Newsletter 216: Cutting Nylon Plastic, Welding Stainless Steel, Marking Wine Corks

SYNRAD, INC. - http://www.synrad.com
Thursday, July 9, 2009
Issue 216

Applications at a glance


Cutting Nylon Plastic	Welding Stainless Steel	Marking Wine Corks

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 Nylon Plastic

Nylon plastic, in its fiber form, is most commonly used to replace traditional organic fibers used in products such as fabrics or ropes. However, in solid form, its abrasion resistance, durability, and light weight also make it an attractive option for manufacturing mechanical parts such as screws and gears. In addition, nylon provides corrosion resistance and electrical insulation that metal parts may lack.

Nylon plastics are thermo-polymers composed of simple linear polymer chains that are easily melted without breaking their bonds. As a result, the laser cutting process is very efficient with no chemical degradation and provides a clean cut with no charring.

Cut Nylon Sample

This 0.125" thick Nylon 6,6 sample was cleanly cut using 400W of power at a speed of 200 inches per minute.

In applications where increased strength and heat resistance is desired, a glass fill can be added to the nylon formulation. However, the polymer structure becomes more rigid and can chemically degrade when melted. As a result, cutting glass-filled nylon may result in charred cut edges.

For this particular nylon cutting application, a Synrad 400W laser was used in conjunction with an X-Y table and a cutting head outfitted with a 2.5" (63.5 mm) focal length lens that provides a 100-micron (0.004") focused spot size. The 0.125" (3.2 mm) thick plain Nylon 6,6 material was cut at a rate of 200 inches per minute (5.1 meters/minute). Clean, dry air at 50 PSI (3.5 bar) was used to shield the focusing lens and eject melt droplets. As seen in the photograph, the cut edge is cleanly cut with no signs of charring or dross.

Welding Stainless Steel

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 the 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. This means reduced thermal distortion, the ability to weld close to heat sensitive parts, and precision welding capabilities.

PCB w/ blue solder mask

These 0.036" thick stainless steel coupons were welded together with 400 watts of power at a speed of 75 IPM using argon shield gas at a flow rate of 1.0 SCFM.

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 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 400W 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.

Marking Wine Corks

For centuries, the traditional wine cork has had two basic purposes: keeping wine in the bottle and keeping oxygen out. However, in this age of advertising perhaps we could add a third purpose - branding. Wine manufacturers have branded their corks for years; however laser marking adds yet another dimension. In addition to providing consistent branding over long production runs, a laser marker allows a winery to mark or brand cork for short runs, produce custom cork for special events (like weddings or birthdays), or generate limited edition labeling. You can laser mark wine corks with any combination of text or logos, serial numbers, and even date codes.

For this application, the winery requested that we mark a bitmap graphic. Although natural cork exhibits many useful properties including non-permeability and heat insulation, the most useful feature for our purposes is that cork marks well at very low power.

We marked this grape image on wine cork using only 10W of power at a speed of 75 inches per second in a cycle time of 4.0 seconds.

Our test setup included a Synrad sealed CO2 laser, an FH Series marking head, and a copy of our WinMark Pro laser marking software. After installing a 125 mm focusing lens, which provides a 180-micron (0.007") spot with a 3 mm (0.118") depth of focus, we created a new 125 mm drawing file in WinMark Pro and then imported a bitmap image of a grape leaf.

On WinMark Pro's Marking tab, we set a Power (duty cycle percentage) corresponding to 10 watts and a mark Velocity of 1905 millimeters per second (75 inches/sec). At these settings, we marked this particular grape image in a cycle time of 4.0 seconds per cork. The lightly engraved mark displays well in sharp contrast to the cork's natural color. During this trial, we also marked several variations of the winery's logo and achieved cycle times of 1.37 seconds per mark for their filled TrueType image.

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