Research Of Tool Brittle Failure Under Variable Loading Condition In Extreme Heavy-Duty Cutting

Because of large cylinder and other heavy axial forgings are forged by the ton water hydraulic press, the periphery of cylinder has great eccentricity. And the processing condition of surface which has scale, scab, ditches and various forging defects is so serious that there is heavy impact on tool and machine system. Thus the tool brittle failure caused by impact and fatigue failure affects tool life seriously under extreme heavy-duty condition, and the improvement of production efficiency is also hindered by the frequent replacement of tool.Firstly, the kinds of heavy-duty tool breakage are classified in this paper. Through the comparative research of2.25Cr-1Mo-0.25V steel,45steel and1Cr18Ni9Ti steel machinability and the analysis of cutting force and cutting temperature characteristics under extreme heavy-duty condition, the controlling factors of tool brittle fracture are indicated which are the kind and distribution of crack and the facture toughness of cemented carbide tool, and the relationship curve of facture toughness and blade thickness is depicted. Through the analysis of stress in region of heavy-duty tool fracture, the distribution map of stress on rake face and flank is depicted. And the limit condition causing tool fatigue fracture under thermal mechanical coupling effect is determined.Secondly, the fatigue fracture of heavy-duty tool is researched in this paper. The fatigue fracture of heavy-duty tool under variable load is studied in two aspects of mechanical and thermal fatigue. Through the intermittent cutting experiment under alternating load, the mechanism of fatigue crack propagation in heavy-duty blade is revealed. In addition, the dynamic strength of heavy-duty tool is evaluated in the use of allowable stress theory of the first kind and is verified by the simulation analysis of heavy-duty tool under thermal-mechanical coupling effect through the ANSYS software. Finally, the brittle fracture experiment of heavy-duty tool under variable load is designed and described in this paper. In order to simulating the impact load caused by various cutting depth and shell eccentricity, the work piece is installed eccentrically in the experiment, the experimental equipments and instruments are selected reasonably, and two types of cemented carbide tool are adopted for comparative analysis. And the fracture regions of blade are analyzed in the use of electron microscope. The position of fatigue crack under different loading conditions is determined through observation. In addition, the morphology of two kinds of tool under different loads is analyzed comparatively in the micro and macro levels.