Numerical Simulation Of Drilling Mechanism Under Non-steady Cutting Conditions For Dills With Indexable Inserts

The radial cutting forces will be generated due to the asymmetrical radial arrangement of the two carbide inserts of the drill with indexable inserts on tool body during processing, which will affect the quality of the hole to be 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.There are two processing states during the drilling using a drill with indexable inserts, one is called 'steady state' and another is called 'non-steady state'. Steady state is the drilling process in which the cutting section of the drill entirely penetrates into the workpiece, while the non-steady state is the 'drilling in'and 'drilling out' processes. For 'drilling in' the process, from the instance when the drill touches the surface of workpiece to the instance when the cutting section of the drill entirely penetrates into the workpiece, is divided into five phases. For 'drill out' the process, from the instance when the tip of the drill penetrates out of the workpiece to the end of the drilling process, is divided into three phases. The generated radial cutting forces will induce the deflexion of the drill axis, therefore lead to the enlargement of the hole diameter in the 'steady state' and the 'bugle mouth' will alse be generated in 'non-steady state' as well.A model of dynamic geometry analysis for the cutting section of the drill using vector-matrix approach is developed, and a mathematical model for drilling forces prediction based on classical oblique cutting theory combined with empirical formulae is built up. In order to minimize the radial cutting forces, five setting parameters of the inner and outer inserts on the drill body have been optimized with the help of the optimization module of ANSYS software. Thereby the analysis module is utilized to build the FE model of drill body. The stress and deformation distributions are obtained and the enlargement amount of hole drilledin 'steady state' is calculated, and the theoretical enlargement amount of the hole drilled in 'non-steady state' is also predicted baded on them. In order to predict the stress distributions of the inner and outer inserts, their FE models are built up. The multinomial is used to fit the distribution of the load for the cutting section of two inserts in 'steady state' with the help of Matlab software, and the stresses along the cutting edges are analyzed. Five setting parameters are optimized again when cutting conditions are altered and the relevant stress changes for two inserts are simulated as well.The research results show:? The radial cutting forces generated by drills can be reduced to zero by optimizing the five setting parameters of the inserts on the drill body.? The results obtained from FEA show that the maximum stress locates in the ' transition part between the body taper and the front body of the drill and themaximum deflection is at the bottom of the front end of the drill. The maximum stress and deformation appear in the second phase of "drilling in" process.? The FEA reveals that under the same cutting conditions, the enlargment amount of the hole drilled using an optimizated drill is much smaller than that of the hole drilled using a non-optimizated drill, especially in the steady processing, the difference is much more obvious. As a result, the hole dimensional accuracy is greatly improved after optimization of the drill.? Due to the nonlinear force distributions of the active cutting edges, the force distributions can be expressed by polynomial curve fitting mothod offered by Matlab software. The curves show that the load is getting larger and larger with the decrease in coordinate values close to the drill center. The changes of load value for the left cutting edge of insertl are more obvious than others. The load value for the over-centerline point of the drill is maximal.? The stress distributions for two inserts in 'steady state' are effectively predictedby FEM. The analysis results show that the maximum stress occurs at the intersection point of two edges for insert 1 and in the region close to the tip of insert 2. The maximum stress value for insert 1 is larger than that of insert 2, therefore, the ductile material should be choson for insert 1. Though the maximun stress values of insert 1 and insert 2 are all lower than the allowance stress value, the regions where the stress concentrates will be worn out and broken, hence the intersection point of the edges for insert 1 should be filleted and the rake angle is reduced in order to extend the life of the insert.The outcome of the study is of great benefit to improvement of the structural design of the drill, the chip pocket profile design and the parameters determination of the inserts, as well as the usage of the drill with indexable inserts.