| The unequal pitch end mill will change the spectrum characteristics of the milling force due to the unequal distribution of the inter-tooth angle and the helical angle,so that the spectrum line density increases and the milling energy is more dispersed in the frequency domain.Therefore,it has a strong advantage in reducing milling vibration and improving milling stability.For different working conditions,in order to give full play to the vibration suppression performance of unequal pitch end mills under the premise of ensuring milling efficiency,not only reasonable tool structure parameters but also corresponding process parameters are needed.Therefore,based on the real trajectory of the blade,this paper establishes the instantaneous milling force model of the unequal pitch end mill,and calibrates the milling force coefficient for the two typical materials of aluminum alloy Al7075-T6 and titanium alloy TC4.On this basis,the vibration reduction mechanism of the unequal pitch end mill is analyzed.In order to ensure the milling efficiency and reduce the milling vibration,the key parameters of the tooth angle and helix angle of the tool and the matching process parameters are optimized and analyzed when the unequal pitch end mill is milling the two typical materials of side milling and slot milling.The main research contents are as follows :Firstly,according to the milling process and regeneration effect of unequal pitch end milling cutter,the instantaneous milling thickness model based on the real blade trajectory is established.The instantaneous milling force model is established by introducing the instantaneous milling thickness based on the rigid force model,and the milling force coefficient expression is established by the average milling force method,which provides a theoretical basis for subsequent optimization analysis.Secondly,the finite element simulation of unequal pitch end milling cutter milling typical materials is carried out,and the milling force coefficients of aluminum alloy Al7075-T6 and titanium alloy TC4 are calibrated according to the simulation results.The accuracy of simulation results and instantaneous milling force model is verified by experiments,and the feasibility of calibrating milling force coefficient by finite element simulation method is explored.According to the instantaneous milling force model,the influence of different cutter tooth angle,helical angle structure and milling parameters on milling force is analyzed,which provides a reference for the determination of constraints in the subsequent optimization process.Then,according to the established instantaneous milling force model,the milling force time domain signal is transformed by discrete Fourier transform,and the vibration reduction mechanism of unequal pitch end mill is analyzed from the perspective of spectrum energy distribution.In order to ensure the milling efficiency and reduce the milling vibration,the corresponding objective functions are established respectively.The multi-objective optimization of the key structure and process parameters of the unequal pitch end mill under different machining materials and milling methods is carried out by using NSGA-II algorithm,and the appropriate key structure parameters of the tool and the matching process parameters are obtained.Finally,according to the optimization results,the unequal pitch end mill under different working conditions is designed.Using five-axis CNC grinding machine,were ground to meet the demand of unequal pitch end mill and the corresponding equal pitch end mill;the milling experimental research is carried out by using the milled cutter to verify the effectiveness of the designed unequal pitch end mill and its corresponding process parameters.At the same time,the difference between the equal pitch end mill and the unequal pitch end mill in milling force and milling vibration is compared and analyzed,and the superiority of the unequal pitch end mill in improving milling stability is verified. |
