Newsletter 219: Marking UV/IR Coated Glass, Drilling High Density Polyethylene, Marking Zinc-Plated Steel

SYNRAD, INC. - http://www.synrad.com
Thursday, August 20, 2009
Issue 219

Applications at a glance


Marking UV/IR Coated Glass	Drilling High-Density Polyethylene	Marking Zinc-Plated 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.

Marking UV/IR Coated Glass

Standard outdoor window glass allows sunlight into your home; however, it also allows some amount of Ultraviolet (UV) and Infrared (IR) light to pass through. UV wavelengths, in particular, initiate a chemical reaction that causes fabric, carpet, and even hardwood flooring to fade over time. To prevent this potentially damaging energy from passing through the glass, several manufacturers add a coating to block these wavelengths. However, this coating can affect the production process because CO2 lasers (used to mark logos and manufacturing data on the glass) most often produce laser light at 10.6 microns in the IR wavelength band.

To demonstrate the difference in laser power and marking speed caused by these coatings (as well as to demonstrate the effectiveness of the coating), we marked both uncoated and UV/IR coated glass surfaces. For these tests, we set up marking equipment that is commonly used in the glass industry - a SYNRAD 25 W laser and an FH Flyer marking head (equipped with a 200 mm focal length lens) - all controlled by our WinMark Pro laser marking software. This setup produced a focused spot size of 290 mm (0.011") on the glass surfaces.

Our WinMark Pro mark file consisted of 0.20" (5.1 mm) high Arial TrueType® and Simple stroke text objects. For the uncoated glass surface, the mark Velocity property was set to 10 inches per second (254 mm/sec). The total cycle time to perform the resulting mark was 2.69 seconds.

For the UV/IR coated glass surface, the mark Velocity was lowered to three inches/second (76 mm/sec) to achieve the same quality mark. Total cycle time for this mark was 8.91 seconds. At faster velocities, the UV/IR coating reflected a large quantity of the laser energy causing inconsistent marking.

Laser Marked Uncoated Glass Sample

An uncoated glass sample was marked using a 25W laser. The entire mark was produced in a cycle time of 2.69 seconds.

Laser Marked UV-Coated Glass

Similar mark quality was achieved on the UV/IR coated glass sample, but mark speed was reduced.This mark was made in 8.91 seconds.

The results of our testing have shown that marking UV/IR coated glass with CO2 lasers can be done; however, mark speed is reduced by about 70% compared to uncoated glass. For glass marking, there is an approximately linear relationship for power versus speed, so to obtain the same mark velocity and product throughput when marking UV/IR glass, power must be increased to around 80 W to get the same results as uncoated glass marked using 25 W of power.

Drilling High-Density Polyethylene

Products based on high-density polyethylene (HDPE) are commonplace in everyday life. Its purity means that HDPE products are approved by the FDA and USDA for direct contact food-grade use. Blow-molded HDPE jugs are used to package milk, water, and fruit juices, as well as detergents and motor oils. Injection molding processes produce HDPE yogurt and margarine containers. Because HDPE also resists solvents and acids, sheets of HDPE are used as containment liners to prevent soil and groundwater contamination in sanitary landfills.

In this laser-drilling application, the task was to drill 0.71 mm (0.028") diameter holes through the rim of blow-molded HDPE containers. Our drilling setup consisted of a Firestar f201 (200W) laser and a fixed beam delivery system containing a 127 mm (5.0") positive meniscus lens.

Laser-Drilled Hole in HDPE Container

This precise 0.028" diameter hole was drilled through the rim of an HDPE container using 200 watts of power and 50 PSI of air assist in a cycle time of 0.22 seconds per hole.

This optic provides a 203 micron (0.008") focused spot with a 6.35 mm (0.25") depth of focus. In addition, we used an air assist at a pressure of 3.4 bar (50 PSI) to eliminate any melting or heat effect in the drilled area.

To produce the desired hole diameter of 0.71 mm (0.028") with our 127 mm lens, we fixtured the part approximately 5.1 mm (0.20") out of focus. Using a PWM frequency of 5 kHz, we set a power level of 200 watts and fired the laser for 0.22 seconds. The resulting hole diameter in the 1.8 mm (0.07") thick HDPE material meets the customer's specification precisely with no charring or melting of the surrounding material.

Marking Zinc-Plated Steel

The request for this CO2 laser application was to create permanent identifying codes and human-readable text on zinc-plated solenoid housings. Initial trials showed that variations in the zinc plating lead to inconsistencies in absorption - within the space of several millimeters, the mark would vary from being "just right" to being very over-burned. The solution was to coat the mark area of each part with a proprietary coating prior to marking. These coatings (available for glass/ceramic, metal, and plastic substrates) are applied in paint, aerosol, or label form and then permanently fused to the material surface by the intense heat created by the focused beam's extremely high power density. This change allowed us to drop the laser power requirement from 100 watts down to only 20 watts.

This permanent, high-contrast mark was created in only 2.02 seconds on a zinc-plated steel surface after applying a proprietary coating and then laser marking with 20 watts of power at a speed of 5 inches per second.

The customer's mark specification consisted of a rectangular 2D Data Matrix code (containing 21 alphanumeric characters) and three lines of part number/serial number text with a total of 31 characters. After creating and sizing the 2D code object in WinMark Pro, we entered the data string, set the 2D Barcode Shape property to Rectangle and set a 2D Barcode Circle Radius of 70%. On the Marking tab, we entered a Power, duty cycle percentage, corresponding to 20 W, and set a mark Velocity of 127 millimeters per second (5 inches/sec - IPS). For the human-readable part number information, we created a single text object using the "Simple" stroke font at a Text Height value of 1.9 mm (0.075") and used the same mark parameters as the 2D code object.

Due to the diameter of the solenoid housing, we equipped our FH Series marking head with a 200 mm flat-field lens that creates a 290-micron (0.011") spot with a 5 mm (0.196") depth of focus over the extents of the mark field. Using 20 watts of power, the 2D code - with an individual cell size measuring 0.366 mm (0.0144") - and the 31-character text string were both marked in a cycle time of 2.02 seconds per part. As shown in the photograph, this process creates a high-contrast, permanent mark that maintains consistency even across the curved surface while eliminating any mark variations due to plating quality.

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