| Buttress thread is one of the connecting threads, which is used to endure large load and stipulated by American Petroleum Institute (API). With the oil pipe service condition has been worsening, the mechanical property of oil pipe is getting higher and higher, which bring great difficulties for the oil pipe thread cutting and lead to low tool life, high tool cost and low manufacture efficiency.This thesis use experimental method and finite element simulation analysis to research the mach inability of domestic and abroad buttress thread tools when turning high-grade high-Cr steel oil pipe.The mechanism of buttress thread turning has been researched. The difficulties of buttress thread turning include big lead, deep teeth, cooling condition is bad, and thus both cutting force and cutting heat are large.Machining suitability of cutting tool and workpiece material has been investigated. The result shows that rake angle have great influence on cutting force, chip formation and workpiece surface quality. Big rake angle is preferred when buttress thread have enough strength. Chip is difficult to control in machining process and big chip breaker should be chosen to increase deformation of the chip. Burn and flaking of the TiN coating can be found due to the high cutting temperature.The matrix material, chemical composition of coating material, metallurgical structure of domestic and abroad buttress thread turning tool have been study. The result shows that the grain size of domestic tools is not uniform and the bug-ηphase also can be found.Finite element method is used to simulate the turning process of buttress thread, the results show that the TiN coating protects the tool matrix material from heat, but 800℃exceed the working temperature of TiN coating, thus coating which have better high-temperature-resist ability and the cooling liquid is needed. |
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