Proposal of a tilted helical milling technique for high-quality hole drilling of CFRP: analysis of hole surface finish

An innovative machining process, i.e., tilted helical milling (THM), was proposed previously by the authors for high-quality hole drilling of CFRP as an alternative technique to conventional helical milling (CHM). To further develop the THM technique, hole surface finish with THM is analyzed and compared to that finished with CHM in this article. Theoretical analysis results show that a large amount of fiber bending and fiber-matrix debinding in CHM will occur in the hole surface when instantaneous fiber cutting angle lies in the range of 90 degrees to 180 degrees due to the tool pushing. This phenomenon can be mitigated in THM owing to a downward cutting force component along the hole axis, which makes fibers fracture easily. The theoretical analysis results are confirmed by CT scans and SEM results of surface morphology of holes, indicating THM is useful for obtaining high-quality hole surface finish. In addition, compared with CHM, damage generation, such as entrance split and exit delamination of the hole, can be restrained with THM technique.