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.
"This could enable a whole new paradigm for shaping
metals," says
Jan
Schroers, an associate professor of mechanical engineering at Yale. "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."
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.
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