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LASER MARKING: How to choose the best laser for your marking application

2011-08-29 Back to list
䳔Ķ>In laser marking processes, the type of material, quality of mark required, and speed will all play a role in the optimum choice of laser. Although solid-state continuous-wave and CO2 lasers are used for marking, they are generally not used to mark metal, so this article will focus on solid-state pulsed lasers. Within that category, there are several technology options when choosing a pulsed laser for marking. These include Nd:YAG, Nd:YVO4 (vanadate), and fiber lasers, each with its pros and cons.

It is also important to understand how the material to be marked absorbs laser light at the wavelength of the laser chosen. Ferrous and non-ferrous materials have excellent absorption at 1064 nm, while precious metals do so at 355 and 532 nm. Plastics also absorb the higher wavelength laser output (see Fig. 1).

FIGURE 1. The absorption of laser output at different wavelengths varies according to the materials involved.

 

Laser technologies

The Nd:YAG laser was introduced more than 25 years ago and is the workhorse of the industry. Originally these lasers were lamp-pumped, but have subsequently evolved so that diode pumping is now most common. The diode-based systems are robust with excellent mean time before failure (MTBF). Some manufacturers expect more than 35,000 hours of life prior to failure of the diodes. One advantage of Nd:YAG lasers is their beam quality, which leads to a smaller spot size of the laser. The small spot size, along with short pulses, produces high peak power that can be beneficial in deep engraving with crisp, clear marks and small characters.

The vanadate laser can emit at three different wavelengths: 1064, 532 (green), and 355 nm (blue). Vanadate lasers are also diode-pumped and deliver beam quality with pulse-to-pulse stability, making them well suited for ablation marking and heat-affected zone (HAZ) applications. One of the vanadate laser markets is day/night marking—an automotive application in which a top coating is removed to allow light to backlight buttons at night—typically ablating a top coating to expose a lower surface without damaging it.

Approximately six years ago, fiber lasers were introduced to the marking world and have been the topic of discussion in virtually every marking opportunity. The fiber laser does not have the same beam quality as Nd:YAG or vanadate lasers, which limits the amount of peak power available. The fiber laser can anneal stainless steel due to its long pulsewidth and larger spot size, putting more heat in the part to draw the carbon to the surface. It’s worth noting that there only a handful of fiber-laser manufacturers that offer the laser source to a third party for integration into a marking system.

In terms of operating costs and consumables, these three laser technologies are almost identical, so an end user can choose the optimum laser technology without having to make cost tradeoffs. One thing to keep in mind is that the output power of all solid-state lasers degrades over time, but it is possible to calibrate the system to maintain the same power in the laser as the day it left the factory. This will allow the laser to maintain the same mark quality and speed as the day it arrived and was put into production.

 

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