Marking UID Codes

"Tip Processing" Applied to Drilling

Cutting Canvas Fabric

Marking UID Codes

UID (Unique Identification) is a globally unique "part identifier" containing data elements used to track the history of Department of Defense products throughout their service life cycle. UID use is a mandatory U.S. Department of Defense (DoD) requirement for all solicitations issued on or after Jan. 1, 2005.

A UID code is formed by combining the manufacturer's unique identifier with the specific part and serial numbers of the piece to be tracked. This UID data string is then encoded into a 2D Data Matrix^TM ECC200 symbol for marking. Because the UID code is critical to tracking the part’s history, a permanent mark is necessary. This requirement makes CO₂ laser marking the leading option for creating UID codes.

For metals, such as aluminum, brass, or copper that can't be marked directly by CO₂ lasers, or in situations where a lower power (< 100W) laser is being used, TherMark^TM laser markable coatings provide high contrast, permanent marks on a variety of different metals. The heat generated by the laser beam bonds the coating into the surface of the part, leaving a permanent black mark. After marking is complete, the excess coating is removed. The UID code shown here was marked on an aluminum frame covered with TherMark tape (that can be machine applied) using a Synrad laser and an FH Flyer marking head with our WinMark Pro marking software. The code measures 7.6 mm by 7.6 mm (0.3" x 0.3") square, with individual cells measuring 13.6 mils (0.35 mm or 0.0136").

The FH Flyer head used a 125 mm focal length lens to get a 180-micron (0.007") diameter spot size. To mark the 39-character 2D code, we specified a Power value of 25 watts, a Velocity of 127 millimeters per second (5 inches/sec) and a Resolution value of 600 scan lines per inch. The total marking time to create this permanent grade "A" UID code was 6.92 seconds.

For further information on Department of Defense UID requirements, as well as other applicable marking standards and specifications (MIL, NASA, ISO/IEC) for UID and Machine Readable Information (MRI), see Synrad's UID information page at: http://www.synrad.com/UID/dod_uid.htm.

"Tip Processing" Applied to Drilling

CO₂ lasers excel at drilling small holes (small defined as less than 0.01" in diameter). Small holes are drilled directly without trepanning, resulting in reduced cycle times. Direct drilling also highlights one of the unique characteristics of lasers - the focused spot from a single laser can produce a range of hole sizes in a range of different materials.

The term "tip processing" means that only the central part of the gaussian beam is used for drilling. As the circular diameter of the gaussian beam decreases, the power density at the outer edge increases. This power density level corresponds to an effective beam diameter. Every material has a threshold of power density required for processing; below this level, the material is unaffected, hence the term "tip processing".

Ultimately, the wavelength of the laser will limit how small a focused spot can be. For a Synrad laser, the 10.6 micron CO₂ wavelength allows spot sizes as small as 100 microns without the addition of specialized optics. With a properly sized expander/collimator and an aspheric lens however, spot sizes down to 25-30 microns (roughly 2.5 times the CO₂ wavelength) are possible. With a smaller diameter beam, power density is concentrated in a smaller area resulting in a smaller heated area.

In the case of the polyacetal nozzles shown in the photo above, a burst or train of pulses from the laser delivered a precise amount of energy into the material. The final hole diameter depends on where that energy level matches the threshold of the material on the beam's gaussian profile. Additionally, the number of pulses, pulse duration, and pulse frequency enter into the equation. Alter the number of pulses to make small increases in hole diameter; change pulse duration and/or frequency to create larger holes. In many cases, you can hold laser power to a constant value while changing only the laser's pulsing characteristics. To produce holes larger than the spot diameter, use excessive pulse power to enlarge the hole via heat conduction. In the case of larger holes, assist gas is not required since it can disrupt the drilling process causing ragged outer edges.

In the case of the polyacetal plastic shown
here, nozzle diameters ranged from 75 microns
to over 300 microns. This variety of hole
diameters is due to two features of the laser:
(1) the Gaussian mode of the beam, and (2) the
fine energy input control.

As shown in the illustration above, the method
of drilling a hole smaller than the spot size is
to precisely control the laser's energy input in combination with a high threshold material.

Cutting Canvas Fabric

Cotton canvas fabric is used in a variety of indoor and outdoor products spanning the alphabet from awnings to upholstery. As is the case with most fabrics, laser cutting provides a sealed edge that resists fraying, which eliminates the need for additional manufacturing steps to seal or tape mechanically cut edges.

This application test calls for cutting 22 mil, 9.5-ounce canvas in order to determine edge quality and cut speeds at various laser powers. Our cutting setup consisted of a Synrad Firestar laser mounted on a "flying optics" XY table. The X- and Y-axis flying mirrors direct the beam down through the cutting head as it traverses the extents of a 0.5-meter square cutting area.

The 22-mil (0.56 mm) material thickness narrows the optics choice to a 63.5 mm (2.5") positive meniscus lens that produces a 100-micron (0.004") spot with a 1.8 mm (0.07") depth of focus. For assist gas, we chose clean, dry air (CDA) at a pressure of 1.7 bars (25 PSI).

After setting 25 watts of power, we achieved speeds of 2.54 meters per minute (100"/min). We ran this sample at other power levels to demonstrate the linear cut speed as power is increased. Using 50 watts, our cut speed was 5.08 meters/minute (200"/min) and at 100 watts, we obtained cut rates of 10.16 meters/minute (400"/min). On all samples, the edges are cleanly cut with only very slight discoloration on the edge itself.