Synrad Applications News

SYNRAD, INC. - http://www.synrad.com
Thursday, October 1, 2009
Issue 222

Applications at a glance

Marking Printed Labels
Cutting Open-Cell Polyurethane Foam
Spot Welding Stainless Steel


Laser Marking Printed Labels


Cutting Open-Cell Polyurethane Foam


Spot Welding Stainless Steel

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.


Laser Marking Printed Labels

In many packaging applications, the combination of a preprinted label and laser marking is a perfect fit. In addition to the base label color, the images on a label can include several spot colors or even a four-color process print for realistic full-color graphics. Laser marking adds the ability to add customized information including date codes or lot numbers on-the-fly at the time of actual product packaging.

A case in point is this packaging for processed meats, which consists of a self-adhesive gold foil label that is overprinted with both spot and process color. At the time the product is packaged and sealed, the manufacturer is required to mark a date code on the package. The CO2 laser makes a perfect non-contact marking tool and ablates the ink away from the gold foil, leaving an impressive gold-colored mark that matches the packaging perfectly.

    

Laser Marked Printed Packaging

Using 25 watts of power, we ablated the ink on this printed label to reveal the gold underlayer. The eight-character mark was created at a rate of 25 inches per second in a cycle time of 0.13 seconds per label.

To create the mark, we set up an FH Flyer marking head with a 370 mm lens that provides a 540-micron (0.021") spot with a 20 mm (0.788") depth of focus over the extents of a 241 mm x 297 mm (9.5" x 11.7") mark field. In our WinMark Pro laser marking software, we created an eight-character date code using the European Standard (DD.MM.YY) format. Using WinMark Pro's automated Date Code Text property forces WinMark Pro to read the computer's internal date/time clock prior to each mark so the date is always accurate. When FH Flyer is operated in stand-alone mode, Flyer's real-time clock accurately keeps track of date and time parameters, even when power to the head is cycled off.

The date code text measures 3.18 mm (0.125") tall with 0.46 mm (0.018") of Extra Character Spacing and was created using European, one of WinMark Pro's twelve built-in stroke fonts. We then set a Power, duty cycle percentage, equivalent to 25 watts and set a marking Velocity of 635 millimeters per second (25 inches/second). At these parameters, we cleanly ablated the ink away from the gold label in a cycle time of 0.13 seconds per label.


Cutting Open-Cell Polyurethane Foam

Open-cell polyurethane foams are used in numerous products including particulate filters, furniture cushions, bedding, and instrument packaging. In addition to its mechanical properties, polyurethane has excellent acoustical properties and is frequently used for sound control and dampening.

We performed tests on two different types of open-cell polyurethane foam to determine optimum cut speeds using 100 watts and 200 watts of CO2 power. The first material was a 3.2 mm (0.126") thick medium-density foam while the other type was a 24.2 mm (0.95") thick sheet of low-density polyurethane.

    

Laser Cut Polyurethane Foam Sample

We cut this section of 0.126" thick medium-density polyurethane foam at a speed of 850 inches per minute using our 200-watt Firestar f201 laser.

Our cutting setup consisted of a cutting head mounted on an XY gantry system. The head was equipped with a 63.5 mm (2.5") positive meniscus lens that provides a 100-micron (0.004") spot with a 1.8-mm (0.07") depth of field over the extents of the cutting area. Even though the foam is thicker than the depth of focus, it waveguides well enough that cut edges are perpendicular to the surface. Our assist gas setup consisted of 2.8 bars (40 PSI) of clean, dry air from a high-purity (bottled) source.

For the medium-density 3.2 mm thick foam, we achieved cut speeds of 10.2 meters per minute (400 inches per minute) using 100 watts of power and speeds of 21.6 meters/minute (850 IPM) at the 200-watt power level. When processing the low-density 24.2 mm thick polyurethane foam with 100 watts, we cut at a rate of 1.3 meters/minute (50 IPM) and at a rate of 2.5 meters/minute (100 IPM) using 200 watts. In all cases cut edges are clean and free of any debris or discoloration.

Spot Welding Stainless Steel

This application test was performed to quantify the spot welding capability of our firestar f400 laser. The goal was to determine weld penetration depth into 1.22 mm (0.048") thick 304 stainless steel at various pulse widths.

Beam delivery for our spot welding setup consisted of a 101.6 mm (4.0") focusing lens that produces a 0.13 mm (0.005") diameter spot with a 3.1 mm (0.122") depth of focus. With an expanded incoming beam diameter of 11.3 mm (0.44"), this optical setup is equivalent to an ƒ9 lens speed where the ƒ-number equals lens focal length / incoming beam diameter at the optic.

At this material thickness, initial trials showed little difference between helium and argon assist except at weld speeds of 508 millimeters per minute (20 inches/minute) where helium penetrates deeper due to its higher ionization potential and smaller welding plume. Based on this information, we chose argon assist at a pressure of 0.34-0.69 Bars (5-10 PSI) to obtain a flow rate of 110-153 liters per minute (3.9-5.4 CFM) through a 3.2 mm (0.125") diameter nozzle.

At a power level of 400 watts, we fired pulses of 5, 10, 20, 40 and 80 milliseconds (ms) into the stainless steel. After cross-sectioning (see the accompanying close-up photographs), penetration depths and surface weld widths were measured and recorded as shown in the table below.

Pulse Width
(ms)
Penetration Depth
mm (in.)
Surface Weld Width
mm (in.)
5
0.51 (0.020)
0.36 (0.014)
10
0.56 (0.022)
0.43 (0.017)
20
0.61 (0.024)
0.61 (0.024)
40
0.71 (0.028)
0.66 (0.026)
80
0.76 (0.030)
0.84 (0.033)

The post weld analysis shows only a slight increase in penetration as pulse width is lengthened, because of increased losses due to heat conduction. The most efficient penetration into the 1.22 mm (0.048") thick 304 stainless steel is achieved with pulse durations between 5-20 ms.

 

 


    






5 and 10ms spot welds at 400W

5 ms and 10 ms spot welds at 400W.

 

20 and 40ms spot welds at 400W

20 ms and 40 ms spot welds at 400W.


80ms spot welds at 400W

80 ms spot weld at 400W.

 




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