Surface unevenness of stainless steel casting

Question

Surface unevenness of stainless steel casting

SJmetallurgist (Mechanical)

(OP)

27 May 16 11:15

Hello

Please refer the attached photographs. These pictures belong to a cast product. I have observed some unevenness/modulation in the surface. this unevenness is evident on touching also. This is inherent of teh casting. Note that the casting is now in machined condition. I have also notice the same surface unevenness in Ni alloys (the second photograph belongs to Ni alloy material (inconel 625).
I would be glad if an expert could comment on the reason of such modulation occuring in the material. Some details given below.

Photograph 1:
a. Material CF8M.
b. Hardness - 240 BHN.
c. Casting.
d. Unevenness observed on face and RTJ groove wall.

Photograph 2 & 3:
a. Material Inconel 625.
b. Hardness - 260 BHN.
c. Casting.
d. Unevenness observed on face and RTJ groove wall.

Cheers!

http://files.engineering.com/getfile.aspx?folder=f9504a84-d447-4329-928e-f1

btrueblood (Mechanical) · Answer 1 · 2016-05-27 16:29:43

Looks like a dull cutter, or a cutter with poor swarf removal was used, and chips from the cutting face got smeared back into the wall. Is there evidence of chatter in the base of the groove? Sometimes you see that kind of finish when the cutting edge is vibrating/chattering.

MikeHalloran (Mechanical) · Answer 2 · 2016-05-27 16:34:51

Photographs can't convey touch very well, but from here, it looks like your machinist was using a flexible cutter setup, possibly a dull cutter, and ignoring the acoustic noise generated during the cut.

Do you have access to a profilometer?
Data from that should be reviewed against your print's surface finish spec, which may need to be revised to prevent production of similar scrap in future.

Mike Halloran
Pembroke Pines, FL, USA

arunmrao (Materials) · Answer 3 · 2016-05-28 15:36:29

The cutter was screaming and squealing demanding attention, alas, it fell on deaf ears. Result, those cold flow marks on the casting.

Nothing wrong as a casting.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

SJmetallurgist (Mechanical) · Answer 4 · 2016-05-28 19:33:34

Well, I will sure check with a profilometer. However something gives me a feeling that this is an inherent property of the casting of these material, as I see this prob mostly in CK3MCUN, CF8M, Inconel material. Though I understand that all of you must have seen these castings and have not observed such problem. If it is so then we are left to two possibilities:
1. there is something wrong with the tool being used. Which is a little unlikely as all castings show this problem and this one is frequent.
2. They are using wrong tool altogether. I will update here the tool that is being used.
3. Something about the way they are being cast. Casting supplier is same Foundry company in all these material. He may be observing some incorrect practice while performing casting. This aspect I am most doubtful about.
Will revert to you on first two points (these points sort of sum up observations of the three of you).

Thanks anyways. update you shortly.
Regards

EdStainless (Materials) · Answer 5 · 2016-05-31 17:22:18

You are cutting this in one pass, correct?
You need more rigid tooling, much more rigid.
When you get a coarse grain size in SS (such as a casting) it is very difficult to get a smooth cut.
The keys are rigid tooling, lots of high flow cold clean coolant, and making one full depth cut (even if mean very slow feed). These material work harden so much that if you try to rough them and then take a light finish pass the second pass will in very hard material.

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Surface unevenness of stainless steel casting