Interactive software tool makes complex mold design simple
August 17, 2018
Most of the plastic objects we see are created using injection molding,
but designing such molds is a difficult task, usually requiring experts.
Now, computer scientists from the Institute of Science and Technology
Austria (IST Austria), the University of Tokyo, and CONICET have created
an interactive design tool that allows non-experts to create molds for
an object of their choice. The software will be presented at this year's
prestigious SIGGRAPH conference, one of IST Austria's five successful
These are objects created using
the new design tool using resin casting or injection molding.
Molding is a popular method for the mass production of objects.
Essentially, two (or more) mold pieces are fit together, leaving the
shape of the desired object as a hole. During fabrication, a fluid is
introduced into this cavity and is allowed to harden. Once the fluid has
solidified, the pieces of the mold are removed, leaving behind the
molded object. While the process is fairly simple, creating the mold to
produce an object is extremely difficult, and a multitude of
considerations go into its creation. How should the object be oriented
and divided to ensure that the pieces of the mold can be removed? If the
object should be hollow, how should it be decomposed into pieces?
Figures with loops or holes add further complications, as do aesthetic
considerations, such as avoiding a parting line through a face. In mass
fabrication, the high costs of the initial mold design are offset by the
low per-unit cost of production. For a small-scale designer, however, or
a novice interested in experimenting with injection molds, hiring a
professional mold designer is impractical, and creating the molds
unaided infeasible. Similarly, 3D-printing the desired number of objects
would be far too time- and resource-intensive.
CoreCavity, a new interactive design tool, solves this problem, and
allows users to quickly and easily design molds for creating hollow,
free-form objects. Created by Kazutaka Nakashima, a PhD student from the
University of Tokyo visiting IST Austria, Thomas Auzinger (IST Austria),
Emmanuel Iarussi (CONICET, IST Austria), Ran Zhang (IST Austria), Takeo
Igarashi (University of Tokyo), and Bernd Bickel (IST Austria), this
software tool opens up opportunities for small businesses and
enthusiasts. Given a 3D-scan of an object, the software analyzes the
object, and creates a "thin shell", essentially a hollow version of the
object, where particularly small gaps are considered solid--another of
the team's innovations. The software then proposes a decomposition of
the object into pieces; each piece will be created by one mold, then
joined together at the end. Moreover, the program is able to suggest
slight modifications to the original design, for instance to eliminate
tiny hooks that might complicate unmolding. "Previous tools were unable
to suggest such changes," says Thomas Auzinger, a postdoc at IST
Austria. The user can adjust the decomposition simply by clicking, and
choose to accept or reject any proposed modifications. When the user is
satisfied, the software automatically produces the mold templates, which
can then be 3D-printed and used for molding.
decompositions suggested by the design tool are often surprising: "The
computer is able to find solutions that are very unintuitive," says
Bernd Bickel, professor at IST Austria. "The two halves of the rabbit,
for instance, have a curving, complicated connection--it would have been
extremely difficult for a human to come up with that." Industry
designers, as well as previous design programs, generally rely on
straight cuts through the object. In practice, this often leads to a
larger number of pieces, as well as "unnatural" divisions. "The software
tool could also be extremely useful in industry--it would fit seamlessly
into the production process," adds Bickel.
The team has already tested some of their molds at an injection-mold
factory near Linz. "The factory employees were surprised at how easy it
was to extract the finished objects, as well as how durable the
3D-printed molds were. Even after creating a hundred objects, the molds
were still working," says Auzinger. The team already has further
improvements in mind. One idea is the inclusion of connectors that snap
together to ease the final assembly of the object.