posted on November 18, 2011 06:08
Electrical Discharge Machining or EDM Machining makes it possible to work with hard metals for which traditional machining techniques are inadequate. But the limitation of EDM machining is it will only work with materials that are electrically conductive. The materials that cannot be cut with sinker EDM because they are not electrically conductive include hard and soft ferrite materials and epoxy-rich bonded magnetic materials.
Any conductive material can be machined using Sinker EDM such as aluminum, brass, carbide, copper, stainless steel, tool steels, titanium etc. Sinker EDM is a versatile process, allowing for a variety of sized parts ranging from small handy ones that can fit in the palm to massive parts that weigh over 1,000 pounds. The electrodes for Sinker EDM machining are generally made from copper, graphite, or tungsten depending upon the work piece material and electrode wear requirements. The EDM Process is generally used in Tool & Die industries for making molds. Lately, EDM process is employed for making prototype and production parts in aerospace and electronics industries. There are two major types of EDM - Wire EDM and Sinker EDM. The principal difference between the two is the type of electrode used. Wire EDM uses wire as the electrode. As its name implies, Sinker EDM literally sinks a required shape into the work piece.
The Sinker EDM Machining, also called cavity type EDM or volume EDM, is a process whereby two metal parts kept submerged in an insulating liquid are connected to a current source which is automatically switched on and off - in keeping with the parameters set on the controller. When the current is allowed to pass, an electric tension is created between the two metal parts.
By bringing the two parts together to less than an inch, the electrical tension is discharged and a spark leaps across. At the point where it strikes, the metal is heated up so much that it melts. These sparks happen in huge numbers at seemingly random locations between the electrode and the work piece. Numerous such sparks spray - not simultaneously but in quick succession - and gradually shape the desired form in the piece of metal, according to the shape of the electrode. Please remember that several hundred thousand sparks fly per second before erosion actually takes place.
The on-time setting determines the length or duration of the spark. Thus, a longer on-time setting creates a deeper cavity for that spark as also all subsequent sparks for that cycle, creating a rougher finish on the work piece. The reverse becomes obviously true for shorter on-time settings. These settings can be maintained in micro seconds. Off time indicates the period of time that one spark is replaced by another.
The EDM machining process came into being during the 1770s when it was discovered by an English Scientist. However, the process was not widely used until 1943 when Russian scientists discovered how the erosive effects of the technique could be controlled and used for machining work.
The Sinker EDM process is recommended for a wide variety of applications including blind cavities, complex details, sharp corners, extra fine finishes, machining threads into hardened parts – amongst many others.