Newsletter 220: Marking PET Bottles, Cutting 304L Stainless Steel Tubing, Marking Ferrite Insulators

SYNRAD, INC. - http://www.synrad.com
Thursday, September 3, 2009
Issue 220

Applications at a glance


	Marking Plastic PET Bottles		Cutting 304L Stainless Steel Tubing	Marking Ferrite Insulators

SYNRAD's sealed CO2 lasers are used in a variety of industrial processes including cutting, welding, drilling, and marking. This news brief showcases some of the interesting materials and products that are processed daily by Synrad's line of CO2 lasers and marking heads.

Marking Plastic PET Bottles

Polyethylene terephthalate, better known as PET, is a naturally clear plastic that provides a good boundary against many common liquids while minimizing the absorption of plastic residuals into the liquid. As a result, it is widely used to manufacture different types of beverage bottles, such as those used for soft drinks and bottled water.

PET is a thermoplastic, which means that the plastic typically exhibits some melting, but does not chemically degrade when marked by CO2 lasers. The resulting marks have a white semi-transparent look, and are slightly raised above the surface, providing a nice tactile feel to the bottle. The most common CO2 laser application during bottling is marking simple expiration date codes, but intricate logos and decorations are easily marked as well. This provides added flexibility to bottle design, as no new molds are needed for each raised pattern required on the bottle's surface.

For this application, a bottle was marked with a flower pattern. The marking setup consisted of an FH Flyer marking head and a 48-2 (25 W) laser controlled by our WinMark Pro laser marking software. The Flyer head was equipped with a 200 mm focal length lens that provides a 290 µm (0.011") spot size and a large (5 mm) depth of focus. This was important to get consistent mark quality across the curved surface of the bottle. A depth of focus that is too shallow would cause marks to fade out along the far edges.

Flower Graphic Marked on PET Bottle

This plastic PET bottle was marked with a 25W laser at a velocity of 40"/second. The flower graphic was completed in a cycle time of 1.80 seconds.

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The mark object consisted of a vector graphic imported into WinMark Pro from a .plt file. For this particular object, the mark Velocity was set to 1016 millimeters per second (40 inches/sec) and the Power was set to provide 25 W. The resulting white semi-transparent flower graphic was marked in a cycle time of 1.80 seconds.

Cutting 304L Stainless Steel Tubing Type 304L stainless steel is a variation of 304 stainless, containing a maximum carbon content of 0.03%, which eliminates chromium carbide precipitation when exposed to the high temperatures inherent in welding operations. Carbide precipitation leads to localized corrosion and cracking, which is not desirable considering that 304L stainless tubing is frequently used in food preparation equipment and to transport solutions used in textile, pharmaceutical, and chemical processing industries. For this application, we were asked to laser cut Type 304L stainless tubing. Although this tubing will not be welded, it is subjected to other forming operations that could lead to stress cracking if the heat-affected zone (HAZ) in the cut region becomes too large. Our cutting setup consisted of a Firestar f400 laser delivering its beam through X-Y "flying optics" into a cutting head holding a 63.5 mm (2.5") positive meniscus lens. This lens provides a 100-micron (0.004") spot with a 1.8 mm (0.07") depth of focus. To enhance the laser cutting process, our gas assist consisted of 99.996% pure oxygen at a pressure of 5.5 bar (80 PSI).			Using 400 watts of power, we cut this 2.25" diameter Type 304L stainless tubing at a rate of 140 inches per minute in 3.03 seconds. See this application in action! (260KB) WMV Get Windows Media Player
For material handling, we held the 57.15 mm (2.25") diameter tubing in a rotary chuck turning at 20 RPM. At a power output of 400 watts, we were able to cut through the 1.27 mm (0.050") thick Type 304L tubing in one revolution, which translates to a linear cut speed of 3.56 meters per minute (140 inches/minute), in a cycle time of 3.03 seconds per part. As shown in the photograph, the cut edge is clean with no dross and a near non-existent HAZ region.

Marking Ferrite Insulators

Ferrite is a class of ceramic electromagnetic material known for its high magnetic permeability and high electrical resistivity. Ferrite toroids are used as cores for transformers and inductors in power conversion devices while ferrite beads are commonly used as RF chokes or EMI (electromagnetic interference) suppressors. Although ferrite varies in color from silver-gray to black, enough contrast is created by the CO2 laser interaction to provide visible text and readable 2D Data Matrix codes.

To mark the ferrite insulator core shown in the photograph, we fitted an FH Series marking head with a 125 mm lens to obtain a 180-micron (0.007") spot with a 3 mm (0.118") depth of focus. This allowed us to mark 15 mil (0.015") cells with an overall 2D code size of 4.6 mm (0.18") square using 25 watts of power at a mark velocity of 18 inches per second.

We engraved this contrasting 2D code on a ferrite insulator core at a speed of 18 inches per second using 25W of power in an overall cycle time of 0.48 seconds.

Because filled cells sometimes overlap unfilled cells, leading to poor print growth values during verification, careful attention to resolution settings is important. In this case, we set a marking Resolution of 250 to prevent overscanning. These settings resulted in the completion of a raster-scanned code in a cycle time of 0.48 seconds. Using an RVSI CM4000 vision system, we obtained read rates averaging nine milliseconds while achieving an overall AIM (Association for Automatic Identification and Mobility) grade of "A" AIM's Bar Code Print Quality Guideline allows verification systems to grade directly marked codes for acceptability with grades ranging from A to F for Contrast, Axial Uniformity, Print Growth, and Error Correction properties.

Browse Synrad's Applications Database

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