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Blanchard, lapping machine or double disk? Options to make hard steel parts flat?

Have you considered clamping them between plates and stress relieving them. That is done at a much lower temperature than hardening. You could do it in a kitchen oven.
Before q&t, you mean ? Or after ? Often (usually ? always with 8620 or 9310) they will stress relieve after quench otherwise you get cracking.

I would have some doubts about stress relief after helping much, because the temps are not high enough to really do much .... maybe the "between plates" part is just bending them ?

edit: Mill, the site you directed is talking about before heat treat, after rough machinging but before finish machining. That's what I always call normalizing but probably really isn't. Maybe more steps than Garwood really wants to do, if he can avoid it. Better than trying to double-disc grind them tho. Especially since he's carburizing, so if you grind off all the case, what's the point ?
 
Part looks like a pair of eyeglasses laid flat. Not much surface area at all.

The hardness of the faces doesn't matter. Just the .130" sides. Case is around .020". I can go .060" or more, but there's no point.

There's no kitchen oven stuff. Parts are currently made in batches of a thousand. Potentially need to make 10K+/month soon. Market potential is 80,000,000 units in the North American market alone. It's not like that's a sure thing, I know a thing or two about how this works, but I do have to keep it in mind so the design and processes can scale if necessary. I want to minimize handling time and total # of processes. That's kind of why I was thinking some kind of grinding op because it eliminates several steps. I don't need to deburr laser dross before machining, don't need to sort for flatness and don't need to tumble to remove carburizing smut.

I'm considering a redesign so the part sits on 3 points and doesn't matter if it's flat or not. It's more complex than it sounds though. There's a lot going on and it has an important job to do. Seating on 3 points would make flatness immaterial. Also if these keep going up past the 5k/month range we will step up to a progressive tool and run them from a coil, laser's too slow.
 
Part looks like a pair of eyeglasses laid flat. Not much surface area at all.

The hardness of the faces doesn't matter. Just the .130" sides. Case is around .020". I can go .060" or more, but there's no point.

There's no kitchen oven stuff. Parts are currently made in batches of a thousand. Potentially need to make 10K+/month soon. Market potential is 80,000,000 units in the North American market alone. It's not like that's a sure thing, I know a thing or two about how this works, but I do have to keep it in mind so the design and processes can scale if necessary. I want to minimize handling time and total # of processes. That's kind of why I was thinking some kind of grinding op because it eliminates several steps. I don't need to deburr laser dross before machining, don't need to sort for flatness and don't need to tumble to remove carburizing smut.

I'm considering a redesign so the part sits on 3 points and doesn't matter if it's flat or not. It's more complex than it sounds though. There's a lot going on and it has an important job to do. Seating on 3 points would make flatness immaterial. Also if these keep going up past the 5k/month range we will step up to a progressive tool and run them from a coil, laser's too slow.

Here is a far out idea. Use a Smaller sacrificial plate clamped in between your plates that leave exposed the rim that you need carburize. They would be as deep as you can stack them. Warpage would be minimal. You will have your hardened rim with hellaciously high compressive residual stresses. Sacrifice plates should be reusable.
 








 
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