Newsletter 146: Trepanning Rubber, Marking Polypropylene, Cutting Leather

SYNRAD, INC. - http://www.synrad.com
Thursday, September 21, 2006
Issue 146


Trepanning Rubber Weatherstripping	Batch Marking Polypropylene	Laser Cutting Leather

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.

Trepanning Rubber Weatherstripping

Rubber weatherstripping, as found in many automotive and industrial applications, is not produced from natural rubber, but is manufactured primarily from polymer compounds such as silicone, EPDM (Ethylene Propylene Diene Monomer), or TPV (ThermoPlastic Vulcanizate). Although cut speeds vary slightly depending on the exact chemical makeup, rubber compounds in general (those listed above plus butyl and neoprene) exhibit similar 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 high-quality 3 mm-diameter holes through
1.3 mm (0.05”) thick rubber weatherstripping
using 200 watts of power in a cycle time of
0.2 seconds per hole.

This application trial was performed to test the laser’s ability to trepan, or cut, 3 mm (0.118”) diameter holes in 1.3 mm (0.05”) thick weatherstripping as it is extruded during the manufacturing process. Our test setup consisted of a Firestar f201 laser focused through a 125 mm optic mounted on an FH Series Tracker marking head. The 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”). The Tracker head provides the ability to use either intermittent motion—where the weatherstripping stops during the cut, or continuous motion—where the cut is made “on-the-fly” as the material continues to move through the machine.

After creating and positioning a 3 mm circle in WinMark Pro, we set a Power (duty cycle percentage) corresponding to 200 watts and a Velocity of 50.8 mm per second (2 inches/sec). At these settings, we achieved cycle times of 0.2 seconds per cut, which equates to a tracking line speed of 28 meters per minute (91 feet/min) in a continuous motion application.

Batch Marking Polypropylene

One of the more powerful features designed into our WinMark Pro laser marking software is the ability to mark a batch or tray of products at a single time. For example, you can create a single object and then create an array of identical objects with a few keystrokes. If these objects are serialized, you can choose to mark each part in the batch with the same, or different, part numbers.

This feasibility test was to mark lot codes on a 6-up polypropylene part that is later cut into six individual pieces. We began by creating two text objects using the European stroke font and set a Text Height of 3.9 mm (0.15”) with 0.5 mm (0.02”) Extra Character Spacing. After rotating both objects to the correct angles, we then created an array of one column and three rows using Array Columns and Array Rows properties and set Row Spacing to 29 mm (1.14”).

Using only 10 watts of power, we marked six lot codes on this 6-up polypropylene part in a cycle time of 0.23 seconds per part.

On the Marking tab, we set a mark Velocity of 1651 mm/second (65”/s), a Power, duty cycle percentage, corresponding to 10 watts, set Off Vector Velocity to 3810 mm/s (150”/s), and finally set the following delays to achieve crisp text marks at the specified galvo speed: Pline Start Delay—250; Pline End Delay—200; Interseg Delay—0; and Off Vector Delay to 100.

To mark the parts shown, we fitted an FH Series head with our standard 200 mm lens that produces a 290-micron (0.011”) spot with a 5 mm (0.196”) depth of focus. Using 10 watts of power, we marked the polypropylene part with six separate lot codes in a cycle time of 0.23 seconds per 6-up part. In an application with a continuously moving conveyor, we can mark these parts at a rate of 26.1 meters per minute (85.6 ft/min).

Laser Cutting Leather

Natural and synthetic fabrics are cut very well by CO₂ lasers as seen by the increasing use of lasers in the garment industry as well as in other fabric-related industries such as sailmaking. Another growing market segment for lasers is in the cutting and trimming of fabric and carpet for automotive and aircraft interiors. The laser’s non-contact cutting method eliminates tool wear and replacement and in the case of synthetic materials, the cut edge is sealed, which prevents fraying.

The first example shows a section of 1.9-mm (0.07”) thick leather suitable for a seat covering or heavyweight jacket. The cut edge, which is usually not visible in the final product, exhibits the type of edge charring often seen when laser cutting leather. It is important to note however, that the material facing itself does not exhibit any charring or discoloration. The second photo shows a piece of suede leather measuring 0.75 mm (0.03”) thick. Notice how the suede material exhibits a cleanly cut edge with no discoloration.

We setup our applications test using a Firestar f201 laser with the beam directed into an X-Y flying optics system. The cutting head was equipped with a 63.5 mm (2.5”) positive meniscus lens that creates a 100-micron (0.004”) focused spot with a 1.8 mm (0.07”) depth of field.

This leather sample, measuring 0.07” thick, was cut at a speed of 450 IPM using 200 watts of power.

We cut this 0.03” thick suede leather material
using 200 watts at a cut speed of 1000 IPM.

The final step was to apply an air assist at 2.8 bars (40 PSI) coaxially with the beam through the nozzle. For laser processing, we highly recommend that assist air be bottled breathing grade; compressed shop air may only be used when it is dried and filtered to better than 99.9950% purity, oil- and water-free, and particulate filtered to less than 1.0 micron.

At a power level of 100 watts, we cut the thicker 1.9 mm leather at a speed of 5.7 meters per minute (225 inches per minute – IPM). Using 200 watts of power, we obtained cut speeds of 11.4 meters/ minute (450 IPM). When processing the 0.75-mm thick suede leather, we achieved cut speeds of 12.7 meters/minute (500 IPM) using 100 watts and speeds of 25.4 meters/minute (1000 IPM) using 200 watts of power.

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Synrad, Inc.

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Mukilteo, WA 98275

Tel: 1-425-349-3500

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