Experimental Study And Element Simulation Of The Sawtooth Chips Morphology In Whirlwind Milling Process Of Screw

Screw whirlwind milling is a process for cutting thread features,in which multi-cutters cut a workpiece intermittently and incrementally with coupling motions.It has been widely used due to its advantages of high efficiency,precision and green.Because this cutting method is different from the ordinary turning and milling process in the machining principle,the geometric features of the chips produced by this process have special time-varying characteristic,which will cause periodic changes of cutting force and cutting temperature during machining;on the other hand,saw-tooth features are distributed on the cutting chips,and the formation of the serrations will lead to complex fluctuations in cutting force and heat during each cutting period.The above phenomena in the cutting process will have an impact on tool wear,machining efficiency and surface quality of the workpiece.An in-depth understanding of the formation mechanism of cyclone milling is important for extending tool life,improving economics and stability of process,surface integrity of workpieces and performance of components.So,in this paper,experimental studies are conducted on the macro and micro morphological features of thread whirlwind milling chips to analyze their characteristics of distribution and changes;and finite element simulation studies are carried out to figure out the evolution mechanism of saw-tooth formation.The main work is as follow:Firstly,according to the principle of whirlwind milling,the time-varying shape of chips is described,which provides theoretical basis and observation guidance for subsequent experiments and finite element analysis of chips collected from cutting experiment.Based on it,the whirlwind milling experiment was carried out,and the observation of macro and micro morphology with its properties of chips was conducted.Then,the macro-morphology of the chips is analyzed.The special section shape and reverse bending characteristics of experimental chips are studied,and the causes of its formation are discussed;the variations of chip length,width and bending degree at different cutting speed,cutting depth and number of tools are compared.Further,for the micro saw-tooth morphology,its distribution characteristics on the longitudinal section of chip are experimentally studied from three aspects: saw-tooth geometry,microstructure and nanohardness,and the phenomena of force,heat and material structure changes during the formation of serrations reflected by these distribution characteristics are analyzed;moreover,the sawtooth characteristics at different cutting parameters are compared,and the influence mechanism of cutting parameters is discussed.Finally,in order to research the evolution of sawtooth formation,a 2D finite element cutting model of whirlwind milling is established by using the finite element simulation software Abaqus/Explicit to simulate the deformation,damage and failure during saw-tooth chip formation.And then the accuracy of the simulation model is validated.According to the simulation results of strain,temperature,stress and cutting force obtained by the model,the conditions of deformation,mechanical and thermal effect of single saw-tooth during the whole forming process(from its initialization to fracture)are analyzed.In addition,the simulation results of the chip formation at different cutting speeds and depths are comparatively discussed.