Manufacturing Part Numbers 




Arguments for Nonsignificant Part Numbers

There are a host of reasons to be cautious about going to a significant part numbering system. Not the least of these, as described earlier, is the amount of effort required to get one established, and then to maintain it. A significant part numbering scheme can even slow down implementation of an MRP system. But there are other, more compelling reasons to avoid significant part numbers:

Making the part number significant makes it a descriptor rather than simply a unique identifier. Once you change the nature of the part number, you also create the possibility of misinterpreta­tion. For instance, a significant part numbering system that includes the value of parts (like resistors, capacitors, etc.) would

probably use a system with two or three significant digits and an exponent, like: 2700 Ohms would be indicated as 273, meaning 2.7 x 103. What is to prevent someone from mistakenly interpre­ting "273" as 27 xlO3, or 27,000 Ohms? Nothing, but there is an order of magnitude of difference. This kind of error is impossible if the part number is not subject to interpretation.

Another problem with significant part numbers is their tendency toward length. They often seem to expand to the maximum length allowable in the item master. With length, generally, comes the need for other characters to break up the character string, so alphabet characters and punctuation are often added. (If you don't, you'll find yourself speaking in terms like "part number one hundred and ten million, three hundred and seventy-three thou­sand, two hundred and forty-six.") With long length, alphanu­meric strings, and punctuation, a multitude of evils enter in:

• It takes longer to enter long, alphanumeric part numbers than short, numeric part numbers. A 15-digit alphanumeric part number takes at least 2 times as long to enter as a six-digit number—probably more like 4 times as long, when you consider that most computer terminals have a separate keypad for rapid number entry, but the entire keyboard must be used if letters and punctuation are included. (Most people operating computer keyboards are not touch typists!)

• More errors will be entered with significant part numbers. The usual figure cited for keyboard entry is one error per 300 keystrokes. That means that with a 15-digit significant part number, one out of every 20 part numbers will have an error, while with a six-digit number, it would take 50 part numbers to be entered before an error would occur. Again, it is likely that the difference is even greater when comparing long part numbers with alphanumeric characters and punctuation to numeric part numbers.

• Errors can be effectively prevented from getting into the system by adding a checksum digit to the end of a simple numeric part number. It may be impossible to add a checksum digit to the end of a long, significant part number.

• Operator fatigue will be greater with longer part numbers. This is especially important in repetitive, high-volume situa­tions, and can lead to even more errors, carpal tunnel syn­drome, etc.

• Using alpha characters and punctuation as part of the part number would seem to make it possible to sort part numbers in a spreadsheet or database, and automatically categorize all the parts in your database. Unfortunately, the different spreadsheet and database programs on the market don't all use the same conventions for sorting. In one program, punctuation may come before numbers—in another, it may be after the letters. Do letters or numbers come first? It all depends on the program—so if one person uses a DBMS (database manage­ment system) and another uses a spreadsheet or even another brand of DBMS, chances are they won't get the same answer.

Aren't these effects mitigated by bar code? Yes, but: bar code will only make a difference in those transactions that can be standardized, such as receiving, inspection, parts picking, and shipping. What about transactions like:

• structuring bills of material?

• entering customer orders?

• entering parts costs or supplier quotes?

• inquiring into parts balances?

• allocating inventory?

Also, just because using bar codes will help mitigate the problems with manual entry of long, significant part numbers, don't forget that long bar codes aren't good either. Requiring alphanumerics and punctuation will force you into particular bar code symbolo-gies, and may require that you use larger (i.e. more expensive) bar code labels. Bar code labels will take longer to print, too. And it increases the risk of misreads, possibly forcing you to use more expensive equipment as well.3

A quick discussion of multiplant environments is appropriate. Some organizations will use different part numbers for different manufacturing facilities. Sometimes this is necessary, because differences in specifications mean that parts from one plant are not really identical in form, fit and function to parts used at another plant. In these cases, all plants should at least use the same commodity coding structure to help uncover similar parts, group them by commodity, and use that information to negotiate with vendors (and, perhaps, with each other—to eliminate unnecessary differences in specifications). Otherwise, each plant should try to use the same part numbers. Using the same part number with a unique plant designator prefix is just as bad as using totally different part numbers—they will be equally difficult to group together in databases and reports.

A final argument against the use of significant part numbers is their lack of flexibility, and the consequences of that deficiency. An example given by Elliot ' cites a casting that was switched from aluminum to zinc. Because the material was encoded into the part number, the part number had to be changed on all the bills of material, engineering drawings, purchase orders, and other documents referencing that part—even though it was the same in terms of form, fit and function. This can actually make a company less competitive; your purchasing department may stop chasing savings of pennies per part when it begins costing a significant amount of money to make the change. This same lack of flexibility can lead to parts being overspecified. If I buy a number 10 wood screw, I may not care if it's made of steel or brass—but the part numbering system will make me specify one or the other (or come up with a special designator that indicates both are acceptable). Then, I run the risk of parts being rejected by Incoming Inspection for a parameter I don't even care about!


To be Continued


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