Speaking of Precision Blog

Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

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5 comments

The First Tool I Look At

Posted March 18, 2011 8:30 AM by Milo

As a steel company Metallurgist and Quality Director, I was the guy who got the call to visit a shop because the material we sent wasn't machining right.

"This stuff won't drill! Help!"

"This stuff is killing my OD form tool. Can you check the steel?"

"This steel you sent is acting crazy. It machines fine on one machine, but not on the other one."

As the fellow responsible for the processes and quality system that produced the bars, and having visited my hot mill upstream suppliers, I was always confident that I had provided conforming product.

But how could I make sense of the problems reported?

Listen! There is a reason they have canaries in the coal mine.

My solution was to always look at the wrong tool - first.

If they complained about the drill, I asked them to show me the cut off tool.

If they complained about the rough, finish form, or shave tool, I asked them to show me the cut off tool first.

They said "Hey Mr. Free, you aren't paying attention. I said the drill is giving me trouble, not the cut off tool."

To which I cheerfully replied "Yes?"

After letting that sink in for a bit, I would ask the following appreciative inquiry type of question to lead their thinking:

"If the cutoff tool sees every aspect of the steel provided - the very surface of the outside diameter (OD), the sub-surface, the mid-radius, the core, and it does not have any abnormal issues resulting from this material - what is there about this material that you think would allow it to affect this one tool, but not the cutoff?"

Then we focused on the aspects of the operation that inevitably were found to be the cause.

How does the steel know to only interfere with the drill, let's say? Or the the finish form? While leaving the cut off tool unscathed?

While there can be material conditions that are specific to a certain zone in the steel and thus would manifest on a particular tool, that conditon would also have an impact on the cut off.

If the cut off tool is A-OK, it's probably not the steel.

This is the tool that will tell the tale.

It may not look like a canary, but a cutoff tool can sing a song about your process, if you can listen with your eyes.

Canary.

Cutoff.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which originally appeared here.

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#1

Re: The First Tool I Look At

03/18/2011 11:32 PM

Excellent pointer. Thank you.

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#2

Re: The First Tool I Look At

03/19/2011 2:53 AM

Milo -- Real interesting story and lesson here.

I seem to remember an incident some 35 years ago when I worked for the centrifuge company. I was pretty close to the company metallurgists. Pretty sharp guys they were and had to be because the business involved some pretty exotic uses of titanium alloys. There was a situation I touched where we had an expensive accident in a piece of stress testing equipment when a highly stresses rotor part disintegrated at speed. Turned out there were isolated stringers in the 1.5" dia 6-6-2 Ti bar stock. I think the bar was rolled from a billet rather than extruded.

My questions now are does that sort of thing happen in commercial low alloy rolled steel bar? I mean the kind that would be used for highly stressed machine shafts like AISI 1040, 4140 or 8620?

If and when it does what kinds of failures at the mill would create such conditions?

Are there any outward signs of such defects in a given hot rolled steel bar?

Are such defects more likely in steels made in particular melting processes or made from particular scrap feedstocks in the case of work done by minimills with electric furnaces?

Note these questions are from a mechanical engineer who knows just enough about practical metallurgy to be dangerous (LOL)

Ed Weldon

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#3
In reply to #2

Re: The First Tool I Look At

03/19/2011 10:10 AM

Ed, those stringers sound like they were "exogenous" materials that got into the material during solidification. Slag perhaps or refractory.

In the steel industry we have special " clean steel practices" that minimize slag carry over and reduce frequency and severity of normally expected inclusions. Vacuum degassing argon rinsing, desulfurization, different tapping methods.

Commercial steels have normally expected inclusions-sulfides, silicates, aluminates, etc. They are routine and rated according to ASTM e 45.

Great idea for a new post! Watch this space.

milo

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#4

Re: The First Tool I Look At

03/19/2011 10:50 AM

It always bothered me when an outside expert never asked me a question I didn't have an answer for. Almost as much as when they didn't believe my answers. I spent a lot of time on semantics. I have answered the "wrong" question because my terminology was different, not wrong, just different. Of course, after having consultants ask things like about the cutoff tool, I didn't have to have as many outside experts come in.

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#5
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Re: The First Tool I Look At

03/19/2011 11:28 AM

Hi wsjackman. Your efforts to get the language right were key. Local terminology and ways thinking can be barriers to understanding, not facilitate it. Thats why i went to the machine, talked to the operator, and looked at the cut-off...

milo

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