Wire EDM Question

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Re: Wire EDM Question

Post by Harold_V » Thu Apr 29, 2021 3:27 pm

One of the things that will aid you is to NOT use cold rolled materials. Start with hot rolled, and rough machine all features. I'd suggest you leave at least 1/16" to be removed. Once roughed, stress relieve by furnace. By following this procedure, you'll have pretty much eliminated any potential problems with stresses. How the parts react to heat treat is another matter, however.

Using a metal box, you can do the pack hardening in your furnace. A little research will help you determine how long you leave them to absorb carbon, but rule of thumb is that depth is achieved at the rate of approximately .010" per hour.

The one potential trouble spot will be quenching. I'd recommend you avoid the use of water. Also, do not quench a part by inserting on the flat side. Plunge the part(s) so the ends are introduced first, with both sides cooled at the same rate. That helps prevent any bowing of the part. Plunge the parts up and down, don't circulate them sideways, as that, too, tends to create a bow in the part.

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Re: Wire EDM Question

Post by Dick_Morris » Thu Apr 29, 2021 4:16 pm

For the full sized locomotive we have been using a commercial heat treater in Minnesota to case harden all our suspension and brake gear bushings. The cost has been reasonable and they give us quick turnaround.

For my model Consolidation I will be pack hardening some parts myself. For my box I have a piece of two inch black iron pipe with caps.

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Re: Wire EDM Question

Post by rkcarguy » Thu Apr 29, 2021 4:52 pm

I have little experience with EDM, but do know that all the machined and hardened work we did would be machined slightly oversized, hardened, and then finish ground on anything that had to be accurate. The steel moves too much during heat treat to be finish machined and hardened(again-for highly accurate parts).

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Re: Wire EDM Question

Post by gcarsen » Thu Apr 29, 2021 9:00 pm

Hello Duck,
I deal with this kind of work all the time and I have my own e
Equipment to get it done , cnc and edm .

Several issues to consider
First you need to check the link and see how badly worn it is , no use replacing the block and the link has a ton of west in it too , take an adjustable parallel and along the slot measure the width , and check if the surfaces are still parallel and not wallowed out
If so I would set the link up and reskim it a tad larger that will cover the worn area .
Then I would make anew block to fit with the required operating clearance. Easy peasy.
Issues to contend with , getting some one to wire through a spray welded surfaces could be fun ! First question I have is how good is the welder? Any slag , piece of carbon or other crap in that weld could kill the cut part way through . I got into some cold rolled mild steal one time , it would cut along perfectly at a good rate then die or slow to a crawl while the edm cut wallowwd around a salt size piece of loose carbon !! Funniest thing I seen in edm nice surface then this ripple to get around this embedded stray carbon particle!! Brought in the steel sales guy , he admitted it was a defect in there steel but it was my problem , explained to him I’d never buy any more steel from them and showed him the door very quickly!! Never have came across this issue with other suppliers steel !! But have came across this ad hen cutting welds!
Now the fun part case hardened or flame hardened is like ordering your eggs at a restaurant! How do you want them ??
Need to specify a depth and hardness !
Typically in heat treatment it takes an hour per thousands depth for case treatment, then the temperature and tempering for hardness . This typically will remove machine , and case hardened then wire edm as you won’t have a case hardened surface on the cut area , and having a piece of steel that size in a furnace for the time it takes to get a case built up , that piece will move !!! Garuntead !
My suggestion, check the link , probably reskim it so it’s right , machine out a new block leaving stock on the working surface, wire edm the radius’s on the block
Instead of flame hardened or case hardened I would seriously look into having the parts then nitrided, it’s a form of case hardening but way lower temperatures for shorter time , supposedly harder surface but you still have the soft core your wanting for strength with out any growth or distortion, pacific machinery and tool steel really push this .

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