Newsletter 128: Cutting Airbags, Cutting PETG, Marking Passivated Stainless Steel

SYNRAD, INC. - http://www.synrad.com
Thursday, January 5, 2006
Issue 128


Cutting Multi-Layer Airbag Material	Cutting PETG	Marking Passivated 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.

Cutting Multi-Layer
Airbag Material

We are all aware of the vital role that airbags play in augmenting automobile passenger safety. The advent of the single steering-wheel mounted airbag in the late 1980s quickly evolved into dual front airbags and today many auto manufacturers offer side-impact airbags as well as side-curtain airbags for both front seat and rear seat occupants.

Cutting single-layer and multi-layer airbag materials have long been an excellent CO₂ laser application and this particular job is no different. For this project, we were asked to trepan mounting holes that fasten the driver’s side airbag to its retaining hub inside the steering wheel. The “flying optics“ beam delivery setup consists of a 35 mm (1.4”) clear aperture cutting head mounted on an XY gantry system.

This close-up photo of the nylon airbag hub
illustrates a typical CO₂ laser cut – clean,
sealed edges with no discoloration and no
mechanical stressing of the fabric.

The cutting head holds a 63.5 mm (2.5”) positive meniscus lens and also provides a port so that assist gas is delivered coaxially with the beam through a copper nozzle. The air bag’s mounting area comprises seven layers of nylon with an overall thickness of 3 mm (0.118”). Using 200 watts of power, we achieved cut speeds of 175 inches per minute (IPM) with 2.8 bar (40 PSI) of air assist. For the 76.2 mm (3.0”) diameter center hole, this equates to a cycle time of 3.23 seconds. Each 6.3 mm (0.25”) diameter fastener hole is trepanned in a cycle time of 0.26 seconds per hole. As the photo shows, all cut edges are clean and free of debris or discoloration.

Cutting PETG

PETG, or glycol-modified polyethylene terephthalate, is a form of polyester (PET) used to create blister packaging, display units, and bottles for soaps and detergents. PETG is also approved for packaging food and pharmaceuticals. Products manufactured from PETG provide excellent clarity and impact resistance, are die-cut and thermoformed without affecting structural integrity, print easily when graphics are required, and resist stress whitening when bent. PETG offers many of the same advantages as polycarbonate, but at a much lower cost.

When considering material specifications for products that will require CO₂ laser processing such as cutting, drilling, or degating, PETG provides another distinct advantage over polycarbonate—a cleanly cut edge with no yellowing or discoloration.

This PETG sample illustrates the edge quality possible when laser cut. We cut this 0.08”
thick sheet at 75 IPM using 100 watts.

To verify this behavior, we setup our XY table to cut sheets of 2 mm (0.08”) thick PETG. For beam delivery, we chose 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 focus. Clean, dry air at 5.5 bar (80 PSI) was used as gas assist to remove vapor and molten material from the cut area. At a power level of 100 watts, we achieved cut speeds of 1.9 meters per minute (75 inches/minute). Edge quality, as shown in the photo, is clean with a slight amount of underside dross. Note the clarity of the PETG’s cut edge; it exhibits none of the yellowing or vapor deposition that is often present on polycarbonates.

Marking Passivated Stainless Steel

Passivated stainless steel is stainless that has been chemically treated with a mild acidic solution to dissolve iron compounds embedded in the steel during forming or machining. The passivation process removes iron contamination created when microscopic particles of iron flake off the tooling and also aids the renewal of the stainless steel’s corrosion-resistant, protective oxide film.

In order to mark these stainless steel pipe repair clamps, we setup our FH Series marking head with a 200 mm focusing lens. The 200 mm optic offers two benefits in this particular case. First, the large 134 mm by 165 mm (5.3” × 6.5”) field size easily accommodates the necessary data about the part as well as manufacturer information. The second benefit is that the 5 mm (0.197”) depth of focus helps to maintain the required power density for marking across the curvature of the clamp surface.

We marked this permanent, high-contrast image
on stainless steel with 200 watts of power at a
speed of 3 inches per second. Cycle time was
11.34 seconds per part.

All text objects in the mark file use WinMark Pro’s “Simple” stroke font and Text Height values range from 2.6 mm (0.102”) to 6.8 mm (0.269”). The manufacturer’s logo was created in a CAD program and imported directly into WinMark as a DXF file. Using 200 watts of power at a Velocity of 3 inches per second (IPS), we marked the information shown in the photograph in a cycle time of 11.34 seconds.

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