SYNRAD, INC. - http://www.synrad.com  
Thursday, September 30, 2004
Issue 97

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.

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 accompanying diagram illustrates heat transfer profiles of both low-energy (arc) and high-energy (laser) weld processes.

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. Major applications for sub-kilowatt lasers are in precision 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.

Cutting Carbon Steel with 400 Watts

Carbon steel (often referred to as mild steel) is the most common type of metal cut by lasers because it provides high cut speeds and good edge quality. Laser cutting steel is done in conjunction with an oxygen assist gas delivered coaxially with the focused beam. The oxygen assist augments the melt shearing cut process by reacting exothermally with the steel to provide additional cut energy and to force molten metal through the cut kerf under pressure. This action creates a striation pattern of vertical lines caused by periodic ejection of molten material, which is characteristic of the melt shearing process.

As an example, we cut this 0.104” thick carbon steel using 400 watts of power at a speed of 70 inches per minute (IPM). The cut edge is exceptionally clean with no underside dross; note the striation pattern of the cut edges in the close-up photo. This metal cutting quality is due in part to our new Firestar f400 laser since power density, not laser wavelength, ultimately determines cutting performance. In this application, the f400’s power density at the focal point was on the order of 49–52 million watts per square inch, which is far above the 5 MW/in² threshold required for vaporizing mild and stainless steels. This intense power density is a direct result of the f400’s outstanding mode (TEM₀₀, 98% purity) and beam quality (M² value less than 1.1 ±0.1) specifications.

Marking Plastic

Marking and cutting plastics are excellent CO₂ laser applications since plastics exhibit high absorptivity to the 10.6 µm CO₂ wavelength. Plastics also possess low thermal conductivity meaning that very little power is wasted in heating material outside the cut or mark area.

Plastics provide two basic types of marks: contrasting marks or engraved marks. True contrasting marks create a color change through either surface discoloration or surface melting mechanisms. Engraved marks are created by removal of the material substrate and often exhibit some contrast because the engraved depression reflects light differently than the adjacent flat surface.

The engraved mark on this plastic assembly was created with an FH Series marking head and 125 mm lens using only 10 watts of power. Focused spot size was 180 microns (0.007”) with a 3 mm (0.118”) depth of focus.

The seven-character part code was created in WinMark Pro using one of our twelve built-in stroke fonts (Simple). Text Height was set to 0.0825” and Extra Character Spacing was set to 0.01”; all other object properties were kept at their default values. At a marking Velocity of 10 inches per second, the cycle time for this mark is 0.15 seconds.

Browse Synrad's Applications Database

Search our online library for more applications of Synrad's sealed CO₂ laser technology. Sort by material, process, or industry.

http://www.synrad.com/search_apps/Default.htm

To unsubscribe, please reply to this email and type REMOVE in the subject line.

Copyright (c) 2004 SYNRAD, Inc. All rights reserved.

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.