Material Specifications using Performance Values on Mechanical Drawings

[93ramvert]

We are an AS9100 Registered Company. We currently have a fairly new V.P. of Engineering. Of course we are already clashing. Go figure. Anyway our manual basically states that engineering will provide a material specification on drawings, basically to provide purchasing with detailed information when sourcing out material for manufacturing pieces. The engineer is using performance values of the material he wants used as an example:

Material: Steel with minimum material characteristics of 16% Elongation, 95ksi Yield Strength, and 115ksi Ultimate Tensile Strength.

His reasoning: In this case, we could have said to use 4340, but that is really overkill. We could not say to use 4150 because there are different heat treats for it, some of which have the necessary properties and some don’t. By giving the material properties, Bill can use available 4150 if he has acceptable certs for it.

At this point the Pres. is backing him, I just want to make sure that come audit time I'm covered, because of course it's going to be my fault when we get written up for it.

Could someone please tell me if this would be an acceptable practice?

 

[Jeff Frost]

You will find in the aerospace your customers will call out conformance to material specifications like, ASTM and these specifications will govern the procurement of materials. Your suppliers will likely also require you to specify the specific specification the metal must meet before accepting the order.

 

[93ramvert]

The President of the company has so far sided with engineering (he is an engineer as well). He believes that engineering should be able to put Aluminum as the material on mechanical drawings, because it doesn't matter what type it is. I'm certainly not a metallrugist, but I'm sure there may be an aluminum you don't want to use in some cases. I don't know, I'm feeling just a bit lost.

 

[Jim Wynne]

The President of the company has so far sided with engineering (he is an engineer as well). He believes that engineering should be able to put Aluminum as the material on mechanical drawings, because it doesn't matter what type it is. I'm certainly not a metallrugist, but I'm sure there may be an aluminum you don't want to use in some cases. I don't know, I'm feeling just a bit lost.

Does it matter what type it is?

 

[93ramvert]

Does it matter what type it is?

Well what they are saying in some cases no, and in some cases yes. I quess what I'm concerned about is they are saying is in some cases we are going to tell them what we need in the line of performance of the material, and the vendor will tell us what they are going to give us. Such as yield strength, elongation etc... Now, obviously I can't necessarily have our 18 year old receiver sign-off the material as acceptable, it will have to go through engineering for verification against there performance call out.

Where as if the drawing says Material to AMS 5663, my receiver can look at the certs and positively i.d. that the cert states AMS 5663, and can now receive it.

Let me use the aluminum call out for a second. Say the purchaser goes out to the metal vendor and says I need Aluminum doesn't matter what kind, give me a cheap drop that will match this size. The vendor ships a drop of 7075 aluminum (Now it's aluminum right) right, Now the technician has to do his thing and now needs to weld it. Guess what it's very difficult to weld, and the tech can't get it done. I'm sure there is other differences there has to be, corrision, strength etc. differences from the highest costing to the lowest piece of crap aluminum you can get. To me as just as a person in the company, the decision should not be up to another company, or another department to decide what to get, Engineering should detail this up front. Maybe I'm over thinking it, I'm just very concerned that this is going to bite us.

 

[CarolX]

I don't mean to simplify this or demean your situation - but ask both the Pres and VP - would they fly on that plane?

I worked for an aircraft parts manufacture about 20 years ago. If we had an ouot of tolerance part, and the engineer was unsure of it's usability, I would ask "Would you fly on the plane that had that part?". Always helped him with his decision.

 

[Jim Wynne]

Well what they are saying in some cases no, and in some cases yes. I quess what I'm concerned about is they are saying is in some cases we are going to tell them what we need in the line of performance of the material, and the vendor will tell us what they are going to give us. Such as yield strength, elongation etc... Now, obviously I can't necessarily have our 18 year old receiver sign-off the material as acceptable, it will have to go through engineering for verification against there performance call out.

Where as if the drawing says Material to AMS 5663, my receiver can look at the certs and positively i.d. that the cert states AMS 5663, and can now receive it.

Let me use the aluminum call out for a second. Say the purchaser goes out to the metal vendor and says I need Aluminum doesn't matter what kind, give me a cheap drop that will match this size. The vendor ships a drop of 7075 aluminum (Now it's aluminum right) right, Now the technician has to do his thing and now needs to weld it. Guess what it's very difficult to weld, and the tech can't get it done. I'm sure there is other differences there has to be, corrision, strength etc. differences from the highest costing to the lowest piece of crap aluminum you can get. To me as just as a person in the company, the decision should not be up to another company, or another department to decide what to get, Engineering should detail this up front. Maybe I'm over thinking it, I'm just very concerned that this is going to bite us.

I think your concerns are valid. Relying on suppliers deelop important design requirements after a contract has been agreed to is asking for trouble. Is this a matter of ignorance on the part of your designer(s)? Do they not have the requisite knowledge to specify what's needed, or are they just being lazy? Why not have your designer(s) meet with the suppliers before designs are released, so that the information can be put on the drawings?

 

[Jeff Frost]

Ask your engineering how they propose to meet the validation requirements contained in 7.4.3 of the standard. Procured raw materials must be re-tested to assure accuracy of supplier test reports. A reference to a specification states a specific method for testing and the requirements.

Since in your original post you also stated you’re an AS9100 house this means your organization must also look a regulatory, statutory and customer requirements related to design of product. The big boys in the industry have a lot to say about raw materials, control of designs and what they will and not accept on a drawing based on these three requirements.