Abstract
This paper first develops a cryogenic cutting system with adjustable jet temperature (− 196~20 °C), and then carries out a series of dry cutting and cryogenic turning experiments for titanium alloy. Metallographic microscope is used to observe the chip morphology of titanium alloy and the geometric characteristic parameters of the chip are measured using a Digimizer image measurement software. The influence of cutting speed and cooling conditions on the chip morphology, chip height ratio, and serrated pitch has been analyzed. The experimental results reveal that the cutting speed and cooling conditions play significant roles on the chip morphology and serrated characteristics of titanium alloy. During the cryogenic cutting process, with the increase of cutting speed, the chip height ratio and serrated pitch of titanium alloy chip increase. It has been found that under the condition of cryogenic cutting, the lower jet temperature, the more obvious serrated characteristic of titanium alloy chip. It is also found that the fibrous adiabatic shear band exists in the shear zone; the chip height ratio and serrated pitch remarkably increase.
Highlights
The rapid tool wear, the poor machined surface quality and machining accuracy, the low processing efficiency, and the pollution of cutting environment are all the difficult problems in cutting of difficult-to-machine materials such as titanium alloy and high temperature alloy
It was observed that compared with dry cutting, the cutting temperature can be reduced by 60%, and the microhardness of machined surface can be increased by 40%, and the surface roughness can be reduced by 25–40%
The results revealed that the cryogenic cooling is more effective than dry cutting for reducing tool wear, lowering cutting force, improving surface roughness, and eliminating contamination of the machined part
Summary
The rapid tool wear, the poor machined surface quality and machining accuracy, the low processing efficiency, and the pollution of cutting environment are all the difficult problems in cutting of difficult-to-machine materials such as titanium alloy and high temperature alloy. Schoop et al [12] explored the influence of rake angle, cutting speed and pre-cooling temperature on surface roughness and tool wear in cryogenic machining of porous tungsten using a polycrystalline diamond tool. The results revealed that the cryogenic cooling is more effective than dry cutting for reducing tool wear, lowering cutting force, improving surface roughness, and eliminating contamination of the machined part. Compared with dry cutting, the utilization of cryogenic cooling reduced the cutting force to 23% and improved the surface roughness to a maximum of 88%. This can be attributed to the capacity of cryogenic machining to provide better cooling and lubrication through the reduction of heat generation at the cutting zone. It was found that the treated inserts showed a better performance than the untreated ones of up to 34 and 53% in terms of flank wear and crater wear, respectively
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