CFRP/钛合金叠层结构高速分离超声螺旋铣孔机理研究

As a new flexible assembly hole-making technology for aircraft, helical milling technology can hardly take into account the reasonable matching between high-speed cutting of CFRP and low-speed cutting of titanium alloy when machining CFRP/titanium alloy stacks. As a result, the low-speed or high and low speed combination cutting mode is usually adopted, which leads to the problem of low quality and low efficiency. Based on the cutting mode and micro-cutting theory, a high-speed separation ultrasonic helical milling, in which differential separation between cutting edge and workpiece with ultrasonic frequency can still be achieved under high-speed cutting, is proposed and the mechanism of this new process is deeply studied. The aim of this project is to achieve high-speed helical milling for CFRP/titanium alloy stacks. The research work on kinematics of high-speed separation ultrasonic helical milling, the relationship between cutting speed and cutting temperature as well as tool life, the evolution mechanism of hole surface geometry and the process validity are carried out. The key scientific issue of the behavior state of cooling medium and its influence on heat exchange at the cutting interface under the ultrasonic differential motion of cutting edge and workpiece in the cutting zone are also clarified. Thus, a new method and theory of high-speed separation ultrasonic helical milling is preliminarily established which provides a new research idea and theoretical basis for the high-quality and high-efficiency helical milling of CFRP/titanium alloy stacks.

作为一种新兴的飞机柔性装配制孔技术，螺旋铣孔工艺在加工CFRP/钛合金叠层结构时很难兼顾CFRP高速切削和钛合金低速切削的合理匹配，通常采用低速或高低速组合的加工模式，导致低质低效问题。本项目从切削模式和微细切削理论出发，提出在高速切削下仍然能够实现切削刃与工件超声频微分离的高速分离超声螺旋铣孔方法，并对CFRP/钛合金叠层结构高速分离超声螺旋铣孔加工机理进行深入研究，实现CFRP/钛合金叠层结构高速螺旋铣孔。开展高速分离超声螺旋铣孔运动学、切削速度影响切削温度及刀具耐用度的量化关系、孔表面几何性状演变机制、工艺有效性验证等方面的研究工作，阐明切削刃-工件超声频微分离运动下切削区冷却介质的行为状态及其对切削界面热量交换的影响规律这一关键科学问题。初步建立高速分离超声螺旋铣孔新方法及理论，为CFRP/钛合金叠层结构高质高效螺旋铣孔难题提供新的研究思路和理论依据。

现代飞机设计为了满足轻量化和高机动性能的要求大量采用高性能CFRP复合材料蒙皮和钛合金整体结构件，导致CFRP/钛合金叠层结构已经成为现代飞机的典型机构特征。作为一种新兴的飞机柔性装配制孔技术，螺旋铣孔技术因两种材料最佳切削速度差距较大无法实现CFRP/钛合金叠层孔的高质高效加工。高速分离超声切削过程中刀具和工件的周期性分离能够脉动式打开传统切削中封闭的切削界面，使得冷却介质能瞬间大量进入从而实现冷却降温，进而大幅提升切削线速度。通过试验探究了超声振动下刀具-工件润滑界面流场规律，建立了高速分离超声切削分离界面冷却的温度变化模型，阐明了高速超声振动切削区的降热机理，进而提出了高速分离超声螺旋铣孔方法，研制了非接触感应供电双弯椭圆超声铣削刀柄。基于螺旋铣孔刀具侧刃与端刃同时参与切削的特点，分别深入研究了高速分离超声侧铣、端铣和螺旋铣的运动学理论、材料去除原理、刀具磨损机理，建立了高速分离超声铣削切削力理论模型，揭示了加工参数对加工表面完整性的影响规律，并对复合材料、钛合金高速分离超声螺旋铣孔开展了工艺参数优化研究，最高切削线速度达到了200m/min，实现了复/钛叠层结构的高速兼容螺旋铣孔，为复/钛叠层结构高质高效加工难题提供了新的研究思路和理论依据。