The absorption of a focused laser light alters the surface of the workpiece and produces the desired marking effect. Compared to other inline marking techniques, such as inkjet, hot stamping or mechanical scribing, laser marking and laser engraving offer many advantages such as flexibility, speed, indelibility, reliability, free of consumables and high cleanliness.Laser marking/engraving uses pulsed lasers with typical pulse durations below 1 µs.
Laser marking can be realized by black carbonization, annealing, bleaching or changing the color of the material, physical modification of the surface finish by micro melting, scribing a shallow groove into the material (engraving) or a combination of them. The mark can be numbers, texts, graphics, bar codes or 2D symbols (ID matrix).
Metals are commonly marked using Q-switched Nd:YAG lasers at 1.06 µm wavelength. Due to the high reflectivity of most metals at 10.6 µm wavelength, CO2 lasers are not suitable for marking polished metals, but widely used for marking painted and anodized metals, plastics, woods and glass. Both pulsed CO2 and Nd:YAG lasers can provide good marking results on ceramics and semiconductor materials. The line width produced by Nd:YAG lasers is narrower than that of CO2 lasers. Thus higher resolution is achievable with this laser type
.The average power of marking lasers is between 10W and 20W for diode-pumped Nd:YAG-, vanadate (Nd:YVO4) and fiber lasers. CO2 lasers with power up to 60W are used for combined marking and cutting systems. Higher power and high beam quality Nd:YAG lasers (up to 100W) are selected for deep engraving of metal surfaces of die and mould components. In some cases, second and third harmonic Nd:YAG lasers at 532 and 355 nm, as well as ultraviolet excimer lasers are the optimum choice to mark highly transparent materials.
Recently air-cooled pulsed fiber lasers with high repetition rates (up to 200 kHz) have become the popular laser source for metal marking. Their advantages include high beam quality, long diode lifetime, low running costs, no need of maintenance. A controlled process of oxidation (growth of the oxide layer) can produce corrosion resistant smooth marks on stainless steel material at different colors such as gold, red, blue, green, grey and black.Lasers mark plastics by carbonization (dark marking on light background), material foaming (raised light mark on darker background), material evaporation (engraving of thermoplastics) or selective removing of surface layers from the base material (day/night backlit car components).
A change of colors or a fading of the plastic material can be obtained by using special color pigments or additives (so-called laser optimized plastics). The pigment in the resin determines the chroma or hue, while laser process parameters determine the intensity or shade. Leading suppliers or custom laser-markable plastics include BASF, Bayer, Merck Chemicals. Ticona, RTP, Clariant, PolyOne, Ferro Corp. A. Schuman and LNP Engineering Plastics. A broad range of colors (white to grey to black on any color substrate, or blue, red or green on dark substrates) can be realized.
For plastics, the sealed CO2 laser is the most widely used, followed by solid-state Nd:YAG lasers and most recently, the fiber lasers. The CO2 laser ablates the plastic surface by evaporation, resulting in a contrasting mask but little or no true color change. If the contrast is not strong enough or excessive melting occurs, the use of YAG or fiber lasers is recommended.
An up-to-date laser marking system can change the key parameters online such as pulse power, frequency or speed to create an artistic image. In this case either the engraving depth or the dot spacing is modified accordingly to every required gray levels of the image. There are two different types of laser marking systems, which are based on two different beam motion mechanisms (galvo and flatbed).
Galvanometer systems use two mirrors and a F-theta lens to scan and focus the beam on the workpiece surface. The key advantage of these systems is that the relative movement of the laser beam as well as its acceleration and deceleration are extremely fast. Scanning speeds of up to 5 m/s are possible. Practically, there are no wear parts and they can easily be integrated into existing production lines. Fully automated galvanometer systems in production lines deliver low marking unit costs at high throughput.The main drawback of galvanometer systems is the limited size of the working area (typical: 120 mm x 120 mm for a focal length of 160 mm). The focal spot size increases if a larger marking area is required. Therefore, fine resolution marking typically cannot accomplish over a large area. In this case, an additional xy stage can be used for part indexing.
Flatbed systems are similar to laser plotters and can produce higher quality in comparison to galvo systems over working areas that are several times larger, but at lower marking speed. Furthermore, one can mark an array of workpieces at once and thus the handling time is significantly reduced.Flatbed systems use high-speed belt driven motors to move a tiny beam directing optic and a short focal length focusing and thus produce a laser beam that is, when compared with galvo systems, better focused and delivered always perpendicular to the workpiece. Focusing lenses of flatbed systems are single standard plano-convex lenses with short focal lengths (40 – 60 mm). This enables a resolution of 1000 dots per inch (dpi). The flying optic travels at high speed up to 140 in/s (3.5 m/s). This travel speed requires a laser source that is pulsable at more than 100 kHz and has a focal diameter of 25 ?m.
- Raster marking of images, which are composed of dots only
- Vector marking (scribing) of images using point to point movement of the laser beam
- 3 dimensional marking of complex surfaces with optical adjustment of the z-axis
- Tubular marking, 2D matrix or barcode marking
- Marking by removal of coatings
- Projection marking with a mask
- Color marking of selected metals via controlled surface oxidation or annealing
- Marking of two parts simultaneously by using two scanner heads and a beam splitter
- On-the-fly marking with continuous motion of the parts
KJ Laser Micromachining provides both laser marking and laser engraving services, mainly for companies in Canada and the USA. Our expertise covers a wide range of laser marking technology, including laser color marking via controlled surface oxidation, annealing or selective layer removal. We use a wide range of laser wavelengths from CO2- to Nd:YAG- and UV lasers to mark metals, ceramics, plastics, woods and other materials. We also select the right laser power, beam delivery and material handling for every particular application. We mark texts, graphics and 2D matrices using scanner heads or flatbed systems. Equipped with rotary devices, our marking system are able to mark cylindrical components.
Practically every material can be marked with lasers. The proper choice of laser wavelength will ensure adequate absorption and good marking. Occasionally, we use assisted gases, additives or coatings to achieve adequate laser absorption or color changes.
Our marking services include prototyping and contract manufacturing of medium to high quantities of parts.
KJ Laser Micromachining can help you to customize and integrate laser marking systems into your specific production line for the high-volume and automated manufacture of parts or components.