Historical development of Electrical discharge machining

Electrical discharge machining process is a well-known process and has been known for centuries. In the year 1786, Prestley a British Physicist detected small craters in the electrodes formed during the spark was generated. This process played a vital role in World War I and II for producing various geometries. At the beginning, the process lagged control and thus the possibilities of the technique were negated. Initially for the first time, wear was same for electrode and the workpiece. Later the gap was controlled by vibrating systems which helped in reducing part wear to some extent. The first successful attempt of the technology was made in Moscu in the year 1943 by Dr. Boris and Dr.N.Lazarenko who developed a spark generator and a servo control circuit to maintain a constant spark gap.The developed RC circuit is shown in below figure.

Later in the year 1964 a transistorized spark generator was made which further improved the process. A big step forward in the technology came in 1969 with the invention of wire EDM process by Prof. B. Schumacher. After that the process improved significantly by introduction of electronic control circuits, process automation, increased number of controlled axes etc. which led to increased productivity, decreased electrode wear, better surface finish and improved material properties. Present research is basically focused on machining various difficult to machine materials with higher degree of accuracy and also to produce very highly intricate structures which are a dream to manufacture using conventional machining. The general working process is shown in the figure below.

The process basically involves material removal in the from of vaporization and melting of the workpiece material. The main advantage of this process is that it is independent of the hardness of workpiece material. The foremost requirement of this process is that the workpiece material should be electrically conductive.

Historical development of Electro-chemical machining

The electo-chemical machining process was actually derived from electro-polishing or electroplating process already being used in the year 1911 by E Shpitalsky. In the beginning of 20th century much research took place in USA, Russia and Western Europe for developing electroplating as a machining process. Success came in 1928 when Russian scientists started flushing the electrolyte and thus facilitating the material removal. The first traditional model of ECM came into existence in the year 1959 introduced by Anocut Engineering Company situated in USA. In mid-1960’s much development took place in Europe in electrochemical technologies. In mid-1980’s passivation of oxygen contained electrolyte through impulse processing was introduced. Later much work is carried out in improving the surface finish obtained by the process. The general working principle of ECM process is shown in the figure below.

In the 21st century the process was tested and modified for various difficult to cut materials and was successful. The present research is based on microsecond ECM machining which can produce very small intricate shapes. As shown in the figure, two electrodes were inserted in an electrolytic solution where anode is connected to the workpiece and cathode to the tool. Then the current is passed resulting into electrolysis process and the material removal takes place by electrolysis. The machining is accurate and surface finish obtained is very good. The process is slow but provides with high degree of accuracy.

Historical development of USM machining process

Ultrasonic machining is the machining process in which there is a softer tool than the material to be cut which vibrates at a particular frequency that produces the force required for machining. A abrasive slurry is passed through the gap between the tool and the workpiece. The vibrational force impinges the abrasive particles to impinge on to the workpiece causing the material removal. Balamuth in 1945 firstly described the process and later in the year 1953-54 the first ultrasonic machining tool was developed. With passage of time, in 1960’s, various tools for the process were available and commercial use of the system started to begin. Later in in1966 two monographs developed that brought together most of the matter together. In 1989 much work was carried out on fatigue strength of machined surface. The present research is basically focused on the use of system in machining various materials and increasing the material removal rate by variation in tool design. Working of ultrasonic machining is shown in figure below.

Above diagram depicts the basic working principle of ultrasonic machining which uses a horn that vibrates at certain frequency. Abrasive particles in form of slurry are passed between the vibrating horn and the workpiece resulting in material removal by the abrasive particles by rubbing and bond breakage caused due to brittle fracture.

Historical development of Abrasive Water jet machining

The inability of water jet machining of cutting hard materials led to the development of abrasive water jet machining. As we discussed earlier that use of high velocity water jet was unable to cut harder materials and thus lot of research was going on which led to the development of AWJ machining in the year 1980 and the first commercial abrasive entrainment AWJM system was made available in the year 1983. In this process, abrasives were added to the water jet, which would then strike the work material with high velocity that they obtain from the kinetic energy of the water jet. This resulted in enhanced metal removal rate than that of conventional water jet machining process. Later many developments were made in the process namely in the type of abrasives used for different materials, nozzle design, velocity and pressure variation etc… 

Later a suspended type of AWJM system was developed which led to the introduction of air along with abrasives in the water stream which simplified the system and thus, at present, most commonly used in the industry. A general layout of abrasive water jet machining system is shown below.

Historical development of Water jet machining

Water at high pressure was being used for erosion purpose in the mid 1800’s for the purpose of hydraulic mining. In 1933, the use of water jet as a narrow stream for cutting purpose was started by Paper Patents Company situated in Wisconsin where water jet was being used for cutting a thin sheet of continuously moving paper. Since then many researchers developed various techniques for cutting of various materials using water jet at high pressure as the cutting source. Although there were many researches for this cutting process, there was no significant development in the cutting ability of the process to cut metals. In the year 1956, AteCarl Johnson developed a method for cutting plastics. With time the pressure and velocity of the water jet increased and in the year 1958, Bille of North America used this process for cutting hard materials. John Alson along with his fellow researchers further improved the cutting ability of the process in 1970’s. The recent advances in the technology led to the development of five axis water jet machining. The basic process of water jet machining is shown in the figure.

This process is further modified by addition of abrasive particles in the water stream converting the process into abrasive-water jet machining. The process is much more efficient and results in higher material removal rate than plain water jet machining process.

Historical development of abrasive jet machining

In 1970’s water jet was being started to be used as a source of cutting soft materials such as leather, frozen meat, thin Aluminium sheets etc… Later in the 1980’s abrasives were being added to the water jet to increase the cutting action so that much high strength materials such as steel, cast iron can be machined through the process. This addition of abrasives led to the idea that if abrasives are made to impinge at high velocity on the material then material removal would take place. Thus abrasive jet machining evolved that used a nozzle for impinging the abrasive particles at high velocity on to the work material. Significant amount of research is carried on this process to increase the material removal rate and also on the type and shape of abrasives used for a particular type of material. The advantage of this process is that intricate shapes can be produced by this process but the material removal rate is rather low. The abrasive jet machining setup is shown in the figure below.

The above diagram shows a schematic of abrasive jet machining showing various components of a abrasive jet machining setup.

History of manufacturing processes- an introduction

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