View A Video on EDM - A Quick Introduction
Rather than using abrasion or impact,
EDM machining erodes the material in the path of the EDM tool using electrical discharges, or sparks created by the electrode which is connected to a power source. The tool electrode forms an arc to the work piece as the two are brought closer together, creating an intense electric field between the two components which is responsible for removing material. EDM is often referred to as spark machining, spark eroding and die sinking. For extreme precision parts,
micro EDM is used as it can achieve tooling and machining on very small scales.
Wire EDM (or wire erosion) and
sinker EDM, also know as
plunge EDM,
conventional EDM or
ram EDM, are the two main types of EDM machining differing in their method of achieving the electrical discharge required. Sinker EDM uses an electrode whereas wire EDM uses a wire, typically made of brass, to transmit sparks to the work piece. Sinker, or plunge EDM is capable of boring holes into metal work pieces, creating holes, patterns and at times three dimensional objects, while wire EDM cuts patterns and shapes. Both are effective methods and are widely used.
Small hole EDM is a type of EDM drilling which is also required as a pretreatment for wire EDM in order for the wire to be fed through a part.
Using this process is extremely accurate, reliable and affordable, so it is becoming an increasingly popular choice for many manufacturers. Some of the common applications for electrical discharge machining include producing plastic molds, die casting dies from hardened steel and forging dies which are typically made from hard metals which other machining processes are less effective with. Other purposes for EDM include the manufacturing of engine parts like compressor blades of titanium alloys and nickel based super alloys. Industries that benefit from the use of the electrical discharge machining process include food and beverage, automobile, stamping, extruding, defense, electronics, aerospace and medical. Diverse materials such as the following can be cut with electrical discharge machining: aluminum, copper, zinc, bronze, tin, silicon, titanium, stainless steel, gold, lead, silver, iron, cobalt, nickel, tungsten and many other compounds. Not only is EDM machining capable of accurately cutting these materials, but the preheating of hard metals which is necessary in mechanical tooling is unnecessary with EDM, saving manufacturers both time and money in the cutting process.
The actual electrical discharge machining is accomplished through sparks or electrical discharges that can generate heat anywhere from eight to twenty thousand degrees. A shaped tool, electrode or wire is connected to a power source and used to generate the series of sparks. There is no actual contact between the electrode and the work piece, but rather a conductive path that is established between the two components. This electrical field wears away the surface of the work piece in the desired shape or pattern. The EDM process takes place in a bath of water based dielectric fluid, which prevents premature sparking and flushes away debris. It also conducts electricity between the electrode and the work piece, allowing the unwanted material to be eroded. Both wire EDM and sinker EDM use the same general process, including immersion in dielectric fluid. For wire EDM processing, a hole or perforation must already be made in the metal - this is usually done by small hole EDM; a thin brass wire is fed through the work piece and clamped on both ends by diamond guides, then the wire cuts through the metal in a specified pattern guided by CNC EDM machine arms. Wire EDM is used for cutting shapes through a selected part or assembly. Sinker EDM uses machined graphite or copper electrodes to erode the desired shape into the part or assembly and the process is used for more complex geometries. CNC machines are used to guide, monitor and control the machining process, as well as CAD/CAM software. As well as dimensional factors of size and shape, an important consideration when using EDM is the material of the work piece, since the material of the electrode should be matched.
Electrical discharge machining has advantages over other machining techniques due to its ability to create complex and intricate parts with a high degree of accuracy. This process is able to machine hard materials where other machining processes have difficulties, as well as delicate materials that would break easily under impact. Another advantage of EDM is its ability to machine parts on an extremely small scale. While using this process, the work piece is not deformed from impact because there is no direct contact between the electrode and the material, and likewise the work piece is burr-free after completion and saved from heat damage because very little material-damaging heat is generated during the procedure. It is a time-consuming process and the electrodes need to be replaced often, but the advantages of EDM machining outweigh the drawbacks.
|
|
Image Provided by Wire
Cut Company, Inc. |
Image Provided by Twin
City EDM |
|
Image Provided by Milco
Wire EDM, Inc. |
EDM Types
-
is an EDM method that uses rotating electrodes to erode a revolving
workpiece, creating different workpiece shapes by blending the comparative
locations and angular velocities of the workpiece and the electrode.
- uses electrical energy to shape and form metal parts.
- uses a revolving electrically conductive wheel
as the electrode tool for electrical discharge erosion. EDG
is an alternative method for sharpening diamond and carbide tipped
cutting tools, reducing the extreme cost of diamond grinding
wheels.
- use a tool electrode to gradually
impress a mirror image of the electrode onto a workpiece.
- is a miniature ram type machine that usually
uses a diamond V-groove to spin the tool electrode up to 10,000 rpm.
Electrode diameters as low as five microns are possible for the production
of micro-holes and other shapes in thin, electrically conductive materials.
- use a tungsten wire electrode that has a diameter as
small as 10µm to machine parts from .1 to 1 mm in size; the size
of these parts makes it impossible to form them through normal semiconductor
processes. These machines use a specially designed wire movement system,
spark generator and monitoring system able to analyze and control extremely
low energy levels.
- , also known as plunge EDM and ram EDM, removes metal with rapid electrical discharges.
- uses electrical discharges to create microscopic holes.
-
is a common EDM process that removes material with a wire electrode
moving longitudinally through the workpiece. A CNC machine with special
software maintains the movement of the wire electrode relative to the
workpiece.
EDM Terms
- A mechanically altered zone on a metal surface that is created
by the EDM process.
- An uncut block of graphite
provided by a manufacturer.
- Slang term for the EDM process.
- An electrical unit
that stores electricity.
- Dielectric fluid
that is pumped through the workpiece or electrode for flushing purposes.
- Small holes on the
workpiece surface left over from the EDM sparks, also referred to as pits.
- A nonconductive
liquid that fills the space between the electrode workpiece and insulates
it until the needed space and voltage are reached. At that point, the
fluid ionizes, becoming an electrical conductor, and causes the current
or spark to flow to the workpiece; it also cools the material and flushes
away the particles produced by the spark.
-
The difference in size between the electrode and the size of the crater
the electrode makes.
- The spark in the
electrical discharge machining process.
- An apparatus initiated
by electricity that helps accurately locate the workpiece in relation
to the electrode. When any part of a workpiece comes to within about 0.0001
inches of any position alongside the electrode, a buzzer or signal light
will alert the operator.
- The tool used in
the EDM procedure, which must be made from an electrically conductive
material. The shape and form of the electrode is a mirror of the completed
shape desired in the workpiece with dimensional compensation for the
overcut.
- The elimination of
material through electrical discharge machining.
- The surface texture
in the EDM process, usually expressed as min Ra (U.S.).
- The last cut done
on a workpiece. The finer the finish preferred, the more time the finish
cut will take, so the rough cuts should be planned to leave just the material
the finish cut will remove in order to attain both the final size and
finish needed.
- The forcing of dielectric
fluid through the gap for the removal of detritus resulting from EDM.
- A measurement
of the voltage at two different points in one complete cycle. The open
gap voltage is the voltage read across the electrode and workpiece space
prior to the spark; the working gap voltage is read across the space as
the spark current discharges.
- One of four types
of carbon, used for electrode material because of its high resistance
to heat. Graphite is the most common electrode material and the simplest
to machine.
- The
layer below the recast layer. Its metal properties change due to the increased
heat exposure.
- The time between
the sparks in the EDM process.
- The variation between
the size of the electrode and the size of the cavity since an EDM crater
is always bigger than the electrode machining it. There are two different
types of overcut to take into consideration: total overcut, also known
as diametrical overcut (the most common), or overcut per side.
- The highest amount
of current that is available from every pulse of the power supply.
- A layer that
results from melted metal solidifying on the surface of the workpiece.
- An
EDM method that eliminates the most material in the least amount of
time.
- The electrical discharge between two conductors.
- The space between
the workpiece and the electrode at the point of discharge.
- The energy
that is contained in each spark.
- Comparative
smoothness or coarseness of a machined workpiece surface, typically
measured in min Ra in the U.S.
- Erosion the electrode
undergoes during the EDM process.
- Any metal part to
which an electrical discharge machining process is applied.
