Injection Molding of Soft Robots

To date, injection molding has not been a practical manufacturing method for soft robots due to machine costs, large volumes of liquid silicones required, and the inability to change materials quickly between shots. Injection molds are typically machined from metals to allow for high pressure and clamping forces, which further limits the ability to rapidly prototype soft robots when molds could cost thousands of dollars. To circumvent these issues, a low-cost injection molding system and process are pioneered. In this article, the apparatus, design process, economics, and workflow are described using standard stereolithography and polyjet 3D printers to rapidly iterate on soft robot designs. The mold design process is further detailed to allow for proper material flow, clamping, alignment, and rapid curing times. Static mixing nozzle efficacy is characterized with common silicone materials compared to manual mixing and centrifugal planetary mixing. Lastly, a number of applications that could only be achieved through injection molding due to geometry, embedded components, or cure times are presented.