SYNRAD, INC. - http://www.synrad.com  
Thursday, February 16, 2006
Issue 131

Cutting Polyester Film

Marking Polycarbonate Filter Cases

 Trepanning Rubber Seals

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.


Cutting Polyester Film

One of the many uses for polyester is in the production of polyester film, which is widely used in the printing and graphics arts industries due to its durability and scuff resistance as well as its ink anchorage and color definition properties. Polyester film is printed by any number of methods including flexography, offset, silk-screen, and digital label presses. Polyester provides a high gloss and extremely sharp print definition, which makes it the perfect material for optical encoder discs where precisely printed light and dark regions within multiple tracks are key elements that allow the encoder to determine the absolute position of mechanical elements connected to its input.





These optical encoder discs, printed on 15 mil polyester film, are precisely laser-trimmed to
size using 60 watts of power at a speed of
22 inches per second.

In order to complete the manufacturing process, each encoder disc must be cut or trimmed from a larger printed sheet. Fortunately, polyester film reacts as well to CO2 laser energy as it does to ink. For this study, we were asked to trim 15 mil (0.015” or 0.38 mm) thick polyester discs using 60 watts of power. Based on the sheet size and overall ease of integration, we chose to use a Firestar t-Series laser for power and an FH Series Index marking head for beam delivery. Equipped with a 125-mm focusing optic, the FH head can place a 180-micron (0.007”) diameter beam anywhere within a maximum mark field of 85 mm × 105 mm (3.4” × 4.2”) with a position accuracy of 0.02 mm (0.0007”).

At a power level of 60 watts and a galvanometer speed of 558 mm/second (22”/s), we cut both the inner disk (left) and outer disc (right) from the film sheet in an overall cycle time of 0.3 seconds. As shown in the photo, the polyester film exhibits an exceptionally clean, high-quality edge with no dross, discoloration, or vapor deposition present.


Marking Polycarbonate Filter Cases

Polycarbonate is commonly used to fabricate products such as bulletproof windows, automotive headlamp covers, CDs/DVDs, and housings for appliances, cell phones, and computers. Polycarbonate, as do most plastics, processes very well with CO2 lasers because of its high absorptivity. As a general rule, marking polycarbonate provides engraved marks with some contrast, while multiple passes at higher powers exhibit a darker contrast. When marking transparent, opaque, or colored polycarbonates using laser powers less than 10 watts, it is possible to achieve a condition where the surface boils—then rapidly cools—leaving a white, raised mark that contrasts with the surrounding surface.







This translucent polycarbonate sample exhibits
a nicely contrasting mark using 10 watts at a
speed of 20 inches per second.

We obtained this type of contrasting mark on these polycarbonate filter cases using a Synrad 48 Series laser, FH Series marking head, and our WinMark Pro laser marking software. For this project, we created an eight-digit text object and set the Auto Text Type to Date Code Text. To generate the automatic date format, we created a custom date string using WinMark Pro’s format identifiers for a two-digit day, two-digit month, and four-digit year. Before each mark, WinMark Pro reads the system date and time, then generates the correct date (and/or time) information.

To create the mark, we specified an FH Series 125 mm lens that provides a 180-micron (0.007”) spot with a 3 mm (0.118“) depth of field. The ratio of character height (3 mm or 0.108”) to spot size (0.18 mm) is over twice the recommended ratio of 7:1, which allows the formation of sharp, crisp alphanumeric text. With mark power set to 10 watts and a mark Velocity of 508 mm/second (20 in/sec), we obtained cycle times of 0.09 seconds per part.


Trepanning Rubber Seals

Modern rubber seals are found in many automotive sealing applications. On the typical passenger vehicle, there are a variety of seal constructions and material compounds—one for sunroofs, another for doors, and yet another for trunk lids. These “rubber” seals are not produced from natural rubber, but are primarily manufactured from polymer compounds such as silicone, EPDM (Ethylene Propylene Diene Monomer), or TPV (ThermoPlastic Vulcanizate).

Fortunately, rubber compounds in general (those listed above plus butyl and neoprene) exhibit the same type of behavior when cut or marked with CO2 lasers. Rubber’s absorptivity at the CO2 wavelength is high enough that the cutting process is by vaporization—instantaneous absorption of the beam’s energy causes the rubber to simply vaporize into a gas, while CO2 laser marking produces engraved, slightly contrasting marks.







We cut these high-quality 3 mm-diameter holes through 1.8 mm (0.0725”) thick rubber seal
material using 100 watts of power in a cycle
time of 0.17 seconds per hole.


This application request tested the laser’s ability to trepan, or cut, holes in rubber door seals. The trepanning process is used to cut a circular path in cases where the required hole size is much larger than can be created by simply drilling with the laser beam. During our tests, we used an FH Series Tracker marking head coupled to a Firestar t-Series, 100 W laser. The flexibility of the Tracker head gives the system integrator the ability to design either an intermittent motion machine—where the motion of the rubber seal stops during the cut, or a continuous motion machine—where the cut is made “on-the-fly” as the seal continues to move through the machine.

We setup our Tracker head with a 125 mm HP (High-Power) lens that provides a 180-micron (0.007”) spot over a maximum mark field of 80 mm × 99 mm (3.2” × 3.9”). Using 100 watts of power at a Velocity of 63.5 mm per second (2.5 in/sec), we cut 3 mm (0.118”) diameter holes in a cycle time of 0.17 seconds per hole. Using the FH head’s Tracker feature, in conjunction with a minimum hole spacing of 99 mm, we could achieve line speeds of 33.5 meters per minute (110 ft/min) in a continuous motion application.


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