When the first commercially available blue industrial laser shipped over five years ago, it began to transform materials processing applications. Its rapid adoption followed, based on the fact that all metals absorb blue light much better than infrared (IR) light, especially copper, aluminum and gold, all of which are highly reflective in IR. . This fundamental physical advantage leads directly to improved performance for metal processing applications. It first impacted welding, where better light absorption leads directly to improved welding speed and part quality. The blue laser now brings these same advantages to additive manufacturing.
Additive manufacturing began as a method of producing prototype parts from plastics and other polymers. While useful for verifying form, fit and function, this limited range of materials dictates an equally limited range of applications. It is only with the extension of additive manufacturing to the manufacture of metal parts that the applications can be extended. Industrial blue laser technology has now advanced to allow integration into laser-based metal 3D printing methods such as direct energy deposition (DED) and powder bed fusion (PBF).
Additive manufacturing presents unique challenges that the blue laser is designed to overcome. For example, the manufacturing speed, efficiency and quality of blue laser 3D printing opens up the possibility of mass production. Advances in laser technology and additive manufacturing processes will drive growth and enable new applications.
A foundation in fundamental physics
The electronic structure of metal atoms dictates their interaction with electromagnetic radiation. For a wide range of reflective metals – copper, aluminum, gold and others – their inherent atomic structure makes them very poor absorbers of infrared radiation. Therefore, very high IR power densities are required to initiate even energy transfer in metals. At low IR power density, the IR light is simply reflected from the surface.
As the power density increases, the beam forms a hole in the part, with infrared radiation reflecting off the sides of the hole several times, resulting in a dramatic increase in absorption. This dramatic increase leads to a runaway condition, with increased absorption resulting in violent vaporization, creating voids and spatter which results in a poor quality weld. Conversely, as shown in Figure 1, these same metals absorb blue light very well. Therefore, melting reflective metals with blue laser energy is a smooth and well-controlled process.
For an application like welding, the objective is to achieve a mechanically (and sometimes electrically) robust joint, characterized by an even and continuous weld. With the precise process control offered by the blue laser, a wide selection of speed, spot size, beam energy and other parameters will produce a high quality weld. This means that different combinations of metals, thicknesses and part geometries can be accommodated. In contrast, with the IR laser, the window for these process parameters is extremely narrow, which not only limits productivity, but is sometimes so narrow that it is impossible to achieve a high quality weld using an IR laser.
Additive metal manufacturing is essentially sequential welding done on a small scale. Raw material is presented and an energy source melts the raw material, joining it to adjacent material. Laser-based additive manufacturing is attractive for the same reasons that lasers are optimal solutions in many applications: they deliver energy flexibly and reliably to a precise location without requiring physical contact between the laser and the material. DED and PBF are alternative approaches to presenting the raw material. The DED, for example, directs the raw material to the laser printhead, while the PBF lays down an even layer of powdered material over which the laser travels in a specified pattern.
The same fundamental physics of welding applies: poor absorption of reflective metals such as copper, gold, and aluminum presents IR laser additive manufacturing with two challenges. First, when fusing reflective materials with a high intensity IR laser beam, there is a substantial amount of vaporization of the smaller powder particles, leading to the need to manage the redeposition of these vaporized particles.
Second, if you are using a ring laser, a significant amount of energy is wasted preheating the powder in front of the higher brightness laser source.
Blue light is predictably absorbed by most metals, so a low-light laser can be used to create a well-controlled fusion puddle and vaporization can be minimized. This provides a way to expand multilaser systems without having to resort to complex gas flow management schemes. Therefore, blue lasers can provide high part densities, higher print speeds, and a way to increase production speeds with multiple parallel lasers. As shown in Figure 2, the blue laser produces 3D printed metal parts of equivalent density more efficiently than infrared sources.
While fundamental physics is a necessary component for industrial blue laser success in materials processing applications, realizing the promise requires real-world engineering. Early blue laser performance tests in DED and PBF machines demonstrate the tangible benefits of blue over IR. For example, copper blocks made with both methods achieved a density greater than 97% and showed excellent surface quality and dimensional accuracy, while stainless steel test coupons had a minimum density of 98%, all before process optimization.
Representative quantitative improvements of blue versus IR are summarized in Figure 3. The key build rate efficiency metric – essentially a measure of build rate per watt – was also found to be 1 .4X to over 7X better than IR. These advantages are consistent for stainless steel, titanium, copper and the GrCop alloy, and demonstrate the basis for growth in additional application areas.
Specifically, IR printing of highly reflective materials such as gold, pure copper, or aluminum is slow and IR lasers struggle with print quality. The blue laser is opening up applications in jewelry, dentistry, and medical implants, and the benefits of the blue laser extend to printing gold and manufacturing pure copper parts such as those required for components in aerospace and electric vehicles. For example, Figure 4 shows a representative 3D printed part – a scaled down version of a rocket engine nozzle, including the complex internal cooling channels. Higher speed, coupled with better throttle management, will democratize 3D printing for mass-produced parts and lead to wider adoption of 3D printing.
Current Capabilities, Future Possibilities
Since its introduction in 2017, blue industrial laser specifications have rapidly improved. Obtaining key measurements for power and brightness has expanded the scope of applications. Early designs excelled in battery cell manufacturing applications, where dozens or dozens of thin sheets needed to be joined with good mechanical strength and uncompromising electrical fidelity.
Building on this early success, as the blue laser reached higher levels of output power – breaking the 500 W and then 1000 W milestones – its range of applications also expanded. For example, it has become possible to join battery sheets, tabs, busbars and enclosures with a single laser system. Additional advancements allowed the laser to be integrated into standard industrial scanning systems, introducing efficiencies that enabled fast, high-quality throughput for consumer electronics applications. These applications, in turn, have spurred the development of assembly processes for electric vehicle components, as well as aerospace and medical applications. Until now, laser improvements and process developments have happened in parallel, and this trend will certainly continue with additive manufacturing.
We anticipate that much of the development in automotive and similar applications will focus on process optimization to further improve the efficiency of volumetric printing. The blue laser technology being developed today will greatly support the future expansion of additive manufacturing by delivering higher print speeds, with high resolution and quality. Higher luminosity blue lasers will directly impact today’s 3D printers by providing a plug-and-play replacement for IR lasers, resulting in an immediate improvement in performance and material extent that can be printed. Figure 5 shows the simple integration of a blue laser into a commercial 3D printer.
Rapid and steady improvement
The next leap in industrial blue laser capabilities will come with surface printing, which is a very promising technology but still in the early stages of development – a development that NUBURU is pursuing under a demonstration contract from the US Air Force. Parallel continuous improvement of blue laser and optimization of parameters for processes such as surface printing will face the same challenges as any new technological development. Improving technical performance is key to growing applications for any new product, but logistics must also meet market needs. The benefits of industrial blue laser material processing are leading to rapid adoption across a range of industries, necessitating, by necessity, changes in the supply chain; but as these changes occur, other blue laser applications will open up in other industries, such as healthcare, display, and bioinstrumentation.
With past history as an indicator, the growth promised by the blue laser seems almost inescapable. Additive manufacturing offers efficiency in the use of materials, rapid time to market for innovative designs in all sectors and significant net reductions in operating and maintenance costs. But these benefits cannot be realized if metal 3D printing remains expensive and slow. The industrial blue laser breaks down these barriers to deliver fast, cost-effective, high-quality manufacturing of metal parts, and enables additive manufacturing to deliver on its promise.