Multi-Axes CNC Turn-Mill-Hob Machining Center and Its Applications in Biomedical Engineering

With the ever increasing demand for reduced size and increased complexity and accuracy, traditional machine tools have become ineffective for machining miniature components. A typical example is the dental implant and the other is the pinion used mechanical watch movement. With complex geometry and tight tolerance, few machine tools are capable of making these parts. We designed and built a CNC Turn-Mill-Hob Machining Center that is capable of machining various complex miniature parts. The machining center has 8 axes, an automatic bar feeder, an automatic part collection tray, and a custom-made CNC controller. In particularly, the CNC controller gives not only higher accuracy but also ease of use. In addition, to improve the accuracy, a software based volumetric error compensation system is implemented. Based on the experiment testing, the machining error is +/- 4 microm for turning, +/- 7 microm for milling, and the maximum profile error is less than +/- 7.5 microm for gear hobbing.;Many biomedical parts are axial asymmetric parts. While these parts can be machined using conventional CNC machining methods, the efficiency is low and the cost is high. We proposed a new CNC machining method based on polar coordinate interpolation, which is better than the Cartesian coordinate interpolation when rotational axes are involved. To facilitate the use the polar coordinate interpolation module, a special G code is developed. This module is integrated into our CNC Turn-Mill-Hob Machining Center.;Another important development is the use of hobbing method for machining axial symmetric / asymmetric parts. Invented some 100 years ago, hobbing is the most efficient method for machining gears. Its efficiency lies on multiple teeth simultaneous cutting. Presently, gear hobbing is a standard manufacturing process making millions of gears every day. Though, no one has used it for machining axial asymmetrical parts. After carefully examining the gear hobbing, it is found that the profile of the gear tooth is determined by a combination of the profile of the hob tooth and the relative position and motion between the hob and the workpiece. Therefore, by tuning the hob tooth profile and controlling the relative position and motion between the hob and the workpiece, it is possible to machine various axial symmetrical and asymmetrical parts, such as a start, a hexagon and etc. This method is efficient to machine continuously changed axial asymmetrical parts. This is validated by means of experiments. The experiments also indicate that the new method is much more efficient than the conventional milling method.;Our machining center and new machining methods have many practical applications. Dental implant is a typical example. It is estimated that 10% of the people will need dental implants in their life time. Presently, there are a number of brands in the market, though these implants may not fit for patients who have special oral conditions. In this case, custom-made implants are necessary. The key problem of the custom-made dental implant is manufacturing. Our multi-axes CNC Turn-Mill-Hob Machining Center and the new machining method can effectively machine the custom-made dental implants. Moreover, the efficient is good.