Custom 450 SS Machining Issue

Question

Custom 450 SS Machining Issue

forging82 (Materials)

(OP)

10 Dec 13 11:27

I have some parts that are being machined and there is more vibration than usual. Usually there is less than .015" of movement and with the current batch there is more than .05" of movement. I looked at the heat treat charts and mechanical property results and nothing looks out of the ordinary. The customer is leaning towards a material issue. Does anyone have any idea what might be causing the excess vibration?
Thanks.

EdStainless (Materials) · Answer 1 · 2013-12-10 15:37:03

Tooling.
It isn't the material, there is noting that could be changed in the properties that would do this.

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Plymouth Tube

MikeHalloran (Mechanical) · Answer 2 · 2013-12-11 09:15:04

Like Ed said.

After you've changed the inserts and tightened everything, if it still doesn't machine right, check that the buyer didn't get a special deal from some new supplier, "complete with copies of any certs you'd like", so to speak.

I'm curious about any machining operation where either deflection or vibration amplitude is considered 'normal' at .015", let alone .050". I'm guessing one damn long boring bar...

Mike Halloran
Pembroke Pines, FL, USA

forging82 (Materials) · Answer 3 · 2013-12-11 09:21:30

I am from the company that produced the forgings. I personally looked at the mill certs and test records and didn't find anything different than previous runs. I don't know enough about the machining so I am just trying to make sure there wasn't something we did wrong that would cause the excess vibration.

dgallup (Automotive) · Answer 4 · 2013-12-11 10:24:51

You don't say what type of machining is being done. Is the workpiece stationary or is it rotating? We get some large bar stock that is not straight enough and the vibration shakes the entire building when we try to turn it.

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tbuelna (Aerospace) · Answer 5 · 2013-12-13 18:56:56

forging82- Can you provide a specific description of what you mean by .015" of movement or .05" of movement ?

forging82 (Materials) · Answer 6 · 2013-12-16 07:08:38

I was not involved in the machining process and have no idea how they were machined. I am responsible for the material. It sounds like from what everyone is saying there might have been a problem within the machining process. Thanks for your help.

kumkumvijay (Materials) · Answer 7 · 2014-02-18 11:21:02

what is the material grade ? Is it plain carbon steel. If you want to ensure the material is not reasong , i would suggest to check the following:
1. Check the hardness value ?
2. check the microstructure ?

If material is a reason, vibration can be due to in the material from steel mill or after forging
1. Hardness increase
2. non metalic inclusion
3. Banding ( preferred solidification of ferrite and carbon related phase)
4. if its heat treated, hardenability ( change of hardness from surface to core area)

If its machined in forged condition:
1. check the temperature of the part after forging
2. is it air cooled after forging ( normalizing)
3. Parting line defect and scale

forging82 (Materials) · Answer 8 · 2014-02-18 13:48:41

The material is custom 450. All of the mechanical testing came back in spec and similar to the results we've gotten in the past. Microstructure was good too. As far as we're concerned the issue was not with the material because there were no issues with testing or with other parts made from the same heat.

tbuelna (Aerospace) · Answer 9 · 2014-02-20 00:14:02

What is the form of the forgings? Are they rolled rings or hollow cylinders? Are they die forgings with axial asymmetry? Are the forgings rough machined prior to delivery?

Sounds like there might be surface runout or dynamic balance issue with the forgings as delivered.

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Custom 450 SS Machining Issue