Abstract: In order to improve the difficult-to-machine property of DD5 Ni-based single crystal superalloys, a high-speed milling transition criteria and chip edge formation mechanism were proposed with the variable of cutting speed based on adiabatic shear theory and using the method of single factor experiments and FEM simulation. According to the measurement results of the chip sawtooth level and intervals, the chip free surface transforms from lamellar structure to serrated structure when cutting speed reaches 37.7 m/min, which shows the milling has entered into high-speed zone. The stress concentrated on the grooves intersected between the chip side and adiabatic shear band induces the longitudinal crack formation and expansion, which causes the transverse and longitudinal stress distribution variations. Then, the transverse cracks were generated. The longitudinal and transverse crack formation was the main reason of the chip edge generation. With the increasing of milling speed, the chip edge morphology transformed from flat and smooth trapezoid to narrow and defective triangle. Compared with the traditional machining, high-speed cutting is beneficial to the reduction of cutting force, chip edge height and intervals, and restrain the lateral crack expansion at the same time.

Key words: Ni-based single crystal superalloy, high-speed milling, sawtooth chip, chip edge

摘要： 为改善DD5镍基单晶高温合金难加工特性，基于绝热剪切理论，以切削速度为变量，采用单因素实验及有限元仿真方法，提出了高速铣削判据及切屑毛边成形机理。根据切屑锯齿间距和锯齿化程度的测量结果,当切削速度达到37.7 m/min时，切屑自由表面从片层状结构转变为明显的锯齿状结构，由此判断切削进入了高速区。切屑边缘与绝热剪切带交汇处凹槽侧面的应力集中触发了切屑纵向裂纹的形成，而纵向裂纹的扩展引起了切屑横、纵两向应力分布的变化，从而导致切屑横向裂纹的产生；切屑侧面横、纵两向裂纹的形成和扩展是切屑毛边形成的主要原因。随着切削速度的增大，毛边形态由平整的梯形转变为狭长且有缺陷的三角形。相比于传统加工，高速加工有益于切削力的减小及切屑毛边高度和间距的下降，同时可抑制侧向裂纹的扩展。

关键词: 镍基单晶高温合金, 高速铣削, 锯齿状切屑, 切屑毛边