Research On Stability And Formation Of Material Plastic Side Flow In High Speed Precision Turning Process Of Hardened Steel

Precision hard cutting is one of the advanced manufacturing techniques for hardened steel because of its high machining efficiency, good machining flexibility, low energy consumption and less pollution. However, there are still many special cutting principles yet to be systematicly researched in expertise, especially in theory and technology of the stability of cutting process and formation of material plastic side flow, for even wider application of the advanced technique in practical production.By using the method of hard cutting experiment, combined with FEM numerical simulation of two-dimensional cutting and microscopic analysis of chip cross-sectional, the chip morphology and deformation characteristics of serrate chip are investigated. And the boundary of the chip alternation from band form to serrated one is also determined.The dynamics parameters measurement of hardened steel precision cutting system is carried out in the descriminating experiment. On the basis of system dynamics model set up in regeneration type precision hard turning, with numerical simulation methods through Matlab, taking the effects of cutting speed, cutting width, feed rate, tool geometry and workpiece hardness into consideration, stability limit prediction of a multi-parameter system for hardened steel precision cutting is completed, and the hard turning system vibration suppression measures are tried and proposed by adjusting the dynamic parameters and cutting parameters of the turning system.With the single-parameter method and method of depth-variable cutting, the test is made to verify the prediction of limit stability. The predicted results are basically consistent with the actual ones. By spectral analysis, the vibration signal in hard turning process is studied, findings indicating that the forced vibration and system vibration noise play the leading role in smooth-turning operation. However, regeneration vibration is the main mode in chatter.Material plastic side flow in high speed precision turning of hardened steel is investigated. The formation mechanism of material plastic side flow is researched and proposed with finite element simulation, deriving the process criteria on material plastic side flow. Plastic model of flow peak, geometric model of residual height on the turned surface including arc edge and straight edge, and a surface roughness model with the effects of high degree of plastic side flow, are established. The effects of feeding and cutter arc radius on the material plastic side flow are studied, which indicates the degree of material plastic side flow will increase with the decrease of the feed and the increase of tools-tip arc radius, meanwhile, the surface roughness produce suffers negative influence. By optimization of orthogonal cutting test, the ideal type of hardened steel machined surface is obtained.In this work, the characteristics of chip formation, prediction of stability limit and formation of material plastic side flow are studied by means of combination of theoretical analysis, numerical simulation and experimental study in high speed precision cutting of hardened steel GCrl5 with PCBN tools, which provides an important theoretical basis and technological support for the further development, popularization and application of hard turning process.