What is Laser Marking?
Laser markers have been used in manufacturing to produce permanently marks for decades. Since the pulsed fiber laser was developed and gained traction as a marking source in the mid to late 2000’s there has been significant demand for this technology. These pulsed fiber lasers combined with CO2, Nd:YVO4, picosecond and femtosecond lasers offer a marking solution for almost every material. Today, laser marking provides a cost-effective, high-speed, high-quality solution for many markets and countless applications, driven by the need for tracking and traceability.
How does a Laser Mark
A laser can create a permanent mark on a wide variety of materials including metals, plastics, glass and ceramics. The mark is directly marked onto the part by three main methods – surface contrast, surface melting, and engraving.
A laser marker comprises of a laser source, scan head for motion and F-theta lens for focus. The laser provides the energy/power used to create the mark, the scan head contains two orthogonal mirrors called galvanometers that move the laser quickly in x and y to trace the path of the mark, and the F theta lens focuses the laser onto the part. A beam expander is typically used to produce the correct focused spot size. The mark or engrave pattern is created using simple software that downloads the executable motion program to the scan head controller. Once downloaded the scan head executes the motion controlling the on/off firing of the laser.
Laser markers and engravers are extremely flexible capable of creating any mark; alphanumerics, machine readable codes (e.g. DataMatrix codes), graphics and logos with high resolution and quality. The process is non-contact process, does not require any consumables, and is used across every manufacturing industry.
Lasers for Marking
Fiber |
Pulsed fiber lasers operating around 1 micron are well-matched to the absorption characteristics of most metals, generally making them the first choice for marking and engraving of these materials. In addition, there are many plastics that the pulsed fiber laser can also mark. These lasers offer a cost-effective marking solution with low cost of ownership, high reliability, long lifetime, excellent beam quality, and ease of implementation. Two main variants of the pulsed fiber laser markers exist; Q switched and MOPA (master oscillator power amplifier). The Q switched version provides nanosecond pulses with a pulse shape, pulse width and peak power as a function of the frequency. The MOPA offers more flexibility, able to select pulse shape, duration and peak somewhat independent of frequency, which can be especially useful for marking plastics. |
CO2 |
CO2 lasers output in the far infrared, around 10 microns, that aligns well with organic materials and plastics. This makes them ideal for marking and engraving wood, and engraving plastics. For plastics, the typically non-contrasting engraved mark is read using ambient or external lighting that interacts with the engrave depth “creating” contrast to the base material. |
Nd:YVO4 |
Nd:YVO4 or vanadate lasers are diode-pumped solid-state lasers (DPSS) that offer laser wavelengths around 1 micron, green and UV. These lasers provide the best mark quality due to excellent beam quality, and very short pulses (<20ns) with high peak power (>20kW). DPSS lasers, particularly in green, offer excellent laser sources for the semiconductor industry, while UV lasers offer high contrast marks on plastics. |
Picosecond & femtosecond lasers |
Both picosecond and femtosecond lasers have very short pulse durations and very high peak powers that can mark challenging materials or mark requirements. Examples applications include glass marking with no cracking or the corrosion resistant dark marking of stainless steel for medical devices. |
What Materials Can Be Marked with Lasers?
Lasers can mark many materials, with the selection of laser depending on mark resolution, quality, contrast, and budget.
Plastics: Almost every plastic can marked using either a CO2, nanosecond fiber or Nd:YVO4 laser. Common materials include nylons, PET, polycarbonates, polyethylene, polypropylene, ABS, the list goes on! In many cases the mark needs to have contrast, and this can usually be achieved using a pulsed fiber or Nd:YVO4 laser. These lasers create contrast by melting the plastics, with either a “foaming” or “carbonization” effect, the latter typically light colored and the former dark colored. The Nd:YVO4 laser offers green and UV light options that can mark plastics with high surface contrast by a photochemical process known as bleaching. This type of mark does not modify or change the physical surface of the part. If contrast, resolution and mark quality can be relaxed, the CO2 laser provides an excellent cost-effective laser source.
Metals: A wide variety of metals can be marked or engraved including stainless steels, carbon steels, aluminum, nickel, and titanium. Contrasting marks can be achieved in a variety of ways; creating oxide layers, re-melting the surface or engraved into the surface.
For medical device manufacturing a black or dark mark is used that provides high contrast with no effect on the surface morphology. The mark cannot be felt on the surface of the part, which is very important in avoiding any collection areas of dirt or debris that may become a growth site for bacteria. For titanium this can be a blue mark that has a very cool appearance!
The black or dark mark for reusable medical devices may need to survive passivation or autoclaving, in this case a picosecond laser with an optimized process for part material and shape creates a mark that can survive the harshest passivation and many autoclave cycles.
For metal engraving high power laser markers are recommended, typically 50-100W, having sufficient power to deliver engrave depths with fast cycle times.
Ceramics and glasses: Glass can be marked using CO2, Nd: YVO4 UV wavelength, and picosecond and femtosecond lasers. The choice of laser depends on the marking requirements. CO2 lasers produce surface or slightly subsurface microcracks to create the mark, commonly used for soda-lime glass, such as wine bottles. UV nanosecond lasers create finer microcracked marks and can make a sub-surface mark inside of glass. Femtosecond lasers offer the ultimate mark quality, marking inside glass without microcracking and only visible under certain lighting conditions, ideal for anti-counterfeiting. For ceramics, Nd:YVO4 lasers are typically used, either at the 1 micron wavelength or sometimes at the green wavelength, depending on the mark quality and ceramic type.
Epoxies and resin: These materials, such as those used in electrical boxes, are typically markable with 1 micron lasers, either fiber or Nd:YVO4, providing good contrasting marks. For semiconductors, marking IC chips made of epoxy or elastomer is accomplished using 1 micron or green lasers. In certain SEMI applications, mark penetration must be controlled to around 10 microns, usually achieved with Nd:YVO4 lasers.
What are the benefits of Laser Marking
- There are many benefits of laser marking
- Non-contact process – no mechanical force on the part
- Permanent marks – marks will not rub off
- Easy to use, simply line integration – simple software makes use and integration plug & play
- No consumables – an environmentally friendly process with no inks, stylus, chemicals to replace
- Extremely reliable – laser markers are extremely robust, mature technology
- Long lifetime – typically ten’s of thousands of operation hours, for example pulsed fiber lasers can last well beyond 50,000 hours of operation
- Mark almost any material – metals, plastics, ceramics, glasses, ceramics, epoxies
- Mark any pattern; alphanumerics, machine codes, graphics and logos
- Flexibility – dynamically size the mark, single or multiple parts, stationary or on the fly, custom serialization, database incremented codes, you name it, it can do it!