Direct Part Marking (DPM) is a process of permanently marking parts with product information, including serial numbers, part numbers, date codes, and barcodes. This is done in order to enable permanent tracing of components over their entire life cycle.
The interpretation of “permanent” often depends on the context in which the part is used. In the aerospace industry, an aircraft part can be in service for over 30 years. In the telecommunications and computer industries, the life cycle can only be a few years.
DPM is widely used by automotive, aerospace, and electronics manufacturers to provide reliable part identification. This can be helpful for data logging for security and guarantee reasons and meet the legal requirements. In the military industry, too, physical markings are often required in connection with the unique identification of the object.
There are many ways to encode information into machine-readable code. The preferred codes are the Data Matrix code and the QR code. Data matrix codes are used by Motorola and NASA, among others, for marking parts. In the automotive industry, QR codes are also used in addition to the Data Matrix code. This is due to the fact that this code was originally developed by Denso Wave (a global manufacturer of automotive components) to trace components in vehicle construction.
Methods for producing permanent markings include embossing, casting, forging, etching, laser marking, adhesives or adhesive labels, ink jets, liquid metal jets or milling.
The marking method depends on various factors:
- Component function:
Non-disruptive marking methods are recommended for components that are used in safety-critical applications such as aircraft engines or high-pressure and high-voltage systems.
- Part geometry:
It is more difficult to place a DataMatrix code on a curved surface than on a flat surface.
Highly polished metal surfaces should be textured before marking to reduce glare. The structured area should be one symbol width greater than the marking limits.
- Part size:
If a 2D code is used, the size of the part is not a relevant factor as it reduces the available marking area.
- Operating environment:
It should be checked whether the marking method used can survive in the intended environment and remain legible for the life cycle of the part.
- Surface roughness / finish:
A rough surface is more difficult for a 2D barcode because the data elements must be recognized accordingly. Laser and scribing systems can achieve legible marking in rougher surfaces.
- Surface thickness:
Surface thickness must be taken into account when making markings to prevent deformation or excessive weakening of the part.
- Manufacturing conditions:
The marking method must be selected so that the generated code survives the manufacturing conditions. In particular, rough environmental conditions (high temperatures, chemical solvents) represent a challenge.