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3D electrodes Vs 2D electrodes

HSM_CHIEF

Aluminum
Joined
Aug 2, 2017
Could someone please help me understand the difference between a (2D) edm burn and a (3D) or spherical burn? Can you burn everything 3D or everything 2D or are there reasons some things needs to be burnt 3D vs 2D... also along with what the difference in the electrode would be between a 3D under sized electrode or 2D under sized electrode...
 
Hi HSM Chief:
A lot of people will do virtually all burning with 3D or "spherical" orbit, which behaves exactly like the name states.
One detail however is that the path typically is a 2D simple orbit almost all the way down to depth and then expands as the burn energy drops for finishing while sitting above the bottom of the cavity by the orbit offset, then finishes the last bit by decreasing the orbit until there is no X-Y orbit at all right at the bottom of the burn.
Some machines may do it differently and move in all 3 axes at the same time, but the Hansvedt I'm most familiar with does it this way and I believe the older Charmilles machines do it that way too.

The principal consequence of this orbit path is that an electrode with sharp corners will burn a cavity with radii in those corners that is the same size as the orbit.
This can be a help or a hindrance.
When you want small radii in the corners of your cavity it's often easier to orbit them in than it is to mill them onto the electrode.
If you DON'T want them, you have to pick out the corners with vectoring toolpaths after the main burn is done.
Other big benefits of spherical orbits is that you always have space between the electrode and the developing cavity so flushing is better than with any other strategy.
You can make all your electrodes the same size and just increase the orbit to bring cavities to size and to final finish.
That means no dedicated roughers with different dimensions to plan and keep track of.

Spherical orbit also allows you to keep the electrode planning simple; a way I've used often is to take my cavity, and cut a plug from that cavity model (this is in my design software).
I then shell that plug with a shell that is the same thickness as my overburn.
I then cut another plug from the inside of that shell, and that's the geometry the trode needs...no planning, no thinking, just cut my shape and cook it into the job.
You can only do that simple protocol with spherical orbit...all other orbit strategies require more complex planning so the cavity ends up the shape you want.

Sometimes all this is not necessary; if you are burning a keyway or some other simple shape for example, you just make the electrode undersize and either do a 2D orbit or vector the trode toward each corner depending on whether radii are desirable in the corners or not.

So none of it is rocket science; a common truism is that 2D orbits are good for 2D shapes and 3D orbits are good for 3D shapes and for the most part that's not a bad rule.

If you can split up your cavity to get the 2D shapes or the ones that need sharp corners with separate trodes, and burn everything else with spherical orbit, you can cover most things that I've ever had to burn.
The other strategy that's super useful of course, is vectoring, which is not an orbiting strategy but basically points the electrode into the direction you want to go.
A simple Z axis burn is a vector toolpath that just happens to point in Z negative.

The classical place to use this toolpath in moldmaking is to use it to burn subgates without tilting the insert or mold base up on an angle.
Basically you point the tilted trode in the direction you want it to go, align it at the start point of the path and let 'er rip along the axis of the subgate trode.
It's fast and accurate and avoids a great deal of pissing around, so it's super popular for that task, but you can use it wherever you need sharp corners, by simply pointing the trode into the corner you want sharp and picking the corner out.

So a common way to make a sharp cornered square pocket for example, is to spherical orbit down to depth and then vector diagonally down in 3D into each corner in turn using the same trode you used for the main burn and just kissing the faces you've already burned.

That should help you to visualize how these various paths work and what they are particularly good for...your own ingenuity will tell you when and where to apply them.
Other orbits are left overs from another age; on many older machines for example, you can walk around the edges of a rectangular or other straight sided cavity almost as if you were milling it, but very few use these anymore as they have significant shortcomings and not much in the way of unique benefits.
With spherical and vectoring, there isn't much I cannot burn, and I suspect that most EDM guys do much the same.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

BTW just as an afterthought; you're probably going to get a lot more traction on this thread if you re-post it with a link to this one on the EDM sub-forum.
That's where the guys are who know this stuff in a lot more detail.

MC
 
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I think Marcus covered it pretty well.

2D orbits are faster to run than 3d orbits, since the electrode can come down in Z and just orbit out in the XY direction. But it only works for simpler shapes.

Imagine trying to burn a ball/cup shape into a part, if you came down to depth with a ball shaped electrode and just orbited out in XY you would end up with a flat in the center.

So a spherical orbit will instead come down and make smaller and smaller orbits until it gets to depth, so that the ball shape is maintained.

The way I think of it when it comes to cutting electrodes, an electrode made for a 3D orbit is just a direct surface offset. So if you wanted to make an electrode for a .003" spherical "orbit" you pretty much could just copy the shape you need to burn and set your surface offset in CAM to -.003" and you would get what you need.

Cutting a 2d orbit is a bit trickier if you don't have software built for it, since you only want the electrode undersized in the XY direction.

I've never done it myself, but one way to achieve this is by "lying" to the system about the cutter size you're using. If you plan on using a .250" endmill to cut a given electrode, you can tell the CAM software it's a .246" diameter and the part will end up .003"/side smaller but still maintain it's nominal size in the Z direction.
 
Thanks guys for the response they both helped!! I guess my real question is how do you guys go about making your electrodes or what my CAM software does when I’m running negative stock to leave amounts... when I cut an electrode that we want .005/s Over burn and I can run either a negative stock to leave radially or axially... when I’m running just a negative radial stock to leave all of my 3D radi get sharper and when I run both radially and axially the radi on my electrode come out to whatever size is on my 3D cam model. But my depths are all .005 deeper due to the over burn? I hope I’m doing a good job explaining this... I think what it boils down to is that I need a cam model that’s made to finish electrode size to get around from this negative offset stuff...
 
Hi again HSM Chief:
I use Solidworks as my CAD program so I can speak only to how I do it in that software.
I'm also a bit of a Luddite and did not invest in the most modern way to do it, but my way works well for me.
I build a decent number of molds each year so that's where my experience mostly comes from.

Here's how I do it:
I take my part model and make a dumb copy of it with the shrinkage and everything I need to produce a mold cavity.
I cut it in half along the parting line.
I shell it out leaving a shell that's the thickness of my orbit plus my estimated overburn.

I make another lump that will be my electrode and make an assembly that mates the two.
I do a cavity cut between the electrode blank and the shell.
I trim the other bits away that I need to remove for convenience and for flushing access and to avoid burning into the parting line when the electrode is fully to depth.
I establish my flushing hole locations.

Now I mount a bit of Telco copper and cut exactly what I've modeled.
No lying about the cutter size.
No negative offsets to keep track of.
No fancy-pants planning, or mucking about or screwups...what I've modeled is what I cut.

When I have a 2D part to break out, I simply select both the top and bottom faces of my part for the shell operation, and end up with a shell that's open at both ends.

So it's all super simple and works very well for me.

I do believe there are Solidworks Add-Ins that can do this automatically.
There's probably other, better software out there too.
But this is a cheap and cheerful way to get there that has never let me down, and is CHEAP...I like cheap!.

Of course, if the electrode shape ends up to be something you can't mill, you have to break the trode down into simpler bits that you can machine.
That becomes obvious as soon as you look at the trode shape, and you can then plan accordingly without pain.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
I do it a slightly different way than Marcus but it works for me. I'm using Mastercam 2019. I'm doing mostly replacement inserts so I have existing models of the inserts. In Mastercam solids there is an Impression function. I create a boundary to enclose the area to be burned and using the Impression function I extract the burn area to another layer, this is the basis of the electrode.I then modify/move any areas that I don't want to burn(parting lines and the like). Then when I apply toolpaths to the electrode model I set negative stock on all the finish toolpaths. I use the same over burn for everything so I just have to make sure that the field is filled in correctly in the toolpath menu. I also have a library of proven toolpaths that I just need to select geometry for and make sure that the max depth is correct. So far the burned geometry has matched the model geometry within a couple of tenths. These are Orthodontic bracket molds so they are tiny.
 
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In modern EDM Sinkers there are a number of different 2D and 3D orbit patterns. It looks like the 3D discussion is centered around spherical, which is the most commonly used. Also keep in mind most machines can utilize different orbits in each of the quadrants but we'll keep it simple and assume you going to use the same pattern in all four quadrants.

The simplest way to program Spherical is to extract your trode from the cavity/core model and program it using negative stock which is your OB amount. All the radii and geometry will come out decently accurate. If you have a decent cad/cam system, everything will be associated so model and program changes are a snap.

The simplest way to program 2D round orbit is to cheat bullnosed cutters but NOT ball cutters. This will give you a good results on walls, horizontal and vertical radii but this method is really only good for models with minimal draft. Large draft, such as 30-45 deg will usually result in extra stock left on the steel because most modern sinker edm's raise slightly for final orbit. This is acceptable for some shops but not accurate for others; it depends on your parts.

If your trodes are square(ish) and have little draft you can use 2D square orbit too, but I recommend this only for square(ish) detail, if you have a single straight wall, a slot or similar. Square works nice for walls which are in the principal axis because the trode makes more contact along the wall verses round orbit hitting only a small contact area as it moves through the round orbit pattern. If you have a square orbit trode which has vertical blends then you have to account properly for that. Modeling these requires some trickery so please post back and ask about if you want to try it out. I consider this more of a niche pattern lol.

I'm not sure what your machines are but some machines can do round orbit in all of the principal vectors but not in 3D vectors. With a 3D vector round orbit is commonly not possible so then you have to do a 3D burn such as spherical.

If you plan to inspect trodes in a cmm there are some considerations. Spherical orbit trodes are a no brainer but inspecting round orbit trodes can be tricky because the software, such as PC-DMIS, is unable to compensate for trodes which do not have OB built in. You could model trodes with OB built in but this only feasible on relatively simple trodes. Sperical orbit trodes aren't that hard to create but why spend extra time you don't have to? My philosophy throughout my entire cad/cam workflow is to create the least amount of extra geometry possible.
 
when I cut an electrode that we want .005/s Over burn and I can run either a negative stock to leave radially or axially... when I’m running just a negative radial stock to leave all of my 3D radi get sharper and when I run both radially and axially the radi on my electrode come out to whatever size is on my 3D cam model. But my depths are all .005 deeper due to the over burn?

The software I'm using has built in settings for electrode orbits, but for an electrode with a 3d orbit the toolpath would be exactly the same using the setting for .005 overburn and 0 "stock to leave" (radially and axially) or using 0 overburn and -.005 stock to leave. There is no difference.

So yes all horizontal levels would be .005 lower than they are in the model. The rads should all be smaller (external rads) or larger (internal) by this same .005 amount.
 
Hi All:
What I'm seeing emerge is two schools of thought about the lesser of evils; whether it's going to all the trouble of making a CAD model of exactly what you intend to cut or whether it's using an existing model of what you intend to get and offsetting the geometry in CAM to extrapolate what you need to cut.


I have tried it both ways, and for my personal style there is great comfort in being able to interrogate my electrode and saying: "Yes, it matches the model of what my electrode has to look like to get my desired outcome", rather than having to say: "If I mentally subtract 0.010" from this dimension and 0.005" from this other dimension, and calculate where this point is supposed to be so my CMM can compare etc etc etc"

Also, since I work in Solidworks with HSM works, if for some reason I want to change the amount of orbit, I just edit the orbit thickness in the shell command and everything updates, including all my toolpaths, and they're all still correct.

It just seems easier to say to myself (or others who may be working with me): "Here...make this!".
No discussions, no arguments, no ambiguity.
In a world where there are so many ways to skin the cat, I really really like the certainty I get this way, and to me, it's worth the extra CAD work.

Obviously, your mileage may vary.
Those who are doing it successfully some other way are doing it just as right as I am...the proof is in the outcome.
But I'm a lazy old fart and my way is mentally easy, at least for me.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
...I have tried it both ways, and for my personal style there is great comfort in being able to interrogate my electrode and saying: "Yes, it matches the model of what my electrode has to look like to get my desired outcome", rather than having to say: "If I mentally subtract 0.010" from this dimension and 0.005" from this other dimension, and calculate where this point is supposed to be so my CMM can compare etc etc etc"...

...It just seems easier to say to myself (or others who may be working with me): "Here...make this!".
No discussions, no arguments, no ambiguity.
In a world where there are so many ways to skin the cat, I really really like the certainty I get this way, and to me, it's worth the extra CAD work...

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Oh how I would love to do that! I fully recommend models compensated OB if possible. The models I work with can hardly ever be adjusted as such mainly because they are large and complex. At one point I evaluated three other top tier softwares albeit with not much luck. The results varied a bit but none of them consistently performed the task. Spherical compensation was easy but 2D round or square orbit tended to be problematic.
 
Oh how I would love to do that! I fully recommend models compensated OB if possible. The models I work with can hardly ever be adjusted as such mainly because they are large and complex. At one point I evaluated three other top tier softwares albeit with not much luck. The results varied a bit but none of them consistently performed the task. Spherical compensation was easy but 2D round or square orbit tended to be problematic.
Please educate me on 2-d round orbits. Would this be similar to expand . Isn't a 2-d down orbit actually moving in a round pattern of spark gap - allowances for overburn on set power levels for surface finish. Also I'm curious about what software's you tested.

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Please educate me on 2-d round orbits. Would this be similar to expand . Isn't a 2-d down orbit actually moving in a round pattern of spark gap - allowances for overburn on set power levels for surface finish. Also I'm curious about what software's you tested.

Sent from my SM-G960U using Tapatalk

2D round orbit is what it says but different machine brands have different ways to approach the same thing. I know our Makino's spherical is way different than my friends old Agie sinkers but achieves the same thing. Back to 2D, our Makinos will always try to raise up slightly to finish walls in 2D round orbit after finishing floors so this can lead to inaccuracies with larger drafts. Modern sinkers are very sophisticated and do a lot of different movements whether it's a simple 2D round pattern or a complex 3D orbit with a mixture of different patterns in each quadrant. There are ways to keep the trode down more when finish orbiting walls but the operator really needs to stay on top of which control he is using because there are major differences in control versions. Our newer controls have way more features than the old controls but the old machines are still very capable, accurate machines.

For software I assisted a colleague at another company who did an extensive eval and they did very similar work as we did but for different industries. (their trodes were typical small and complex with tight tolerances and our are more large and complex with more open tolerances) I don't recall them all but the eval included Cam-Tool, Cimatron, Tebis, Hypermill as well as a couple stand alone modelers like Spaceclaim. I don't think the latter did dedicated trode modeling though. There was other software but I don't recall which ones.
 
I should add that my electrodes are typically large with a lot of detail, that's our niche. Sometimes we have just pick burns but it's common for us to burn large, complicated trodes. Many shops only need to do pick burns and there's a lot of cam software which is awesome at creating electrodes for that. Our NX guys do most of our edm trode programming but our MC guys have an add-on which works great too. I can't recall what it is but I want to say it's ACIS modeling based.
 
Hey everyone thanks for all the information I’ve just been sitting back and reading them all... I’m currently doing my programming with fusion 360... I really have no complaints about... the problem I run into most is when I’m doing some finishing work with a .2mm ball .0079 dia and I can only run a negative offset equal to my tool dia so I can only offset .0039 a side... we run most of our electrodes at .009/s... so I guess does anyone know how I could go about offsetting a model in fusion to make it finished electrode size so I don’t have to worry about the negative offset problem anymore... I hope I’m doing a well enough job of explaining this...
 
Hey everyone thanks for all the information I’ve just been sitting back and reading them all... I’m currently doing my programming with fusion 360... I really have no complaints about... the problem I run into most is when I’m doing some finishing work with a .2mm ball .0079 dia and I can only run a negative offset equal to my tool dia so I can only offset .0039 a side... we run most of our electrodes at .009/s... so I guess does anyone know how I could go about offsetting a model in fusion to make it finished electrode size so I don’t have to worry about the negative offset problem anymore... I hope I’m doing a well enough job of explaining this...
Running a. 2mm cutter with .009 sg is a waste of time. The orbit will wipe out the detail. On internal corners you can add your sg to get min cutter radius. For a sharp corner you can use a .018 dia cutter max with .009 sg.

Sent from my SM-G960U using Tapatalk
 
I should add that my electrodes are typically large with a lot of detail, that's our niche. Sometimes we have just pick burns but it's common for us to burn large, complicated trodes. Many shops only need to do pick burns and there's a lot of cam software which is awesome at creating electrodes for that. Our NX guys do most of our edm trode programming but our MC guys have an add-on which works great too. I can't recall what it is but I want to say it's ACIS modeling based.
The best part of this forum is learning from others. Qwan what's a typical size of these large trodes. If highly detailed do you run into spark gap issues fighting efficiency of burn time over dealing with intricate detail not allowing enough sg creating wear issues and needing extra trodes to maintain tolerance. What brand of machinery do you guys use? 3 axis or 5 axis? Thanks for your time.

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The best part of this forum is learning from others. Qwan what's a typical size of these large trodes. If highly detailed do you run into spark gap issues fighting efficiency of burn time over dealing with intricate detail not allowing enough sg creating wear issues and needing extra trodes to maintain tolerance. What brand of machinery do you guys use? 3 axis or 5 axis? Thanks for your time.

Large for us can be 16" x 16" x 12", give or take and about 3000 cubic inches of graphite. We build medium size tooling, about 20K pounds maximum. We try to keep an eye on trode surface area because we can run into hydraulic issues of the edm fluid unless there are places for the fluid to move. The trodes can get fairly complicated with detail but fortunately even when there is a lot of 3D geometry there is usually enough thickness on the ribbing and small details to maintain a decent SG. .010/s OB is common for us and sometimes program for .012"-.020" if we feel the need for a roughing trode, assuming the edm that the job is planned to go into has a booster on the control to support the big spark gap. The fluid chillers work hard to keep the fluid temp down when we're pulling a lot of current. Back to the trodes, unless ribs and detail are small we don't get much wear and can typically get away with two trodes per burn. We're doing everything on 3-axis machines but once in a while we do 4-axis cutting if we have some small detail on trode walls so then we're able to cut on the sides with short cutters. Any time I do 4-axis trode programming I'm almost always using negative stock and spherical orbit because it's so much easier to when dealing with 4-5 sides of a trode.
 
Thanks Qwan, we specialize in mostly medical parts where thin ribs are a norm. I have used Cimatron for at least 15 yrs now. I really like it. I came from a 15 year mastercam background and couldn't imagine going back. The last project typical rib thickness was around .025 with multiple slide and lifter details. Most spark gaps were .004 .we mainly cut our trodes on a Mikron hsm 400 lp. We use a 450 u 5 axis for deep details to minimize cutter length. Yes using mainly isog style programming. We have also moved into the micro edm style work where .010 wide details are common with .001- .002 sg is used. I like getting the jobs with big trodes and large sg are used. Easier on my old eyes.

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Thanks Qwan, we specialize in mostly medical parts where thin ribs are a norm. I have used Cimatron for at least 15 yrs now. I really like it. I came from a 15 year mastercam background and couldn't imagine going back. The last project typical rib thickness was around .025 with multiple slide and lifter details. Most spark gaps were .004 .we mainly cut our trodes on a Mikron hsm 400 lp. We use a 450 u 5 axis for deep details to minimize cutter length. Yes using mainly isog style programming. We have also moved into the micro edm style work where .010 wide details are common with .001- .002 sg is used. I like getting the jobs with big trodes and large sg are used. Easier on my old eyes.

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Medical is very interesting work and a lot of it is delicate, not to mention high tolerance as well. I have heard a lot of great things about Cimatron. It definitely sounds like an awesome 3D programmers software. The only time I've seen was in the eval I mentioned. My friend was looking for a "silver bullet" software and found none. In the end they stayed with NX because they have a lot customized C and VB software to automate much of their workflow but he did speak highly of the other software and said if they were looking to start from nothing, the choice would be harder to make.

By the way we see a lot more wear on thin ribs too and usually have to make a 3rd, or more, electrode(s). It's the nature of the beast, lol.
 








 
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