Beam-Steered Laser Marking of Plastics
Beam-steered Nd:YAG (Neodymium:Yttrium Aluminum Garnet) laser marking offers a distinctive blend of speed, permanence, and imaging flexibility in a noncontact marking process. Laser marking can generate substantial discounts in decreased producing and tooling fees elimination of secondary procedures and consumable disposal and lowered inventory cost, good quality-management expenditures, and routine maintenance downtime. Laser marking usually enhances the aesthetic physical appearance of the marking picture, thus growing the product’s perceived price.
Of all materials, plastics are the most complicated in conditions of the laser’s interaction with the product and the necessary graphic quality. The vast assortment of material chemistries and colors and the aesthetic requirements of most plastics purposes need unique thought in each content chemistry and imaging procedures. The successful implementation of laser marking know-how demands a doing the job expertise of the laser marker’s perform and abilities and a dedicated, workforce method by the person.
Marking Fundamentals
Laser marking is a thermal approach that employs a substantial-depth beam of focused laser mild to build a contrasting mark on the substance floor. As the goal product absorbs the laser gentle, the surface area temperature increases to induce a coloration change in the material and/or vaporization of content to engrave the surface.
Beam-steered laser marking employs mirrors mounted on higher-pace, laptop-controlled galvanometers to immediate the laser beam across the concentrate on surface. Each individual galvanometer presents 1 axis of beam motion in the marking subject. A multi-element, flat-subject lens assembly subsequently focuses the laser mild to obtain superior electricity density on the get the job done area although keeping the centered-location travel on a flat aircraft. The laser output is gated to blank the beam in between marking strokes.
Marking can be completed at speeds of up to 5000 mm/sec with positioning speeds involving marking strokes of 50,000 mm/sec. Due to the fact the system relies on heat conduction into the plastic, marking speeds are commonly slower than the system’s maximum functionality to enable sufficient conduction to reach the desired results.
The beam-steered marker can replicate almost any black-and-white picture, which includes variable line widths and images as small as .0001 inch. Existing personal computer-imaging know-how provides highly intricate graphics with line widths, resolution, and accuracy nicely down below .001 inch. Mainly because the image is developed by “drawing” with the laser beam, the marking time is dependent on the volume and complexity of the text and graphics. With pc-created imaging, any graphic component or the total marking plan can be instantly altered ahead of a new component is positioned for marking.
Nd:YAG lasers amplify gentle of 1.06mm wavelength in the near-infrared. They are distinctive between the diverse styles of lasers in that they operate a lot like an “optical capacitor.” In pulsed procedure, the Nd:YAG laser shops strength involving pulses, resulting in peak powers of kilowatts of mild power. A Nd:YAG laser emitting 75 watts of continual light, pulsed at 1 kHz, emits a prepare of pulses with peak powers of 110,000 watts. The “optical capacitor” influence delivers the peak electric power vital to vaporize material. For plastics purposes, the laser will have to also be operate in a “major hat” manner, in which the electrical power distribution is relatively even across the cross segment of the laser beam in order to remove “scorching spots” in the marking path.
The beam-steered Nd:YAG marker often replaces acid and electro-etch programs, stamping and punching techniques, and these other marking programs that forever mark items by imprinting or engraving. It also replaces other, a lot less lasting printing units, which includes ink jet.
Uncoated Plastics
Most uncoated plastics need to be doped with a content reflective to the laser wavelength to avoid in excess of-absorption of the laser gentle, which effects in reduction of management of the temperature increase and excessive melting on the area. Light-colored plastics are doped with mica, titanium dioxide or carbon-that contains products. The warmth created by absorption of the laser gentle leads to the carbon to migrate to the area, generating a contrasting dark mark from the unaltered history plastic.
Plastics are semitransparent to the in close proximity to-infrared wavelength of the Nd:YAG laser. Depending on the degree of transparency and the laser output electric power, the laser beam can change the material surface area to depths of much more than .025 mm with out obtaining vaporization temperature on the surface area. If content vaporization happens, the layer of carbon is thinned and the marking image will appear washed out.
There has been appreciable achievement in altering the depth of carbon migration to develop grey-scale graphics on gentle plastics. Changing the electrical power and/or pulse amount of the laser controls the depth of penetration and therebv the darkness of the mark. Expanding the laser electricity will boost the general depth of penetration and thickness of the carbon layer. Rising the pulse level will final result in a more time pulse width and decrease peak electrical power. The more time exposure also boosts the depth of penetration and involved carbon layer.
Dark plastic is doped with a content that generates a lighter coloration as the product expands and the density decreases. As the temperature of the plastic improves, the plastic expands to form a “blister” on the area and a lighter-coloured mark. As with mild plastics, the temperature must be tightly controlled to avoid around absorption. If the temperature rises also higher and the blister bursts, materials is misplaced and the mark will drop contrast.
Not all plastics have to have dopant to reach a contrasting mark. Many plastics do produce superb results without additives for illustration, most black polycarbonates generate a snow-white mark with no altering the chemistry.
Coated Plastics
Coated plastics consist of a stable, translucent, or transparent plastic with just one or extra coats of ink or paint. The marking picture is created by achieving vaporization temperature on the surface area to take away the top coat and expose the underlying plastic or second coat.
Coated plastics let a wonderful offer of handle over coloration range and marking distinction. Transparent plastics allow the designer to use an fundamental component to set up the track record color (marking graphic) although the top rated coat decides the foreground color. Sound plastics set up their personal background with the shade of the plastic. Translucent plastics are frequently used for again-lit applications. The plastic is to begin with coated with a white paint and overlaid with a darkish top coat. The laser gets rid of the best coat, exposing the white paint for daytime visibility. When the component is again-lit at night, the lighting illuminates the translucent plastic from behind and the marking graphic seems in the coloration of the plastic.
The paint or ink utilised should be conducive to laser processing. Normal paints and inks are neither predictable nor controllable when exposed to the laser output. The inks burn very easily and can blend with the underlying plastic whilst in the molten liquid point out. Laser-suitable inks are mixed with a silicone-primarily based substance reflective to the laser output, thus lowering the ink’s mild absorption and fee of thermal reaction. Paints ought to be suited for large-temperature processing and be free of any contaminants that may perhaps absorb the laser wavelength and velocity up the thermal rise.
To reach a excellent picture, the top coat have to be wholly eliminated with small impact on the fundamental plastic or secondary coat. To increase the ratio of light absorption amongst the two layers, the major coat need to usually be a dark color and the contrasting fundamental layer have to be a mild coloration. The dark color will soak up a comparatively larger share of the laser mild, resulting in a bigger surface temperature, whilst the light shade reflects a larger share and minimizes the temperature rise. The fundamental plastic, paint, or ink really should also be thick adequate to tolerate a slight amount of material removal for the duration of marking.
Marking coated plastics is a multi-step system in which the to start with marking go removes the bulk of the top rated coating. The remaining residue is removed with a next, lower-electricity go to decrease the outcome to the underlying product. For exact edge definition, the define of the impression is marked prior to filling in the picture. The define is marked with a major edge pass (i.e., 50 kHz, 250 mm/sec, 2.5 watts) followed by a lessen-electrical power cleanup go (50 kHz, 250 mm/sec,1.75 watts). The picture is then loaded, if wanted, with a heavy fill move (50 kHz, 650 mm/sec, 6 watts) and subsequent cleanup go (50 kHz, 6.50 mm/sec, 4.5 watts). Treatment in determining the procedure parameters for just about every move and the edge and fill beam paths will outcome in a crisp, large-distinction, superior-high-quality marking image.
Preparing and Set up
Potentially the most essential component in the profitable application of laser marking is the composition of the part courses. When changing an existing marking technological know-how, a single have to let up to 6 months for conversion of existing artwork function to portion-marking computer system courses. Even if the current artwork resides in AutoCAD documents, time need to be allotted to change the files to optimized marking packages.
Numerous users start with countless numbers of sheets of Mylar artwork. (Mylar is a DuPont trade identify.) Each and every Mylar film is scanned to produce a bitmap impression. The scanned bitmap could be specifically transformed to the laser marker format with fantastic picture high-quality, but the cycle time would be unnecessarily extensive, with abnormal marking line overlap.
For most effective success, import the scanned bitmap into AutoCAD as a positional template. Produce a individual marking “symbol” for just about every alphanumeric character and graphic graphic, and, in AutoCAD, place each symbol in position on a individual layer, employing the bitmap template as a positioning guidebook. A library of optimized logos facilitates the creation of courses from the scanned artwork, makes it possible for nonstandard textual content kerning and line main, and makes certain small cycle time and high impression high quality. Right after all the logos are in area, the template layer is taken out, and the remaining CAD file is converted to the laser marker system format.
If the artwork get the job done now exists in a CAD file format, the image components could be optimized without the need of utilizing a independent library of logos. Each and every element including repetitive factors shared involving drawings must be individually optimized. It will get substantially for a longer period to change substantial quantities of information, and there is no assurance that each clement is optimized properly. It is significantly far more effective to use the authentic AutoCAD file as the placement template for optimized logos.
Implementation of beam-steered laser marking calls for a team effort. With cooperative implementation. manufacturing can make certain solution flow and integration with current controls, the products division ensures that plastics and coatings are acceptable for laser marking, and engineering will develop part-marking packages with minimal cycle occasions and large-high-quality pictures. Watchful group planning, preparing, and execution will outcome in a easy software of laser marking technological innovation and the associated added benefits in producing efficiencies, excellent, and product worth.