Beam-Steered Laser Marking of Plastics

Beam-steered Nd:YAG (Neodymium:Yttrium Aluminum Garnet) laser marking supplies a exclusive blend of speed, permanence, and imaging versatility in a noncontact marking procedure. Laser marking can deliver substantial savings in lessened manufacturing and tooling charges elimination of secondary procedures and consumable disposal and lessened stock expenditure, high quality-management expenses, and maintenance downtime. Laser marking often increases the aesthetic visual appearance of the marking graphic, thereby growing the product’s perceived worth.

Of all elements, plastics are the most challenging in phrases of the laser’s conversation with the material and the necessary graphic high-quality. The extensive wide variety of substance chemistries and colours and the aesthetic specifications of most plastics programs have to have exclusive thing to consider in each substance chemistry and imaging approaches. The thriving implementation of laser marking know-how necessitates a working awareness of the laser marker’s functionality and abilities and a committed, team method by the consumer.

Marking Fundamentals

Laser marking is a thermal approach that employs a substantial-depth beam of centered laser gentle to create a contrasting mark on the materials area. As the concentrate on substance absorbs the laser gentle, the floor temperature raises to induce a shade improve in the materials and/or vaporization of material to engrave the floor.

Beam-steered laser marking employs mirrors mounted on large-velocity, laptop or computer-controlled galvanometers to direct the laser beam across the target area. Just about every galvanometer provides just one axis of beam motion in the marking industry. A multi-component, flat-field lens assembly subsequently focuses the laser light to obtain significant electric power density on the do the job surface when protecting the concentrated-spot vacation on a flat plane. The laser output is gated to blank the beam involving marking strokes.

Marking can be achieved at speeds of up to 5000 mm/sec with positioning speeds between marking strokes of 50,000 mm/sec. Because the method depends on heat conduction into the plastic, marking speeds are typically slower than the system’s maximum capability to make it possible for ample conduction to attain the ideal outcomes.

The beam-steered marker can duplicate virtually any black-and-white graphic, which include variable line widths and visuals as modest as .0001 inch. Existing laptop or computer-imaging technological innovation makes extremely intricate graphics with line widths, resolution, and accuracy very well under .001 inch. Since the impression is produced by “drawing” with the laser beam, the marking time is dependent on the amount of money and complexity of the text and graphics. With computer-generated imaging, any graphic element or the whole marking software can be immediately altered just before a new part is positioned for marking.

Nd:YAG lasers amplify light-weight of 1.06mm wavelength in the in the vicinity of-infrared. They are exclusive among the diverse styles of lasers in that they run a great deal like an “optical capacitor.” In pulsed procedure, the Nd:YAG laser stores vitality in between pulses, resulting in peak powers of kilowatts of gentle strength. A Nd:YAG laser emitting 75 watts of steady light-weight, pulsed at 1 kHz, emits a teach of pulses with peak powers of 110,000 watts. The “optical capacitor” influence delivers the peak energy vital to vaporize product. For plastics programs, the laser need to also be operate in a “prime hat” manner, in which the energy distribution is reasonably even across the cross part of the laser beam in get to reduce “scorching places” in the marking route.

The beam-steered Nd:YAG marker commonly replaces acid and electro-etch methods, stamping and punching devices, and these other marking techniques that permanently mark goods by imprinting or engraving. It also replaces other, a lot less permanent printing units, such as ink jet.

Uncoated Plastics

Most uncoated plastics will have to be doped with a materials reflective to the laser wavelength to protect against more than-absorption of the laser light, which benefits in reduction of regulate of the temperature rise and too much melting on the area. Mild-colored plastics are doped with mica, titanium dioxide or carbon-made up of supplies. The warmth produced by absorption of the laser gentle triggers the carbon to migrate to the floor, creating a contrasting dim mark versus the unaltered history plastic.

Plastics are semitransparent to the around-infrared wavelength of the Nd:YAG laser. Relying on the diploma of transparency and the laser output electric power, the laser beam can change the materials surface area to depths of additional than .025 mm with out reaching vaporization temperature on the surface area. If content vaporization takes place, the layer of carbon is thinned and the marking graphic will seem washed out.

There has been appreciable accomplishment in altering the depth of carbon migration to generate gray-scale graphics on light plastics. Altering the power and/or pulse level of the laser controls the depth of penetration and therebv the darkness of the mark. Rising the laser electricity will improve the general depth of penetration and thickness of the carbon layer. Increasing the pulse amount will final result in a for a longer period pulse width and reduce peak ability. The longer exposure also will increase the depth of penetration and affiliated carbon layer.

Dim plastic is doped with a materials that produces a lighter coloration as the content expands and the density decreases. As the temperature of the plastic increases, the plastic expands to type a “blister” on the floor and a lighter-coloured mark. As with light-weight plastics, the temperature should be tightly managed to prevent more than absorption. If the temperature rises much too high and the blister bursts, substance is misplaced and the mark will drop contrast.

Not all plastics call for dopant to accomplish a contrasting mark. Numerous plastics do yield great effects without the need of additives for instance, most black polycarbonates deliver a snow-white mark devoid of altering the chemistry.

Coated Plastics

Coated plastics consist of a reliable, translucent, or transparent plastic with just one or a lot more coats of ink or paint. The marking image is developed by accomplishing vaporization temperature on the surface area to clear away the leading coat and expose the underlying plastic or second coat.

Coated plastics permit a terrific offer of manage in excess of color range and marking distinction. Transparent plastics permit the designer to use an underlying part to establish the history shade (marking image) while the leading coat determines the foreground coloration. Good plastics set up their possess track record with the coloration of the plastic. Translucent plastics are commonly used for again-lit apps. The plastic is to begin with coated with a white paint and overlaid with a dark leading coat. The laser eliminates the top rated coat, exposing the white paint for daytime visibility. When the component is back-lit at night, the lighting illuminates the translucent plastic from driving and the marking impression seems in the colour of the plastic.

The paint or ink applied ought to be conducive to laser processing. Typical paints and inks are neither predictable nor controllable when exposed to the laser output. The inks burn up quickly and can combine with the fundamental plastic although in the molten liquid state. Laser-compatible inks are mixed with a silicone-based material reflective to the laser output, thus lessening the ink’s gentle absorption and price of thermal response. Paints should be appropriate for substantial-temperature processing and be cost-free of any contaminants that may perhaps take in the laser wavelength and velocity up the thermal rise.

To attain a high-quality picture, the prime coat ought to be completely taken out with minimum impression on the underlying plastic or secondary coat. To maximize the ratio of mild absorption between the two levels, the best coat should generally be a dark shade and the contrasting fundamental layer have to be a light color. The darkish colour will take in a comparatively larger share of the laser light-weight, resulting in a larger surface area temperature, though the light-weight colour displays a bigger proportion and minimizes the temperature increase. The fundamental plastic, paint, or ink need to also be thick plenty of to tolerate a minor sum of material removing throughout marking.

Marking coated plastics is a multi-phase procedure in which the to start with marking go removes the the vast majority of the major coating. The remaining residue is eliminated with a 2nd, decrease-ability move to decrease the effect to the underlying content. For precise edge definition, the outline of the graphic is marked prior to filling in the impression. The outline is marked with a large edge move (i.e., 50 kHz, 250 mm/sec, 2.5 watts) followed by a reduced-power cleanup go (50 kHz, 250 mm/sec,1.75 watts). The picture is then crammed, if wanted, with a heavy fill pass (50 kHz, 650 mm/sec, 6 watts) and subsequent cleanup pass (50 kHz, 6.50 mm/sec, 4.5 watts). Treatment in deciding the course of action parameters for each individual pass and the edge and fill beam paths will result in a crisp, substantial-distinction, superior-excellent marking image.

Preparing and Installation

Maybe the most significant ingredient in the effective application of laser marking is the composition of the aspect plans. When changing an current marking technologies, one ought to allow for up to 6 months for conversion of current artwork work to part-marking laptop or computer packages. Even if the current artwork resides in AutoCAD data files, time must be allotted to convert the information to optimized marking packages.

Quite a few customers start with 1000’s of sheets of Mylar artwork. (Mylar is a DuPont trade title.) Every Mylar movie is scanned to generate a bitmap graphic. The scanned bitmap could be straight converted to the laser marker structure with fantastic graphic good quality, but the cycle time would be unnecessarily extensive, with excessive marking line overlap.

For finest benefits, import the scanned bitmap into AutoCAD as a positional template. Make a individual marking “emblem” for each alphanumeric character and graphic picture, and, in AutoCAD, position just about every symbol in posture on a different layer, applying the bitmap template as a positioning information. A library of optimized logos facilitates the creation of packages from the scanned artwork, lets nonstandard text kerning and line top, and assures small cycle time and higher image top quality. After all the logos are in area, the template layer is taken off, and the closing CAD file is converted to the laser marker software structure.

If the artwork operate already exists in a CAD file structure, the image components could be optimized without employing a individual library of logos. Just about every ingredient like repetitive elements shared amongst drawings need to be separately optimized. It will just take noticeably for a longer time to transform substantial quantities of information, and there is no assure that each and every clement is optimized accurately. It is far much more productive to use the initial AutoCAD file as the placement template for optimized logos.

Implementation of beam-steered laser marking calls for a workforce hard work. With cooperative implementation. manufacturing can assure product or service move and integration with existing controls, the resources office makes sure that plastics and coatings are correct for laser marking, and engineering will deliver aspect-marking programs with lower cycle occasions and high-good quality photographs. Watchful staff organizing, preparation, and execution will outcome in a clean application of laser marking know-how and the associated rewards in manufacturing efficiencies, excellent, and item price.