国外关于什么是电火花的介绍

看看国外关于什么是电火花的介绍--编者-wolfee

What is EDM? A Brief History

The acronym EDM is derived from Electrical Discharge Machining.

The EDM process we know today started with the observations of Joseph Preistly in 1770. He noticed that electrical discharges had removed material from the electrodes in his experiments. This is also known as electro-discharge erosion.

In the 1940's Soviet researchers developed a machining process that formed the foundation for modern EDM.

Charmilles introduced their spark erosion

machine at the 1955 European Machine Tool Exhibition in Milan.

Features of the Wire EDM Process

Low work holding forces

Low cutting forces

Very accurate process tolerances held +/- 0.0001"

Complex profile capability

No tool wear (the wire is continually replenished)

Environmentally friendly (by products are easily recycled)

Hardened materials are easily machined

Spark Properties

Conventional machining produces high cutting forces, requiring high work holding forces, cutting fluids, high temperatures at the work

Electric Discharge Machining

The

basic EDM process is really quite simple. An electrical spark is

created between an electrode and a work piece. The spark is visible

evidence of the flow of electricity. This electric spark produces

intense heat with temperatures reaching 8000 to 12000 degrees Celsius,

melting almost anything. The spark is very carefully controlled

and localized so that it only affects the surface of the material.

The EDM process usually does not affect the heat treat below the

surface. With wire EDM the spark always takes place in the dielectric

of deionized water. The conductivity of the water is carefully controlled

making an excellent environment for the EDM process. The water acts

as a coolant and flushes away the eroded metal particles.

Wire Cutting

EDM wire cutting uses a metallic wire to cut a programmed contour in a workpiece. Extrusion dies and blanking punches are very often machined by wire cutting. Cutting is always through the entire workpiece. To start machining it is first necessary to drill a hole in the workpiece or start from the edge. On the machining area, each discharge creates a crater in the workpiece and an impact on the tool. The wire can be inclined, thus making it possible to make parts with taper or with different profiles at the top and bottom. There is never any mechanical contact between the electrode and workpiece (see above). The wire is usually made of brass or stratified copper, and is between 0.1 and 0.3 mm diameter.

Depending

on the accuracy and surface finish needed a part will either be

one cut or it will be roughed and skimmed. On a one cut the wire

ideally passes through a solid part and drops a slug or scrap piece

when it is done. This will give adequate accuracy for some jobs

but most of the time skimming is necessary. A skim cut is where

the wire is passed back over the roughed surface again with a lower

power setting and low pressure flush. There can be from one to nine

skim passes depending on the accuracy and surface finish required.

Usually there are just two skim passes. A skim pass can remove as

much as 0.002" of material or a as little as 0.0001".

During roughing ( i.e. the first cut) the water is forced into the

cut at high pressure in order to provide plenty of cooling and eliminate

eroded particles as fast as possible. During skimming (accuracy

/ finish cuts) the water is gently flowed over the burn so as not

to deflect the wire.

Small Hole EDM