Advantages and Disadvantages of Copper and Graphite Electrodes

Both copper and Graphite

Electrode provide approximately the same end result, so it is important for a shop

to consider the advantages and disadvantages of each material in order to discover what

would work best in their shopfloor environment.

When it comes time to decide whether to use graphite or copper electrodes in your

shop, it's important to look at the big picture. According to Stu Haley, regional

manager of Madison Heights, MI-based Belmont Technologies, Inc., a provider of EDM

supplies, tooling, accessories and machines, "To say which electrode works best is

very difficult, it is totally applications-driven. So much depends on what you have to

work with on your shop floor in the way of support equipment. Both copper and graphite

provide approximately the same end result. The difference is time to EDM the work and

electrode manufacturing time and cost."

Haley explains that choosing an electrode material is often a result of where you

were born and what type of EDM equipment you use. "For example,

RP Graphite Electrode was

basically developed in the United States back in the early 1960s, so the American EDM

equipment manufacturers in those days concentrated on the graphite circuitry when

designing their equipment," he says. "Whereas, since the European and Asian

EDM equipment manufacturers didn't have access to graphite, they developed copper

circuitry.

Graphite

Advantages and Benefits

Sold by grades, HP Graphite

Electrode cuts approximately three times faster than copper, according to Haley.

"What makes a good grade or a poor grade is particle size," he explains.

"Particle size gives you strength, machinability and greatly influences the metal

removal rate, wear and the surface finish. Graphite is made up of carbon particles that

are put through a graphitizing process to produce graphite. The smaller the particle

size is, the better the graphite. Particle sizes in different grades of graphite can be

.0006" for general-purpose use to .00004" for the extremely fine detail and

superior surface finishes. Graphite can be purchased in big blocks, and then cut up to

be machined, or it can be ordered precut or ground into the size you require.

"Graphite machines very easily - you can mill it, grind it, turn it, drill it,

tap it, even file it to whatever shape you want," Haley continues. "Another

advantage of UHP Graphite

Electrode is that it doesn't burr. You can put it on a duplicating machine or

a graphite high-speed mill and cut out complex shapes and forms, and once it's cut

you are finished - with no deburring."

Additionally, graphite's high melting temperature results in less wear than

other electrode materials, so a mold could be cut with one or two electrodes on a CNC

EDM machine with very little wear, Haley adds. "A CNC sinker may need a third or

fourth electrode to finish the mold," he notes. "It depends on the age of the

EDM machines."

Limitations

If your shop has older fabricating equipment, machining graphite electrodes will

result in dust particles on the shop floor and in the nearby machines. However, the new

high-speed mills that are sold today are specially designed to machine

Graphite Powder. "They are

totally enclosed and have a vacuum system to remove all of the dust," Haley points

out, "and there are some machines that can even cut square internal corners."

Another important point to keep in mind is that the finish on any electrode is the

finish that will be put in the mold. "So, if you have a lot of cutters or grinding

marks on the electrode, you will reproduce that in your mold," Haley says.

"Normally, the finish on the graphite should be as good as you need in the

mold."

Copper

Advantages and Benefits

Haley notes that copper can be cut on wire EDM machines, but there are only certain

Graphite Blocks that can be cut on

a wire machine - the particle size should be five microns or less. Copper also is a

little more forgiving in a poor flush situation than graphite. "In EDM, if the

flush doesn't remove the eroded particles or chips out of the cutting area,

there's something that can occur where you get a non-pulsating, direct flow of

current from the electrode to the workpiece," Haley explains. "The result of

this is a pit in the workpiece. Copper is more forgiving in those applications - all

metallic electrodes are - they won't arc out as fast. But some of the newer EDM

power supplies have adaptive logic or fuzzy logic, which eliminates the problem

altogether. Copper - when used at specific settings with the correct flushing techniques

using a CNC machine or a machine with an orbiting system - can produce a mirror-like

surface finish. This is useful in small cavities where it is difficult to polish."

When you add tungsten to copper (copper tungsten), the result is an electrode

material that has extremely good wear characteristics but is very difficult to machine,

Haley notes. "When EDM'ing carbide, this is the best metallic electrode

material to use. The best graphite material would be copper graphite, which is graphite

impregnated with copper," he says.