Basic EDM Question

How do they start an internal shape in a block of material?

Do they drill a hole through the block first and then thread the wire through the hole and then do the EDM process?

Thank you,

Arnie

yes!!!!!!!!!!!

first you drill a hole, thread thru it then hole center and your good to go.

Yes, think of it like a band saw.

A very small band saw.

And if the work piece is hardened you now know why 'small hole edm's' or 'hole poppers' are popular.

KilrB said:

Yes, think of it like a band saw.
A very small band saw.

Click to expand...

Yep, as Eric used to post here - "the electric band saw". A very slow, relatively expensive, incredibly and minutely accurate, electric band saw...

its not really a bandsaw as the wire Never touches the workpiece.

Thank you everyone.
I've been watching some YouTube videos and I get it now.

mdynac said:

its not really a bandsaw as the wire Never touches the workpiece.

Click to expand...

What's a meta for?

Of course you can start from the outside of the part and just erode into the side of the part too. Depends on the shape of the part you want, how you are holding it, shape of the blank. You don't have to start from a hole in the part. Its common , but not required.

spedini,

This is a block of text I used to have online many years ago on my web site. Might answer some basic questions for you:


Wire EDM is an ultra-precise method to cut virtually any electrically conductive material, regardless of alloy or hardness.

A thin wire is rapidly charged to a voltage. When the voltage reaches a certain level, a spark jumps the gap to the part, creates a plasma due to the extreme temperature (on a very microscopic level) and melts a tiny bit of material. This "spark erosion" happens continuously, and appears to the eye as being a steady "burning away" of material.

The entire process typically happens while submerged in very pure, deionized, temperature-controlled water. This water is what continually flushes away microscopic particles of removed material.

There is no physical contact between the wire and the part being machined, so there are no cutting forces as in other methods of machining.

The wire is "continuous", and constantly fed from a large spool (typical range of speed would be 60mm-300mm per second). It passes through the work area (the part) and is discarded out the back of the machine. The wire is not consumed or "burned up" as it passes through the area where the "spark erosion" occurs, however wire is never re-used. Wire diameters range from .0008"-.013" although .004" to .012" is the range most typically used. Wire can be anything from plain brass (in varying hardnesses) to coated brass or copper (plated with zinc, zinc oxide, or some other formulation that promotes better cutting in certain materials), to moly, or even pure tungsten.

The position/movement of the wire through the workpiece is controlled by a computer and servo motors, not unlike any other CNC machine (although generally more accurately than a CNC mill or lathe).

The hardness of the workpiece material has no adverse effect on the cutting speed, and cutting parts after heat treating is quite common and often desireable.

A modern Wire EDM machine has 4 independent axes of movement (5 if counting Z). The position of the wire guides can be independently and precisely controlled both above and below the part which allows "tipping" of the wire in any direction (often to 30° or even more). The 2 axes "below" the part are known as X/Y, and the 2 axes "above" the part are known as U/V. The U and V axis are actually "differential" axis in that moving X/Y moves the entire wire in relation to the part while keeping it vertical, while moving U and/or V moves the top of the wire relative to X/Y.
This allows the cutting of tapered parts, as well as other very complex shapes. The only limitation is that the wire must be able to pass through or by the workpiece (since the wire is continuous). In the past few years, additional axis have become available. Usually this would be a rotary axis (exactly like an A or B axis on a CNC milling machine), and even a tilting rotary axis is possible. Needless to say, programming complexity increases significantly if there is simultaneous movement of X/Y, U/V and an A axis!

When cutting an inside/contained shape, a "start hole" is required to feed the wire through. This hole can either be drilled (if the material is not too thick, and not heat treated) or it can be burned through using a special type of edm machine made specifically for this purpose.

The Wire EDM cutting process can be accurate and repeatable to ±.0001" or even better under certain conditions (even sub-micron accuracies are now possible on latest generation machines). When extreme accuracy and/or super-fine surface finishes are required, it is common to take "multiple cuts" across the same surface -- these are known as "rough" and "trim" passes. The amount of material removed on "trim" passes is rarely more than .001" or .002", and can be as little as .0001" or .000050". Typically a rough pass would be done using a high power setting, and then subsequent trim passes (as few as 1 and as many as 4 or 5) use less and less power to obtain the very high accuracy and fine finish that might be required.

Since there are no cutting forces and no burrs, extremely delicate and/or small parts can be cut. Quite literally, it is possible to cut parts that can only be seen under a microscope.

On the other end of the scale, parts as thick as 10" or more can be cut as well. Some custom machines can even cut parts over 20" thick!

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What kind of material can be cut?

Any material that conducts electricity, regardless of hardness.
Aluminum, magnesium, copper, brass, titanium, steel of any type/alloy/hardness, carbide, gold, silver, platinum, graphite, and many others. Even PCD (polycrystalline diamond) can be cut as it contains around 8% "binder" material which is conductive (typically nickel and iron).


How fast is the wire edm cutting process?

Typically, the wire edm process is slower in material removal than other "conventional" machining processes. However, this does not necessarily mean that completing a part is slow.
There are times when even though a part can be made using conventional machining methods, it can be made faster with wire edm. An example of this might be when a thin, delicate part has to be made from a large block of material due to its configuration -- conventional machining would require all the excess material be machined away, whereas wire edm might be used to drop out all the excess material with one or two simple cuts.
Direct comparison between conventional machining methods and wire edm can not be "generalized" however, and must be looked at on a case by case basis.


What determines cutting speed?

Cutting speed is primarily determined by...
1) Size of wire used
2) Thickness of the part
3) Density of the material
4) Profile/shape being cut


What is the range of wire sizes used?

Wire size ranges from .0008" (20 micron) to .013". Most wire edm machines are designed to run .006" to .010" diameter wire. Machines using .0008" wire are very specialized, and typically have a very small "work area" designed primarily for tiny parts used in the medical or electronics industry.


What determines the size wire used?

Typically, wire size is determined by the smallest inside radius required on the part. For example; a part might contain a square hole with a maximum radius of .003" in the corners. In this case, the choice would probably be .004" wire. Generally speaking, it's advantageous to use the largest wire possible as that will cut the fastest (large wire can carry more power proportionally to the amount of material being cut away). There are occasionally situations where using smaller wire is beneficial though... primarily when cutting thin material with intricate/fine details.


How thick a part can be cut?

Most wire edm machines have a "Z" capacity in the 10" to 12" range. Larger capacity machines may be able to handle parts as thick as 16" or more, and very specialized machines have been built that will cut parts 24" thick or more. On the opposite end of the scale, ultra-fine wire machines using 20 micron wire may only have a Z capacity of 2 or 3 inches.


How thin a part can be cut?

Cutting .001" or even .0005" thick material is simple. When cutting very thin parts, the material is usually "captured" between two sacrificial plates, and the entire "stack" is cut as a unit. Of course one can also "stack" many thin parts, and cut the entire stack. It's entirely possible to cut 1000 or 2000 very thin parts in one cut (one operation), provided they are tightly squeezed together so that the wire edm machine "thinks" it's cutting one solid piece.


How accurate is the wire edm cutting process?

More accurate than any conventional machining process.
Wire edm has one distinct advantage over any form of conventional machining -- there are no cutting forces. The wire never contacts the workpiece, so the "path" that the wire takes through the part is not influenced by any mechanical forces. Additionally, wire cutting is typically done submerged in very pure, temperature-controlled water, so dimensional changes due to temperature are minimized or completely eliminated. An extra benefit to having no cutting forces is that parts can be held very lightly, which minimizes or completely eliminates the distortion due to clamping forces seen in conventional machining methods. Thin/delicate parts can be cut very precisely using wire edm.
In order to achieve very high accuracy though, it is often necessary to make more than "one pass" on a profile.

Why is more than one cut ever required?

Two reasons; greater accuracy and/or finer surface finish (the two go hand-in-hand). When cutting using a "single pass", power settings are usually quite high and consequently the surface finish will have a "glass-beaded" texture to it after cutting. Additionally, two other factors can slightly influence wire position during the first pass of a wire cut -- electromagnetic forces on the wire, and high "flushing pressure" used to continually wash away the eroded material. These forces do not move the wire very much (a few tenths possibly), but this neverthess affects accuracy.
In order to achieve greater accuracy, multiple cuts are employed where the "offset" of the wire is reduced (easier to think of it as "spark gap"), and the electrical settings are altered (lower power and different waveform). When very fine finishes are required (Ra10 / 10 micro-inches or better ), as many as 4 or 5 additional "trim passes" can be used after the initial cut. Each pass will have less offset and lower power than the previous one. Whether it's fine finishes or ultra-precise tolerances that are required, multiple passes are the way it's done in wire edm.


What is the biggest limitation of wire edm?

The single biggest limitation of wire edm is that it must be possible to pass the wire by or through the part. The wire is continuous... so it's not possible to cut a "blind" cavity using wire edm.


Can complex shapes be cut?

Yes, within some reasonable limits. Most modern wire edm machines can cut up to 30° taper (or more precisely; the wire can be inclined up to 30°). Note that since the upper axis on a wire edm machine is typically a "differential" axis (it translates relative to X/Y), a 30° angle is possible up to a certain part thickness, and after that the available angle reduces relative to the height of the part. Obviously if the part itself can be tipped or rotated, any angle is then possible.
Additionally, the angle of the wire can be continuously changed while cutting, which allows the cutting of complex surfaces. Essentially; if a straight line can be passed along a contour, it can probably be cut by wire edm. To see a simple yet illustrative example, take a look at the twisted cube. Note that there are surfaces that would "appear" impossible to cut with a straight wire, yet this was easily done. As you can see; "morphing" a shape on one end of a part into a different shape on the other end of the part is possible.


How accurately can you cut a feature on my existing parts?

The key words in that question are "existing parts". Since an existing part is often fixtured on a previously machined surface (or surfaces), the limitation in accuracy is often those already-machined surfaces. If a particular feature is cut via wire edm, that feature will have all the accuracy that the wire edm machine is capable of, but positional accuracy may be dependent on previous work. In a one-off situation, this issue can sometimes be negated by "touching off" on all previously machined surfaces and striking the best possible balance of dimensions to achieve positional accuracy. In production however, fixtures may be used that rely on previous machining to mount/clamp parts quickly, and if those parts are not consistent, accuracy may suffer.
Wire edm is really no different than any other form of machining in this regard, except that wire edm machines are typically much more accurate than other types of CNC machines, so small variations in accuracy from part to part become obvious and glaring errors when compared to what is possible in the wire edm machine.

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Hope this helps your understanding.

PM

Wow, PM...! That's a wonderful write-up, there. Well done, Sir. Well done. < golf clap >

Thanks.

It was something I wrote up just so I didn't have to explain basics to most every customer that gave me a call.

Everyone here is free to take that block of text if it's of use to you... copy it verbatim, modify it, use it any way you see fit. I love wire edm, and even though I'm not currently in that business, I like doing whatever I can to "get the word out".

PM

I reference a "twisted cube" in the big block of text I posted earlier. Here is the photo. (A quick-to-cut part that I often used to illustrate what could be cut via wire edm).



PM

I always thought that the submersion liquid was conductive but non conductive makes more sense. You need the nonconductivity to facilitate the spark gap. Awesome article, thanks

Wire edm reminds me of early cnc work. When CNC first hit the scene, parts were incredibly expensive; a simple part would cost from hundreds of dollars to thousands. Now, parts are way cheaper to produce because home cnc machines are readily available to the general public for the same price that one part used to cost.
Currently, WEDM is expensive now, because the availability of the machinery is at the same place that CNC was years ago and shops take advantage of that. Asking for a quote on something as simple as the raceways cut for a bolt action receiver is like taking to a redneck repair guy: "how much you got?"
When WEDM becomes more accessible to the small shop owner the days of charging $300 for simple work will be a thing of the past. When the crooks aren't the only game in town, it's harder for them to charge an arm and a leg.

The question I have for edm shops is why is it so expensive? Is it the fact that it's precise? No, there are other technologies that are precisely controlled that cost way less. Is it the time it takes? No, other things take longer but are cheaper. Is it the electricity used? No, heat treating for hours in an electric heat treating oven uses massive amounts of power and it's relatively cheap.
The cost comes with the exclusivity of the machinery.
We have the machine and you don't so we're going to charge you as much as we possibly can.

I think you generally get what you pay for. Modern WEDMs split tenths. They make internal radii down to a couple of thousandths. The downside is that they are about the slowest thing in any shop, and are expensive. They require expensive tooling, dedicated software/training and lots of maintenance.

If you are looking at a lower tolerence then you could go with a cheaper alternative, like waterjet or laser, or a Moly Wire EDM.

You need a hole popper if for instance your going to wire out a die plate that is already hardened. K1C | Small Hole EDM | Small Hole Driller | Hole Popper

kd0afk said:

Wire edm reminds me of early cnc work. When CNC first hit the scene, parts were incredibly expensive; a simple part would cost from hundreds of dollars to thousands. Now, parts are way cheaper to produce because home cnc machines are readily available to the general public for the same price that one part used to cost.
Currently, WEDM is expensive now, because the availability of the machinery is at the same place that CNC was years ago and shops take advantage of that. Asking for a quote on something as simple as the raceways cut for a bolt action receiver is like taking to a redneck repair guy: "how much you got?"
When WEDM becomes more accessible to the small shop owner the days of charging $300 for simple work will be a thing of the past. When the crooks aren't the only game in town, it's harder for them to charge an arm and a leg.

Click to expand...

kd0afk said:

The question I have for edm shops is why is it so expensive? Is it the fact that it's precise? No, there are other technologies that are precisely controlled that cost way less. Is it the time it takes? No, other things take longer but are cheaper. Is it the electricity used? No, heat treating for hours in an electric heat treating oven uses massive amounts of power and it's relatively cheap.
The cost comes with the exclusivity of the machinery.
We have the machine and you don't so we're going to charge you as much as we possibly can.

Click to expand...

Curiosity question for you, kd0afk - How many WEDM machines do you own? How much programming of WEDM have you done? How much WEDM work have you sold and delivered?

I ask because your responses read like someone that has not had much experience with any of those questions. I'm not saying that you don't, because I simply do not know the answer. Hence, my asking. But your responses definitely read like you do have not.

I say this in such an out of hand manner because quite frankly, these points are so blatantly obvious and contrary/opposite to what you have written to anyone that has.