440c rusting in wire EDM tank

hello my fellow EDM enthusiasts,

we are running into a few issues with 440C stainless steel parts rusting in our WEDM machines.
parts are made from round stock (turned on a lathe, then milled, then heat treat and finally put on the WEDM machine.
parts are heat treated.
we see rust after 10-15 hours of cutting. sometimes its surface rust which wipes right off.
other times it pits severely resulting in them being scrap.
DI bottle is new, resistivity is never below 65000.
machines are Sodick SLN400s and ALN 400s.

has anyone ever had this issue?

We were running a bunch of tool steel parts on our AL600Gs and running into rusting issues during the cut in about 1.5 horus.

Moved the Resistivity upto 100k and the issues stopped.

Don't know what else is going on, but I support the lowering the of resistivity of the dielectric for now. You’ll burn through more resin over time, but this should help reduce your corrosion problem until you figure this out (considering resin is cheaper than sellable parts).
Suggestion: Because of 440C's higher carbon content (1-1.2%), (specifically for its magnetic work-holding and hardening properties), try demagnetizing it several times before WEDM'ing. You might be surprised
(I demagnetize everything, including carbide. Everything.)
Let us know if this had any effect.

nlancaster said:

Moved the Resistivity upto 100k and the issues stopped.

Click to expand...

Bud Guitrau said:

I support the lowering the of resistivity of the dielectric

Click to expand...

Just to be clear, for the sake of the OP; most machines use a resistivity approach, I've run some that measure conductivity. That being said, raising the resistivity is the same as lowering the conductivity and vice versa. I'm certain that making the dielectric less conductive is what's called for here, but it seems that Mr. Lancaster and Mr. Guitrau are not in agreement, even while Bud sounds like he's on board.

SO. With all due respect to Mr. Guitrau and his vast understanding of all things EDM (much, MUCH respect!!), I'm pretty sure he meant to say 'the raising of the resistivity'.

Right?

Dan

OffsetLeft said:

Just to be clear, for the sake of the OP; most machines use a resistivity approach, I've run some that measure conductivity. That being said, raising the resistivity is the same as lowering the conductivity and vice versa. I'm certain that making the dielectric less conductive is what's called for here, but it seems that Mr. Lancaster and Mr. Guitrau are not in agreement, even while Bud sounds like he's on board.

SO. With all due respect to Mr. Guitrau and his vast understanding of all things EDM (much, MUCH respect!!), I'm pretty sure he meant to say 'the raising of the resistivity'.

Right?

Dan

Click to expand...

You are correct, Dan. I mixed them up. Sorry for any confusion.
Thanks for the gentle correction.

Bud

lfran827 said:

hello my fellow EDM enthusiasts,

we are running into a few issues with 440C stainless steel parts rusting in our WEDM machines.
parts are made from round stock (turned on a lathe, then milled, then heat treat and finally put on the WEDM machine.
parts are heat treated.
we see rust after 10-15 hours of cutting. sometimes its surface rust which wipes right off.
other times it pits severely resulting in them being scrap.
DI bottle is new, resistivity is never below 65000.
machines are Sodick SLN400s and ALN 400s.

has anyone ever had this issue?

Click to expand...

I have had the same issue on some parts in the past. I did exactly what everyone has suggested and helped, I hate water marks or rust on a fresh burnt piece.

My opinion ....Dump some rust preventative into the water. I had some severe rusting on a job and about a gallon of solution stopped it.....

lfran827,​

Has the changing of your Resistivity setting as suggested been helpful in resolving some of your rusting issues?

Some machines measure the water by Conductivity and others by Resistivity...

- Conductivity (conductive flow) is a measure of how electrically conductive the water is, and a lower conductivity level means the water is more pure and less reactive
- Resistivity (resist to flow) is a measure of the water's electrical insulating characteristics, and a higher value mean the water is more pure and less reactive
- In both cases, the Di-Resin serves to remove the free-ions from a water molecule to control the flow of electric current in the Spark Gap

Out of curiosity, are you using Regenerated or Virgin Di-Resin? Regen Resin can sometimes contain contaminants from its previous use and left-over acid from the resin cleaning process that may be a contributing factor to your issue. Beyond your 440C material rusting, are you noticing any other differences in your machine such as the work table or other machine components rusting or looking different than they usually do? This can sometimes be the case of a pH imbalance, and this can be checked using a simple pH strip you can get on-line or at any pool or spa store.

- Brian