Experimental Study Of Multi-signal Monitoring Based On Hard Milling

At present, a majority of the parts manufactured in the mold, aerospace andautomotive sector need to be hardened to HRC55above, and generally a certaindegree of deformation has happened after quenching. Then it need further processingcorrection. Usually this kind of hardened steel can only be fit for grinding. With thedevelopment of the modern processing technology and the advent of the superhardcutting tool materials, it has become possible that the new machining methods aboutmilling instead of grinding and milling instead of EDM（Electrical DischargeMachining）are used for efficient and economical milling, and the methods have madesignificant economic benefits in production. Hard milling means milling the steel ofwhose hardness is over HRC56or strength Rm is over2000Newton per squaremillimeter. So not only the machining cycle become much shorter, but also themachining quality has been guaranteed reliably. At the same time, the hard millinghas some advantages such as reducing the micro-structural changes of the workpiece,none significant increase of the surface microhardness and improving the fatiguestrength. While the hard milling also has obvious disadvantages, namely the tool lifedecreases dramatically, and the risk of wear and fracture become larger. Therefore, itis particularly important to do multi-signal monitoring and analysis on the machiningprocess of the hard milling and to control the state of the processing real-timely. Sothe tool can be changed in a timely manner to avoid affecting the accuracy of theworkpiece and even irreparable damage. This article includes a series of test andresearch work which focus on the hard milling.Firstly, a set of signal acquisition system based on virtual instrument is used tocellect the acoustic emiision, vibration and temperature signal during the hard millingprocess of the hardned steel. Then the signal is processed with the wavelet transform,wavelet packet transform and hilbert transform methods in order to extract some lawswhich can reflect the process characteristics of the hard milling. so the laws are usedfor optimizing the process parameters and assuring the machining quality. In thispaper, two different kinds of workpiece material, namely T10A and Cr12MoV, areselected, and each kind of workpiece material includes hardness of HRC57andHRC21. Through a large number of experiments, the hard milling process is analyzedfrom different angles, and then some useful conclusions are extracted.Secondly, a fuzzy control system based on an electro-hydraulic digital valve is established. This system can adjust adaptively the cutting fluid flows from the nozzleaccording to the change of the cutting temperature in order to ensure that the cuttingtemperature of the milling process is maintained within a given range, so as to achievethe fuzzy control on the cutting temperature of the hard milling process.Finally, the feasible experimental study about electrolysis assisting hard millingand electric hot milling are done. In this paper, the electrolysis machining is applied tothe hard milling. Namely, the tool and workpiece are energized in the milling process,and then the electrolyte is powered to make the electrolysis and milling simultaneous.The experiment of the electric hot hard milling means that the tool and workpiece areenergized in the milling process, then the heat is used to intenerate the workpiece, tochange the cutting performance of the workpiece and to assist the hard milling. Thistwo tests both focus on using other machining methods to assist the hard milling inorder to reduce the tool burden, to reduce the tool wear and to improve the efficiencyof hard milling.