Wire EDM of long parts

[Luke.kerbey]

Hi Folks,

Of late I’ve started doing taller work pieces than I’m used to.

I cut a lot of stuff up to 75mm with no issue at all.

This last job was a 300mm brass outer diameter of 65mm pre machined and I had to bore the centre to 55mm.

The job held well in the work holding and took 8 hours in total.

My only two problems are

The centre was under size by around 20 microns per side.

The top 50mm over cut on the first cut by around 70 microns a side.

The over cut is my biggest problem. I didn’t scrap the part but how can I preempt this overcut and reduce it?

Is it flushing too high?
My conditions only go up to 150mm for copper based. Should I make my own condition for 300mm material?
What could have caused this?

I’ve not got dozens of these to try and perfect on so any tips would be appreciated.

 

[Mechanola]

Does the contour justify the process? Can the profile be accomplished by other methods? Wire EDM is there predominantly for hard stuff. I know that parts have become overcomplicated. Sometimes a broach is appropriate. Reduces 8 hours to 8 seconds.

 

[plastikdreams]

That's a long slug and a lot of area to try to get flushing through. This can affect the wire when cutting. I would get the largest start hole possible and make a program that spirals out. This leaves plenty of flushing and also leaves no slug.

 

[Shane030173]

I would reach out to Sodick Applications about your cutting conditions. Cutting 300mm with 150mm settings could be an issue.

 

[Waakzaamheid]

I've always used Steel settings when cutting brass and had good results that way. You may have tech that goes to that height. The more skims the better.

The "hourglass" effect you are describing is common with taller parts. You can generally adjust your Voltage Gap on your skim cuts to straighten it out. It being smaller in the middle and bigger on the ends generally means your skim was running a bit too fast, and you would need to increase your VG to straighten it out. It's kind of a trial and error type thing but it does work.

 

[AGMantz]

I usually do exactly as wdevine says I intentionally shrink my profile by a .001-.0005 to give myself some play, then crank up my VG by a few points. My rule of thumb is generally raising the VG by 2 to 3 volts for every .0001/side that is convexed. Then if its a repeat job I dial in the VG by the 3rd part, record or make a mental note of what I need to set the VG too in order to eliminate the convex and then return the profile to the normal size and start cranking them out.

Good Luck,
-AGMantz

 

[Luke.kerbey]

That's a long slug and a lot of area to try to get flushing through. This can affect the wire when cutting. I would get the largest start hole possible and make a program that spirals out. This leaves plenty of flushing and also leaves no slug.

If it was smaller I would but boring out a 65mm diameter OD lump to 55mm ID or so would create so much stress inside. I would worry about distortion after finishing on the wire. But it would solve the flushing issue!

 

[Luke.kerbey]

I would reach out to Sodick Applications about your cutting conditions. Cutting 300mm with 150mm settings could be an issue.

I think so too. Im waiting for a new contact as my current one has moved on. That’ll be a good ice breaker!

 

[Luke.kerbey]

I've always used Steel settings when cutting brass and had good results that way. You may have tech that goes to that height. The more skims the better.

The "hourglass" effect you are describing is common with taller parts. You can generally adjust your Voltage Gap on your skim cuts to straighten it out. It being smaller in the middle and bigger on the ends generally means your skim was running a bit too fast, and you would need to increase your VG to straighten it out. It's kind of a trial and error type thing but it does work.

When I get time I’ll stick a scrap lump up and see how it cuts on steel settings. That could make all the difference.

 

[Luke.kerbey]

I usually do exactly as wdevine says I intentionally shrink my profile by a .001-.0005 to give myself some play, then crank up my VG by a few points. My rule of thumb is generally raising the VG by 2 to 3 volts for every .0001/side that is convexed. Then if its a repeat job I dial in the VG by the 3rd part, record or make a mental note of what I need to set the VG too in order to eliminate the convex and then return the profile to the normal size and start cranking them out.

Good Luck,
-AGMantz

That’s the issue here, i make one of these a year or less. If I had a decent batch I could perfect the process my self.

 

[Luke.kerbey]

Thanks for all the replies folks. That’s definitely food for thought and some different things to try.

I wish I could show you the job, but it’s a company design by the previous manager, and it’s not for public eyes

 

[plastikdreams]

Private eyes...they're watching you...

They see your every move.

 

[M. Roberts]

Did you run the G51 or G52 offset command? I have found it useful for compensating for the wear of the wire on taller cuts....

 

[Waakzaamheid]

That’s the issue here, i make one of these a year or less. If I had a decent batch I could perfect the process my self.

Even on the single part, next time you run these I would just bump your VG up on your skims maybe 7 notches, and run with a +.0005 clearance, or something in that range. You will most likely get a better part and you can just try something a little different the next time.