Lv Dongxi, Chen Mingda, Yao Youqiang, Yan Chun, Chen Gang, Zhu Yingdan
Institute of Advanced Manufacturing Technology, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, PR China.
Institute of Advanced Manufacturing Technology, Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, PR China; Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, PR China.
Ultrasonics. 2021 Aug;115:106448. doi: 10.1016/j.ultras.2021.106448. Epub 2021 Apr 16.
This investigation represented a fundamental research on the potential effects of the high-frequency vibration on the hole integrity involved in rotary ultrasonic drilling (RUD) of carbon fiber-reinforced plastic (CFRP) composites. It was found the increased thickness of the CFRP plate shrunk the flowing velocity of the coolant, which brought about the residual chippings gradually accumulated at the radial clearance between the tool and the material. Furthermore, the chipping accumulation at the clearance seriously increased the friction effects and the resultant thermal load, thus leading to the chipping adhesions on the tool surface and machined cylinder jamming at the central hole of the tool. The mutual constrain between two vertical bundles brought the delamination around the holes generated in conventional drilling (CD) process to a termination at the bundle interface. The ultrasonic superimposition reduced the thrust force of the diamond tool which provided inadequate energy for the delaminated fibers reaching the bundle interface. Moreover, hole position on the two-dimensional orthogonal fabrics significantly influenced the propagation of the delaminated fibers, which weakened the effects of the drilling parameters on the delamination dimensions. Additionally, superimposing an ultrasonic vibration prolonged the abrasive trajectories and increased their overlapping probability, and the induced smoothing effects resulted in the obvious reduction of the surface roughness. The tensile stress exerted on the margin of the machined surface was responsible for the initiation of the CD delamination. After the delaminated fibers reached the bundle interface, the further extrusion of tool brought about the margin suffered from the shear stress, thus leading to the collapse of the machined cylinder. Considering the thrust force of the diamond tool and the undrilled thickness of the machined surface, the critical conditions of the delamination initiation were developed, which revealing that the decreasing of the thrust force caused the reduction of the critical undrilled thickness.
本研究是关于高频振动对碳纤维增强塑料（CFRP）复合材料旋转超声钻削（RUD）中孔完整性潜在影响的基础研究。研究发现，CFRP板厚度增加会使冷却液流速降低，导致切屑在刀具与材料之间的径向间隙处逐渐堆积。此外，间隙处的切屑堆积严重增加了摩擦效应和由此产生的热负荷，从而导致切屑粘附在刀具表面，加工圆柱在刀具中心孔处堵塞。两个垂直束之间的相互约束使传统钻削（CD）过程中孔周围产生的分层在束界面处终止。超声叠加降低了金刚石刀具的推力，为分层纤维到达束界面提供的能量不足。此外，二维正交织物上的孔位置显著影响分层纤维的传播，这削弱了钻削参数对分层尺寸的影响。另外，叠加超声振动延长了磨料轨迹并增加了它们的重叠概率，产生的平滑效果使表面粗糙度明显降低。施加在加工表面边缘的拉应力是CD分层产生的原因。分层纤维到达束界面后，刀具的进一步挤压使边缘受到剪应力，从而导致加工圆柱坍塌。考虑到金刚石刀具的推力和加工表面的未钻削厚度，得出了分层起始的临界条件，结果表明推力的减小导致临界未钻削厚度的减小。
