A method of CFRP drilling assisted by ultrasonic, cryogenic temperature and ice support
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摘要: 提出一种超声振动+超低温液氮+由超低温环境形成的冰冻支撑层(Ultrasonic vibration+Cryogenic liquid nitrogen+Frozen support layer，UCF)来辅助碳纤维增强树脂基复合材料(Carbon fiber reinforced polymer， CFRP)钻削制孔，有效降低钻削缺陷的加工方法。该方法的基本原理为：利用超声作用下的钻头高频振动实现轴向钻削力的弱化，利用超低温液氮以及形成的冰冻支撑层来实现钻削出口侧材料的约束和支撑，并有效降低加工过程的钻削热影响。基于UCF的基本原理，开展了相应的UCF辅助加工实验，通过微观检测表征和缺陷因子计算等手段，与传统钻削模式(Traditional drilling， TD)、低温液氮+冰冻支撑模式(Cryogenic liquid nitrogen +Freezing support，CF)下的CFRP制孔质量进行了对比分析。结果表明，采用UCF模式和CF模式均会引起轴向力增加，但UCF模式下的最大轴向力增幅相对较小；与TD模式相比，采用UCF辅助加工方法最大可使CFRP钻削出口的毛刺因子降低75%，撕裂因子降低8.9%，分层因子降低34.6%，孔壁表面粗糙度Ra降低53.6%。Abstract: A method of ultrasonic vibration + cryogenic liquid nitrogen + frozen support layer (UCF) is proposed to assist carbon fiber reinforced polymer (CFRP) drilling and effectively reduce machining defects. The basic principle of this method is as follows: the high frequency vibration of the drill bit under ultrasonic action is used to weaken the axial drilling force; the cryogenic temperature liquid nitrogen and the formation of frozen support layer are used to realize the constraint and support of the material at the drilling exit side, and effectively reduce the whole process of drilling heat effect. Based on the basic principle of UCF, corresponding experiment of UCF assisted drilling were carried out, and the hole quality of CFRP under traditional drilling mode (TD) and cryogenic liquid nitrogen + freezing support mode (CF) was compared and analyzed by means of microscopic inspection and characterization and defect factor calculation. The results show that both UCF and CF can increase the axial force, but the maximum axial force increased little. Compared with TD mode, UCF can reduce burr factor by 75%, tear factor by 8.9%, delamination factor by 34.6% and surface roughness Ra by 53.6%.
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Key words:
- CFRP /
- machining defects /
- back plate support /
- cryogenic drilling /
- axial force
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图 1 UCF辅助CFRP制孔原理：(a) UCF示意图；(b)传统钻削出口；(c)冰冻约束条件下的出口
Figure 1. Principle of UCF assisted CFRP drilling: (a) UCF flow diagram; (b) Traditional drilling outlet; (c) Outlet under frozen constraint
n—Rotational speed; f—Frequency
图 2 存在支撑时的钻削出口分层示意图
Figure 2. Delamination diagram of drilling outlet with backup
FR—Reaction force of frozen layer; FB—Axial drilling force; a—Radius of layered area; b—Radius of action of circumferential support force; c—Radius of hole; H—Thickness of CFRP laminate; h—Crack depth
图 5 CFRP钻削缺陷示意图
Figure 5. Schematic diagram of CFRP drilling defects
Ad—Actual area of layered area; Si—Area of burr; D0—Nominal diameter of hole; DTmax—Maximum nominal diameter corresponding to tear position; Dmax—Maximum nominal diameter corresponding to layered area
图 6 CFRP不同钻削模式下的轴向力时变曲线
Figure 6. Time varying curve of axial force for CFRP under different drilling modes
图 7 CFRP不同钻削模式下最大轴向力与制孔数量的关系
Figure 7. Relationship between maximum axial force and number of holes in different drilling modes for CFRP
图 8 CFRP切屑形态： (a)粉状切屑；(b)块状切屑
Figure 8. Chip form of CFRP: (a) Powder chip; (b) Block chip
图 9 CFRP不同钻削模式下的入口和出口形貌：(a) TD模式；(b) CF模式；(c) UCF模式
Figure 9. Inlet and outlet morphologies of CFRP under different drilling modes:(a) TD mode; (b) CF mode; (c) UCF mode
图 10 CFRP不同钻削模式下的缺陷因子
Figure 10. Defect factors of CFRP under different drilling modes
图 11 CFRP不同钻削模式下的孔壁形貌： (a) TD模式；(b) CF模式；(c) UCF模式
Figure 11. Morphology of hole wall of CFRP under different modes: (a) TD mode; (b) CF mode; (c) UCF mode
图 12 CFRP不同钻削模式的孔壁表面粗糙度：(a) TD模式；(b) CF模式；(c) UCF模式
Figure 12. Surface roughness of hole wall of CFRP with different modes: (a) TD mode; (b) CF mode; (c) UCF mode
图 13 CFRP不同钻削模式的孔壁损伤形貌：(a) TD模式；(b) CF模式；(c) UCF模式
Figure 13. Damage morphology of hole wall of CFRP with different modes: (a) TD mode; (b) CF mode; (c) UCF mode
表 1 CFRP的性能参数
Table 1. Performance parameters of CFRP
Parameter Value Tensile strength/MPa 950 Compressive strength/MPa 570 Young’s modulus/GPa 61.5 Shear modulus/GPa 3.7 Poisson’ ratio 0.3 Density/(kg·m−3) 155 Hardness (HRB) 70-75 
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表 2 CFRP钻削模式设定
Table 2. Setting of CFRP drilling mode
Mode Auxiliary factor Cryogenic liquid nitrogen Support by freezing Ultrasonic vibration TD × × × CF √ √ × UCF √ √ √ Notes: TD—Traditional drilling; CF—Cryogenic liquid nitrogen +
Freezing support; UCF—Ultrasonic vibration + Cryogenic liquid nitrogen + Frozen support layer.
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