Material Callout's - Specifications but not specifics 1

[BIG_SHAFE]

Hi,

I'm looking for some input on how others specify and interpret material call out's.

For example, when a drawing/BOM calls out a material, something like "STEEL BAR ASTM A108", I don't know how to interpret it. I'm trying to place myself in the fab house/vendor's shoes as being given that information, looking at the ASTM spec, and then trying to select a material to order. In the A108 spec, I don't see a default material when not specified, like in some other specs. There are a plethora of materials and then it can be further compounded with heat treatments.

My designer, who has decades more experience than me, is also doing this with some of his material call out's. When I look through some of the spec's I can't figure out what someone would order/use if its not specified. Does this just mean anything in the spec is fair game?

I'm doing an engineering analysis/check of the designs and when evaluating loads/stresses on certain parts, I find strengths greatly varying in the spec. I would prefer to call out something rather than leave it open, but I'm not looking to add a ton of work for him to do or cost unnecessarily. Especially if I'm missing something.

Also, for materials that have trade names like Delrin, Inconel, etc. do you typically just call out the trade name that usually has a spec associated with it or both the spec and the trade name? In the case of Delrin, the ASTM only has alpha-numeric designations and doesn't recognize the name. Delrin does have an associated alpha-numberic designation from what I could find from the manufacturer's information. So I'm proposing either calling out the trade name or the alpha-numeric designation with ASTM spec, thoughts?

Just looking to see if I'm really missing something or this line of thinking is right. In previous employers we used the same 3-5 materials (automotive), so this wasn't an issue. My current employer does much different type of work (build to print) that seems to cover vast material types across multiple standards (ASME, ASTM, SAE, etc.). So this is some unfamiliar territory for me.

Thanks.

 

[ctopher]

I only call out the material and it's spec (ASME/MS/etc). I never use raw material spec (bar, round, whatever). Let the machinist, or whoever is making the part, figure out what material size/shape/etc to use.

ctopher, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[IRstuff]

Seems to me that your drawings are not doing their jobs; they should be sufficiently specific that any material meeting the drawing requirements will meet the design requirements.

If not, then someone dropped their ball.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[3DDave]

I've been jammed up like that also. They picked a material from the steel supplier catalog and just wrote down the specification without noting the alloy or any treatment that might apply.

I thought about going whistle blower on them for illegal material substitution, but I didn't care about either the guys in my QA department who did this or the customer who deserved what they got, even though it was a foreign military sales contract.

I tried to get the prototype back to see what they had actually used to pass the qual tests, plus the hundred or more deviations or other omissions from the drawings, but hey, why not make each unit different.

Typical trade names are for a line of products so just the name is like saying "plastic" and being close. Sometimes it matters, but not always.

Ask what procurement is actually buying and add that so when problems come up at least it's only one known material rather than dozens that need to be analyzed.

For more fun, ask the stress analyst what they used to confirm any of their calculations.

As for my situation? QA threw out all the paperwork for the prototype as soon as it shipped. No need for keeping records of any kind and manufacturing bypassed procurement to get the material. Just grab and weld.

 

[BUGGAR]

Suppliers brag that their material meets ASTM A513 but never say what strength grade. ASTM says the buyer must specify this or the supplier can supply the weaker grade.

 

[EdStainless]

Look at the section of the ASTM spec that says

3. Ordering Information
3.1 It is the responsibility of the purchaser to specify all
requirements that are necessary for material ordered under this
specification. Such requirements may include, but are not
limited to, the following:

This is followed by a list. Make sure that you call out the ones that matter to you (grade, strength, test report, NDT, manufacture method). Many ASTM specs cover a broad group of materials. Now if it really doesn't matter if they use the lowest strength hot finished grade from that spec then fine. But if you want anything but the very minimum possible it is up to you to call it out.
There sill be cases where you don't care if they start from round bar, shaped bar, or a piece of cut plate. In those then call out the alloy using the UNS number and any applicable HT/strength/NDT requirements and let them select the product from and spec.

And NEVER use trade names. You are inferring that the material must be purchased from the holder of that trademark. And besides there are 35 grades of Inconel.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[JStephen]

Agree with IRStuff's statement above.
Whoever picked that spec should also pick the grade. If it doesn't matter, check availability and put the common one.
Note that toughness, impact resistance, machineability, formability, corrosion resistance, etc., may all vary by grade, so you can't just conservatively pick the "strong" one, either.
For trade names, check availability.
For minor non-critical parts, we'll sometimes just call out the McMaster-Carr number and may also specify "or equal" so we can pick it up the local Lowes if available.

 

[drawoh]

BIG_SHAFE,

Specify what you need. If you need CARBON STEEL, call that up on your drawing.

Tips on Designing Cost Effective Machined Parts

The author points out that he selects the cheapest material available that meets the specification. You save money.

I claim that if you systematically provide detailed, elaborate specifications and your vendor learns that you do not really mean it, you will be in trouble when you do.

--
JHG

 

[BIG_SHAFE]

Thanks everyone for your replies.