A study on the milling temperature and tool wear of difficult-to-machine 508III steel

Abstract

Difficult-to-machine 508III steel is widely applied in the water-chamber heads of steam generators for nuclear power stations of AP1000 nuclear islands. The dominant machining process for these components is heavy-duty cutting. Since 508III endures significant mechanical impacts and alternating thermal loads during milling, the cutting temperature is relatively high. High temperatures reduce the surface quality of the workpieces and accelerate insert wear, which shortens the insert service life and reduces cutting efficiency. In this article, the welding set and amplifying circuit of thermocouples were designed. Coated cemented carbide inserts were adopted. The wired half-artificial thermocouple method was utilized to conduct 508III steel milling temperature tests. The influence regularity of cutting parameters on the milling temperature was analyzed, and the regression model of the milling temperature was constructed, which provided boundary conditions for insert simulation analysis. Second, finite element simulations of the milling process and milling inserts were carried out to analyze the temperature variation regularity and insert temperature distribution during milling. The simulation results were compared with the experimental results for validation. Finally, the wear behavior of the 508III milling insert was characterized by analyzing the wear condition of both the rake surface and flank surface of the milling insert, as well as the wear amount of the flank surface. The interactive influence regularity between the insert wear and milling temperature was explored. The milling temperature distribution and insert wear state obtained from the simulation agreed with the experimental results. The availability and reliability of the designed milling temperature test system were validated, which provides theoretical foundations and technical support for developing inserts and improving the cutting efficiency of difficult-to-machine materials.