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SYNRAD, INC. - http://www.synrad.com |
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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. |
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Cutting airbag material, both single-layer and multi-layer, is a common CO2 laser application. Nylon 6,6 is the most commonly used airbag material on the market due to the lighter weight and superior energy absorption of nylon yarn. For this application trial, we were asked to determine the maximum cut speed for triple-layer woven airbag material measuring 0.71 mm (0.028) thick. The cutting head on our XY table was fitted with a 63.5 mm (2.5) positive meniscus lens that provides a 100-micron (0.004) focused spot and a 1.8 mm (0.07) depth of focus. The cutting head also provides a gas port that delivers assist gas coaxially with the laser beam through the nozzle.
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Using 400 watts of power, we achieved cut speeds of 36.8 meters per minute (1450 inches/minute) while cutting though the three-layer (0.028 thick) material using 1.7 bar (25 PSI) of clean, dry air assist. As seen in the photo, cut edges are clean and free of debris and discoloration.
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Welding processes are split into two categories: (1) low energy density, and (2) high energy density processes. Low energy density processes are those such as traditional arc and resistance welding technologies that rely on heat conduction through the material from a surface point to provide melting. High energy density processes using lasers create a heating filament, known as the keyhole, which penetrates to depth and offers two-dimensional line heating, causing a highly efficient heat transfer into the weld joint. The key advantages of laser welding are a small heat affected zone (HAZ), accurate control of heat input, and the ability to direct the beam precisely to the weld point. The benefits of these factors are reduced thermal distortion, the ability to weld close to heat sensitive parts, and precision welding capabilities. |
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Major applications for sub-kilowatt lasers are in precision-welding and heat-sensitive welding processes, such as hermetic sealing, because the typical focused beam diameter of 100 microns localizes temperature rises around the weld to fractions of an inch. We welded these stainless steel coupons using our Firestar f400 sealed CO2 laser. The 0.9 mm (0.036) thick stainless steel was fixtured with the ends tightly aligned to create a butt type weld. Because most laser welding processes do not use filler wire, but instead rely on the molten material to create the weld joint, part fit up for a laser weld must be free of any gaps or voids in order to achieve strong, consistent joints. As with conventional welding processes, creating initial spot welds at intervals along the joint helps to prevent material separation during the actual weld pass. Full weld penetration through the stainless steel was achieved using 400 watts of power at a weld speed of 1.9 meters per minute (75 inches/minute IPM). Beam delivery for this application was accomplished using a 63.5 mm (2.5) positive meniscus lens, which produced a 100-micron (0.004) spot and 1.8 mm (0.07) depth of focus. During welding, argon shield gas at a flow rate of 1.0 SCFM prevents the molten weld pool from reacting with the surrounding atmosphere. At this material thickness and weld speed, there is no difference between argon and helium assist. When welding thicker stainless material at higher speeds, helium shielding provides deeper weld penetration due to its higher ionization potential and smaller weld plume.
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Because plastics exhibit a high absorptivity to the CO2 lasers 10.6-micron wavelength, plastic cutting is one of the more common CO2 applications. Laser cutting is very efficient because the low thermal conductivity of plastic materials means that very little input power is wasted in heating the region around the cut area. There are two main types of plastics: thermoplastics, which lend themselves to being shaped and molded when hot; and thermosets (crosslinked polymers), which are shaped cold and then set by the crosslinking, or heating, process. Thermoplastics will exhibit much better cut edge quality with no apparent discoloration while the edges of thermoset materials tend to char and discolor. The table at the end of this article lists common types of thermoplastic and thermoset materials and categorizes them by the type of edge quality typically obtained when laser cut. As examples, we cut three different thermoplastic materials. The first sample, 3.4 mm (0.135) thick acrylic, was cut using 400 watts of power at a speed of 12.1 meters per minute (475 inches/minute IPM). Notice that the cut edge is clean and smooth with no discoloration or charring a typical acrylic cut! Our 3.3 mm (0.130) thick HDPE (high density polyethylene) sample was cut using 400 watts at 1.7 meters/minute (65 IPM). The cut edge is clean and char-free with only a slight melt back visible. The last thermoplastic sample was a strip of LDPE (low density polyethylene). This piece, 3.2 mm (0.125) thick, was cut using 400 watts at a speed of 2.4 meters/minute (95 IPM). Although the cut edge is clean and exhibits no charring or discoloration, it does show some melt back on both upper and lower surfaces.
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All samples were cut on our XY stage using a Firestar f400 laser. For gas assist, we used 0.7 bar (10 PSI) nitrogen for the acrylic samples and 1.4 bar (20 PSI) nitrogen when cutting the polyethylene samples. Beam delivery was via a 63.5 mm (2.5) focusing lens, which provides a 100-micron (0.004) spot size with a 1.8 mm (0.07) depth of focus.
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Synrad, Inc. 4600 Campus Place Mukilteo, WA 98275 Tel: 1-425-349-3500 Fax: 1-425-349-3667 E-mail: synrad@synrad.com |
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SYNRAD and Synrad product names are trademarks or registered trademarks of SYNRAD, Inc. All other trademarks or registered trademarks are the property of their respective owners. |
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