航空铝合金7075-T651高速铣削锯齿形切屑的形成机理研究

目的分析航空铝合金高速铣削锯齿形切屑的形成过程及机理,为提高工件表面质量、延长刀具使用寿命提供理论依据。方法考虑航空铝合金在高速铣削过程中铣削厚度变化的特点,选用合理的本构模型及材料断裂准则,将三维铣削简化为二维变厚度的正交切削热力耦合有限元模型,对锯齿形切屑的形成过程进行有限元模拟,并经铣削试验验证有限元模型的准确性。结果在2～16 m/s的切削速度范围内,铣削力、切削温度、锯齿形切屑形貌均得到了准确的仿真。随着切削速度的增加,切屑厚度、切屑连续部分高度和剪切带间距都有减小的趋势,相反,剪切角随切削速度的增加而增大。切削速度为16m/s时,锯齿形切屑在切屑厚度较大的一侧出现,并随着切屑厚度减小而逐渐消失,变为均匀带状切屑,准确仿真了切削厚度变化下锯齿形切屑形貌。结论提出考虑剪切带宽度变化的三阶段锯齿形切屑形成模型,通过剪切带内外的应变、应变率和温度的变化分析了绝热剪切过程,并使用分割强度比参数量化锯齿形切屑应变程度,控制锯齿形切屑形态。

Formation Mechanism of Sawtooth Chip in High Speed Milling of Aeronautical Aluminum Alloy 7075-T651

The work aims to analyze the formation process and mechanism of high-speed milling sawtooth chip in aerospace aluminum alloy so as to provide a theoretical basis for improving the surface quality of the workpiece and prolonging the service life of the tool. By considering the characteristics of milling thickness variation during high-speed milling of aerospace aluminum alloys, reasonable constitutive model and material fracture criterion were selected to simplify the 3D milling as 2D variable thickness orthogonal cutting thermal coupled finite element model and the formation process of sawtooth chips was simulated to verify the accuracy of finite element model through milling experiments. The milling force, milling temperature and morphology of sawtooth chip were accurately predicted within the cutting speed range of 2~16 m/s. As the cutting speed increased, the thickness of the chip, the height of the continuous portion and the shear band spacing all decreased. On the contrary, the shear angle increased as the cutting speed increased. When the cutting speed was 16 m/s, the saw-toothed chips appeared on the side with the larger chip thickness, and gradually disappeared with the reduction of the chip thickness and then became uniform strip-shaped chips. The sawtooth chip was accurately simulated under the change of cutting thickness. A three-stage sawtooth chip formation model considering the variation of the shear band width is proposed. The adiabatic shear process is analyzed by the changes of stress, strain, strain rate temperature inside and outside of the shear band, and the segmentation intensity ratio parameter is used to quantify the degree of sawtooth chip strain and control the shape of the sawtooth chip.