Industrial Blue lasers reach milestone in solving metal processing challenges

The first generation of industrial blue lasers based on semiconductor laser diode technology was first launched in 2017. Since then, these lasers have mainly been used in copper and aluminum applications such as welding and 3D printing, which benefit from the increased absorption of (infrared) lasers relative to infrared. Even so, the brightness of these lasers still does not meet the requirements of industrial two-dimensional galvanoscope scanning systems used in many materials processing solutions. With the launch of the second generation of industrial blue lasers, NUBURU has made a breakthrough in the design and manufacture of these lasers and can now use them in industrial 2D scanning systems (see Figure 1).

The breakthrough is based on advanced manufacturing processes that produce laser beams with smaller spot sizes and divergence angles. For reflective metalworking applications such as welding and 3D printing, a laser beam is usually characterized by its brightness or beam parameter product (BPP), defined as the product of the beam radius (measured at the waist of the beam) and the half Angle of the beam divergence. The second generation of 450 nm blue laser modules is now available with a power of 125 or 250 W and a BPP of less than 5 mm*mrad - nearly two times the power and three times the BPP compared to the first generation laser module. This generation is also more compact, more reliable, and designed specifically for power scalability.

Most importantly, brightness levels are now sufficient for integration with industrial scanning systems, thus opening the door to wider adoption of the technology in a range of applications.

Make a breakthrough

NUBURU's first-generation laser system uses pre-packaged linear arrays of semiconductor laser diodes that are manually assembled on the module backplane. Each individual laser diode light is then collimated through a fast and slow axis lens. The laser module produced by this process has 150 W power and 15 mm*mrad BPP.

The second generation manufacturing process offers significant improvements in manufacturing, performance, size, and reliability, as summarized in the table.

These changes begin at the laser level. The first-generation system uses a pre-packaged linear array of laser diodes, while the second-generation system uses a single laser component in a base-on-a-chip (COS) configuration. Steering separate laser diodes has the advantage of allowing each laser to be driven individually rather than driving a linear laser array. In a linear array, if a single diode fails, the entire array will go offline and may result in a significant reduction in laser power. In the new design, if a single laser fails, the drop in light output is minimal. This also benefits overall system reliability.

With Gen 1 laser arrays, positioning and packaging are predetermined, and these arrays are manually placed on the driver backplane. In the Gen 2 module, automatic mounters are used to place each device in a tighter configuration. This more accurate registration helps maintain the polymerization brightness.

The next step is to attach the microlens to each laser diode. These lenses employ very asymmetric laser output profiles to create collimated beam profiles. In the first generation of modules, these were semi-manually placed and secured. In the Gen 2 module, they are automatically placed and secured in place in a dynamic manner. That is, the light output is actively monitored by optimizing the position and rotation of each lens for total beam performance. This automated assist positioning and lens placement is a key reason why BPP has been improved in the Gen 2 module.

Understand the benefits

The new COS base design offers significant improvements. Perhaps the most impressive aspect is brightness or BPP performance. For welding and 3D printing applications, it is important to optimize power density, defined as power divided by the beam area at the workpiece. The beam diameter at the workpiece is directly related to its Angle of divergence (BPP), but optimizing the Angle of divergence can provide greater cost performance. Why? Because power density is linear to power, but BPP is a power of two. So while the increase in power from Gen 1 modules to Gen 2 modules (150 to 250 W) is impressive, the improvement in BPP is even more impressive (from 15 to 5 mm*mrad).

The second generation manufacturing process also makes the laser module more compact. This is possible because of the laser diode's tightly packed flexibility and the tight integration of collecting microlenses. The size of the Gen 2 laser module is about one-tenth the volume of the Gen 1 module.

The new process also benefits laser reliability. Consistently apply contamination control by controlling each step of the preparation and handling of the Class 1000 clean room neutron assembly. Robotic assembly results in a more consistent manufacturing process with fewer opportunities for error caused by the operator. Most importantly, robotics enables scalable, repeatable processes to increase productivity.

Free space configuration

To date, a large number of materials processing applications have been developed using blue lasers, but all have welded lenses and other beam transmission capabilities. What is missing is a blue laser system that can be coupled to industrial two-dimensional scanning systems. The new Gen 2 brightness is now at a level where you can use this option. In addition, the compact size can be coupled directly to scanners up to 250 W (see Figure 2).

Figure 3 shows how this is done. Industrial scanners require spot sizes up to 30 mm. This is significantly larger than the spot size of the laser module, so a beam expander assembly is provided to create the desired spot size. The module/extender assembly can now be bolted directly to the scanning system for the first time.

Small BPPS can not only use scanning systems, but also have a significant impact on welding performance. FIG. 4 compares the results of two 500 W fiber-coupled blue lasers with different BPP values: 30 mm*mrad for blue data and 15 mm*mrad for red data. The data show that the BPP differs by a factor of 2, resulting in a 1.6-fold increase in penetration of the material at different fixed speeds, or a 3-4 fold increase in velocity at the same penetration depth. Greater penetration depths may be required for better control of metal melt and flow, while faster speeds may be required to reduce costs. The key is that the BPP determines the welding speed and penetration - the smaller the BPP, the faster and deeper the weld. Similar data development is underway for a free-space coupled scanner system with 5 mm*mrad BPP.

3D printing

3D printing is another area where blue lasers are gaining commercial use. 3D printing of metals can be achieved through a variety of strategies: powder bed fusion (PBF), direct energy deposition (DED), or wire feeding fusion (WFF). Although these methods vary in detail, they all require the metal to be heated to the point of melting (softening to melting). As with welding, the goal is to transfer energy from the beam to the metal. The more efficiently the process is done, the faster it will be and the higher the quality of the finished parts. Figure 5 illustrates the integration of the laser module into the scanner via a beam expander in a commercial 3D printer (powder bed).

Historically, infrared lasers have also been used for these applications, but the same advantages offered by blue laser welding are applicable to laser-assisted additive manufacturing. Recently, NUBURU replaced IR fiber lasers with BL blue lasers at DED and compared the results of the two technologies under the same conditions. The results are quantified in the most important metric: the build rate in cubic centimeters per hour (see Figure 6). Copper is manufactured 7 times faster than IR, stainless steel 3 times faster, and titanium 1.5 times faster.

Compared with the first generation laser, the brightness is increased by 3 times, the power is increased by 2 times, and the performance is significantly improved. As a result, it enables new integration with industrial scanning systems for laser welding and laser-assisted additive manufacturing.

Source: Laser Net