Researchers at the Beijing Key Laboratory of CryoBiomedical Engineering have developed a metal 3D printing process that uses low melting point metal alloy Inks. The inks liquefy just above room temperature and will quickly solidify once they are printed – or deposited – into a bath of cooling liquid.
3D printing with metal has emerged as one of the more important additive manufacturing applications in recent years, with uses for the production of cars, consumer electronics, medical devices and it even helped launch a rocket into space. Currently, selective laser sintering, selective laser melting and laser metal deposition are producing extremely complex and fully solid metal parts that are virtually impossible to create with any other method. But it is still a time consuming process as the parts generally have a low print resolution and still need to be cooled and post-processed significantly before the parts are useful. They also use materials with high melting points, often needing temperatures well over 300 degrees celsius.
Chinese engineers Lei Wang and Jing Liu suggest in a recently released research paper that 3D printing with metal might become easier if we use different, smarter materials and printing methods. Wang and Liu explore using liquid phase 3D metal printing to speed up the process of metal 3D printing, reduce the time it takes prints to cool and increase the rate that objects can be rapid prototyped. They began experimenting with metals and metal alloys that melt at lower temperatures and can be cooled and solidified quickly.
They settled on an alloy comprised of four elements called Bi35In48.6Sn15.9Zn0.4, which just rolls off the tongue. The combination of zinc, bismuth, tin and indium has a melting point of just over room temperature, so it can easily be kept in a liquid state, deposited uniformly enough to construct three dimensional parts, and cooled quickly in order to retain the desired shape. The method can be used with other alloys and inks however, and select nanoparticles like copper and silver can be added without disrupting the process. The inks can also be combined with plastic materials that can create easily removable support structures.
As with any additive manufacturing process, an STL model is sliced into layers and each layer has the liquid metal deposited on the printing surface. But rather than a traditional 3D printing nozzle, the metal ink is deposited by an array of specialized syringes that can be easily replaced with various sized needles depending on the needs of the structure being built. The droplets of liquid metal are printed into a trough full of a cooling fluid comprised of water or ethanol that will cause it to rapidly solidify and fuse together.
Metals with low melting points already have extensive applications for the manufacture of computer chips, cooling systems and microfluidics. Using the materials with a 3D printing process will enhance it the same way that traditional metal 3D printing enhances part manufacturing. It will allow the creation of customized and complex metal parts quickly and efficiently for a lower cost, with less time investment and a smaller expenditure of energy.
