Research On The Cryogenic Cutting Machinability And The Chip Morphology Of Difficult-to-Cut Alloys

Difficult-to-cut alloys usually have poor machinability,such as high cutting force,easy hardening,severe tool wear and poor surface quality.Processing these materials with advanced low-temperature cutting technology can reduce friction between the tool and the work piece,between the tool and the chip,enhance heat transfer,and reduce tool wear.The development of cryogenic jet equipment and cryogenic cutting mechanism is of great significance for improving the machinability of difficult-to-cut alloys.In this paper,the low temperature jet cooling system developed by ourselves is used to carry out a low temperature jet assisted milling experiment on FV520 B stainless steel.The low-temperature jetting assisted turning experiment of FV520 B stainless steel and TC4 titanium alloy was carried out to observe the micro structure evolution.The change law and the reason of the chip deformation characteristic parameters with the cutting speed and the temperature of the low-temperature jet was analyzed.The main results are as follows:(1)This paper has developed a set of low temperature jet cooling system,whose jet temperature can be realized between-190?and 18?.This paper focuses on the development of the core components of the jet governor--jet mixer,and the best structural parameters of the jet mixer were selected.By temperature calibration experiment,the flow of liquid nitrogen and compressed air needed for the-190 ?-18 ?jet were determined;The time required to stabilize the jet was 150 s.(2)Through the experiment of milling FV520 B stainless steel at low temperature,it is found that with the increase of feed rate and axial cutting depth of each tooth,the milling force increases continuously,and the influence of cutting speed on the milling force is not obvious.Under the conditions of cutting parameters and jet temperature,there is no flutter phenomenon,but the vibration amplitude of milling increases with the increase of cutting speed,axial cutting depth and feed rate of each tooth.Among the three kinds of cutting parameters,each tooth feed has the most obvious influence on the surface roughness.When the low temperature jet assisted cutting,as long as the tool does not occur chipping edge damage,the lower the temperature of the low temperature jet,the stronger the tool durability.The temperature below-100 ? of jet can significantly improve the machinability,reduce the temperature of cutting zone and the effect of strain hardening,so as to reduce the cutting force and vibration,improve the processing surface quality,improve the tool life.(3)By observing the microcosmic morphology of the chip of FV520 B stainless steel and TC4 titanium alloy in low temperature turning,it is found that adiabatic shear still occurs in the chip when cutting the refractory alloy under the condition of low temperature jet cooling.The sensitivity of the two materials to adiabatic shear is different,so the degree of change of the serrated chip micro structure is different,but the evolution of the serrated chip micro structure has the same trend,with the increase of cutting speed or the decrease of jet temperature,the chip from the ribbon chip into serrated chip;The serrated pitch and shear Angle increase with the increase of serrated degree.The micro structure of shear zone roughly passes through the transition from deformation zone to transition zone and gradually produces the transition zone with cracks.The low temperature condition promotes the formation of adiabatic shear zone and the localized fracture of the chip along the adiabatic shear zone.