Metals have a tendency to get dirty, to corrode and to have unexciting surface finishes. To solve these issues coatings may be applied to metals. Aluminum gets anodized, steel gets painted and stainless steel gets passivated. In all of these instances, you may have to inscribe something on these coatings or remove them altogether and that can be done by laser.
Markings may take different forms such as 2D and 1D barcodes, a brand logo or a simple alphanumeric serial number. In order to answer to the growing demand for industrial traceability, numerous metal marking techniques such as laser direct part marking (DPM) has been developed.
Laser direct part marking has many advantages here is the most commonly quoted:
- It uses no consumable
- it is easy to automate
- It requires only light maintenance.
Laserax’s laser technology experts have established, for its clients in the primary metal and the automotive industries, the parameters for perfect laser marking on a lot of metals under different conditions. If you want to know if laser direct part marking is a good fit for your project, get in touch with our laser technology experts.
There are two categories of laser marking; Laser ablation modifies the surface of the metal and laser annealing leaves it unchanged. In this post, we will focus on laser ablation.
Laser Ablation: The Controlled Vaporisation of Materials
Laser ablation is probably the marking techniques that can modify the most deeply the material about 0.5 mm per pass.
In order to ablate metals, highly intense pulses of laser light are focalized on the surface of the material. The energy transferred to the metallic surface is sufficient to remove layers of material by vaporization.
Laser marking by ablation is well-adapted to metals that are passivated, oxidized or that have been coated with a protective surface treatment. Such metals include stainless steel, anodized aluminum, painted aluminum, and painted steel.
Uncoating Anodized Aluminum with Laser Ablation
While the anodization of aluminum is mostly done to protect the metal from corrosion, it is also used to change the metal’s color for aesthetic reasons.
By proper adjustment of the laser parameters, the laser beam removes only the coating and only at precise locations. Removing the colored layer of anodization reveals the metal underneath (substrate). It provides a great contrast and an exceptional legibility of the message.
Watch a video about the uncoating of anodized aluminum.
It is also possible to remove anodization for other purposes than laser marking. You might need to contact points for electrical connections for instance. Should you want to learn more about laser cleaning and who it works, we have a post for that.
How to Prevent the Metallic Substrate from Being Ablated
The ablation phenomenon only happens when the intensity of the laser beam is superior to the material’s ablation threshold, as seen in the image below.
For a given optical power, the intensity of the laser beam can be adjusted by controlling the duration of the light pulses of the laser.
You increase the peak power of the beam (and thus the intensity transferred to the surface) by reducing the pulse duration. The intensity of the beam decreases when the pulse duration is increased.
Figure 1 - Laser parameters settings for laser ablation
The trick is to set the laser parameters so that the intensity of the beam is sufficiently high to ablate the anodization (the contaminant in figure 1) while remaining low enough so that it won’t affect the substrate, you have to attain the sweet spot. Laserax’s laser technology experts can help you with that.
Using less intense pulses is generally preferable because it limits the heating of the substrate.
Other Applications for Laser Ablation
The same basic principles hold true for laser oxide and rust removal, for localized paint removal, for laser surface preparation, for laser weld cleaning and other such applications.
Any application that requires the removal of contaminants from a substrate. Where the substrate has to remain undamaged and the contaminants have lower ablation thresholds than that of the substrate is a good fit for laser ablation cleaning.
Typical applications for laser cleaning are laser oxide and rust removal, localized paint removal, laser surface preparation, and laser weld cleaning
You can read more about laser cleaning applications in Three Industrial Laser Cleaning Applications for Metal.