| Antarctica is the only continent without human activities on the earth.Ice core drilling has become an important research around the world since 20thcentury.The ancient microorganisms in the intact,continuous and deep ice core record the precious paleoclimate and paleoenvironment information,which is of great strategic significance to infer the past climate evolution process and predict the future trend of the earth.Cable-suspended electromechanical coring drill technology is widely used in polar deep ice core drilling projects due to its advantages as light weight,low power consumption,high penetration rate,high drilling efficiency and good performance in extreme environments.It has been successfully drilled in polar ice caps with maximum hole depth 3769.3 m.However,several ice drilling spots pointed out that"warm ice"layer exists in the deep part of the polar ice sheet indeed.The warm ice layer has the characteristics of low melting point and high temperature along with low fragility and high viscoelastic property,poor capacity in drilling as well.Chips produced during rotary drilling are easy to agglomerate and adhere to the surface of the drill bit and cutting tool,resulting in low drilling efficiency,low coring quality,difficult circulation of drilling medium and sticking drill tools frequently.Based on the above problems,this article carried out the research on the temperature field of the ice rotary drilling cutting tool,and explored the law and magnitude of the cutting heat generation of drilling under different parameters,so as to select a set of parameter combinations with low cutting temperature and high drilling efficiency.Practical core drilling used in Antarctic scientific research.The cutting model and force model of ice rotary drilling is also established by referring to the theory of metal cutting,so as the heat transfer law of the cutting heat in this paper.The heat generated by the cutting tool during ice rotary drilling is calculated,including the heat produced from the shear deformation of the ice layer that results from the cutting tool and the heat generated by the friction.In the meantime,the influence of drilling speed,cutting tool's rake angle,as well as the rotary rate and the environmental temperature on the heat generated during cutting has been exiled.After the analyze of theories above,the theoretical model of cutting tool temperature calculation under drilling fluid circulation is established,with the comparing of cutting temperature under the same drilling parameters in drying cutting.The theoretical calculation results show that with or without circulating medium,the cutting temperature decreases while the rake angle of cutting tool increase.Besides,the increase of rotational speed and drilling speed can lead to the cutting temperature rising while the ambient temperature gradually decreases followed the cutting temperature increases.By taking advantages of engineering simulation software ABAQUES,the ice drilling simulation was developed.The rotary cutting model of multiple cutting tool rake angles and ice layer was established,and different drilling parameters were set up.The temperature variation law and distribution area characteristics under the conditions of changing drilling speed,cutting tool rake angle,rotary speed and environmental temperature were obtained.Results indicate that when the drilling speed ranges from 1mm/s to 2.5mm/s,the temperature rise increases from 5.94°C to8.49°C;When the rake angle ranges from 15°to 60°,the temperature rise of the cutting tool transformed from 8.35°C to 6.2°C.When the rotational speed increases from 50r/min to 200r/min,the temperature rise largest is 8.54°C while the minimum is 6.59°C.When the ambient temperature decreases from-10°C to-25°C,the temperature rise increases from 3.41°C to 7.58°C.Referring to the principle of lathe metal cutting,the temperature test bench for rotary drilling cutting tool in ice layer is independently designed and processed.The test bench is equipped with diamond drilling machine,electric linear actuator,temperature sensing device,wire-pull displacement sensor,proximity switch etc.With the multi-purpose data acquisition system established based on MATLAB programming,the generation law of cutting heat under the conditions of changing drilling speed,cutting tool rake angle,rotary speed,ambient temperature and whether there is drilling fluid circulation can be experimentally explored.The test results show that under dry cutting conditions,when the drilling speed changes from 1mm/s to2.5mm/s,the temperature gradually increases from 6.97°C to 7.79°C.When the rake angles of the cutting tool are 15°,30°,45°and 60°,the temperature rise of the cutting tool is 6.17°C,7.41°C,7.18°C and 4.25°C.When the rotational speed increases from50r/min to 200r/min,the temperature rise of the cutting tool increases from 5.21°C to7.62°C,and increases with the increase of rotational speed.When the ambient temperature decreases from-10°C to-25°C,the temperature rise of the cutting tool increases from 3.31°C to 7.18°C,which increases with the decrease of the ambient temperature.Under drilling fluid conditions,the law of temperature rise of cutting tool is consistent with that under drying cutting conditions.When the drilling speed changes from 1mm/s to 2.5mm/s,the cutting tool temperature rises from 1.69°C to 2.11°C;When the rake angles of the cutting tool are 15°,30°,45°and 60°,the temperature rise of the cutting tool is 1.63°C,1.92°C,1.74°C and 1.09°C.When the rotational speed increases from 50r/min to 200r/min,the temperature rise of the cutting tool increases from 1.21°C to 2.12°C,and increases with the increase of rotational speed.When the ambient temperature decreases from-10°C to-25°C,the temperature rise of the cutting tool increases from 0.58°C to 1.74°C,and increases with the decrease of the ambient temperature.Compared with theoretical calculation,numerical simulation and test,the temperature rise law of cutting tool obtained by changing different parameters is basically the same,which provides a reliable basis for solving the problems in actual drilling in warm ice. |
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