Historically Mil-Std-130 has been the definitive authority for permanent part marking. It covers part markings for both Human Readable Information (HRI) and Machine Readable Information (MRI). If you see Mil-Std-130 as a requirement in a contract, it may not mean that IUID is a requirement. It may simply mean that the part needs to be marked with Human Readable Data. When IUID is the specific requirement, it most often will be spelled out using DFARS clause 252.211-7007 and DFARS Final Rule 252.211-7007.
Life of the Part
One of the critical requirements is that a part mark should last the useful life of the part. The reasoning makes sense. When an item is at the end of its useful life the part mark will make reordering much easier. The other reason for permanency is encountered with items that are reworked or repaired in the field. In many cases the correct repair or refurbishment is impossible without knowing exactly the part number or serial number of the item to be worked on. The impact of this requirement means that any tag or label that is affixed to an item must be capable of withstanding everything the part may reasonably endure in its lifetime such as temperature extremes, ultraviolet light, humidity, salt-spray, chemicals, abrasion, and impacts. IUID tags are in-effect engineered-products that must therefore be specified to match these conditions. Any contractor with IUID requirements should have a specification of the materials, layout, and formatting of the data.
Testing and Verification
The most critical feature of IUID markings is the DataMatrix barcode. Organizations involved in IUID production must be equipped with specialized verification equipment. Like all barcodes, there are international standards which help define how the contrasting elements of a Datamatrix barcode are constructed from a dimensional standpoint and schematic standpoint. Additionally the data within the barcode needs to follow additional standards for data formatting. Verification and testing must support the production of the UID Tags. It is not enough to successfully scan the data using a smartphone, the barcode needs to be verified for both barcode quality and data formatting criteria and yes this equipment is expensive.
Depending on the performance requirements there may be one or more candidate materials. Practically speaking, most organizations will take a least-cost approach that delivers against the minimal requirements. Generally speaking, the least costly type of UID tags are made using industrial thermal transfer printers. On the other hand, photo-anodic processes and laser processes can be fairly expensive. Like all things in life, higher performance comes at a price.
Minimum vs Recommended Markings
There are two types of marking. Human Readable Information (HRI) is comprised of text and numbers. Machine Readable Information (MRI) is data that can be read by a machine – namely barcodes. By design, the Datamatrix barcode can be produced in very small sizes. When size or function limits the available real-estate for IUID markings, the contractor is allowed to simply mark the item with the Datamatrix barcode alone. Typically we’re talking about ½ inch square or less. Otherwise the contractor is requested to mark both MRI and HRI as part of the marking/label/tag. Once you get more than about 1 inch wide by ½ inch high this MRI + HRI mark is feasible. If you have the ability or desire (or a drawing that demands it) additional linear barcodes that repeat the HRI data may also be part of the design. In the spirit of “less is more” it is our suggestion to skip the use of linear barcodes on IUID tags if you can.
Item Unique Identification is premised on the requirement that any IUID serial number must be globally unique. There are multiple ways to generate and format the IUID data. The IUID’s uniqueness is achieved by pairing, or concatenating, the Serial Number with an Enterprise Identifier (usually in the form of a CAGE Code). This first type is known as Construct #1. To allow for improved and more explicit data management, the uniqueness of the IUID may be achieved by concatenating the Enterprise Identifier with a Part Number and a Serial Number. This second type is known as Construct #2.
Inside the barcode these Construct #1 or Construct #2 data are able to be parsed out based on how they associated, or formatted, with variables known as Data Identifiers. There are two major dialects of formatting known as FORMAT 06, and FORMAT 12. If you have the ability or desire (or a drawing that demands it) you may use FORMAT 12, but we would recommend using the more common FOMRAT 06. Whichever formatting you use, you should try to consistently use the same formatting across your product lines.