25-09-2012, 12:11 PM
Review to EDM by Using Water and Powder-Mixed Dielectric Fluid
EDM by Using Water.pdf (Size: 2 MB / Downloads: 88)
ABSTRACT
Basically Electrical discharge machining (EDM) is a well-established non-conventional
machining process, used for manufacturing geometrically complex or hard and electrically
conductive material parts that are extremely difficult-to-cut by other conventional machining
processes. Erosion pulse discharge occurs in a small gap between the work piece and the
electrode. This removes the unwanted material from the parent metal through melting and
vaporizing in presence of dielectric fluid. Performance measures are different for different
materials, process parameters as well as for dielectric fluids. Presence of metal partials in
dielectric fluid diverts its properties, which reduces the insulating strength of the dielectric fluid
and increases the spark gap between the tool and work piece. As a result, the process becomes
more stable and metal removal rate (MRR) and surface finish increases. The EDM process is
mainly used for making dies, moulds, parts of aerospace, automotive industry and surgical
components etc. This paper reviews the research trends in EDM process by using water and
powder mixed dielectric as dielectric fluid.
INTRODUCTION
In 1770 English scientist Joseph Priestly firstly invented the erosive effect of electrical discharge
machining. After that in 1930s, the machining of metals and diamond with electrical discharges
has been done. Due to evaluation of spark, erosion was caused by intermittent arc discharges
occurring in air between the electrode and workpiece which is connected to a DC power supply.
Overheating of the machining area restricts the applications of this process, so it is known as “arc
machining” [1]. In 1943 at the Moscow University revolutionary work on electrical discharge machining was carried out by two Russian scientists, B.R. and N.I. Lazarenko [2]. Refined and a
controlled process for machining of materials was developed by analyzing the destructive
effects. It becomes easy to maintain and control gap between the electrode and workpiece with
the introduction of RC (resistance–capacitance) relaxation circuit in 1950s, which provided the
first consistent dependable control of pulse times and also a simple servo control circuit. Later
stage RC circuit used as the model for successive developments in EDM technology. In America
at same time three employees came up with same results by using electrical discharges to remove
broken taps and drills from hydraulic valves. With the reference of this work vacuum tube EDM
machine and an electronic circuit servo system that automatically provided the proper electrodeto-
workpiece spacing (spark gap) for sparking.
EDM Process
EDM is basically a non conventional machining process but the technique of material erosion
employed in EDM is still debatable [5]. The basic principal followed is the conversion of
electrical energy into thermal energy through a series of discrete electrical discharges occurring
between the electrode (tool) and workpiece immersed in a dielectric fluid [6]. Due to the
insulating effect of the dielectric which is used in EDM process is very important because it
avoids electrolysis of the electrodes during the EDM process. Spark is initiated when high
voltage is applied between the electrode and workpiece at smallest point distance as shown in
Figure 1. Metal starts eroding from both the surfaces of workpiece as will as electrode. After
each discharge, the capacitor is recharged from the DC source through a resistor Figure 2, and
the spark that follows is transferred to the next narrowest gap. At the end sparks spread over the
entire workpiece surface leads to its erosion, or machining to a shape which is mirror image of
the tool.