Numerical Simulation Of Cutting Forces Generated By Drills With Indexable Inserts And Optimization For Drill Parameters

Due to the asymmetrical radial arrangement of the two carbide inserts of the drill with indexable inserts on tool body, the radial cutting forces will be generated during processing, which will lead to the deflexion of the drill axis, and hence affect the quality of the hole machined. Therefore, it is the key issue to be solved in the design and manufacture of the drill to minimize the radial cutting forces in drilling. In this dissertation, a theoretical model for predicting the forces and torque generated in steady drilling state is established. This model involves three parts. First of all, a model of dynamic geometry analysis for the cutting section of the drill using vector-matrix approach is developed, with the help of this model, the cutting edge inclination angle, normal clearance angle,cutting edge angle and the overlapped amount of the inserts can be obtained. Secondly, a mathematical model for drilling forces prediction based on classical oblique cutting theory combined with empirical formulae is built up. The relationship between the drill geometry, cutting conditions and the physical properties of the material to be machined and the drilling forces is given in the model for one type of workpiece material. Using this model, the effect of the factors mentioned above on the drilling forces and torque can be investigated within a broad range. Finally, In order to analyze the influence of different workpiece materials to be machined upon the drilling forces and torque, a predictive model by adding the specific cutting force at each unit cutting edge is established. Based on the model proposed above, numerical emulations for cutting forces and torque in drilling are conducted using different drill diameters, different machining data and different materials to be machined. According to the numerical emulations, a nonlinear and constrained optimization model, with the radial cutting force and torque as the objective function and five setting parameters of the inner and outer inserts on the drill body as design variables is established. With the help of this optimization model, the optimized drill structure, which will generate minimum radial cutting force and torque, can be determined for different cutting conditions. The optimum results are analyzed and how the optimal parameters affect the radial cutting force, the relationship between the drill diameter and the optimal parameters, the relationship between the machining data and the optimal parameters, the relationship between the material to be machined and the optimal parameters, and the comparison between the optimized drills and the drills without optimization are investigated. The research results show that the radial cutting forces generated by drills with different diameters can be reduced to zero by optimizing the five setting parameters of the inserts on the drill body. Among the five parameters, ψhas greatest influence on the radial cutting force while βhas smallest influence on the radial cutting force, thus, when the drills with indexable inserts are designed and manufactured, the tolerance limits for ψshould be strictly controlled. At the same time, the optimal parameters vary with machining conditions, and the five optimal parameters are also different for different drill diameter of the same type. The influence of the physical properties of the workpiece material to be machined upon the optimal parameters are minor. The outcome of the study will provide the theoretical basis and valuable optimized parameters for the design and manufacture of high performance and high quality drills.