Since the technology for laser marking has developed market opportunities have emerged to make use of rapid marking speeds as well being more precise marking accuracy as well as imaging capability. The constant advancements in laser-cavity design as well as beam-steering and focusing opticals as well as computer hardware and software is expanding the use of systems.
Letting the beam steer
Of the various marking technologies available Laser marking systems that are beam-steered offer users the highest degree of flexibility for images in the fastest, most permanent non-contact marking process. As processes in manufacturing become more automated, and after-sales tracking becomes becoming more popular, laser marking systems are typically the only way that can create distinctive permanent images at a high speedfiber laser marking machine factory.
Laser marking systems that beam steer typically comprise either a CO2 or Nd:YAG laser. The CO2 laser produces continuous-wave signals within the infrared (10.6-um length) however the Nd.YAG laser emits light in the infrared near (1.06 millimeters) in either the pulsed or CW modes (1 -50 kHz). The Nd:YAG laser is distinct in its ability to generate extremely small, high-peak-power pulses it is operated in a pulsed mode. For instance the typical 60-W average-power Nd:YAG laser could produce peak powers in excess of 90 kW when operating at a 1 kHz pulse rate.
The delivery optics are either a basic focusing lens assembly, or a combination fixed upcollimator with a flat-field lens assembly. In either case laser light is directed over the surface of the work area by mirrors that are mounted on two high-speed computer-controlled galvanometers.
The simple focusing assembly has the benefits of low-cost and the use of fewer optical components. It is commonly used in conjunction by CO2 lasers. The flat field lens even though it is more expensive keeps the focus of the beam marking on a flat surface for better image quality throughout the field of marking. It also provides greater power density on the work surface than a simple focusing system due to its shorter effective focal length. The flat-field lens model is the preferred choice for applications that require high-quality and precise images and is often incorporated using NdYAG lasers.
Both models give the user various lenses to define both the diameter of the marking field as well as the width of the line marking. Longer focal length lenses offer greater working areas, however the width of the line is expanded, which reduces the power output on the surface. The user has to compensate by increasing the output power of the laser or decreasing the speed at which the marking is made that is usually comprised of two lenses. It can be placed in any part of the beam path prior to the lens that is focusing. The beam expander is often utilized instead of extending the beam path by 10 feet more in which the beam expands due to its natural tendency to diverge when it exits the cavity of the resonator. A spatial filter integrated into the beam expander provides the highest quality mode in systems with close coupling, by directing this beam via a narrow aperture.
The final optical element laser beams encounter is the focus lens. In CO2 lasers the lens is typically constructed from one of the following substances: Zinc selenide (ZnSe) or gallium arsenide (GaAs) or germanium (Ge). ZnSe is a hard yellow substance that is translucent for visible wavelengths is the most commonly used of these materials. It is also the most versatile, as it lets a low-power HeNe laser beam to pass through to align purposes. This is a major benefit against GaAs or Ge that are indistinct to light coming from the visible spectrum. spectrum.
Nd:YAG lasers typically use beam expansion, generally within the 2x-5x range due to their initial small beam diameters. Space filters in CO2 lasers have to be external, however the ones for Nd:YAG lasers may be installed within the laser cavity and various sizes are available to select the mode.
Lasers that use Nd:YAG employ optical glasses, such as BK-7 and fused silica lenses. Its 1.06-um length of wavelengths of such lasers is near enough to visible light that it allows adapting standard optical equipment with the proper AR coating that directs laser light. For instance, microscope objectives are able to deliver Nd:YAG laser light onto the surface of VLSI circuitry to micro-machine conductor pathways. As we have discussed, delivering an Nd:YAG laser beam using fiber optics provides a wealth of advantages when compared to traditional fixed-optic beam delivery. The fiber benefit is exclusive to Nd:YAG lasers, and has resulted in a huge increase in their usage for industrial processing of materials.
Delivery of fiber optics for the Nd:YAG
The utilization of fiber delivery using YAG lasers is widespread in the field that it is worth discussing in greater depth. About 90 percent of the new Nd:YAG welding projects involve fiber optical delivery. Since that the 1.06-um wavelength is carried by glass optics, it is able to be utilized in fiber optics that are standard. Traditional beam delivery is heavy, susceptible to contamination and misalignment to the optics. Additionally, it can be costly because of custom layouts. Fiber is the solution to all these issues. Benefits include:
- Fibers transmit laser energy across distances that in the real world would be impossible to achieve with traditional optics. Distances up 50 meters can be achieved frequently.
- Stability and accuracy are enhanced as only the final focus optics have to be held in a perfect relation with the piece of work.
The majority of apps can be managed by traditional delivery hardware (avoiding the need for custom designs).
- Flexible fibers in the limits of a bend radius that is minimal they can take any route to get to the piece of work.
The workpiece can be kept in place while the output and fiber optics move throughout processing, making them the ideal distribution system to use with robots.
- Fibers can make the design of energy and time using beam sharing systems an achievable possibility. The utilization of these systems dramatically enhances the flexibility and adaptability of lasers, permitting them to connect to multiple workstations or generate multiple outputs simultaneously.
- The access to the head of the laser to perform routine maintenance is easier because the position of the head isn’t controlled through the beam distribution system.
The fiber with a low cost is able to be delivered to areas that pose a risk because of radiation or explosives while the head of the laser is in an area that is safe.
- The size of the spot at focus doesn’t change with the variations in average power.
Fiber delivery’s optics are straightforward and simple. Fiber optics utilized to deliver lasers are usually step-index fibers. This kind of fiber is comprised of an optically consistent core of between 200 to 1500 um in diameter. It is covered by a thin cladding that has slight differences in optical properties.
There are a variety of options for fiber laser beam delivery. One of them is single-fiber delivery by one laser. This kind of delivery is usually employed for a specific production procedure or in labs for development in which the transfer of beams to workstations in other locations is rarely. The decision to use a single-fiber delivery can be justified by its convenience and integration with workstations, and the ability to upgrade the system with different options in the near future. The other reasons to use single-fiber delivery include robotic delivery of laser beams and other multiaxissystems , where traditional delivery is difficult. Fibers are used to deliver the output. The housing is attached to the final motion component. This means that the integration is extremely cost-effective and easy.
Another option for fiber delivery is time sharing. This means that all the laser’s output can be directed to any of the many fibers available upon demand. A single laser that is part of this type of system can deliver laser power to a variety of workstations that switch between them up to 40 milliseconds. They are usually utilized for laser welding at several workstations, or to distribute an laser beam into distinct parts of a large assembly station.
The final option is known as energy sharing. These systems split the output of lasers and transmit the energy to multiple fibers simultaneously. Mirrors skim the portions of the beam that are generated by the laser, and redirect them into the housings of input for each fiber.
The extent to which each mirror skimming is inserted in the beam path determines the ratio of sharing. Energy-share systems typically split beams into as much as 4 fibers. These systems can be used to weld multiple components simultaneously to improve throughputor remove the distortions to the parts which are often caused by the sequential welding of an assembly.
The computer system creates marking images by sending beam-motion signals to galvanometer drivers , while also blanking the laser beam in between marking strokes. The movement of the galvanometer mounted mirrors directs the beam of marking across the surface of the target as a pencil is used to draw graphic and alphanumeric images.
Laser marking utilizes the power density of the laser beam to create heat on the surface, causing an ensuing thermal reaction. A visible, distinct line is created by raising the surface’s temperatures for annealing, melting point or the temperature at which vaporization occurs. Melting and annealing are utilized to produce a striking color shift on a range of metallic’s as well ceramics, plastics, and nonmetallic’s. The fastest speed of marking is achieved by raising temperatures to the point of vaporization to engrave metallic’s as well as many nonmetallic’s.
The near-infrared wavelength of Nd:YAG laser is well-suited to most metals as well as numerous plastics. The Nd:YAG laser can melt or anneal in the CW and pulsed modes and provide the high-frequency pulsed power needed to create a trough. With a variety of substances, the Nd.YAG can simultaneously engrave a surface and create a contrast color within the cut surface.
The wavelength of the far-infrared spectrum of CO2 lasers is compatible with ceramics, plastics and other organic compounds. However, since it lacks the peak-power capability needed to reach temperatures for vaporization the CO2 laser is only able to melt or anneal the surface.
Laser beam marking has several advantages over other methods of marking. It is most evident that it is the only blend of efficiency, stability and the versatility of computer control. While other methods can provide only one or two of these characteristics however, none of the other methods can offer all three attributes to the same extent.
Many customers benefit from the non-contact characteristics of laser marking. The only force that applies to the object during the marking process is the localized thermal effect produced by that laser’s beam. There is no additional force used except for any suitable part-handling motion that is built within the system. Silicon wafers and silicon disk drive read/write heads , and several medical devices are examples of devices which are too fragile to use any mechanical marking. Additionally, laser marking offers the durability needed to meet requirements for image life-time and printed marking is not.
Laser-marking systems also excel in creating graphic images with intricate details. Lasers that use Nd:YAG can create marking line widths to 0.001 centimeters or less. This when combined with marking resolutions of 0.0002 inch/step, produces images with more detail than stencil or mechanical contact systems.
Whatever the reasons for the process that justify incorporating laser-based markings, use of this technology could yield significant savings in cost. Operating costs are a major factor for the Nd-YAG system, users have reported savings of more than 90 percent , and also reductions in quality control as well as cost of inventory.
As the manufacturing industries continue to automatize their processes for manufacturing, integrate aftershipment traceability and reduce production times, use advanced graphics and create products that require different marking methods, manufacturers of laser markings continue to enhance the speed, power of image generation, user-friendliness and the capabilities of their equipment.