A system includes a heating section configured to heat a sheet of plastic to generate a heated sheet of plastic. The system includes a plate configured to secure a mold associated with a dental arch of a patient. The plate includes a locking mechanism. The mold includes feature configured to interface with the locking mechanism. The system further includes a thermoforming chamber configured to thermoform the heated sheet of plastic to the mold that is secured to the plate via an interface of the locking mechanism with the feature to generate a thermoformed sheet of plastic. The locking mechanism is configured to extend through the mold and overlap an upper surface of the mold to lock the mold in a z-direction that is orthogonal to a plane defined by the plate. The system further includes a cutting tool configured to trim an aligner from the thermoformed sheet of plastic.