Worldwide Research and Activities in EDM
Although once considered a “nontraditional” machining process, EDM has been replacing drilling, milling, grinding and other traditional machining operations in many industries throughout the world. Since its early days as a “tap busting” method over 50 years ago, EDM has developed into one of the most advanced machining technologies. Today’s EDM equipment uses advanced Computer Numerical Control (CNC) with up to six-axes simultaneous operation and state of-the-art power supply technology, which can produce a mirror surface finish and “split-tenth” accuracy.
The tremendous advancements in EDM technology have been achieved through the collective efforts of many dedicated engineers employed by the major EDM builders and by researchers from some of the world’s leading institutions and research centers. This report provides an overview of the research studies and developments of these institutions and the activities of professional societies and other organizations throughout the world that are contributing to the continued advancements of Electrical Discharge Machining.
Mechanisms of Technology Transfer
Mechanisms of Technology Transfer According to the Federal Laboratories Consortium, there are several channels for bringing about the transfer of technology from government or private research centers to industry. The following list is a sample of the various mechanisms used:
1. Cooperative research projects between industry and laboratories.
2. Workshops, seminars, and briefings.
3. Exclusive/non-exclusive licensing.
4. Sponsored research where industry reimburses a lab for work done at the facility.
5. Consulting by lab personnel.
6. Employee exchange where researchers from the lab and industry trade assignments in areas of mutual interests.
7. Use of lab facilities where certain capabilities are not available at a particular company.
8. Laboratory visits to share information and discuss technical problems.
9. Publications and other printed literature.
10. Membership in industrial affiliate organizations that are associated with research lab’s.
As defined in items 9 and 10, one of the objectives of EDM Technology Transfer (EDMTT) has been to provide a mechanism or source of gathering information from research centers with projects relating to EDM, and making this information available to anyone interested in the EDM process. One reference source published by EDMTT is the “EDM Technology” volume series, which contain EDM technical reports by universities, EDM manufacturers, or other technical research centers around the world.
International and National EDM Conferences and Discussion Forums
In an effort to establish a forum for the discussion of EDM research and developments, and help provide a course of instruction in basic and advanced EDM technology, several technical societies and other groups have established international or national conferences on EDM.
Japan
?Japan Society of Electrical Machining Engineers(JSEME)
Throughout its forty year history, the JSEME has been the predominant organization and driving force behind the research and development of EDM and the dissemination of this information in Japan. All of the major Japanese EDM builders and university EDM researchers present technical reports on the latest EDM research and developments at their annual conferences. At the JSEME “All Japan Conference” held in October 1994, thirty-five new EDM reports were presented, including the latest research by Mitsubishi, Sodick, Makino, Hitachi, and the leading research centers established at Japanese universities. The “Journal of the Japan Society of Electrical Machining Engineers” (Japanese language only) is their official publication which provides the latest technical information on the Japanese EDM industry.
From a recent announcement by Professor Yasuo Kimoto, current President of JSEME, the Society will coordinate a new “International Journal of Electrical Machining” (IJEM). The aims of the IJEM are: 1) to propagate the latest scientific and technological news in the field of electrical machining methods, 2) to exchange experiences in putting electrical machining into practice, and 3) inform about the current state-ofthe-art and suggest directions of further development. IJEM editorial board members include representatives from Mitsubishi, Sodick, the leading Japanese research centers, and will also include members from outside Japan.
U.S.A.
?Society of Manufacturing Engineers (SME)
SME sponsors an annual EDM clinic and a fundamentals course.
?American Society of Mechanical Engineers (ASME)
Starting in 1985, the Production Engineering Division of ASME began a session on nontraditional machining during their Winter Annual Meeting with EDM as the major topic of discussion.
?Modern Machine Shop/Gardner Management
Beginning in 1989, Modern Machine Shop Magazine and Gardner Management Services has sponsored the largest EDM conference and exhibition in the United States. EDMTT has attended all of these conferences.
?National Institute of Standards & Technology (NIST)
Organized under the U.S. Department of Commerce Technology Administration, NIST has held conferences on the “Machining of Advanced Materials” and presents technical information on using EDM.
International
Beginning in the sixties, the “International Institution for Production Engineering Research” has coordinated an international delegation of the world’s major EDM manufacturer’s and researchers for the “International Symposium for Electro-Machining” (ISEM). The International Institution for Production Engineering Research is also known officially as CIRP, which stands for “College International pour I’Etude Scientifique des Techniques de Production Mechanique”. ISEM has been a forum of exchange for technical information on EDM, Laser, ECM and other high-technology machining processes. ISEMXI will be held in Switzerland and cover topics on EDM Process and Physics, EDM Machinery, EDM Technology, EDM Control and EDM Applications.
EDM Research and Development Centers
Although EDM represents only a small portion of the total machine tool industry worldwide, the number of laboratories throughout the world performing EDM research and development studies has been growing steadily for several years. The more in-depth and well organized EDM research programs at various technical centers are funded by the major EDM builders or through government research grants. Several EDM manufacturers have also donated machines and supplies to universities with limited funds, which has helped to provide a program for future engineers to obtain a hands-on understanding of the capabilities of the EDM process.
The following institutions have established research and development programs on EDM. They represent only a partial list of the laboratories and research projects throughout the world that contribute to the advancements in EDM technology. In addition to the work at advanced research laboratories setup by the major EDM manufacturers, the work performed at these institutions should have a direct impact on future developments in the EDM industry.
U.S.A.
Nontraditional Manufacturing Research Center, University of Nebraska-Lincoln
Under the direction of Professor K. P. Rajurkar, this institution has established one of the world’s leading centers for academic studies and experimental research in EDM and other high technology machining processes. Courses taught in advanced manufacturing processes cover a broad range of topics and provide the student with an in depth study of EDM technology. Besides EDM, about 30 other advanced manufacturing processes are covered. The following graduate level course description provides a summary of these studies:
Course Title: Advanced Manufacturing Processes (IE 970) Description:
Advanced manufacturing processes provide an alternative (or sometimes the only alternative) for manufacturing complex shapes in a wide variety of materials. This course deals with topics ranging from the principles of operation, to the integration of these advanced processes into future flexible manufacturing systems. About thirty-one nontraditional manufacturing processes including Electrical Discharge Machining (EDM),
Electro-Chemical Machining (ECM), Laser Beam Machining (LBM), Abrasive Jet Machining (AJM), Electrochemical Arc Machining (ECAM), Electron Beam Welding, etc. are covered in this course. In the context of these advanced manufacturing processes, the following topics are covered:
1. Process Mechanism, Modeling and Simulation
2. Surface Integrity
3. Tool Design, CAD
4. Design of Related Machine Tools
5. Adaptive Control
6. Expert Systems, Neural Networks, Fuzzy Logic Applications
7. Integration within CIM Environment
8. Applications
9. Environmental and Safety Issues
In addition to the class lectures, experimental projects on Die-Sinking EDM and Wire EDM are also required.
The following list of projects provide an overview of past and future EDM research work conducted at the University of Nebraska’s Nontraditional Manufacturing Research Center.
Projects Conducted Over Past Two Years
Effect of cryogenic treatment of electrode on EDM performance
This project attempts to study the effect of cryogenic treatment of work and tool electrodes on EDM process performance. Cryogenic treatment of the work piece material and electrodes (for EDM and WEDM) was done by RPM Carbide, Inc. of Ohio. During cryogenic treatment, the material is cooled at 77 K for 24 hours and brought back to ambient temperature. Experiments on WEDM have been carried out using treated wire and untreated wire. It was experimentally found that the risk of wire rupture was reduced by 30% when using cryogenically treated wire. Experimental work on Die-sinking EDM and WEDM is continuing.
?Wire EDMing of Polycrystalline Diamond (PCD)
An experimental study has been carried out to determine the effects of parameter settings in a state of the art WED machine on the machining performance. The WEDM performance in cutting different layers of materials, such as PCD and WC, in the workpiece have been experimentally and theoretically determined. The mathematical model(s) of thermal stress for a theoretical explanation of the removal mechanism of diamond grain based on the numerical solution of Stefan problem is continuing.
?WEDM of Beryllium Copper Alloys
The main objective of this project is to develop a database of optimal machine parameter settings for machining of Beryllium copper alloys of different heights during WEDM. This project is conducted with a Charmilles Robofil 100 WED machine. The relationships between the machine settings and machining characteristics such as machining speed, surface roughness, and overcut are determined experimentally. The machine setting parameters are charge frequency, charge current, pulse duration, capacitance, wire speed, wire tension and wire material. The optimization of parameter settings consists of two objectives, i.e. to maximize the machining speed and to maximize surface finish. A database of input parameters for both criteria is being developed.
Study of discharge distributions in die-sinking EDM using divided electrode spark detection method
The principal objective of this project is to study the influence of machining parameters (peak current and pulse on-time) and flushing methods on spark characteristics such as sparking efficiency and geometrical distribution of sparks in the machining gap. Peak current and pulse on-time change the machining conditions in the gap leading to changes in the sparking efficiency and spark distribution. A new method of spark detection system is employed to obtain the spark data. The solid tool is divided into number of smaller sections to identify each spark in different areas in the gap at different instants. This spark detection methodology can also be effectively used to find the efficiency of machining when subjected to different machining conditions.
Adaptive control systems for die-sinking EDM
The arc damage in the die-sinking EDM process reduces the machining productivity, decreases the machined surface quality, and increases the machining cost. The main objective of this project is to develop adaptive control systems for EDM to improve the process stability, avoid arc damage, and increase the machining rate. In this project, a digital EDM gap monitor was developed to precisely detect the time ratios of gap states including gap open, normal spark, transient arc, stable arc and short circuit. The unique feature of this system is the high frequency (HF) detecting technology that detects not only the occurrence of arc damage, but also the transient arc regarded as the forecasting signal of arc damage. The HF detection is the most reliable method in all EDM arc damage detecting technologies. A model reference adaptive control system and a self-tuning regulating system for EDM have been developed. These adaptive control systems detect gap state parameters through the EDM gap monitor and control the servo feed in real-time. The productivity with these control systems has been shown to be improved by 50% when machining under poor flush conditions. An EDM auto jumping controller using the PI self-tuning approach has also been developed on a state-of-the-art Mitsubishi K35 ED machine. This system adaptively adjusts the cycle time of the periodical retraction of the main spindle according to the detected EDM gap parameters. The arcing damage can be completely avoided, and the productivity is improved by 50% as compared to the manually set jumping cycle time.
?Advanced Wire-EDM control system
In the WEDM process, wire rupture reduces the machining rate. This problem is caused by high power density along the wire, which is regarded as the ratio of sparking frequency to spark distribution length determined by the workpiece height. With most of the state-of-the-art WEDM equipment, the sparking frequency can not be on-line monitored and controlled, and an optimal pulse off-time to determine the sparking frequency for a given workpiece height is selected in accordance with manufacturer supplied database. The main objective of this project is to develop an advanced WEDM monitoring and control system that monitors on-line the change of workpiece height and control the spark frequency at optimal levels. A recently developed control system consists of a digital spark frequency monitor and a PC used as the main controller with an interface for power generator and servo system control. The PC monitors on-line the gap voltage, spark frequency, and the table feed rate to identify the workpiece height. This system regulates the table feed at optimal rates and adjusts the pulse off-time in real-time to control the spark frequency at optimal levels determined by the identified workpiece height. The spark frequency is always adjusted at a safe and highly productive level, and is able to follow the change in workpiece height to avoid wire rupture and to maintain an optimal cutting speed. The error of the workpiece height identification is 1 mm and the response of the identification to changes in workpiece height is 1 second. With this control system, procedures of NC programming and machine operations are simplified, and the machine operator does not need to input the workpiece height data into the machine and insert the power generator setting commands into the CNC program when cutting a multiple height workpiece.
Future Projects at the University of Nebraska
?Abrasive assisted Electrical Discharge Grinding for machining advanced materials
The machining rate with mechanical grinding of advanced materials, including electrically conductive ceramics, sintered carbides, and polycrystalline diamonds (PCD), is very low due to their high hardness and toughness. The EDM process provides an effective alternative to machine advanced materials. However, the surface quality generated by EDM is poor due to the recast layer and micro-cracks on the machined surface. The objective of this project is to develop an Electrical Discharge Grinding (EDG) process with an assistance of mechanical abrasive effects for improving the flushing condition and removing the damaged layer when machining advanced materials. During machining, the grinding electrode rotates in high speed, the spark discharges take place in the gap between the electrode and workpiece, and the machining gap is controlled by an EDM servo system. The preliminary experimental study indicates that the abrasive effect not only improves the surface quality of EDG, but also improve the gap flushing condition by effectively removing the eroded chips and particles, and providing higher normal spark ratio and better machining stability.
?Advanced on-line monitoring and control system for die-sinking EDM
Graphite electrodes are popular for die-sinking EDM operations in U.S. industries because of higher machining rates and easy of fabrication. During EDM with graphite electrodes, the arc damage occurs frequently and is difficult to avoid. The main objective of this project is to develop an advanced monitoring and control system for die-sinking EDM when using graphite electrodes. In this project, an advanced and commercial available digital EDM monitor will be developed to detect the time ratios of gap states. The neural network technology will be used to analyze the gap voltage and current signals and the data of gap states collected from the EDM monitoring system. A neural network and fuzzy logical identification system will be developed to predict the arc damage during the EDM process with graphite electrodes. An advanced control system will be developed to control on-line the discharge power, auto-jumping of tool electrode, and the servo system.
?EDM power generator for advanced materials
When using EDM to machine the high thermal resistant materials including tungsten carbide, conductive ceramics, PCD and PCB, the discharge waveforms strongly influence the process performance. Most commercially available EDM power generators provide only square discharge current pulses. However, with square discharge pulses, the thermal energy can not be highly concentrated, therefore, the material removal rates for many advanced materials including tungsten carbide and conductive ceramics are very low. This project is proposed to developed an EDM pulse generator to provide particular discharge waveforms suitable to machine advanced materials. The prototype of the proposed pulse power generator will be developed to provide the transistor controlled RC pulse, multi-level waveforms with wider peak current and voltage ranges than current commercially available EDM power generators. A computer can program the discharge waveform and select different pulse parameters. The optimal waveforms for different material and machining requirements will be determined by the theoretical study of thermal modeling and analysis of the EDM process for advanced materials.
University of California/Davis
Research in several EDM fields, including (but not limited to) advanced EDM control systems aimed at increasing production and reducing operator attention and studies in wire breakage on WEDM.
Texas A&M University
EDM studies on difficult to machine materials such as tungsten carbide/cobalt composites, titanium diboride or other ceramic composite materials.
Tennessee Technological University
Machining of ceramic materials by EDM.
Japan
Institute of Industrial Science, University of Tokyo
Under the direction of Professor T. Masuzawa, this institution is considered one of the leaders of EDM research in Japan. Their studies cover all fields of EDM, including: fine surface quality, wire electro-discharge grinding (WEDG) for micro-machining, Mole EDM, studies in EDM flushing, microhole EDM, and other areas of EDM research.
The Institute of Industrial Science, Nippon Institute of Technology and Toyama University collaborated together in research and development of trueing and/or dressing of metal bond diamond grinding wheels using the EDM process. This method produces a higher grinding ratio and lower grinding forces than wheels trued by conventional methods.
Recently published research at the Institute of Industrial Science include a report on the development of a microhole EDM electrode feed mechanism using a piezoelectric translation device. They have also developed a 3-axis CNC micro-EDM which produces a surface finish of 0.1μm Rmax.
Another recent report involves the study on the wear ratio of copper electrodes when machining several kinds of carbon steels. It was learned that electrode wear ratio is strongly affected by not only the structure, but also the quantity of carbon layer which covers the electrode. If a sufficiently thick carbon layer could be generated on the surface of the electrode, a significantly lower wear ratio was achieved.
Nagaoka Technical Science University
Some of their most recent research work (also performed in conjunction with Toyota Technical College and the Hitachi Manufacturing Facility) include an interesting report on the EDM profiling of non-conductive ceramics. With the exception of a few limited EDM methods, normally only ceramic materials which have conductive properties are machinable by EDM. Here, researchers are working on a newly developed method for deep hole machining and cutoff machining of non-conductive ceramics using a standard electrical discharge machine.
Nippon Institute of Technology
Investigations on the possibility performing die-sinking EDM on a machining center to reduce the processing time required for manufacturing molds and dies.
Osaka Prefectural Industrial Technology Research Institute
Most recent work involves surface integrity studies which help to achieve highly functional, corrosion and wear resistant finished EDM surfaces. Previous work involved development of a transformer coupling circuit for suppressing electrolytic effects on WEDM.
Research Institute for Applied Mechanics, Kyushu University
Machining of ceramic materials and development of ceramic-metal bonding using EDM to increase bond strength and reduce residual stress.
Toyota Technical College
Through joint efforts with Japanese EDM manufacturers, their past research included some of the first thorough studies using silicon, aluminum and graphite powders in EDM dielectric fluids to enhance EDM surface finishes and produce a mirror-like surface. By dispersion of the discharge current from powder suspension, their early studies produced a surface finish of 0.8μm Rmax or better and with a significant decrease in finishing times. Some EDM manufacturers now offer a powder mixture dielectric system to produce high quality surface finishes on die-sinking and wire EDMs.
Most recent research work at Toyota Technical College include microhole EDM, studies of carbon deposits on EDM electrodes, EDMing of non-conductive ceramics, and electrode wear studies.
Toyama Prefectural University
Recently published research include a report on the studies of the wire bending in WEDM and how it effects machining accuracy. Wire variations were measured using optical fibers and an investigation of the forces from electrical discharge pulses acting on the wire were studied.
Through joint efforts with Mitsubishi Electric, Toyama University completed another recent project on “An Attempt to Measure a Temperature Distribution of Wire on Wire EDM.” Since the maximum cutting speed of WEDM is limited by a wire rupture during the process, then it is important to know the real wire temperature to develop the machining speed on WEDM. The wire temperature distribution was measured from discharging currents and voltages during WEDM. It was found that a discharge concentration occurs just before the wire broke and that this discharge concentration may be the main reason for the wire rupture. Results also showed that the average wire temperature may be 1000C or less.
Okayama University
Recent work with rotating disk electrodes to improve MRR for deep groove machining. Other EDM studies on Titanium, Inconel, and Copper Alloy materials.
Yamagata University
EDM studies on Oxide-Superconductor Ceramics.
Europe
Transfer Technology, Ltd. (Birmingham, England)
TransTec was created as a vehicle for the research, development, and marketing of advanced technology from universities and other research institutions for the manufacturing industry. Scientific and commercial programs have been established between TransTec and at the universities of Birmingham, Edinburgh and Nottingham. TransTec research and developments are concentrated in the following three distinct product categories of machining and control technology fields:
1. Electrical Discharge Machining
2. Electro-Chemical Machining
3. Electrical Discharge Texturing
?
Products include:
Flexible machining cell (FMC) with multi-axis electrical discharge machining, electrical discharge texturing machines, radio frequency (RF) adaptive control for EDM, CNC adaptive control for EDM, Ram-type EDMs, and CNC electro-chemical drilling machines with adaptive control systems.
Catholic University of Leuven (Belgium)
This University has been involved with EDM research for more than 20 years—beginning with a fundamental mathematical analysis of EDM by Van Dijck in 1973. Cooperation between CUL researchers and Charmilles Technologies started in the late ‘70’s and continues today.
Past CUL research includes:
? Wire and die-sinking EDM process/pulse analyzer
? Adaptive Control Optimization for Wire EDM—an on-line adaptive control strategy was developed to optimize cutting speed without wire rupture.
? Studies on geometrical accuracy of WEDM
? WEDM wire rupture studies
? Through the support of Charmilles Technologies (Switzerland), they also developed an optimum strategy for planetary EDM, defining on-line the machining steps from roughing to finishing, which guarantees that the EDM machine is continuously used at the highest possible MRR, with respect to precision and surface roughness.
? Application of Artificial Intelligence
Most recent EDM research work at CUL involves:
? Computer Aided Process Planning and Manufacturing for EDM
The aim of this research project is a full integration of CAD/CAM and Electrical Discharge Machines. The integration comprises the development of a feature modeling module, a CAPP (Computer Aided Process Planning) module, a CAM-EDM module (Computer Aided Manufacturing), and a NC-postprocessor. Within this research work, new features have been defined to describe workpieces completely or partly machined by EDM.
?
? Metallographic investigation of the Heat Affected Zone in EDM
Research on developing a better understanding of the metallographic and micro structural characteristics of the HAZ in order to improve the surface quality of a workpiece. There are two main application fields of this study:
1. Tools exposed to impact, bending and tensile forces. Current research tries to develop new EDM generators and will define optimal machine and generator settings in order to remove the white layer completely during the EDM process.
2. Tools exposed to abrasive and chemical wear. Current research tries to use the advantages of the white layer (hardness, chemical resistance), in order to achieve a white layer which can be used as an “alternative coating”. This research involves collaboration with Agie and Charmilles Technologies.
?
Institute of Machine Tools and Production Engineering and the Fraunhofer Institute of Production Technology (Germany)
? Electropolishing of EDM’ed molds and dies.
? Study on waterbased dielectrics for forging dies.
? Properties of ceramics after EDM.
? EDM of semiconductive materials.
? Advanced super finish wire EDM and coating technologies for improved tool production.
? Wire EDM polishing.
University of Linkoping (Sweden)
Developed a system for monitoring the discharge position during die-sinking EDM to provide an extended analysis of the EDM process. The method used was based on the assumption that the release of energy from a spark is transformed into an ultrasonic pulse in the workpiece.
University of Dundee (Dundee, Scotland)
Previous joint research with Mitsubishi Electric Corporation (Nagoya, Japan) on the use of high frequency AC source for achieving submicron surface finishes in WEDM. Also performs research on electrode characteristics in EDM.
Bucharest Polytechnic Institute (Romania)
Research on achieving higher EDM performance by changing the properties of the electrode material by cooling the electrode to cryogenic temperatures with freon and nitrogen.
?
Institute of Technology (Budapest, Hungary)
Computer aided planning of die-sinking EDM.
Central Mechanical Engineering Institute (Bulgaria)
Research on adaptive control systems for WEDM.
Other EDM Research Centers
Experimental Research Machine Tool Institute (Moscow, Russia)
Research on control of EDM machine servo systems and studies on the effects of electrode orbital motion on metal removal rates.
?
Indian Statistical Institute (Bangalore, India)
Process optimization of WEDM by statistical analysis based on Taguchi principals.
?
Institute of Electro-Machining Technology (Beijing, China)
Various studies on WEDM and investigations on the physical nature of the EDM process. Also performed grinding and polishing studies on ceramics, PCD, and silicon carbide using a combination of ultrasonics and high frequency EDM.
?
Iskra Design & Technology Office (Ufa, Russia)
Flexible manufacturing systems development for electrical machining methods.
National University of Singapore (Singapore)
Studies in EDM surface defects on tool steels.
Shen Zhen University (Shenzhen, China)
Joint research with Shanghai Jiao Tong University (Shanghai, China) on fuzzy logic control systems for improving process stability and increasing machining rates on WEDM.
Suzhou Electro-Machining Machine Tool Research Institute of the Ministry of Machine Building and Electronic Industry (Suzhou, China
关于凝华