Electrical Discharge Machining

Edm is mainly used for machining molds and parts with complex shapes of holes and cavities; Processing various conductive materials, such as hard alloy and hardened steel; Processing deep and fine holes, special-shaped holes, deep grooves, narrow joints and cutting thin slices, etc.; Machining various forming tools, templates and thread ring gauges, etc.

The processing principle

During EDM, the tool electrode and the workpiece are respectively connected to the two poles of the pulse power supply and immersed in the working liquid, or the working liquid is charged into the discharge gap.The tool electrode is controlled to feed the workpiece through the gap automatic control system. When the gap between the two electrodes reaches a certain distance, the impulse voltage applied on the two electrodes will break down the working liquid and generate spark discharge.

In the micro channel of discharge, a large amount of heat energy is concentrated instantaneously, the temperature can be as high as 10000℃ and the pressure also has a sharp change, so that the local trace metal materials on the working surface of this point immediately melt and vaporize, and explode into the working liquid, quickly condense, form solid metal particles, and be taken away by the working liquid.At this time on the surface of the workpiece will leave a tiny pit marks, the discharge stopped briefly, the working fluid between the two electrodes to restore the insulation state.

The next pulse voltage then breaks down at another point where the electrodes are relatively close to each other, producing a spark discharge and repeating the process.Thus, although the amount of metal corroded per pulse discharge is very small, more metal can be eroded due to thousands of pulse discharges per second, with a certain productivity.

Under the condition of keeping the constant discharge gap between the tool electrode and the workpiece, the metal of the workpiece is corroded while the tool electrode is continuously fed into the workpiece, and finally the shape corresponding to the shape of the tool electrode is machined.Therefore, as long as the shape of the tool electrode and the relative motion mode between the tool electrode and the workpiece, a variety of complex profiles can be machined.Tool electrodes are usually made of corrosion-resistant materials with good conductivity, high melting point and easy processing, such as copper, graphite, copper-tungsten alloy and molybdenum.In the process of machining, the tool electrode also has loss, but less than the amount of corrosion of the workpiece metal, or even close to no loss.

As a discharge medium, the working fluid also plays a role in cooling and chip removal during the processing.Common working fluids are medium with low viscosity, high flash point and stable performance, such as kerosene, deionized water and emulsion.Electric spark machine is a kind of self-excited discharge, its characteristics are as follows: the two electrodes of spark discharge have a high voltage before discharge, when the two electrodes approach, the medium is broken down, then spark discharge occurs.Along with the breakdown process, the resistance between the two electrodes decreases sharply, and the voltage between the electrodes also decreases sharply.The spark channel must be extinguished in time after being maintained for a short period of time (usually 10-7-10-3s) to maintain the “cold pole” characteristics of the spark discharge (i.e., the heat energy of the channel energy conversion does not reach the depth of the electrode in time), so that the channel energy is applied to a minimum range.The effect of channel energy can cause the electrode to be corroded locally.The method that the corrosion phenomenon that produces when using spark discharge undertakes dimensional machining to the material is called electric spark machining.Edm is a spark discharge in a liquid medium within a lower voltage range.According to the form of tool electrode and the characteristics of relative movement between tool electrode and workpiece, edM can be divided into five types.Wire-cut edM cutting of conductive materials using axially moving wire as tool electrode and workpiece moving along the desired shape and size;Edm grinding using wire or forming conductive grinding wheel as tool electrode for keyhole or forming grinding;Used for machining thread ring gage, thread plug gage [1], gear etc.Small hole processing, surface alloying, surface strengthening and other kinds of processing.Edm can process materials and complex shapes which are difficult to be cut by ordinary machining methods.No cutting force during machining;Does not produce burr and cutting groove and other defects;The tool electrode material need not be harder than the workpiece material;Direct use of electric power processing, easy to achieve automation;After processing, the surface produces a metamorphosis layer, which in some applications must be further removed;It is troublesome to deal with the smoke pollution caused by the purification and processing of working fluid.

Post time: Jul-23-2020