Direct Part Marking: Enabling Cradle-to-Grave Traceability

Product traceability over its complete lifecycle is one of the key issues driving marking technology today. Manufacturers are looking for cradle-to-grave traceability to improve product quality and make sure all their suppliers fall in line with quality standards. Oh, and let’s not forget they also want to make it easier and less costly to engage in product recalls.

A variety of marking methods are available, but in my book, laser marking is the fastest and cleanest marking technology, with the added benefits of flexible automation, improved environmental profile, and low cost of ownership.

Direct part marking basics

What is direct part marking (DPM)? Simple: making a mark directly on the part. Not on a label which goes onto the part, but on the part itself. Non-direct marking techniques like labels don’t guarantee lifelong traceability since the information printed on a sticker may unreadable through wear or even detached altogether. So, more and more companies are migrating to direct part marking, which permanently marks the parts with a serial code and other important data.

There are a few methods being used for DPM today, including laser marking, abrasive blasting, dot peen, stamping, electro-chemical etching, and ink jet. So how does one determine which technique to use? It will depend on a variety of factors, including material type, part function, part geometry, surface finish/roughness, mark quality, mark dimension/part size, mark serialization, and coating thickness.

There are also production line implementation considerations to be taken into account, like whether the part is moving or static, what access you have to the part, what to do if there are multiple materials or point of use, and remote operations and programming.

Consider these factors as you evaluate your DPM options:

• Material type – Fragile materials require a non-contact method that won’t damage the surface beyond making the mark itself. Dot peen cannot mark plastics. Ink won’t adhere to some plastics.
• Part function – Non-intrusive marking methods are recommended for parts used in safety critical, or high pressure/high stress applications like aircraft engines. Ink cannot be used for medical parts. Wear resistant marks are required for automotive applications. Medical passivation requires chemically resistant marks.
• Part geometry – It is more difficult to place a serial code on a curved surface than it is on a flat surface. In most cases, however, the serial code is small in comparison to the curvature of the part. Recessed mark aresa, and marks made on different levels/areas (for example, for electrical breakers) will affect the type of marking system that should be used.
• Surface finish/roughness ­– Highly polished metal surfaces and, conversely, rough surfaces prove more difficult to read marks like serial codes. Therefore, additional techniques to roughen (in the case of polished) or smooth the surface (if too rough) may be required.
• Mark dimensions/ part size – The finished size of the serial code to be marked is important to consider when determining which DPM to use. Lasers provide excellent resolution and are infinitely scalable within field size.
• Mark content (text, graphics, codes) ­­– All techniques do well with alphanumeric characters; dot peen and ink jet struggle making logos.
• Coating thickness – Is there a plating/coating on the part? If so, the thickness of that coating must be taken into account when applying intrusive markings to prevent deformation or excessive weakening of the part. This is most often seen in the electronics industry with gold or nickel plated parts, but is also a consideration for small parts in other industries.
• Mark serialization – Lasers can easily handle barcode serialization, custom text strings, and database connection, while inkjet and dot peen tend to be simple systems, incapable of that kind of flexibility.
• Mark quality – It may sound silly, but mark quality matters not only for readability/traceability purposes, but also for perceived quality of the finished part. Ink jet and dot peen struggle with mark quality and visibility.
• Environmental profile – Ink jet and chemical etching both require the use toxic chemicals; lasers are perceived as a “greener” technology.

Laser direct part marking provides a solution for all of the considerations. A variety of laser marking techniques are available, including laser etching, engraving, annealing, or bleaching. Regular readers of this blog will know that each technique has been covered in an earlier post, but to sum it up the best laser technology depends upon the application, mark type needed, and material to be marked.