How do manufacturers decide to use serial numbers on items or not?

Factual Questions
21

They always have some code to make traceability possible, but whether it is a SN (or equivalent, such as a VIN), a manufacturing date, expiration date or batch number will depend on the nature of the product. Sometimes the numbers themselves codify information: some poultry coops stamp every individual egg with a code including when was it laid, what farm it comes from… it’s not a serial number, but again it’s about traceablity.

[soap box]
Traceability has different benefits for different parties; they’re mostly related to quality control, process improvements (not only in Production, but also in Logistics, Quality or Maintenance), maintenance and logistics.

Logistics: one of the advantages of traceability is that, by having a shipment number and some way to interact with the shipper’s computers (person to person contact or web-based), both the recipient and the sender can find out where the item is at any given time. It isn’t a matter of “ship it and it will arrive whenever it does”, as it used to be.

Quality: tracking what went into making a problematic item, when was it made, by whom, using what machines. If you discover that one of your components is bad, you can find out which produced batches/series it affected and act accordingly (analyze what you still have in storage, recall product, contact your clients to warn them of the issue and provide a fix…)

Process improvement: since you can analyze all the information about when, how and with what was an item made, you can get a better view of the causes and hopefully improve the process to avoid reoccurrence. Depending on what the cause was, the process that needs to be improved may not be a Production one: you may need to control certain products more often (for example, runs under one day get inspected once, longer runs get inspected once-a-day instead of only once), or to clean the machines better (literal quote: “how many times have I told you that when you drop copper sulfate on the scale it has to be cleaned yesterday!”). You may also find out that the wrong truck was used (food-container instead of chemicals-container comes to mind), or that a product clearly labeled “protect from sunlight” spent three months sitting in a yard under the tropical sun: yep, it grew colonies and I don’t mean the kind that smell well.

Maintenance: only people with serious anatomical problems worry about which individual monkey wrench was used to close a valve, but the valve itself can cost anywhere from a few cents to six figures. When your valves cost more than three times your salary, you kind of want to be able to track when any of them was bought, when was it installed, when was it cleaned, whether any of them has been refitted, that one was removed from location A then refitted then installed in location B… It can help you do things such as convince your boss that it really is worth it to buy the ones that cost 150K and last 2 years rather than the ones which only cost 60K but last 3 months (yes, that is a real example).

I could go on for hours but I don’t want to bore you more. My area of expertise (that sounds so posh) is Operations: Production, Quality, Maintenance (both internal and for customers), a bit of EHS… so I work with and for people who often need to be convinced that they really, really, really do not need to track this or that detail specifically (the computer will do it for them, yes I love redundancy too but seriously, in this case it’s additional work for no additional safety or security. Cross my heart).

22

Banana oil!

(More information, fir sooch a nize baby.)

23

How is that similar to anything to do with serial-numbers on products? Is WallMart taking note of the serial numbers of maglites they sell and then catching a random sample of maglites in the wild to see how large a percentage they have of the market?

24

I see now that Senegoid was probably refering to the Tank Problem mentioned several posts above, which did use serial numbers to estimate the total “population” of tanks.

25

Nava has provided a good general exposition, but I’d like to know exactly the reasoning behind why the Maglite people decided to give a serial number to their torches, but the Energizer people did not, given that both products cost me the same, and perform near-identical functions.

From the discussion so far, the most likely reason is mere branding: At Maglite we make quality, and you can tell because our products have serial numbers. At Energizer, we make so-so plastic stuff, we don’t claim otherwise, so we aren’t going to bother wasting our money on individual serial numbers.

26

Well, to have the two companies’ exact answers for those two specific items we’d need to have here people from each who were involved in the decisions; all we can do is guess.

The decisions are often taken at a higher level than that of individual models. It’s highly possible that Maglite has an “every product has a Serial Number” policy while Energizer has one of “batteries get best-before date stamped on package, anything else does not get dates, serial numbers or any of that”. If the immense majority of your products have an SN, it’s more routine, therefore easier and cheaper to put SNs on every product than to have a few outliers .

27

Food in cans, at least, get cooked in retorts in batches, so an id per batch is all that is required (which involves a date code.) If one can from the batch is bad, you need to toss all of them. Dates are important because cans are often held before shipment. For a reason - when my wife was quality control director at a vegetable cannery one batch did not go into the retort bank because of a shift change. A week later the cans blew up as the bacteria inside thrived. Better to clean up the warehouse floor than the customer.

Serial numbers are sometimes pointers. The one you find on a wine label is a key for various databases which give you information about its production, including corks, barrels, and the location of all the grapes that went into that wine within a few meters.

Depends on the product. Small electronic components like capacitors get lot ids. Big ones like microprocessors get die ids which give you traceability back to a lot, wafer, and location on the wafer. Very important to have.

28

One more really important reason is security. Chip manufacturers have a big problem with counterfeiting and the gray market. Parts that fail tests can vanish and be resold. Traceability allows the manufacturer to prove that the part is not legitimate.
It is also important to catch counterfeiters. I know one large electronics manufacturer who was able to prove parts were counterfeit by showing that the fake serial id was not in their database.
And there is warranty. The owner of five systems might extend the warranty for only one. If a component fails in one of the other four, just send it back and claim it came from the first. If you know what components are in what systems, you can tell which parts are eligible for warranty repair.

There is a standard for traceability information in one or several EPROMs within a system, which lets you (with permission of the owner) build up a database of what is where. Very useful in several cases.

29

As mentioned, traceability is all about deciding just what information you might need to know later.

Suppose I process a bunch of chemicals in a vat, undergo a process of reactions, and end up with a resulting product. This is performed in batches, runs, i.e. each vat of chemicals. Thus these get a “batch number”, because that’s the finest I can trace that product. I can tell the chemicals and amounts that went in from records, I can test the output product, and it should all be consistent. A problem with one item from this batch later can mean the whole batch is suspect, because I cannot parse any finer why this can is off while that can is not.

Similarly, some physical components are made in groups, or lots. They receive a number that says “all of these parts were made at the same time with the same equipment and same sourced-pieces”, i.e. a lot number.

Other items are assemblies of lots of components, and more of a unique assembly when completed. These items are given a serial number, i.e. this is unit 1, this is unit 10, this is unit 7003, etc. This allows tracing the history of that specific unit.

Sometimes the manufacturer wants to trace history throughout the delivery process. Sometimes the customer wants to track usage. Sometimes that usage can expose problems that the manufacturer needs to be aware of, as it can be an unrecognized problem with fabrication.

Sometimes they need to track the materials sources going in. Is the steel really the right alloy steel, did it really get the right heat treatment? Etc. Electronics are the same.

All of that speaks to reasons why manufacturers assign traceability numbers, and why they assign the kind of traceability number they do.

We can only guess. Your guess seems reasonable. I do not know why Maglite would really need to know “this specific unit” when it sells it to you. Even for a warranty, there’s no necessity they know the specific unit ID. It may have to do with quality control feedback. If they warranty workmanship and you return the product, how important is it that they track down the manufacturing flaw and try to prevent future occurrences? A cheap flashlight manufacturer may not care and just send you a replacement, relying on the statistical error rate to assume you will get a better replacement. Maglite may be concerned enough about their product brand that they wish to take your feedback (how were you using it? What is the failure?) and go back through their process line to see where that defect arose.

Or, it could just be marketing hype.