EDM Article

   
 


 

 

HOME

Contact

Free Airplane Plans

Free EDM Plans

=> EDM Article

Engine Plans

 


     
 




 
Sparks of electricity now cut slots, bore holes and curve intricate designs out of the hardest ol metals. Some of flit' jobs that the sparks perform could be done, before, only by diamonds. Others were just impossible.

This new spark process, called Method X. is expected to replace present costly and laborious methods of shaping tungsten carbide, the char gray alloy that is one of the hardest inatrrj.ds known. Thus dies could be made of it, to turn out by the millions such things as razor blades and laminations for electric motors. Outlasting all others, a tungsten carbide die may produce as many" as 10.000,000 pieces before it wears out. And Method X will shape other materials that have been machinists' nightmares— Stellite, Vitalium, S-816, tantalum carbide, titanium carbide and .such promising new metals as pure zirconium, titanium, vanadium, molybdenum and tungsten. One experimental application is in shaping blades of heat-resisting tantalum carbide for the turbines of jet aircraft.


You see no fireworks when you visit the Pittsburgh plant where Method X is applied. Instead, you find businesslike machines resembling drill presses. They are considered the most revolutionary metalworking invention since the introduction of the lathe.
One of them is boring a hole in a disk of tungsten carbide, and you are invited by Edmund E. Teubner, 36-year-old inventor of Method X, to watch it in action.
A brass electrode dips into an eight-gallon tank of kerosene, where the disk is clamped beneath the liquid. There is no visible spark or glow. But it looks and sounds as if the kerosene were boiling.
Its  surface   ripples   and   bubbles.    Wisps of white vapor ascend. Voices must be raised to be heard above a .sputtering noise like that of a pot boiling violently on a stove. Gingerly Col lowing Teubner's example. ou put your finger in the liquid— and find it is only lukewarm. Here is what is happening:
The tungsten disk is the positive terminal and the brass electrode the negative terminal of an electric circuit. A motor drive keeps the electrode almost, but not quite, touching the work. Intermittently a condenser discharges and tiny sparks leap the gap, breaking down the thin insulating barrier of kerosene. Lasting a few millionths of a second, each spark produces an enormous mechanical stress near the surface of the tungsten carbide.

A microscopic particle of tungsten carbide flies off, leaving a crater. As successive sparks dance over the surface, the resulting craters merge to form a hole. The advancing brass electrode enters the material and goes right on through it-
Return a few hours later, and you find the job completed. A worker drains the kerosene, extracts the disk, and hands it to you. The newly formed hole is smooth and true. Making it has taken just three hours. By diamond grinding, the only other possible method, the job would have required at least a week,
When the electrode simply descends vertically, as in this case, it makes a hole with a cross section like its own. Ring-shaped and if car-shaped recesses can be cut similarly by electrodes of corresponding shape.

To make more complicated cuts, the work table may be traversed length wise, side-wise and vertically during the cutting. The electrode also may be rotated. A tungsten carbide piece has been pierced with a hole circular at one end. but gradually changing to oblong tit the other. Another sample has a hole with screw threads; (he electrode was a rotating, advancing brass screw. No other method could have produced some of these tricky carvings in super alloys.
An alternate name for Method X is "spark machining." It should not be confused, its sponsors emphasize, with attempts to machine hard metals by the thermal action of an electric arc. ft does not melt or burn metal away.
Electricity from a shop's regular 2l0 volt line is converted to direct current of a modest ]00 to 150 volts and no more than 10 to 15 amperes -hardly enough (o form an arc at all, in the usual sense. And the principal purpose of (lie liquid hath— which may be kerosene, fuel oil or a special compound called Pielectro X—is to prevent an arc from forming.
Just how, then, do the sparks rear apart the toughest of metals? Or. E. M. Williams of Carnegie Tech, who has made a study of Method X and arrived at what he believes is its first satisfactory scientific explanation, ascribes (he results lo "spark erosion."
The atoms of an electrical conductor such as tungsten carbide contain two kinds of particles: negatively charged "free" electrons, and posilivt1 ions, the remaining portions. Applying a voltage to a conductor sets up an electric field, whose force1 drives the tree electrons toward the positive pole. Likewise the positive ions tend to move toward the negative pole—but usually cannot, because the tensile strength of the material restrains them.
But when a spark jumps to a conductor's surface, it gives; an enormous "current density in a pinpoint area. So strong is the result electric field I hat it acts on the positive ions with a pull of hundreds of thousands of pounds lo the square inch, that is enough to break their bonds and start them going places. So these tangible hits of mailer fly off the work piece with explosive violence, in the form of tungsten carbide particles measuring ii]i to 1 10 of i millimeter or 1 /250 inch in size. Some are hurled clear through the kerosene and into the air and ha c been found in nil droplets spattered from the tank.

Check out my updated plans for EDM machine at
WEBSTORE
 

 
 

Today, there have been 1 visitors (4 hits) on this page!