical discharge milling (SEDM) machine can be used to produce high–aspect ratio cylindrical tools with diameters as low as 200 µm. In this article, the influence of process variables on the surface integrity generated by the ISEDM process is presented. An experimental model aiming at the prediction of both surface finish and thickness of the recast layer as a function of the spark characteristics is developed. The influence of process variables is then analyzed. The model was validated with a high degree of agreement by carrying out experimental tests on submicron sintered high-speed steel micro-pins. Micro-tools with a diameter 335 µm and an aspect ratio as high as 90:1 can be manufactured using this novel technique with a surface finish below Ra 0.7 µm and thickness of recast layer below 3 µm.

Characterization of the Response of Embedded Thermocouples in Grinding

Temperature measurement in grinding has been a widely analyzed field in the study of the process. Temperatures in grinding are too difficult to measure due to the high gradients in the ground workpiece. A lot of different methods have been employed by many researches in the last years. In this paper the use of thermocouples is analyzed attending to the mathematical characterization of their response. It will be shown that correct modeling of the thermocouple’s response permits the avoidance of the problem of thermal inertia, making thus possible the use commercial thermocouples for temperature measurement in grinding.

Industrial Application of the MCG (Minimum Coolant Grinding) Technology

The use of fluids in grinding is necessary to carry out an optimized process that avoids any kind of damage in the ground workpieces. However, the use of fluids in machining processes presents some problems as the economic one and the environmental one. The present work analyzes the industrial viability of a new solution to avoid the use of fluids in grinding, the MCG system. This system combines the use of a MQL (Minimum Quantity Lubricant) commercial system and a gas supplied at low temperatures. In this case the grinding of a component of the engine of a competition motorcycle with the MCG (Minimum Coolant Grinding) system is compared with the classic fluid flow system.

Electrodischarge dressing (EDD) applied to contour grinding

Superabrasive grinding is a high efficiency process used in special applications such as high speed grinding, creep feed grinding, and Quick-Point. Although the maximum efficiency is obtained by metallic bonded wheels due to their wear resistance, their hardness makes almost impossible to dress them properly. Vitrified bonded wheels are now being used instead of metallic bonded ones since they have superior self-dressing capability. With the aim of obtaining maximum efficiency of these special grinding processes, in the last years a number of non-conventional dressing processes have been developed allowing the use of metallic bonded wheels. In this work, a methodology to introduce the electro-discharge dressing (EDD) of superabrasive conductive metallic bonded wheels is presented. The efficiency of EDD process to regenerate shaped wheels applied in Quick-Point or peel grinding has been studied by grinding hard metal rollers. Results show that EDD is able to remove the run-out and regenerate cutting capability.

New Technologies for Increasing the Capacities of WEDM Machines

The process of Wire Electrical Discharge Machining (WEDM) has experienced a dramatic growth in the last years. Together with the new requirements imposed by customer needs, globalization of the markets has brought about a new scenario in which competitiveness is the keyword. In the case of WEDM, it is only possible from a perspective that integrates developments in hardware, software and know-how, to generate the required added-value with respect to competitors. For instance, it is not enough to give an answer to the demand of a high-speed first cut: economy must be achieved together with a high accuracy and using low-cost wires. In this paper the research actions currently running aiming at the development of a new generation of WEDM machines are presented. The objective of this paper is to present an integrated research approach focused on industrial needs, covering the following aspects: Accuracy and productivity; automation and machine intelligence; eco-efficiency.

Two FEM Thermal Models for Shallow and Deep Grinding

Grinding is a stochastic process applied in the last stages of the manufacturing cycle. In last decades, grinding research has focused on prediction of thermal damage on ground workpiece since it is of considerable importance from both research and industrial perspectives. A number of numerical and analytical thermal models have been carried out so far. However, new grinding processes such as peel grinding, creep feed grinding and others such as plongee grinding need new models which consider the effect of higher depth of cuts, but there is no information about the minimum depth of cut to consider the elimination of grounded material in FEM models. This article establishes the frontier from which the removed ground material should be physically eliminated to obtain an accurate FEM thermal model. Results show valuable information to decide which kind of model (with or without element elimination) is enough accurate for their purpose and application.

About the Importance of Simulation Tools in the Learning Process of Metal Forming and Moulding

The European Higher Education Area has entailed some upheaval since it has involved deep changes in university education. Among the subjects taught in technical education such as Manufacturing Technologies, which involve strong experimental contents, the use of specific tools is helpful for better understanding of such subjects. This article highlights the need for the use of simulation tools in the field of manufacturing processes. The student may achieve optimal understanding and learning from them. They can understand, in a more visual way, complex phenomena that govern different processes and the influence of key variables. Applications related to sheet metal forming, forging and casting processes are presented. The main objective is to enable students to better understand the phenomena that govern the processes of moulding and forming, with the invaluable help of simulation software. The final aim is to ensure that the student reaches an optimum knowledge of moulding and forming processes using simulation software.

Analysis of EDD Accuracy for Profiling Metal-Bonded Grinding Wheels

Grinding process using superabrasive metal-bonded wheels is unavoidably linked to long and inefficient truing and dressing processes. This document presents the application of electro-discharge dressing process as an alternative to form wheels. The accuracy of the process and its efficiency has been analyzed on wheels of different grit size. To do so, complex geometry has been completely profiled to a 1A1 type wheels. Results show that the process can provide the desired geometry at the cost of a high processing time. The comparison between fine and large grit size grinding wheels shows that there is apparently no geometric limitation imposed by the grit size apart from that associated to grit diameter in corners and inner radii.