Dynamic And Reliability Analysis Of CNC Turret

As the core functional component of the CNC machine tool,the CNC servo turret directly participating in the cutting operation.It is used as a device for assembling multiple lathe tools,quickly changing the tool position.The appearance of the CNC turret shortens the auxiliary time of the cutting operation and can effectively reduce the machining error caused by the machining operation,the performance of turrets will play a key role in the evaluation of the performance of the CNC machine tool.As a rising performer in the CNC turret industry,Chinese government has been continuously increasing the investment and research on the middle and high-grade CNC turret in recent years.China's turret products have made great progress,but also exposed a lot of shortcomings.In this paper,a domestic high-grade CNC turret is taken as the research object,and the dynamic characteristics of the turret are evaluated by combining finite element simulation and dynamic test.The reliability analysis and optimization of the end-toothed disc bolt connection are carried out.The fatigue strength of the end-toothed disc and the precision degradation caused by the wear of the meshing surface are analyzed.The main research contents and results of this paper are summarized as follows:(1)The turret model was simplified and assembled in 3D software SolidWorks.Combined with the structural characteristics and working characteristics of the CNC turret,the finite element model of the turret is established in the CAE software HyperMesh.In the established finite element model the equivalent contact area method was used to simulate the bolt connection.At the same time,the virtual material method was used to equivalent bearing constraint.Better simulation results are obtained while solving the nonlinear problem.After the pretreatment is completed,import the model to Abaqus for static and dynamic calculations,including modal analysis,harmonic response analysis and static stiffness analysis.Through the analysis of the simulation results,the static and dynamic characteristics of the turret were evaluated,and the weak parts in the turret structure were found.(2)A dynamic test platform is built to ensure the turret in working state.The platform includes a CNC center,a hydraulic station and two equipments that can realize the constraint of different state of turret.The turret can realize the function of transposition tool changing and hydraulic locking in the platform,and can be installed independently from the machine tool.The two kinds of tool carrier in the platform can realize the modal analysis of the tool carrier under different constraints more accurately.Then,based on the dynamic test platform of the CNC turret,the modal analysis of the turret under different constraints conditions is carried out,and the dynamic parameters such as the natural frequency and the vibration mode of the turret are obtained.The static stiffenss test platform of the turret was built by the CNC lathe,and the tangential static stiffness test was carried out on the turret to obtain the maximum deformation parameters of the turret.After obtaining the above parameters,the finite element simulation results are compared with the test datas.Not only verifying the accuracy of the finite element simulation results,but also the dynamic characteristics of the turret are more fully understood,which confirms the weakness parts of the turret structure.(3)Based on the reliability design principle,the reliability model of the tool rest subsystem is established,and the influence of the bolt connection of the end-toothed disc on the overall reliability of the turret is analyzed according to the the actual situation of production and the simulation test results of the tool rest.According to the stress-strength interference model,the reliability of the bolt connection of the end-toothed disc is analyzed.Based on the analysis results,the nominal diameter,strength level and the number of bolt groups of the bolts are optimized to improve the reliability of the bolt connection.(4)Aiming at the core position of the end-toothed disc in the turret structure,the fatigue strength and precision degradation of end-tooth disk were analyzed.Firstly,the turret model is introduced into the fatigue analysis software Fe-Safe,focusing on the analysis of the fatigue life,and the fatigue life of the inner toothed disc is obtained.It can be seen from the results that the life of the inner tooth disc is long.Then,based on the Archard model,the meshing surface wear model of the end-toothed disc was modeled,the mapping relationship between the degree of meshing surface wear and the accuracy of the turret was established,and the relationship between the number of tool changes of the turret and the accuracy degradation of the end-toothed disc was analyzed.The model can be used to predict the trend of wear between the meshing surfaces of the end-toothed disc and the influence of wear on the degradation of tool rest precision.