What is EDM ?
The Electrical Discharge Machining Machine(EDM for short) is a kind of mechanical processing machines mainly used for electrical discharge machining. Widely used in the manufacturing of various metal molds and mechanical equipment, it is a special processing method for removing conductive materials by electro-erosion caused by pulse discharges between two electrodes immersed in a working fluid, which is also called spark machining or spark eroding.
Electrical discharge machining is mainly used to make molds and parts with complex-shaped holes and cavities; process various conductive materials, such as cemented carbide and hardened steel; create deep pores, special-shaped holes, deep grooves, narrow slits and cut sheets, etc.; produce tools, such as various forming tools, templates, and thread ring gauges.
How EDM Works
When performing EDM, the tool electrode and the workpiece are respectively connected to the two electrodes of the pulse power supply, and immersed in a working fluid, or the working fluid is filled into the spark gap. Under the control of the automatic gap control system, the tool electrode moves toward the workpiece. When the gap between the two electrodes reaches a certain distance, the pulse voltage applied on the two electrodes breaks down the working fluid to generate a spark discharge.
A large amount of thermal energy instantly concentrates in the fine plasma channel, where the temperature is able to reach as high as 10,000°C or above, while the pressure also changes drastically, so that the trace amount of metal material on the local working surface is immediately melted, vaporized, explosively splashed into the working fluid, and then quickly condenses to form solid metal particles, which are carried away by the working fluid. At this time, a slight pit mark is left on the surface of the workpiece. After that, the discharge briefly pauses, and the working fluid between the two electrodes returns to be insulative.
Immediately thereafter, the next pulse voltage breaks down another point where the two electrodes are relatively close, to generate a spark discharge and repeat the above process. In this way, although the amount of metal removed by each pulse discharge is extremely small, there are tens of thousands of pulse discharges per second, so a considerable amount of metal can be removed, representing a certain efficiency.
Under the condition that a constant discharge gap is maintained between the tool electrode and the workpiece, the tool electrode continuously moves toward the workpiece while the workpiece metal is being eroded, and finally the shape corresponding to the shape of the tool electrode is produced. Therefore, the shape of the tool electrode, and the relative movement between the tool electrode and the workpiece can be changed to form various complicated profiles. The tool electrode is made of electro-erosion resistant materials, such as copper, graphite, copper-tungsten alloy and molybdenum, which have great electrical conductivity, a high melting point and are easy to process. During the processing, the tool electrode also experiences losses, but less than the amount of metal removed from the workpiece, or even close to zero loss.
The working fluid acts as a discharge medium, while also performing the tasks of cooling and chip removing during the processing. Commonly used working fluids are mediums with low viscosity, high flash point and stable performance, such as kerosene, deionized water and emulsion.
Mirror surface EDM
As the best EDM today, it is able to achieve the mirror surface effect. The EDM-produced mold can be used directly in production without polishing, thus saving labor and improving efficiency. Moreover, the mirror surface EDM features high precision, especially suitable for application to the making of precision molds. The cost of mirror surface EDMs are high – the cost of the imported ones ranges from RMB 700,000-800,000 to over 1 million. In recent years, China has also introduced the mirror surface EDM by establishing joint ventures with foreign mirror surface EDM manufacturers.
EDM for Plastic Molds
This refers to the commonly seen EDM, mainly used for electrical discharge machining of plastic molds. More commonly seen in China, they are cheaper, but more widely used, with an average price of no higher than CNY 100,000.