The commercial use of lasers for marking first appeared in the 1970s and was based on solid-state Nd:YAG and CO2 sources. The laser technologies offered a novel and attractive, noncontact, consumable-free marking process for a broad range of materials. Initial offerings were expensive and dogged with maintenance issues, but the evolution of the technology steadily made lasers the first choice for product marking applications. The introduction of nanosecond pulsed fiber lasers represented a significant step change in technology, and these sources quickly became the laser of choice for marking applications. Offering a compact “fit and forget” solution with no alignment or maintenance issues, fiber lasers were an innovative and disruptive technology that has since built up an 80% share of the marking market over the past decade. In recent years, the marking systems market has reportedly exceeded revenues of $2 billion. As many as 100,000 systems are being sold per annum, and pulsed fiber laser sources are being deployed expressly for laser marking applications. This growth is fueled by the ever-expanding demand for marking systems to support product traceability, coding, customization, and design. While lasers often create black marks in anodized aluminum, they can also selectively remove the anodized layer to reveal the bright aluminum below, creating white marks. Courtesy of TRUMPF. Laser marking has applications in just about every industry. From automotive to medical device manufacture and from white goods to consumer electronics — just about every product available needs some sort of mark on it. In some sectors, legislation is actively driving requirements for greater traceability. Marking applications can be broken down into several categories, including basic alphanumeric text, barcodes, data matrix and quick response (QR) codes, design elements, and graphics. Laser marking still competes with nonphotonic marking processes, such as inkjet printing and mechanical engraving. But it requires no consumables, and it generates no potential wear on the tools used. Lasers offer a noncontact process that is flexible, reconfigurable, and highly reproducible, enabling high-speed marking of a wide range of materials. The 1-µm IR wavelength generated by fiber lasers is suitable for the vast majority of materials that are conventionally marked. However, materials such as organics, ceramics, and some polymers have limited absorption at this wavelength. As a consequence, CO2 lasers emitting in the MIR, or diode-pumped solid-state sources operating in the green or UV, may be more appropriate for these applications. Inside the box Fiber lasers emit nanosecond pulses focused to a point that generates a dot in the material to be marked. By scanning the focal point over the workpiece, successive dots combine to form a legible mark. The lasing magic happens within an optical fiber that is not much thicker than a human hair. This continuous fiber also allows flexible delivery of the laser energy right up to the scanner component that controls the marking process. There are no optics to adjust or clean in a fiber laser, and it is not uncommon for these tools to operate for over 50,000 hours with no degradation in output performance. Over the past 20 years, these sources have consistently set higher standards for reliability in industrial environments and have helped to transform lasers from scientific instruments to robust industrial equipment. A quick response (QR) code created using a combination of black and white marking on mirror-polished stainless steel to enhance contrast. Lasers typically mark stainless steel via a controlled localized heating of the surface to temperatures that promote oxide growth, and it is this oxide that produces the high-contrast mark. Courtesy of TRUMPF. Laser energy can cause black plastics to turn white, or it can selectively remove the paint layer from painted plastics, without damaging the underlying surface. This technique is the basis for marking the back-illuminated switches and displays that are commonly used in the automotive industry. Courtesy of TRUMPF. Although lasers are often used to create black marks in stainless steel, the marks can also be re-created in the colors of the rainbow by controlling the oxide thickness, which, in turn, renders the appearance of various colors. Courtesy of TRUMPF. A clock face created with the help of a fiber laser marking system. The laser removed the black anodized layer of an aluminum sheet to engrave the intricate 3D relief pattern. Courtesy of TRUMPF. Pulsed fiber lasers come in two basic forms. They are either based on a Q-switch, which has a fixed pulse duration and limited pulse frequency, or on a more flexible master oscillator power amplifier (MOPA) design that offers the ability to change pulse duration and operate over a far broader frequency range. Today’s MOPA fiber lasers can generate pulses as short as a few nanoseconds to several microseconds in length and operate at frequencies from single pulses up to 4 MHz. Their ability to change pulse duration and frequency over such a dynamic range offers end users far greater scope in optimizing pulse parameters for both marking quality and speed, by controlling the way the energy is delivered. A significant proportion of marking applications can be addressed with a basic 20-W laser source. But suppliers such as TRUMPF offer systems with output powers up to 200 W that can increase productivity where required or enable more demanding applications. Marking metal One key strength of fiber lasers is their ability to mark metallic materials. These marks can take many forms, from surface modifications that leave the surface virtually undisturbed to deep engravings in which a significant amount of material is removed. With materials such as stainless steel, using lasers to form black marks is now commonplace. These marks are oxidative surface marks produced without any melting of the metal. Instead, the laser generates a controlled localized heating of the surface to temperatures that promote oxide growth, and it is this oxide that produces the high-contrast mark. Although typically black, the marks can also be re-created in the colors of the rainbow by controlling the oxide thickness, giving the optical illusion of color. Alternatively, white marks can be made at much higher speed, but they offer less contrast. Black marking of stainless steel is extensively used in medical device manufacturing per regulations by some governments. Such marks are more challenging to make due to additional requirements that the marks resist fading after repeated autoclave sterilization cycles. However, the use of ultrashort pulse lasers in a process known as laser-induced periodic surface structuring greatly enhances such resistance to fading. Anodized aluminum can also be black marked. But, unlike stainless steel, the laser creates a subsurface mark by modifying the material via a controlled heat treatment in the region between the aluminum base material and the anodized layer. These marks are used extensively in the manufacture of consumer electronics, where best results are achieved using short pulses at the high frequencies available from the MOPA design. Alternatively, using a laser to selectively remove the aluminum’s anodized layer reveals the bright aluminum below. This technique is widely applied when manufacturing components such as the faceplates and tags used on a wide range of goods. More durable marks can be made in metals by using an engraving process by which actual material is removed, typically through a combination of vaporization and melt ejection. The creation of such marks tends to be a slower process that requires more heat input, but it is nevertheless competitive with mechanical marking methods. One application in which this approach is often required is marking automotive vehicle identification numbers (VINs). These marks need to be more resistant to removal by grinding and so require typical mark depths greater than 0.3 mm. Today’s 200-W nanosecond pulsed lasers can engrave an 18-character alphanumeric set suitable for VIN marking in just under 9 s. Laser marking is also used extensively to provide anti-counterfeiting measures. The depth requirement given above is one example of what’s possible. But fiber lasers can alternatively be used to make marks that are less than 10 µm in width, making them virtually invisible to the naked eye but easily detectable by anti-counterfeiting equipment. Fiber lasers further offer the flexibility to selectively polish and mark rough surfaces, such as brushed finishes, by using laser energy to remelt the metal. Upon resolidification, the metal’s surface tension helps to reduce surface roughness. This technique benefits from the use of longer pulses with higher pulse energies and low peak powers. Conversely, using shorter pulses with low pulse energies and high peak powers can effectively help to clean surfaces. Laser cleaning is effective at removing oils and surface contaminates, and even oxides and rust. Localized laser cleaning or microroughening can also be used to significantly increase the bond strength of adhesives used in glued joints, where the treated surface offers improved keying. In some applications, a combination of processes can be used to enhance the quality and finish of a mark. A good example is the processing of steel, notably stainless steel, where the engraving process can leave surfaces that are relatively rough or tarnished by surface oxidation. A subsequent cleaning or polishing pass can significantly enhance the aesthetics of the mark. Marking polymers Fiber lasers can also mark plastics and polymers, but the material must adequately absorb the IR laser light. Polymers such as ABS (acrylonitrile butadiene styrene) and polycarbonate are readily marked at this wavelength, whereas other materials — particularly those that are white, translucent, or transparent — can pose more of a challenge. Polyurethane, poly(methyl methacrylate) (PMMA), and polytetrafluoroethylene (PTFE) are all polymers that have virtually no absorption in the IR and need to be modified to be marked with fiber lasers. Many plastics are first compounded using commercially available IR absorbing pigments to make them easier to mark. The marking mechanisms for polymer materials encompass sublimation, carbonization, bleaching, and even foaming, where gaseous expansion in the irradiated layer of the polymer gives rise to high-contrast marks. Laser energy can cause black plastics to turn white or can selectively remove the paint layer from painted plastics without damaging the underlying surface. This technique is the basis for marking the back-illuminated switches and displays that are commonly used in the automotive industry. Pulsed fiber lasers can create subsurface black marks in anodized aluminum by using nanosecond pulses to generate a controlled heat treatment between the aluminum base material and the anodized layer. Courtesy of TRUMPF. Marking ceramic materials presents a different challenge for fiber lasers, due to the inherently low absorption that these materials exhibit at 1-µm wavelengths. In some cases, such as transparent glass, either CO2 lasers or ultrafast sources may be more effective marking tools. In many instances, however, it’s a case of “try it and see.” Fiber lasers are suitable tools, for example, when marking commonly used ceramics, such as aluminum nitride (AlN) and aluminum oxide (Al2O3), where laser energy can either mark or engrave the material. Scanning the future Today’s laser marking systems are typically based on either galvo mirror-based beam manipulation or on an xy plotter arrangement that moves the laser beam relative to the workpiece. However, marking systems vary widely in their sophistication, ranging from simple galvos with full manual adjustment for basic marking of flat parts to more advanced systems offering 3D-marking fields that enable reliable marking of curved surfaces. Additional vision systems can even provide real-time part recognition, allowing users to feed randomly oriented parts into their marking system. The vision component will identify the part, locate the marking area, and automatically adjust the software to make the mark with micron accuracy. Naturally, these solutions come at a price, but the variety of laser marking solutions available today offers options for virtually any budget. Fiber laser-based marking systems are also scalable, allowing them to mark components of every size, whether a part is as big as a bus or as small as a grain of rice. From simple desktop solutions with limited marking fields to large gantry- or robot-mounted galvanometer-based systems, there are integrators capable of meeting marking requirements, whatever the challenge. Over the past 20 years, fiber lasers have revolutionized the laser marking market by providing affordable and reliable solutions that are industrially robust. The versatility of lasers has shown them to be not only capable of marking the vast majority of materials but also of supporting a range of allied processes. Fiber lasers are a genuine industrial multitool for the current age. Meet the author Jack Gabzdyl is industry manager for electronics at TRUMPF and has over 35 years of experience in laser materials processing; email: jack.gabzdyl@trumpf.com.