Theoretical Study On Dynamic Characteristics And Flutter Stability Of Micro-end Mill Incorporating Gradient Effect

Micro-milling has unique advantages in the micro-fabrication of composite microstructures and three-dimensional complex topography,and is one of promising micro-manufacturing technologies.When feature sizes are on the micron or submicron scale,the micro-scale tool needs to move toward smaller.Because the mechanical properties of micron-scale materials have a strong micro-scale size dependence,the mechanical behavior of micro-path milling cutters will also be significantly different from the traditional macroscopic conditions.There is still insufficient understanding of the micro-scale effect of the micro-tool system.The problem of micro-milling cutter dynamics and flutter stability considering the micro-scale effect cannot be solved if it is not properly solved,which will restrict the diameter of the micro-milling cutter.The development of smaller and smaller dimensions has led to the solution of this problem to the theoretical bottleneck and technical difficulties in the analysis of the dynamic properties and flutter stability of micromill.For this reason,this paper makes some explorations and attempts to study the effects of micro-scale effects on the theoretical modeling,dynamic characteristics and flutter stability of micromill system,and strives to establish a set of dynamic characteristics and flutter stability analysis for the micro-tool system.The modeling theory and analysis methods will lay a certain theoretical foundation for the dynamic design of the micronized milling cutter system.In the framework of the nonlocal strain gradient elasticity theory considering micro-scale effects,based on the Hamilton principle,a non-classical tension rod model,a non-classical torsion shaft model,non-classical Timoshenko and Euler-Bernoulli beams models for micromills considering gradient effect are established.Various kinetic models of micro-tools can be used to study the micro-scale effects on the dynamic characteristics of micro-tools by introducing additional material length scale parameters(or strain gradient parameters)and non-local parameters(or stress gradient parameters).These established theoretical models lay a foundation for studying the dynamic characteristics and flutter stability characteristics of the micro milling cutter considering the gradient effect.In order to solve the problem of solving the cantilever micromilling cutter,a numerical solution technique was developed,and then a set of non-classical finite element methods was proposed to solve the theoretical models of the non-classical tension rod model,the non-classical torsion shaft model,and the non-classical Euler-Bernoulli beam model under the conditions of clamped-free ends.The predicted natural frequency of the established finite element model of the milling cutter can be in good agreement with the experimental results.In addition,the gradient parameters of the material play an important role in the dynamic behavior of the micro-milling cutter structure.In order to determine the stress gradient parameter and the strain gradient parameter of a specific material,the material is identified by comparison with typical micro-dynamic experiments.The stress and strain gradient parameters are identified,and the applicable ranges of the two gradient parameters of the two metal materials are given.Using the micro-milling model considering the gradient effect,the influence of geometric parameters on the dynamic characteristics of the micro-milling tool is studied in detail.Studies have shown that as the cutter head diameter becomes smaller to micrometers,the gradient effect can not be ignored in the dynamic characteristics of micro milling.Considering the gradient effect and regenerative delay effect,the theoretical model of the chattering stability domain of micro-milling is established based on the proposed non-classical finite element method and the cutting load including the regenerative delay effect.The full-discrete algorithm was used to study the size-dependent mechanical behavior of flutter instability for micro-tools.The study shows that as the cutter head diameter becomes smaller to the micron level,the gradient effect is highlighted in the micro-milling stability behavior,so the theoretical model of the flutter stabilization domain considering the gradient effect needs to be considered.In summary,this dissertation proposes a non-classical tension rod model,a non-classical torsion shaft model,non-classical Timoshenko and Euler-Bernoulli beams models based on the non-local gradient linear elasticity theory considering micro-scale effects.A set of non-classical finite element methods was used to solve these theoretical models.The dynamic characteristics and flutter stability characteristics of the micro milling cutter considering the gradient effect are studied in detail.It is revealed that the gradient effect is significant in the dynamic characteristics and micro milling stability behavior of the micrometer-sized micro-tool.