Grinding Form Dies

[Scra99tch]

Hello,

I am looking at different tool steels that I grind for cold forming threads. What I have been finding is that dies we buy from a vendor often marked, M1, D2, M4, etc, almost always grind better than stuff we buy M2, D2, DC53, DCMX. All of these are not drastically different in their makeup and are all within a few points of Rockwell C hardness 59-63.

This leads me to believe that the metal itself is not the issue, the issue I feel is how the metal is heat treated.

My question is what could a heat treatment facility do differently for a vendor vs someone off the street looking for just some specific hardness.

The reason I feel this may be the case is I can run roughly the same parameters on my grinder, wheel speed, feed rate, dressing ratio, depth of cut and the vendor die cuts very clean and the material we buy will burn right away.

I've still got a ways to go to hone my grinding parameters but it just bugs me that there is that big of a difference across the board of all the materials I've bought vs the vendor material I regrind.

We've had a few reports done on the make up of "their" material vs ours. What I have noticed is that the M1 specifically does have a 1.5% makeup of tungsten which I believe resists the re-tempering of the steel when heat is applied.

The other option is to grind soft, heat treat, then finish grind but this will add quite a bit of lead time and does not make sense as I am able to grind "vendor" dies no problem at their final hardness, with my current wheel technology.

Thank you and looking forward to any thoughts on the matter. If you think this may do better in a grinding machining specific forums just let me know.

 

[Scra99tch]

One thing I forgot to mention is that I've considered stress relieving the dies after grinding. Although I can visually see the burn from the material reports we had done which resulted in a 8 point drop in hardness at the heat affect area on the flanks. But would stress relieving result in maybe some benefit so that cracking does not propagate further.

 

[SwinnyGG]

My question is what could a heat treatment facility do differently for a vendor vs someone off the street looking for just some specific hardness.

The short answer is... everything

A hunk of D2 (or whatever) that's been purchased as a die is, without a doubt, going to have been heat treated in a very specific way by the vendor, vs D2 bought as raw stock (which is likely delivered in the annealed condition unless you're specifying otherwise).

I very much doubt that a manufacturer of forming dies is going to tell you the recipe for the special sauce they use to treat their components... but the only way you will ever know is to ask them.

 

[EdStainless]

How the stock was made and the size at HT also makes a difference.
With some tool steel grades retained austenite is a big issue. These alloys benefit from a cryo treatment.
They often also use a double temper treatment.
If you are getting any grind burn then your grinding process needs a lot of work.

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P.E. Metallurgy, consulting work welcomed

 

[Scra99tch]

Just by looking at the process I have, I notice right off the bat the chip thickness which uses in its equation Q'w or MRR on the root of the cut (radial infeed) vs what is cutting on the flanks is so drastic that without expanding the profile there is no real way to increase the "chip thickness" thus reducing heat generation on the flanks.

But your right both of you pointed to my gut feeling that the other component of this problem is strictly the heat treatment problem. We send these dies to a facility that does the work for our other vendors we still buy from so I figure they would be able to do it "right". Obviously those other vendors might have a extra step or two added at additional expense to achieve some desired result.

We get these dies coated which extends their life significantly I am going to have the coater also stress relieve them to see if that helps.