Milling Dynamics On Assembled Hardened Steel With Different Hardness

Hardened steel is high carbon steel or alloyed steel with high hardness (more than50HRC) after heat processing. Hardened steel owning excellent hardenability and wear-resistance is suitable for manufacturing of assembled die and body mold for cold-working punching mould. Assembled hardened steel with different hardness consists of a lot hardened steel single bodies with different material trademarks and hardness after accurate cutting. Special assembling and technical process was used to deal with assembled hardened steel with different hardness to own low assembling space (less than0.3μm). So assembled hardened steels with different hardnesses are widely applied in the fields of large-scale mould, manufacturing of assembled mould.Chattering dither always happens in the assembled hardened steel machining process under dynamic milling force for the hardness difference. So the machining quality cannot steadily keep high level. The structural mechanics, finite element (FE) analysis, modal synthesis and experimental investigation are introduced in the present study. The target of present thesis is to investigate the milling force, vibration and stability in the milling process of the assembled hardened steel. The model of milling chattering dither steadily is established. FE emulation analysis about the steadily is conducted, and corresponding experiments are completed. So the works completed in the present thesis is significative for revealing milling mechanism of assembled hardened steel with different hardness, promoting basic theory of hard cutting, enhancing technical level of hardened steel milling.The main contents and conclusions:(1) Numerical mechanical model of cutting process of assembled hardened steel with different hardness is established based on mechanical constitutive model and hardness feature. The cutting force used for machining assembled hardened steel with different hardness is simulated. The influence of workpiece hardness on cutting force is investigated. Based on aforementioned works, the orthogonal design method is introduced to investigate the cutting force when ball end miller is employed to deal with declivity surface of hardened steel. The regular pattern of influence of cutting parameters on cutting force is owned;(2) One kind of method of operational modal dynamic analysis about cutting system is given based on least squares complex exponential (LSCE) multi-reference method (LSCE) operational modal dynamic (OMA) method. Cross-spectral function among response points of basic shaft under impulse excitation in hammering process is calculated. Modal parameter of basic shaft is extracted based on LSCE. OMA is used to conduct dynamic modal analysis, the results is compared to the modal parameter owned from analysis of the traditional frequency response function in hammering process. The availability of this new method is proved;(3) Two-degree milling dynamics model is established based on regenerative chattering dither method. And then, universal milling stability prediction model is established. The influence of technical parameters (milling force coefficient, radial cutting-in) on milling stability is analyzed by emulation method. The experiment of milling stability proves the correctness of Stability lobes;(4) The milling experiments of hardened steels assembled with different hardness under ball end miller are conducted. The correctness of correlative investigation conclusions in this study are proved based on aforementioned experimental results. Some key problems, such as cutting vibration, wear mechanism, cutting morphology, are also discussed. The milling parameters of the transient area of assembled hardened steel with different hardness are optimized. The surface roughness of the machining surface and wear extent of tool are employed to be evaluating indicator. Finally, the select principle of cutting technical parameter under assembled condition is given.