How materials should be identified on prints? 1

[latigid]

When creating a print for a finished good that will be produced in-house, what's the best way to identify the required materials on the print.

For example, a company purchases and inventories 5/8" diameter x 16' long bars of CR 1018 steel under an internally created part number AA123 per the companies ERP system. When this material is required to make one of the companies products, should the material be called out on prints as 5/8" diameter x 16' long bars of CR 1018 or should it be identified as AA123?

What is good engineering practice? I've looked into the ASME design standards but I haven't found anything that address how materials and components should be identified on prints, i.e. by industry standard or by the internally created part numbers companies use to purchase their materials.

 

[KENAT]

Based on my experience I would say they should normally be called out by industy standard terms/grades rather than internal part numbers. Internal part numbers can be problematic if you merge or are aquired by another company etc. Also, while you may make the part in house at present, if you decide in future to out source it then only having internal part numbers can be a disadvantage.

I'd go further than this, unless you are keeping the 'stock' dimensions on the finished part you should only call out the grade. This allows them the freedome to machine the parts from different size stock if required.

Many government contracts, and possibly some of their specs, require that the grade be given along with the specific material spec & in many cases an approved alternative also be listed.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[IceStationZebra]

There is no right or wrong answer. There are benefits to doing it both ways.

For example, lets say you are making several different parts with this material. If you reference AA123 and then change to HR 1018 you only have to change the base print not multiples.

ISZ

 

[kchan711]

Many of the companies I have worked with put a standard Bill of Materials on the front sheet that includes, with item number, quantity, description (such as length and diameter), material and an in-house part #. If the part was purchased rather than made, they still use their own part number; however, they try to include the vendor and vendor's part number in the description. I always identify the material on the Bill Table simply for the fact it makes the process simple for reference.

Kyle Chandler

http://www.chiefengineering.net

 

[hydtools]

Don't use the internal number if it describes a bar of material. If you use that number on the print, indicates you want to use the full bar. If someone uses your drawing for material take-off for inventory reasons, inventory will not be correct.
Use only the material spec and/or an internal code for that spec. Don't use the number assigned for the raw material as purchased and stocked.

Ted

 

[IRstuff]

Another reason for using the actual material specification is that an internal procurement specification might have slightly different requirements, which might allow substitutions with "equivalent" materials that might not be equivalent for your specific application.

TTFN

FAQ731-376

 

[drawoh]

latigid,

The various departments where I work, have different policies regarding numbers used on BOMs. I watched one of our electrical engineers curse a parts list with nothing but stock codes on it. The stock code system was inaccessible to him, so he could make no sense of the components of the PCB he was trying to figure out.

I have been told by one of our manufacturing guys that he would prefer BOMs with nothing but stock codes because that would allow us to change part numbers without revising all of our BOMs. He was assuming that we would have a good specification control system in place, which would have solved the engineer's problems, noted above. I was comfortable with his idea because I figure I could set up SolidWorks to create several types of BOMs, depending on the end user.

I would say that your ERP stock code is perfectly functional if there is a good reference explaining it. If the number is buried in ERP's database, inaccessible to engineering, you are in trouble.

If you want something to be 5/8" in size, you should apply the dimension 5/8" on your drawing, with your required tolerance. The material is CR[ ]1018. Who cares what the raw material was?

JHG

 

[btrueblood]

IRstuff hit in on the head. The question is "who controls the part numbers"? In some companies, the part descriptor or internal specification is part of the normal document control system, but in others, the purchasing dept. "owns" them. I have had more than a few projects get snarled when the purchasing dept. found cheaper substitutes for the fancy materials those dang engineers kept specifying.

 

[MiketheEngineer]

Use both??

 

[rb1957]

use either ? ... consider the final part, did it Have to be made from AA123, or would any other bar stock have done the job ? now the paper trail of the part would pick up that the final part XYZ123 was made from AA123 or AA124 or ...
but from an engineering perspective, you'd want to specify bar stock 2" OD, finished ...

 

[griffengm]

How is the material inventoried and purchased?
If one material is purchased per pound but used in linear units(ft, inches, mm etc) then someone will need to do a conversion to keep inventories near correct. It seems to work best if consumption is listed in the units your operator will most likely use.
After a number of years of taking inventory, checking prints, and troubleshooting production issues, I find that the more information on the print, the better. If a print has only stock numbers and I am on the line looking at a problem then I do not trust my memory as to the description of for each number and must get to a computer terminal to check descriptions. This assumes that whoever set up the part numbers was generous with their time and did not list 200 part numbers with the identical description "connector" or "lid". When I have had to go to a supplier catalog to find a description of a $100 motor because data entry could not be bothered to make another ten keystrokes, I really wonder about the values of company management. Ten KS at a 30 wpm rate equals about .067 minute vs the 10-15 minutes to research the part number.
If the company has done their homework then special stock sizes are on hand because of specific needs or cost savings. Using a different material causes variations in either quality or cost. If an operator must make a substitution then the more information he has at hand the better he can make the call.
Griffy

 

[IceStationZebra]

You have all proved my point that there are benefits to doing it both ways. Either way it affects other departments, some positive and some negative. Accounting likes tight control while the shop usually likes standard material call-outs to save time.

I also don't buy the "internal procurement specification" line of reasoning. If the print for AA123 doesn't call out an allowance for a particular substitution, then why are they allowed to substitute? A lack of control in the purchasing department should be dealt with instead of changing your engineering policies, otherwise there will be no end to your misery.

The companies I have worked for in the past have done it both ways depending on what made the most sense for the particular part and standard factory process. Rubber hose would be a good example - it was bought in bulk under one part number but cut into shorter pieces with different part numbers. Stock steel did not normally have a part number as it would make inventory control a nightmare (bad parts, end cuts, waste, etc.).

ISZ