Study On Stiffness Of Ceramic Bearing Without Inner Ring And Its Influence On Dynamic Characteristis Of Electric Spindle

Compared with the common motorized spindle,the ceramic spindle without inner ring has higher rotation precision,faster rotational speed,smaller temperature rise and longer service life.In recent years,ceramic motorized spindle has become a new favorite in the manufacturing industry.The development of ceramic motorized spindle plays a great role in promoting the processing and manufacturing level of a country.High precision has been the development trend of ceramic motorized spindle.The stiffness of ceramic bearing without inner ring has a great influence on the working precision of ceramic motorized spindle.However,because of the short history of research and development of ceramic bearings without inner ring,they belong to the new scientific research field.The precision of state analysis needs to be improved.Supported by the National Natural Science Foundation of China(51675353)and the Innovation team Project(IRT-15R45)of the Ministry of Education,this paper takes the 170SD30-SY ceramic spindle without inner ring as the research object.The main research contents are as follows:(1)The characteristics of heat generation,heat transfer and centrifugal effect of ceramic bearings without inner ring are analyzed,and the rigidity law of bearings under the combined action of heat field and centrifugal force is also analyzed.(2)On the basis of thermodynamics and dynamics theory,the theoretical calculation formula of the stiffness of ceramic bearing without inner ring is deduced under the condition that the stiffness hardening effect of bearing caused by thermal expansion and the stiffness softening effect of bearing caused by centrifugal force exist at the same time.(3)The finite element analysis model of ceramic bearing without inner ring was established by using pseudo statics method,and the relationship between bearing stiffness and rotational speed was explored.Results show that there is a difference of 3.2%between the calculation method provided in this paper and calculation method for stiffness hardening effect of bearing caused by thermal expansion,and the difference between the calculation method provided in this paper and calculation method of bearing stiffness softening effect caused by neglecting centrifugal force is 16.1%.(4)The finite element model of ceramic motorized spindle without inner ring is established to study the influence of bearing stiffness on the natural frequency of motorized spindle.The results are as follows:the natural frequency of ceramic spindle increases with the increase of bearing stiffness,and the natural frequency of ceramic spindle increases with the decrease of the diameter of the center hole of the hollow shaft.With the support span approaching to the optimal span,the natural frequency of the ceramic motorized spindle increases.The influence of bearing stiffness on the natural frequency of ceramic motorized spindle is greater and the sensitivity is higher.The influence of the diameter of the center hole of the hollow shaft is slightly greater than that of the support span,but the difference between the two is not obvious.The influence of both on the natural frequency of ceramic spindle is less than that of bearing stiffness.(5)The experimental platform of ceramic spindle without inner ring is built and the stiffness of ceramic bearing without inner ring is tested.The results show that the calculation model established in this paper can accurately reflect the actual situation and the error is not more han 3.6%.(6)The modal test of ceramic motorized spindle is carried out by hammering method.The overall error between the experimental results and the finite element simulation results is less than 10%and the partial error is less than 5%.It can be concluded that the established model can accurately simulate the ceramic motorized spindle under actual working conditions and can be used to calculate variable parameters with high accuracy.