Wire EDM Guide

Why a Wire EDM ? and what will it cost ?

Wire EDM (Electrical Discharge Machining) is a process that uses a fine brass wire submerged in water to cut through a conductive material using electricity. The water acts as a dielectric to control the spark gap between the wire and the piece being cut, typically around 0.0015". The water also clears away cut debris and keeps the whole process under a very accurate temperature controlled environment. All of this allows the machine to cut down to tolerances of 0.0002" and finishes to 0.4Ra.

The brass wire is a consumable item and can only be used once, typically consuming 1lb/hr. The water is filtered continuously while also being checked for conductivity, and then adjusted accordingly using a deionisation resin. The water is considerably purer than from the tap while being maintained at 20 deg C for part thermal stabilisation.

All in all it makes wire EDM the most maintenance intensive machining out there, and of course that cost can reflect in the price. The initial cost of the machine along with these consumables often makes it the most expensive machining method out there. I aim to break this mold, and offer it at a reasonable price.

3D model of a brass rod with a silver clamp-like component attached.

How long does it take?

Wire EDM is quite a slow process and has many factors to consider when machining a part. The brass wire can only carry a certain amount of current, the thicker the wire, the faster it can cut. The diameter is determined by the design, or more strictly the minimum radius that is allowed in corners. Typically a 0.01" wire is used which will leave a 0.006" radius in corners. Wire diameters can go down to 0.002" but that would increase machining times tenfold.

Basing on 0.01" wire it can be expected to cut between 8 and 12cuin per hour. The cleaner and generally harder a material is, the faster it will cut. In general anything with mill scale, paints or oxides are a no no. I price initial quotes at 8cuin/hr to be realistic, but will improve pricing if parts cut much faster. A plate 2 inch thick at 4 inches long equates to 8cuin/hr and therefore would take an hour to make a pass.

It is quite easy to hit a ± 0.001" tolerance on a single pass, while multiple passes can theoretically achieve tolerances of ± 0.0002". Multiple passes will also increase the surface finish, these are known as skim passes. Skim passes are usually faster than the roughing pass, unless very fine finishes are required.

Also aluminum cuts considerably faster at a rate of 30cuin/hr.

Example 1

Here are some timing pulleys I needed to make for a machine. Each started with a 4140 billet with a hole drilled through the middle, then welded to a bar to hold each piece in the machine. This pulley does not exist on the shelf and is unusual due to its height and very large bore.

These parts are 2.25 inch tall, an inside circumference of 3.75 inches and an outside circumference of 7 inches. The inside requires a second pass as to improve accuracy, this will be press fit onto a servo motor shaft. (2.25 * 3.75 * 2 = 16.875cuin), (2.25 x 7.0 = 15.75cuin), a total of 32.625cuin, at a rate of 10cuin/hr. Therefore a total time of 3.25hrs. EDM rate is $120 per hour and cost of the slug $35 (an hour at $120, 4 parts, $20 material). A total of $425 per part.

A total of 4 pulleys were required for the project, therefore a total of $1700 quoted.

Things to consider. I quoted this part at 10cuin/hr because it is the optimal height, around 2 inches, and is from a fairly clean material. The part in fact ran at 11.5cuin/hr on the inside and outside roughing passes, and ran at 25cuin/hr on the inside skim pass. So a repeat order and the customer could be expecting to pay $335 per part or $1340 total. I could ask the same price on a repeat order, but honesty is my policy.

Bonus ! Parts were done for next day !

Example 2

Here are some drive rollers that needed a key in the bore. The bore is 2 inches and requires a 0.5 inch key. The overall height is 3 inches tall which is on the limit for a standard broach, especially in 4140. Normally a key this size and length would be done on a broaching machine.

The parts are already bored out and require just the key, that is a path of 0.25" + 0.50" + 0.25". This is a 3cuin rough pass at an estimated 8cuin/hr and a fast skim past at around 20cuin/hr. With the setup it will take around 40 minutes per part, equating to $80 per part.

A total of 4 rollers were required for the project, therefore a total of $320 quoted.

Example 3

This is a key for the above, it is 0.5 x 0.5 x 3 inch long. It is quite likely that this piece could be bought for $10, but maybe the customer is in a rush, either way it's a good example of pricing.

The outer circumference is around 7 inches and the material is plain 0.5 inch mild steel, equating to 3.5cuin. Wire EDMs become inefficient at cutting below a certain thickness, normally around 1 inch. Knowing it's a dirty material and not ideal conditions I can assume a rutting rate of 8cuin/hr. With a single pass it would take around 30 minutes each to produce, or $60 per part, material cost being negligible.

Parts like these may cost more to make than the mass produced, but sometimes it is cheaper than down-time on waiting for a part to arrive.

Example 4

These are soft jaws that are used in another one of my machining processes, basically machinable lathe jaws for holding parts accurately. They of course can be bought for a reasonable price, and they don't quite warrant the use of a wire EDM, but it is a good example of part design. Normally the serrations would be cut on a hobbing machine in a large quantity.

The serrations on these jaws fit into serrations on the lathe chuck. Care has to be taken when considering the radius that the wire EDM cuts, with the more efficient 0.01" wire it will leave a 0.006" radius. If the serrations on the chuck were to a sharp point then the design has to compensate for this, so the valleys are made to accommodate this. Likewise the serrations on the jaws themselves have the sharp points cut off as to give clearance to the chuck.

This part is 1.5 inches tall, but with the slot through the middle it makes there serrated part only 0.9 inches thick. It is around the optimal thickness and in a good grade of steel that is not too dirty, I can expect a rate of 10cuin/hr. The machining volume is around 9cuin, which would make the part take just under an hour. A cost of $120 each.

Note that while these parts can be easily machined out of steel using conventional methods at a cheaper rate, the wire EDM allows any conductive material to be cut at extreme tolerances. I can also save tooling and setup costs making smaller batches cheaper than the usual methods.

Example 5

This is an example of a very special part that would be difficult to create in a single process. It would require the dog bone teeth cut in a milling machine and then transferred over to a gear hob cutting machine to make the rack. On a small run of parts it would be extremely expensive to setup.

The wire EDM is a perfect choice for making this part accurately . The circumference of the part is 13.3 inches at a height of 0.25 inches. Wire EDM's don't perform as efficiently on thin materials as they do on thicker, so on this part I stacked 5 pieces. With that it means 13.3 * 1.25 = 16.65cuin, and at a rate of 8cuin/hr it will take around 2 hours to make these 5 parts. This was customer supplied material, so just the machining would cost $48 per part. Considering that the part is 316 stainless it is very harsh on milling tools, requiring careful observation maintaining tolerances. The wire EDM can cut 1 or 1000 exactly the same, once the first part has been tuned to hit the tolerances, all parts afterwards will be exactly the same.

Example 6

This is a custom HTD 8mm timing pulley that is around 4 inch in diameter with a thickness of 1.5 inches. It would be extremely difficult to make this pulley without a gear hobbing machine and setup would be exceedingly expensive.

The wire EDM is a perfect choice for making this part accurately. It first requires me to cut a slug and then bore it out on the lathe, then face each side flat to the correct height. The circumference of the part is 20 inches at a height of 1.5 inches. With that it means 20 * 1.50 = 30.0cuin, and at a rate of 8cuin/hr it will take around 3.75 hours to make this one part, plus around 45 minutes for the lathe work, totaling 4.5 hours.

This material cost was around $50 being a one off. That added with time to lathe and EDM cut it would total the part at $590, quoted.

However for a larger order the customer could expect to pay much less. With even just 10 pieces that would drop the material price down to $30 per part. This part also ran at 10cuin a minute which took 3 hours to cut. The lathe time would only be around 10 minutes maximum per part. So for multiple pieces it would be $410 per part.

I'm always looking for faster ways to cut, so changing to a larger and premium wire for this part could potentially reduce it down to $300 per part. The upgrade is quite expensive on my part so I would require a larger order to justify the cost.

Example 7

A little bit of festive fun, some stainless snowflakes.

The flakes are 0.25 inches thick and about 0.5 inches across, it would be almost impossible to make these very detailed parts with any other process, and to a very high degree of accuracy. The material is 316 stainless which is very clean to cut estimating a 10cuin/hr cutting speed. I stacked 5 pieces of material together which should achieve the optimal cutting thickness. The circumference of these parts is very large at 6 inches in length. With that it means 0.25 * 5 * 6 = 7.5cuin, and at a rate of 10cuin/hr it will take around 45 minutes to make 5 parts.

These cut at a considerably faster speed than expected at 15cuin/hr completing these parts in just 30 minutes. With that the customer would be paying $12 in labour per part.

I made a total of 60 snowflakes as shown in the video, a labour cost total of $720.

Example 8

A customer supplied part requiring some keys.

The part was quite large at 18 inches in diameter meaning that it would not fit in the table but rather on top of it. With the height being 4 inches it meant it was the limit due to sitting on the table, it also meant that the flushing nozzle could not work effectively on the bottom of the part, slowing cutting speeds. The steel is A36 plate which is generally quite dirty, also effecting cutting speed.

The part is recessed in the back making the height of the key 3 inches. Overall each keyway would require 10cuin each, a total of 20cuin of cutting. The bore is also very large at 7 inches meaning it would take around 10 minutes to probe. With the bottom flushing not being ideal and the material I would estimate a cutting of 8cuin/hr. There would also be a skim pass of around 25cuin/hr to improve finish and tolerance. So overall it would take 2.5 hours to rough, 40minutes to finish and 10 minutes to probe, at $120/hr that would be $400 per part.

I was quite surprised to find that I was considerably cheaper than what the customer had been quoted by someone broaching it.

It did actually take me slightly longer to cut at 7cuin/hr, however I stick by my quotes.

Wire EDM Quoting and Reducing Part Cost

I've aimed to make this page as a guide to give you the customer an idea of what it takes and the potential cost of your part. How to reduce cost.

Flat Parts - Water flushes debris more efficiently when flat, increasing cutting speed.

Large Radii - Large radii mean a larger wire, more power and therefore more speed.

Quantity - One offs don't allow tuning to better increase speed.

Tolerance - The larger the tolerance, 0.001" or more allows fewer passes.

Surface Finish - Higher surface finish requires more passes and more time.

Extra Stock - Supporting material either side of the wire adds stability and increases accuracy, it allows high pressure flushing. Side skimming is slower for roughing as the flushing pressure needs to be reduced to maintain accuracy, reducing debris flushing and leading to longer cut times.

I generally don't charge for setup or programming time, however if a part takes less than 10 minutes to cut then there is a minimum charge of $25 per part. This allows time to remove and setup the next part.

Machined Plastics and EASY CNC Calgary

Wire EDM Guide

Why a Wire EDM ? and what will it cost ?

How long does it take?

Example 1

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Machine Capabilites

Wire EDM Quoting and Reducing Part Cost

Wire EDM Guide

Why a Wire EDM ? and what will it cost ?

How long does it take?

Example 1

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Machine Capabilites

Wire EDM Quoting and Reducing Part Cost

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