Abstract: In a method for automating design of a locking mechanism for a hearing instrument, a computerized 3D file of an ear impression shell surface is provided based on a 3D scan of a 3D ear impression of a patient's ear. The ear impression shell surface includes a locking surface comprising at least one of a helix or canal concha portion of the patient's ear. A 3D file is provided of a hearing aid shell. With a computer, the hearing aid shell is placed in a desired location in the ear impression shell surface where the hearing aid shell is to be locked in position. With the computer, a volume surface as a 3D file is created representing the locking mechanism by utilizing a profile of the ear impression shell surface to be used as the locking surface. The volume surface runs from the ear impression shell surface and along the profile of the locking surface.