钛合金切削挤压复合攻丝研究

 将切削挤压复合攻丝新方法成功地用于高强度钛合金内螺纹的加工，这种方法不仅可以减小挤压扭矩而且能够强化螺纹根部。加工的挤压螺纹表面有一层纤维沿其牙形连续分布。利用云纹干涉法测得牙根处的最大残余压应力为120MPa左右。疲劳对比试验结果表明，在相同应力水平下，经挤压强化螺纹的疲劳寿命大约是未强化螺纹的３倍，这主要归因于挤压螺纹表面高的残余压应力，高的纤维密度和低的粗糙度。

COMBINED CUT AND FORM FAPPING OF INTERNAL THREADS IN TITANIUM ALLOY

A new thread tapping method, called combined cut and form tapping, was successfully used for producing threads in high strength titanium alloy, which may not only reduce forming torque but also strengthen the thread root where initial fatigue cracks very often occur. The microstructure of the thread machined by form tapping showed a layer of fine fiber distribution along the thread profile. Residual stresses near the root measured by moire interferometry were about -120MPa, depending on different forming conditions. The result of fatigue tests showed that average fatigue lives of strengthened threads by forming tap were about three times longer than those of cut threads at the same stress level. That could be contributed to the high compressive residual stress, the high fiber density and the decrease in surface roughness.