Research And Application Of The Static Characteristics Of Bolt Joint

As an important component of machine joints,the performance of bolt joint directly affects the stiffness of whole machine and machining accuracy.However,the current bolt joint model is often simplified or omitted during the performance prediction and analysis at the design stage of the whole machine.As a result,the characteristics of whole machine can't be predicted accurately.In order to provide strong technical support for precision or super-precision equipment manufacturing technology,it is important to study the bolt joint characteristics and establish accurate and general mathematic model.This paper studies the static characteristics of the bolt joint both theoretically and experimentally on the basis of the fundamental characteristic of joint surface in unit area.The main contents of the dissertation are as following:(1)To measure the static performance of bolt joint accurately,a mathematical analysis model of bolt element interface with basic characteristic parameters is established,and a multi-stage equivalent load and based stiffness equivalent load analyzing algorithm are presented to solve non-linear equations of interface displacement more quickly and accurately.A series of loading tests is conducted using self-designed various directions loading devices for bolt joint.The consistence between computational and experimental results validates the correctness of analytic model,which provides theoretical and test support for investigating static performance of mechanical interface.(2)In finite element analysis of machine tools,it is quite difficult to create model with joint directly because of non-linear implicit function relationship between external loads and deformation of interface,a linear discretization method of equivalent compound string and surface element is put forward to analyze bolt element joint.that is,the complex assembly containing joints can be equivalent with a simple component without joints by adding to it a virtual surface element constituted of another different material.Meanwhile,the stiffness of equivalent string are obtained,and the physical parameters of virtual material such as elastic modulus and Poisson's ratio are derived according to basic characteristic parameters of interface and principle of strain energy.In finite element analysis process,the interface between two components of the bolt joint is equivalent with several equivalent spring or surfaces tangentially,and the spring stiffiness or the paraneters of virtural material are imported.then model with bolt joint characteristic is established.More accurate analysis results were acquired and the complex assembly containing joints can be equivalent with a simple component.The results of engineering analysis show that the deformation condition of bolt joint incorporated with virtual material surface element can simulate the actual part joint deformation,thus providing theoretical foundation for accurate joint modeling and an efficient and simplified calculating method for solving deformation problem of interface in practice.(3)A novel full load applying simulation method and device are presented on the basis of research of experiment of the varying situation of the cutting position as the cutting tool is subject to the action of full load of force and torque under machining process..According to distributing principle of cutting force,a full loading device has been developed through the coordinate transformation of force-bearing point and its corresponding direction.The ratio between several forces in various directions is verified by loading tests.Moreover,the device has been applied to stiffness distribution test of NC turning centers,and the displacement of each measured point is obtained when the cutting tool is at different positions.The experimental results provide referencing data for evaluating and improving construction of machine tool,and find their application in the prediction and modification of design scheme.The experiments also indicate that the stiffness of the headstock is increased after the design scheme of bolt joint for turning center is modified based on inspecting experiments,FEM analysis and research of bolt joints.