By taking advantage of instantaneous high-temperature plasma generation, high-temperature metals such as tungsten can be transformed in additive manufacturing processes. Jian Liu, founder and president of PolarOnyx, has pioneered and led the product development of a femtosecond laser (femtolaser) 3D printing system (Tungsten-LAM, 2016 R&D 100 Award winner).
Tungsten-LAM (Laser Additive Manufacturing) is a powder-bed based additive manufacturing system. Equipped with high power and high energy femtosecond fiber laser, Tungsten-LAM is capable of manufacturing various materials, especially high melting temperature materials, such as tungsten. Tungsten-LAM is an ideal solution for industrial applications ranging from functional prototyping to rapid manufacturing. The printed parts are fully dense and have exceptional detail, surface finish and overall accuracy.
Dr. Liu explained all the technology behind the Tungsten-LAM system in an article which appeared on Photonics Media. Below you can find a summary, to read the full article and the truly amazing possibilities illustrated by Dr. Liu please view the original article on Photonics Media.
Femtosecond (fs) lasers have long been a workhorse in subtractive manufacturing, prized for their unique ability to athermally ablate materials. They are commonly used in surface structuring, drilling and thin-film scribing. However, few thought that an fs laser could be used in additive manufacturing (AM). By taking advantage of instantaneous high-temperature plasma generation, a recently developed fs fiber laser can melt high-temperature metals such as tungsten. Employing the fs fiber laser, parts created using tungsten achieved 99 percent density. Moreover, researchers have shown that the fs laser can deposit metals on glass substrate.
Laser additive manufacturing centers on selective laser melting, using material powders to build three-dimensional parts with complicated structures. It’s an efficient, robust and cost-effective technique for the next generation of manufacturing.
Rapid delivery of energy
The main characteristic of the ultrashort laser pulse is the high-peak intensity that results in rapid (ps) delivery of energy into the material, independent of material absorption characteristics, to cause ionization, which is much faster than the plasma expansion (ns to µs), therefore the local temperature is rapidly increased to over 6000 °C (controllable through energy and pulse number) and the thermal damages to surroundings are reduced or eliminated.
Compared with CW laser additive manufacturing, the fs laser approach creates instantaneous high temperatures to melt high-temperature and high-thermal-conductivity metals, forming much stronger microscale welding/bonding between similar or dissimilar refractory metal powders in various shapes and sizes. This multifunctionality could significantly reduce building time and cost, which is not achievable for CW laser additive manufacturing.
Closer look at the AM process
A simplified look at the mechanisms of the AM process (Figure 2) shows that the ablation of the fs fiber laser incurs ionization and recombination of materials in the ps regime to form new grains and microstructures during supercooling and solidification from a few ps to a few ms.
Figure 3. Samples of tungsten parts on tungsten substrates with various shapes and density. The gear has a 1/2-in. diameter (left), while the thin wall (right) has a thickness of 100 µm. Courtesy of PolarOnyx.
By varying process parameters such as fs fiber laser parameters (energy, power, pulse repetition rate), scanning speed and pattern, any type of sample can be made with controllable porosity, microstructure, density (up to 99 percent), shapes and structures.
Tungsten powders can be used to make various components, including thin walls and gears, on Tungsten substrates (Figure 3). It is also important to note that the microstructure can be varied by changing the pulse width (Figure 4) to tailor the mechanical properties of AM parts.