Raymond Snoeys

Current Trends in Non-Conventional Material Removal Processes

Summary The so-called non-conventional machining methods can no longer be called “non-traditional”, since they found a wide range of applications. Moreover, these electro-physical and electro-chemical material removal methods often do compete with the more traditional machining techniques. Those non-conventional machining methods allow the machining of complex shapes, not at least because of the use of advanced CNC-technology. The cutability of material often suggests the use of these techniques, e.g. when hard steel alloys and special composite materials are concerned. Evidence is given of the growing economical importance and the enlarged scope of applications covered by these non-conventional manufacturing methods. This is illustrated by a number of specific examples. Some recent developments and new trends are highlighted as well. Some industrial examples illustrate how some of these techniques can be competitive with classical manufacturing methods. In many other cases they are the only efficient solution for realising specific industrial products. In combination with conventional machining methods Improved performances may be achieved.

Improved adaptive control system for EDM processes

Summary Current research in spark erosion deals with further improvement of the automation of the process. It is essential to obtain accurate process information in order to decide when control interactions should be taken. This paper focusses on the K.U. Leuven approach. It describes briefly some optimization approaches, developed to search for maximum process efficiency. (i.e. maximum Metal Removal Rate Z w ). To reach this goal, two important control parameters are controlled adaptively: Servo Reference Voltage Us (i. e. proportional with gap width), and Pulse Interval Time to. An extensive machining tetst program has Seen carried out applying different process settings corresponding with finishing and roughing. The discharge current and discharge time have been changed in a broad range. Different electrode polarities as well as various material combinations (electrode-workpiece) have been used to test the ACO system. The same strategies could be used to handle all those different situations without requiring any modification of the basic control strategy.

Comparison of Various Approaches to Model the Thermal Load on the EDM-Wire Electrode

One of the most important constraints in EDM-wire cutting, is the occurance of wire rupture. This phenomenon actually limits the maximum attainable cutting speed; in case of rupture, machining time increases drastically while at the same time permanent marks on the workpiece surface may be left behind. On-line information about the power dissipation between electrode and workpiece is made feasible by using the EDM-Pulse Discriminator as detection system during real-time measurements preceeding wire rupture. According to these results, the thermal load on the wire seems to govern the wire rupture phenomenon. A preliminar thermal model is formulated to evaluate the thermal load of the wire. An analytical solution is compared with a numerical finite-difference method. The influence of various machining parameters on the temperature distribution of the wire can be derived. A first attempt to cover randomly occuring pulses is also presented.

Knowledge-Based System for Wire EDM

The paper proposes an all-round solution to a number of problems, related to the wire-EDM process. The solution is based on the development of a Knowledge-based system. It enables process monitoring and control, making use of a reliable rupture probability parameter. An expert system for operator assistance, fault diagnosis and training is also included. Machine settings are determined automatically by means of a work-preparation module. Experiential and theoretical knowledge about the process is stored in separate knowledge bases.

Survey of adaptive control in electro discharge machining

Abstract This contribution deals with control systems for the electro discharge machining process. Special attention is paid to techniques of inprocess evaluation of the EDM process. The paper focuses on adaptive control systems used to optimize the process performances. Existing adaptive controllers for EDM are surveyed. Economic benefits as well as practical results which could be achieved with adaptive control systems are discussed.

A thermal model to investigate the wire rupture phenomenon for improving performance in EDM wire cutting

Abstract A continuous trend towards automation can be noticed in wire cutting electro discharge machining due to the relatively low machining speed and large investments required. In this respect, the wire rupture phenomenon may be considered a major problem, limiting the overall efficiency of the operation. The thermal load on the wire seems to be a governing factor determining wire rupture. This has been proven by a number of tests using an EDM pulse analyzing system. In order to examine the relative influence of various process parameters on the thermal load of the wire, a mathematical thermal model was developed. The model enables the calculation of the temperature rise in the wire due to heat input by electrical discharges and from Joules heat. The result of this analysis can be used in an adaptive control optimization system in order to maximize the cutting speed, without enhancing the risk of wire rupture.

Survey of EDM Adaptive Control and Detection Systems

This contribution reviews research work on Adaptive Control Systems for Electric Discharge Machining processes (EDM). Investigations on process phenomena have lead to modern, efficient, and reliable wire-cutting machines as well as die-sinkers. Because Adaptive Control Systems imply detection and monitoring hardware, a survey is presented of actual EDM measuring equipment for on-line monitoring of the process. To control EDM processes, very fast process control equipment is required to avoid that unefficient situations may develop and occur. For example, trends to arcing ought to be quickly detected and recognized so that proper actions can be taken in order to disrupt suchlike trends. The basic concepts of a new monitoring device, an “EDM Pulse Discriminator” (EDMPD) designed and developed at the K. U. Leuven are treated. This device is to be used in an Adaptive Control System for minimizing tool-wear or maximization of metal-removal rate. Performance and initial results obtained are presented.

DEVELOPMENT OF IMPROVED EXTERNALLY PRESSURIZED GAS BEARINGS

As a result of recent research and development work at the K.U. Leuven(Belgium), a number of airbearings with non-parallel airgaps have been designed for which some disadvantages(high costs, low load carrying capacity, small bearing stiffness and sensitivity to pneumatic hammering) have been eliminated or strongly attenuated. The conically shaped airgaps yield a larger thrust force and an increased bearing stiffness.The dynamic behaviour of the air film may be fully characterized as a function of bearing parameters, enabling one to predict the stability limits for a particular application.

Additive damping treatments for mechanical structures

The prediction and optimisation of structural damping has become a matter of primary interest in the design of machines and structures. A succesful way of increasing structural damping is the utilisation of damping materials in additive layer treatments. In this paper emphasis is put on the recently developed high damping materials. Results of a comparative study of the dynamic properties, stiffness and damping, are presented. Techniques to predict the effect of free and constrained layers are discussed. For complex structures, these calculations are based on modal parameters. This is illustrated with practical case-studies.

Adaptive control optimization of the EDM process using minicomputers

Abstract Electro-Discharge Machining (EDM) is an electro-physical machining process fulfilling a number of requirements making it suitable for the application of adaptive control. This paper describes the EDM machine with its adaptive control system, including a minicomputer, some sensors and control devices and their respective interfaces. Software, including some strategies implemented for searching optimal working conditions, are reported. Some preliminary results illustrate the overall performance of the adaptive control system.