Research On The Key Technology Of NC Grinding Process For Blisk Structural Components

Blisk(blade integrated disk)is used extensively in the field of aerospace,nuclear industry,energy source and so on due to its good performance in raising the thrust weight ratio of engine.With the continuous improvement of advanced control and measuring technique,the manufacturing technology of blisk has been developed rapidly in recent years.However,compared with the mature rough machining process for blisk,its finishing process,like grinding process,is still in the stage of manual processing.Because of the poor quality consistency,low precision and inefficiency in manual grinding process,not only the fatigue life of blisk is decreased,but also the manufacturing cycle of engine is seriously affected.Therefore,in order to get rid of the traditional manual grinding process,the research on blisk automatic grinding technique is of great significance.Besides,it is of great importance to carry on the study of blisk automated production line.Based on the analysis of existing problems in current blisk grinding process,the new NC grinding machine with flexible grinding spindle,the basic contact theory between tool and workpiece,the control method and algorithm of grinding force,and the grinding parameter optimization are studied deeply in this thesis.The main research work and achievements of this thesis is summarized and highlighted as the following aspects:The major difficulties and challenges in grinding process,brought by the complex structural feature of blisk,are analyzed in the first part.To solve these problems,the automatic grinding method is put forward based on the experience of manual grinding process.And the NC grinding machine with a floating spindle mechanism is designed accordingly.After the briefly describing of the structure,the composition,and the key components of this grinding machine,the operation principle of the special floating grinding spindle,which is the core function component in this design,is introduced in detail.Then the mathematic model of spindle posture adjustment procedure is constructed depending on the accessible region analysis of this spindle.According to the traditional belt grinding knowledge and Hertz theory,the elastic contact behaviors between grinding tool and workpiece,such as the contact area size,the pressure distribution and the material removal rate,are studied deeply.Through the contact machining experiments,the influence mechanism of the abrasive grain,the abrasive tool diameter,the spindle speed,the theoretic grinding depth and the workpiece curvature radius to the contact area feature are proposed.Afterwards,under the both convex and comcave contact condition,the state equation of pressure distribution is established.And the material removal rate model in this elastic contact case is established too based on the Preston equation.It is showed that the model established features high reliability.On the basis of grinding spindle mechanism and force empirical equation,the real time indirect force control method is proposed in the third part of this thesis.And the grinding force control model is presented.Considering the complexity,nonlinearity,uncertainty and instability in the practical process,the fuzzy-PID control algorithm is applied in this control system to achieve precise control.The simulation results show that,compared with the traditional control method,the control strategy with fuzzy-PID controller runs well with quick dynamic response,small overshoots and high accuracy of the steady-state.The adaptability of control system is also verified through the simulation with different load.In addition,the method to calculate the normal grinding force is established utilizing the sensor in proportional valve.The thesis goes on with a detailed analysis of the grinding process and quality characterization parameters in this part.The influence of process parameters on machining quality is presented in accordance with the single factor experiments result.Through the L9 orthogonal experiments,the empirical formulas of the roughness,the profile accuracy,the material removal efficiency and grinding force are constructed respectively based on the regression analysis.Finally,the parameter optimization is carried out under the condition of different objective functions.And the optimized process parameters are obtained with several constraints using Matlab tool.The machining experiments are carried out to verify the effectiveness of the methods proposed above at the end of this thesis.On the one hand,the actual grinding depth and normal grinding force are detected to validate the reliability of spindle posture mini-displacement adjustment and force control process respectively.On the other hand,the surface roughness,profile accuracy and machining time are detected to demonstrate that the machining quality and efficiency are improved significantly in grinding process under the condition of optimized grinding parameters.In addition,the contrast experiments are also conducted between NC grinding and manual grinding.The results show the practibility,feasibility and reliability of NC grinding method.