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Laser Marking Before Heat Treatment for Traceability

Raw material traceability has become the norm in the manufacturing industry, enabling multiple industries to trace each component from the moment raw materials enter the factory to the moment final products are shipped.

As supply chain visibility has grown increasingly important, laser marking — the most reliable solution for identification — has grown in prominence. As a technology, laser marking allows parts to be marked before hard processes such as heat treatments, and it ensures identifier reliability after the process.

But why are heat treatments so important? Valued at USD 90.7 billion in 2016 the global heat-treating market size has expanded at an annual rate of 3.5% for the past several years a clear sign that the process is growing in value.

In general, heat treatments — which include techniques like annealing, tempering, carburizing, and case hardenings — are used in different stages of the manufacturing process in industries like metalworking, machinery, and automotive. They also improve the properties of metals and alloys by heating or cooling them to often extreme temperatures, ultimately making the parts stronger as well as more durable and ductile.

All in all, laser technology has revolutionized traceability capabilities which were once limited by previous marking technologies — including labels, inkjet, and dot peen.

How do heat treatments affect traceability?

Traceability is the capacity to track parts, products, and raw materials across the supply chain along with their manufacturing information. Heat treating is a hard process that alters the microstructure of metals and alloys. It offers key benefits, but the process can also interfere with traceability.

For maximum traceability, parts need to be identified before heat treatments, and identifiers need to maintain their readability after. But heat treatments can be hard on marks, decreasing their legibility whether you’re using labels, inkjet, or dot peen.

While labels have traditionally been a prominent marking method, most labels used to track parts can’t resist heat treatment and will be damaged, lose their adhesiveness, or simply fall off, negatively impacting traceability as a result. Improvements have been made in label technology in recent years, but these improvements come with high costs associated with new tools, high levels of consumables, and increased production steps

Dot peen marks, created through micro-percussion, are typically more resilient as the mark is deeply embedded in the material, allowing these markings to resist hard processes such as heat treatments. However, the dot peen method produces low contrast markings, meaning their legibility can occasionally be impacted by hard processes.

On top of this, dot pen marks are limited to alphanumeric characters and industry codes, meaning that they can carry less information, a quality that can negatively impact traceability. On a more procedural level, the method also remains relatively slow and can bog down production lines as a result.


How to keep legible marks after heat treatments

Laser marking is often praised for its ability to achieve high-quality and high-contrast identifiers, but there’s more to it as well. Unlike labels and dot peen markings, laser marks are permanent and maintain a high level of legibility even after being subjected to heat treatments that transform product surfaces.  

When a part has been treated with heat, it undergoes thermal expansion before returning to its normal form and dimensions. As a result, many forms of identification will lose legibility. One common way to combat this outcome is by increasing the cell and code size of the identifier.

Laser marking systems can enable reliable traceability of your products even after heat treatments, by providing highly customized identifiers with adjustable sizes that allow for individual parts identification, even on non-planar surfaces.

This is why mark dimension is so critical. With other methods, like dot peening, traceability is constrained by a maximum mark size — in other words, only so much information can be fit into a mark of a particular size. Laser marking technology, in contrast, offers a wider variety of dimensions that will fit your particular needs.

To reach full traceability and maximize your identifier’s value, you’ll need to think about mark size and the level of information encoded in it. If you’re putting less information into the mark, you can go with a smaller size, but if you need the mark to carry more information, you’ll need a larger mark size.
 

Two main applications, or methods, can be used to keep marks legible after heat treatments:

  • Laser engraving. Laser engraving creates deep crevices in the material that enhance legibility, and it works with most metals, primarily steel and aluminum. However, it takes a large amount of time to create these deep crevices.
  • Laser etching. Laser etching is faster by far than laser engraving, and it is the most common marking method for heat-treated parts. This process can be used before heat treatments with excellent results if the parameters are well set.

How does a fiber laser work?

A fiber laser gets its name from the fact that its laser is produced by an optical fiber that has been treated with rare elements. These elements have unique structures that enable low energy inputs to produce high energy outputs — in other words, a strong laser effect.

A fiber laser works by sublimating the material surface to create etchings and crevices, creating more space and contrast between the sections of the marking. As a result, these marks are less likely to lose their readability after a hard process like heat treating, and can furthermore retain a high amount of information. 

While other marking methods can achieve individual part traceability before a part undergoes a hard process, laser marking maintains the high degree of legibility necessary for that level of traceability even after heat treatment. In today’s manufacturing environment, that degree of specificity, which other methods like labels and dot peen can’t achieve, is essential — if there’s a product recall, for instance, it’s possible to recall individual parts rather than entire batches.

Laser technology is the only method that can consistently achieve individual identification both before and after heat treatment without slowing down the overall supply chain. To achieve that degree of marking and keep pace with the rest of the production line, avoiding bottlenecks, the process only requires laser power between only 50W and 100W.

Dust, temperature, moisture, and other environmental factors can impact a laser’s effectiveness. IP ratings are used to guarantee that lasers operate in the ideal environment of an effectively sealed electrical enclosure. For best results, a high IP rating of around IP 67 is necessary. A cooling cabinet will also be needed to regulate the laser’s high temperature.

The importance of traceability 

Without reliable traceability, you’ll struggle to improve production efficiency and optimize product quality control — and if you’re unable to trace products before heat treating has occurred, you’re only tackling half the problem.

In today’s manufacturing environment, Industry 4.0 technologies have brought digitalization to the factory floor and created a data-driven environment that’s cost effective and highly profitable. To stay competitive in this new environment, it’s a basic fact that you need to invest in traceability.

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