Research On CNC Grinding Complex Shaped Cutter Using Spherical Grinding Wheel

Complex shaped cutters with complex shaped cutting edge and revolving body (such as cone, ellipsoid) are widely used in aerospace, automobile, and die & mold industries. Presently, the manufacture of high quality complex shaped cutters in China is mainly based on foreign manufacture technologies, facilities and softwares.Modular-based mathematical model of cutting edge for complex shaped cutters is proposed with the help of the thought of modularization in programming and reconfiguration in manufacturing. In order to establish the basic modulars which are the components of the modular-based mathematical model of cutting edge, the mathematical models and boundary conditions of a helical cutting edge with constant helical angle or constant lead and the planer cutting edge through the tip of cutter's ball-end are deduced. Using the modular-based mathematical model of cutting edge, the AutoCAD-based design modular for complex shaped cutter is developed.A novel method using a spherical grinding wheel to grind the complex shaped cutters is proposed. This method utilizes the self-adaptation characteristics of a sphere to decrease the number of simultaneous cooperative axes of CNC tool grinder and to smooth the rake face on the transition area between the different geometrical bodies of the cutter. In order to obtain accurate normal rake angle actively and simplify the calculation of CL (cutter location), a moving coordinate system based on the required normal rake angle and the cutting edge is established. The constraint conditions for CL calculation are built and the formulations to determine the position and orientation of spherical grinding wheel are deduced. The post-process of CL data is also explored. The number of simultaneous cooperative axes of CNC tool grinder can be decreased from 5 to 4 and the smooth transition of rake face is realized by proposed method using spherical grinding wheel to grind complex shaped cutters, compared with the grinding method using standard dish shaped grinding wheel.Corresponding to the presented grinding method for complex shaped cutters with spherical grinding wheel, a new configuration of CNC tool grinder is introduced, which is quite different from what existed in the tool making industry. In order to resharpen mills on-site or to innovate on the structure of tool grinder originality, several structural model of the new CNC tool grinder are established.A method based on 3D simulation of grinding process to determine the parameters of spherical grinding wheel is presented, considering that the rake face of complex shaped cutter is enveloped passively and approximately while the cutting edge is being ground. The effects of the parameters of spherical grinding wheel on rake face, groove and strength of the cutter to be ground are inducted, which are bases of determining the parameters of spherical grinding wheel.A 3D simulation software of CNC grinding process based on VC++ and OpenGL is developed independently. The method to construct the virtual environment for machining simulation is explored. The geomerictial simulation of material removing process is relized by means of 'discreting - finding intersecting point - filtering - reconstruction'. Based on the radial lag angle of the point on the cutting edge to be ground, the algorithm to discrete workblank adaptively is proposed, considering the accuracy and the efficiency of machining simulation. In order to obtain the contours of discreted cross-sections of the cutter being ground, the method to find the dominant points produced by intersection of spherical grinding wheel and discreted cross-sections is presented and the inclusion principle is established, which should be obeyed in filtering dominant points. In order to reconstruct the cutter being ground in real-time, the method to identify the correlation of valid dominant points and the corresponding algorithm are studied. The result of rake face grinding simulation for a taper ball-end mill shows that the time can be shorten from 375s to 11s by 3D simulation software based on VC++ and OpenGL, compared with the 3D simulation modular based on AutoCAD.By means of 3D simulation modular, rake face grinding for a taper ball-end mill as a typical example was given to confirm the feasibility of the proposed grinding method, the availability of the new moving coordinate system and the correctness of the CL formulations, the method to find the dominant points and the algorithm to reconstruct the cutter being ground. The results of grinding experiments show that the smooth transition of rake face on the transition area between the different geometrical bodies of the cutter can be realized by the proposed grinding method using spherical grinding wheel.