To reduce the manufacturing costs of making tungsten tools, a team of researchers at the U.S. Army Research Laboratory has figured out how to 3D print it into the exact size and shape they want, with little to no post-machining required, according to a U.S. patent application first made public on Thursday. Tungsten carbide is hard, so hard that it’s expensive to make it into useful tools and shapes. The current manufacturing process takes five steps, the last being grinding for quality control.
Army Weaponry Applications
Tungsten is nearly twice as hard and twice as dense as steel, and when you shoot it into hard targets it penetrates, which is why the U.S. Army likes it for armor-piercing bullets (it’s currently used in the M993 ammunition, a 7.62×51mm NATO armor-piercing round), but it also makes awesome drill bits for mining, surgical cutlery, and industrial grinders. Due to the high hardness, machining of the densified material is very time and cost-intensive. Also, the subtractive nature of the machining process limits the complexity of part shapes. The Army’s patent-pending tungsten carbide additive manufacturing process builds on a technique called powder bed fusion with selective laser melting. Machines that can perform this process are commercially available.
But in contrast to other efforts, the Army research team is experimenting with different binder materials, in hopes of finding a replacement for cobalt, which is expensive and carcinogenic, according to the National Toxicology Program. In a proof-of-concept study, the Army research team produced tungsten test shapes using an iron-nickel-zirconium binder with four, commercially available tungsten carbide powder particle sizes, and analyzed them for micro-cracks using optical and scanning electron microscopes. Even with the relatively low binder content, most of the samples possessed structural integrity, with theoretical skeletal densities as high as 95% with macroscale open porosity, they wrote in their research paper.
Although the starting particle size was submicron, there were grains in the SLM-processed sample that had grown to several microns in size. These large grains were typically present in pocketed regions of the sample, while other areas exhibited more ‘ideal’ microstructures, suggesting that further refinement of this technique could prove to be a suitable manufacturing method of cemented tungsten carbide.
Patent Now Public
With the patent application now public, U.S. businesses can pursue patent licensing agreements with the Army, which allows private parties to leverage the Army’s research and development efforts to boost their business. This is prime for several markets in addition to the military application. There’s obviously value in getting rid of the cobalt with the new binder, value in eliminating steps in the current manufacturing process, and also value in licensing the IP that protects the additive manufacturing technique.