1. Fieid of the Invention
The present invention relates to a free form machining tool having a spherical surface machining section on a lower end for machining a freely curved surface.
2. Description of the Related Art
FIG. 1A shows a conventional free form machining tool. FIG. 1B typically shows a freely curved surface to be machined by this machining tool. A conventional free form machining tool 1 is, for example, a ball nose grinder or a ball end mill. The machining tool 1 has a spherical machining surface (such as a grinder or a cutting blade) on the lower end thereof (in this drawing). The machining tool 1 is rotated around an axis z. A freely curved surface 2 is, for example, a pressing mold, an aspherical lens or the like. The free form machining tool 1 is rotated around the axis z at high speed, while the lower end is moved along the freely curved surface 2 so as to work (grind or cut) the freely curved surface 2. A repetition of such a work allows the freely curved surface such as a mold or aspherical lens to be freely machined by the machining tool 1.
The aforementioned free form machining tool 1 is rotated around the axis z. Thus, the surface to be machined has a peripheral speed of zero (0) on the axis (radius: 0). Therefore, even if a triaxial (X-Y-Z) NC machining apparatus is used, the position of the axis (radius: 0) is a dead spot. Disadvantageously, this position cannot be excellently machined. Thus, the free form machining tool 1 has been heretofore mounted to a multi-axial NC machining apparatus having four or five axes. For machining a portion (for example, a portion A) where the freely curved surface is perpendicular to the z-axis, a program is made so that the axis z of the machining tool 1 may be appropriately angled with respect to the z-axis. However, such programming is complicated and difficult. Furthermore, the multi-axial NC machining apparatus having four or more axes is expensive. Accordingly, there is a problem that this has little general-purpose properties.