| The machine tool is a kind of equipment which contains many supports and joint surfaces.The internal stiffness,damping and mass constitute a complex system.The research on the static and dynamic stiffness matching relationship between different parts can provide guidance for the design and improvement of the machine tool structure.In this paper,the widely used horizontal lathe with flat bed is taken as the research object,and the substructure modal synthesis method is taken as the theoretical basis.Combined with modal test and finite element simulation,the dynamic characteristic analysis and theoretical modeling of the lathe are carried out,and the rigidity matching design method for the machine structure is proposed.The main contents of this paper are as follows:(1)Tangential stiffness estimation method of lathe joint based on modal testAccording to the stress and vibration performance of the lathe in the actual work,the structure and movement of the lathe are reasonably simplified,and the lumped mass model is established.The natural frequency obtained from the modal test of the lathe and the rigidity of the bed foot obtained from the static simulation are substituted into the equation.According to the natural vibration mode of the test mode of the lathe,the interference term is eliminated,and the tangential rigidity range of the joint surface is solved.(2)Modeling of lathe substructure by modal synthesisBased on the modal test of lathe and bed,the mass distribution of lathe is divided into several lumped masses,and the rigidity of each part and joint surface is simplified as the elastic rod connecting the lumped masses.The whole machine is divided into three substructures for separate analysis,and the differential equation of motion of the whole machine is derived by using the substructure mode synthesis method.(3)Identification of tangential stiffness and calculation of normal stiffness of main joint surfaces of latheThe identification of the joint stiffness is regarded as an optimization problem,and the natural frequency calculated by the model approximates the test value as the goal.According to the conclusion in(1)to limit the parameter range,the tangential stiffness of each joint is identified by genetic algorithm.Based on the fractal theory and MB model,the relationship between the dimensionless normal stiffness and the tangent stiffness of the same interface is derived,and the corresponding normal stiffness is calculated according to the tangent stiffness of each interface.The virtual material layer is introduced into the finite element model of the whole machine to test the stiffness of the joint surface.The results of modal simulation of the whole machine are consistent with the experimental modal,and the corresponding frequency error is small.It is proved that the substructure modeling of the lathe and the identification and calculation results of the joint surface stiffness are correct.(4)Research on the matching method of machine tool stiffnessThe concept and connotation of machine tool stiffness matching are defined.The principle of machine tool stiffness matching is elaborated from three aspects of improving static stiffness,natural frequency and dynamic stiffness respectively.It is proved that the dynamic stiffness of machine tool is positively related to its natural frequency.Therefore,the natural frequency of machine tool can be taken as the main index to measure the dynamic performance of machine tool.Using the substructure model of lathe as a tool,the sensitivity of the natural frequency of the whole machine to the mass,stiffness of the parts and the stiffness of the joint surface of the lathe is studied,and the key stiffness and quality links that should be coordinated when matching the rigidity of the lathe are analyzed in detail.(5)Optimization of lathe structure based on rigidity matching methodAccording to the idea of stiffness matching,the key parts in the performance optimization of lathe are selected and the improvement direction is determined.Taking the static stiffness of substructure as the optimization objective and the prediction value of natural frequency of the whole machine as the constraint condition,the comprehensive optimization of the dynamic and static stiffness of the whole lathe is carried out,which proves the effectiveness of the rigidity matching method of the lathe. |
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