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April, 2012 Laser Marking: Scratching the Surface By Jensen Huddleston, Marketing Manager, RMI Laser, LLC, Lafayette, CO
tooling and manufactured goods. These laser types were the first to be brought to the marketplace and they were quite useful for their time. Focusing solely on the laser marking side of these technolo- gies, each unit was causing Heat Affected Zones (HAZ), Recasting/ Remelt Layers, Stress Risers, and/or, Micro-Cracking. HAZ is the area of base
I
material where the microstruc- ture and properties were altered by the heat intensive marking operation. This heating, then sub- sequent cooling causes this change in the surrounding area of the marking. Recast ing/re-melt layer is the surrounding area of the marking affected by the heat. Stress risers and micro-cracking are the location of a part where stress can be concentrated. Parts, or anything for that matter, are strongest when forces are distributed evenly. If marking damages the surface or causes drastic surface irregularities, the stress is no longer distributed evenly, but rather focused on the spe- cific region and this reduction in sur- face area can propagate cracking and ultimately will lead to part failure.
Outdated Specs Many specs of the past which are
still in use today, (e.g. SAE AS478) have been written to almost exclude laser marking systems in spite of the many changes in both the industry
n the past, CO2 and Nd: YAG lasers dominated the marking,
cutting and welding of industrial
and the technology being offered. Today, direct part marking is being done more by that of Nd: YVO4 and Fiber Laser Technologies as they offer more in terms of life cycles and mark- ing controls. CO2 lasers are still very
U20 laser system set up for test.
prominent for cutting and still very useful for marking woods, papers, acrylics, leathers, fabrics and other materials typically used in industries like Gifts and Awards. Nd: YAG has mostly been phased out as the Nd: YVO4 laser marking systems offer far better life cycles for both the crystal and the diode, while also offering the same benefits for direct part marking.
Fiber Lasers Fiber Lasers have really taken
off in the last few years with the claim of 50,000 to 100,000 hours Mean Time Between Failure (MTBF) but there are limitations and issues that this technology causes when it comes to marking sensitive compo- nents or when there is a requirement
for surface marking, without any surface degradation. These issues and specs have inhibited companies from utilizing laser marking and they are instead using Dot Peen, Chemical/Acid Etching, or Ink-Jet printing. Each of these methods requires constant maintenance, while using up consumables, and do not offer the same bene- fits that laser marking does. Dot Peen is fast but it is impact marking and will cause micro- cracking and stress risers, and only provides the ability to mark basic alpha-numerics and low grade 2D Data Matrices. Chemical/Acid etching requires the disposal of the chemicals after use and also creates the need for stencils to be made after 20- 30 markings. If serialization is need- ed, a new stencil will need to be made each time and the marking is not consistent which increases the reject rate on finished goods. Ink-Jets are fast and offer the full RGB or CMYK color swatches, but they require con- sumable inks, daily maintenance, and the ink must be baked on after- wards to ensure permanence. However, in time, these markings will fade out or in some cases, will completely disappear. To settle these disparate theo-
ries, RMI Laser had a third party perform metallurgical surface analy- sis on three different laser marks. These markings were performed on a 1-in. Titanium tube that is used for fuel lines on airplanes, chosen because they have very strict stan-
dards for surface irregularities and are currently not utilizing lasers for marking in the existing assembly or automated processes. The markings were performed by RMI Laser’s U- 20, 20 Watt Nd: YVO4 laser marker, the UF-30, 30 Watt Fiber laser mark- er, and the UM-1, 1 Watt Nd: YAG
Photomicrograph showing laser- drilled holes that form letters.
laser marker. There were two mark- ings each, on two different tubes, one which would be a faster cycle time and lesser contrast, and the other
Tubing as marked in test.
with extremely high contrast and slower cycle times. This test shows that the UF-30
Fiber Laser is causing the most sur- face irregularities and the largest
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