A Yale University research group is blow molding miniature
resonators for microelectromechanical systems (MEMS)
from a recently developed alloy of bulk metal glasses (BMG).
By blow molding the BMGs, the team was able to perform shaping, joining and finishing in one step that took less than a minute.
Bulk metallic glasses have a disordered atomic-scale structure in contrast to most metals, which have a highly ordered arrangement of atoms.
Metallic glass was originally discovered at the California Institute of Technology in 1960. A company called Liquidmetal sells titanium-based BMGs that are based on research at Caltech. More recently, amorphous metal has been produced that demonstrates strengths greater than traditional steel alloys.
Design News broke the story last year that Apple has acquired an exclusive license to use Liquidmetal technology in personal electronics devices.
The Yale research shows potential for BMGs as a blow molded material, creating the possibility of different types of shapes than are possible in injection molding or casting processes.
Stronger than steel
So far the Yale team has created a number of complex shapes, including seamless metallic bottles, watch cases, miniature resonators and biomedical implants that can be molded in less than a minute and are twice as strong as typical steel.
According to Schroers, the materials cost about the same as high-end steel. The alloys are made up of different metals, including zirconium, nickel, titanium and copper.
The team blow molded the alloys at low temperatures and low pressures, where the bulk metallic glass softens dramatically and flows as easily as plastic but without crystallizing like regular metal. It's the relatively low temperatures and low pressures that allowed the team to shape the BMGs with unprecedented ease, versatility and precision, Schroers said. Temperature are around 430C, and pressures are also low, around 1 atmosphere.
In order to carefully control and maintain the ideal temperature for blow molding, the team shaped the BMGs in a vacuum or in fluid. "Vacuum levels can be very low, just to reduce thermal conductivity of the environment," says Schroers. "Lots of shapes do not require vacuum at all. The liquid process is for very complex shapes."
"The trick is to avoid friction typically present in other forming techniques," Schroers said. "Blow molding completely eliminates friction, allowing us to create any number of complicated shapes, down to the nanoscale."
"This could enable a whole new paradigm for shaping metals," Schroers said. "The superior properties of BMGs relative to plastics and typical metals, combined with the ease, economy and precision of blow molding, have the potential to impact society just as much as the development of synthetic plastics and their associated processing methods have in the last century."
The Yale group has formed a company to commercialize the technology. Schroers told Design News this it would be "very realistic" for the company to making large volumes within two years.