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Different steels, different speeds... our toolroom argument.

  • Thread starter Luke.kerbey
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Luke.kerbey

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Hi guys,

Not posted in a while but I need some expert info on why some steels cut quicker then others in EDM. This applies to WEDM, sinker and hole drilling.

We have been doing some jobs recently where we’ve been able to directly compare cutting times of different materials and we have found a variation of cutting speeds in steels.

From my own experience and reading. The materials hardness is 100% irrespective of cutting speed and in fact it’s the material conductivity that affects speed.

My colleagues seem to think that the hardness does have a direct impact on speed. And we can’t seem to agree.

So I’m starting to lean towards that varying hardness and the minute density variation of steels have a minute change of any steels conductivity? Or also a steels purity and alloying elements are having an effect also?
Such as the way that EDM swarf could behave in certain ways when rich in chrome, that can cause flushing issues, which then slow speeds?

I’m literally taking stabs in the dark. So can anyone explain any logical reasons or technical information on why some steels appear to cut faster/slower then others? As always, all input is appreciated!

Thanks,
Luke
 
I don't have anything to back it up (not done my own wire work in a while), but always heard steel vs same steel, cuts better/faster hard. Obviously steel cuts slower than alum, and titanium will cut different than "steel". Are we talking massive differences?
 
These differences are in the seconds. But we’ve been doing highly repetitive forms. so these seconds are all forming large differences over the jobs duration.
 
We find very little difference in A-2 , D-2, S-7, M2, soft or hard or any alloy of stainless. Most variation is caused by flush conditions, condition of the power contacts, and cable conditions, water resistivity. More variation in hot and cold rolled because of impurities and parts moving from stress being released. Carbide is another story altogether. Haven't done enough Inconel , titanium, hasteloy to compare. Aluminium is fast buy chews up filters if they are not well coated.
 
Hi All:
I think RJT has nailed it; the cut speed is so critically influenced by so many variables, that pinning it on the composition of the steel is hard to prove.

Just the temperature of the water has a major influence.
We've probably all torn out hair out over a job that won't cut only to have all problems resolved as soon as we put on a new spool of wire.
Ever fought with incessant wire breaks only to remember to index the power contacts and have the problem go away?

To a tiny degree, every successive minute of burning is making the water hotter and more loaded with ions.
It's wearing away the power contacts.
It's heating up the circuits in the guts of the machine.
It's doing all kinds of other "stuff".

Certainly it's POSSIBLE the alloy influences the burn rate, but I'm not sure it makes enough difference to notice compared to all those other variables.

Some, like Luke apparently, need to care about seconds, and will try to do what it takes to be right on the bleeding edge for cut speed.
I assume those shops will do everything to try to keep all relevant conditions unvarying and maintain their machines like priests at the altar of the wire EDM God...problem is there are a lot of conditions to count and the wire EDM God is fussy!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
In WEDM I don’t think conductivity in tool steels has much to do with it. I think hardness does only because of how it clears the gap. I was mostly cutting stamping tooling, so I didn’t cut a lot of soft steel, but when I did I could never get the speeds out of soft that I got in the same material hard.

The quality of the steel absolutely impacts cutting speed. I had a customer that was doing the mill work and heat treat on large punch blocks. They switched to imported tool steel to reduce cost. I was hitting “junk” in the material that was causing impasses, so it was much slower. They switched back to the good stuff.

With sinkers its harder to compare, because you would need to have exactly the same geometry and flushing conditions to make a good comparison.
 
Lots of good thoughts and replies on this one...figure I'd add to the fun!

From a Wire EDM prospective, most Tool Steels will machine the same way and should be within 5% of each other during machining given all machine variables and flushing items are equal. Wire EDMing of hardened steels WILL be more stable, as the heat treat process helps to remove any impurities in the material (also removes alloy elements designed for "free-machining" in the soft state). Not all Tool Steel or specialty super alloy materials are created equal. You should begin to see a slow-down in machining as certain alloy element percentages are increased, such as the heavy metals V, Cr, Mo, Ni, Mo. The change in machining speed won't be very drastic, but it will be there as a result in the increased electrical resistance and melting point temperature associated with a specific alloy. For example, WEDMing A2 Tool Steel will be faster than machining Inconel 718 (high nickel alloy - 50~60% Ni).

The affect in machining speed from the EDM Drilling side should be minimal across the typical standard alloy tool steels. Cycle Time can vary slightly but should be in the same range seen with Wire EDM. The most noticeable item might be a change and increase in electrode wear characteristics. Drilling of smaller holes (0.040” and under) should result in just additional electrode wear with higher alloy materials, but the drilling of larger hole sizes might experience more issues (especially with break-thru) as a result of more uneven wear and bullet-nosing of the electrode tip.

The changes in machining performance with different alloy materials will be more noticeable from a Sinker EDM standpoint. Both machining speed and electrode wear characteristics are impacted as alloy content is increased. A lot depends on the work piece feature size and type of SEDM operations being performed, but the alloy type and content will also impact the best possible surface finish that can be attained. There are still many other processing variables in play, such as type and grade of electrode material being used (copper or graphite – both have different types of grades available) that impact the best surface finish that can be produced.

- Brian
 
Thanks for those answers. So I’m assuming that as melting temperature increases, the cutting speed slows?

Also I’ve not heard that hardening of tool-steel with free machining elements will remove said elements? That’s a new one for me!
 








 
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