Benefits and Disadvantages of Marking with Beam-Steered Lasers

This year, over 1/3rd of all material processing lasers will be installed for product or combo marking applications. Since their introduction in the early-1970's, laser engravers have evolved as an efficient tool for manufacturers who need a collaboration of speed, longevity, and image flexibility not accessible from more conventional etching technologies.

Two engraving system designs have emerged with notably dissimilar strengths and weaknesses. Earnest consideration of these laser and imaging optics combinations can provide the ideal tool for a wide range of engraving requirements.

===Process Fundamentals===

Laser etching is a thermal process that employs a high-intensity beam of focused laser light to fabricate a contrasting mark. The laser beam increases the surface temperature to bring about either a pigment change in the material and/or discharge material by vaporization to engrave the surface. Both marking system configurations use this basis of surface modification but contrast in the method used to project the laser beam and construct the etching image.

The beam-steered laser marker supplies the optimal degree of image coordination. To devise the marking image, two beam-steering mirrors installed on high-speed, computer-controlled galvanometers direct the laser beam across the target surface. Each galvanometer supplies one axis of beam movement in the etching field. The beam projects through a multi-element, flat-field lens assembly after reflecting off the final steering mirror. The lens assembly focuses the laser light to accomplish the best power density possible on the work surface while maintaining the focused spot travel on a flat plane. The laser output is gated in the middle of etching strokes. This design offers the user the benefits of a computer generated marking image and utilization of the entire laser output for the best marking power achievable.

The mask or "stencil" etching system sacrifices image quality and variety for compellingly increased etching speed. The marking image is created by enlarging the laser beam, projecting it through a copper stencil of the desired image, and refocusing the beam on the target surface to "burn" the image into the material. A single pulse of the laser creates the whole image. If the alphanumeric characters must be altered part-to-part, (i.e., serialization, etc.), computer-controlled rotary stencil wheels index the characters. This method is aesthetically limiting in that images exhibit a "stencil" appearance with breaks in the marking lines. Since the mask blocks a high percentage of the laser beam, engraving power and resultant surface penetration is limited.

===Laser and Imaging combinations===

Beam-steered Nd:YAG
The collaboration of the Nd:YAG (Neodymium:Yttrium Aluminum Garnet) laser and the beam-steered delivery optics marks the widest range of materials and supplies the versatility of computer controlled image generation.

Nd:YAG lasers amplify light in the near-infrared at 1.06 mm. Tinny items absorb a comparatively high percentage of the light in this region of the spectrum. In the pulsed mode, the Nd:YAG laser produces peak powers considerably higher than the normal continuous-wave output. A 90 watt CW Nd:YAG laser, pulsed at 1 kHz, will emit a train of pulses with peak powers of 110,000 watts. The Nd:YAG lasers ability to emulate an "optical capacitor" provides the power imperious to vaporize metallics and other items. The high peak power will vaporize material up to 0.005 inches deep in a single pass or better with multiple passes. The non-metallic items normally associated with the far-infrared wavelength of the CO2 laser are mostly extremely reflective to the Nd:YAG. However, the high peak power of the Nd:YAG can repeatedly overcome the higher reflectivity. Some overlap does occur amidst abundant plastics that absorb both wavelengths equally well.

The beam-steered marker can regenerate essentially any vector graphic image with adjustable line widths and images as small as 0.010 inch or less. In addition, the computer can instantly change any graphic element or the whole engraving program before a new part is positioned for etching.
The Nd:YAG laser offers a greater range of adjustable Process variables to accomplish a specific material modification but at a correspondingly higher purchase price than the CO2 laser.

===Beam-steered CO2===

The continuous-wave CO2 laser can also be accompanying with the beam-steered delivery system.
CO2 lasers emit a narrow bandwidth of light in the far infrared at 10.6 mm. This wavelength is most suitable for organic items such as paper and other wood products, many plastics, removing thin layers of ink or paint from a substrate, and for engraving ceramics. It does not produce high peak powers when pulsed.

Typically utilizing laser powers up to 50 watts, these systems combine the far infrared wavelength with the image control and flexibility of beam-steered image generation. Customary uses include serialization of ceramic and plastic products that entail high-quality graphics such as company logos and/or noteworthy amounts of additional alphanumeric text. The curtailed power CO2 marker does not provide the power to "engrave" substrates but, due to the comparative simplicity of design, can be purchased at a reduced cost than the beam-steered Nd:YAG marker.

===Mask CO2===

Applications that involve high speed but not high power and don't vary the marking image except for alphanumeric text (i.e., serialization, date code, etc.) utilize the mask CO2 marker. The CO2 laser is pulsed at rates of up to 1,200 pulses per minute. The high repetition rate provides marking of parts "on-the-fly" at high part-transfer speeds. Computer controlled masks can alter up to three lines of text at speeds of up to 720 parts per minute if the alphanumeric code must be changed.

===Benefits and Disadvantages===

Beam-steered Nd:YAG
The beam-steered Nd:YAG supplies numerous engraving power and far superior imaging than any other laser marker configuration. The accessible high peak power can characteristic or engrave a wide variety of items with hardened metallics. Present computer technology produces immensely delicate graphics with linewidths and accuracy's of less than 0.001 inch. Because “drawing” with the laser beam creates the image, the etching time is conditioned on the amount of text and the complexity of any graphics. The Nd:YAG laser marker is the most costly of the three system configurations.

The beam-steered Nd:YAG marker routinely replaces acid and electro-etch systems, stamping and punching systems, and those other etching systems which permanently mark products by imprinting or engraving. It also replaces ink jet and other color printing systems. Classical applications encompass marking pistons, bearings, valves, gears, and a multitude of other components in the automotive industry; heart pacemakers, replacement hip joints, and surgical tools in the medical business; computer chassis, disk drives, and integrated circuits in the electronics business; tool holders, drill bits, and cutting tools in the tool industry; and writing pens, nameplates, and golf club grips.

===Beam-steered CO2===

The acquisition and operating costs of the beam-steered CO2 marker are reduced than the Nd:YAG marker due to the relative simplicity of the laser. Image generation is equal to that of the other beam-steered system while speed and depth of penetration are prominent diminished due to the curtailed power of the CO2 laser. Although not as popular as the beam-steered Nd:YAG and mask CO2 markers, the beam-steered CO2 system is continually used for etching general plastics and plastic and ceramic connectors and packages within the electronics industry.

===Mask CO2===

Although the mask CO2 does not give the imaging abilities of the beam-steered design, it is far superior in speed. Because a single pulse of the laser creates the whole image, throughput is typically limited only by the pulse rate of the laser and the transfer speed of the parts handling system. While the part must be stationary while marking with the beam-steered design, parts are marked in action with mask systems. Depth of penetration is less than the beam-steered CO2 marker since the laser output is spread over a large area with correspondingly low power density.

Masked CO2 markers most often compete with ink-jet engraving. The mask CO2 laser is often the marker of choice for sequenced coding, batch coding, open or closed date coding, and real-time coding of paper or cardboard, ink or paint coatings, glass, plastics, coated metals, and ceramics.

While the beam-steered design provides superior imaging and material penetration and the mask design supplies superior speed, either system supplies a improved collaboration of speed, long standing, and imaging ease of use than other marking techniques. many users also benefit from the non-contact nature of laser engraving and the elimination of additive items such as inks or paints.

The development of a prevailing etching application requires careful consideration of the laser output characteristics, the design of the optical beam delivery and image generation system, the properties of the target material, and the aesthetic and physical properties of the desired mark. Industrial laser engraving systems provide prospective users with several system designs from which to choose to match the very best marking performance with the users different requirements.

Article Source: http://www.rightbiz.com

Richard Stevenson is the Sales Director for Control Micro Systems, Inc. a manufacturer of beam-steered laser etching systems. He has published and presented numerous specialized papers and articles on laser engraving in trade publications. For information on Plastic Welding or call 407-679-9716.

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