The technology of 3D printing in metal has so far been thought of as rather arduous and limiting because it takes a long time, can only be performed using metal with high melting points, uses a lot of energy, and can be cost-prohibitive. Innovators and scientists have been hard-pressed to backtrack on this technology though, because of the potential they know lies in metal 3D printing in areas such as construction innovation, electronics, and breakthroughs in the medical industry. The current methods being applied are that of laser sintering, laser melting, and laser metal deposition.
So, how can we 3D print in metal, and how can we do it faster, better, and more affordably? Beijing engineers Lei Wang (Chinese Academy of Sciences) and Jing Liu (Tsinghua University) may have our answer, as they came to the obvious conclusion that if we want to reap the benefits of 3D printing with metal, we need to look beyond conventional methods. What if we could instead use metal for 3D printing that melts at a lower temperature? What if we could cool the product off faster—and we could 3D print everything in a more energy-efficient way which also offers the possibility of greater diversity in product?
Wang and Liu’s research paper, Liquid Phase 3D Printing for Quickly Manufacturing Conductive Metal Objects with Low Melting Point Alloy Ink (Wang, L. and Liu, J., Science China Technological Sciences, 2014, Volume 57) is a concise, clear view of how we can fix the current issues with liquid phase 3D printing, while offering greater affordability and more options. While they haven’t nailed it down to a completely streamlined, perfect process, major progress is obviously being made.
For liquid phase 3D printing, the engineers were searching for an alloy with melting points above room temperature and less than the traditional 300°C. These choices include gallium-, bismuth- and indium-based alloys, with which copper and silver particles can be mixed to make diverse and functional inks. While liquid phase 3D printing presented resolutions for all the current problems at the front end, the next challenge was in choosing a metal that did not result in the end-product melting.
The engineers settled on one particular alloy: Bi35In48.6Sn15.9Zn0.4, which is composed of bismuth, indium, tin and zinc. Then, they used an experimental device to work with issues regarding flow (they had to avoid solidification and 
The liquid phase 3D printing uses syringes as their printing “nozzles,” which deposit droplets into the cooling fluid. Upon rapid cooling, the droplets solidify and fuse onto each other, over and over, until they complete the 3D structure being printed. This method works because the droplets melt so easily and then again retain their shape. Again though, with issues regarding melting and solidifying, manipulating the temperature of the alloy in the syringe was a consideration. Because the alloy they were using was just above room temperature, it was prone to settling back into shape and blocking up the syringes they were using to inject the liquid metal into the cooling fluid. The engineers were able to solve this problem by keeping the syringes at a constant temperature with a temperature controller.
With the proper temperature being controlled and air pressure being provided by a regulated nitrogen cylinder, the process works when the syringe is immersed in the liquid cooling fluid, which was water and ethanol for the purposes of this experiment—causing a dripping of metal droplets, rapidly and repetitively, which creates the desired 3D printed shape. Different shapes can be used, also, such as lines. The engineers point out that this method is much better than air cooling in that the buoyancy and ‘superior thermal qualities’ of the ethanol cooling fluid allow for rapid cooling—and rapid production.
Temperature, air pressure, and properties of the printer ink have to be controlled to produce the desired 3D printing effect. The engineers point out that this process would obviously require some refining, but they see it as a good start for enhancing current 3D printing in metal, with the suggestion that moving to adopt the combination between the ‘syringe pump array’ and the ‘syringe needle array’ as the best system–with the pump extracting fluid metal, and the needle injecting it for printing. Conveniently, the injection needles can be interchanged depending on the printing project.
Wang and Lie point out that in terms of using their new principle that all low melting point metals should be able to be used in this process in the right cooling conditions, different properties of ink can affect the actual printing itself, as well as speed. The study overall is obviously very positive for the future of 3D printing with metal, as the conclusion of the study points out that liquid phase 3D printing:
- Is faster and can develop a wider variety of 3D printed bodies, including some unique metal structures.
- Is a process that can be used with other materials—such as plastic—to create supports and conductive devices.
- Is more energy efficient and cost effective.
Have you been involved in any metal 3D printing projects? What do you think of this research? Share your thoughts with us at the Liquid Phase 3D Metal Printing forum at 3DPB.com.
