Parameters Identification Of Instantaneous Milling Force Model And Its Experimental Investigation

Prediction of instantaneous milling force is precondition for optimizing milling parameters, predicting tool deflection and wear, analyzing dynamic stability and predicting surface error. So, it is essential for improving the processing efficiency and accuracy. The key of this field is how to efficiently identify the parameters involved in the milling force model, e.g., the instantaneous cutting force coefficients and the runout parameters, etc. In this paper, the parameters identification of instantaneous milling force model is systematically investigated by means of theoretic analysis, numerical simulation and experimental verification.Tool-chip contact characteristics of typeⅠmilling and typeⅡmilling in end milling are analyzed and expressed descripted in unified form with the Heaviside unit step function. Cutting force coefficients are expressed as the instantaneous cutting force coefficients, instantaneous average cutting force coefficients and average cutting force coefficients respectively, and the corresponding milling force models are presented. Also, the influencing factors of the instantaneous milling force, e.g., runout, cutter deformation and stiffness of feed system, are analyzed, and three methods to compute instantaneous chip thickness are proposed.Based on analysis of the key techniques of cutting simulation, a finite element model is developed and employed to simulate the oblique cutting process of cutting edge discrete element for the A16061-T6 milling. With the simulation results, variation of cutting force and temperature distribution are obtained, and the relationships between cutting force coefficients and chip thickness are obtained which are exponential functions. Predicted milling force using evaluated coefficients are shown to match experimental results and simulation results based on cutter solid model with satisfactory accuracy. Then, the identification method of instantaneous cutting force coefficients is validated.Several methods are presented to identify the instantaneous cutting force coefficients and runout parameters separately or simultaneously with the experimental milling force. The instantaneous cutting force coefficients are identified using average milling force components with multiple experiments, and also identified using nominal milling force components which are extracted from experimental results with one experiment. Using the evaluated coefficients, the runout parameters are calibrated according to the minimum squared difference between the measured and predicted milling force. Moreover, another method to obtain the runout parameters is presented which is independent of the coefficients. To calibrate the parameters simultaneously, two methods are provided. In the first method, the parameters are identified by one dimensional search. The second method uses the particle swarm optimization(PSO) to calibrate the parameters. And the PSO is improved by introducing nonlinear decline inertial weights and probability distribution density function, which can improve global searching ability of the PSO to identify the parameters involved in the instantaneous milling force model. A series of experiments are conducted to realize the presented methods. Comparisons between the identified results with different methods and different experiments show that the methods are valid and consistent.Formation of surface error is analyzed, and cutter deformation is obtained using surface error of two experiments completed with different axial cutting depth only. Then, a new approach for the determination of parameters involved in the instantaneous milling force model is proposed. The method can eliminate influences of the other factors except cutter deformation and runout. A set of experiments are designed, and the results are used to identify the parameters. With the evaluated coefficients and runout parameters, the instantaneous milling force and surface error are predicted when the large length-diameter ratio cutter is employed. A good agreement between predicted results and experimental results is achieved and shows that the method is efficient, and influence of runout to surface error is not negligible.