huangyhg

material not being supplied with certs - general market tren
i thought i would post here because i respect the opinion of most people that follow this forum on manufacturing and documentation procedures. this issue is not necessarily a gdt or drafting issue directly.
we have been hearing from our purchasing department that our material suppliers are either refusing to give certs for cold worked material, or they are quoting price adders for certs. the price adders can be pretty expensive. are we being duped, or from your perspective is there a more general trend in the market to either charge (almost exorbitant prices) for certs on cold worked material or not offer them at all? our people tell us the material vendors tell them they can supply certs for hot rolled/formed material but not for cold worked material. has anyone else been running into this? recently we have received some material without a cert, and had it tested and found it to be roughly half the yield strength that it should have been. we have also seen an increase in material received with a cert that is basically fraudulent. can anyone comment on your experiences? have you seen a general trend in this regard?
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if they are a reputable company, they should have certs for all materials. your qa docs should list that certs are required.
chris
solidworks 07 4.0/pdmworks 07
autocad 06
we have stopped asking for certs a long time ago. we put certs on the drawing, but do not require certs with the parts. we do not sell machines or parts. all our stuff is used in house.
bradley
solidworks premim 2007 x64 sp4.0
pdm works, dell xps intel(r) pentium(r) d cpu
3.00 ghz, 5 gb ram, virtual memory 12577 mb, nvidia 3400
well i know we pay more for certs. it makes sense to. the material supplier has to perform testing on each cert'd material. if you don't requre a cert, then they only have to qa to (usually) some internal spec. i know we charge more depending on the level of testing we do on our product.
as for the cold worked material not being able to cert i can't really help you. however, if you find out why this is, please post and let us know. i'd bet money on the type of cert your documentation is asking for. often conflicts between what is called out on the drawing and the current cert standard do not get processed through the purchasing dept. i find it best to cut out the middle man and call the vendor directly on this kind of problem.
wes c.
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no trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.
wes, we call out astm specs where possible, and where not possible we list a minimum yield value. sometimes our drawings are left a little more general, so that our erp description/bom can be changed quickly without affecting the drawing. the erp description is what gets used for the langauage on the purchase order. engineering is responsible for the erp description being defined.
pete
wes, can you say how much you pay for a cert?
pete
honestly i can not say. we had a presentation at our last all hands meeting regarding when, and when not, to ask for a cert, specifically due to the fact that the cost goes up when you ask for a cert. how much that is though, i am not aware. i would imagine that it is upards of 25% at minimum, since they made such a big deal about it.
wes c.
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no trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.
wes,
would you mind enquiring as to the cost increase your folks are seeing. can they point at any supplier policies for certs?
pete
anyone with any specific experience in cold worked material? pete, do you have more information about what you mean about cold worked material? what industry is this in?
my general experience (not to be applied to any specific scenario) is that the supplier of the material will be able provide material certs if they state their material meets some standard. they are able to do this at extra charge because they need to perform the test or to qualify their process (or both) in order to state their material is of that standard. (even more so if nist in applied) there's no reason to make an individual customer pay for this since it is amortized across all customers as a cost of doing business.
if no standard is applied, then there's no reason to even have a cert at all unless the customer is specifically asking for a particular material to their own specifications that the vendor has agreed to make. in this case, it would be acceptable to charge the customer for the work that goes into the certification process because the material is custom to the customer.
any other thoughts about this?
matt
cad engineer/ecn analyst
silicon valley, ca
cold working is a secondary process in steel production. with certain materials you can increase the tensile and yield strength of a material by cold wokring. this may include forcing material through a die slightly smaller than the hot rolled diameter or rolling the material on large rollers. sometimes people refer to the effect as strain hardening. strain hardening is what happens when you take a paper clip and bend it back and forth several times. if you do this you will notice the material becoming harder in the area it is bending. this area is also increasing in tensile and yield strength. if you excessively bend it back and forth, the material becomes too brittle and breaks. the same thing is happening to material that is being forced through a die or rolled on large rollers - although in a much more controlled and less severe fashion. generally, smaller diameter bars can be cold worked more severely and have higher yield strenghts. with larger diameter bars, the surface stresses due to forcing a greater volume of material through a die become to greate and cause material surface failures before it can reach similar strengths of smaller diamters. there are certain specifications that call out minimum mechancial strengths of materials at different sizes that have been cold worked. astm a 311 is a perfect example. i recommend you look at the spec to get an idea. the specification lists minimum tensile and yield strength values for materials that have been cold worked. this is not at all uncommon in steel production. i am trying to get a feel of what otheres are seeing their vendors telling them in reference to supplying cold worked material to a known yield value. seems odd that material suppliers would be selling cold worked material, and when you asked for a cert they would not easily be able to provide one.
i think i'm in agreement. if they state they are providing a material to a particular astm test, the should be able to certify that easily.
matt
cad engineer/ecn analyst
silicon valley, ca

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