Research On Precision Milling Performance For Micro Weak Stiffness Structure Based On Critical Chip Formation Condition

In the manufacturing of miniature equipment,the demand for precision machining of small-size parts is constantly increasing.At the same time,the micro-cutting processing technology that can meet the requirements of high processing precision and high processing efficiency has become an important processing method of small parts.Flexible joint is a key element in the dynamic tuning gyroscope.The thin neck structure of flexible joint of high strength elastic alloy 3J33B,is a small weak stiffness structure.Precision cutting of thin neck structure of flexible joint involves the critical chip formation of weak stiffness structure and the elastic recovery of the workpiece surface on tool flank wear.This paper studied the precision milling machining properties of weak stiffness structure,from the micro cutting mechanism,elastic recovery of material and so forth.And then,thin neck structure of flexible joint was made by micro milling.The elastic recovery properties of high strength elastic alloy 3J33B material and the effect on tool flank wear was researched in the present dissertation.A regression model between elastic recovery rate and load of 3J33B materials under two load conditions was established.The loading condition of the tool in micro milling 3J33B was studied.The relationship,which involves elastic recovery rate and yield strength of workpicec material,tool flank angle,average sliding friction coefficient between the tool and workpiece,tool flank wear width and cutting width,was established.And,the influence of the elastic recovery on tool flank wear was revealed.The critical chip formation mechanism in micro cutting was improved in this dissertation,and the effect factors of minimum cutting thickness were studied by using finite element analysis method.The modified modle of critical chip formation in micro cutting was established by introducing the influence of tool flank wear on the critical chip formation.The model was used to detemrmine the minimum cutting thickness.In this study,it is found that the critical chip formation condition will change with the change of egde radius and the wear width of tool flank face.The milling performance of elastic alloy 3J33B was studied.The influence of the critical chip formation condition and tool flank wear on the dimensional accuracy,surface roughness,burr length,surface residual compressive stress and hardening of the workpiece material was analyzed by the experiments.The results showed that the tool flank was in the stage of stable wear when the cutting length was from 20 to 100 mm.A smaller ratio of feed to edge radius f/r and a larger wear width l can lead to a large dimensional error.The surface roughness Ra increased with the increase of f/r and l.The burr length was greatly affected by the tool flank wear.A larger flank wear width can result in a large burr length.The burr length increased with the increase of f/r,but increasing gradient was small.The residual stress of machined surface was compressive stress.The smaller the f/r and larger l,the greater is the residual compressive stress of the workpiece.The residual compressive stress was the minimum when f/r was closed to 1.0.The hardening of machined surface increased with the increase of degree of tool flank wear.The precision milling parameters of micro weak stiffness structure of high strength elastic alloy were optimized based on the critical chip formation condition in micro cutting.The dimension error of thin neck structure of flexible joint can be controlled based on a machining compensation strategy of tool flank wear.Finally,the milling process of a thin neck structure of flexible joint was completed.A thin neck structure of flexible joint can be obtained to meet the machining accuracy.