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Ductile iron casting bore

K7gixxer6

Plastic
Joined
Feb 22, 2018
Hello everyone,


I am running ductile iron casting 80-55-06 (AS-Cast) on a CNC mill. The material is 0.270” thick, and we are boring out a 1.0012” diameter hole (not a full diameter hole), with a tollerence of +/- 0.0002”. We need an Ra finish of 24 or less.

We are using a Kennametal Romicron boring bar with a 40 radius carbide insert. We have this bore running at 2200rpms, and feeding at 1.5 inches per minute. Before the Romicron (finish bore) runs, we have a separate rough bore run, to leave 0.002” in diameter for the Romicron.

There are 2 of these bored holes per part, and on a new insert, we can hold our 24 or better Ra finish for the first two parts (not always). After the first two parts we have to start hitting the bore with 400 grit sand paper and a die grinder to get our Ra 24 or better finish, wich can sometimes be a pain.

My question is, there has to be a better way to maintain and get that surface finish out of the machine?? Hope someone can help, thanks in advance !
 
For the numbers you're trying to achieve, I would either use CBN inserts for the finish cuts (if the material is at least RC 40), or set up a honing op for the final size and finish.
 
Rule of thumb for boring is you need to bury the corner rad. I recommend a combination of leaving more stock and a smaller rad.

.04 rad seems kinda big for the depth of the bore. Try a .016?
 
The "not a full diameter hole" part is the killer. That probably leaves out roller burnishing and honing. Might be looking at a form tool with ZBN or something.
 
I didn't understand the "not full D" part, b/c he said that he is boring it rather than milling it.
Maybe he meant that the hole breaks out? If so - yeah, those methods won't work well at all.


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Think Snow Eh!
Ox
 
Yes, it is not a full diameter bore. As in, not a full circle I guess the best way i can explain.. More like a C or half circle. So yes, honing is taken out of the equation here. We are rough milling, then finishing with finish end mill, leaving 0.012” for the rough bore, then the rough bore leaves 0.002” for the finish bore.
 
Rule of thumb for boring is you need to bury the corner rad. I recommend a combination of leaving more stock and a smaller rad.

.04 rad seems kinda big for the depth of the bore. Try a .016?

I’m sorry, 0.04” radius was a serious typo. I’m actually running a 0.008” radius.
 








 
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