【转帖】redesigning part - bom change

yang686526

redesigning part - bom change
my question is similar to an earlier post -
i would give it a new part number.
if your company requires to make it a new rev - same part, then i would remove the parts from the bom, add "removed" and add the new parts to a new bom item #.
chris
solidworks 07 3.0/pdmworks 07
autocad 06
or, if allowed, add the new assembly as a dash number.  of course, this depends on how your numbering system is set up.
i would not exchange items in the current bom.  if you are going to give the assembly a new number, then i think your problem as stated ceases to exist.  i didn't research your other thread, does your company have an erp system or other means of bom control?
"art without engineering is dreaming; engineering without art is calculating."
i considered making it a new part number, but that would require me to update the part number on every installation that uses this assembly. since the fit and function aren't changing and the form change will not create any interference issues on the installations, i opted against it. our part number system does not allow for dash numbers, so that was not an option either.  our company is comparitively small and we build oilfeild equipment so we do not require alot of stringent tracking or certifications of materials. we have not yet started using any intellegent erp or plm systems so none of the issues inhierent to the use of these come into play.  our company also does not follow any written standards for drafting, and although i am largely familiar with standard drafting practices, many of our drafters are not. i appreciate all of the input and it seems to support my origial thoughts as well. i just wanted some other opinions before i mark up the drawings for the drafter and have to deal with the arguments that may arise from other designers or engineers.
good luck to you.
chris
solidworks 07 3.0/pdmworks 07
autocad 06
quote:
  i am redesigning a part that is a welded assembly. it's form is changing slightly, but it's fit and function are not, therefore, i want to keep the same part number...
if you are changing parts within the weldment, then your form changes are not slight.  i would recommend pulling a new number for the weldment.  since you opted against this option, it might be best to not do anything else that you feel is going to be confusing.  exchanging item numbers on the bom could be confusing, particular since you don't have a plm system in place.
matt
cad engineer/ecn analyst
silicon valley, ca
the design change being made to the form of the part is removing combinations of plates, and channels, welded together with cut gussets and complicated welded pieces and exchanging them with simpler formed sheet metal parts. therefore it is essentially the same finished part, with simplified assembly method. the drafter assigned to the drawing complained when i took back the mark-up that it would take up extra room on the drawing to add items to the bom and that's why he basically completely rebuilt the bom.
there is a common misunderstanding of form-fit-function.  form is not necessarily the same thing as part envelope.  
here's a good general rule:
quote:
form, fit, or function (fff) 鈥?characteristics of physical items.
form 鈥?item materialfff">, compositionfff">, or general shape.
fit 鈥?item size, mating, mounting, attachment, or connection.
function 鈥?item purpose, operation or performance (such as: method of use, operating range, safety, compatibility, reliability, accuracy, etc).
good luck with your task.
matt
cad engineer/ecn analyst
silicon valley, ca
from what i've been taught:
more important than just 'function form or fit' is effectively whether it is interchangeable - forward/backward compatible.  assessing function form and fit are ways to help judge this.
if it is interchangeable then you'll probably get away with the same number and just a rev change.
function, form and fit are defined in i think it is asme y14.35 revision of drawings (or something like that).
out of interest anyone know in which us standard it talks about when something can be a rev and when it needs to be a new part number, especially for non government work.  i thought it would be y14.35 but it didn't jump out at me when i looked.  in the uk it was in a def stan (equivalent of mil std) for the government programs i was working on.
ideally i wouldn't change the item numbers once assigned, so would do what ctopher suggests, but in some cad systems this is easier said than done.
kenat,
where possible, i personally do try to keep the same number.  in the case of draftsmandon's situation (as described), i would likely pull a new number since the part/process used to make the part substantially changed.  first, it was no longer capabiable (fit) with the previous components draftsmandon removed from it.  second, several parts that did go into it (form) where completely different.  it could confuse the welders and make bom changes very complex and hard to follow.  even worse, if this was a fastened assembly, if a part needed to be replaced in a repair activity, the older components would be useless on a new rev, and the newer components would be useless on the old rev.  however, there may be some room for forgiveness since this is a weldment.  in my experience, based on what draftsmandon has mentioned, i say the save bet is to pull a new part number for the weldment.
matt
cad engineer/ecn analyst
silicon valley, ca