The method of manufacturing internal threads with chipless taps, including mutual pumping of the tool and the workpiece, as in the manufacture of external thread profiles, so it cannot be entered into the knurling methods. Due to the specific features of the thread extrusion process, the study of the operational characteristics of rubber manufactured by chipless taps is of practical interest.
The extrusion of threads occurs at a temperature not reaching the temperature of recrystallization of the metal of the workpiece, however, the physic mechanical properties of the surface layer of the metal of the threaded profile change.
As a result of cold displacement of the threaded profile, the metal flows in the threaded contour. Extrusion of internal threads by chipless taps is a method of plastic deformation of a metal, in which a special tapping rod with a profile of the necessary thread is screwed into a workpiece opening, which has a diameter equal to approximately the average diameter of the thread. Under the action of torque, the tops of the turns of the tapered intake part of the tap penetrate the surface of the billet hole, the displaced metal moves in the radial direction, gradually increasing the height of the threaded profile.
The actual geometry of the vertices of the tool cross-section contour has a significant effect on the thread extrusion process. Depending on the ratio of the contact planes of the tool and the workpiece, depending on the permissible amount of backing, the greatest torque is observed in hexagonal taps, and the smallest in trihedral taps.
Depending on the accepted backing value, the ratio between the lengths and areas of the contacting sections, and accordingly, the ratio between the torques for taps with a different number of faces, also changes. It should be noted that in addition to the magnitude of the torque, the second parameter characterizing the process of extruding threads is the stability of the taps, which is not directly related to the magnitude of the torque, then the optimal number of faces is n = 3. If the optimal number of faces simultaneously satisfies two criteria (minimum torque and maximum tool life), then the optimal number of faces is determined experimentally in a specific case
Optimal number of faces for fast self-folding kirigami
